[
  {
    "text": "Greenhouse gases (GHGs) are the gases in an atmosphere that trap heat, raising the surface temperature of astronomical bodies such as Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). Human-induced warming has been increasing at an unprecedented rate since it has started being measured, reaching 0.27±0.1 °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6±5.2 Gt CO2e per year over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling.\nThe five most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are: water vapor, carbon dioxide, methane, nitrous oxide, ozone. Other greenhouse gases of concern include chlorofluorocarbons (CFCs and HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons, SF6, and NF3. Water vapor causes about half of the greenhouse effect, acting in response to other gases as a climate change feedback.\nHuman activities since the beginning of the Industrial Revolution (around 1750) have increased carbon dioxide by over 50%, and methane levels by 150%. Carbon dioxide emissions are causing about three-quarters of global warming, while methane emissions cause most of the rest. The vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels, with remaining contributions from agriculture and industry. Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. The carbon cycle takes thousands of years to fully absorb CO2 from the atmosphere, while methane lasts in the atmosphere for an average of only 12 years.\nNatural flows of carbon happen between the atmosphere, terrestrial ecosystems, the ocean, and sediments. These flows have been fairly balanced over the past one million years, although greenhouse gas levels have varied widely in the more distant past. Carbon dioxide levels are now higher than they have been for three million years. The 2023 annual update of key indicators reveals that human-induced temperature rise, greenhouse gas concentrations, and the Earth's energy imbalance have all reached new records. If current emission rates continue, then global warming will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070. This is a level which the Intergovernmental Panel on Climate Change (IPCC) says is \"dangerous\".\n\nProperties and mechanisms\n\nGreenhouse gases are infrared active, meaning that they absorb and emit infrared radiation in the same long wavelength range as what is emitted by the Earth's surface, clouds and atmosphere.\n99% of the Earth's dry atmosphere (excluding water vapor) is made up of nitrogen (N2) (78%) and oxygen (O2) (21%). Because their molecules contain two atoms of the same element, they have no asymmetry in the distribution of their electrical charges, and so are almost totally unaffected by infrared thermal radiation, with only an extremely minor effect from collision-induced absorption. A further 0.9% of the atmosphere is made up by argon (Ar), which is monatomic, and so completely transparent to thermal radiation. On the other hand, carbon dioxide (0.04%), methane, nitrous oxide and even less abundant trace gases account for less than 0.1% of Earth's atmosphere, but because their molecules contain atoms of different elements, there is an asymmetry in electric charge distribution which allows molecular vibrations to interact with electromagnetic radiation. This makes them infrared active, and so their presence causes greenhouse effect.\n\nRadiative forcing\n\nEarth absorbs some of the radiant energy received from the sun, reflects some of it as light, and reflects or radiates the rest back to space as heat. A planet's surface temperature depends on this balance between incoming and outgoing energy. When Earth's energy balance is shifted, its surface becomes warmer or cooler, leading to a variety of changes in global climate. Radiative forcing is a metric calculated in watts per square meter, which characterizes the impact of an external change in a factor that influences climate. It is calculated as the difference in top-of-atmosphere (TOA) energy balance immediately caused by such an external change. A positive forcing, such as from increased concentrations of greenhouse gases, means more energy arriving than leaving at the top-of-atmosphere, which causes additional warming, while negative forcing, like from sulfates forming in the atmosphere from sulfur dioxide, leads to cooling.\nWithin the lower atmosphere, greenhouse gases exchange thermal radiation with the surface and limit radiative heat flow away from it, which reduces the overall rate of upward radiative heat transfer. The increased concentration of greenhouse gases is also cooling the upper atmosphere, as it is much thinner than the lower layers, and any heat re-emitted from greenhouse gases is more likely to travel further to space than to interact with the fewer gas molecules in the upper layers. The upper atmosphere is also shrinking as the result.\n\nContributions of specific gases to the greenhouse effect\nAnthropogenic changes to the natural greenhouse effect are sometimes referred to as the enhanced greenhouse effect.\nThis table shows the most important contributions to the overall greenhouse effect, without which the average temperature of Earth's surface would be about −18 °C (0 °F), instead of around 15 °C (59 °F). This table also specifies tropospheric ozone, because this gas has a cooling effect in the stratosphere, but a warming influence comparable to nitrous oxide and CFCs in the troposphere.\n\nSpecial role of water vapor\n\nWater vapor is the most important greenhouse gas overall, being responsible for 41–67% of the greenhouse effect, but its global concentrations are not directly affected by human activity. While local water vapor concentrations can be affected by developments such as irrigation, it has little impact on the global scale due to its short residence time of about nine days. Indirectly, an increase in global temperatures will also increase water vapor concentrations and thus their warming effect, in a process known as water vapor feedback. It occurs because the Clausius–Clapeyron relation holds that more water vapor will be present per unit volume at elevated temperatures. Thus, local atmospheric concentration of water vapor varies from less than 0.01% in extremely cold regions up to 3% by mass in saturated air at about 32 °C.\n\nGlobal warming potential (GWP) and CO2 equivalents\n\nList of all greenhouse gases\n\nThe contribution of each gas to the enhanced greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame. Since the 1980s, greenhouse gas forcing contributions (relative to year 1750) are also estimated with high accuracy using IPCC-recommended expressions derived from radiative transfer models.\nThe concentration of a greenhouse gas is typically measured in parts per million (ppm) or parts per billion (ppb) by volume. A CO2 concentration of 420 ppm means that 420 out of every million air molecules is a CO2 molecule. The first 30 ppm increase in CO2 concentrations took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014. Similarly, the average annual increase in the 1960s was only 37% of what it was in 2000 through 2007.\nMany observations are available online in a variety of Atmospheric Chemistry Observational Databases. The table below shows the most influential long-lived, well-mixed greenhouse gases, along with their tropospheric concentrations and direct radiative forcings, as identified by the Intergovernmental Panel on Climate Change (IPCC). Abundances of these trace gases are regularly measured by atmospheric scientists from samples collected throughout the world. It excludes water vapor because changes in its concentrations are calculated as a climate change feedback indirectly caused by changes in other greenhouse gases, as well as ozone, whose concentrations are only modified indirectly by various refrigerants that cause ozone depletion. Some short-lived gases (e.g. carbon monoxide, NOx) and aerosols (e.g. mineral dust or black carbon) are also excluded because of limited role and strong variation, along with minor refrigerants and other halogenated gases, which have been mass-produced in smaller quantities than those in the table. and Annex III of the 2021 IPCC WG1 Report\n\nFactors affecting concentrations\nAtmospheric concentrations are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water).\n\nAirborne fraction\n\nThe proportion of an emission remaining in the atmosphere after a specified time is the \"airborne fraction\" (AF). The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions. The annual airborne fraction for CO2 had been stable at 0.45 for the past six decades even as the emissions have been increasing. This means that the other 0.55 of emitted CO2 is absorbed by the land and atmosphere carbon sinks within the first year of an emission. In the high-emission scenarios, the effectiveness of carbon sinks will be lower, increasing the atmospheric fraction of CO2 even though the raw amount of emissions absorbed will be higher than in the present.\n\nAtmospheric lifetime\n\nMajor greenhouse gases are well mixed and take many years to leave the atmosphere.\nThe atmospheric lifetime of a greenhouse gas refers to the time required to restore equilibrium following a sudden increase or decrease in its concentration in the atmosphere. Individual atoms or molecules may be lost or deposited to sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations. The average time taken to achieve this is the mean lifetime. This can be represented through the following formula, where the lifetime \n \n \n \n τ\n \n \n {\\displaystyle \\tau }\n \n of an atmospheric species X in a one-box model is the average time that a molecule of X remains in the box.\n\n \n \n \n τ\n \n \n {\\displaystyle \\tau }\n \n can also be defined as the ratio of the mass \n \n \n \n m\n \n \n {\\displaystyle m}\n \n (in kg) of X in the box to its removal rate, which is the sum of the flow of X out of the box\n(\n \n \n \n \n F\n \n out\n \n \n \n \n {\\displaystyle F_{\\text{out}}}\n \n),\nchemical loss of X\n(\n \n \n \n L\n \n \n {\\displaystyle L}\n \n),\nand deposition of X\n(\n \n \n \n D\n \n \n {\\displaystyle D}\n \n)\n(all in kg/s):\n\n \n \n \n τ\n =\n \n \n m\n \n \n F\n \n out\n \n \n +\n L\n +\n D\n \n \n \n \n \n {\\displaystyle \\tau ={\\frac {m}{F_{\\text{out}}+L+D}}}\n \n.\nIf input of this gas into the box ceased, then after time \n \n \n \n τ\n \n \n {\\displaystyle \\tau }\n \n, its concentration would decrease by about 63%.\nChanges to any of these variables can alter the atmospheric lifetime of a greenhouse gas. For instance, methane's atmospheric lifetime is estimated to have been lower in the 19th century than now, but to have been higher in the second half of the 20th century than after 2000. Carbon dioxide has an even more variable lifetime, which cannot be specified down to a single number. Scientists instead say that while the first 10% of carbon dioxide's airborne fraction (not counting the ~50% absorbed by land and ocean sinks within the emission's first year) is removed \"quickly\", the vast majority of the airborne fraction – 80% – lasts for \"centuries to millennia\". The remaining 10% stays for tens of thousands of years. In some models, this longest-lasting fraction is as large as 30%.\n\nDuring geologic time scales\n\nMonitoring\n\nGreenhouse gas monitoring involves the direct measurement of atmospheric concentrations and direct and indirect measurement of greenhouse gas emissions. Indirect methods calculate emissions of greenhouse gases based on related metrics such as fossil fuel extraction.\nThere are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments, such as the range-resolved infrared differential absorption lidar (DIAL). Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and through networks of ground stations such as the Integrated Carbon Observation System.\nThe Annual Greenhouse Gas Index (AGGI) is defined by atmospheric scientists at NOAA as the ratio of total direct radiative forcing due to long-lived and well-mixed greenhouse gases for any year for which adequate global measurements exist, to that present in year 1990. These radiative forcing levels are relative to those present in year 1750 (i.e. prior to the start of the industrial era). 1990 is chosen because it is the baseline year for the Kyoto Protocol, and is the publication year of the first IPCC Scientific Assessment of Climate Change. As such, NOAA states that the AGGI \"measures the commitment that (global) society has already made to living in a changing climate. It is based on the highest quality atmospheric observations from sites around the world. Its uncertainty is very low.\"\n\nData networks\n\nTypes of sources\n\nNatural sources\n\nThe natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence. Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid. It can then acidify the surfaces it touches, thereby be absorbed by rocks through weathering, or be washed into the ocean contributing to ocean acidity.\n\nHuman-made sources\n\nThe vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation. Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. Rice paddies are a significant agricultural source of greenhouse gas emissions, contributing 22% of total agricultural methane and 11% of nitrous oxide emissions.\nIf current emission rates continue then temperature rises will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070, which is the level the United Nations' Intergovernmental Panel on Climate Change (IPCC) says is \"dangerous\".\n\nMost greenhouse gases have both natural and human-caused sources. An exception are purely human-produced synthetic halocarbons which have no natural sources. During the pre-industrial Holocene, concentrations of existing gases were roughly constant, because the large natural sources and sinks roughly balanced. In the industrial era, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests.\n\nReducing human-caused greenhouse gases\n\nNeeded emissions cuts\n\nRemoval from the atmosphere through negative emissions\n\nSeveral technologies remove greenhouse gas emissions from the atmosphere. Most widely analyzed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture, or to the soil as in the case with biochar. Many long-term climate scenario models require large-scale human-made negative emissions to avoid serious climate change.\nNegative emissions approaches are also being studied for atmospheric methane, called atmospheric methane removal.\n\nHistory of discovery\n\nIn the late 19th century, scientists experimentally discovered that N2 and O2 do not absorb infrared radiation (called, at that time, \"dark radiation\"), while water (both as true vapor and condensed in the form of microscopic droplets suspended in clouds) and CO2 and other poly-atomic gaseous molecules do absorb infrared radiation. In the early 20th century, researchers realized that greenhouse gases in the atmosphere made Earth's overall temperature higher than it would be without them. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901.\nDuring the late 20th century, a scientific consensus evolved that increasing concentrations of greenhouse gases in the atmosphere cause a substantial rise in global temperatures and changes to other parts of the climate system, with consequences for the environment and for human health.\n\nOther planets\n\nGreenhouse gases exist in many atmospheres, creating greenhouse effects on Mars, Titan, and particularly in the thick atmosphere of Venus. While Venus has been described as the ultimate end state of runaway greenhouse effect, such a process would have virtually no chance of occurring from any increases in greenhouse gas concentrations caused by humans, as the Sun's brightness is too low and it would likely need to increase by some tens of percents, which will take a few billion years.\n\nSee also\n\nCarbon accounting – Processes used to measure emissions of carbon dioxide equivalents\nCarbon budget – Limit on carbon dioxide emission for a given climate impact\nCarbon sequestration – Storing carbon in a carbon pool\nClimate change feedbacks – Feedback related to climate change\n\nReferences\n\nExternal links\n\n Media related to Greenhouse gases at Wikimedia Commons\nCarbon Dioxide Information Analysis Center (CDIAC), U.S. Department of Energy, archived from the original on 13 August 2023, retrieved 26 July 2020\nAnnual Greenhouse Gas Index (AGGI) from NOAA\nAtmospheric spectra of GHGs and other trace gases. Archived 25 March 2013 at the Wayback Machine.",
    "source": "wikipedia:Greenhouse gas",
    "domain": "climate"
  },
  {
    "text": "Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The modern-day rise in global temperatures is driven by human activities, especially fossil fuel (coal, oil and natural gas) burning since the Industrial Revolution. Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases. These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Earth's atmosphere now has roughly 50% more carbon dioxide, the main gas driving global warming, than it did at the end of the pre-industrial era, reaching levels not seen for millions of years.\nClimate change has an increasingly large impact on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common. Amplified warming in the Arctic has contributed to thawing permafrost, retreat of glaciers and sea ice decline. Higher temperatures are also causing more intense storms, droughts, and other weather extremes. Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct. Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise.\nClimate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, and economic loss. Human migration and conflict can also be a result. The World Health Organization calls climate change one of the biggest threats to global health in the 21st century. Societies and ecosystems will experience more severe risks without action to limit warming. Adapting to climate change through efforts like flood control measures or drought-resistant crops partially reduces climate change risks, although some limits to adaptation have already been reached. Poorer communities are responsible for a small share of global emissions, yet have the least ability to adapt and are most vulnerable to climate change.\n\nMany climate change impacts have been observed in the first decades of the 21st century, with 2024 the warmest on record at +1.60 °C (2.88 °F) since regular tracking began in 1850. Additional warming will increase these impacts and can trigger tipping points, such as melting all of the Greenland ice sheet. Under the 2015 Paris Agreement, nations collectively agreed to keep warming \"well under 2 °C\". However, with pledges made under the Agreement, global warming would still reach about 2.8 °C (5.0 °F) by the end of the century. \nThere is widespread support for climate action worldwide, and most countries aim to stop emitting carbon dioxide. Fossil fuels can be phased out by stopping subsidising them, conserving energy and switching to energy sources that do not produce significant carbon pollution. These energy sources include wind, solar, hydro, and nuclear power. Cleanly generated electricity can replace fossil fuels for powering transportation, heating buildings, and running industrial processes. Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that store carbon in soil.\n\n \n\nTerminology\nBefore the 1980s, it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution. Scientists used the term inadvertent climate modification to refer to human impacts on the climate at this time. In the 1980s, the terms global warming and climate change became more common, often being used interchangeably. Scientifically, global warming refers only to increased global average surface temperature, while climate change describes both global warming and its effects on Earth's climate system, such as precipitation changes.\nClimate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history as result of natural processes. The term anthropogenic climate change is sometimes used to describe climate change resulting from human activities. \nGlobal warming—used as early as 1975—became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. Since the 2000s, usage of climate change has increased. Various scientists, politicians and media may use the terms climate crisis or climate emergency to talk about climate change, and may use the term global heating instead of global warming.\n\nGlobal temperature rise\n\nTemperatures prior to present-day global warming\n\nOver the last few million years the climate cycled through ice ages. One of the hotter periods was the Last Interglacial, around 125,000 years ago, where temperatures were between 0.5 °C and 1.5 °C warmer than before the start of global warming. This period saw sea levels 5 to 10 metres higher than today. The most recent glacial maximum 20,000 years ago was some 5–7 °C colder. This period has sea levels that were over 125 metres (410 ft) lower than today.\nTemperatures stabilized in the current interglacial period beginning 11,700 years ago. This period also saw the start of agriculture. Historical patterns of warming and cooling, like the Medieval Warm Period and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions. Climate information for that period comes from climate proxies, such as trees and ice cores.\n\nWarming since the Industrial Revolution\n\nAround 1850 thermometer records began to provide global coverage.\nBetween the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from sulfur dioxide emissions. Sulfur dioxide causes acid rain, but it also produces sulfate aerosols in the atmosphere, which reflect sunlight and cause global dimming. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.\n\nOngoing changes in climate have had no precedent for several thousand years. Multiple datasets all show worldwide increases in surface temperature, at a rate of around 0.2 °C per decade. The 2014–2023 decade warmed to an average 1.19 °C [1.06–1.30 °C] compared to the pre-industrial baseline (1850–1900). Not every single year was warmer than the last: internal climate variability processes can make any year 0.2 °C warmer or colder than the average. From 1998 to 2013, negative phases of two such processes, Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) caused a short slower period of warming called the \"global warming hiatus\". After the \"hiatus\", the opposite occurred, with 2024 well above the recent average at more than +1.5 °C. This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.\nA wide range of other observations reinforce the evidence of warming. The upper atmosphere is cooling, because greenhouse gases are trapping heat near the Earth's surface, and so less heat is radiating into space. Warming reduces average snow cover and forces the retreat of glaciers. At the same time, warming also causes greater evaporation from the oceans, leading to more atmospheric humidity, more and heavier precipitation. Plants are flowering earlier in spring, and thousands of animal species have been permanently moving to cooler areas.\n\nDifferences by region\nDifferent regions of the world warm at different rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global average surface temperature. This is because oceans lose more heat by evaporation and oceans can store a lot of heat. The thermal energy in the global climate system has grown with only brief pauses since at least 1970, and over 90% of this extra energy has been stored in the ocean. The rest has heated the atmosphere, melted ice, and warmed the continents.\nThe Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Local black carbon deposits on snow and ice also contribute to Arctic warming. Arctic surface temperatures are increasing between three and four times faster than in the rest of the world. Melting of ice sheets near the poles weakens both the Atlantic and the Antarctic limb of thermohaline circulation, which further changes the distribution of heat and precipitation around the globe.\n\nFuture global temperatures\n\nThe World Meteorological Organization estimates there is almost a 50% chance of the five-year average global temperature exceeding +1.5 °C between 2024 and 2028. The IPCC expects the 20-year average to exceed +1.5 °C in the early 2030s.\nThe IPCC Sixth Assessment Report (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8 °C under a scenario with very low emissions of greenhouse gases, 2.1–3.5 °C under an intermediate emissions scenario,\nor 3.3–5.7 °C under a very high emissions scenario. The warming will continue past 2100 in the intermediate and high emission scenarios, with future projections of global surface temperatures by year 2300 being similar to millions of years ago.\nThe remaining carbon budget for staying beneath certain temperature increases is determined by modelling the carbon cycle and climate sensitivity to greenhouse gases. According to UNEP, global warming can be kept below 2.0 °C with a 50% chance if emissions after 2023 do not exceed 900 gigatonnes of CO2. This carbon budget corresponds to around 16 years of current emissions.\n\nCauses of recent global temperature rise\n\nThe climate system experiences various cycles on its own which can last for years, decades or even centuries. For example, El Niño events cause short-term spikes in surface temperature while La Niña events cause short term cooling. Their relative frequency can affect global temperature trends on a decadal timescale. Other changes are caused by an imbalance of energy from external forcings. Examples of these include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.\nTo determine the human contribution to climate change, unique \"fingerprints\" for all potential causes are developed and compared with both observed patterns and known internal climate variability. For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed. Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.\n\nGreenhouse gases\n\nGreenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time.\nWhile water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they primarily change as a function of temperature and are therefore mostly considered to be feedbacks that change climate sensitivity. On the other hand, concentrations of gases such as CO2 (≈20%), tropospheric ozone, CFCs and nitrous oxide are added or removed independently from temperature, and are therefore considered to be external forcings that change global temperatures.\nBefore the Industrial Revolution, naturally occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence. Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere. In 2022, the concentrations of CO2 and methane had increased by about 50% and 164%, respectively, since 1750. These CO2 levels are higher than they have been at any time during the last 14 million years. Concentrations of methane are far higher than they were over the last 800,000 years.\n\nGlobal human-caused greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of CO2. Of these emissions, 75% was CO2, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases. CO2 emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity. Additional CO2 emissions come from deforestation and industrial processes, which include the CO2 released by the chemical reactions for making cement, steel, aluminium, and fertilizer. Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction. Nitrous oxide emissions largely come from the microbial decomposition of fertilizer.\nWhile methane only lasts in the atmosphere for an average of 12 years, CO2 lasts much longer. The Earth's surface absorbs CO2 as part of the carbon cycle. While plants on land and in the ocean absorb most excess emissions of CO2 every year, that CO2 is returned to the atmosphere when biological matter is digested, burns, or decays. Land-surface carbon sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO2 emissions. The ocean has absorbed 20 to 30% of emitted CO2 over the last two decades. CO2 is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.\n\nLand surface changes\n\nAround 30% of Earth's land area is largely unusable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland and 34% is agricultural land. Deforestation is the main land use change contributor to global warming, as the destroyed trees release CO2, and are not replaced by new trees, removing that carbon sink. Between 2001 and 2018, 27% of deforestation was from permanent clearing to enable agricultural expansion for crops and livestock. Another 24% has been lost to temporary clearing under the shifting cultivation agricultural systems. 26% was due to logging for wood and derived products, and wildfires have accounted for the remaining 23%. Some forests have not been fully cleared, but were already degraded by these impacts. Restoring these forests also recovers their potential as a carbon sink.\nLocal vegetation cover impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also modify the release of chemical compounds that influence clouds, and by changing wind patterns. In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler. At latitudes closer to the poles, there is a cooling effect as forest is replaced by snow-covered (and more reflective) plains. Globally, these increases in surface albedo have been the dominant direct influence on temperature from land use change. Thus, land use change to date is estimated to have a slight cooling effect.\n\nOther factors\n\nAerosols and clouds\nAir pollution, in the form of aerosols, affects the climate on a large scale. Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed. This phenomenon is popularly known as global dimming, and is primarily attributed to sulfate aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like coal and bunker fuel. Smaller contributions come from black carbon (from combustion of fossil fuels and biomass), and from dust. Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.\nAerosols also have indirect effects on the Earth's energy budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight. Indirect effects of aerosols are the largest uncertainty in radiative forcing.\nWhile aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050. The effect of decreasing sulfur content of fuel oil for ships since 2020 is estimated to cause an additional 0.05 °C increase in global mean temperature by 2050.\n\nSolar and volcanic activity\n\nAs the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. Solar irradiance has been measured directly by satellites, and indirect measurements are available from the early 1600s onwards. Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the troposphere). The upper atmosphere (the stratosphere) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.\nThis is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.\nExplosive volcanic eruptions can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapour into the atmosphere, which adds to greenhouse gases and increases temperatures. These impacts on temperature only last for several years, because both water vapour and volcanic material have low persistence in the atmosphere. volcanic CO2 emissions are more persistent, but they are equivalent to less than 1% of current human-caused CO2 emissions. Volcanic activity still represents the single largest natural impact (forcing) on temperature in the industrial era. Yet, like the other natural forcings, it has had negligible impacts on global temperature trends since the Industrial Revolution.\n\nClimate change feedbacks\n\nThe climate system's response to an initial forcing is shaped by feedbacks, which either amplify or dampen the change. Self-reinforcing or positive feedbacks increase the response, while balancing or negative feedbacks reduce it. The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net cloud feedback. The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature. In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of CO2 on plant growth. Feedbacks are expected to trend in a positive direction as greenhouse gas emissions continue, raising climate sensitivity.\nThese feedback processes alter the pace of global warming. For instance, warmer air can hold more moisture in the form of water vapour, which is itself a potent greenhouse gas. Warmer air can also make clouds higher and thinner, and therefore more insulating, increasing climate warming. The reduction of snow cover and sea ice in the Arctic is another major feedback, this reduces the reflectivity of the Earth's surface in the region and accelerates Arctic warming. This additional warming also contributes to permafrost thawing, which releases methane and CO2 into the atmosphere.\nAround half of human-caused CO2 emissions have been absorbed by land plants and by the oceans. This fraction is not static and if future CO2 emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it'll still absorb more carbon than now, but the overall fraction will decrease to below 40%. This is because climate change increases droughts and heat waves that eventually inhibit plant growth on land, and soils will release more carbon from dead plants when they are warmer. The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution. Uncertainty over feedbacks, particularly cloud cover, is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.\n\nModelling\n\nA climate model is a representation of the physical, chemical and biological processes that affect the climate system. Models include natural processes like changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. Models are used to estimate the degree of warming future emissions will cause when accounting for the strength of climate feedbacks. Models also predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere.\nThe physical realism of models is tested by examining their ability to simulate current or past climates. Past models have underestimated the rate of Arctic shrinkage and underestimated the rate of precipitation increase. Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations. The 2017 United States-published National Climate Assessment notes that \"climate models may still be underestimating or missing relevant feedback processes\". Additionally, climate models may be unable to adequately predict short-term regional climatic shifts.\nA subset of climate models add societal factors to a physical climate model. These models simulate how population, economic growth, and energy use affect—and interact with—the physical climate. With this information, these models can produce scenarios of future greenhouse gas emissions. This is then used as input for physical climate models and carbon cycle models to predict how atmospheric concentrations of greenhouse gases might change. Depending on the socioeconomic scenario and the mitigation scenario, models produce atmospheric CO2 concentrations that range widely between 380 and 1400 ppm.\n\nImpacts\n\nEnvironmental effects\n\nThe environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Changes may occur gradually or rapidly. Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations. Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency. Extremely wet or dry events within the monsoon period have increased in India and East Asia. Monsoonal precipitation over the Northern Hemisphere has increased since 1980. The rainfall rate and intensity of hurricanes and typhoons is likely increasing, and the geographic range likely expanding poleward in response to climate warming. The frequency of tropical cyclones has not increased as a result of climate change.\n\nGlobal sea level is rising as a consequence of thermal expansion and the melting of glaciers and ice sheets. Sea level rise has increased over time, reaching 4.8 cm per decade between 2014 and 2023. Over the 21st century, the IPCC projects 32–62 cm of sea level rise under a low emission scenario, 44–76 cm under an intermediate one and 65–101 cm under a very high emission scenario. Marine ice sheet instability processes in Antarctica may add substantially to these values, including the possibility of a 2-meter sea level rise by 2100 under high emissions.\nClimate change has led to decades of shrinking and thinning of the Arctic sea ice. While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C. Higher atmospheric CO2 concentrations cause more CO2 to dissolve in the oceans, which is making them more acidic. Because oxygen is less soluble in warmer water, its concentrations in the ocean are decreasing, and dead zones are expanding.\n\nTipping points and long-term impacts\n\nGreater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state. For instance, the Greenland ice sheet is already melting, but if global warming reaches levels between 1.7 °C and 2.3 °C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5 °C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place. While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major ocean currents like the Atlantic meridional overturning circulation (AMOC), and irreversible damage to key ecosystems like the Amazon rainforest and coral reefs can unfold in a matter of decades. The collapse of the AMOC would be a severe climate catastrophe, resulting in a cooling of the Northern Hemisphere.\nThe long-term effects of climate change on oceans include further ice melt, ocean warming, sea level rise, ocean acidification and ocean deoxygenation. The timescale of long-term impacts are centuries to millennia due to CO2's long atmospheric lifetime. The result is an estimated total sea level rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years. Oceanic CO2 uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years. Deep oceans (below 2,000 metres (6,600 ft)) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date. Further, the West Antarctic ice sheet appears committed to practically irreversible melting, which would increase the sea levels by at least 3.3 m (10 ft 10 in) over approximately 2000 years.\n\nNature and wildlife\n\nRecent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. For instance, the range of hundreds of North American birds has shifted northward at an average rate of 1.5 km/year over the past 55 years. Higher atmospheric CO2 levels and an extended growing season have resulted in global greening. However, heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear. A related phenomenon driven by climate change is woody plant encroachment, affecting up to 500 million hectares globally. Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics. The size and speed of global warming is making abrupt changes in ecosystems more likely. Overall, it is expected that climate change will result in the extinction of many species.\nThe oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land. Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds. Ocean acidification makes it harder for marine calcifying organisms such as mussels, barnacles and corals to produce shells and skeletons; and heatwaves have bleached coral reefs. Harmful algal blooms enhanced by climate change and eutrophication lower oxygen levels, disrupt food webs and cause great loss of marine life. Coastal ecosystems are under particular stress. Almost half of global wetlands have disappeared due to climate change and other human impacts. Plants have come under increased stress from damage by insects.\n\nHumans\n\nThe effects of climate change are impacting humans everywhere in the world. Impacts can be observed on all continents and ocean regions, with low-latitude, less developed areas facing the greatest risk. Continued warming has potentially \"severe, pervasive and irreversible impacts\" for people and ecosystems. The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.\n\nHealth and food\n\nThe World Health Organization calls climate change one of the biggest threats to global health in the 21st century. Scientists have warned about the irreversible harms it poses. Extreme weather events affect public health, and food and water security. Temperature extremes lead to increased illness and death. Climate change increases the intensity and frequency of extreme weather events. It can affect transmission of infectious diseases, such as dengue fever and malaria. According to the World Economic Forum, 14.5 million more deaths are expected due to climate change by 2050. 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths. By 2100, 50% to 75% of the global population would live in such areas.\nWhile total crop yields have been increasing in the past 50 years due to agricultural improvements, climate change has already decreased the rate of yield growth. ",
    "source": "wikipedia:Global warming",
    "domain": "climate"
  },
  {
    "text": "Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The modern-day rise in global temperatures is driven by human activities, especially fossil fuel (coal, oil and natural gas) burning since the Industrial Revolution. Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases. These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Earth's atmosphere now has roughly 50% more carbon dioxide, the main gas driving global warming, than it did at the end of the pre-industrial era, reaching levels not seen for millions of years.\nClimate change has an increasingly large impact on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common. Amplified warming in the Arctic has contributed to thawing permafrost, retreat of glaciers and sea ice decline. Higher temperatures are also causing more intense storms, droughts, and other weather extremes. Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct. Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise.\nClimate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, and economic loss. Human migration and conflict can also be a result. The World Health Organization calls climate change one of the biggest threats to global health in the 21st century. Societies and ecosystems will experience more severe risks without action to limit warming. Adapting to climate change through efforts like flood control measures or drought-resistant crops partially reduces climate change risks, although some limits to adaptation have already been reached. Poorer communities are responsible for a small share of global emissions, yet have the least ability to adapt and are most vulnerable to climate change.\n\nMany climate change impacts have been observed in the first decades of the 21st century, with 2024 the warmest on record at +1.60 °C (2.88 °F) since regular tracking began in 1850. Additional warming will increase these impacts and can trigger tipping points, such as melting all of the Greenland ice sheet. Under the 2015 Paris Agreement, nations collectively agreed to keep warming \"well under 2 °C\". However, with pledges made under the Agreement, global warming would still reach about 2.8 °C (5.0 °F) by the end of the century. \nThere is widespread support for climate action worldwide, and most countries aim to stop emitting carbon dioxide. Fossil fuels can be phased out by stopping subsidising them, conserving energy and switching to energy sources that do not produce significant carbon pollution. These energy sources include wind, solar, hydro, and nuclear power. Cleanly generated electricity can replace fossil fuels for powering transportation, heating buildings, and running industrial processes. Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that store carbon in soil.\n\n \n\nTerminology\nBefore the 1980s, it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution. Scientists used the term inadvertent climate modification to refer to human impacts on the climate at this time. In the 1980s, the terms global warming and climate change became more common, often being used interchangeably. Scientifically, global warming refers only to increased global average surface temperature, while climate change describes both global warming and its effects on Earth's climate system, such as precipitation changes.\nClimate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history as result of natural processes. The term anthropogenic climate change is sometimes used to describe climate change resulting from human activities. \nGlobal warming—used as early as 1975—became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. Since the 2000s, usage of climate change has increased. Various scientists, politicians and media may use the terms climate crisis or climate emergency to talk about climate change, and may use the term global heating instead of global warming.\n\nGlobal temperature rise\n\nTemperatures prior to present-day global warming\n\nOver the last few million years the climate cycled through ice ages. One of the hotter periods was the Last Interglacial, around 125,000 years ago, where temperatures were between 0.5 °C and 1.5 °C warmer than before the start of global warming. This period saw sea levels 5 to 10 metres higher than today. The most recent glacial maximum 20,000 years ago was some 5–7 °C colder. This period has sea levels that were over 125 metres (410 ft) lower than today.\nTemperatures stabilized in the current interglacial period beginning 11,700 years ago. This period also saw the start of agriculture. Historical patterns of warming and cooling, like the Medieval Warm Period and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions. Climate information for that period comes from climate proxies, such as trees and ice cores.\n\nWarming since the Industrial Revolution\n\nAround 1850 thermometer records began to provide global coverage.\nBetween the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from sulfur dioxide emissions. Sulfur dioxide causes acid rain, but it also produces sulfate aerosols in the atmosphere, which reflect sunlight and cause global dimming. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.\n\nOngoing changes in climate have had no precedent for several thousand years. Multiple datasets all show worldwide increases in surface temperature, at a rate of around 0.2 °C per decade. The 2014–2023 decade warmed to an average 1.19 °C [1.06–1.30 °C] compared to the pre-industrial baseline (1850–1900). Not every single year was warmer than the last: internal climate variability processes can make any year 0.2 °C warmer or colder than the average. From 1998 to 2013, negative phases of two such processes, Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) caused a short slower period of warming called the \"global warming hiatus\". After the \"hiatus\", the opposite occurred, with 2024 well above the recent average at more than +1.5 °C. This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.\nA wide range of other observations reinforce the evidence of warming. The upper atmosphere is cooling, because greenhouse gases are trapping heat near the Earth's surface, and so less heat is radiating into space. Warming reduces average snow cover and forces the retreat of glaciers. At the same time, warming also causes greater evaporation from the oceans, leading to more atmospheric humidity, more and heavier precipitation. Plants are flowering earlier in spring, and thousands of animal species have been permanently moving to cooler areas.\n\nDifferences by region\nDifferent regions of the world warm at different rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global average surface temperature. This is because oceans lose more heat by evaporation and oceans can store a lot of heat. The thermal energy in the global climate system has grown with only brief pauses since at least 1970, and over 90% of this extra energy has been stored in the ocean. The rest has heated the atmosphere, melted ice, and warmed the continents.\nThe Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Local black carbon deposits on snow and ice also contribute to Arctic warming. Arctic surface temperatures are increasing between three and four times faster than in the rest of the world. Melting of ice sheets near the poles weakens both the Atlantic and the Antarctic limb of thermohaline circulation, which further changes the distribution of heat and precipitation around the globe.\n\nFuture global temperatures\n\nThe World Meteorological Organization estimates there is almost a 50% chance of the five-year average global temperature exceeding +1.5 °C between 2024 and 2028. The IPCC expects the 20-year average to exceed +1.5 °C in the early 2030s.\nThe IPCC Sixth Assessment Report (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8 °C under a scenario with very low emissions of greenhouse gases, 2.1–3.5 °C under an intermediate emissions scenario,\nor 3.3–5.7 °C under a very high emissions scenario. The warming will continue past 2100 in the intermediate and high emission scenarios, with future projections of global surface temperatures by year 2300 being similar to millions of years ago.\nThe remaining carbon budget for staying beneath certain temperature increases is determined by modelling the carbon cycle and climate sensitivity to greenhouse gases. According to UNEP, global warming can be kept below 2.0 °C with a 50% chance if emissions after 2023 do not exceed 900 gigatonnes of CO2. This carbon budget corresponds to around 16 years of current emissions.\n\nCauses of recent global temperature rise\n\nThe climate system experiences various cycles on its own which can last for years, decades or even centuries. For example, El Niño events cause short-term spikes in surface temperature while La Niña events cause short term cooling. Their relative frequency can affect global temperature trends on a decadal timescale. Other changes are caused by an imbalance of energy from external forcings. Examples of these include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.\nTo determine the human contribution to climate change, unique \"fingerprints\" for all potential causes are developed and compared with both observed patterns and known internal climate variability. For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed. Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.\n\nGreenhouse gases\n\nGreenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time.\nWhile water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they primarily change as a function of temperature and are therefore mostly considered to be feedbacks that change climate sensitivity. On the other hand, concentrations of gases such as CO2 (≈20%), tropospheric ozone, CFCs and nitrous oxide are added or removed independently from temperature, and are therefore considered to be external forcings that change global temperatures.\nBefore the Industrial Revolution, naturally occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence. Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere. In 2022, the concentrations of CO2 and methane had increased by about 50% and 164%, respectively, since 1750. These CO2 levels are higher than they have been at any time during the last 14 million years. Concentrations of methane are far higher than they were over the last 800,000 years.\n\nGlobal human-caused greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of CO2. Of these emissions, 75% was CO2, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases. CO2 emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity. Additional CO2 emissions come from deforestation and industrial processes, which include the CO2 released by the chemical reactions for making cement, steel, aluminium, and fertilizer. Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction. Nitrous oxide emissions largely come from the microbial decomposition of fertilizer.\nWhile methane only lasts in the atmosphere for an average of 12 years, CO2 lasts much longer. The Earth's surface absorbs CO2 as part of the carbon cycle. While plants on land and in the ocean absorb most excess emissions of CO2 every year, that CO2 is returned to the atmosphere when biological matter is digested, burns, or decays. Land-surface carbon sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO2 emissions. The ocean has absorbed 20 to 30% of emitted CO2 over the last two decades. CO2 is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.\n\nLand surface changes\n\nAround 30% of Earth's land area is largely unusable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland and 34% is agricultural land. Deforestation is the main land use change contributor to global warming, as the destroyed trees release CO2, and are not replaced by new trees, removing that carbon sink. Between 2001 and 2018, 27% of deforestation was from permanent clearing to enable agricultural expansion for crops and livestock. Another 24% has been lost to temporary clearing under the shifting cultivation agricultural systems. 26% was due to logging for wood and derived products, and wildfires have accounted for the remaining 23%. Some forests have not been fully cleared, but were already degraded by these impacts. Restoring these forests also recovers their potential as a carbon sink.\nLocal vegetation cover impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also modify the release of chemical compounds that influence clouds, and by changing wind patterns. In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler. At latitudes closer to the poles, there is a cooling effect as forest is replaced by snow-covered (and more reflective) plains. Globally, these increases in surface albedo have been the dominant direct influence on temperature from land use change. Thus, land use change to date is estimated to have a slight cooling effect.\n\nOther factors\n\nAerosols and clouds\nAir pollution, in the form of aerosols, affects the climate on a large scale. Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed. This phenomenon is popularly known as global dimming, and is primarily attributed to sulfate aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like coal and bunker fuel. Smaller contributions come from black carbon (from combustion of fossil fuels and biomass), and from dust. Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.\nAerosols also have indirect effects on the Earth's energy budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight. Indirect effects of aerosols are the largest uncertainty in radiative forcing.\nWhile aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050. The effect of decreasing sulfur content of fuel oil for ships since 2020 is estimated to cause an additional 0.05 °C increase in global mean temperature by 2050.\n\nSolar and volcanic activity\n\nAs the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. Solar irradiance has been measured directly by satellites, and indirect measurements are available from the early 1600s onwards. Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the troposphere). The upper atmosphere (the stratosphere) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.\nThis is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.\nExplosive volcanic eruptions can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapour into the atmosphere, which adds to greenhouse gases and increases temperatures. These impacts on temperature only last for several years, because both water vapour and volcanic material have low persistence in the atmosphere. volcanic CO2 emissions are more persistent, but they are equivalent to less than 1% of current human-caused CO2 emissions. Volcanic activity still represents the single largest natural impact (forcing) on temperature in the industrial era. Yet, like the other natural forcings, it has had negligible impacts on global temperature trends since the Industrial Revolution.\n\nClimate change feedbacks\n\nThe climate system's response to an initial forcing is shaped by feedbacks, which either amplify or dampen the change. Self-reinforcing or positive feedbacks increase the response, while balancing or negative feedbacks reduce it. The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net cloud feedback. The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature. In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of CO2 on plant growth. Feedbacks are expected to trend in a positive direction as greenhouse gas emissions continue, raising climate sensitivity.\nThese feedback processes alter the pace of global warming. For instance, warmer air can hold more moisture in the form of water vapour, which is itself a potent greenhouse gas. Warmer air can also make clouds higher and thinner, and therefore more insulating, increasing climate warming. The reduction of snow cover and sea ice in the Arctic is another major feedback, this reduces the reflectivity of the Earth's surface in the region and accelerates Arctic warming. This additional warming also contributes to permafrost thawing, which releases methane and CO2 into the atmosphere.\nAround half of human-caused CO2 emissions have been absorbed by land plants and by the oceans. This fraction is not static and if future CO2 emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it'll still absorb more carbon than now, but the overall fraction will decrease to below 40%. This is because climate change increases droughts and heat waves that eventually inhibit plant growth on land, and soils will release more carbon from dead plants when they are warmer. The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution. Uncertainty over feedbacks, particularly cloud cover, is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.\n\nModelling\n\nA climate model is a representation of the physical, chemical and biological processes that affect the climate system. Models include natural processes like changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. Models are used to estimate the degree of warming future emissions will cause when accounting for the strength of climate feedbacks. Models also predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere.\nThe physical realism of models is tested by examining their ability to simulate current or past climates. Past models have underestimated the rate of Arctic shrinkage and underestimated the rate of precipitation increase. Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations. The 2017 United States-published National Climate Assessment notes that \"climate models may still be underestimating or missing relevant feedback processes\". Additionally, climate models may be unable to adequately predict short-term regional climatic shifts.\nA subset of climate models add societal factors to a physical climate model. These models simulate how population, economic growth, and energy use affect—and interact with—the physical climate. With this information, these models can produce scenarios of future greenhouse gas emissions. This is then used as input for physical climate models and carbon cycle models to predict how atmospheric concentrations of greenhouse gases might change. Depending on the socioeconomic scenario and the mitigation scenario, models produce atmospheric CO2 concentrations that range widely between 380 and 1400 ppm.\n\nImpacts\n\nEnvironmental effects\n\nThe environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Changes may occur gradually or rapidly. Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations. Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency. Extremely wet or dry events within the monsoon period have increased in India and East Asia. Monsoonal precipitation over the Northern Hemisphere has increased since 1980. The rainfall rate and intensity of hurricanes and typhoons is likely increasing, and the geographic range likely expanding poleward in response to climate warming. The frequency of tropical cyclones has not increased as a result of climate change.\n\nGlobal sea level is rising as a consequence of thermal expansion and the melting of glaciers and ice sheets. Sea level rise has increased over time, reaching 4.8 cm per decade between 2014 and 2023. Over the 21st century, the IPCC projects 32–62 cm of sea level rise under a low emission scenario, 44–76 cm under an intermediate one and 65–101 cm under a very high emission scenario. Marine ice sheet instability processes in Antarctica may add substantially to these values, including the possibility of a 2-meter sea level rise by 2100 under high emissions.\nClimate change has led to decades of shrinking and thinning of the Arctic sea ice. While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C. Higher atmospheric CO2 concentrations cause more CO2 to dissolve in the oceans, which is making them more acidic. Because oxygen is less soluble in warmer water, its concentrations in the ocean are decreasing, and dead zones are expanding.\n\nTipping points and long-term impacts\n\nGreater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state. For instance, the Greenland ice sheet is already melting, but if global warming reaches levels between 1.7 °C and 2.3 °C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5 °C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place. While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major ocean currents like the Atlantic meridional overturning circulation (AMOC), and irreversible damage to key ecosystems like the Amazon rainforest and coral reefs can unfold in a matter of decades. The collapse of the AMOC would be a severe climate catastrophe, resulting in a cooling of the Northern Hemisphere.\nThe long-term effects of climate change on oceans include further ice melt, ocean warming, sea level rise, ocean acidification and ocean deoxygenation. The timescale of long-term impacts are centuries to millennia due to CO2's long atmospheric lifetime. The result is an estimated total sea level rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years. Oceanic CO2 uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years. Deep oceans (below 2,000 metres (6,600 ft)) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date. Further, the West Antarctic ice sheet appears committed to practically irreversible melting, which would increase the sea levels by at least 3.3 m (10 ft 10 in) over approximately 2000 years.\n\nNature and wildlife\n\nRecent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. For instance, the range of hundreds of North American birds has shifted northward at an average rate of 1.5 km/year over the past 55 years. Higher atmospheric CO2 levels and an extended growing season have resulted in global greening. However, heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear. A related phenomenon driven by climate change is woody plant encroachment, affecting up to 500 million hectares globally. Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics. The size and speed of global warming is making abrupt changes in ecosystems more likely. Overall, it is expected that climate change will result in the extinction of many species.\nThe oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land. Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds. Ocean acidification makes it harder for marine calcifying organisms such as mussels, barnacles and corals to produce shells and skeletons; and heatwaves have bleached coral reefs. Harmful algal blooms enhanced by climate change and eutrophication lower oxygen levels, disrupt food webs and cause great loss of marine life. Coastal ecosystems are under particular stress. Almost half of global wetlands have disappeared due to climate change and other human impacts. Plants have come under increased stress from damage by insects.\n\nHumans\n\nThe effects of climate change are impacting humans everywhere in the world. Impacts can be observed on all continents and ocean regions, with low-latitude, less developed areas facing the greatest risk. Continued warming has potentially \"severe, pervasive and irreversible impacts\" for people and ecosystems. The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.\n\nHealth and food\n\nThe World Health Organization calls climate change one of the biggest threats to global health in the 21st century. Scientists have warned about the irreversible harms it poses. Extreme weather events affect public health, and food and water security. Temperature extremes lead to increased illness and death. Climate change increases the intensity and frequency of extreme weather events. It can affect transmission of infectious diseases, such as dengue fever and malaria. According to the World Economic Forum, 14.5 million more deaths are expected due to climate change by 2050. 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths. By 2100, 50% to 75% of the global population would live in such areas.\nWhile total crop yields have been increasing in the past 50 years due to agricultural improvements, climate change has already decreased the rate of yield growth. ",
    "source": "wikipedia:Climate change",
    "domain": "climate"
  },
  {
    "text": "Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at normally-encountered concentrations it is odorless. As the source of carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater.\nIt is a trace gas in Earth's atmosphere at 428 parts per million (ppm), or about 0.043% (as of July 2025) having risen from pre-industrial levels of 280 ppm or about 0.028%. Burning fossil fuels is the main cause of these increased CO2 concentrations, which are the primary cause of climate change.\nIts concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by organisms and geological features. Plants, algae and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water in a process called photosynthesis, which produces oxygen as a waste product. In turn, oxygen is consumed and CO2 is released as waste by all aerobic organisms when they metabolize organic compounds to produce energy by respiration. CO2 is released from organic materials when they decay or combust, such as in forest fires. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate (HCO−3), which causes ocean acidification as atmospheric CO2 levels increase.\nCarbon dioxide is 53% denser than dry air, but is long-lived and thoroughly mixes in the atmosphere. About half of excess CO2 emissions to the atmosphere are absorbed by land and ocean carbon sinks. These sinks can become saturated and are volatile, as decay and wildfires result in the CO2 being released back into the atmosphere. CO2, or the carbon it holds, is eventually sequestered (stored for the long term) in rocks and organic deposits like coal, petroleum and natural gas.\n\nNearly all CO2 produced by humans goes into the atmosphere. Less than 1% of CO2 produced annually is put to commercial use, mostly in the fertilizer industry and in the oil and gas industry for enhanced oil recovery. Other commercial applications include food and beverage production, metal fabrication, cooling, fire suppression and stimulating plant growth in greenhouses.\n\nChemical and physical properties\n\nStructure, bonding and molecular vibrations\n\nThe symmetry of a carbon dioxide molecule is linear and centrosymmetric at its equilibrium geometry. The length of the carbon–oxygen bond in carbon dioxide is 116.3 pm, noticeably shorter than the roughly 140 pm length of a typical single C–O bond, and shorter than most other C–O multiply bonded functional groups such as carbonyls. Since it is centrosymmetric, the molecule has no electric dipole moment.\n\nAs a linear triatomic molecule, CO2 has four vibrational modes as shown in the diagram. In the symmetric and the antisymmetric stretching modes, the atoms move along the axis of the molecule. There are two bending modes, which are degenerate, meaning that they have the same frequency and same energy, because of the symmetry of the molecule. When a molecule touches a surface or touches another molecule, the two bending modes can differ in frequency because the interaction is different for the two modes. Some of the vibrational modes are observed in the infrared (IR) spectrum: the antisymmetric stretching mode at wavenumber 2349 cm−1 (wavelength 4.25 μm) and the degenerate pair of bending modes at 667 cm−1 (wavelength 15.0 μm). The symmetric stretching mode does not create an electric dipole so is not observed in IR spectroscopy, but it is detected in Raman spectroscopy at 1388 cm−1 (wavelength 7.20 μm), with a Fermi resonance doublet at 1285 cm−1.\nIn the gas phase, carbon dioxide molecules undergo significant vibrational motions and do not keep a fixed structure. However, in a Coulomb explosion imaging experiment, an instantaneous image of the molecular structure can be deduced. Such an experiment has been performed for carbon dioxide. The result of this experiment, and the conclusion of theoretical calculations based on an ab initio potential energy surface of the molecule, is that none of the molecules in the gas phase are ever exactly linear. This counter-intuitive result is trivially due to the fact that the nuclear motion volume element vanishes for linear geometries. This is so for all molecules except diatomic molecules.\n\nIn aqueous solution\n\nCarbon dioxide is soluble in water, in which it reversibly forms H2CO3 (carbonic acid), which is a weak acid, because its ionization in water is incomplete.\n\nCO2 + H2O ⇌ H2CO3\nThe hydration equilibrium constant of carbonic acid is, at 25 °C:\n\n \n \n \n \n K\n \n \n h\n \n \n \n =\n \n \n \n \n [\n \n H\n \n 2\n \n \n \n \n \n \n CO\n \n 3\n \n \n \n \n \n ]\n \n \n \n \n [\n \n CO\n \n 2\n \n (\n aq\n )\n \n \n \n \n \n \n ]\n \n \n \n \n =\n 1.70\n ×\n \n 10\n \n −\n 3\n \n \n \n \n {\\displaystyle K_{\\mathrm {h} }={\\frac {{\\ce {[H2CO3]}}}{{\\ce {[CO2_{(aq)}]}}}}=1.70\\times 10^{-3}}\n \n\nHence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as CO2 molecules, not affecting the pH.\nThe relative concentrations of CO2, H2CO3, and the deprotonated forms HCO−3 (bicarbonate) and CO2−3(carbonate) depend on the pH. As shown in a Bjerrum plot, in neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater. In very alkaline water (pH > 10.4), the predominant (>50%) form is carbonate. The oceans, being mildly alkaline with typical pH = 8.2–8.5, contain about 120 mg of bicarbonate per liter.\nBeing diprotic, carbonic acid has two acid dissociation constants, the first one for the dissociation into the bicarbonate (also called hydrogen carbonate) ion (HCO−3):\n\nH2CO3 ⇌ HCO−3 + H+\nKa1 = 2.5 × 10−4 mol/L; pKa1 = 3.6 at 25 °C.\nThis is the true first acid dissociation constant, defined as\n\n \n \n \n \n K\n \n \n a\n 1\n \n \n \n =\n \n \n \n \n [\n \n HCO\n \n 3\n \n \n −\n \n \n ]\n \n \n [\n \n H\n \n +\n \n \n ]\n \n \n \n \n [\n \n H\n \n 2\n \n \n \n \n \n \n CO\n \n 3\n \n \n \n \n \n ]\n \n \n \n \n \n \n {\\displaystyle K_{\\mathrm {a1} }={\\frac {{\\ce {[HCO3- ][H+]}}}{{\\ce {[H2CO3]}}}}}\n \n\nwhere the denominator includes only covalently bound H2CO3 and does not include hydrated CO2(aq). The much smaller and often-quoted value near 4.16 × 10−7 (or pKa1 = 6.38) is an apparent value calculated on the (incorrect) assumption that all dissolved CO2 is present as carbonic acid, so that \n\n \n \n \n \n K\n \n \n a\n 1\n \n \n \n \n \n (\n a\n p\n p\n a\n r\n e\n n\n t\n )\n \n \n =\n \n \n \n \n [\n \n HCO\n \n 3\n \n \n −\n \n \n ]\n \n \n [\n \n H\n \n +\n \n \n ]\n \n \n \n \n [\n \n H\n \n 2\n \n \n \n \n \n \n CO\n \n 3\n \n \n \n \n \n ]\n \n +\n \n [\n \n CO\n \n 2\n \n (\n aq\n )\n \n \n \n \n \n \n ]\n \n \n \n \n \n \n {\\displaystyle K_{\\mathrm {a1} }{\\rm {(apparent)}}={\\frac {{\\ce {[HCO3- ][H+]}}}{{\\ce {[H2CO3] + [CO2_{(aq)}]}}}}}\n \n\nSince most of the dissolved CO2 remains as CO2 molecules, Ka1(apparent) has a much larger denominator and a much smaller value than the true Ka1.\nThe bicarbonate ion is an amphoteric species that can act as an acid or as a base, depending on pH of the solution. At high pH, it dissociates significantly into the carbonate ion (CO2−3):\n\nHCO−3 ⇌ CO2−3 + H+\nKa2 = 4.69 × 10−11 mol/L; pKa2 = 10.329\nIn organisms, carbonic acid production is catalysed by the enzyme known as carbonic anhydrase.\n\nIn addition to altering its acidity, the presence of carbon dioxide in water also affects its electrical properties. When carbon dioxide dissolves in desalinated water, the electrical conductivity increases significantly from below 1 μS/cm to nearly 30 μS/cm. When heated, the water begins to gradually lose the conductivity induced by the presence of \n \n \n \n \n C\n \n O\n \n 2\n \n \n \n \n \n {\\displaystyle \\mathrm {CO_{2}} }\n \n , especially noticeable as temperatures exceed 30 °C.\nThe temperature dependence of the electrical conductivity of fully deionized water without CO2 saturation is comparably low in relation to these data.\n\nChemical reactions\nCO2 is a potent electrophile having an electrophilic reactivity that is comparable to benzaldehyde or strongly electrophilic α,β-unsaturated carbonyl compounds. However, unlike electrophiles of similar reactivity, the reactions of nucleophiles with CO2 are thermodynamically less favored and are often found to be highly reversible. The reversible reaction of carbon dioxide with amines to make carbamates is used in CO2 scrubbers and has been suggested as a possible starting point for carbon capture and storage by amine gas treating.\nOnly very strong nucleophiles, like the carbanions provided by Grignard reagents and organolithium compounds react with CO2 to give carboxylates:\n\nMR + CO2 → RCO2M\nwhere M = Li or MgBr and R = alkyl or aryl.\nIn metal carbon dioxide complexes, CO2 serves as a ligand, which can facilitate the conversion of CO2 to other chemicals.\nThe reduction of CO2 to CO is ordinarily a difficult and slow reaction:\n\nCO2 + 2 e− + 2 H+ → CO + H2O\nThe redox potential for this reaction near pH 7 is about −0.53 V versus the standard hydrogen electrode. The nickel-containing enzyme carbon monoxide dehydrogenase catalyses this process.\nPhotoautotrophs (i.e. plants and cyanobacteria) use the energy contained in sunlight to photosynthesize simple sugars from CO2 absorbed from the air and water:\n\nn CO2 + n H2O → (CH2O)n + n O2\n\nPhysical properties\n\nCarbon dioxide is colorless. At low concentrations, the gas is odorless; however, at sufficiently high concentrations, it has a sharp, acidic odor. At standard temperature and pressure, the density of carbon dioxide is around 1.98 kg/m3, about 1.53 times that of air.\nCarbon dioxide has no liquid state at pressures below 0.51795(10) MPa (5.11177(99) atm). At a pressure of 1 atm (0.101325 MPa), the gas deposits directly to a solid at temperatures below 194.6855(30) K (−78.4645(30) °C) and the solid sublimes directly to a gas above this temperature. In its solid state, carbon dioxide is commonly called dry ice.\n\nLiquid carbon dioxide forms only at pressures above 0.51795(10) MPa (5.11177(99) atm); the triple point of carbon dioxide is 216.592(3) K (−56.558(3) °C) at 0.51795(10) MPa (5.11177(99) atm) (see phase diagram). The critical point is 304.128(15) K (30.978(15) °C) at 7.3773(30) MPa (72.808(30) atm). Another form of solid carbon dioxide observed at high pressure is an amorphous glass-like solid. This form of glass, called carbonia, is produced by supercooling heated CO2 at extreme pressures (40–48 GPa, or about 400,000 atmospheres) in a diamond anvil. This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like silicon dioxide (silica glass) and germanium dioxide. Unlike silica and germania glasses, however, carbonia glass is not stable at normal pressures and reverts to gas when pressure is released.\nAt temperatures and pressures above the critical point, carbon dioxide behaves as a supercritical fluid known as supercritical carbon dioxide.\n\nTable of thermal and physical properties of saturated liquid carbon dioxide:\n\nTable of thermal and physical properties of carbon dioxide (CO2) at atmospheric pressure:\n\nBiological role\nCarbon dioxide is an end product of cellular respiration in organisms that obtain energy by breaking down sugars, fats and amino acids with oxygen as part of their metabolism. This includes all plants, algae and animals and aerobic fungi and bacteria. In vertebrates, the carbon dioxide travels in the blood from the body's tissues to the skin (e.g., amphibians) or the gills (e.g., fish), from where it dissolves in the water, or to the lungs from where it is exhaled. During active photosynthesis, plants can absorb more carbon dioxide from the atmosphere than they release in respiration.\n\nPhotosynthesis and carbon fixation\n\nCarbon fixation is a biochemical process by which atmospheric carbon dioxide is incorporated by plants, algae and cyanobacteria into energy-rich organic molecules such as glucose, thus creating their own food by photosynthesis. Photosynthesis uses carbon dioxide and water to produce sugars from which other organic compounds can be constructed, and oxygen is produced as a by-product.\nRibulose-1,5-bisphosphate carboxylase oxygenase, commonly abbreviated to RuBisCO, is the enzyme involved in the first major step of carbon fixation, the production of two molecules of 3-phosphoglycerate from CO2 and ribulose bisphosphate, as shown in the diagram at left.\nRuBisCO is thought to be the single most abundant protein on Earth.\n\nPhototrophs use the products of their photosynthesis as internal food sources and as raw material for the biosynthesis of more complex organic molecules, such as polysaccharides, nucleic acids, and proteins. These are used for their own growth, and also as the basis of the food chains and webs that feed other organisms, including animals such as ourselves. Some important phototrophs, the coccolithophores synthesise hard calcium carbonate scales. A globally significant species of coccolithophore is Emiliania huxleyi whose calcite scales have formed the basis of many sedimentary rocks such as limestone, where what was previously atmospheric carbon can remain fixed for geological timescales.\nPlants can grow as much as 50% faster in concentrations of 1,000 ppm CO2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients. Elevated CO2 levels cause increased growth reflected in the harvestable yield of crops, with wheat, rice and soybean all showing increases in yield of 12–14% under elevated CO2 in FACE experiments.\nIncreased atmospheric CO2 concentrations result in fewer stomata developing on plants which leads to reduced water usage and increased water-use efficiency. Studies using FACE have shown that CO2 enrichment leads to decreased concentrations of micronutrients in crop plants. This may have knock-on effects on other parts of ecosystems as herbivores will need to eat more food to gain the same amount of protein.\nThe concentration of secondary metabolites such as phenylpropanoids and flavonoids can also be altered in plants exposed to high concentrations of CO2.\nPlants also emit CO2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are only net absorbers during the day. Though a growing forest will absorb many tons of CO2 each year, a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g., fallen branches) as is used in photosynthesis in growing plants. Contrary to the long-standing view that they are carbon neutral, mature forests can continue to accumulate carbon and remain valuable carbon sinks, helping to maintain the carbon balance of Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean and thereby promotes the absorption of CO2 from the atmosphere.\n\nToxicity\n\nCarbon dioxide content in fresh air (averaged between sea-level and 10 kPa level, i.e., about 30 km (19 mi) altitude) varies between 0.036% (360 ppm) and 0.041% (412 ppm), depending on the location.\nIn humans, exposure to CO2 at concentrations greater than 5% causes the development of hypercapnia and respiratory acidosis. Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour. Concentrations of more than 10% may cause convulsions, coma, and death. CO2 levels of more than 30% act rapidly leading to loss of consciousness in seconds.\nBecause it is heavier than air, in locations where the gas seeps from the ground (due to sub-surface volcanic or geothermal activity) in relatively high concentrations, without the dispersing effects of wind, it can collect in sheltered/pocketed locations below average ground level, causing animals located therein to be suffocated. Carrion feeders attracted to the carcasses are then also killed. Children have been killed in the same way near the city of Goma by CO2 emissions from the nearby volcano Mount Nyiragongo. The Swahili term for this phenomenon is mazuku.\n\nAdaptation to increased concentrations of CO2 occurs in humans, including modified breathing and kidney bicarbonate production, in order to balance the effects of blood acidification (acidosis). Several studies suggested that 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a submarine) since the adaptation is physiological and reversible, as deterioration in performance or in normal physical activity does not happen at this level of exposure for five days. Yet, other studies show a decrease in cognitive function even at much lower levels. Also, with ongoing respiratory acidosis, adaptation or compensatory mechanisms will be unable to reverse the condition.\n\nBelow 1%\nThere are few studies of the health effects of long-term continuous CO2 exposure on humans and animals at levels below 1%. Occupational CO2 exposure limits have been set in the United States at 0.5% (5000 ppm) for an eight-hour period. At this CO2 concentration, International Space Station crew experienced headaches, lethargy, mental slowness, emotional irritation, and sleep disruption. Studies in animals at 0.5% CO2 have demonstrated kidney calcification and bone loss after eight weeks of exposure. A study of humans exposed in 2.5 hour sessions demonstrated significant negative effects on cognitive abilities at concentrations as low as 0.1% (1000 ppm) CO2 likely due to CO2 induced increases in cerebral blood flow. Another study observed a decline in basic activity level and information usage at 1000 ppm, when compared to 500 ppm.\nHowever a review of the literature found that a reliable subset of studies on the phenomenon of carbon dioxide induced cognitive impairment to only show a small effect on high-level decision making (for concentrations below 5000 ppm). Most of the studies were confounded by inadequate study designs, environmental comfort, uncertainties in exposure doses and differing cognitive assessments used. Similarly a study on the effects of the concentration of CO2 in motorcycle helmets has been criticized for having dubious methodology in not noting the self-reports of motorcycle riders and taking measurements using mannequins. Further when normal motorcycle conditions were achieved (such as highway or city speeds) or the visor was raised the concentration of CO2 declined to safe levels (0.2%).\n\nVentilation\n\nPoor ventilation is one of the main causes of excessive CO2 concentrations in closed spaces, leading to poor indoor air quality. Carbon dioxide differential above outdoor concentrations at steady state conditions (when the occupancy and ventilation system operation are sufficiently long that CO2 concentration has stabilized) are sometimes used to estimate ventilation rates per person. Higher CO2 concentrations are associated with occupant health, comfort and performance degradation. ASHRAE Standard 62.1–2007 ventilation rates may result in indoor concentrations up to 2,100 ppm above ambient outdoor conditions. Thus if the outdoor concentration is 400 ppm, indoor concentrations may reach 2,500 ppm with ventilation rates that meet this industry consensus standard. Concentrations in poorly ventilated spaces can be found even higher than this (range of 3,000 or 4,000 ppm).\nMiners, who are particularly vulnerable to gas exposure due to insufficient ventilation, referred to mixtures of carbon dioxide and nitrogen as \"blackdamp\", \"choke damp\" or \"stythe\". Before more effective technologies were developed, miners would frequently monitor for dangerous levels of blackdamp and other gases in mine shafts by bringing a caged canary with them as they worked. The canary is more sensitive to asphyxiant gases than humans, and as it became unconscious would stop singing and fall off its perch. The Davy lamp could also detect high levels of blackdamp (which sinks, and collects near the floor) by burning less brightly, while methane, another suffocating gas and explosion risk, would make the lamp burn more brightly.\nIn February 2020, three people died from suffocation at a party in Moscow when dry ice (frozen CO2) was added to a swimming pool to cool it down. A similar accident occurred in 2018 when a woman died from CO2 fumes emanating from the large amount of dry ice she was transporting in her car.\n\nIndoor air\nHumans spend more and more time in a confined atmosphere (around 80-90% of the time in a building or vehicle). According to the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) and various actors in France, the CO2 rate in the indoor air of buildings (linked to human or animal occupancy and the presence of combustion installations), weighted by air renewal, is \"usually between about 350 and 2,500 ppm\".\nIn homes, schools, nurseries and offices, there are no systematic relationships between the levels of CO2 and other pollutants, and indoor CO2 is statistically not a good predictor of pollutants linked to outdoor road (or air, etc.) traffic. CO2 is the parameter that changes the fastest (with hygrometry and oxygen levels when humans or animals are gathered in a closed or poorly ventilated room). In poor countries, many open hearths are sources of CO2 and CO emitted directly into the living environment.\n\nOutdoor areas with elevated concentrations\nLocal concentrations of carbon dioxide can reach high values near strong sources, especially those that are isolated by surrounding terrain. At the Bossoleto hot spring near Rapolano Terme in Tuscany, Italy, situated in a bowl-shaped depression about 100 m (330 ft) in diameter, concentrations of CO2 rise to above 75% overnight, sufficient to kill insects and small animals. After sunrise the gas is dispersed by convection. High concentrations of CO2 produced by disturbance of deep lake water saturated with CO2 are thought to have caused 37 fatalities at Lake Monoun, Cameroon in 1984 and 1700 casualties at Lake Nyos, Cameroon in 1986.\n\nHuman physiology\n\nContent\n\nThe body produces approximately 2.3 pounds (1.0 kg) of carbon dioxide per day per person, containing 0.63 pounds (290 g) of carbon. In humans, this carbon dioxide is carried through the venous system and is breathed out through the lungs, resulting in lower concentrations in the arteries. The carbon dioxide content of the blood is often given as the partial pressure, which is the pressure which carbon dioxide would have had if it alone occupied the volume. In humans, the blood carbon dioxide contents are shown in the adjacent table.\n\nTransport in the blood\nCO2 is carried in blood in three different ways. Exact percentages vary between arterial and venous blood.\n\nMajority (about 70% to 80%) is converted to bicarbonate ions HCO−3 by the enzyme carbonic anhydrase in the red blood cells, by the reaction:\nCO2 + H2O → H2CO3 → H+ + HCO−3\n5–10% is dissolved in blood plasma\n5–10% is bound to hemoglobin as carbamino compounds\nHemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2 bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of allosteric effects on the hemoglobin molecule, the binding of CO2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. This is known as the Haldane Effect, and is important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of CO2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the Bohr effect.\n\nRegulation of respiration\nCarbon dioxide is one of the mediators of local autoregulation of blood supply. If its concentration is high, the capillaries expand to allow a greater blood flow to that tissue.\nBicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO2 in their blood. Breathing that is too slow or shallow causes respiratory acidosis, while breathing that is too rapid leads to hyperventilation, which can cause respiratory alkalosis.\nAlthough the body requires oxygen for metabolism, low oxygen levels normally do not stimulate breathing. Rather, breathing is stimulated by higher carbon dioxide levels. As a result, breathing low-pressure air or a gas mixture with no oxygen at all (such as pure nitrogen) can lead to loss of consciousness without ever experiencing air hunger. This is especially perilous for high-altitude fighter pilots. It is also why flight attendants instruct passengers, in case of loss of cabin pressure, to apply the oxygen mask to themselves first before helping others; otherwise, one risks losing consciousness.\nThe respiratory centers try to maintain an arterial CO2 pressure of 40 mmHg. With intentional hyperventilation, the CO2 content of arterial blood may be lowered to 10–20 mmHg (the oxygen content of the blood is little affected), and the respiratory drive is diminished. This is why one can hold one's breath longer after hyperventilating than without hyperventilating. This carries the risk that unconsciousness may result before the need to breathe becomes overwhelming, which is why hyperventilation is particularly dangerous before free diving.\n\nConcentrations and role in the environment\n\nAtmosphere\n\nOceans\n\nOcean acidification\nCarbon dioxide dissolves in the ocean to form carbonic acid (H2CO3), bicarbonate (HCO−3), and carbonate (CO2−3). There is about fifty times as much carbon dioxide dissolved in the oceans as exists in the atmosphere. The oceans act as an enormous carbon sink, and have taken up about a third of CO2 emitted by human activity.\n\nHydrothermal vents\nCarbon dioxide is also introduced into the oceans through hydrothermal vents. The Champagne hydrothermal vent, found at the Northwest Eifuku volcano in the Mariana Trench, produces almost pure liquid carbon dioxide, one of only two known sites in the world as of 2004, the other being in the Okinawa Trough. The finding of a submarine lake of liquid carbon dioxide in the Okinawa Trough was reported in 2006.\n\nSources\nThe burning of fossil fuels for energy produces 36.8 billion tonnes of CO2 per year as of 2023. Nearly all of this goes into the atmosphere, where approximately half is subsequently absorbed into natural carbon sinks. Less than 1% of CO2 produced annually is put to commercial use.\n\nBiological processes\nCarbon dioxide is a by-product of the fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages and in the production of bioethanol. Yeast metabolizes sugar to produce CO2 and ethanol, also known as alcohol, as follows:\n\nC6H12O6 → 2 CO2 + 2 CH3CH2OH\nAll aerobic organisms produce CO2 when they oxidize carbohydrates, fatty acids, and proteins. The large number of reactions involved are exceedingly complex and not described easily. Refer to cellular respiration, anaerobic respiration and photosynthesis. The equation for the respiration of glucose and other monosaccharides is:\n\nC6H12O6 + 6 O2 → 6 CO2 + 6 H2O\nAnaerobic organisms decompose organic material producing methane and carbon dioxide together with traces of other compounds. Regardless of the type of organic material, the production of gases follows well defined kinetic pattern. Carbon dioxide comprises about 40–45% of the gas that emanates from decomposition in landfills (termed \"landfill gas\"). Most of the remaining 50–55% is methane.\n\nCombustion\nThe combustion of all carbon-based fuels, such as methane (natural gas), petroleum distillates (gasoline, diesel, kerosene, propane), coal, wood and generic organic matter produces carbon dioxide and, except in the case of pure carbon, water. As an example, the chemical reaction between methane and oxygen:\n\nCH4 + 2 O2 → CO2 + 2 H2O\nIron is reduced from its oxides with coke in a blast furnace, producing pig iron and carbon dioxide:\n\nFe2O3 + 3 CO → 3 CO2 + 2 Fe\n\nBy-product from hydrogen production\nCarbon dioxide is a byproduct of the industrial production of hydrogen by steam reforming and the water gas shift reaction in ammonia production. These processes begin with the reaction of water and natural gas (mainly methane).\n\nThermal decomposition of limestone\nIt is produced by thermal decomposition of limestone, CaCO3 by heating (calcining) at about 850 °C (1,560 °F), in the manufacture of quicklime (calcium oxide, CaO), a compound that has many industrial uses:\n\nCaCO3 → CaO + CO2\nAcids liberate CO2 from most metal carbonates. Consequently, it may be obtained directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or dolomite. The reaction between hydrochloric acid and calcium carbonate (limestone or chalk) is shown below:\n\nCaCO3 + 2 HCl → CaCl2 + H2CO3\nThe carbonic acid (H2CO3) then decomposes to water and CO2:\n\nH2CO3 → CO2 + H2O\nSuch reactions are accompanied by foaming or bubbling, or both, as the gas is released. They have widespread uses in industry because they can be used to neutralize waste acid streams.\n\nCommercial uses\n\nAround 230 Mt of CO2 are used each year, mostly in the fertiliser industry for urea production (130 million tonnes) and in the oil and gas industry for enhanced oil recovery (70 to 80 million tonnes). Other commercial applications include food and beverage production, metal fabrication, cooling, fire suppression and stimulating plant growth in greenhouses.\nTechnology exists to capture CO2 from industrial flue gas or from the air. Research is ongoing on ways to use captured CO2 in products and some of these processes have been deployed co",
    "source": "wikipedia:Carbon dioxide",
    "domain": "climate"
  },
  {
    "text": "Methane (US: METH-ayn, UK: MEE-thayn) is a chemical compound that has the chemical formula CH4 (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes it an economically attractive fuel, although capturing and storing it is difficult because it is a gas at standard temperature and pressure. In the Earth's atmosphere methane is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Methane is an organic hydrocarbon, and among the simplest of organic compounds.\nNaturally occurring methane is found both below ground and under the seafloor and is formed by both geological and biological processes. The largest reservoir of methane is under the seafloor in the form of methane clathrates. When methane reaches the surface and the atmosphere, it is known as atmospheric methane.\nThe Earth's atmospheric methane concentration has increased by about 160% since 1750, with the overwhelming percentage caused by human activity. It accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases, according to the 2021 Intergovernmental Panel on Climate Change report. Strong, rapid and sustained reductions in methane emissions could limit near-term warming and improve air quality by reducing global surface ozone.\nMethane has also been detected on other planets, including Mars, which has implications for astrobiology research.\n\nProperties and bonding\nMethane is a tetrahedral molecule with four equivalent C–H bonds. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H. The lowest-energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting \"three-over-one\" bonding scheme is consistent with photoelectron spectroscopic measurements.\nMethane is an odorless, colourless and transparent gas at standard temperature and pressure. It does absorb visible light, especially at the red end of the spectrum, due to overtone bands, but the effect is only noticeable if the light path is very long. This is what gives Uranus and Neptune their blue or bluish-green colors, as light passes through their atmospheres containing methane and is then scattered back out.\nThe familiar smell of natural gas as used in homes is achieved by the addition of an odorant, usually blends containing tert-butylthiol, as a safety measure. Methane has a boiling point of −161.5 °C at a pressure of one atmosphere. As a gas, it is flammable over a range of concentrations (5.4%–17%) in air at standard pressure.\nSolid methane exists in several modifications, of which nine are known. Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system (space group Fm3m). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it is a plastic crystal.\n\nChemical reactions\nThe primary chemical reactions of methane are combustion, steam reforming to syngas, and halogenation. In general, methane reactions are difficult to control.\n\nSelective oxidation\nPartial oxidation of methane to methanol (CH3OH), a more convenient, liquid fuel, is challenging because the reaction typically progresses all the way to carbon dioxide and water even with an insufficient supply of oxygen. The enzyme methane monooxygenase produces methanol from methane, but cannot be used for industrial-scale reactions. Some homogeneously catalyzed systems and heterogeneous systems have been developed, but all have significant drawbacks. These generally operate by generating protected products which are shielded from overoxidation. Examples include the Catalytica system, copper zeolites, and iron zeolites stabilizing the alpha-oxygen active site.\nOne group of bacteria catalyze methane oxidation with nitrite as the oxidant in the absence of oxygen, giving rise to the so-called anaerobic oxidation of methane.\n\nAcid–base reactions\nLike other hydrocarbons, methane is an extremely weak acid. Its pKa in DMSO is estimated to be 56. It cannot be deprotonated in solution, but the conjugate base is known in forms such as methyllithium.\nA variety of positive ions derived from methane have been observed, mostly as unstable species in low-pressure gas mixtures. These include methenium or methyl cation CH+3, methane cation CH+4, and methanium or protonated methane CH+5. Some of these have been detected in outer space. Methanium can also be produced as diluted solutions from methane with superacids. Cations with higher charge, such as CH2+6 and CH3+7, have been studied theoretically and conjectured to be stable.\nDespite the strength of its C–H bonds, there is intense interest in catalysts that facilitate C–H bond activation in methane (and other lower numbered alkanes).\n\nCombustion\n\nMethane's heat of combustion is 55.5 MJ/kg. Combustion of methane is a multiple step reaction summarized as follows:\n\nCH4 + 2 O2 → CO2 + 2 H2O\nΔH = −802 kJ/mol, at standard conditions (for water vapor, ΔH = −891 kJ/mol for liquid water)\nPeters four-step chemistry is a systematically reduced four-step chemistry that explains the burning of methane.\n\nMethane radical reactions\nGiven appropriate conditions, methane reacts with halogen radicals as follows:\n\n•X + CH4 → HX + •CH3\n•CH3 + X2 → CH3X + •X\nwhere X is a halogen: fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). This mechanism for this process is called free radical halogenation. It is initiated when UV light or some other radical initiator (like peroxides) produces a halogen atom. A two-step chain reaction ensues in which the halogen atom abstracts a hydrogen atom from a methane molecule, resulting in the formation of a hydrogen halide molecule and a methyl radical (•CH3). The methyl radical then reacts with a molecule of the halogen to form a molecule of the halomethane, with a new halogen atom as byproduct. Similar reactions can occur on the halogenated product, leading to replacement of additional hydrogen atoms by halogen atoms with dihalomethane, trihalomethane, and ultimately, tetrahalomethane structures, depending upon reaction conditions and the halogen-to-methane ratio.\nThis reaction is commonly used with chlorine to produce dichloromethane and chloroform via chloromethane. Carbon tetrachloride can be made with excess chlorine.\n\nUses\nMethane may be transported as a refrigerated liquid (liquefied natural gas, or LNG). While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of the cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component.\n\nFuel\nMethane is used as a fuel for ovens, homes, water heaters, kilns, automobiles, rockets, turbines, etc.\nAs the major constituent of natural gas, methane is important for electricity generation by burning it as a fuel in a gas turbine or steam generator. Compared to other hydrocarbon fuels, methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than that of any other hydrocarbon, but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) than other complex hydrocarbons. In many areas with a dense enough population, methane is piped into homes and businesses for heating, cooking, and industrial uses. In this context it is usually known as natural gas, which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot. Liquefied natural gas (LNG) is predominantly methane converted into liquid form for ease of storage or transport.\n\nRocket propellant\n\nRefined liquid methane as well as LNG is used as a rocket fuel, when combined with liquid oxygen, as in the TQ-12, BE-4, Raptor, YF-215, and Aeon engines. Due to the similarities between methane and LNG such engines are commonly grouped together under the term methalox.\nAs a liquid rocket propellant, a methane/liquid oxygen combination offers the advantage over kerosene/liquid oxygen combination, or kerolox, of producing small exhaust molecules, reducing coking or deposition of soot on engine components. Methane is easier to store than hydrogen due to its higher boiling point and density, as well as its lack of hydrogen embrittlement. The lower molecular weight of the exhaust also increases the fraction of the heat energy which is in the form of kinetic energy available for propulsion, increasing the specific impulse of the rocket. Compared to liquid hydrogen, the specific energy of methane is lower but this disadvantage is offset by methane's greater density and temperature range, allowing for smaller and lighter tankage for a given fuel mass. Liquid methane has a temperature range (91–112 K) nearly compatible with liquid oxygen (54–90 K). The fuel currently sees use in operational launch vehicles such as Zhuque-2, Vulcan and New Glenn as well as in-development launchers such as Starship, Neutron, Terran R, Nova, and Long March 9.\n\nChemical feedstock\nNatural gas, which is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. Steam methane reforming (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50 million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas. Much of this hydrogen is used in petroleum refineries, in the production of chemicals and in food processing. Very large quantities of hydrogen are used in the industrial synthesis of ammonia.\nAt high temperatures (700–1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield a mixture of CO and H2, known as \"water gas\" or \"syngas\":\n\nCH4 + H2O ⇌ CO + 3 H2\nThis reaction is strongly endothermic (consumes heat, ΔHr = 206 kJ/mol).\nAdditional hydrogen is obtained by the reaction of CO with water via the water-gas shift reaction:\n\nCO + H2O ⇌ CO2 + H2\nThis reaction is mildly exothermic (produces heat, ΔHr = −41 kJ/mol).\nMethane is also subjected to free-radical chlorination in the production of chloromethanes, although methanol is a more typical precursor.\nHydrogen can also be produced via the direct decomposition of methane, also known as methane pyrolysis, which, unlike steam reforming, produces no greenhouse gases (GHG). The heat needed for the reaction can also be GHG emission free, e.g. from concentrated sunlight, renewable electricity, or burning some of the produced hydrogen. If the methane is from biogas then the process can be a carbon sink. Temperatures in excess of 1200 °C are required to break the bonds of methane to produce hydrogen gas and solid carbon. Through the use of a suitable catalyst the reaction temperature can be reduced to between 550 and 900 °C depending on the chosen catalyst. Dozens of catalysts have been tested, including unsupported and supported metal catalysts, carbonaceous and metal-carbon catalysts.\nThe reaction is moderately endothermic as shown in the reaction equation below.\n\nCH4(g) → C(s) + 2 H2(g)\n(ΔH° = 74.8 kJ/mol)\n\nRefrigerant\nAs a refrigerant, methane has the ASHRAE designation R-50.\n\nGeneration\n\nMethane can be generated through geological, biological or industrial routes.\n\nGeological routes\n\nThe two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic (abiotic). Thermogenic methane occurs due to the breakup of organic matter at elevated temperatures and pressures in deep sedimentary strata. Most methane in sedimentary basins is thermogenic; therefore, thermogenic methane is the most important source of natural gas. Thermogenic methane components are typically considered to be relic (from an earlier time). Generally, formation of thermogenic methane (at depth) can occur through organic matter breakup, or organic synthesis. Both ways can involve microorganisms (methanogenesis), but may also occur inorganically. The processes involved can also consume methane, with and without microorganisms.\nThe more important source of methane at depth (crystalline bedrock) is abiotic. Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes or via water-rock reactions that occur at low temperatures and pressures, like serpentinization.\n\nBiological routes\n\nMost of Earth's methane is biogenic and is produced by methanogenesis, a form of anaerobic respiration only known to be conducted by some members of the domain Archaea. Methanogens occur in landfills and soils, ruminants (for example, cattle), the guts of termites, and the anoxic sediments below the seafloor and the bottom of lakes.\nThis multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is:\n\nCO2 + 4 H2 → CH4 + 2 H2O\nThe final step in the process is catalyzed by the enzyme methyl coenzyme M reductase (MCR).\n\nWetlands\n\nWetlands are the largest natural sources of methane to the atmosphere, accounting for approximately 20–30% of atmospheric methane. Climate change is increasing the amount of methane released from wetlands due to increased temperatures and altered rainfall patterns. This phenomenon is called wetland methane feedback.\nRice cultivation generates as much as 12% of total global methane emissions due to the long-term flooding of rice fields.\n\nRuminants\nRuminants such as cattle belch out methane, accounting for about 22% of the U.S. annual methane emissions to the atmosphere. One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane. A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions. Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments, and to trap the gas to use its combustion energy.\n\nSeafloor sediments\nMost of the subseafloor is anoxic because oxygen is removed by aerobic microorganisms within the first few centimeters of the sediment. Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in gas hydrates. These other organisms that utilize methane for energy are known as methanotrophs ('methane-eating'), and are the main reason why little methane generated at depth reaches the sea surface. Consortia of Archaea and Bacteria have been found to oxidize methane via anaerobic oxidation of methane (AOM); the organisms responsible for this are anaerobic methanotrophic Archaea (ANME) and sulfate-reducing bacteria (SRB).\n\nIndustrial routes\n\nGiven its cheap abundance in natural gas, there is little incentive to produce methane industrially. Methane can be produced by hydrogenating carbon dioxide through the Sabatier process. Methane is also a side product of the hydrogenation of carbon monoxide in the Fischer–Tropsch process, which is practiced on a large scale to produce longer-chain molecules than methane.\nAn example of large-scale coal-to-methane gasification is the Great Plains Synfuels plant, started in 1984 in Beulah, North Dakota as a way to develop abundant local resources of low-grade lignite, a resource that is otherwise difficult to transport for its weight, ash content, low calorific value and propensity to spontaneous combustion during storage and transport. A number of similar plants exist around the world, although mostly these plants are targeted towards the production of long chain alkanes for use as gasoline, diesel, or feedstock to other processes.\nPower to methane is a technology that uses electrical power to produce hydrogen from water by electrolysis and uses the Sabatier reaction to combine hydrogen with carbon dioxide to produce methane.\n\nLaboratory synthesis\nMethane can be produced by protonation of methyl lithium or a methyl Grignard reagent such as methylmagnesium chloride. It can also be made from anhydrous sodium acetate and dry sodium hydroxide, mixed and heated above 300 °C (with sodium carbonate as byproduct). In practice, a requirement for pure methane can easily be fulfilled by steel gas bottle from standard gas suppliers.\n\nOccurrence\nMethane is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields, with coal seam gas extraction becoming a major source (see coal bed methane extraction, a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other hydrocarbon fuels, and sometimes accompanied by helium and nitrogen. Methane is produced at shallow levels (low pressure) by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain oil.\nMethane is generally transported in bulk by pipeline in its natural gas form, or by LNG carriers in its liquefied form; few countries transport it by truck.\n\nAtmospheric methane and climate change\n\nMethane is an important greenhouse gas, responsible for around 30% of the rise in global temperatures since the industrial revolution.\nMethane has a global warming potential (GWP) of 29.8 ± 11 compared to CO2 (potential of 1) over a 100-year period, and 82.5 ± 25.8 over a 20-year period. This means that, for example, a leak of one tonne of methane is equivalent to emitting 82.5 tonnes of carbon dioxide. Burning methane and producing carbon dioxide also reduces the greenhouse gas impact compared to simply venting methane to the atmosphere.\n\nAs methane is gradually converted into carbon dioxide (and water) in the atmosphere, these values include the climate forcing from the carbon dioxide produced from methane over these timescales.\nAnnual global methane emissions are currently approximately 580 Mt, 40% of which is from natural sources and the remaining 60% originating from human activity, known as anthropogenic emissions. The largest anthropogenic source is agriculture, responsible for around one quarter of emissions, closely followed by the energy sector, which includes emissions from coal, oil, natural gas and biofuels.\nHistoric methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol/mol during the warm interglacial periods. A 2012 NASA website said the oceans were a potential important source of Arctic methane, but more recent studies associate increasing methane levels as caused by human activity.\nGlobal monitoring of atmospheric methane concentrations began in the 1980s. The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century. In 2013, atmospheric methane accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. Between 2011 and 2019 the annual average increase of methane in the atmosphere was 1866 ppb. From 2015 to 2019 sharp rises in levels of atmospheric methane were recorded.\nIn 2019, the atmospheric methane concentration was higher than at any time in the last 800,000 years. As stated in the AR6 of the IPCC, \"Since 1750, increases in CO2 (47%) and CH4 (156%) concentrations far exceed, and increases in N2O (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence)\".\nIn February 2020, it was reported that fugitive emissions and gas venting from the fossil fuel industry may have been significantly underestimated.\n The largest annual increase occurred in 2021 with the overwhelming percentage caused by human activity.\nClimate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a climate change feedback. Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere.\nOver 100 countries have signed the Global Methane Pledge, launched in 2021, promising to cut their methane emissions by 30% by 2030. This could avoid 0.2 °C of warming globally by 2050, although there have been calls for higher commitments in order to reach this target. The International Energy Agency's 2022 report states \"the most cost-effective opportunities for methane abatement are in the energy sector, especially in oil and gas operations\".\n\nClathrates\nMethane clathrates (also known as methane hydrates) are solid cages of water molecules that trap single molecules of methane. Significant reservoirs of methane clathrates have been found in arctic permafrost and along continental margins beneath the ocean floor within the gas clathrate stability zone, located at high pressures (1 to 100 MPa; lower end requires lower temperature) and low temperatures (< 15 °C; upper end requires higher pressure). Methane clathrates can form from biogenic methane, thermogenic methane, or a mix of the two. These deposits are both a potential source of methane fuel as well as a potential contributor to global warming. The global mass of carbon stored in gas clathrates is still uncertain and has been estimated as high as 12,500 Gt carbon and as low as 500 Gt carbon. The estimate has declined over time with a most recent estimate of ≈1800 Gt carbon. A large part of this uncertainty is due to our knowledge gap in sources and sinks of methane and the distribution of methane clathrates at the global scale. For example, a source of methane was discovered relatively recently in an ultraslow spreading ridge in the Arctic. Some climate models suggest that today's methane emission regime from the ocean floor is potentially similar to that during the period of the Paleocene–Eocene Thermal Maximum (PETM) around 55.5 million years ago, although there are no data indicating that methane from clathrate dissociation currently reaches the atmosphere. Arctic methane release from permafrost and seafloor methane clathrates is a potential consequence and further cause of global warming; this is known as the clathrate gun hypothesis. Data from 2016 indicate that Arctic permafrost thaws faster than predicted.\n\nPublic safety and the environment\n\nMethane \"degrades air quality and adversely impacts human health, agricultural yields, and ecosystem productivity\".\nThe 2015–2016 methane gas leak in Aliso Canyon, California was considered to be the worst in terms of its environmental effect in American history. It was also described as more damaging to the environment than Deepwater Horizon's leak in the Gulf of Mexico.\nIn May 2023 The Guardian published a report blaming Turkmenistan as the worst in the world for methane super emitting. The data collected by Kayrros researchers indicate that two large Turkmen fossil fuel fields leaked 2.6 million and 1.8 million metric tonnes of methane in 2022 alone, pumping the CO2 equivalent of 366 million tonnes into the atmosphere, surpassing the annual CO2 emissions of the United Kingdom.\n\nExtraterrestrial methane\n\nMethane is abundant in many parts of the Solar System and potentially could be harvested on the surface of another Solar System body (in particular, using methane production from local materials found on Mars or Titan), providing fuel for a return journey.\nMethane has been detected on all planets of the Solar System and most of the larger moons. With the possible exception of Mars, it is believed to have come from abiotic processes.\n\nInterstellar medium\nInfrared astronomy has detected methane in molecular clouds of the interstellar medium.\n\nMars\n\nThe Curiosity rover has documented seasonal fluctuations of atmospheric methane levels on Mars. These fluctuations peaked at the end of the Martian summer at 0.6 parts per billion. Methane could be produced by a non-biological process called serpentinization involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars. There has been some speculation that methanogenic microbes, such as bacteria in the sub-surface, could also be responsible for methane on Mars; however there is no other evidence that such lifeforms exist.\nMethane has been proposed as a possible rocket propellant on future Mars missions due in part to the possibility of synthesizing it on the planet by in situ resource utilization. An adaptation of the Sabatier methanation reaction may be used with a mixed catalyst bed and a reverse water-gas shift in a single reactor to produce methane and oxygen from the raw materials available on Mars, utilizing water from the Martian subsoil and carbon dioxide in the Martian atmosphere.\n\nTitan\n\nMethane has been detected in vast abundance on Titan, the largest moon of Saturn. It comprises a significant portion of its atmosphere and also exists in a liquid form on its surface, where it comprises the majority of the liquid in Titan's vast lakes of hydrocarbons, the second largest of which is believed to be almost pure methane in composition.\nThe presence of stable lakes of liquid methane on Titan, as well as the surface of Titan being highly chemically active and rich in organic compounds, has led scientists to consider the possibility of life existing within Titan's lakes, using methane as a solvent in the place of water for Earth-based life and using hydrogen in the atmosphere to derive energy with acetylene.\n\nHistory\n\nThe discovery of methane is credited to Italian physicist Alessandro Volta, who characterized numerous properties including its flammability limit and origin from decaying organic matter.\nVolta was initially motivated by reports of inflammable air present in marshes by his friend Father Carlo Giuseppe Campi. While on a fishing trip to Lake Maggiore straddling Italy and Switzerland in November 1776, he noticed the presence of bubbles in the nearby marshes and decided to investigate. Volta collected the gas rising from the marsh and demonstrated that the gas was inflammable.\nVolta notes similar observations of inflammable air were present previously in scientific literature, including a letter written by Benjamin Franklin.\nFollowing the Felling mine disaster of 1812 in which 92 men perished, Sir Humphry Davy established that the feared firedamp was in fact largely methane.\nThe name \"methane\" was coined in 1866 by the German chemist August Wilhelm von Hofmann. The name was derived from methanol.\n\nEtymology\nEtymologically, the word methane is coined from the chemical suffix \"-ane\", which denotes substances belonging to the alkane family; and the word methyl, which is derived from the German Methyl (1840) or directly from the French méthyle, which is a back-formation from the French méthylène (corresponding to English \"methylene\"), the root of which was coined by Jean-Baptiste Dumas and Eugène Péligot in 1834 from the Greek μέθυ méthy (wine) (related to English \"mead\") and ὕλη hýlē (meaning \"wood\"). The radical is named after this because it was first detected in methanol, an alcohol first isolated by distillation of wood. The chemical suffix -ane is from the coordinating chemical suffix -ine which is from Latin feminine suffix -ina which is applied to represent abstracts. The coordination of \"-ane\", \"-ene\", \"-one\", etc. was proposed in 1866 by German chemist August Wilhelm von Hofmann.\n\nAbbreviations\nThe abbreviation CH4-C can mean the mass of carbon contained in a mass of methane, and the mass of methane is always 1.33 times the mass of CH4-C. CH4-C can also mean the methane-carbon ratio, which is 1.33 by mass. Methane at scales of the atmosphere is commonly measured in teragrams (Tg CH4) or millions of metric tons (MMT CH4), which mean the same thing. Other standard units are also used, such as nanomole (nmol, one billionth of a mole), mole (mol), kilogram, and gram.\n\nSafety\nMethane is an asphyxiant gas, meaning that it is non-toxic and the primary health hazard is displacement of oxygen in high enough concentrations, potentially causing death by asphyxiation. No systemic toxicity has been detected at 5% concentration in air.\nMethane is an extremely flammable gas at normal ambient temperature. It may form explosive mixtures with air. Methane gas explosions are responsible for many deadly mining disasters. A methane gas explosion was the cause of the Upper Big Branch coal mine disaster in West Virginia on April 5, 2010, killing 29. Natural gas accidental release has also been a major focus in the field of safety engineering, due to past accidental releases that concluded in the formation of jet fire disasters.\n\nSee also\n\nExplanatory notes\n\nCitations\n\nCited sources\nHaynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. ISBN 978-1-4987-5429-3.\n\nExternal links\n\nMethane at The Periodic Table of Videos (University of Nottingham)\nInternational Chemical Safety Card 0291\nGas (Methane) Hydrates – A New Frontier – United States Geological Survey (archived 6 February 2004)\nLunsford, Jack H. (2000). \"Catalytic conversion of methane to more useful chemicals and fuels: A challenge for the 21st century\". Catalysis Today. 63 (2–4): 165–174. doi:10.1016/S0920-5861(00)00456-9.\nCDC ",
    "source": "wikipedia:Methane",
    "domain": "climate"
  },
  {
    "text": "The greenhouse effect occurs when heat-trapping gases in a planet's atmosphere prevent the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source (as in the case of Jupiter) or come from an external source, such as a host star. In the case of Earth, the Sun emits shortwave radiation (sunlight) that passes through greenhouse gases to heat the Earth's surface. In response, the Earth's surface emits longwave radiation that is mostly absorbed by greenhouse gases, reducing the rate at which the Earth can cool off.\nWithout the greenhouse effect, the Earth's average surface temperature would be as cold as −18 °C (−0.4 °F). This is much less than the 20th century average of about 14 °C (57 °F). In addition to naturally present greenhouse gases, burning of fossil fuels has increased amounts of carbon dioxide and methane in the atmosphere. As a result, global warming of about 1.2 °C (2.2 °F) has occurred since the Industrial Revolution, with the global average surface temperature increasing at a rate of 0.18 °C (0.32 °F) per decade since 1981.\nAll objects with a temperature above absolute zero emit thermal radiation. The wavelengths of thermal radiation emitted by the Sun and Earth differ because their surface temperatures are different. The Sun has a surface temperature of 5,500 °C (9,900 °F), so it emits most of its energy as shortwave radiation in near-infrared and visible wavelengths (as sunlight). In contrast, Earth's surface has a much lower temperature, so it emits longwave radiation at mid- and far-infrared wavelengths. A gas is a greenhouse gas if it absorbs longwave radiation. Earth's atmosphere absorbs only 23% of incoming shortwave radiation, but absorbs 90% of the longwave radiation emitted by the surface, thus accumulating energy and warming the Earth's surface.\nThe existence of the greenhouse effect (while not named as such) was proposed as early as 1824 by Joseph Fourier. The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901.\n\nDefinition\nThe greenhouse effect on Earth is defined as: \"The infrared radiative effect of all infrared absorbing constituents in the atmosphere. Greenhouse gases (GHGs), clouds, and some aerosols absorb terrestrial radiation emitted by the Earth's surface and elsewhere in the atmosphere.\"\nThe enhanced greenhouse effect describes the fact that by increasing the concentration of GHGs in the atmosphere (due to human action), the natural greenhouse effect is increased.\n\nTerminology\nThe term greenhouse effect comes from an analogy to greenhouses. Both greenhouses and the greenhouse effect work by retaining heat from sunlight, but the way they retain heat differs. Greenhouses retain heat mainly by blocking convection (the movement of air). In contrast, the greenhouse effect retains heat by restricting radiative transfer through the air and reducing the rate at which thermal radiation is emitted into space.\n\nHistory of discovery and investigation\n\nThe existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier. The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. She concluded that \"An atmosphere of that gas would give to our earth a high temperature...\"\nJohn Tyndall was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a very small proportion of the atmosphere, with the main gases having no effect, and was largely due to water vapor, though small percentages of hydrocarbons and carbon dioxide had a significant effect. The effect was more fully quantified by Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901.\n\nMeasurement\n\nMatter emits thermal radiation at a rate that is directly proportional to the fourth power of its temperature. Some of the radiation emitted by the Earth's surface is absorbed by greenhouse gases and clouds. Without this absorption, Earth's surface would have an average temperature of −18 °C (−0.4 °F). However, because some of the radiation is absorbed, Earth's average surface temperature is around 15 °C (59 °F). Thus, the Earth's greenhouse effect may be measured as a temperature change of 33 °C (59 °F).\nThermal radiation is characterized by how much energy it carries, typically in watts per square meter (W/m2). Scientists also measure the greenhouse effect based on how much more longwave thermal radiation leaves the Earth's surface than reaches space. Currently, longwave radiation leaves the surface at an average rate of 398 W/m2, but only 239 W/m2 reaches space. Thus, the Earth's greenhouse effect can also be measured as an energy flow change of 159 W/m2. The greenhouse effect can be expressed as a fraction (0.40) or percentage (40%) of the longwave thermal radiation that leaves Earth's surface but does not reach space.\nWhether the greenhouse effect is expressed as a change in temperature or as a change in longwave thermal radiation, the same effect is being measured.\n\nRole in climate change\n\nStrengthening of the greenhouse effect through additional greenhouse gases from human activities is known as the enhanced greenhouse effect. As well as being inferred from measurements by ARGO, CERES and other instruments throughout the 21st century, this increase in radiative forcing from human activity has been observed directly, and is attributable mainly to increased atmospheric carbon dioxide levels.\n\nCO2 is produced by fossil fuel burning and other activities such as cement production and tropical deforestation. Measurements of CO2 from the Mauna Loa Observatory show that concentrations have increased from about 313 parts per million (ppm) in 1960, passing the 400 ppm milestone in 2013. The current observed amount of CO2 exceeds the geological record maxima (≈300 ppm) from ice core data.\nOver the past 800,000 years, ice core data shows that carbon dioxide has varied from values as low as 180 ppm to the pre-industrial level of 270 ppm. Paleoclimatologists consider variations in carbon dioxide concentration to be a fundamental factor influencing climate variations over this time scale.\n\nEnergy balance and temperature\n\nIncoming shortwave radiation\n\nHotter matter emits shorter wavelengths of radiation. As a result, the Sun emits shortwave radiation as sunlight while the Earth and its atmosphere emit longwave radiation. Sunlight includes ultraviolet, visible light, and near-infrared radiation.\nSunlight is reflected and absorbed by the Earth and its atmosphere. The atmosphere and clouds reflect about 23% and absorb 23%. The surface reflects 7% and absorbs 48%. Overall, Earth reflects about 30% of the incoming sunlight, and absorbs the rest (240 W/m2).\n\nOutgoing longwave radiation\n\nThe Earth and its atmosphere emit longwave radiation, also known as thermal infrared or terrestrial radiation. Informally, longwave radiation is sometimes called thermal radiation. Outgoing longwave radiation (OLR) is the radiation from Earth and its atmosphere that passes through the atmosphere and into space.\nThe greenhouse effect can be directly seen in graphs of Earth's outgoing longwave radiation as a function of frequency (or wavelength). The area between the curve for longwave radiation emitted by Earth's surface and the curve for outgoing longwave radiation indicates the size of the greenhouse effect.\nDifferent substances are responsible for reducing the radiation energy reaching space at different frequencies; for some frequencies, multiple substances play a role. Carbon dioxide is understood to be responsible for the dip in outgoing radiation (and associated rise in the greenhouse effect) at around 667 cm−1 (equivalent to a wavelength of 15 microns).\nEach layer of the atmosphere with greenhouse gases absorbs some of the longwave radiation being radiated upwards from lower layers. It also emits longwave radiation in all directions, both upwards and downwards, in equilibrium with the amount it has absorbed. This results in less radiative heat loss and more warmth below. Increasing the concentration of the gases increases the amount of absorption and emission, and thereby causing more heat to be retained at the surface and in the layers below.\n\nEffective temperature\n\nThe power of outgoing longwave radiation emitted by a planet corresponds to the effective temperature of the planet. The effective temperature is the temperature that a planet radiating with a uniform temperature (a blackbody) would need to have in order to radiate the same amount of energy.\nThis concept may be used to compare the amount of longwave radiation emitted to space and the amount of longwave radiation emitted by the surface:\n\nEmissions to space: Based on its emissions of longwave radiation to space, Earth's overall effective temperature is −18 °C (0 °F).\nEmissions from surface: Based on thermal emissions from the surface, Earth's effective surface temperature is about 16 °C (61 °F), which is 34 °C (61 °F) warmer than Earth's overall effective temperature.\nEarth's surface temperature is often reported in terms of the average near-surface air temperature. This is about 15 °C (59 °F), a bit lower than the effective surface temperature. This value is 33 °C (59 °F) warmer than Earth's overall effective temperature.\n\nEnergy flux\nEnergy flux is the rate of energy flow per unit area. Energy flux is expressed in units of W/m2, which is the number of joules of energy that pass through a square meter each second. Most fluxes quoted in high-level discussions of climate are global values, which means they are the total flow of energy over the entire globe, divided by the surface area of the Earth, 5.1×1014 m2 (5.1×108 km2; 2.0×108 mi2).\nThe fluxes of radiation arriving at and leaving the Earth are important because radiative transfer is the only process capable of exchanging energy between Earth and the rest of the universe.\n\nRadiative balance\n\nThe temperature of a planet depends on the balance between incoming radiation and outgoing radiation. If incoming radiation exceeds outgoing radiation, a planet will warm. If outgoing radiation exceeds incoming radiation, a planet will cool. A planet will tend towards a state of radiative equilibrium, in which the power of outgoing radiation equals the power of absorbed incoming radiation.\nEarth's energy imbalance is the amount by which the power of incoming sunlight absorbed by Earth's surface or atmosphere exceeds the power of outgoing longwave radiation emitted to space. Energy imbalance is the fundamental measurement that drives surface temperature. A UN presentation says \"The EEI is the most critical number defining the prospects for continued global warming and climate change.\" One study argues, \"The absolute value of EEI represents the most fundamental metric defining the status of global climate change.\"\nEarth's energy imbalance (EEI) was about 0.7 W/m2 in 2015, indicating that Earth as a whole was accumulating thermal energy and is in a process of becoming warmer. By 2024, the longer-term trend had grown to about twice that rate.\nOver 90% of the retained energy goes into warming the oceans, with much smaller amounts going into heating the land, atmosphere, and ice.\n\nDay and night cycle\nA simple picture assumes a steady state, but in the real world, the day/night (diurnal) cycle, as well as the seasonal cycle and weather disturbances, complicate matters. Solar heating applies only during daytime. At night the atmosphere cools somewhat, but not greatly because the thermal inertia of the climate system resists changes both day and night, as well as for longer periods. Diurnal temperature changes decrease with height in the atmosphere.\n\nEffect of lapse rate\n\nLapse rate\n\nIn the lower portion of the atmosphere, the troposphere, the air temperature decreases (or \"lapses\") with increasing altitude. The rate at which temperature changes with altitude is called the lapse rate.\nOn Earth, the air temperature decreases by about 6.5 °C/km (3.6 °F per 1000 ft), on average, although this varies.\nThe temperature lapse is caused by convection. Air warmed by the surface rises. As it rises, air expands and cools. Simultaneously, other air descends, compresses, and warms. This process creates a vertical temperature gradient within the atmosphere.\nThis vertical temperature gradient is essential to the greenhouse effect. If the lapse rate was zero (so that the atmospheric temperature did not vary with altitude and was the same as the surface temperature) then there would be no greenhouse effect (i.e., its value would be zero).\n\nEmission temperature and altitude\n\nGreenhouse gases make the atmosphere near Earth's surface mostly opaque to longwave radiation. The atmosphere only becomes transparent to longwave radiation at higher altitudes, where the air is less dense, there is less water vapor, and reduced pressure broadening of absorption lines limits the wavelengths that gas molecules can absorb.\nFor any given wavelength, the longwave radiation that reaches space is emitted by a particular radiating layer of the atmosphere. The intensity of the emitted radiation is determined by the weighted average air temperature within that layer. So, for any given wavelength of radiation emitted to space, there is an associated effective emission temperature (or brightness temperature).\nA given wavelength of radiation may also be said to have an effective emission altitude, which is a weighted average of the altitudes within the radiating layer.\nThe effective emission temperature and altitude vary by wavelength (or frequency). This phenomenon may be seen by examining plots of radiation emitted to space.\n\nGreenhouse gases and the lapse rate\n\nEarth's surface radiates longwave radiation with wavelengths in the range of 4–100 microns. Greenhouse gases that were largely transparent to incoming solar radiation are more absorbent for some wavelengths in this range.\nThe atmosphere near the Earth's surface is largely opaque to longwave radiation and most heat loss from the surface is by evaporation and convection. However radiative energy losses become increasingly important higher in the atmosphere, largely because of the decreasing concentration of water vapor, an important greenhouse gas.\nRather than thinking of longwave radiation headed to space as coming from the surface itself, it is more realistic to think of this outgoing radiation as being emitted by a layer in the mid-troposphere, which is effectively coupled to the surface by a lapse rate. The difference in temperature between these two locations explains the difference between surface emissions and emissions to space, i.e., it explains the greenhouse effect.\n\nInfrared absorbing constituents in the atmosphere\n\nGreenhouse gases\nA greenhouse gas (GHG) is a gas which contributes to the trapping of heat by impeding the flow of longwave radiation out of a planet's atmosphere. Greenhouse gases contribute most of the greenhouse effect in Earth's energy budget.\n\nInfrared active gases\nGases which can absorb and emit longwave radiation are said to be infrared active and act as greenhouse gases.\nMost gases whose molecules have two different atoms (such as carbon monoxide, CO), and all gases with three or more atoms (including H2O and CO2), are infrared active and act as greenhouse gases. (Technically, this is because when these molecules vibrate, those vibrations modify the molecular dipole moment, or asymmetry in the distribution of electrical charge. See Infrared spectroscopy.)\nGases with only one atom (such as argon, Ar) or with two identical atoms (such as nitrogen, N2, and oxygen, O2) are not infrared active. They are transparent to longwave radiation, and, for practical purposes, do not absorb or emit longwave radiation. (This is because their molecules are symmetrical and so do not have a dipole moment.) Such gases make up more than 99% of the dry atmosphere.\n\nAbsorption and emission\nGreenhouse gases absorb and emit longwave radiation within specific ranges of wavelengths (organized as spectral lines or bands).\nWhen greenhouse gases absorb radiation, they distribute the acquired energy to the surrounding air as thermal energy (i.e., kinetic energy of gas molecules). Energy is transferred from greenhouse gas molecules to other molecules via molecular collisions.\nContrary to what is sometimes said, greenhouse gases do not \"re-emit\" photons after they are absorbed. Because each molecule experiences billions of collisions per second, any energy a greenhouse gas molecule receives by absorbing a photon will be redistributed to other molecules before there is a chance for a new photon to be emitted.\nIn a separate process, greenhouse gases emit longwave radiation, at a rate determined by the air temperature. This thermal energy is either absorbed by other greenhouse gas molecules or leaves the atmosphere, cooling it.\n\nRadiative effects\nEffect on air: Air is warmed by latent heat (buoyant water vapor condensing into water droplets and releasing heat), thermals (warm air rising from below), and by sunlight being absorbed in the atmosphere. Air is cooled radiatively, by greenhouse gases and clouds emitting longwave thermal radiation. Within the troposphere, greenhouse gases typically have a net cooling effect on air, emitting more thermal radiation than they absorb. Warming and cooling of air are well balanced, on average, so that the atmosphere maintains a roughly stable average temperature.\nEffect on surface cooling: Longwave radiation flows both upward and downward due to absorption and emission in the atmosphere. These canceling energy flows reduce radiative surface cooling (net upward radiative energy flow). Latent heat transport and thermals provide non-radiative surface cooling which partially compensates for this reduction, but there is still a net reduction in surface cooling, for a given surface temperature.\nEffect on TOA energy balance: Greenhouse gases impact the top-of-atmosphere (TOA) energy budget by reducing the flux of longwave radiation emitted to space, for a given surface temperature. Thus, greenhouse gases alter the energy balance at TOA. This means that the surface temperature needs to be higher (than the planet's effective temperature, i.e., the temperature associated with emissions to space), in order for the outgoing energy emitted to space to balance the incoming energy from sunlight. It is important to focus on the top-of-atmosphere (TOA) energy budget (rather than the surface energy budget) when reasoning about the warming effect of greenhouse gases.\n\nClouds and aerosols\n\nClouds and aerosols have both cooling effects, associated with reflecting sunlight back to space, and warming effects, associated with trapping thermal radiation.\nOn average, clouds have a strong net cooling effect. However, the mix of cooling and warming effects varies, depending on detailed characteristics of particular clouds (including their type, height, and optical properties). Thin cirrus clouds can have a net warming effect. Clouds can absorb and emit infrared radiation and thus affect the radiative properties of the atmosphere.\n\nBasic formulas\n\nEffective temperature\nA given flux of thermal radiation has an associated effective radiating temperature or effective temperature. Effective temperature is the temperature that a black body (a perfect absorber/emitter) would need to be to emit that much thermal radiation. Thus, the overall effective temperature of a planet is given by\n\n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n =\n (\n \n O\n L\n R\n \n \n /\n \n σ\n \n )\n \n 1\n \n /\n \n 4\n \n \n \n \n {\\displaystyle T_{\\mathrm {eff} }=(\\mathrm {OLR} /\\sigma )^{1/4}}\n \n\nwhere OLR is the average flux (power per unit area) of outgoing longwave radiation emitted to space and \n \n \n \n σ\n \n \n {\\displaystyle \\sigma }\n \n is the Stefan-Boltzmann constant. Similarly, the effective temperature of the surface is given by\n\n \n \n \n \n T\n \n \n s\n u\n r\n f\n a\n c\n e\n ,\n e\n f\n f\n \n \n \n =\n (\n \n S\n L\n R\n \n \n /\n \n σ\n \n )\n \n 1\n \n /\n \n 4\n \n \n \n \n {\\displaystyle T_{\\mathrm {surface,eff} }=(\\mathrm {SLR} /\\sigma )^{1/4}}\n \n\nwhere SLR is the average flux of longwave radiation emitted by the surface. (OLR is a conventional abbreviation. SLR is used here to denote the flux of surface-emitted longwave radiation, although there is no standard abbreviation for this.)\n\nMetrics for the greenhouse effect\n\nThe IPCC reports the greenhouse effect, G, as being 159 W m-2, where G is the flux of longwave thermal radiation that leaves the surface minus the flux of outgoing longwave radiation that reaches space:\n\n \n \n \n G\n =\n \n S\n L\n R\n \n −\n \n O\n L\n R\n \n \n .\n \n \n {\\displaystyle G=\\mathrm {SLR} -\\mathrm {OLR} \\;.}\n \n\nAlternatively, the greenhouse effect can be described using the normalized greenhouse effect, g̃, defined as\n\n \n \n \n \n \n \n g\n ~\n \n \n \n =\n G\n \n /\n \n \n S\n L\n R\n \n =\n 1\n −\n \n O\n L\n R\n \n \n /\n \n \n S\n L\n R\n \n \n .\n \n \n {\\displaystyle {\\tilde {g}}=G/\\mathrm {SLR} =1-\\mathrm {OLR} /\\mathrm {SLR} \\;.}\n \n\nThe normalized greenhouse effect is the fraction of the amount of thermal radiation emitted by the surface that does not reach space.\nBased on the IPCC numbers, g̃ = 0.40. In other words, 40 percent less thermal radiation reaches space than what leaves the surface.\nSometimes the greenhouse effect is quantified as a temperature difference. This temperature difference is closely related to the quantities above.\nWhen the greenhouse effect is expressed as a temperature difference, \n \n \n \n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n \n \n {\\displaystyle \\Delta T_{\\mathrm {GHE} }}\n \n, this refers to the effective temperature associated with thermal radiation emissions from the surface minus the effective temperature associated with emissions to space:\n\n \n \n \n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n =\n \n T\n \n \n s\n u\n r\n f\n a\n c\n e\n ,\n e\n f\n f\n \n \n \n −\n \n T\n \n \n e\n f\n f\n \n \n \n \n \n {\\displaystyle \\Delta T_{\\mathrm {GHE} }=T_{\\mathrm {surface,eff} }-T_{\\mathrm {eff} }}\n \n\n \n \n \n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n =\n \n \n (\n \n \n S\n L\n R\n \n \n /\n \n σ\n \n )\n \n \n 1\n \n /\n \n 4\n \n \n −\n \n \n (\n \n \n O\n L\n R\n \n \n /\n \n σ\n \n )\n \n \n 1\n \n /\n \n 4\n \n \n \n \n {\\displaystyle \\Delta T_{\\mathrm {GHE} }=\\left(\\mathrm {SLR} /\\sigma \\right)^{1/4}-\\left(\\mathrm {OLR} /\\sigma \\right)^{1/4}}\n \n\nInformal discussions of the greenhouse effect often compare the actual surface temperature to the temperature that the planet would have if there were no greenhouse gases. However, in formal technical discussions, when the size of the greenhouse effect is quantified as a temperature, this is generally done using the above formula. The formula refers to the effective surface temperature rather than the actual surface temperature, and compares the surface with the top of the atmosphere, rather than comparing reality to a hypothetical situation.\nThe temperature difference, \n \n \n \n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n \n \n {\\displaystyle \\Delta T_{\\mathrm {GHE} }}\n \n, indicates how much warmer a planet's surface is than the planet's overall effective temperature.\n\nRadiative balance\n\nEarth's top-of-atmosphere (TOA) energy imbalance (EEI) is the amount by which the power of incoming radiation exceeds the power of outgoing radiation:\n\n \n \n \n \n E\n E\n I\n \n =\n \n A\n S\n R\n \n −\n \n O\n L\n R\n \n \n \n {\\displaystyle \\mathrm {EEI} =\\mathrm {ASR} -\\mathrm {OLR} }\n \n\nwhere ASR is the mean flux of absorbed solar radiation. ASR may be expanded as\n\n \n \n \n \n A\n S\n R\n \n =\n (\n 1\n −\n A\n )\n \n \n M\n S\n I\n \n \n \n {\\displaystyle \\mathrm {ASR} =(1-A)\\,\\mathrm {MSI} }\n \n\nwhere \n \n \n \n A\n \n \n {\\displaystyle A}\n \n is the albedo (reflectivity) of the planet and MSI is the mean solar irradiance incoming at the top of the atmosphere.\nThe radiative equilibrium temperature of a planet can be expressed as\n\n \n \n \n \n T\n \n \n r\n a\n d\n e\n q\n \n \n \n =\n (\n \n A\n S\n R\n \n \n /\n \n σ\n \n )\n \n 1\n \n /\n \n 4\n \n \n =\n \n \n [\n \n (\n 1\n −\n A\n )\n \n \n M\n S\n I\n \n \n /\n \n σ\n \n ]\n \n \n 1\n \n /\n \n 4\n \n \n \n .\n \n \n {\\displaystyle T_{\\mathrm {radeq} }=(\\mathrm {ASR} /\\sigma )^{1/4}=\\left[(1-A)\\,\\mathrm {MSI} /\\sigma \\right]^{1/4}\\;.}\n \n\nA planet's temperature will tend to shift towards a state of radiative equilibrium, in which the TOA energy imbalance is zero, i.e., \n \n \n \n \n E\n E\n I\n \n =\n 0\n \n \n {\\displaystyle \\mathrm {EEI} =0}\n \n. When the planet is in radiative equilibrium, the overall effective temperature of the planet is given by\n\n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n =\n \n T\n \n \n r\n a\n d\n e\n q\n \n \n \n \n .\n \n \n {\\displaystyle T_{\\mathrm {eff} }=T_{\\mathrm {radeq} }\\;.}\n \n\nThus, the concept of radiative equilibrium is important because it indicates what effective temperature a planet will tend towards having.\nIf, in addition to knowing the effective temperature, \n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {eff} }}\n \n, we know the value of the greenhouse effect, then we know the mean (average) surface temperature of the planet.\nThis is why the quantity known as the greenhouse effect is important: it is one of the few quantities that go into determining the planet's mean surface temperature.\n\nGreenhouse effect and temperature\nTypically, a planet will be close to radiative equilibrium, with the rates of incoming and outgoing energy being well-balanced. Under such conditions, the planet's equilibrium temperature is determined by the mean solar irradiance and the planetary albedo (how much sunlight is reflected back to space instead of being absorbed).\nThe greenhouse effect measures how much warmer the surface is than the overall effective temperature of the planet. So, the effective surface temperature, \n \n \n \n \n T\n \n \n s\n u\n r\n f\n a\n c\n e\n ,\n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {surface,eff} }}\n \n, is, using the definition of \n \n \n \n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n \n \n {\\displaystyle \\Delta T_{\\mathrm {GHE} }}\n \n,\n\n \n \n \n \n T\n \n \n s\n u\n r\n f\n a\n c\n e\n ,\n e\n f\n f\n \n \n \n =\n \n T\n \n \n e\n f\n f\n \n \n \n +\n Δ\n \n T\n \n \n G\n H\n E\n \n \n \n \n .\n \n \n {\\displaystyle T_{\\mathrm {surface,eff} }=T_{\\mathrm {eff} }+\\Delta T_{\\mathrm {GHE} }\\;.}\n \n\nOne could also express the relationship between \n \n \n \n \n T\n \n \n s\n u\n r\n f\n a\n c\n e\n ,\n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {surface,eff} }}\n \n and \n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {eff} }}\n \n using G or g̃.\nSo, the principle that a larger greenhouse effect corresponds to a higher surface temperature, if everything else (i.e., the factors that determine \n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {eff} }}\n \n) is held fixed, is true as a matter of definition.\nNote that the greenhouse effect influences the temperature of the planet as a whole, in tandem with the planet's tendency to move toward radiative equilibrium.\n\nMisconceptions\n\nThere are sometimes misunderstandings about how the greenhouse effect functions and raises temperatures.\nThe surface budget fallacy is a common error in thinking. It involves thinking that an increased CO2 concentration could only cause warming by increasing the downward thermal radiation to the surface, as a result of making the atmosphere a better emitter. If the atmosphere near the surface is already nearly opaque to thermal radiation, this would mean that increasing CO2 could not lead to higher temperatures. However, it is a mistake to focus on the surface energy budget rather than the top-of-atmosphere energy budget. Regardless of what happens at the surface, increasing the concentration of CO2 tends to reduce the thermal radiation reaching space (OLR), leading to a TOA energy imbalance that leads to warming. Earlier researchers like Callendar (1938) and Plass (1959) focused on the surface budget, but the work of Manabe in the 1960s clarified the importance of the top-of-atmosphere energy budget.\nAmong those who do not believe in the greenhouse effect, there is a fallacy that the greenhouse effect involves greenhouse gases sending heat from the cool atmosphere to the planet's warm surface, in violation of the second law of thermodynamics. However, this idea reflects a misunderstanding. Radiation heat flow is the net energy flow after the flows of radiation in both directions have been taken into account. Radiation heat flow occurs in the direction from the surface to the atmosphere and space, as is to be expected given that the surface is warmer than the atmosphere and space. While greenhouse gases emit thermal radiation downward to the surface, this is part of the normal process of radiation heat transfer. The downward thermal radiation simply reduces the upward thermal radiation net energy flow (radiation heat flow), i.e., it reduces cooling.\n\nSimplified models\n\nSimplified models are sometimes used to support understanding of how the greenhouse effect comes about and how this affects surface temperature.\n\nAtmospheric layer models\nThe greenhouse effect can be seen to occur in a simplified model in which the air is treated as if it is single uniform layer exchanging radiation with the ground and space. Slightly more complex models add additional layers, or introduce convection.\n\nEquivalent emission altitude\nOne simplification is to treat all outgoing longwave radiation as being emitted from an altitude where the air temperature equals the overall effective temperature for planetary emissions, \n \n \n \n \n T\n \n \n e\n f\n f\n \n \n \n \n \n {\\displaystyle T_{\\mathrm {eff} }}\n \n. Some authors have referred to this altitude as the",
    "source": "wikipedia:Greenhouse effect",
    "domain": "climate"
  },
  {
    "text": "Numerical climate models (or climate system models) are mathematical models that can simulate the interactions of important drivers of climate. These drivers are the atmosphere, oceans, land surface and ice. Scientists use climate models to study the dynamics of the climate system and to make projections of future climate and of climate change. Climate models can also be qualitative (i.e. not numerical) models and contain narratives, largely descriptive, of possible futures.\nClimate models take account of incoming energy from the Sun as well as outgoing energy from Earth. An imbalance results in a change in temperature. The incoming energy from the Sun is in the form of short wave electromagnetic radiation, chiefly visible and short-wave (near) infrared. The outgoing energy is in the form of long wave (far) infrared electromagnetic energy. These processes are part of the greenhouse effect.\nClimate models vary in complexity. For example, a simple radiant heat transfer model treats the Earth as a single point and averages outgoing energy. This can be expanded vertically (radiative-convective models) and horizontally. More complex models are the coupled atmosphere–ocean–sea ice global climate models. These types of models solve the full equations for mass transfer, energy transfer and radiant exchange. In addition, other types of models can be interlinked. For example Earth System Models include also land use as well as land use changes. This allows researchers to predict the interactions between climate and ecosystems.\nClimate models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. Scientists divide the planet into a 3-dimensional grid and apply the basic equations to those grids. Atmospheric models calculate winds, heat transfer, radiation, relative humidity, and surface hydrology within each grid and evaluate interactions with neighboring points. These are coupled with oceanic models to simulate climate variability and change that occurs on different timescales due to shifting ocean currents and the much larger heat storage capacity of the global ocean. External drivers of change may also be applied. Including an ice-sheet model better accounts for long term effects such as sea level rise.\n\nUses\n\nComplex climate models enable extreme event attribution, which is the science of identifying and quantifying the role that human-caused climate change plays in the frequency, intensity and impacts of extreme weather events. Attribution science aims to determine the degree to which such events can be explained by or linked to human-caused global warming, and are not simply due to random climate variability or natural weather patterns.\nThere are three major types of institution where climate models are developed, implemented and used:\n\nNational meteorological services: Most national weather services have a climatology section.\nUniversities: Relevant departments include atmospheric sciences, meteorology, climatology, and geography.\nNational and international research laboratories: Examples include the National Center for Atmospheric Research (NCAR, in Boulder, Colorado, US), the Geophysical Fluid Dynamics Laboratory (GFDL, in Princeton, New Jersey, US), Los Alamos National Laboratory, the Hadley Centre for Climate Prediction and Research (in Exeter, UK), the Max Planck Institute for Meteorology in Hamburg, Germany, or the Laboratoire des Sciences du Climat et de l'Environnement (LSCE), France.\nBig climate models are essential but they are not perfect. Attention still needs to be given to the real world (what is happening and why). The global models are essential to assimilate all the observations, especially from space (satellites) and produce comprehensive analyses of what is happening, and then they can be used to make predictions/projections. Simple models have a role to play that is widely abused and fails to recognize the simplifications such as not including a water cycle.\n\nGeneral circulation models (GCMs)\n\nEnergy balance models (EBMs)\nSimulation of the climate system in full 3-D space and time was impractical prior to the establishment of large computational facilities starting in the 1960s. In order to begin to understand which factors may have changed Earth's paleoclimate states, the constituent and dimensional complexities of the system needed to be reduced. A simple quantitative model that balanced incoming/outgoing energy was first developed for the atmosphere in the late 19th century. Other EBMs similarly seek an economical description of surface temperatures by applying the conservation of energy constraint to individual columns of the Earth-atmosphere system.\nEssential features of EBMs include their relative conceptual simplicity and their ability to sometimes produce analytical solutions. Some models account for effects of ocean, land, or ice features on the surface budget. Others include interactions with parts of the water cycle or carbon cycle. A variety of these and other reduced system models can be useful for specialized tasks that supplement GCMs, particularly to bridge gaps between simulation and understanding.\n\nZero-dimensional models\nZero-dimensional models consider Earth as a point in space, analogous to the pale blue dot viewed by Voyager 1 or an astronomer's view of very distant objects. This dimensionless view while highly limited is still useful in that the laws of physics are applicable in a bulk fashion to unknown objects, or in an appropriate lumped manner if some major properties of the object are known. For example, astronomers know that most planets in our own solar system feature some kind of solid/liquid surface surrounded by a gaseous atmosphere.\n\nModel with combined surface and atmosphere\nA very simple model of the radiative equilibrium of the Earth is\n\n \n \n \n (\n 1\n −\n a\n )\n S\n π\n \n r\n \n 2\n \n \n =\n 4\n π\n \n r\n \n 2\n \n \n ϵ\n σ\n \n T\n \n 4\n \n \n \n \n {\\displaystyle (1-a)S\\pi r^{2}=4\\pi r^{2}\\epsilon \\sigma T^{4}}\n \n\nwhere\n\nthe left hand side represents the total incoming shortwave power (in Watts) from the Sun\nthe right hand side represents the total outgoing longwave power (in Watts) from Earth, calculated from the Stefan–Boltzmann law.\nThe constant parameters include\n\nS is the solar constant – the incoming solar radiation per unit area—about 1367 W·m−2\nr is Earth's radius—approximately 6.371 million meters (m)\nπ is the mathematical constant (3.141...)\n\n \n \n \n σ\n \n \n {\\displaystyle \\sigma }\n \n is the Stefan–Boltzmann constant—approximately 5.67×10−8 J·K−4·m−2·s−1\nThe constant \n \n \n \n π\n \n \n r\n \n 2\n \n \n \n \n {\\displaystyle \\pi \\,r^{2}}\n \n can be factored out, giving a nildimensional equation for the equilibrium\n\n \n \n \n (\n 1\n −\n a\n )\n S\n =\n 4\n ϵ\n σ\n \n T\n \n 4\n \n \n \n \n {\\displaystyle (1-a)S=4\\epsilon \\sigma T^{4}}\n \n\nwhere\n\nthe left hand side represents the incoming shortwave energy flux from the Sun in W·m−2\nthe right hand side represents the outgoing longwave energy flux from Earth in W·m−2.\nThe remaining variable parameters which are specific to the planet include\n\n \n \n \n a\n \n \n {\\displaystyle a}\n \n is Earth's average albedo, measured to be 0.3.\n\n \n \n \n T\n \n \n {\\displaystyle T}\n \n is Earth's average surface temperature, measured as about 288 Kelvin (K) as of year 2020\n\n \n \n \n ϵ\n \n \n {\\displaystyle \\epsilon }\n \n is the effective emissivity of Earth's combined surface and atmosphere (including clouds). It is a quantity between 0 and 1 that is calculated from the equilibrium to be about 0.61. For the zero-dimensional treatment it is equivalent to an average value over all viewing angles.\nThis very simple model is quite instructive. For example, it shows the temperature sensitivity to changes in the solar constant, Earth albedo, or effective Earth emissivity. The effective emissivity also gauges the strength of the atmospheric greenhouse effect, since it is the ratio of the thermal emissions escaping to space versus those emanating from the surface.\nThe calculated emissivity can be compared to available data. Terrestrial surface emissivities are all in the range of 0.96 to 0.99 (except for some small desert areas which may be as low as 0.7). Clouds, however, which cover about half of the planet's surface, have an average emissivity of about 0.5 (which must be reduced by the fourth power of the ratio of cloud absolute temperature to average surface absolute temperature) and an average cloud temperature of about 258 K (−15 °C; 5 °F). Taking all this properly into account results in an effective earth emissivity of about 0.64 (earth average temperature 285 K (12 °C; 53 °F)).\n\nModels with separated surface and atmospheric layers\n\nDimensionless models have also been constructed with functionally distinct atmospheric layers from the surface. The simplest of these is the zero-dimensional, one-layer model, which may be readily extended to an arbitrary number of atmospheric layers. The surface and atmospheric layer(s) are each characterized by a corresponding temperature and emissivity value, but no thickness. Applying radiative equilibrium (i.e conservation of energy) at the idealized interfaces between layers produces a set of coupled equations which are solvable.\nThese multi-layered EBMs are examples of multi-compartment models. They can estimate average temperatures closer to those observed for Earth's surface and troposphere. They likewise further illustrate the radiative heat transfer processes which underlie the greenhouse effect. Quantification of this phenomenon using a version of the one-layer model was first published by Svante Arrhenius in year 1896.\n\nRadiative-convective models\n\nWater vapor is a main determinant of the emissivity of Earth's atmosphere. It both influences the flows of radiation and is influenced by convective flows of heat in a manner that is consistent with its equilibrium concentration and temperature as a function of elevation (i.e. relative humidity distribution). This has been shown by refining the zero dimension model in the vertical to a one-dimensional radiative-convective model which considers two processes of energy transport:\n\nupwelling and downwelling radiative transfer through atmospheric layers that both absorb and emit infrared radiation\nupward transport of heat by air and vapor convection, which is especially important in the lower troposphere.\nRadiative-convective models typically use a distributed model of the atmosphere versus elevation. This has advantages over the lumped models and also lays a foundation for more complex models. They can estimate both surface temperature and the temperature variation with elevation in a more realistic manner. In particular, they properly simulate the observed decline in upper atmospheric temperature and the rise in surface temperature when trace amounts of other non-condensible greenhouse gases such as carbon dioxide are included.\nOther parameters are sometimes included to simulate localized effects in other dimensions and to address the factors that move energy about Earth. For example, the effect of ice-albedo feedback on global climate sensitivity has been investigated using a one-dimensional radiative-convective climate model.\n\nHigher-dimension models\nThe zero-dimensional model may be expanded to consider the energy transported horizontally in the atmosphere. This kind of model may well be zonally averaged. This model has the advantage of allowing a rational dependence of local albedo and emissivity on temperature – the poles can be allowed to be icy and the equator warm – but the lack of true dynamics means that horizontal transports have to be specified.\nEarly examples include research of Mikhail Budyko and William D. Sellers who worked on the Budyko-Sellers model. This work also showed the role of positive feedback in the climate system and has been considered foundational for the energy balance models since its publication in 1969.\n\nEarth systems models of intermediate complexity (EMICs)\n\nDepending on the nature of questions asked and the pertinent time scales, there are, on the one extreme, conceptual, more inductive models, and, on the other extreme, general circulation models operating at the highest spatial and temporal resolution currently feasible. Models of intermediate complexity bridge the gap. One example is the Climber-3 model. Its atmosphere is a 2.5-dimensional statistical-dynamical model with 7.5° × 22.5° resolution and time step of half a day; the ocean is MOM-3 (Modular Ocean Model) with a 3.75° × 3.75° grid and 24 vertical levels.\n\nBox models\n\nBox models are simplified versions of complex systems, reducing them to boxes linked by fluxes. The boxes contain reservoirs (i.e. inventories) of species of matter and energy that are assumed to be mixed homogeneously. The concentration of any species is therefore uniform at any time within a box. However, the abundance of a species within a given box may vary as a function of time due to input flows or output flows; and may also vary due to the production, consumption or transformation of a species within the box.\nSimple box models, i.e. box model with a small number of boxes whose properties (e.g. their volume) do not change with time, are often useful to derive analytical formulas describing the dynamical and steady-state abundances of a species. The formulae are called governing equations and are derived from conservation laws (e.g. conservation of energy, conservation of mass, etc.). Larger sets of interacting species and equations are evaluated with numerical techniques to describe behavior of the system.\nBox models are used extensively to simulate environmental systems and ecosystems. In 1961 Henry Stommel was the first to use a simple 2-box model to study the stability of large-scale ocean circulation. A more complex model has examined interactions between ocean circulation and the carbon cycle.\n\nNetworked data models\n\nHistory\n\nIncrease of forecasts confidence over time\n\nThe Coupled Model Intercomparison Project (CMIP) has been a leading effort to foster improvements in GCMs and climate change understanding since 1995.\n\nThe IPCC stated in 2010 it has increased confidence in forecasts coming from climate models:\"There is considerable confidence that climate models provide credible quantitative estimates of future climate change, particularly at continental scales and above. This confidence comes from the foundation of the models in accepted physical principles and from their ability to reproduce observed features of current climate and past climate changes. Confidence in model estimates is higher for some climate variables (e.g., temperature) than for others (e.g., precipitation). Over several decades of development, models have consistently provided a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases.\"\n\nCoordination of research\nThe World Climate Research Programme (WCRP), hosted by the World Meteorological Organization (WMO), coordinates research activities on climate modelling worldwide.\nA 2012 U.S. National Research Council report discussed how the large and diverse U.S. climate modeling enterprise could evolve to become more unified. Efficiencies could be gained by developing a common software infrastructure shared by all U.S. climate researchers, and holding an annual climate modeling forum, the report found.\n\nIssues\n\nElectricity consumption\nCloud-resolving climate models are nowadays run on high intensity super-computers which have a high power consumption and thus cause CO2 emissions. They require exascale computing (billion billion – i.e., a quintillion – calculations per second). For example, the Frontier exascale supercomputer consumes 29 MW. It can simulate a year’s worth of climate at cloud resolving scales in a day.\nTechniques that could lead to energy savings, include for example: \"reducing floating point precision computation; developing machine learning algorithms to avoid unnecessary computations; and creating a new generation of scalable numerical algorithms that would enable higher throughput in terms of simulated years per wall clock day.\"\n\nParametrization\n\nSee also\nAtmospheric reanalysis\nChemical transport model\nAtmospheric Radiation Measurement (ARM) (in the US)\nClimate Data Exchange\nClimateprediction.net\nNumerical Weather Prediction\nStatic atmospheric model\nTropical cyclone prediction model\nVerification and validation of computer simulation models\nCICE sea ice model\n\nReferences\n\nExternal links\n\nTimeline: The History of Climate Modelling CarbonBrief, 16 January 2018\nWhy results from the next generation of climate models matter CarbonBrief, Guest post by Belcher, Boucher, Sutton, 21 March 2019\nClimate models on the web:\n\nNCAR/UCAR Community Climate System Model (CCSM)\nDo it yourself climate prediction\nPrimary research GCM developed by NASA/GISS (Goddard Institute for Space Studies)\nOriginal NASA/GISS global climate model (GCM) with a user-friendly interface for PCs and Macs\nCCCma model info and interface to retrieve model data",
    "source": "wikipedia:Climate model",
    "domain": "climate"
  },
  {
    "text": "The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycle. Carbon is the main component of biological compounds as well as a major component of many rocks such as limestone. The carbon cycle comprises a sequence of events that are key to making Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration (storage) to and release from carbon sinks. At 422.7 parts per million (ppm), the global average atmospheric carbon dioxide has set a new record high in 2024.\nTo describe the dynamics of the carbon cycle, a distinction can be made between the fast and slow carbon cycle. The fast cycle is also referred to as the biological carbon cycle. Fast cycles can complete within years, moving substances from atmosphere to biosphere, then back to the atmosphere. Slow or geological cycles (also called deep carbon cycle) can take millions of years to complete, moving substances through the Earth's crust between rocks, soil, ocean and atmosphere.\nHumans have disturbed the carbon cycle for many centuries. They have done so by modifying land use and by mining and burning carbon from ancient organic remains (coal, petroleum and gas). Carbon dioxide in the atmosphere has increased nearly 52% over pre-industrial levels by 2020, resulting in global warming. The increased carbon dioxide has also caused a reduction in the ocean's pH value and is fundamentally altering marine chemistry. Carbon dioxide is critical for photosynthesis.\n\nMain compartments\nThe carbon cycle was first described by Antoine Lavoisier and Joseph Priestley, and popularised by Humphry Davy. The global carbon cycle is now usually divided into the following major reservoirs of carbon (also called carbon pools) interconnected by pathways of exchange:\n\nAtmosphere\nTerrestrial biosphere\nOcean, including dissolved inorganic carbon and living and non-living marine biota\nSediments, including fossil fuels, freshwater systems, and non-living organic material.\nEarth's interior (mantle and crust). These carbon stores interact with the other components through geological processes.\nThe carbon exchanges between reservoirs occur as the result of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth.\nThe natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence.\n\nAtmosphere\n\nCarbon in the Earth's atmosphere exists in two main forms: carbon dioxide and methane. Both of these gases absorb and retain heat in the atmosphere and are partially responsible for the greenhouse effect. Methane produces a larger greenhouse effect per volume as compared to carbon dioxide, but it exists in much lower concentrations and is more short-lived than carbon dioxide. Thus, carbon dioxide contributes more to the global greenhouse effect than methane.\nCarbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. It can then be absorbed by rocks through weathering. It also can acidify other surfaces it touches or be washed into the ocean.\n\nHuman activities over the past two centuries have increased the amount of carbon in the atmosphere by nearly 50% as of year 2020, mainly in the form of carbon dioxide, both by modifying ecosystems' ability to extract carbon dioxide from the atmosphere and by emitting it directly, e.g., by burning fossil fuels and manufacturing concrete.\n\nIn the far future (2 to 3 billion years), the rate at which carbon dioxide is absorbed into the soil via the carbonate–silicate cycle will likely increase due to expected changes in the Sun as it ages. The expected increased luminosity of the Sun will likely speed up the rate of surface weathering. This will eventually cause most of the carbon dioxide in the atmosphere to be squelched into the Earth's crust as carbonate. Once the concentration of carbon dioxide in the atmosphere falls below approximately 50 parts per million (tolerances vary among species), C3 photosynthesis will no longer be possible. This has been predicted to occur 600 million years from the present, though models vary.\nOnce the oceans on the Earth evaporate in about 1.1 billion years from now, plate tectonics will very likely stop due to the lack of water to lubricate them. The lack of volcanoes pumping out carbon dioxide will cause the carbon cycle to end between 1 billion and 2 billion years into the future.\n\nTerrestrial biosphere\n\nThe terrestrial biosphere includes the organic carbon in all land-living organisms, both alive and dead, as well as carbon stored in soils. About 500 gigatons of carbon are stored above ground in plants and other living organisms, while soil holds approximately 1,500 gigatons of carbon. Most carbon in the terrestrial biosphere is organic carbon, while about a third of soil carbon is stored in inorganic forms, such as calcium carbonate. Organic carbon is a major component of all organisms living on Earth. Autotrophs extract it from the air in the form of carbon dioxide, converting it to organic carbon, while heterotrophs receive carbon by consuming other organisms.\nBecause carbon uptake in the terrestrial biosphere is dependent on biotic factors, it follows a diurnal and seasonal cycle. In CO2 measurements, this feature is apparent in the Keeling curve. It is strongest in the northern hemisphere because this hemisphere has more land mass than the southern hemisphere and thus more room for ecosystems to absorb and emit carbon.\n\nCarbon leaves the terrestrial biosphere in several ways and on different time scales. The combustion or respiration of organic carbon releases it rapidly into the atmosphere. It can also be exported into the ocean through rivers or remain sequestered in soils in the form of inert carbon. Carbon stored in soil can remain there for up to thousands of years before being washed into rivers by erosion or released into the atmosphere through soil respiration. Between 1989 and 2008 soil respiration increased by about 0.1% per year. In 2008, the global total of CO2 released by soil respiration was roughly 98 billion tonnes, about 3 times more carbon than humans are now putting into the atmosphere each year by burning fossil fuel (this does not represent a net transfer of carbon from soil to atmosphere, as the respiration is largely offset by inputs to soil carbon). There are a few plausible explanations for this trend, but the most likely explanation is that increasing temperatures have increased rates of decomposition of soil organic matter, which has increased the flow of CO2. The length of carbon sequestering in soil is dependent on local climatic conditions and thus changes in the course of climate change. \n\nOcean\n\nThe ocean can be conceptually divided into a surface layer within which water makes frequent (daily to annual) contact with the atmosphere, and a deep layer below the typical mixed layer depth of a few hundred meters or less, within which the time between consecutive contacts may be centuries. The dissolved inorganic carbon (DIC) in the surface layer is exchanged rapidly with the atmosphere, maintaining equilibrium. Partly because its concentration of DIC is about 15% higher but mainly due to its larger volume, the deep ocean contains far more carbon—it is the largest pool of actively cycled carbon in the world, containing 50 times more than the atmosphere—but the timescale to reach equilibrium with the atmosphere is hundreds of years: the exchange of carbon between the two layers, driven by thermohaline circulation, is slow.\nCarbon enters the ocean mainly through the dissolution of atmospheric carbon dioxide, a small fraction of which is converted into carbonate. It can also enter the ocean through rivers as dissolved organic carbon. It is converted by organisms into organic carbon through photosynthesis and can either be exchanged throughout the food chain or precipitated into the oceans' deeper, more carbon-rich layers as dead soft tissue or in shells as calcium carbonate. It circulates in this layer for long periods of time before either being deposited as sediment or, eventually, returned to the surface waters through thermohaline circulation.\nOceans are basic (with a current pH value of 8.1 to 8.2). The increase in atmospheric CO2 shifts the pH of the ocean towards neutral in a process called ocean acidification. Oceanic absorption of CO2 is one of the most important forms of carbon sequestering. The projected rate of pH reduction could slow the biological precipitation of calcium carbonates, thus decreasing the ocean's capacity to absorb CO2.\n\nGeosphere\n\nThe geologic component of the carbon cycle operates slowly in comparison to the other parts of the global carbon cycle. It is one of the most important determinants of the amount of carbon in the atmosphere, and thus of global temperatures.\nMost of the Earth's carbon is stored inertly in the Earth's lithosphere. Much of the carbon stored in the Earth's mantle was stored there when the Earth formed. Some of it was deposited in the form of organic carbon from the biosphere. Of the carbon stored in the geosphere, about 80% is limestone and its derivatives, which form from the sedimentation of calcium carbonate stored in the shells of marine organisms. The remaining 20% is stored as kerogens formed through the sedimentation and burial of terrestrial organisms under high heat and pressure. Organic carbon stored in the geosphere can remain there for millions of years.\nCarbon can leave the geosphere in several ways. Carbon dioxide is released during the metamorphism of carbonate rocks when they are subducted into the Earth's mantle. This carbon dioxide can be released into the atmosphere and ocean through volcanoes and hotspots. It can also be removed by humans through the direct extraction of kerogens in the form of fossil fuels. After extraction, fossil fuels are burned to release energy and emit the carbon they store into the atmosphere.\n\nTypes of dynamic\n\nThere is a fast and a slow carbon cycle. The fast cycle operates in the biosphere and the slow cycle operates in rocks. The fast or biological cycle can complete within years, moving carbon from atmosphere to biosphere, then back to the atmosphere. The slow or geological cycle may extend deep into the mantle and can take millions of years to complete, moving carbon through the Earth's crust between rocks, soil, ocean and atmosphere.\nThe fast carbon cycle involves relatively short-term biogeochemical processes between the environment and living organisms in the biosphere (see diagram at start of article). It includes movements of carbon between the atmosphere and terrestrial and marine ecosystems, as well as soils and seafloor sediments. The fast cycle includes annual cycles involving photosynthesis and decadal cycles involving vegetative growth and decomposition. The reactions of the fast carbon cycle to human activities will determine many of the more immediate impacts of climate change.\nThe slow (or deep) carbon cycle involves medium to long-term geochemical processes belonging to the rock cycle (see diagram on the right). The exchange between the ocean and atmosphere can take centuries, and the weathering of rocks can take millions of years. Carbon in the ocean precipitates to the ocean floor where it can form sedimentary rock and be subducted into the Earth's mantle. Mountain building processes result in the return of this geologic carbon to the Earth's surface. There the rocks are weathered and carbon is returned to the atmosphere by degassing and to the ocean by rivers. Other geologic carbon returns to the ocean through the hydrothermal emission of calcium ions. In a given year between 10 and 100 million tonnes of carbon moves around this slow cycle. This includes volcanoes returning geologic carbon directly to the atmosphere in the form of carbon dioxide. However, this is less than one percent of the carbon dioxide put into the atmosphere by burning fossil fuels.\n\nProcesses within fast carbon cycle\n\nTerrestrial carbon in the water cycle\n\nThe movement of terrestrial carbon in the water cycle is shown in the diagram on the right and explained below: \n\nAtmospheric particles act as cloud condensation nuclei, promoting cloud formation.\nRaindrops absorb organic and inorganic carbon through particle scavenging and adsorption of organic vapors while falling toward Earth.\nBurning and volcanic eruptions produce highly condensed polycyclic aromatic molecules (i.e. black carbon) that is returned to the atmosphere along with greenhouse gases such as CO2.\nTerrestrial plants fix atmospheric CO2 through photosynthesis, returning a fraction back to the atmosphere through respiration. Lignin and celluloses represent as much as 80% of the organic carbon in forests and 60% in pastures.\nLitterfall and root organic carbon mix with sedimentary material to form organic soils where plant-derived and petrogenic organic carbon is both stored and transformed by microbial and fungal activity.\nWater absorbs plant and settled aerosol-derived dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) as it passes over forest canopies (i.e. throughfall) and along plant trunks/stems (i.e. stemflow). Biogeochemical transformations take place as water soaks into soil solution and groundwater reservoirs and overland flow occurs when soils are completely saturated, or rainfall occurs more rapidly than saturation into soils.\nOrganic carbon derived from the terrestrial biosphere and in situ primary production is decomposed by microbial communities in rivers and streams along with physical decomposition (i.e. photo-oxidation), resulting in a flux of CO2 from rivers to the atmosphere that are the same order of magnitude as the amount of carbon sequestered annually by the terrestrial biosphere. Terrestrially-derived macromolecules such as lignin  and black carbon  are decomposed into smaller components and monomers, ultimately being converted to CO2, metabolic intermediates, or biomass.\nLakes, reservoirs, and floodplains typically store large amounts of organic carbon and sediments, but also experience net heterotrophy in the water column, resulting in a net flux of CO2 to the atmosphere that is roughly one order of magnitude less than rivers. Methane production is also typically high in the anoxic sediments of floodplains, lakes, and reservoirs.\nPrimary production is typically enhanced in river plumes due to the export of fluvial nutrients. Nevertheless, estuarine waters are a source of CO2 to the atmosphere, globally.\nCoastal marshes both store and export blue carbon. Marshes and wetlands are suggested to have an equivalent flux of CO2 to the atmosphere as rivers, globally.\nContinental shelves and the open ocean typically absorb CO2 from the atmosphere.\nThe marine biological pump sequesters a small but significant fraction of the absorbed CO2 as organic carbon in marine sediments (see below).\n\nTerrestrial runoff to the ocean\n\nTerrestrial and marine ecosystems are chiefly connected through riverine transport, which acts as the main channel through which erosive terrestrially derived substances enter into oceanic systems. Material and energy exchanges between the terrestrial biosphere and the lithosphere as well as organic carbon fixation and oxidation processes together regulate ecosystem carbon and dioxygen (O2) pools.\nRiverine transport, being the main connective channel of these pools, will act to transport net primary productivity (primarily in the form of dissolved organic carbon (DOC) and particulate organic carbon (POC)) from terrestrial to oceanic systems. During transport, part of DOC will rapidly return to the atmosphere through redox reactions, causing \"carbon degassing\" to occur between land-atmosphere storage layers. The remaining DOC and dissolved inorganic carbon (DIC) are also exported to the ocean. In 2015, inorganic and organic carbon export fluxes from global rivers were assessed as 0.50–0.70 Pg C y−1 and 0.15–0.35 Pg C y−1 respectively. On the other hand, POC can remain buried in sediment over an extensive period, and the annual global terrestrial to oceanic POC flux has been estimated at 0.20 (+0.13,-0.07) Gg C y−1.\n\nBiological pump in the ocean\n\nThe ocean biological pump is the ocean's biologically driven sequestration of carbon from the atmosphere and land runoff to the deep ocean interior and seafloor sediments. The biological pump is not so much the result of a single process, but rather the sum of a number of processes each of which can influence biological pumping. The pump transfers about 11 billion tonnes of carbon every year into the ocean's interior. An ocean without the biological pump would result in atmospheric CO2 levels about 400 ppm higher than the present day.\nMost carbon incorporated in organic and inorganic biological matter is formed at the sea surface where it can then start sinking to the ocean floor. The deep ocean gets most of its nutrients from the higher water column when they sink down in the form of marine snow. This is made up of dead or dying animals and microbes, fecal matter, sand and other inorganic material.\nThe biological pump is responsible for transforming dissolved inorganic carbon (DIC) into organic biomass and pumping it in particulate or dissolved form into the deep ocean. Inorganic nutrients and carbon dioxide are fixed during photosynthesis by phytoplankton, which both release dissolved organic matter (DOM) and are consumed by herbivorous zooplankton. Larger zooplankton - such as copepods, egest fecal pellets - which can be reingested, and sink or collect with other organic detritus into larger, more-rapidly-sinking aggregates. DOM is partially consumed by bacteria and respired; the remaining refractory DOM is advected and mixed into the deep sea. DOM and aggregates exported into the deep water are consumed and respired, thus returning organic carbon into the enormous deep ocean reservoir of DIC.\nA single phytoplankton cell has a sinking rate around one metre per day. Given that the average depth of the ocean is about four kilometres, it can take over ten years for these cells to reach the ocean floor. However, through processes such as coagulation and expulsion in predator fecal pellets, these cells form aggregates. These aggregates have sinking rates orders of magnitude greater than individual cells and complete their journey to the deep in a matter of days.\nAbout 1% of the particles leaving the surface ocean reach the seabed and are consumed, respired, or buried in the sediments. The net effect of these processes is to remove carbon in organic form from the surface and return it to DIC at greater depths, maintaining a surface-to-deep ocean gradient of DIC. Thermohaline circulation returns deep-ocean DIC to the atmosphere on millennial timescales. The carbon buried in the sediments can be subducted into the Earth's mantle and stored for millions of years as part of the slow carbon cycle (see next section).\n\nViruses as regulators\nViruses act as \"regulators\" of the fast carbon cycle because they impact the material cycles and energy flows of food webs and the microbial loop. The average contribution of viruses to the Earth ecosystem carbon cycle is 8.6%, of which its contribution to marine ecosystems (1.4%) is less than its contribution to terrestrial (6.7%) and freshwater (17.8%) ecosystems. Over the past 2,000 years, anthropogenic activities and climate change have gradually altered the regulatory role of viruses in ecosystem carbon cycling processes. This has been particularly conspicuous over the past 200 years due to rapid industrialization and the attendant population growth.\n\nProcesses within slow carbon cycle\n\nSlow or deep carbon cycling is an important process, though it is not as well-understood as the relatively fast carbon movement through the atmosphere, terrestrial biosphere, ocean, and geosphere. The deep carbon cycle is intimately connected to the movement of carbon in the Earth's surface and atmosphere. If the process did not exist, carbon would remain in the atmosphere, where it would accumulate to extremely high levels over long periods of time. Therefore, by allowing carbon to return to the Earth, the deep carbon cycle plays a critical role in maintaining the terrestrial conditions necessary for life to exist.\nFurthermore, the process is also significant simply due to the massive quantities of carbon it transports through the planet. In fact, studying the composition of basaltic magma and measuring carbon dioxide flux out of volcanoes reveals that the amount of carbon in the mantle is actually greater than that on the Earth's surface by a factor of one thousand. Drilling down and physically observing deep-Earth carbon processes is evidently extremely difficult, as the lower mantle and core extend from 660 to 2,891 km and 2,891 to 6,371 km deep into the Earth respectively. Accordingly, not much is conclusively known regarding the role of carbon in the deep Earth. Nonetheless, several pieces of evidence—many of which come from laboratory simulations of deep Earth conditions—have indicated mechanisms for the element's movement down into the lower mantle, as well as the forms that carbon takes at the extreme temperatures and pressures of said layer. Furthermore, techniques like seismology have led to a greater understanding of the potential presence of carbon in the Earth's core.\n\nCarbon in the lower mantle\n\nCarbon principally enters the mantle in the form of carbonate-rich sediments on tectonic plates of ocean crust, which pull the carbon into the mantle upon undergoing subduction. Not much is known about carbon circulation in the mantle, especially in the deep Earth, but many studies have attempted to augment our understanding of the element's movement and forms within the region. For instance, a 2011 study demonstrated that carbon cycling extends all the way to the lower mantle. The study analyzed rare, super-deep diamonds at a site in Juina, Brazil, determining that the bulk composition of some of the diamonds' inclusions matched the expected result of basalt melting and crystallisation under lower mantle temperatures and pressures. Thus, the investigation's findings indicate that pieces of basaltic oceanic lithosphere act as the principle transport mechanism for carbon to Earth's deep interior. These subducted carbonates can interact with lower mantle silicates, eventually forming super-deep diamonds like the one found.\nHowever, carbonates descending to the lower mantle encounter other fates in addition to forming diamonds. In 2011, carbonates were subjected to an environment similar to that of 1800 km deep into the Earth, well within the lower mantle. Doing so resulted in the formations of magnesite, siderite, and numerous varieties of graphite. Other experiments—as well as petrologic observations—support this claim, indicating that magnesite is actually the most stable carbonate phase in most part of the mantle. This is largely a result of its higher melting temperature. Consequently, scientists have concluded that carbonates undergo reduction as they descend into the mantle before being stabilised at depth by low oxygen fugacity environments. Magnesium, iron, and other metallic compounds act as buffers throughout the process. The presence of reduced, elemental forms of carbon like graphite would indicate that carbon compounds are reduced as they descend into the mantle.\n\nPolymorphism alters carbonate compounds' stability at different depths within the Earth. To illustrate, laboratory simulations and density functional theory calculations suggest that tetrahedrally coordinated carbonates are most stable at depths approaching the core–mantle boundary. A 2015 study indicates that the lower mantle's high pressure causes carbon bonds to transition from sp2 to sp3 hybridised orbitals, resulting in carbon tetrahedrally bonding to oxygen. CO3 trigonal groups cannot form polymerisable networks, while tetrahedral CO4 can, signifying an increase in carbon's coordination number, and therefore drastic changes in carbonate compounds' properties in the lower mantle. As an example, preliminary theoretical studies suggest that high pressure causes carbonate melt viscosity to increase; the melts' lower mobility as a result of its increased viscosity causes large deposits of carbon deep into the mantle.\nAccordingly, carbon can remain in the lower mantle for long periods of time, but large concentrations of carbon frequently find their way back to the lithosphere. This process, called carbon outgassing, is the result of carbonated mantle undergoing decompression melting, as well as mantle plumes carrying carbon compounds up towards the crust. Carbon is oxidised upon its ascent towards volcanic hotspots, where it is then released as CO2. This occurs so that the carbon atom matches the oxidation state of the basalts erupting in such areas.\n\nCarbon in the core\nAlthough the presence of carbon in the Earth's core is well-constrained, recent studies suggest large inventories of carbon could be stored in this region. Shear (S) waves moving through the inner core travel at about fifty percent of the velocity expected for most iron-rich alloys. Because the core's composition is believed to be an alloy of crystalline iron and a small amount of nickel, this seismic anomaly indicates the presence of light elements, including carbon, in the core. In fact, studies using diamond anvil cells to replicate the conditions in the Earth's core indicate that iron carbide (Fe7C3) matches the inner core's wave speed and density. Therefore, the iron carbide model could serve as an evidence that the core holds as much as 67% of the Earth's carbon. Furthermore, another study found that in the pressure and temperature condition of the Earth's inner core, carbon dissolved in iron and formed a stable phase with the same Fe7C3 composition—albeit with a different structure from the one previously mentioned. In summary, although the amount of carbon potentially stored in the Earth's core is not known, recent studies indicate that the presence of iron carbides can explain some of the geophysical observations.\n\nHuman influence on fast carbon cycle\n\nSince the Industrial Revolution, and especially since the end of WWII, human activity has substantially disturbed the global carbon cycle by redistributing massive amounts of carbon from the geosphere. Humans have also continued to shift the natural component functions of the terrestrial biosphere with changes to vegetation and other land use. Man-made (synthetic) carbon compounds have been designed and mass-manufactured that will persist for decades to millennia in air, water, and sediments as pollutants. Climate change is amplifying and forcing further indirect human changes to the carbon cycle as a consequence of various positive and negative feedbacks.\n\nClimate change\n\nCurrent trends in climate change lead to higher ocean temperatures and acidity, thus modifying marine ecosystems. Also, acid rain and polluted runoff from agriculture and industry change the ocean's chemical composition. Such changes can have dramatic effects on highly sensitive ecosystems such as coral reefs, thus limiting the ocean's ability to absorb carbon from the atmosphere on a regional scale and reducing oceanic biodiversity globally.\nThe exchanges of carbon between the atmosphere and other components of the Earth system, collectively known as the carbon cycle, currently constitute important negative (dampening) feedbacks on the effect of anthropogenic carbon emissions on climate change. Carbon sinks in the land and the ocean each currently take up about one-quarter of anthropogenic carbon emissions each year.\nThese feedbacks are expected to weaken in the future, amplifying the effect of anthropogenic carbon emissions on climate change. The degree to which they will weaken, however, is highly uncertain, with Earth system models predicting a wide range of land and ocean carbon uptakes even under identical atmospheric concentration or emission scenarios. Arctic methane emissions indirectly caused by anthropogenic global warming also affect the carbon cycle and contribute to further warming.\n\nFossil carbon extraction and burning\n\nThe largest and one of the fastest growing human impacts on the carbon cycle and biosphere is the extraction and burning of fossil fuels, which directly transfer carbon from the geosphere into the atmosphere. Carbon dioxide is also produced and released during the calcination of limestone for clinker production. Clinker is an industrial precursor of cement.\nAs of 2020, about 450 gigatons of fossil carbon have been extracted in total; an amount approaching the carbon contained in all of Earth's living terrestrial biomass. Recent rates of global emissions directly into the atmosphere have exceeded the uptake by vegetation and the oceans. These sinks have been expected and observed to remove about half of the added atmospheric carbon within about a century. Nevertheless, sinks like the ocean have evolving saturation properties, and a substantial fraction (20–35%, based on coupled models) of the added carbon is projected to remain in the atmosphere for centuries to millennia.\n\nH",
    "source": "wikipedia:Carbon cycle",
    "domain": "climate"
  },
  {
    "text": "Permafrost (from perma- 'permanent' and frost) is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years. Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than 1,500 m (4,900 ft). Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which freezes and thaws depending on the season.\nAround 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, covering a total area of around 18 million km2 (6.9 million sq mi). This includes large areas of Alaska, Canada, Greenland, and Siberia. It is also located in high mountain regions, with the Tibetan Plateau being a prominent example. Only a minority of permafrost exists in the Southern Hemisphere, where it is consigned to mountain slopes like in the Andes of Patagonia, the Southern Alps of New Zealand, or the highest mountains of Antarctica.\nPermafrost contains large amounts of dead biomass that has accumulated throughout millennia without having had the chance to fully decompose and release its carbon, making tundra soil a carbon sink. As global warming heats the ecosystem, frozen soil thaws and becomes warm enough for decomposition to start anew, accelerating the permafrost carbon cycle. Depending on conditions at the time of thaw, decomposition can release either carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback. The emissions from thawing permafrost will have a sufficient impact on the climate to impact global carbon budgets. It is difficult to accurately predict how much greenhouse gases the permafrost releases because the different thaw processes are still uncertain. There is widespread agreement that the emissions will be smaller than human-caused emissions and are not large enough to result in runaway warming. Instead, the annual permafrost emissions are likely comparable with global emissions from deforestation, or to annual emissions of large countries such as Russia, the United States or China.\nApart from its climate impact, permafrost thaw brings more risks. Formerly frozen ground often contains enough ice that when it thaws, hydraulic saturation is suddenly exceeded, so the ground shifts substantially and may even collapse outright. Many buildings and other infrastructure were built on permafrost when it was frozen and stable, and so are vulnerable to collapse if it thaws. Estimates suggest nearly 70% of such infrastructure is at risk by 2050, and that the associated costs could rise to tens of billions of dollars in the second half of the century. Furthermore, between 13,000 and 20,000 sites contaminated with toxic waste are present in the permafrost, as well as natural mercury deposits, which are all liable to leak and pollute the environment as the warming progresses. Lastly, concerns have been raised about the potential for pathogenic microorganisms surviving the thaw and contributing to future pandemics. However, this is considered unlikely, and a scientific review on the subject describes the risks as \"generally low\".\n\nClassification and extent\n\nPermafrost is soil, rock or sediment that is frozen for more than two consecutive years. In practice, this means that permafrost occurs at a mean annual temperature of 0 °C (32.0 °F) or below. In the coldest regions, the depth of continuous permafrost can exceed 1,400 m (4,600 ft). It typically exists beneath the so-called active layer, which freezes and thaws annually, and so can support plant growth, as the roots can only take hold in the soil that's thawed. Active layer thickness is measured during its maximum extent at the end of summer: as of 2018, the average thickness in the Northern Hemisphere is ~145 centimetres (4.76 ft), but there are significant regional differences. Northeastern Siberia, Alaska and Greenland have the most solid permafrost with the lowest extent of active layer (less than 50 centimetres (1.6 ft) on average, and sometimes only 30 centimetres (0.98 ft)), while southern Norway and the Mongolian Plateau are the only areas where the average active layer is deeper than 600 centimetres (20 ft), with the record of 10 metres (33 ft). The border between active layer and permafrost itself is sometimes called permafrost table.\nAround 15% of Northern Hemisphere land that is not completely covered by ice is directly underlain by permafrost; 22% is defined as part of a permafrost zone or region. This is because only slightly more than half of this area is defined as a continuous permafrost zone, where 90%–100% of the land is underlain by permafrost. Around 20% is instead defined as discontinuous permafrost, where the coverage is between 50% and 90%. Finally, the remaining <30% of permafrost regions consists of areas with 10%–50% coverage, which are defined as sporadic permafrost zones, and some areas that have isolated patches of permafrost covering 10% or less of their area. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The greatest depth of permafrost occurs right before the point where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost with a consistent annual temperature—\"isothermal permafrost\".\n\nContinuity of coverage\nPermafrost typically forms in any climate where the mean annual air temperature is lower than the freezing point of water. Exceptions are found in humid boreal forests, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, where snow acts as an insulating blanket. Glaciated areas may also be exceptions. Since all glaciers are warmed at their base by geothermal heat, temperate glaciers, which are near the pressure melting point throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost. \"Fossil\" cold anomalies in the geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North America and Europe.\n\nDiscontinuous permafrost\n\nThe below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth due to the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below 0 °C (32 °F), permafrost will form only in spots that are sheltered (usually with a northern or southern aspect, in the north and south hemispheres respectively) creating discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between −5 and 0 °C (23 and 32 °F). In the moist-wintered areas mentioned before, there may not even be discontinuous permafrost down to −2 °C (28 °F). Discontinuous permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between −2 and −4 °C (28 and 25 °F), and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between 0 and −2 °C (32 and 28 °F).\nIn soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ. Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11 °C (20 °F) colder than those of today.\n\nContinuous permafrost\n\nAt mean annual soil surface temperatures below −5 °C (23 °F) the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost (abbreviated to CPZ) forms. A line of continuous permafrost in the Northern Hemisphere represents the most southern border where land is covered by continuous permafrost or glacial ice. The line of continuous permafrost varies around the world northward or southward due to regional climatic changes. In the Southern Hemisphere, most of the equivalent line would fall within the Southern Ocean if there were land there. Most of the Antarctic continent is overlain by glaciers, under which much of the terrain is subject to basal melting. The exposed land of Antarctica is substantially underlain with permafrost, some of which is subject to warming and thawing along the coastline.\n\nAlpine permafrost\nA range of elevations in both the Northern and Southern Hemisphere are cold enough to support perennially frozen ground: some of the best-known examples include the Canadian Rockies, the European Alps, Himalaya and the Tien Shan. In general, it has been found that extensive alpine permafrost requires mean annual air temperature of −3 °C (27 °F), though this can vary depending on local topography, and some mountain areas are known to support permafrost at −1 °C (30 °F). It is also possible for subsurface alpine permafrost to be covered by warmer, vegetation-supporting soil.\nAlpine permafrost is particularly difficult to study, and systematic research efforts did not begin until the 1970s. Consequently, there remain uncertainties about its geography. As recently as 2009, permafrost had been discovered in a new area – Africa's highest peak, Mount Kilimanjaro (4,700 m (15,400 ft) above sea level and approximately 3° south of the equator). In 2014, a collection of regional estimates of alpine permafrost extent had established a global extent of 3,560,000 km2 (1,370,000 mi2). However, by 2014, alpine permafrost in the Andes had not been fully mapped, although its extent has been modeled to assess the amount of water bound up in these areas.\n\nSubsea permafrost\n\nSubsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions. These areas formed during the last Ice Age, when a larger portion of Earth's water was bound up in ice sheets on land and when sea levels were low. As the ice sheets melted to again become seawater during the Holocene glacial retreat, coastal permafrost became submerged shelves under relatively warm and salty boundary conditions, compared to surface permafrost. Since then, these conditions led to the gradual and ongoing decline of subsea permafrost extent. Nevertheless, its presence remains an important consideration for the \"design, construction, and operation of coastal facilities, structures founded on the seabed, artificial islands, sub-sea pipelines, and wells drilled for exploration and production\". Subsea permafrost can also overlay deposits of methane clathrate, which were once speculated to be a major climate tipping point in what was known as a clathrate gun hypothesis, but are now no longer believed to play any role in projected climate change.\n\nPast extent of permafrost\nAt the Last Glacial Maximum, continuous permafrost covered a much greater area than it does today, covering all of ice-free Europe south to about Szeged (southeastern Hungary) and the Sea of Azov (then dry land) and East Asia south to present-day Changchun and Abashiri. In North America, only an extremely narrow belt of permafrost existed south of the ice sheet at about the latitude of New Jersey through southern Iowa and northern Missouri, but permafrost was more extensive in the drier western regions where it extended to the southern border of Idaho and Oregon. In the Southern Hemisphere, there is some evidence for former permafrost from this period in central Otago and Argentine Patagonia, but was probably discontinuous, and is related to the tundra. Alpine permafrost also occurred in the Drakensberg during glacial maxima above about 3,000 metres (9,840 ft).\n\nManifestations\n\nBase depth\nPermafrost extends to a base depth where geothermal heat from the Earth and the mean annual temperature at the surface achieve an equilibrium temperature of 0 °C (32 °F). This base depth of permafrost can vary wildly – it is less than a meter (3 ft) in the areas where it is shallowest, yet reaches 1,493 m (4,898 ft) in the northern Lena and Yana River basins in Siberia. Calculations indicate that the formation time of permafrost greatly slows past the first several metres. For instance, over half a million years was required to form the deep permafrost underlying Prudhoe Bay, Alaska, a time period extending over several glacial and interglacial cycles of the Pleistocene.\nBase depth is affected by the underlying geology, and particularly by thermal conductivity, which is lower for permafrost in soil than in bedrock. Lower conductivity leaves permafrost less affected by the geothermal gradient, which is the rate of increasing temperature with respect to increasing depth in the Earth's interior. It occurs as the Earth's internal thermal energy is generated by radioactive decay of unstable isotopes and flows to the surface by conduction at a rate of ~47 terawatts (TW). Away from tectonic plate boundaries, this is equivalent to an average heat flow of 25–30 °C/km (124–139 °F/mi) near the surface.\n\nMassive ground ice\n\nWhen the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy mud to pure ice. Massive icy beds have a minimum thickness of at least 2 m and a short diameter of at least 10 m. First recorded North American observations of this phenomenon were by European scientists at Canning River (Alaska) in 1919. Russian literature provides an earlier date of 1735 and 1739 during the Great North Expedition by P. Lassinius and Khariton Laptev, respectively. Russian investigators including I. A. Lopatin, B. Khegbomov, S. Taber and G. Beskow had also formulated the original theories for ice inclusion in freezing soils.\nWhile there are four categories of ice in permafrost – pore ice, ice wedges (also known as vein ice), buried surface ice and intrasedimental (sometimes also called constitutional) ice – only the last two tend to be large enough to qualify as massive ground ice. These two types usually occur separately, but may be found together, like on the coast of Tuktoyaktuk in western Arctic Canada, where the remains of Laurentide Ice Sheet are located.\nBuried surface ice may derive from snow, frozen lake or sea ice, aufeis (stranded river ice) and even buried glacial ice from the former Pleistocene ice sheets. The latter hold enormous value for paleoglaciological research, yet even as of 2022, the total extent and volume of such buried ancient ice is unknown. Notable sites with known ancient ice deposits include Yenisei River valley in Siberia, Russia as well as Banks and Bylot Island in Canada's Nunavut and Northwest Territories. Some of the buried ice sheet remnants are known to host thermokarst lakes.\n\nIntrasedimental or constitutional ice has been widely observed and studied across Canada. It forms when subterranean waters freeze in place, and is subdivided into intrusive, injection and segregational ice. The latter is the dominant type, formed after crystallizational differentiation in wet sediments, which occurs when water migrates to the freezing front under the influence of van der Waals forces. This is a slow process, which primarily occurs in silts with salinity less than 20% of seawater: silt sediments with higher salinity and clay sediments instead have water movement prior to ice formation dominated by rheological processes. Consequently, it takes between 1 and 1000 years to form intrasedimental ice in the top 2.5 meters of clay sediments, yet it takes between 10 and 10,000 years for peat sediments and between 1,000 and 1,000,000 years for silt sediments.\n\nLandforms\n\nPermafrost processes such as thermal contraction generating cracks which eventually become ice wedges and solifluction – gradual movement of soil down the slope as it repeatedly freezes and thaws – often lead to the formation of ground polygons, rings, steps and other forms of patterned ground found in arctic, periglacial and alpine areas. In ice-rich permafrost areas, melting of ground ice initiates thermokarst landforms such as thermokarst lakes, thaw slumps, thermal-erosion gullies, and active layer detachments. Notably, unusually deep permafrost in Arctic moorlands and bogs often attracts meltwater in warmer seasons, which pools and freezes to form ice lenses, and the surrounding ground begins to jut outward at a slope. This can eventually result in the formation of large-scale land forms around this core of permafrost, such as palsas – long (15–150 m (49–492 ft)), wide (10–30 m (33–98 ft)) yet shallow (<1–6 m (3 ft 3 in – 19 ft 8 in) tall) peat mounds – and the even larger pingos, which can be 3–70 m (10–230 ft) high and 30–1,000 m (98–3,281 ft) in diameter.\n\nEcology\n\nOnly plants with shallow roots can survive in the presence of permafrost. Black spruce tolerates limited rooting zones, and dominates flora where permafrost is extensive. Likewise, animal species which live in dens and burrows have their habitat constrained by the permafrost, and these constraints also have a secondary impact on interactions between species within the ecosystem.\n\nWhile permafrost soil is frozen, it is not completely inhospitable to microorganisms, though their numbers can vary widely, typically from 1 to 1000 million per gram of soil.\nThe permafrost carbon cycle (Arctic Carbon Cycle) deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to the atmosphere, back to vegetation, and finally back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of carbon dioxide and methane between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, dissolved organic carbon, dissolved inorganic carbon, particulate inorganic carbon and particulate organic carbon.\nMost of the bacteria and fungi found in permafrost cannot be cultured in the laboratory, but the identity of the microorganisms can be revealed by DNA-based techniques. For instance, analysis of 16S rRNA genes from late Pleistocene permafrost samples in eastern Siberia's Kolyma Lowland revealed eight phylotypes, which belonged to the phyla Actinomycetota and Pseudomonadota. \"Muot-da-Barba-Peider\", an alpine permafrost site in eastern Switzerland, was found to host a diverse microbial community in 2016. Prominent bacteria groups included phylum Acidobacteriota, Actinomycetota, AD3, Bacteroidota, Chloroflexota, Gemmatimonadota, OD1, Nitrospirota, Planctomycetota, Pseudomonadota, and Verrucomicrobiota, in addition to eukaryotic fungi like Ascomycota, Basidiomycota, and Zygomycota. In the presently living species, scientists observed a variety of adaptations for sub-zero conditions, including reduced and anaerobic metabolic processes.\n\nConstruction on permafrost\nThere are only two large cities in the world built in areas of continuous permafrost (where the frozen soil forms an unbroken, below-zero sheet) and both are in Russia – Norilsk in Krasnoyarsk Krai and Yakutsk in the Sakha Republic. Building on permafrost is difficult because the heat of the building (or pipeline) can spread to the soil, thawing it. As ice content turns to water, the ground's ability to provide structural support is weakened, until the building is destabilized. For instance, during the construction of the Trans-Siberian Railway, a steam engine factory complex built in 1901 began to crumble within a month of operations for these reasons. Additionally, there is no groundwater available in an area underlain with permafrost. Any substantial settlement or installation needs to make some alternative arrangement to obtain water.\nA common solution is placing foundations on wood piles, a technique pioneered by Soviet engineer Mikhail Kim in Norilsk. However, warming-induced change of friction on the piles can still cause movement through creep, even as the soil remains frozen. The Melnikov Permafrost Institute in Yakutsk found that pile foundations should extend down to 15 metres (49 ft) to avoid the risk of buildings sinking. At this depth the temperature does not change with the seasons, remaining at about −5 °C (23 °F).\nTwo other approaches are building on an extensive gravel pad (usually 1–2 m (3 ft 3 in – 6 ft 7 in) thick); or using anhydrous ammonia heat pipes. The Trans-Alaska Pipeline System uses heat pipes built into vertical supports to prevent the pipeline from sinking and the Qingzang railway in Tibet employs a variety of methods to keep the ground cool, both in areas with frost-susceptible soil. Permafrost may necessitate special enclosures for buried utilities, called \"utilidors\".\n\nImpacts of climate change\n\nIncreasing active layer thickness\nGlobally, permafrost warmed by about 0.3 °C (0.54 °F) between 2007 and 2016, with stronger warming observed in the continuous permafrost zone relative to the discontinuous zone. Observed warming was up to 3 °C (5.4 °F) in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2 °C (3.6 °F) in parts of the Russian European North (1970–2020). This warming inevitably causes permafrost to thaw: active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.\nBetween 2000 and 2018, the average active layer thickness had increased from ~127 centimetres (4.17 ft) to ~145 centimetres (4.76 ft), at an average annual rate of ~0.65 centimetres (0.26 in).\nIn Yukon, the zone of continuous permafrost might have moved 100 kilometres (62 mi) poleward since 1899, but accurate records only go back 30 years. The extent of subsea permafrost is decreasing as well; as of 2019, ~97% of permafrost under Arctic ice shelves is becoming warmer and thinner.\nBased on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as the global climate warms, with the extent of the losses determined by the magnitude of warming.\nPermafrost thaw is associated with a wide range of issues, and International Permafrost Association (IPA) exists to help address them. It convenes International Permafrost Conferences and maintains Global Terrestrial Network for Permafrost, which undertakes special projects such as preparing databases, maps, bibliographies, and glossaries, and coordinates international field programmes and networks.\n\nClimate change feedback\n\nAs recent warming deepens the active layer subject to permafrost thaw, this exposes formerly stored carbon to biogenic processes which facilitate its entrance into the atmosphere as carbon dioxide and methane. Because carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, it is a well-known example of a positive climate change feedback. Permafrost thaw is sometimes included as one of the major tipping points in the climate system due to the exhibition of local thresholds and its effective irreversibility. However, while there are self-perpetuating processes that apply on the local or regional scale, it is debated as to whether it meets the strict definition of a global tipping point as in aggregate permafrost thaw is gradual with warming.\n\nIn the northern circumpolar region, permafrost contains organic matter equivalent to 1400–1650 billion tons of pure carbon, which was built up over thousands of years. This amount equals almost half of all organic material in all soils, and it is about twice the carbon content of the atmosphere, or around four times larger than the human emissions of carbon between the start of the Industrial Revolution and 2011. Further, most of this carbon (~1,035 billion tons) is stored in what is defined as the near-surface permafrost, no deeper than 3 metres (9.8 ft) below the surface. However, only a fraction of this stored carbon is expected to enter the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per 1 °C (1.8 °F) of global warming, yet even under the RCP8.5 scenario associated with over 4 °C (7.2 °F) of global warming by the end of the 21st century, about 5% to 15% of permafrost carbon is expected to be lost \"over decades and centuries\".\nThe exact amount of carbon that will be released due to warming in a given permafrost area depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment, and microbial and vegetation activity in the soil. Notably, estimates of carbon release alone do not fully represent the impact of permafrost thaw on climate change. This is because carbon can be released through either aerobic or anaerobic respiration, which results in carbon dioxide (CO2) or methane (CH4) emissions, respectively. While methane lasts less than 12 years in the atmosphere, its global warming potential is around 80 times larger than that of CO2 over a 20-year period and about 28 times larger over a 100-year period. While only a small fraction of permafrost carbon will enter the atmosphere as methane, those emissions will cause 40–70% of the total warming caused by permafrost thaw during the 21st century. Much of the uncertainty about the eventual extent of permafrost methane emissions is caused by the difficulty of accounting for the recently discovered abrupt thaw processes, which often increase the fraction of methane emitted over carbon dioxide in comparison to the usual gradual thaw processes.\n\nAnother factor which complicates projections of permafrost carbon emissions is the ongoing \"greening\" of the Arctic. As climate change warms the air and the soil, the region becomes more hospitable to plants, including larger shrubs and trees which could not survive there before. Thus, the Arctic is losing more and more of its tundra biomes, yet it gains more plants, which proceed to absorb more carbon. Some of the emissions caused by permafrost thaw will be offset by this increased plant growth, but the exact proportion is uncertain. It is considered very unlikely that this greening could offset all of the emissions from permafrost thaw during the 21st century, and even less likely that it could continue to keep pace with those emissions after the 21st century. Further, climate change also increases the risk of wildfires in the Arctic, which can substantially accelerate emissions of permafrost carbon.\n\nImpact on global temperatures\n\nAltogether, it is expected that cumulative greenhouse gas emissions from permafrost thaw will be smaller than the cumulative anthropogenic emissions, yet still substantial on a global scale, with some experts comparing them to emissions caused by deforestation. The IPCC Sixth Assessment Report estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes of carbon dioxide per 1 °C (1.8 °F) of warming. For comparison, by 2019, annual anthropogenic emissions of carbon dioxide alone stood around 40 billion tonnes. A major review published in the year 2022 concluded that if the goal of preventing 2 °C (3.6 °F) of warming was realized, then the average annual permafrost emissions throughout the 21st century would be equivalent to the year 2019 annual emissions of Russia. Under RCP4.5, a scenario considered close to the current trajectory and where the warming stays slightly below 3 °C (5.4 °F), annual permafrost emissions would be comparable to year 2019 emissions of Western Europe or the United States, while under the scenario of high global warming and worst-case permafrost feedback response, they would approach year 2019 emissions of China.\nFewer studies have attempted to describe the impact directly in terms of warming. A 2018 paper estimated that if global warming was limited to 2 °C (3.6 °F), gradual permafrost thaw would add around 0.09 °C (0.16 °F) to global temperatures by 2100, while a 2022 review concluded that every 1 °C (1.8 °F) of global warming would cause 0.04 °C (0.072 °F) and 0.11 °C (0.20 °F) from abrupt thaw by the year 2100 and 2300. Around 4 °C (7.2 °F) of global warming, abrupt (around 50 years) and widespread collapse of permafrost areas could occur, resulting in an additional warming of 0.2–0.4 °C (0.36–0.72 °F).\n\nThaw-induced ground instability\n\nAs the water drains or evaporates, soil structure weakens and sometimes becomes viscous until it regains strength with decreasing moisture content. One visible sign of permafrost degradation is the random displacement of trees from their vertical orientation in permafrost areas. Global warming has been increasing permafrost slope disturbances and sediment supplies to fluvial systems, resulting in exceptional increases in river sediment. On the other hands, disturbance of formerly hard soil increases drainage of water reservoirs in northern wetlands. This can dry them out and compromise the survival of plants and animals used to the wetland ecosystem.\nIn high mountains, much of the structural stability can be attributed to glaciers and permafrost. As climate warms, permafrost thaws, decreasing slope stability and increasing stress through buildup of pore-water pressure, which may ultimately lead to slope failure and rockfalls. Over the past century, an increasing number of alpine rock slope fail",
    "source": "wikipedia:Permafrost",
    "domain": "climate"
  },
  {
    "text": "Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide (CO2) levels exceeding 422 ppm (as of 2024). CO2 from the atmosphere is absorbed by the oceans. This chemical reaction produces carbonic acid (H2CO3) which dissociates into a bicarbonate ion (HCO−3) and a hydrogen ion (H+). The presence of free hydrogen ions (H+) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.\nA change in pH by 0.1 represents a 26% increase in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH units is equivalent to a tenfold change in hydrogen ion concentration). Sea-surface pH and carbonate saturation states vary depending on ocean depth and location. Colder and higher latitude waters are capable of absorbing more CO2. This can cause acidity to rise, lowering the pH and carbonate saturation levels in these areas. There are several other factors that influence the atmosphere-ocean CO2 exchange, and thus local ocean acidification. These include ocean currents and upwelling zones, proximity to large continental rivers, sea ice coverage, and atmospheric exchange with nitrogen and sulfur from fossil fuel burning and agriculture.\nA lower ocean pH has a range of potentially harmful effects for marine organisms. Scientists have observed for example reduced calcification, lowered immune responses, and reduced energy for basic functions such as reproduction. Ocean acidification can impact marine ecosystems that provide food and livelihoods for many people. About one billion people are wholly or partially dependent on the fishing, tourism, and coastal management services provided by coral reefs. Ongoing acidification of the oceans may therefore threaten food chains linked with the oceans.\nOne of the only solutions that would address the root cause of ocean acidification is reducing carbon dioxide emissions. This is one of the main objectives of climate change mitigation measures. The removal of carbon dioxide from the atmosphere would also help to reverse ocean acidification. In addition, there are some specific ocean-based mitigation methods, for example ocean alkalinity enhancement and enhanced weathering. These strategies are under investigation, but generally have a low technology readiness level and many risks.\nOcean acidification has happened before in Earth's geologic history. The resulting ecological collapse in the oceans had long-lasting effects on the global carbon cycle and climate.\n\nCause\n\nIn 2021, atmospheric carbon dioxide (CO2) levels of around 415 ppm were around 50% higher than preindustrial concentrations. According to the National Oceanic and Atmospheric Administration in 2023, atmospheric CO2 levels have risen from approximately 280 parts per million (ppm) in the pre-industrial era to over 410 ppm today, primarily due to human activities such as fossil fuel combustion and deforestation. The current elevated levels and rapid growth rates are unprecedented in the past 55 million years of the geological record. The sources of this excess CO2 are clearly established as human driven: they include anthropogenic fossil fuel, industrial, and land-use/land-change emissions. One source of this is fossil fuels, which are burned for energy. When burned, CO2 is released into the atmosphere as a byproduct of combustion, which is a significant contributor to the increasing levels of CO2 in the Earth's atmosphere. The ocean acts as a carbon sink for anthropogenic CO2 and takes up roughly a quarter of total anthropogenic CO2 emissions. However, the additional CO2 in the ocean results in a wholesale shift in seawater acid-base chemistry toward more acidic, lower pH conditions and lower saturation states for carbonate minerals used in many marine organism shells and skeletons.\nAccumulated since 1850, the ocean sink holds up to 175±35 gigatons of carbon, with more than two-thirds of this amount (120 Gt C) being taken up by the global ocean since 1960. Over the historical period, the ocean sink increased in pace with the exponential anthropogenic emissions increase. From 1850 until 2022, the ocean has absorbed 26% of total anthropogenic emissions. Emissions during the period 1850–2021 amounted to 670±65 gigatons of carbon and were partitioned among the atmosphere (41%), ocean (26%), and land (31%).\nThe carbon cycle describes the fluxes of carbon dioxide (CO2) between the oceans, terrestrial biosphere, lithosphere, and atmosphere. The carbon cycle involves both organic compounds such as cellulose and inorganic carbon compounds such as carbon dioxide, carbonate ion, and bicarbonate ion, together referenced as dissolved inorganic carbon (DIC). These inorganic compounds are particularly significant in ocean acidification, as they include many forms of dissolved CO2 present in the Earth's oceans.\nWhen CO2 dissolves, it reacts with water to form a balance of ionic and non-ionic chemical species: dissolved free carbon dioxide (CO2(aq)), carbonic acid (H2CO3), bicarbonate (HCO−3) and carbonate (CO2−3). The ratio of these species depends on factors such as seawater temperature, pressure and salinity (as shown in a Bjerrum plot). These different forms of dissolved inorganic carbon are transferred from an ocean's surface to its interior by the ocean's solubility pump. The resistance of an area of ocean to absorbing atmospheric CO2 is known as the Revelle factor.\n\nMain effects\nThe ocean's chemistry is changing due to the uptake of anthropogenic carbon dioxide (CO2). Ocean pH, carbonate ion concentrations ([CO32−]), and calcium carbonate mineral saturation states (Ω) have been declining as a result of the uptake of approximately 30% of the anthropogenic carbon dioxide emissions over the past 270 years (since around 1750). This process, commonly referred to as \"ocean acidification\", is making it harder for marine calcifiers to build a shell or skeletal structure, endangering coral reefs and the broader marine ecosystems.\nOcean acidification has been called the \"evil twin of global warming\" and \"the other CO2 problem\". Increased ocean temperatures and oxygen loss act concurrently with ocean acidification and constitute the \"deadly trio\" of climate change pressures on the marine environment. The impacts of this will be most severe for coral reefs and other shelled marine organisms, as well as those populations that depend on the ecosystem services they provide.\n\nReduction in pH value\n\nDissolving CO2 in seawater increases the hydrogen ion (H+) concentration in the ocean, and thus decreases ocean pH, as follows:\nIn shallow coastal and shelf regions, a number of factors interplay to affect air-ocean CO2 exchange and resulting pH change. These include biological processes, such as photosynthesis and respiration, as well as water upwelling. Also, ecosystem metabolism in freshwater sources reaching coastal waters can lead to large, but local, pH changes.\nFreshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.\nThe absorption of CO2 from the atmosphere does not affect the ocean's alkalinity. This is important to know in this context as alkalinity is the capacity of water to resist acidification. Ocean alkalinity enhancement has been proposed as one option to add alkalinity to the ocean and therefore buffer against pH changes.\n\nDecreased calcification in marine organisms\n\nChanges in ocean chemistry can have extensive direct and indirect effects on organisms and their habitats. One of the most important repercussions of increasing ocean acidity relates to the production of shells out of calcium carbonate (CaCO3). This process is called calcification and is important to the biology and survival of a wide range of marine organisms. Calcification involves the precipitation of dissolved ions into solid CaCO3 structures, structures for many marine organisms, such as coccolithophores, foraminifera, crustaceans, mollusks, etc. After they are formed, these CaCO3 structures are vulnerable to dissolution unless the surrounding seawater contains saturating concentrations of carbonate ions (CO2−3).\nVery little of the extra carbon dioxide that is added into the ocean remains as dissolved carbon dioxide. The majority dissociates into additional bicarbonate and free hydrogen ions. The increase in hydrogen is larger than the increase in bicarbonate, creating an imbalance in the reaction:\n\nHCO−3 ⇌ CO2−3 + H+\nTo maintain chemical equilibrium, some of the carbonate ions already in the ocean combine with some of the hydrogen ions to make further bicarbonate. Thus the ocean's concentration of carbonate ions is reduced, removing an essential building block for marine organisms to build shells, or calcify:\n\nCa2+ + CO2−3 ⇌ CaCO3\nThe increase in concentrations of dissolved carbon dioxide and bicarbonate, and reduction in carbonate, are shown in the Bjerrum plot.\nDisruption of the food chain is also a possible effect as many marine organisms rely on calcium carbonate-based organisms at the base of the food chain for food and habitat. This can potentially have detrimental effects throughout the food web and potentially lead to a decline in availability of fish stocks which would have an impact on human livelihoods.\n\nDecrease in saturation state\n\nThe saturation state (known as Ω) of seawater for a mineral is a measure of the thermodynamic potential for the mineral to form or to dissolve, and for calcium carbonate is described by the following equation:\n\n \n \n \n \n Ω\n \n =\n \n \n \n \n [\n \n \n Ca\n \n 2\n +\n \n \n \n ]\n \n \n [\n \n \n CO\n \n 3\n \n \n 2\n −\n \n \n \n ]\n \n \n \n K\n \n s\n p\n \n \n \n \n \n \n {\\displaystyle {\\Omega }={\\frac {\\left[{\\ce {Ca^2+}}\\right]\\left[{\\ce {CO3^2-}}\\right]}{K_{sp}}}}\n \n\nHere Ω is the product of the concentrations (or activities) of the reacting ions that form the mineral (Ca2+ and CO32−), divided by the apparent solubility product at equilibrium (Ksp), that is, when the rates of precipitation and dissolution are equal. In seawater, dissolution boundary is formed as a result of temperature, pressure, and depth, and is known as the saturation horizon. Above this saturation horizon, Ω has a value greater than 1, and CaCO3 does not readily dissolve. Most calcifying organisms live in such waters. Below this depth, Ω has a value less than 1, and CaCO3 will dissolve. The carbonate compensation depth is the ocean depth at which carbonate dissolution balances the supply of carbonate to sea floor, therefore sediment below this depth will be void of calcium carbonate. Increasing CO2 levels, and the resulting lower pH of seawater, decreases the concentration of CO32− and the saturation state of CaCO3 therefore increasing CaCO3 dissolution.\nCalcium carbonate most commonly occurs in two common polymorphs (crystalline forms): aragonite and calcite. Aragonite is much more soluble than calcite, so the aragonite saturation horizon, and aragonite compensation depth, is always nearer to the surface than the calcite saturation horizon. This also means that those organisms that produce aragonite may be more vulnerable to changes in ocean acidity than those that produce calcite. Ocean acidification and the resulting decrease in carbonate saturation states raise the saturation horizons of both forms closer to the surface. This decrease in saturation state is one of the main factors leading to decreased calcification in marine organisms because the inorganic precipitation of CaCO3 is directly proportional to its saturation state and calcifying organisms exhibit stress in waters with lower saturation states.\n\nNatural variability and climate feedbacks\n\nAlready now large quantities of water undersaturated in aragonite are upwelling close to the Pacific continental shelf area of North America, from Vancouver to Northern California. These continental shelves play an important role in marine ecosystems, since most marine organisms live or are spawned there. Other shelf areas may be experiencing similar effects.\nAt depths of 1000s of meters in the ocean, calcium carbonate shells begin to dissolve as increasing pressure and decreasing temperature shift the chemical equilibria controlling calcium carbonate precipitation. The depth at which this occurs is known as the carbonate compensation depth. Ocean acidification will increase such dissolution and shallow the carbonate compensation depth on timescales of tens to hundreds of years. Zones of downwelling are being affected first.\nIn the North Pacific and North Atlantic, saturation states are also decreasing (the depth of saturation is getting more shallow). Ocean acidification is progressing in the open ocean as the CO2 travels to deeper depth as a result of ocean mixing. In the open ocean, this causes carbonate compensation depths to become more shallow, meaning that dissolution of calcium carbonate will occur below those depths. In the North Pacific these carbonate saturations depths are shallowing at a rate of 1–2 m/year.\nIt is expected that ocean acidification in the future will lead to a significant decrease in the burial of carbonate sediments for several centuries, and even the dissolution of existing carbonate sediments.\n\nMeasured and estimated values\n\nPresent day and recent history\n\nBetween 1950 and 2020, the average pH value of the ocean surface is estimated to have decreased from approximately 8.15 to 8.05. This represents an increase of around 26% in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH unit is equivalent to a tenfold change in hydrogen ion concentration). For example, in the 15-year period 1995–2010 alone, acidity has increased 6 percent in the upper 100 meters of the Pacific Ocean from Hawaii to Alaska.\nThe IPCC Sixth Assessment Report in 2021 stated that \"present-day surface pH values are unprecedented for at least 26,000 years and current rates of pH change are unprecedented since at least that time. The pH value of the ocean interior has declined over the last 20–30 years everywhere in the global ocean. The report also found that \"pH in open ocean surface water has declined by about 0.017 to 0.027 pH units per decade since the late 1980s\".\nThe rate of decline differs by region. This is due to complex interactions between different types of forcing mechanisms: \"In the tropical Pacific, its central and eastern upwelling zones exhibited a faster pH decline of minus 0.022 to minus 0.026 pH unit per decade.\" This is thought to be \"due to increased upwelling of CO2-rich sub-surface waters in addition to anthropogenic CO2 uptake\". Some regions exhibited a slower acidification rate: a pH decline of minus 0.010 to minus 0.013 pH unit per decade has been observed in warm pools in the western tropical Pacific.\nThe rate at which ocean acidification will occur may be influenced by the rate of surface ocean warming, because warm waters will not absorb as much CO2. Therefore, greater seawater warming could limit CO2 absorption and lead to a smaller change in pH for a given increase in CO2. The difference in changes in temperature between basins is one of the main reasons for the differences in acidification rates in different localities.\nCurrent rates of ocean acidification have been likened to the greenhouse event at the Paleocene–Eocene boundary (about 56 million years ago), when surface ocean temperatures rose by 5–6 °C. In that event, surface ecosystems experienced a variety of impacts, but bottom-dwelling organisms in the deep ocean actually experienced a major extinction. Currently, the rate of carbon addition to the atmosphere-ocean system is about ten times the rate that occurred at the Paleocene–Eocene boundary.\nExtensive observational systems are now in place or being built for monitoring seawater CO2 chemistry and acidification for both the global open ocean and some coastal systems.\n\nGeologic past\nOcean acidification has occurred previously in Earth's history. It happened during the Capitanian mass extinction, at the end-Permian extinction, during the end-Triassic extinction, and during the Cretaceous–Palaeogene extinction event.\nThree of the big five mass extinction events in the geologic past were associated with a rapid increase in atmospheric carbon dioxide, probably due to volcanism and/or thermal dissociation of marine gas hydrates. Elevated CO2 levels impacted biodiversity. Decreased CaCO3 saturation due to seawater uptake of volcanogenic CO2 has been suggested as a possible kill mechanism during the marine mass extinction at the end of the Triassic. The end-Triassic biotic crisis is still the most well-established example of a marine mass extinction due to ocean acidification, because (a) carbon isotope records suggest enhanced volcanic activity that decreased the carbonate sedimentation which reduced the carbonate compensation depth and the carbonate saturation state, and a marine extinction coincided precisely in the stratigraphic record, and (b) there was pronounced selectivity of the extinction against organisms with thick aragonitic skeletons, which is predicted from experimental studies. Ocean acidification has also been suggested as a one cause of the end-Permian mass extinction and the end-Cretaceous crisis. Overall, multiple climatic stressors, including ocean acidification, was likely the cause of geologic extinction events.\nThe most notable example of ocean acidification is the Paleocene–Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago when massive amounts of carbon entered the ocean and atmosphere, and led to the dissolution of carbonate sediments across many ocean basins. Relatively new geochemical methods of testing for pH in the past indicate the pH dropped 0.3 units across the PETM. One study that solves the marine carbonate system for saturation state shows that it may not change much over the PETM, suggesting the rate of carbon release at our best geological analogy was much slower than human-induced carbon emissions. However, stronger proxy methods to test for saturation state are needed to assess how much this pH change may have affected calcifying organisms.\n\nPredicted future values\n\nImportantly, the rate of change in ocean acidification is much higher than in the geological past. This faster change prevents organisms from gradually adapting, and prevents climate cycle feedbacks from kicking in to mitigate ocean acidification. Ocean acidification is now on a path to reach lower pH levels than at any other point in the last 300 million years. The rate of ocean acidification (i.e. the rate of change in pH value) is also estimated to be unprecedented over that same time scale. These expected changes are considered unprecedented in the geological record. In combination with other ocean biogeochemical changes, this drop in pH value could undermine the functioning of marine ecosystems and disrupt the provision of many goods and services associated with the ocean, beginning as early as 2100.\nThe extent of further ocean chemistry changes, including ocean pH, will depend on climate change mitigation efforts taken by nations and their governments. Different scenarios of projected socioeconomic global changes are modelled by using the Shared Socioeconomic Pathways (SSP) scenarios.\nUnder a very high emission scenario (SSP5-8.5), model projections estimate that surface ocean pH could decrease by as much as 0.44 units by the end of this century, compared to the end of the 19th century. This would mean a pH as low as about 7.7, and represents a further increase in H+ concentrations of two to four times beyond the increase to date.\n\nImpacts on oceanic calcifying organisms\n\nComplexity of research findings\nThe full ecological consequences of the changes in calcification due to ocean acidification are complex but it appears likely that many calcifying species will be adversely affected by ocean acidification. Increasing ocean acidification makes it more difficult for shell-accreting organisms to access carbonate ions, essential for the production of their hard exoskeletal shell. Oceanic calcifying organism span the food chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and molluscs.\nOverall, all marine ecosystems on Earth will be exposed to changes in acidification and several other ocean biogeochemical changes. Ocean acidification may force some organisms to reallocate resources away from productive endpoints in order to maintain calcification. For example, the oyster Magallana gigas is recognized to experience metabolic changes alongside altered calcification rates due to energetic tradeoffs resulting from pH imbalances.\nUnder normal conditions, calcite and aragonite are stable in surface waters since the carbonate ions are supersaturated with respect to seawater. However, as ocean pH falls, the concentration of carbonate ions also decreases. Calcium carbonate thus becomes undersaturated, and structures made of calcium carbonate are vulnerable to calcification stress and dissolution. In particular, studies show that corals, coccolithophores, coralline algae, foraminifera, shellfish and pteropods experience reduced calcification or enhanced dissolution when exposed to elevated CO2. Even with active marine conservation practices it may be impossible to bring back many previous shellfish populations.\nSome studies have found different responses to ocean acidification, with coccolithophore calcification and photosynthesis both increasing under elevated atmospheric pCO2, and an equal decline in primary production and calcification in response to elevated CO2, or the direction of the response varying between species.\nSimilarly, the sea star, Pisaster ochraceus, shows enhanced growth in waters with increased acidity.\nReduced calcification from ocean acidification may affect the ocean's biologically driven sequestration of carbon from the atmosphere to the ocean interior and seafloor sediment, weakening the so-called biological pump. Seawater acidification could also reduce the size of Antarctic phytoplankton, making them less effective at storing carbon. Such changes are being increasingly studied and synthesized through the use of physiological frameworks, including the Adverse Outcome Pathway (AOP) framework.\n\nCoccolithophores\n\nA coccolithophore is a unicellular, eukaryotic phytoplankton (alga). Understanding calcification changes in coccolithophores may be particularly important because a decline in the coccolithophores may have secondary effects on climate: it could contribute to global warming by decreasing the Earth's albedo via their effects on oceanic cloud cover. A study in 2008 examined a sediment core from the North Atlantic and found that the species composition of coccolithophorids remained unchanged over the past 224 years (1780 to 2004). But the average coccolith mass had increased by 40% during the same period.\n\nCorals\n\nWarm water corals are clearly in decline, with losses of 50% over the last 30–50 years due to multiple threats from ocean warming, ocean acidification, pollution and physical damage from activities such as fishing, and these pressures are expected to intensify.\nThe fluid in the internal compartments (the coelenteron) where corals grow their exoskeleton is also extremely important for calcification growth. When the saturation state of aragonite in the external seawater is at ambient levels, the corals will grow their aragonite crystals rapidly in their internal compartments, hence their exoskeleton grows rapidly. If the saturation state of aragonite in the external seawater is lower than the ambient level, the corals have to work harder to maintain the right balance in the internal compartment. When that happens, the process of growing the crystals slows down, and this slows down the rate of how much their exoskeleton is growing. Depending on the aragonite saturation state in the surrounding water, the corals may halt growth because pumping aragonite into the internal compartment will not be energetically favorable. Under the current progression of carbon emissions, around 70% of North Atlantic cold-water corals will be living in corrosive waters by 2050–60.\nAcidified conditions primarily reduce the coral's capacity to build dense exoskeletons, rather than affecting the linear extension of the exoskeleton. The density of some species of corals could be reduced by over 20% by the end of this century.\nAn in situ experiment, conducted on a 400 m2 patch of the Great Barrier Reef, to decrease seawater CO2 level (raise pH) to near the preindustrial value showed a 7% increase in net calcification. A similar experiment to raise in situ seawater CO2 level (lower pH) to a level expected soon after the 2050 found that net calcification decreased 34%.\nHowever, a field study of the coral reef in Queensland and Western Australia from 2007 to 2012 found that corals are more resistant to the environmental pH changes than previously thought, due to internal homeostasis regulation; this makes thermal change (marine heatwaves), which leads to coral bleaching, rather than acidification, the main factor for coral reef vulnerability due to climate change.\n\nStudies at carbon dioxide seep sites\nIn some places carbon dioxide bubbles out from the sea floor, locally changing the pH and other aspects of the chemistry of the seawater. Studies of these carbon dioxide seeps have documented a variety of responses by different organisms. Coral reef communities located near carbon dioxide seeps are of particular interest because of the sensitivity of some corals species to acidification. In Papua New Guinea, declining pH caused by carbon dioxide seeps is associated with declines in coral species diversity. However, in Palau carbon dioxide seeps are not associated with reduced species diversity of corals, although bioerosion of coral skeletons is much higher at low pH sites.\n\nPteropods and brittle stars\nPteropods and brittle stars both form the base of the Arctic food webs and are both seriously damaged from acidification. Pteropods shells dissolve with increasing acidification and the brittle stars lose muscle mass when re-growing appendages. For pteropods to create shells they require aragonite which is produced through carbonate ions and dissolved calcium and strontium. Pteropods are severely affected because increasing acidification levels have steadily decreased the amount of water supersaturated with carbonate. The degradation of organic matter in Arctic waters has amplified ocean acidification; some Arctic waters are already undersaturated with respect to aragonite.\nThe brittle star's eggs die within a few days when exposed to expected conditions resulting from Arctic acidification. Similarly, when exposed in experiments to pH reduced by 0.2 to 0.4, larvae of a temperate brittle star, a relative of the common sea star, fewer than 0.1 percent survived more than eight days.\n\nOther impacts on ecosystems\n\nOther biological impacts\nAside from the slowing and/or reversal of calcification, organisms may suffer other adverse effects, either indirectly through negative impacts on food resources, or directly as reproductive or physiological effects. For example, the elevated oceanic levels of CO2 may produce CO2-induced acidification of body fluids, known as hypercapnia.\nIncreasing acidity has been observed to reduce metabolic rates in jumbo squid and depress the immune responses of blue mussels.\nAtlantic longfin squid eggs took longer to hatch in acidified water, and the squid's statolith was smaller and malformed in animals placed in sea water with a lower pH. However, these studies are ongoing and there is not yet a full understanding of these processes in marine organisms or ecosystems.\n\nAcoustic properties\nAnother potential route to ecosystem impacts is through bioacoustics. This may occur as ocean acidification can alter the acoustic properties of seawater, allowing sound to propagate further, and increasing ocean noise. This impacts all animals that use sound for echolocation or communication.\n\nAlgae and seagrasses\n\nAnother possible effect would be an increase in harmful algal bloom events, which could contribute to the accumulation of toxins (domoic acid, brevetoxin, saxitoxin) in small organisms such as anchovies and shellfish, in turn increasing occurrences of amnesic shellfish poisoning, neurotoxic shellfish poisoning and paralytic shellfish poisoning. Although algal blooms can be harmful, other beneficial photosynthetic organisms may benefit from increased levels of carbon dioxide. Most importantly, seagrasses will benefit. Research found that as seagrasses increased their photosynthetic activity, calcifying algae's calcification rates rose, likely because localized photosynthetic activity absorbed carbon dioxide and elevated local pH.\n\nFish larvae\nOcean acidification can also have effects on marine fish larvae. It internally affects their olfactory systems, which is a crucial part of their early development. Orange clownfish larvae mostly live on oceanic reefs that are surrounded by vegetative islands. Larvae are known to use their sense of smell to detect the differences between reefs surrounded by vegetative islands and reefs not surrounded by vegetative islands. Clownfish larvae need to be able to distinguish between these two destinations to be able to find a suitable area for their growth. Another use for marine fish olfactory systems is to distinguish between their parents and other adult fish, i",
    "source": "wikipedia:Ocean acidification",
    "domain": "climate"
  },
  {
    "text": "A heat wave or heatwave, sometimes described as extreme heat, is a period of abnormally hot weather and natural disaster that lasts for multiple days. A heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season. The main difficulties with this broad definition emerge when one must quantify what the 'normal' temperature state is, and what the spatial extent of the event may or must be. Temperatures that humans from a hotter climate consider normal can be regarded as a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area. Heat waves have become more frequent, and more intense over land, across almost every area on Earth since the 1950s, the increase in frequency and duration being caused by climate change. According to the World Meteorological Organization, heat waves continued to intensify in 2024, with record-breaking temperatures reported in Europe, North America, and China. Many regions experienced consecutive days above 45°C, highlighting the increasing frequency and severity of extreme heat events worldwide..\nHeat waves form when a high-pressure area in the upper atmosphere strengthens and remains over a region for several days up to several weeks. This traps heat near the earth's surface. It is usually possible to forecast heat waves, thus allowing the authorities to issue a warning in advance.\nHeat waves have an impact on the economy. They can reduce labour productivity, disrupt agricultural and industrial processes and damage infrastructure. Severe heat waves have caused catastrophic crop failures and thousands of deaths from hyperthermia. They have increased the risk of wildfires in areas with drought. They can lead to widespread electricity outages because more air conditioning is used. A heat wave counts as extreme weather. It poses a danger to human health, because heat and sunlight overwhelm the thermoregulation in humans.\n\nDefinitions\n\nThere are several definitions of heat waves:\n\nThe IPCC defines a heatwave as \"a period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months.\"\nA definition based on the Heat Wave Duration Index is that a heat wave occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C (9 °F), the normal period being 1961–1990. The same definition is used by the World Meteorological Organization.\nA definition from the Glossary of Meteorology is: \"A period of abnormally and uncomfortably hot and usually humid weather.\"\nMarine heatwaves are generally described as prolonged discrete periods of unusually warm sea surface temperatures in a specific region. At this time the most commonly accepted definition is that proposed by Hobday et. al. which refers to an algorithm that uses percentile values for temperatures, and defines a threshold set as the 90th percentile for a given day of the year, above which one can say a marine heatwave is occurring. This definition can be used with temperature data acquired anywhere in the world, allowing for comparisons across different observations and latitudes.\n\nDefinitions by country\n\nEurope\nDenmark defines a national heat wave (hedebølge) as a period of at least 3 consecutive days in which the average maximum temperature across more than half the country exceeds 28 °C (82.4 °F). The Danish Meteorological Institute also has a definition for a \"warmth wave\" (varmebølge). It defines this using the same criteria for a 25 °C (77.0 °F) temperature. Sweden defines a heat wave as at least five days in a row with a daily high exceeding 25 °C (77.0 °F).\nIn Greece, the Hellenic National Meteorological Service defines a heat wave as occurring over three consecutive days with temperatures at 39 °C (102 °F) or higher. In the same period the minimum temperature is 26 °C (79 °F) or more. During this period, there are either no winds or only weak winds. These conditions occur in a broad area.\nThe Netherlands defines a heat wave as a period of at least five consecutive days in which the maximum temperature in De Bilt exceeds 25 °C (77 °F). During this period the maximum temperature in De Bilt must exceed 30 °C (86 °F) for at least three days. Belgium also uses this definition of a heat wave with Ukkel as a reference point. So does Luxembourg.\nIn the United Kingdom, the Met Office operates a Heat Health Watch system. This places each Local Authority region into one of four levels. Heat wave conditions occur when the maximum daytime temperature and minimum nighttime temperature rise above the threshold for a particular region. The length of time above that threshold determines the level. Level 1 represents normal summer conditions. Level 2 occurs when there is a 60% or higher risk that the temperature will be above the threshold levels for two days and the intervening night. Level 3 arises when the temperature has been above the threshold for the preceding day and night, and there is a 90% or higher chance that it will stay above the threshold in the following day. Level 4 is triggered if conditions are more severe than those of the preceding three levels. Each of the first three levels gives rise to a particular state of readiness and response by the social and health services. Level 4 involves a more widespread response. The threshold for a heat wave occurs when there are at least three days above 25 °C (77 °F) across much of the country. Greater London has a threshold of 28 °C (82 °F).\nIn Ireland, a heat wave is defined as temperatures exceeding 25 °C (77 °F) for five or more consecutive days.\n\nNorth America\nIn the United States, definitions also vary by region. They usually involve a period of at least two or more days of excessively hot weather. In the Northeast, a heat wave is typically when the temperature reaches or exceeds 90 °F (32.2 °C) for three or more consecutive days. This is not always the case. This is because the high temperature ties in with humidity levels to determine a heat index threshold. The same does not apply to drier climates. A heat storm is a Californian term for an extended heat wave. Heat storms occur when the temperature reaches 100 °F (37.8 °C) for three or more consecutive days over a wide area (tens of thousands of square miles). The National Weather Service issues heat advisories and excessive heat warnings when it expects unusual periods of hot weather.\nIn Canada, heat waves are defined using the daily maximum and minimum temperatures, and in most of the country, the humidex as well, exceeding a regional threshold for two or more days. The threshold in which daily maximum temperatures must exceed ranges between 28 °C (82 °F) in Newfoundland and 35 °C (95 °F) in interior British Columbia, though this threshold is much lower in Nunavut, ranging between 22 °C (72 °F) and 26 °C (79 °F).\n\nOceania\nIn Adelaide, South Australia, a heat wave is five consecutive days at or above 35 °C (95 °F), or three consecutive days at or over 40 °C (104 °F). The Australian Bureau of Meteorology defines a heat wave as three or more days of unusual maximum and minimum temperatures. Before this new Pilot Heatwave Forecast there was no national definition for heat waves or measures of heat wave severity.\nIn New Zealand, heat waves thresholds depend on local climatology, with the temperature threshold ranging between 27 °C (81 °F) in Greymouth and 32 °C (90 °F) in Gisborne.\n\nMarine Heatwaves\n\nMarine heatwaves have become a prominent subject of research in recent years, reflecting the fact that since the turn of this century many ocean areas have experienced peaks of temperatures, along with more frequent, more intense, and more prolonged warming events than ever met on record. The genesis of marine heatwaves is mainly driven by a combination of oceanic and atmospheric factors, often triggered by high pressure systems that will reduce cloud cover and increase solar absorption by the sea surface. Human-induced climate change appears bound to play a growing role in the development of marine heatwaves, with increasing impacts on marine ecosystems, such as mass mortality in benthic communities, coral bleaching events, disruptions in fishery catches, and shifts in species distributions.\n\nObservations\n\nIt is possible to compare heat waves in different regions of the world with different climates thanks to a general indicator that appeared in 2015. With these indicators, experts estimated heat waves at the global scale from 1901 to 2010. They found a substantial and sharp increase in the number of affected areas in the last two decades.\nOne study in 2021 investigated 13,115 cities. It found that extreme heat exposure of a wet bulb globe temperature above 30 Celsius tripled between 1983 and 2016, and if the effect of population growth (increasing the urban heat island effect) during those years is excluded, the exposure increased a further 50%. The researchers compiled a comprehensive list of past urban extreme heat events.\n\nCauses\nHeat waves form when a high pressure area at an altitude of 3,000–7,600 metres (9,800–24,900 feet) strengthens and remains over a region for several days and up to several weeks. This is common in summer in both the Northern and Southern Hemispheres. This is because the jet stream 'follows the sun'. The high pressure area is on the equator side of the jet stream in the upper layers of the atmosphere.\nWeather patterns are generally slower to change in summer than in winter. So, this upper level high pressure also moves slowly. Under high pressure, the air sinks toward the surface. It warms and dries adiabatically. This inhibits convection and prevents the formation of clouds. A reduction of clouds increases the shortwave radiation reaching the surface. A low pressure area at the surface leads to surface wind from lower latitudes that brings warm air, enhancing the warming. The surface winds could also blow from the hot continental interior towards the coastal zone. This would lead to heat waves on the coast. They could also blow from high towards low elevations. This enhances the subsidence or sinking of the air and therefore the adiabatic warming.\nIn the eastern regions of the United States a heat wave can occur when a high pressure system originating in the Gulf of Mexico becomes stationary just off the Atlantic Seaboard. Hot humid air masses form over the Gulf of Mexico and the Caribbean Sea. At the same time hot dry air masses form over the desert Southwest and northern Mexico. The southwest winds on the back side of the high continue to pump hot, humid Gulf air northeastwards. This results in a spell of hot and humid weather for much of the eastern United States and into southeastern Canada.\nIn the Western Cape Province of South Africa, a heat wave can occur when the low-pressure area offshore and the high-pressure area inland combine to form a bergwind. The air warms as it descends from the Karoo interior. The temperature will rise about 10 Celsius from the interior to the coast. Humidity is usually very low. The temperature can be over 40 Celsius in summer. The highest temperature recorded in South Africa (51.5 Celsius) occurred one summer during a berg wind along the Eastern Cape coastline.\nThe level of soil moisture can intensify heat waves in Europe. Low soil moisture leads to a number of complex feedback mechanisms. These in turn can result in increased surface temperatures. One of the main mechanisms is reduced evaporative cooling of the atmosphere. When water evaporates, it consumes energy and therefore lowers the surrounding temperature. If the soil is very dry, then incoming radiation from the sun will warm the air. But there will be little or no cooling effect from moisture evaporating from the soil.\n\nClimate change\n\nImpacts on human health\n\nHeat-related health effects for vulnerable humans\n\nMortality\n\nUnderreporting of fatalities\nThe number of heat fatalities is probably highly underreported. This is due to a lack of reports and to misreporting. When considering heat-related illnesses as well, actual death tolls from extreme heat may be six times higher than official figures. This is based on studies of California and Japan.\nPart of the mortality during a heat wave may be due to short-term forward mortality displacement. In some heat waves there is a decrease in overall mortality in the weeks after a heat wave. These compensatory reductions in mortality suggest that heat affects people who would have died anyway, and brings their deaths forward.\nSocial institutions and structures influence the effects of risks. This factor can also help explain the underreporting of heat waves as a health risk. The deadly French heat wave in 2003 showed that heat wave dangers result from a combination of natural and social factors. Social invisibility is one such factor. Heat-related deaths can occur indoors, for instance among elderly people living alone. In these cases it can be challenging to assign heat as a contributing factor.\n\nHeat index for temperature and relative humidity\n\nThe heat index in the table above is a measure of how hot it feels when relative humidity is factored with the actual air temperature.\n\nPsychological and sociological effects\nExcessive heat causes psychological stress as well as physical stress. This can affect performance. It may also lead to an increase in violent crime. High temperatures are associated with increased conflict between individuals and at the social level. In every society, crime rates go up when temperatures go up. This is particularly the case with violent crimes such as assault, murder and rape. In politically unstable countries, high temperatures can exacerbate factors that lead to civil war.\nHigh temperatures also have a significant effect on income. A study of countries in the United States found that the economic productivity of individual days declines by about 1.7 percent for each degree Celsius above 15 °C (59 °F).\n\nSurface ozone (air pollution)\nHigh temperatures also make the effects of ozone pollution in urban areas worse. This raises heat-related mortality during heat waves. During heat waves in urban areas, ground level ozone pollution can be 20 percent higher than usual.\nOne study looked at fine particle concentrations and ozone concentrations from 1860 to 2000. It found that the global population-weighted fine particle concentrations increased by 5 percent due to climate change. Near-surface ozone concentrations rose by 2 percent.\nAn investigation to assess the joint mortality effects of ozone and heat during the European heat waves in 2003 concluded that these appear to be additive.\n\nImpacts on societies\n\nReduced economic outputs\n\nCalculations from 2022 suggest that heat waves will shrink the global economy by about 1 percent decrease by the middle of the 21st century.\nHeat waves often have complex effects on economies. They reduce labour productivity, disrupt agricultural and industrial processes and damage infrastructure that is not suitable for extreme heat. In 2016, a marine heatwave in Chile and its subsequent harmful algal bloom caused $800 million (USD) in export losses for the aquaculture industry as salmon and shellfish died off.\n\nReduced agricultural outputs\n\nHeat waves are a big threat to agricultural production. In 2019 heat waves in the Mulanje region of Malawi involved temperatures as high as 40 °C (104 °F). This and a late rain season scorched tea leaves and reduced yields.\n\nFarmed animals\n\nInfrastructural damage\nHeat waves cause roads and highways to buckle and melt, water lines to burst, and power transformers to detonate, causing fires. A heat wave can also damage railways, by buckling and kinking rails. This can slow down or delay traffic. It can even lead to cancellations of service when rails are too dangerous to traverse by trains.\n\nPower outages\nHeat waves often lead to spikes in electricity demand because there is more use of air conditioning. This can create power outages, making the problem worse. During the 2006 North American heat wave, thousands of homes and businesses went without power, especially in California. In Los Angeles, electrical transformers failed, leaving thousands without power for as long as five days.\nThe early 2009 southeastern Australia heat wave caused major power disruptions in the city of Melbourne. They left over half a million people without power as the heat wave blew transformers and overloaded a power grid.\n\nImpacts on the environment\n\nWildfires\nA heat wave occurring during a drought can contribute to bushfires and wildfires. This is because a drought dries out vegetation, so it is more likely to catch fire. During the disastrous heat wave that struck Europe in 2003, fires raged through Portugal. They destroyed over 3,010 square kilometres (1,160 sq mi) of forest and 440 square kilometres (170 sq mi) of agricultural land. They caused about €1 billion worth of damage. High end farmlands have irrigation systems to back up crops.\n\nFloods\nHeat waves can also contribute to flooding. Because hot air is able to carry more moisture, heatwaves may be followed by extreme rainfall especially in mid-latitude regions. For example, the record-breaking heat wave that afflicted Pakistan beginning in May 2022 led to glacier melt and moisture flow. These were factors in the devastating floods that began in June and claimed over 1,100 lives.\n\nWild animals on land\nResearchers have predicted that roughly 10-40% of all land vertebrate species will be affected by heat waves by 2099, depending on the amount of future greenhouse gas emissions. Heatwaves present an additional form of stress and evolutionary pressure for species that already deal with habitat loss and climate change.\nSpecies have a thermal range of tolerance that describes the temperatures where they perform best. Temperature conditions that are outside of this range may experience decreased fitness and the inability to reproduce. The species with sufficient genetic variation will be able to ensure some individuals can survive frequent days of high temperatures in the future.\n\nOceans\nMarine heatwaves may cause mass mortality in fish populations, especially for species that are better adapted to cooler temperatures. Species that have adapted to warmer temperatures may expand their range during a heatwave. These invasive species may outcompete the native species that experience higher mortality during a heatwave, which disrupts ecosystem functioning. Marine heatwaves have also been correlated with negative impacts on foundation species such as coral and kelp.\n\nOptions for reducing impacts on humans\nA possible public health measure during heat waves is to set up air-conditioned public cooling centres. Adding air conditioning in schools provides a cooler work place. But it can result in additional greenhouse gas emissions unless solar energy is used.\nPolicymakers, funders and researchers have created the Extreme Heat Resilience Alliance coalition under the Atlantic Council. This advocates for naming heat waves, measuring them, and ranking them to build better awareness of their impacts.\n\nRecent examples by country or region\n\nAround the world in 2024\n\nIndia\n\nSoutheast Asia\n\nChina\nA study found the average resident in China was exposed to 16 days of heat waves in 2023, with more than 37,000 heat wave-related deaths. Besides, the number of work hours lost due to heat stress in China was 36.9 billion in 2023, and China's citizens experienced a 60% surge in lost safe outdoor activity hours, with each person losing 2.2 hours on average each day. The study predicted that by the 2060s, annual heat wave-related mortality is expected to reach 29,000 to 38,000 in China, with a 28% to 37% increase in work hours lost.\n\nUnited States\n\nIn July 2019, there were over 50 million people in the United States in jurisdictions with heat advisories. Scientists predicted that many records for highest low temperatures would be broken in the days following these warnings. This means the lowest temperature in a 24-hour period will be higher than any low temperature measured before.\nAccording to a 2022 study, 107 million people in the US will experience extremely dangerous heat in the year 2053.\nHeat waves are the most lethal type of weather phenomenon in the United States. Between 1992 and 2001, deaths from excessive heat in the United States numbered 2,190, compared with 880 deaths from floods and 150 from tropical cyclones. About 400 deaths a year on average are directly due to heat in the United States. The 1995 Chicago heat wave, one of the worst in US history, led to approximately 739 heat-related deaths over 5 days. In the United States, the loss of human life in hot spells in summer exceeds that caused by all other weather events. These include lightning, rain, floods, hurricanes, and tornadoes.\nAbout 6,200 Americans need hospital treatment each summer, according to data from 2008. This is due to excessive heat, and those at highest risk are poor, uninsured or elderly.\nThe relationship between extreme temperature and mortality in the United States varies by location. Heat is more likely to increase the risk of death in cities in the northern part of the country than in southern regions. As a whole, people in the United States appear to be adapting to hotter temperatures further north each decade. This might be due to better infrastructure, more modern building design and better public awareness.\n\nSee also\nCold wave\nList of heat waves\nList of severe weather phenomena\nUrban heat island\n\nReferences",
    "source": "wikipedia:Heat wave",
    "domain": "climate"
  },
  {
    "text": "A drought is a period of drier-than-normal conditions. A drought can last for days, months or years. Drought often has large impacts on the ecosystems and agriculture of affected regions, and causes harm to the local economy. Annual dry seasons in the tropics significantly increase the chances of a drought developing, with subsequent increased wildfire risks. Heat waves can significantly worsen drought conditions by increasing evapotranspiration. This dries out forests and other vegetation, and increases the amount of fuel for wildfires.\nDrought is a recurring feature of the climate in most parts of the world, becoming more extreme and less predictable due to climate change, which dendrochronological studies date back to 1900. There are three kinds of drought effects, environmental, economic and social. Environmental effects include the drying of wetlands, more and larger wildfires, loss of biodiversity.\nEconomic impacts of drought result due to negative disruptions to agriculture and livestock farming (causing food insecurity), forestry, public water supplies, river navigation (due to e.g.: lower water levels), electric power supply (by affecting hydropower systems) and impacts on human health.\nSocial and health costs include the negative effect on the health of people directly exposed to this phenomenon (excessive heat waves), high food costs, stress caused by failed harvests, water scarcity, etc. Drought can also lead to increased air pollution due to increased dust concentrations and wildfires. Prolonged droughts have caused mass migrations and humanitarian crisis.\nExamples for regions with increased drought risks are the Amazon basin, Australia, the Sahel region and India. For example, in 2005, parts of the Amazon basin experienced the worst drought in 100 years. Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. The long Australian Millennial drought broke in 2010. The 2020–2022 Horn of Africa drought surpassed the severe drought in 2010–2011 in both duration and severity. \nThroughout history, humans have usually viewed droughts as disasters due to the impact on food availability and the rest of society. People have viewed drought as a natural disaster or as something influenced by human activity, or as a result of supernatural forces.\n\nDefinition\n\nThe IPCC Sixth Assessment Report defines a drought simply as \"drier than normal conditions\". This means that a drought is \"a moisture deficit relative to the average water availability at a given location and season\".\nAccording to National Integrated Drought Information System, a multi-agency partnership, drought is generally defined as \"a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage\". The National Weather Service office of the NOAA defines drought as \"a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area\".\nDrought is a complex phenomenon − relating to the absence of water − which is difficult to monitor and define. By the early 1980s, over 150 definitions of \"drought\" had already been published. The range of definitions reflects differences in regions, needs, and disciplinary approaches.\n\nCategories\nThere are three major categories of drought based on where in the water cycle the moisture deficit occurs: meteorological drought, hydrological drought, and agricultural or ecological drought. A meteorological drought occurs due to lack of precipitation. A hydrological drought is related to low runoff, streamflow, and reservoir and groundwater storage. An agricultural or ecological drought is causing plant stress from a combination of evaporation and low soil moisture. Some organizations add another category: socioeconomic drought occurs when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply. The socioeconomic drought is a similar concept to water scarcity.\nThe different categories of droughts have different causes but similar effects:\n\nMeteorological drought occurs when there is a prolonged time with less than average precipitation. Meteorological drought usually precedes the other kinds of drought. As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases.\nHydrological drought happens when water reserves available in sources such as aquifers, lakes and reservoirs fall below average or a locally significant threshold. Hydrological drought tends to present more slowly because it involves stored water that is used but not replenished. Due to the close interaction with water use, this type of drought is can be heavily influenced by water management. Both positive and negative human influences have been discovered and strategic water management strategies seem key to mitigate drought impact. Like agricultural droughts, hydrological droughts can be triggered by more than just a loss of rainfall. For instance, around 2007 Kazakhstan was awarded a large amount of money by the World Bank to restore water that had been diverted to other nations from the Aral Sea under Soviet rule. Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out.\nAgricultural or ecological droughts affect crop production or ecosystems in general. This condition can also arise independently from any change in precipitation levels when either increased irrigation or soil conditions and erosion triggered by poorly planned agricultural endeavors cause a shortfall in water available to the crops.\n\nIndices and monitoring\n\nSeveral indices have been defined to quantify and monitor drought at different spatial and temporal scales. A key property of drought indices is their spatial comparability, and they must be statistically robust. Drought indices include:\n\nPalmer drought index (sometimes called the Palmer drought severity index (PDSI)): a regional drought index commonly used for monitoring drought events and studying areal extent and severity of drought episodes. The index uses precipitation and temperature data to study moisture supply and demand using a simple water balance model.\nKeetch-Byram Drought Index: an index that is calculated based on rainfall, air temperature, and other meteorological factors.\nStandardized precipitation index (SPI): It is computed based on precipitation, which makes it a simple and easy-to-apply indicator for monitoring and prediction of droughts in different parts of the world. The World Meteorological Organization recommends this index for identifying and monitoring meteorological droughts in different climates and time periods.\nStandardized Precipitation Evapotranspiration Index (SPEI): a multiscalar drought index based on climatic data. The SPEI accounts also for the role of the increased atmospheric evaporative demand on drought severity. Evaporative demand is particularly dominant during periods of precipitation deficit. The SPEI calculation requires long-term and high-quality precipitation and atmospheric evaporative demand datasets. These can be obtained from ground stations or gridded data based on reanalysis as well as satellite and multi-source datasets.\nIndices related to vegetation: root-zone soil moisture, vegetation condition index (VDI) and vegetation health index (VHI). The VCI and VHI are computed based on vegetation indices such as the normalized difference vegetation index (NDVI) and temperature datasets.\nDeciles index\nStandardized runoff index\nHigh-resolution drought information helps to better assess the spatial and temporal changes and variability in drought duration, severity, and magnitude at a much finer scale. This supports the development of site-specific adaptation measures.\nThe application of multiple indices using different datasets helps to better manage and monitor droughts than using a single dataset, This is particularly the case in regions of the world where not enough data is available such as Africa and South America. Using a single dataset can be limiting, as it may not capture the full spectrum of drought characteristics and impacts.\nCareful monitoring of moisture levels can also help predict increased risk for wildfires.\n\nCauses\n\nGeneral precipitation deficiency\n\nMechanisms of producing precipitation include convective, stratiform, and orographic rainfall. Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation over a longer duration.\nPrecipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice.\nDroughts occur mainly in areas where normal levels of rainfall are, in themselves, low. If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought can be triggered by a high level of reflected sunlight and above average prevalence of high pressure systems, winds carrying continental, rather than oceanic air masses, and ridges of high pressure areas aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Once a region is within drought, feedback mechanisms such as local arid air, hot conditions which can promote warm core ridging, and minimal evapotranspiration can worsen drought conditions.\n\nDry season\n\nWithin the tropics, distinct, wet and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough. The dry season greatly increases drought occurrence, and is characterized by its low humidity, with watering holes and rivers drying up. Because of the lack of these watering holes, many grazing animals are forced to migrate due to the lack of water in search of more fertile lands. Examples of such animals are zebras, elephants, and wildebeest. Because of the lack of water in the plants, bushfires are common. Since water vapor becomes more energetic with increasing temperature, more water vapor is required to increase relative humidity values to 100% at higher temperatures (or to get the temperature to fall to the dew point). Periods of warmth quicken the pace of fruit and vegetable production, increase evaporation and transpiration from plants, and worsen drought conditions.\n\nEl Niño–Southern Oscillation (ENSO)\n\nThe El Niño–Southern Oscillation (ENSO) phenomenon can sometimes play a significant role in drought. ENSO comprises two patterns of temperature anomalies in the central Pacific Ocean, known as La Niña and El Niño. La Niña events are generally associated with drier and hotter conditions and further exacerbation of drought in California and the Southwestern United States, and to some extent the U.S. Southeast. Meteorological scientists have observed that La Niñas have become more frequent over time.\nConversely, during El Niño events, drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America. Winters during the El Niño are warmer and drier than average conditions in the Northwest, northern Midwest, and northern Mideast United States, so those regions experience reduced snowfalls. Conditions are also drier than normal from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana. Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing bush fires, worsening haze, and decreasing air quality dramatically. Drier-than-normal conditions are also in general observed in Queensland, inland Victoria, inland New South Wales, and eastern Tasmania from June to August. As warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it causes extensive drought in the western Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.\n\nClimate change\n\nGlobally, the occurrence of droughts has increased as a result of the increase in temperature and atmospheric evaporative demand. In addition, increased climate variability has increased the frequency and severity of drought events. Moreover, the occurrence and impact of droughts are aggravated by anthropogenic activities such as land use change and water management and demand.\nThe IPCC Sixth Assessment Report also pointed out that \"Warming over land drives an increase in atmospheric evaporative demand and in the severity of drought events\" and \"Increased atmospheric evaporative demand increases plant water stress, leading to agricultural and ecological drought\".\nThere is a rise of compound warm-season droughts in Europe that are concurrent with an increase in potential evapotranspiration.\n\nVegetation changes, erosion and human activities\n\nHuman activity can directly trigger exacerbating factors such as over-farming, excessive irrigation, deforestation, and erosion adversely impact the ability of the land to capture and hold water. In arid climates, the main source of erosion is wind. Erosion can be the result of material movement by the wind. The wind can cause small particles to be lifted and therefore moved to another region (deflation). Suspended particles within the wind may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation. Woody plant encroachment can increase soil porosity and therewith the chances of soil drought.\n\nImpacts\n\nDrought is one of the most complex and major natural hazards, and it has devastating impacts on the environment, economy, water resources, agriculture, and society worldwide.\nOne can divide the impacts of droughts and water shortages into three groups: environmental, economic and social (including health).\n\nEnvironmental and economic impacts\n\nEnvironmental effects of droughts include: lower surface and subterranean water-levels, lower flow-levels (with a decrease below the minimum leading to direct danger for amphibian life), increased pollution of surface water, the drying out of wetlands, more and larger wildfires, higher deflation intensity, loss of biodiversity, worse health of trees and the appearance of pests and dendroid diseases. Drought-induced mortality of trees lacks in most climate models in their representation of forests as land carbon sink.\nEconomic losses as a result of droughts include lower agricultural, forests, game and fishing output, higher food-production costs, lower energy-production levels in hydro plants, losses caused by depleted water tourism and transport revenue, problems with water supply for the energy sector and for technological processes in metallurgy, mining, the chemical, paper, wood, foodstuff industries etc., disruption of water supplies for municipal economies.\nFurther examples of common environmental and economic consequences of drought include:\n\nAlteration of diversity of plant communities, which can have an impact on net primary production and other ecosystem services.\nWildfires, such as Australian bushfires and wildfires in the United States, become more common during times of drought and may cause human deaths.\nDust Bowls, themselves a sign of erosion, which further erode the landscape\nDust storms, when drought hits an area suffering from desertification and erosion\nHabitat damage, affecting both terrestrial and aquatic wildlife\nSnake migration, which results in snake-bites\nReduced electricity production due to reduced water-flow through hydroelectric dams\nShortages of water for industrial users\n\nAgricultural impacts\n\nDroughts can cause land degradation and loss of soil moisture, resulting in the destruction of cropland productivity. This can result in diminished crop growth or yield productions and carrying capacity for livestock. Drought in combination with high levels of grazing pressure can function as the tipping point for an ecosystem, causing woody encroachment.\nWater stress affects plant development and quality in a variety of ways: firstly drought can cause poor germination and impaired seedling development. At the same time plant growth relies on cellular division, cell enlargement, and differentiation. Drought stress impairs mitosis and cell elongation via loss of turgor pressure which results in poor growth. Development of leaves is also dependent upon turgor pressure, concentration of nutrients, and carbon assimilates all of which are reduced by drought conditions, thus drought stress lead to a decrease in leaf size and number. Plant height, biomass, leaf size and stem girth has been shown to decrease in maize under water limiting conditions. Crop yield is also negatively effected by drought stress, the reduction in crop yield results from a decrease in photosynthetic rate, changes in leaf development, and altered allocation of resources all due to drought stress. Crop plants exposed to drought stress suffer from reductions in leaf water potential and transpiration rate. Water-use efficiency increases in crops such as wheat while decreasing in others, such as potatoes.\nPlants need water for the uptake of nutrients from the soil, and for the transport of nutrients throughout the plant: drought conditions limit these functions leading to stunted growth. Drought stress also causes a decrease in photosynthetic activity in plants due to the reduction of photosynthetic tissues, stomatal closure, and reduced performance of photosynthetic machinery. This reduction in photosynthetic activity contributes to the reduction in plant growth and yields. Another factor influencing reduced plant growth and yields include the allocation of resources; following drought stress plants will allocate more resources to roots to aid in water uptake increasing root growth and reducing the growth of other plant parts while decreasing yields.\n\nSocial and health impacts\nThe most negative impacts of drought for humans include crop failure, food crisis, famine, malnutrition, and poverty, which lead to loss of life and mass migration of people.\nThere are negative effects on the health of people who are directly exposed to this phenomenon (excessive heat waves). Droughts can also cause limitations of water supplies, increased water pollution levels, high food-costs, stress caused by failed harvests, water scarcity, etc. Reduced water quality can occur because lower water-flows reduce dilution of pollutants and increase contamination of remaining water sources.\nThis explains why droughts and water scarcity operate as a factor which increases the gap between developed and developing countries.\nEffects vary according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food-sources. Areas with populations that depend on water sources as a major food-source are more vulnerable to famine.\n\nFurther examples of social and health consequences include:\n\nWater scarcity, crop failure, famine and hunger – drought provides too little water to support food crops; malnutrition, dehydration and related diseases\nMass migration, resulting in internal displacement and international refugees\nSocial unrest\nWar over natural resources, including water and food\nCyanotoxin accumulation within food chains and water supply (some of which are among the most potent toxins known to science) can cause cancer with low exposure over the long term. High levels of microcystin appeared in San Francisco Bay Area salt-water shellfish and fresh-water supplies throughout the state of California in 2016.\nSevere drought has been noted to cause unrest and precede in some cases periods of political upheaval.\n\nLoss of fertile soils\n\nWind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.\nLoess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (Aeolian) sediment. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.\n\nRegions particularly affected\n\nAmazon basin\n\nIn 2005, parts of the Amazon basin experienced the worst drought in 100 years. A 2006 article reported results showing that the forest in its present form could survive only three years of drought. Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a \"tipping point\" where it would irreversibly start to die. It concludes that the rainforest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate. According to the WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.\n\nAustralia\n\nThe 1997–2009 Millennium Drought in Australia led to a water supply crisis across much of the country. As a result, many desalination plants were built for the first time (see list).\nBy far the largest part of Australia is desert or semi-arid lands commonly known as the outback. A 2005 study by Australian and American researchers investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago. Regular burning by these settlers could have prevented monsoons from reaching interior Australia. In June 2008 it became known that an expert panel had warned of long term, maybe irreversible, severe ecological damage for the whole Murray-Darling basin if it did not receive sufficient water by October 2008. Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. Australian environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth in Western Australia could become the world's first ghost metropolis, an abandoned city with no more water to sustain its population. The long Australian Millennial drought broke in 2010.\n\nEast Africa\nEast Africa, including for example Ethiopia, Eritrea, Kenya, Somalia, South Sudan, Sudan, Tanzania, and Uganda, has a diverse climate, ranging from hot, dry regions to cooler, wetter highland regions. The region has considerable variability in seasonal rainfall and a very complex topography. In the northern parts of the region within the Nile basin (Ethiopia, Sudan), the rainfall is characterized by an unimodal cycle with a wet season from July to September. The rest of the region has a bimodal annual cycle, featuring long rains from March to May and the short rains from October to December. The frequent occurrence of hydrological extremes, like droughts and floods, harms the already vulnerable population suffering from severe poverty and economic turmoil. Droughts prompted food shortages for example in 1984–85, 2006 and 2011.\nThe Eastern African region experiences the impacts of climate change in different forms. For instance, below-average rainfall occurred for six consecutive rainy seasons in the Horn of Africa during the period 2020–2023 leading to the third longest and most widespread drought on record with dire implications for food security (see Horn of Africa drought (2020–present)). Conversely, other parts experienced extreme floods, e.g., the 2020 East Africa floods in Ethiopia, Rwanda, Kenya, Burundi, and Uganda, and the 2022 floods in South Sudan.\nA key feature in the region is the heterogeneous distribution of hydrologic extremes in space and time. For instance, El Niño can cause droughts in one part of the region and floods in the other. This is also a common situation within a country, e.g., in Ethiopia. The recent years with consecutive droughts followed by floods are a testament to the need to better forecast these kinds of events and their impacts.\n\nHimalayan river basins\nApproximately 2.4 billion people live in the drainage basin of the Himalayan rivers. India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. Drought in India affecting the Ganges is of particular concern, as it provides drinking water and agricultural irrigation for more than 500 million people. In 2025, the UN warned that retreating glaciers could threaten the food and water supply of 2 billion people worldwide.\n\nNorth America\nThe west coast of North America, which gets much of its water from glaciers in mountain ranges such as the Rocky Mountains and Sierra Nevada, also would be affected.\n\nBy country or region\nDroughts in particular countries:\n\nSee also:\n\nDroughts and famines in Russia and USSR\nDroughts in California\nDroughts in the Sahel\n2021 Madagascar food crisis\n2010 China drought and dust storms\nCape Town water crisis in 2015–2018\n\nProtection, mitigation and relief\n\nAgriculturally, people can effectively mitigate much of the impact of drought through irrigation and crop rotation. Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by ever-increasing population densities.\nStrategies for drought protection or mitigation include:\n\nDams – many dams and their associated reservoirs supply additional water in times of drought.\nCloud seeding – a form of intentional weather modification to induce rainfall. This remains a hotly debated topic, as the United States National Research Council released a report in 2004 stating that to date, there is still no convincing scientific proof of the efficacy of intentional weather modification.\nLand use – Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years.\nTransvasement – Building canals or redirecting rivers as massive attempts at irrigation in drought-prone areas.\nWhen water is scarce due to droughts, there are a range of options for people to access other sources of water, such as wastewater reuse, rainwater harvesting and stormwater recovery, or seawater desalination.\n\nHistory\n\nThroughout history, humans have usually viewed droughts as disasters due to the impact on food availability and the rest of society. Drought is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the Biblical story of Joseph's arrival in and the later Exodus from ancient Egypt. Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon, as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.\nDroughts can be scientifically explained in terms of physical mechanisms, which underlie natural disasters and are influenced by human impact on the environment.\nBeliefs about drought are further shaped by cultural factors including local knowledge, perceptions, values, beliefs and religion. In some places and times, droughts have been interpreted as the work of supernatural forces. Globally, people in many societies have been more likely to explain natural events like drought, famine and disease in terms of the supernatural than they are to explain social phenomena like war, murder, and theft.\nHistorically, rituals have been used in an attempt to prevent or avert drought. Rainmaking rituals have ranged from dances to scapegoating to human sacrifices. Many ancient practices are now a matter of folklore while others may still be practiced.\nIn areas where people have limited understanding of the scientific basis of drought, beliefs about drought continue to reflect indigenous beliefs in the power of spirits and Christian philosophies that see drought as a divine punishment. Such beliefs can influence people's thinking and affect their resilience and ability to adapt to stress and respond to crises. In the case of Creationism, curricula sometimes give religious explanations of natural phenomena rather than scientific ones. Teaching explicitly denies evolution, that human agency is affecting climate, and that climate change is occurring.\nSome historical droughts include:\n\nThe 4.2-kiloyear event, a megadrought that took place in Africa and Asia between 5,000 and 4,000 years ago, has been linked with the collapse of the Old Kingdom in Egypt, the Akkadian Empire in Mesopotamia, the Liangzhu culture in the lower Yangtze River area, and the Indus Valley Civilization.\nThe longest drought in recorded history started 400 years ago in the Atacama Desert in Chile and still continues.\nDrought might have been a contributing factor to Classic Maya collapse between the 7th and 9th centuries.\n1540 Central Europe, said to be the \"worst drought of the millennium\" with eleven months without rain and temperatures of 5–7 °C above the average of the 20th century\n1900 India killing between 250,000 and 3.25 million.\n1921–22 Soviet Union in which over 5 million perished from starvation du",
    "source": "wikipedia:Drought",
    "domain": "climate"
  },
  {
    "text": "A flood is an overflow of water (or rarely other fluids) that submerges land that is usually dry. In the sense of \"flowing water\", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding. Examples for human changes are land use changes such as deforestation and removal of wetlands, changes in waterway course or flood controls such as with levees. Global environmental issues also influence causes of floods, namely climate change which causes an intensification of the water cycle and sea level rise. For example, climate change makes extreme weather events more frequent and stronger. This leads to more intense floods and increased flood risk.\nNatural types of floods include river flooding, groundwater flooding coastal flooding and urban flooding sometimes known as flash flooding. Tidal flooding may include elements of both river and coastal flooding processes in estuary areas. There is also the intentional flooding of land that would otherwise remain dry. This may take place for agricultural, military, or river-management purposes. For example, agricultural flooding may occur in preparing paddy fields for the growing of semi-aquatic rice in many countries. \nFlooding may occur as an overflow of water from water bodies, such as a river, lake, sea or ocean. In these cases, the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries. Flooding may also occur due to an accumulation of rainwater on saturated ground. This is called an areal flood. The size of a lake or other body of water naturally varies with seasonal changes in precipitation and snow melt. Those changes in size are however not considered a flood unless they flood property or drown domestic animals.\nFloods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if these buildings are in the natural flood plains of rivers. People could avoid riverine flood damage by moving away from rivers. However, people in many countries have traditionally lived and worked by rivers because the land is usually flat and fertile. Also, the rivers provide easy travel and access to commerce and industry. \nFlooding can damage property and also lead to secondary impacts. These include in the short term an increased spread of waterborne diseases and vector-bourne diseases, for example those diseases transmitted by mosquitos. Flooding can also lead to long-term displacement of residents. Floods are an area of study of hydrology and hydraulic engineering. \nA large amount of the world's population lives in close proximity to major coastlines, while many major cities and agricultural areas are located near floodplains. There is significant risk for increased coastal and fluvial flooding due to changing climatic conditions. \n\nTypes\n\nAreal flooding\n\nFloods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can either infiltrate or run off. The excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which effectively stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms. Infiltration also is slow to negligible through frozen ground, rock, concrete, paving, or roofs. Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation.\n\nRiver flooding\n\nFloods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.\nSlow-rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climates, since they may have large basins but small river channels, and rainfall can be very intense in smaller areas of those basins.\nIn extremely flat areas, such as the Red River Valley of the North in Minnesota, North Dakota, and Manitoba, a type of hybrid river/areal flooding can occur, known locally as \"overland flooding\". This is different from \"overland flow\" defined as \"surface runoff\". The Red River Valley is a former glacial lakebed, created by Lake Agassiz, and over a length of 550 mi (890 km), the river course drops only 236 ft (72 m), for an average slope of about 5 inches per mile (or 8.2 cm per kilometer). In this very large area, spring snowmelt happens at different rates in different places, and if winter snowfall was heavy, a fast snowmelt can push water out of the banks of a tributary river so that it moves overland, to a point further downstream in the river or completely to another streambed. Overland flooding can be devastating because it is unpredictable, it can occur very suddenly with surprising speed, and in such flat land it can run for miles. It is these qualities that set it apart from simple \"overland flow\". \nRapid flooding events, including flash floods, more often occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier. In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1,500 cubic feet per second (1.4 to 42 m3/s) in just one minute. Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days. The deadly flood resulted from a thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was already saturated. \nFlash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of the flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant.\n\nCoastal flooding\n\nCoastal areas may be flooded by storm surges combining with high tides and large wave events at sea, resulting in waves over-topping flood defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. A storm surge is \"an additional rise of water generated by a storm, over and above the predicted astronomical tides\". Due to the effects of climate change (e.g. sea level rise and an increase in extreme weather events) and an increase in the population living in coastal areas, the damage caused by coastal flood events has intensified and more people are being affected.\nFlooding in estuaries is commonly caused by a combination of storm surges caused by winds and low barometric pressure and large waves meeting high upstream river flows.\n\nUrban flooding\n\nIntentional floods\nThe intentional flooding of land that would otherwise remain dry may take place for agricultural, military or river-management purposes. This is a form of hydraulic engineering. Agricultural flooding may occur in preparing paddy fields for the growing of semi-aquatic rice in many countries.\nFlooding for river management may occur in the form of diverting flood waters in a river at flood stage upstream from areas that are considered more valuable than the areas that are sacrificed in this way. This may be done ad hoc, or permanently, as in the so-called overlaten (literally \"let-overs\"), an intentionally lowered segment in Dutch riparian levees, like the Beerse Overlaat in the left levee of the Meuse between the villages of Gassel and Linden, North Brabant.\nMilitary inundation creates an obstacle in the field that is intended to impede the movement of the enemy. This may be done both for offensive and defensive purposes. Furthermore, in so far as the methods used are a form of hydraulic engineering, it may be useful to differentiate between controlled inundations and uncontrolled ones. Examples for controlled inundations include those in the Netherlands under the Dutch Republic and its successor states in that area and exemplified in the two Hollandic Water Lines, the Stelling van Amsterdam, the Frisian Water Line, the IJssel Line, the Peel-Raam Line, and the Grebbe line in that country. \nTo count as controlled, a military inundation has to take the interests of the civilian population into account, by allowing them a timely evacuation, by making the inundation reversible, and by making an attempt to minimize the adverse ecological impact of the inundation. That impact may also be adverse in a hydrogeological sense if the inundation lasts a long time.\nExamples for uncontrolled inundations are the second Siege of Leiden during the first part of the Eighty Years' War, the flooding of the Yser plain during the First World War, and the Inundation of Walcheren, and the Inundation of the Wieringermeer during the Second World War).\n\nCauses\n\nFloods are caused by many factors or a combination of any of these generally prolonged heavy rainfall (locally concentrated or throughout a catchment area), highly accelerated snowmelt, severe winds over water, unusual high tides, tsunamis, or failure of dams, levees, retention ponds, or other structures that retained the water. Flooding can be exacerbated by increased amounts of impervious surface or by other natural hazards such as wildfires, which reduce the supply of vegetation that can absorb rainfall.\nDuring times of rain, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, and the rest travels over the land as surface runoff. Floods occur when ponds, lakes, riverbeds, soil, and vegetation cannot absorb all the water.\nThis has been exacerbated by human activities such as draining wetlands that naturally store large amounts of water and building paved surfaces that do not absorb any water. Water then runs off the land in quantities that cannot be carried within stream channels or retained in natural ponds, lakes, and human-made reservoirs. About 30 percent of all precipitation becomes runoff and that amount might be increased by water from melting snow.\n\nUpslope factors\n\nRiver flooding is often caused by heavy rain, sometimes increased by melting snow. A flood that rises rapidly, with little or no warning, is called a flash flood. Flash floods usually result from intense rainfall over a relatively small area, or if the area was already saturated from previous precipitation.\nThe amount, location, and timing of water reaching a drainage channel from natural precipitation and controlled or uncontrolled reservoir releases determines the flow at downstream locations. Some precipitation evaporates, some slowly percolates through soil, some may be temporarily sequestered as snow or ice, and some may produce rapid runoff from surfaces including rock, pavement, roofs, and saturated or frozen ground. The fraction of incident precipitation promptly reaching a drainage channel has been observed from nil for light rain on dry, level ground to as high as 170 percent for warm rain on accumulated snow.\nMost precipitation records are based on a measured depth of water received within a fixed time interval. Frequency of a precipitation threshold of interest may be determined from the number of measurements exceeding that threshold value within the total time period for which observations are available. Individual data points are converted to intensity by dividing each measured depth by the period of time between observations. This intensity will be less than the actual peak intensity if the duration of the rainfall event was less than the fixed time interval for which measurements are reported. Convective precipitation events (thunderstorms) tend to produce shorter duration storm events than orographic precipitation. Duration, intensity, and frequency of rainfall events are important to flood prediction. Short duration precipitation is more significant to flooding within small drainage basins.\nThe most important upslope factor in determining flood magnitude is the land area of the watershed upstream of the area of interest. Rainfall intensity is the second most important factor for watersheds of less than approximately 30 square miles or 80 square kilometres. The main channel slope is the second most important factor for larger watersheds. Channel slope and rainfall intensity become the third most important factors for small and large watersheds, respectively.\nTime of Concentration is the time required for runoff from the most distant point of the upstream drainage area to reach the point of the drainage channel controlling flooding of the area of interest. The time of concentration defines the critical duration of peak rainfall for the area of interest. The critical duration of intense rainfall might be only a few minutes for roof and parking lot drainage structures, while cumulative rainfall over several days would be critical for river basins.\n\nDownslope factors\nWater flowing downhill ultimately encounters downstream conditions slowing movement. The final limitation in coastal flooding lands is often the ocean or some coastal flooding bars which form natural lakes. In flooding low lands, elevation changes such as tidal fluctuations are significant determinants of coastal and estuarine flooding. Less predictable events like tsunamis and storm surges may also cause elevation changes in large bodies of water. Elevation of flowing water is controlled by the geometry of the flow channel and, especially, by depth of channel, speed of flow and amount of sediments in it Flow channel restrictions like bridges and canyons tend to control water elevation above the restriction. The actual control point for any given reach of the drainage may change with changing water elevation, so a closer point may control for lower water levels until a more distant point controls at higher water levels.\nEffective flood channel geometry may be changed by growth of vegetation, accumulation of ice or debris, or construction of bridges, buildings, or levees within the flood channel.\nPeriodic floods occur on many rivers, forming a surrounding region known as the flood plain. Even when rainfall is relatively light, the shorelines of lakes and bays can be flooded by severe winds—such as during hurricanes—that blow water into the shore areas.\n\nClimate change\n\nCoincidence\nExtreme flood events often result from coincidence such as unusually intense, warm rainfall melting heavy snow pack, producing channel obstructions from floating ice, and releasing small impoundments like beaver dams. Coincident events may cause extensive flooding to be more frequent than anticipated from simplistic statistical prediction models considering only precipitation runoff flowing within unobstructed drainage channels. Debris modification of channel geometry is common when heavy flows move uprooted woody vegetation and flood-damaged structures and vehicles, including boats and railway equipment. Recent field measurements during the 2010–11 Queensland floods showed that any criterion solely based upon the flow velocity, water depth or specific momentum cannot account for the hazards caused by velocity and water depth fluctuations. These considerations ignore further the risks associated with large debris entrained by the flow motion.\n\nNegative impacts\n\nFloods can be a huge destructive power. When water flows, it has the ability to demolish all kinds of buildings and objects, such as bridges, structures, houses, trees, and cars. Economical, social and natural environmental damages are common factors that are impacted by flooding events and the impacts that flooding has on these areas can be catastrophic.There is an interconnectedness between floods and agriculture, climate, economy, and disease (FACED).\n\nImpacts on infrastructure and societies\n\nThere have been numerous flood incidents around the world which have caused devastating damage to infrastructure, the natural environment and human life. \nFloods can have devastating impacts to human societies. Flooding events worldwide are increasing in frequency and severity, leading to increasing costs to societies. \nCatastrophic riverine flooding can result from major infrastructure failures, often the collapse of a dam. It can also be caused by drainage channel modification from a landslide, earthquake or volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding, most commonly resulting from undersea earthquakes.\n\nEconomic impacts\nThe primary effects of flooding include loss of life and damage to buildings and other structures, including bridges, sewerage systems, roadways, and canals. The economic impacts caused by flooding can be severe.\nEvery year flooding causes countries billions of dollars' worth of damage that threatens the livelihood of individuals. As a result, there is also significant socio-economic threats to vulnerable populations around the world from flooding. For example, in Bangladesh in 2007, a flood was responsible for the destruction of more than one million houses. And yearly in the United States, floods cause over $7 billion in damage.\n\nFlood waters typically inundate farm land, making the land unworkable and preventing crops from being planted or harvested, which can lead to shortages of food both for humans and farm animals. Entire harvests for a country can be lost in extreme flood circumstances. Some tree species may not survive prolonged flooding of their root systems.\nFlooding in areas where people live also has significant economic implications for affected neighborhoods. In the United States, industry experts estimate that wet basements can lower property values by 10–25 percent and are cited among the top reasons for not purchasing a home. According to the U.S. Federal Emergency Management Agency (FEMA), almost 40 percent of small businesses never reopen their doors following a flooding disaster. In the United States, insurance is available against flood damage to both homes and businesses.\nEconomic hardship due to a temporary decline in tourism, rebuilding costs, or food shortages leading to price increases is a common after-effect of severe flooding. The impact on those affected may cause psychological damage to those affected, in particular where deaths, serious injuries and loss of property occur.\n\nHealth impacts\n\nFatalities connected directly to floods are usually caused by drowning; the waters in a flood are very deep and have strong currents. Deaths do not just occur from drowning, deaths are connected with dehydration, heat stroke, heart attack and any other illness that needs medical supplies that cannot be delivered.\nInjuries can lead to an excessive amount of morbidity when a flood occurs. Injuries do not just affect those who were directly in the flood: rescue teams and even people delivering supplies can sustain an injury. Injuries can occur before, during and after the flood. During floods accidents occur with falling debris or any of the many fast moving objects in the water. After the flood rescue attempts are when large numbers injuries can occur.\nCommunicable diseases are increased due to many pathogens and bacteria that are being transported by the water. There are many waterborne diseases such as cholera, hepatitis A, hepatitis E and diarrheal diseases, to mention a few. Gastrointestinal disease and diarrheal diseases are very common due to a lack of clean water during a flood. Clean water supplies are often contaminated when flooding occurs. Hepatitis A and E are common because of the lack of sanitation in the water and in living quarters, depending on where the flood is and how prepared the community is for a flood.\nWhen floods hit, people can lose nearly all their crops, livestock, and food reserves and face starvation.\nFloods also frequently damage power transmission and sometimes power generation, which then has knock-on effects caused by the loss of power. This includes loss of drinking water treatment and water supply, which may result in loss of drinking water or severe water contamination. It may also cause the loss of sewage disposal facilities. Lack of clean water combined with human sewage in the flood waters raises the risk of waterborne diseases, which can include typhoid, giardia, cryptosporidium, cholera and many other diseases depending upon the location of the flood.\nDamage to roads and transport infrastructure may make it difficult to mobilize aid to those affected or to provide emergency health treatment.\nFlooding can cause chronically wet houses, leading to the growth of indoor mold and resulting in adverse health effects, particularly respiratory symptoms. Respiratory diseases are common after the disaster has occurred. This depends on the amount of water damage and mold that grows after an incident. Research suggests that there will be an increase of 30–50% in adverse respiratory health outcomes caused by dampness and mold exposure for those living in coastal and wetland areas. Fungal contamination in homes is associated with increased allergic rhinitis and asthma. Vector-borne diseases also increase, due to the residual still water after the floods have settled. The diseases that are vector borne are malaria, dengue, West Nile, and yellow fever. Floods may have a huge impact on victims' psychosocial integrity. People suffer from a wide variety of losses and stress. One of the most treated illnesses in long-term health problems are depression caused by the flood and all the tragedy that flows with one.\n\nLoss of life\n\nBelow is a list of the deadliest floods worldwide, showing events with death tolls at or above 100,000 individuals.\n\nPositive impacts (benefits)\nFloods (in particular more frequent or smaller floods) can also bring many benefits, such as recharging ground water, making soil more fertile and increasing nutrients in some soils. For this reason, periodic flooding was essential to the well-being of ancient peoples along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges and the Yellow River among others.\nFlood waters provide much needed water resources in arid and semi-arid regions where precipitation can be very unevenly distributed throughout the year and kills pests in the farming land. Freshwater floods particularly play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity. Flooding can spread nutrients to lakes and rivers, which can lead to increased biomass and improved fisheries for a few years.\nFor some fish species, an inundated floodplain may form a highly suitable location for spawning, with few predators and enhanced levels of nutrients or food. Fish such as the weather fish use floods to reach new habitats. Bird populations may also profit from the boost in food production caused by flooding.\nThe viability of hydropower, a renewable source of energy, is also higher in flood-prone regions.\n\nProtections against floods and associated hazards\n\nFlood management\n\nFlood management examples\nIn many countries around the world, waterways prone to floods are often carefully managed. Defenses such as detention basins, levees, bunds, reservoirs, and weirs are used to prevent waterways from overflowing their banks. When these defenses fail, emergency measures such as sandbags or portable inflatable tubes are often used to try to stem flooding. Coastal flooding has been addressed in portions of Europe and the Americas with coastal defenses, such as sea walls, beach nourishment, and barrier islands.\nIn the riparian zone near rivers and streams, erosion control measures can be taken to try to slow down or reverse the natural forces that cause many waterways to meander over long periods of time. Flood controls, such as dams, can be built and maintained over time to try to reduce the occurrence and severity of floods as well. In the United States, the U.S. Army Corps of Engineers maintains a network of such flood control dams.\nIn areas prone to urban flooding, one solution is the repair and expansion of human-made sewer systems and stormwater infrastructure. Another strategy is to reduce impervious surfaces in streets, parking lots and buildings through natural drainage channels, porous paving, and wetlands (collectively known as green infrastructure or sustainable urban drainage systems (SUDS)). Areas identified as flood-prone can be converted into parks and playgrounds that can tolerate occasional flooding. Ordinances can be adopted to require developers to retain stormwater on site and require buildings to be elevated, protected by floodwalls and levees, or designed to withstand temporary inundation. Property owners can also invest in solutions themselves, such as re-landscaping their property to take the flow of water away from their building and installing rain barrels, sump pumps, and check valves.\n\nFlood safety planning\n\nIn the United States, the National Weather Service gives out the advice \"Turn Around, Don't Drown\" for floods; that is, it recommends that people get out of the area of a flood, rather than trying to cross it. At the most basic level, the best defense against floods is to seek higher ground for high-value uses while balancing the foreseeable risks with the benefits of occupying flood hazard zones. Critical community-safety facilities, such as hospitals, emergency-operations centers, and police, fire, and rescue services, should be built in areas least at risk of flooding. Structures, such as bridges, that must unavoidably be in flood hazard areas should be designed to withstand flooding. Areas most at risk for flooding could be put to valuable uses that could be abandoned temporarily as people retreat to safer areas when a flood is imminent.\nPlanning for flood safety involves many aspects of analysis and engineering, including:\n\nobservation of previous and present flood heights and inundated areas,\nstatistical, hydrologic, and hydraulic model analyses,\nmapping inundated areas and flood heights for future flood scenarios,\nlong-term land use planning and regulation,\nengineering design and construction of structures to control or withstand flooding,\nintermediate-term monitoring, forecasting, and emergency-response planning, and\nshort-term monitoring, warning, and response operations.\nEach topic presents distinct yet related questions with varying scope and scale in time, space, and the people involved. Attempts to understand and manage the mechanisms at work in floodplains have been made for at least six millennia.\nIn the United States, the Association of State Floodplain Managers works to promote education, policies, and activities that mitigate current and future losses, costs, and human suffering caused by flooding and to protect the natural and beneficial functions of floodplains – all without causing adverse impacts. A portfolio of best practice examples for disaster mitigation in the United States is available from the Federal Emergency Management Agency.\n\nFlood clean-up safety\nClean-up activities following floods often pose hazards to workers and volunteers involved in the effort. Potential dangers include electrical hazards, carbon monoxide exposure, musculoskeletal hazards, heat or cold stress, motor vehicle-related dangers, fire, drowning, and exposure to hazardous materials. Because flooded disaster sites are unstable, clean-up workers might encounter sharp jagged debris, biological hazards in the flood water, exposed electrical lines, blood or other body fluids, and animal and human remains. In planning for and reacting to flood disasters, managers provide workers with hard hats, goggles, heavy work gloves, life jackets, and watertight boots with steel toes and insoles.\n\nFlood predictions\n\nA series of annual maximum flow rates in a stream reach can be analyzed statistically to estimate the 100-year flood and floods of other recurrence intervals there. Similar estimates from many sites in a hydrologically similar region can be related to measurable characteristics of each drainage basin to allow indirect estimation of flood recurrence intervals for stream reaches without sufficient data for direct analysis.\nPhysical process models of channel reaches are generally well understood and will calculate the depth and area of inundation for given channel conditions and a specified flow rate, such as for use in floodplain mapping and flood insurance. Conversely, given the observed inundation area of a recent flood and the channel conditions, a model can calculate the flow rate. Applied to various potential channel configurations and flow rates, a reach model can contribute to sel",
    "source": "wikipedia:Flood",
    "domain": "climate"
  },
  {
    "text": "A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (), typhoon (), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon is the same thing which occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as \"tropical cyclones\". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more. \nTropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, cyclones rarely form within 5° of the equator. South Atlantic tropical cyclones are very rare due to consistently strong wind shear and a weak Intertropical Convergence Zone. In contrast, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea. \n\nHeat energy from the ocean acts as the accelerator for tropical cyclones. This causes inland regions to suffer far less damage from cyclones than coastal regions, although the impacts of flooding are felt across the board. Coastal damage may be caused by strong winds and rain, high waves, storm surges, and tornadoes. Climate change affects tropical cyclones in several ways. Scientists have found that climate change can exacerbate the impact of tropical cyclones by increasing their duration, occurrence, and intensity due to the warming of ocean waters and intensification of the water cycle. Tropical cyclones draw in air from a large area and concentrate the water content of that air into precipitation over a much smaller area. This replenishing of moisture-bearing air after rain may cause multi-hour or multi-day extremely heavy rain up to 40 km (25 mi) from the coastline, far beyond the amount of water that the local atmosphere holds at any one time. This in turn can lead to river flooding, overland flooding, and a general overwhelming of local water control structures across a large area. \n\nDefinition and terminology\nA tropical cyclone is the generic term for a warm-cored, non-frontal synoptic-scale low-pressure system over tropical or subtropical waters around the world. The systems generally have a well-defined center which is surrounded by deep atmospheric convection and a closed wind circulation at the surface. A tropical cyclone is generally deemed to have formed once mean surface winds in excess of 35 kn (65 km/h; 40 mph) are observed. It is assumed at this stage that a tropical cyclone has become self-sustaining and can continue to intensify without any help from its environment.\nDepending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as \"tropical cyclones\", and such storms in the Indian Ocean can also be called \"severe cyclonic storms\".\nTropical refers to the geographical origin of these systems, which form almost exclusively over tropical seas. Cyclone refers to their winds moving in a circle, whirling round their central clear eye, with their surface winds blowing counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The opposite direction of circulation is due to the Coriolis effect. \n\nFormation\n\nTropical cyclones tend to develop during the summer, but have been noted in nearly every month in most tropical cyclone basins. Tropical cyclones on either side of the Equator generally have their origins in the Intertropical Convergence Zone (ITCZ), where winds blow from either the northeast or southeast. Within this broad area of low-pressure, air is heated over the warm tropical ocean and rises in discrete parcels, which causes towering thunderstorms to form. These showers dissipate quite quickly; however, they can group together into large clusters of thunderstorms. This creates a flow of warm, moist, rapidly rising air, which starts to rotate cyclonically as it interacts with the rotation of the earth.\nSeveral factors are required for these thunderstorms to develop further, including sea surface temperatures of around 27 °C (81 °F) and low vertical wind shear surrounding the system, atmospheric instability, high humidity in the lower to middle levels of the troposphere, enough Coriolis force to develop a low-pressure center, and a pre-existing low-level focus or disturbance.\nThere is a limit on tropical cyclone intensity which is strongly related to the water temperatures along its path. and upper-level divergence.\nAn average of 86 tropical cyclones of tropical storm intensity form annually worldwide. Of those cyclones, 47 reach strengths higher than 119 km/h (74 mph), and 20 become intense tropical cyclones, of at least Category 3 intensity on the Saffir–Simpson scale.\nClimate oscillations such as El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation modulate the timing and frequency of tropical cyclone development. Rossby waves can aid in the formation of a new tropical cyclone by disseminating the energy of an existing, mature storm. Kelvin waves can contribute to tropical cyclone formation by regulating the development of the westerlies. Cyclone formation is usually reduced 3 days prior to the wave's crest and increased during the 3 days after.\n\nFormation regions and warning centers\n\nThe majority of tropical cyclones each year form in one of seven tropical cyclone basins, which are monitored by a variety of meteorological services and warning centers. Ten of these warning centers worldwide are designated as either a Regional Specialized Meteorological Centre or a Tropical Cyclone Warning Centre by the World Meteorological Organization's (WMO) tropical cyclone programme. These warning centers issue advisories which provide basic information and cover a systems present, forecast position, movement and intensity, in their designated areas of responsibility. \nMeteorological services around the world are generally responsible for issuing warnings for their own country. There are exceptions, as the United States National Hurricane Center and Fiji Meteorological Service issue alerts, watches and warnings for various island nations in their areas of responsibility. The United States Joint Typhoon Warning Center and Fleet Weather Center also publicly issue warnings about tropical cyclones on behalf of the United States Government. The Brazilian Navy Hydrographic Center names South Atlantic tropical cyclones, however the South Atlantic is not a major basin, and not an official basin according to the WMO.\n\nInteractions with climate\n\nEach year on average, around 80 to 90 named tropical cyclones form around the world, of which over half develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more. Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active month. November is the only month in which all the tropical cyclone basins are in season. \nIn the Northern Atlantic Ocean, a distinct cyclone season occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is September 10.\nThe Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere, the tropical cyclone year begins on July 1 and runs all year-round encompassing the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.\nOf various modes of variability in the climate system, El Niño–Southern Oscillation has the largest effect on tropical cyclone activity. Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies. When the subtropical ridge position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. \nDuring La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific Ocean, which increases the landfall threat to China and much greater intensity in the Philippines. The Atlantic Ocean experiences depressed activity due to increased vertical wind shear across the region during El Niño years. Tropical cyclones are further influenced by the Atlantic Meridional Mode, the Quasi-biennial oscillation and the Madden–Julian oscillation.\n\nInfluence of climate change\n\nThe IPCC Sixth Assessment Report summarize the latest scientific findings about the impact of climate change on tropical cyclones. According to the report, we have now better understanding about the impact of climate change on tropical storm than before. Major tropical storms likely became more frequent in the last 40 years. We can say with high confidence that climate change increased rainfall during tropical cyclones. We can say with high confidence that a 1.5 degree warming lead to \"increased proportion of and peak wind speeds of intense tropical cyclones\". We can say with medium confidence that regional impacts of further warming include more intense tropical cyclones and/or extratropical storms.\nClimate change can affect tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, a decrease in overall frequency, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the possible consequences of human-induced climate change. Tropical cyclones use warm, moist air as their fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available. \nBetween 1979 and 2017, there was a global increase in the proportion of tropical cyclones of Category 3 and higher on the Saffir–Simpson scale. The trend was most clear in the North Atlantic and in the Southern Indian Ocean. In the North Pacific, tropical cyclones have been moving poleward into colder waters and there was no increase in intensity over this period. With 2 °C (3.6 °F) warming, a greater percentage (+13%) of tropical cyclones are expected to reach Category 4 and 5 strength. A 2019 study indicates that climate change has been driving the observed trend of rapid intensification of tropical cyclones in the Atlantic basin. Rapidly intensifying cyclones are hard to forecast and therefore pose additional risk to coastal communities.\nWarmer air can hold more water vapor: the theoretical maximum water vapor content is given by the Clausius–Clapeyron relation, which yields ≈7% increase in water vapor in the atmosphere per 1 °C (1.8 °F) warming. All models that were assessed in a 2019 review paper show a future increase of rainfall rates. Additional sea level rise will increase storm surge levels. It is plausible that extreme wind waves see an increase as a consequence of changes in tropical cyclones, further exacerbating storm surge dangers to coastal communities. The compounding effects from floods, storm surge, and terrestrial flooding (rivers) are projected to increase due to global warming.\nThere is currently no consensus on how climate change will affect the overall frequency of tropical cyclones. A majority of climate models show a decreased frequency in future projections. For instance, a 2020 paper comparing nine high-resolution climate models found robust decreases in frequency in the Southern Indian Ocean and the Southern Hemisphere more generally, while finding mixed signals for Northern Hemisphere tropical cyclones. Observations have shown little change in the overall frequency of tropical cyclones worldwide, with increased frequency in the North Atlantic and central Pacific, and significant decreases in the southern Indian Ocean and western North Pacific. \nThere has been a poleward expansion of the latitude at which the maximum intensity of tropical cyclones occurs, which may be associated with climate change. In the North Pacific, there may also have been an eastward expansion. Between 1949 and 2016, there was a slowdown in tropical cyclone translation speeds. (Tropical cyclone translation speed is the speed at which a storm moves across the ocean, measured at consecutive locations at a selected time interval, such as every three hours or every six hours.) It is unclear still to what extent this can be attributed to climate change: climate models do not all show this feature.\nA 2021 study review article concluded that the geographic range of tropical cyclones will probably expand poleward in response to climate warming of the Hadley circulation.\nWhen hurricane winds speed rise by 5%, its destructive power rises by about 50%. Therefore, as climate change increased the wind speed of Hurricane Helene by 11%, it increased the destruction from it by more than twice. According to World Weather Attribution the influence of climate change on the rainfall of some latest hurricanes can be described as follows:\n\nIntensity\nTropical cyclone intensity is based on wind speeds and pressure. Relationships between winds and pressure are often used in determining the intensity of a storm. Tropical cyclone scales, such as the Saffir-Simpson hurricane wind scale and Australia's scale (Bureau of Meteorology), only use wind speed for determining the category of a storm. The most intense storm on record is Typhoon Tip in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 hPa (26 inHg) and maximum sustained wind speeds of 165 kn (85 m/s; 305 km/h; 190 mph). The highest maximum sustained wind speed ever recorded was 185 kn (95 m/s; 345 km/h; 215 mph) in Hurricane Patricia in 2015—the most intense cyclone ever recorded in the Western Hemisphere.\n\nFactors\nWarm sea surface temperatures are required for tropical cyclones to form and strengthen. The commonly accepted minimum temperature range for this to occur is 26–27 °C (79–81 °F), however, multiple studies have proposed a lower minimum of 25.5 °C (77.9 °F). Higher sea surface temperatures result in faster intensification rates and sometimes even rapid intensification. High ocean heat content, also known as Tropical Cyclone Heat Potential, allows storms to achieve a higher intensity. Most tropical cyclones that experience rapid intensification are traversing regions of high ocean heat content rather than lower values. High ocean heat content values can help to offset the oceanic cooling caused by the passage of a tropical cyclone, limiting the effect this cooling has on the storm. Faster-moving systems are able to intensify to higher intensities with lower ocean heat content values. Slower-moving systems require higher values of ocean heat content to achieve the same intensity.\nThe passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, a process known as upwelling, which can negatively influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean with the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days. Conversely, the mixing of the sea can result in heat being inserted in deeper waters, with potential effects on global climate.\nVertical wind shear decreases tropical cyclone predicability, with storms exhibiting wide range of responses in the presence of shear. Wind shear often negatively affects tropical cyclone intensification by displacing moisture and heat from a system's center. Low levels of vertical wind shear are most optimal for strengthening, while stronger wind shear induces weakening. Dry air entraining into a tropical cyclone's core has a negative effect on its development and intensity by diminishing atmospheric convection and introducing asymmetries in the storm's structure. Symmetric, strong outflow leads to a faster rate of intensification than observed in other systems by mitigating local wind shear. Weakening outflow is associated with the weakening of rainbands within a tropical cyclone. Tropical cyclones may still intensify, even rapidly, in the presence of moderate or strong wind shear depending on the evolution and structure of the storm's convection.\nThe size of tropical cyclones plays a role in how quickly they intensify. Smaller tropical cyclones are more prone to rapid intensification than larger ones. The Fujiwhara effect, which involves interaction between two tropical cyclones, can weaken and ultimately result in the dissipation of the weaker of two tropical cyclones by reducing the organization of the system's convection and imparting horizontal wind shear. Tropical cyclones typically weaken while situated over a landmass because conditions are often unfavorable as a result of the lack of oceanic forcing. The Brown ocean effect can allow a tropical cyclone to maintain or increase its intensity following landfall, in cases where there has been copious rainfall, through the release of latent heat from the saturated soil. Orographic lift can cause a significant increase in the intensity of the convection of a tropical cyclone when its eye moves over a mountain, breaking the capped boundary layer that had been restraining it. Jet streams can both enhance and inhibit tropical cyclone intensity by influencing the storm's outflow as well as vertical wind shear.\n\nRapid intensification\n\nOn occasion, tropical cyclones may undergo a process known as rapid intensification, a period in which the maximum sustained winds of a tropical cyclone increase by 30 kn (56 km/h; 35 mph) or more within 24 hours. Similarly, rapid deepening in tropical cyclones is defined as a minimum sea surface pressure decrease of 1.75 hPa (0.052 inHg) per hour or 42 hPa (1.2 inHg) within a 24-hour period; explosive deepening occurs when the surface pressure decreases by 2.5 hPa (0.074 inHg) per hour for at least 12 hours or 5 hPa (0.15 inHg) per hour for at least 6 hours. \nFor rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely high, near or above 30 °C (86 °F), and water of this temperature must be sufficiently deep such that waves do not upwell cooler waters to the surface. On the other hand, Tropical Cyclone Heat Potential is one of such non-conventional subsurface oceanographic parameters influencing the cyclone intensity.\nWind shear must be low. When wind shear is high, the convection and circulation in the cyclone will be disrupted. Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently. However, some cyclones such as Hurricane Epsilon have rapidly intensified despite relatively unfavorable conditions.\n\nDissipation\n\nThere are a number of ways a tropical cyclone can weaken, dissipate, or lose its tropical characteristics. These include making landfall, moving over cooler water, encountering dry air, or interacting with other weather systems; however, once a system has dissipated or lost its tropical characteristics, its remnants could regenerate a tropical cyclone if environmental conditions become favorable.\nA tropical cyclone can dissipate when it moves over waters significantly cooler than 26.5 °C (79.7 °F). This will deprive the storm of such tropical characteristics as a warm core with thunderstorms near the center, so that it becomes a remnant low-pressure area. Remnant systems may persist for several days before losing their identity. This dissipation mechanism is most common in the eastern North Pacific. Weakening or dissipation can also occur if a storm experiences vertical wind shear which causes the convection and heat engine to move away from the center. This normally ceases the development of a tropical cyclone. In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days.\nShould a tropical cyclone make landfall or pass over an island, its circulation could start to break down, especially if it encounters mountainous terrain. When a system makes landfall on a large landmass, it is cut off from its supply of warm moist maritime air and starts to draw in dry continental air. This, combined with the increased friction over land areas, leads to the weakening and dissipation of the tropical cyclone. Over a mountainous terrain, a system can quickly weaken. Over flat areas, it may endure for two to three days before circulation breaks down and dissipates.\nOver the years, there have been a number of techniques considered to try to artificially modify tropical cyclones. These techniques have included using nuclear weapons, cooling the ocean with icebergs, blowing the storm away from land with giant fans, and seeding selected storms with dry ice or silver iodide. These techniques, however, fail to appreciate the duration, intensity, power or size of tropical cyclones.\n\nAssessment methods\n\nA variety of methods or techniques, including surface, satellite, and aerial, are used to assess the intensity of a tropical cyclone. Reconnaissance aircraft fly around and through tropical cyclones, outfitted with specialized instruments, to collect information that can be used to ascertain the winds and pressure of a system. Tropical cyclones possess winds of different speeds at different heights. Winds recorded at flight level can be converted to find the wind speeds at the surface. Surface observations, such as ship reports, land stations, mesonets, coastal stations, and buoys, can provide information on a tropical cyclone's intensity or the direction it is traveling. \nWind-pressure relationships (WPRs) are used as a way to determine the pressure of a storm based on its wind speed. Several different methods and equations have been proposed to calculate WPRs. Tropical cyclones agencies each use their own, fixed WPR, which can result in inaccuracies between agencies that are issuing estimates on the same system. The ASCAT is a scatterometer used by the MetOp satellites to map the wind field vectors of tropical cyclones. The SMAP uses an L-band radiometer channel to determine the wind speeds of tropical cyclones at the ocean surface, and has been shown to be reliable at higher intensities and under heavy rainfall conditions, unlike scatterometer-based and other radiometer-based instruments.\nThe Dvorak technique plays a large role in both the classification of a tropical cyclone and the determination of its intensity. Used in warning centers, the method was developed by Vernon Dvorak in the 1970s, and uses both visible and infrared satellite imagery in the assessment of tropical cyclone intensity. The Dvorak technique uses a scale of \"T-numbers\", scaling in increments of 0.5 from T1.0 to T8.0. Each T-number has an intensity assigned to it, with larger T-numbers indicating a stronger system. Tropical cyclones are assessed by forecasters according to an array of patterns, including curved banding features, shear, central dense overcast, and eye, to determine the T-number and thus assess the intensity of the storm. \nThe Cooperative Institute for Meteorological Satellite Studies works to develop and improve automated satellite methods, such as the Advanced Dvorak Technique (ADT) and SATCON. The ADT, used by a large number of forecasting centers, uses infrared geostationary satellite imagery and an algorithm based upon the Dvorak technique to assess the intensity of tropical cyclones. The ADT has a number of differences from the conventional Dvorak technique, including changes to intensity constraint rules and the usage of microwave imagery to base a system's intensity upon its internal structure, which prevents the intensity from leveling off before an eye emerges in infrared imagery. The SATCON weights estimates from various satellite-based systems and microwave sounders, accounting for the strengths and flaws in each individual estimate, to produce a consensus estimate of a tropical cyclone's intensity which can be more reliable than the Dvorak technique at times.\n\nIntensity metrics\nMultiple intensity metrics are used, including accumulated cyclone energy (ACE), the Hurricane Surge Index, the Hurricane Severity Index, the Power Dissipation Index (PDI), and integrated kinetic energy (IKE). ACE is a metric of the total energy a system has exerted over its lifespan. ACE is calculated by summing the squares of a cyclone's sustained wind speed, every six hours as long as the system is at or above tropical storm intensity and either tropical or subtropical. The calculation of the PDI is similar in nature to ACE, with the major difference being that wind speeds are cubed rather than squared. \nThe Hurricane Surge Index is a metric of the potential damage a storm may inflict via storm surge. It is calculated by squaring the dividend of the storm's wind speed and a climatological value (33 m/s or 74 mph), and then multiplying that quantity by the dividend of the radius of hurricane-force winds and its climatological value (96.6 km or 60.0 mi). This can be represented in equation form as:\n\n \n \n \n \n \n (\n \n \n v\n \n 33\n \n \n m\n \n /\n \n s\n \n \n \n \n )\n \n \n 2\n \n \n ×\n \n (\n \n \n r\n \n 96.6\n \n \n k\n m\n \n \n \n \n )\n \n \n \n \n {\\displaystyle \\left({\\frac {v}{33\\ \\mathrm {m/s} }}\\right)^{2}\\times \\left({\\frac {r}{96.6\\ \\mathrm {km} }}\\right)\\,}\n \n\nwhere \n \n \n \n v\n \n \n {\\textstyle v}\n \n is the storm's wind speed and \n \n \n \n r\n \n \n {\\textstyle r}\n \n is the radius of hurricane-force winds. The Hurricane Severity Index is a scale that can assign up to 50 points to a system; up to 25 points come from intensity, while the other 25 come from the size of the storm's wind field. The IKE model measures the destructive capability of a tropical cyclone via winds, waves, and surge. It is calculated as:\n\n \n \n \n \n ∫\n \n V\n o\n l\n \n \n \n \n 1\n 2\n \n \n p\n \n u\n \n 2\n \n \n \n d\n \n v\n \n \n \n \n \n {\\displaystyle \\int _{Vol}{\\frac {1}{2}}pu^{2}d_{v}\\,}\n \n\nwhere \n \n \n \n p\n \n \n {\\textstyle p}\n \n is the density of air, \n \n \n \n u\n \n \n {\\textstyle u}\n \n is a sustained surface wind speed value, and \n \n \n \n \n d\n \n v\n \n \n \n \n {\\textstyle d_{v}}\n \n is the volume element.\n\nClassification and naming\n\nClassification\n\nAround the world, tropical cyclones are classified in different ways, based on the location (tropical cyclone basins), the structure of the system and its intensity. For example, within the Northern Atlantic and Eastern Pacific basins, a tropical cyclone with wind speeds of over 65 kn (120 km/h; 75 mph) is called a hurricane, while it is called a typhoon or a severe cyclonic storm within the Western Pacific or North Indian oceans. When a hurricane passes west across the International Dateline in the Northern Hemisphere, it becomes known as a typhoon. This happened in 2014 for Hurricane Genevieve, which became Typhoon Genevieve. \nWithin the Southern Hemisphere, it is either called a hurricane, tropical cyclone or a severe tropical cyclone, depending on if it is located within the South Atlantic, South-West Indian Ocean, Australian region or the South Pacific Ocean. The descriptors for tropical cyclones with wind speeds below 65 kn (120 km/h; 75 mph) vary by tropical cyclone basin and may be further subdivided into categories such as \"tropical storm\", \"cyclonic storm\", \"tropical depression\", or \"deep depression\".\n\nNaming\n\nThe practice of using given names to identify tropical cyclones dates back to the late 1800s and early 1900s and gradually superseded the existing system—simply naming cyclones based o",
    "source": "wikipedia:Tropical cyclone",
    "domain": "climate"
  },
  {
    "text": "A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of combustible vegetation. Some natural forest ecosystems depend on wildfire. Modern forest management often engages in prescribed burns to mitigate fire risk and promote natural forest cycles. However, controlled burns can turn into wildfires by mistake.\nWildfires can be classified by cause of ignition, physical properties, combustible material present, and the effect of weather on the fire. Wildfire severity results from a combination of factors such as available fuels, physical setting, and weather. Climatic cycles with wet periods that create substantial fuels, followed by drought and heat, often precede severe wildfires. These cycles have been intensified by climate change, and can be exacerbated by curtailment of mitigation measures (such as budget or equipment funding), or sheer enormity of the event.\nWildfires are a common type of disaster in some regions, including Siberia (Russia); California, Washington, Oregon, Texas, Florida (United States); British Columbia (Canada); and Australia. Areas with Mediterranean climates or in the taiga biome are particularly susceptible. Wildfires can severely impact humans and their settlements. Effects include for example the direct health impacts of smoke and fire, as well as destruction of property (especially in wildland–urban interfaces), and economic losses. There is also the potential for contamination of water and soil.\nAt a global level, human practices have made the impacts of wildfire worse, with a doubling in land area burned by wildfires compared to natural levels. Humans have impacted wildfire through climate change (e.g. more intense heat waves and droughts), land-use change, and wildfire suppression. The carbon released from wildfires can add to carbon dioxide concentrations in the atmosphere and thus contribute to the greenhouse effect. This creates a climate change feedback.\nNaturally occurring wildfires can have beneficial effects on those ecosystems that have evolved with fire. In fact, many plant species depend on the effects of fire for growth and reproduction.\n\nIgnition\nThe ignition of a fire takes place through either natural causes or human activity (deliberate or not).\n\nNatural causes\nNatural occurrences that can ignite wildfires without the involvement of humans include lightning, volcanic eruptions, sparks from rock falls, and spontaneous combustions.\n\nHuman activity\nSources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture such as the slash-and-burn farming. In the tropics, farmers often practice the slash-and-burn method of clearing fields during the dry season.\nIn middle latitudes, the most common human causes of wildfires are equipment generating sparks (chainsaws, grinders, mowers, etc.), overhead power lines, and arson.\nArson may account for over 20% of human caused fires, although human activities, including campfires, power line failures, and equipment use, are responsible for approximately 85% of wildfires. The combination of these ignition sources with dry conditions leads to more frequent and severe fires. However, in the 2019–20 Australian bushfire season \"an independent study found online bots and trolls exaggerating the role of arson in the fires.\" In the 2023 Canadian wildfires false claims of arson gained traction on social media; however, arson is generally not the main cause of wildfires in Canada. In California, generally 6–10% of wildfires annually are arson.\nCoal seam fires burn in the thousands around the world, such as those in Burning Mountain, New South Wales; Centralia, Pennsylvania; and several coal-sustained fires in China. They can also flare up unexpectedly and ignite nearby flammable material.\n\nSpread\n\nThe spread of wildfires varies based on the flammable material present, its vertical arrangement and moisture content, and weather conditions. Fuel arrangement and density is governed in part by topography, as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be generally characterized by their fuels as follows:\n\nGround fires are fed by subterranean roots, duff on the forest floor, and other buried organic matter. Ground fires typically burn by smoldering, and can burn slowly for days to months, such as peat fires in Kalimantan and Eastern Sumatra, Indonesia, which resulted from a riceland creation project that unintentionally drained and dried the peat.\nCrawling or surface fires are fueled by low-lying vegetative matter on the forest floor such as leaf and timber litter, debris, grass, and low-lying shrubbery. This kind of fire often burns at a relatively lower temperature than crown fires (less than 400 °C or 750 °F) and may spread at slow rate, though steep slopes and wind can accelerate the rate of spread. This fuel type is especially susceptible to ignition due to spotting (see below).\nLadder fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and vines. Kudzu, Old World climbing fern, and other invasive plants that scale trees may also encourage ladder fires.\nCrown, canopy, or aerial fires burn suspended material at the canopy level, such as tall trees, vines, and mosses. The ignition of a crown fire, termed crowning, is dependent on the density of the suspended material, canopy height, canopy continuity, sufficient surface and ladder fires, vegetation moisture content, and weather conditions during the blaze. Stand-replacing fires lit by humans can spread into the Amazon rain forest, damaging ecosystems not particularly suited for heat or arid conditions.\n\nPhysical properties\n\nWildfires occur when all the necessary elements of a fire triangle come together in a susceptible area: an ignition source is brought into contact with a combustible material such as vegetation that is subjected to enough heat and has an adequate supply of oxygen from the ambient air. A high moisture content usually prevents ignition and slows propagation, because higher temperatures are needed to evaporate any water in the material and heat the material to its fire point.\nDense forests usually provide more shade, resulting in lower ambient temperatures and greater humidity, and are therefore less susceptible to wildfires. Less dense material such as grasses and leaves are easier to ignite because they contain less water than denser material such as branches and trunks. Plants continuously lose water by evapotranspiration, but water loss is usually balanced by water absorbed from the soil, humidity, or rain. When this balance is not maintained, often as a consequence of droughts, plants dry out and are therefore more flammable.\nA wildfire front is the portion sustaining continuous flaming combustion, where unburned material meets active flames, or the smoldering transition between unburned and burned material. As the front approaches, the fire heats both the surrounding air and woody material through convection and thermal radiation. First, wood is dried as water is vaporized at a temperature of 100 °C (212 °F). Next, the pyrolysis of wood at 230 °C (450 °F) releases flammable gases. Finally, wood can smolder at 380 °C (720 °F) or, when heated sufficiently, ignite at 590 °C (1,000 °F). Even before the flames of a wildfire arrive at a particular location, heat transfer from the wildfire front warms the air to 800 °C (1,500 °F), which pre-heats and dries flammable materials, causing materials to ignite faster and allowing the fire to spread faster. High-temperature and long-duration surface wildfires may encourage flashover or torching: the drying of tree canopies and their subsequent ignition from below.\n Wildfires have a rapid forward rate of spread (FROS) when burning through dense uninterrupted fuels. They can move as fast as 10.8 kilometres per hour (6.7 mph) in forests and 22 kilometres per hour (14 mph) in grasslands. Wildfires can advance tangentially to the main front to form a flanking front, or burn in the opposite direction of the main front by backing. They may also spread by jumping or spotting as winds and vertical convection columns carry firebrands (hot wood embers) and other burning materials through the air over roads, rivers, and other barriers that may otherwise act as firebreaks. Torching and fires in tree canopies encourage spotting, and dry ground fuels around a wildfire are especially vulnerable to ignition from firebrands. Spotting can create spot fires as hot embers and firebrands ignite fuels downwind from the fire. In Australian bushfires, spot fires are known to occur as far as 20 kilometres (12 mi) from the fire front.\nEspecially large wildfires may affect air currents in their immediate vicinities by the stack effect: air rises as it is heated, and large wildfires create powerful updrafts that will draw in new, cooler air from surrounding areas in thermal columns. Great vertical differences in temperature and humidity encourage pyrocumulus clouds, strong winds, and fire whirls with the force of tornadoes at speeds of more than 80 kilometres per hour (50 mph). Rapid rates of spread, prolific crowning or spotting, the presence of fire whirls, and strong convection columns signify extreme conditions.\n\nIntensity variations during day and night\nIntensity also increases during daytime hours. Burn rates of smoldering logs are up to five times greater during the day due to lower humidity, increased temperatures, and increased wind speeds. Sunlight warms the ground during the day which creates air currents that travel uphill. At night the land cools, creating air currents that travel downhill. Wildfires are fanned by these winds and often follow the air currents over hills and through valleys. Fires in Europe occur frequently during the hours of 12:00 p.m. and 2:00 p.m. Wildfire suppression operations in the United States revolve around a 24-hour fire day that begins at 10:00 a.m. due to the predictable increase in intensity resulting from the daytime warmth.\n\nClimate change effects\n\nIncreasing risks due to climate change\nClimate change promotes the type of weather that makes wildfires more likely. In some areas, an increase of wildfires has been attributed directly to climate change. Evidence from Earth's past also shows more fire in warmer periods. Climate change increases potential evapotranspiration. This can cause vegetation and soils to dry out when potential evaporation exceeds precipitation and available moisture from the given ecosystem. The vapor pressure deficit also contributes to increasing wildfire risk and has been worsening in the warming climate. When a fire starts in an area with very dry vegetation, it can spread rapidly. Higher temperatures can also lengthen the fire season. This is the time of year in which severe wildfires are most likely, particularly in regions where snow is disappearing.\nWeather conditions are raising the risks of wildfires. But the total area burnt by wildfires has decreased. This is mostly because savanna has been converted to cropland, so there are fewer trees to burn.\nClimate variability including heat waves, droughts, and El Niño, and regional weather patterns, such as high-pressure ridges, can increase the risk and alter the behavior of wildfires dramatically. Years of high precipitation can produce rapid vegetation growth, which when followed by warmer periods can encourage more widespread fires and longer fire seasons. High temperatures dry out the fuel loads and make them more flammable, increasing tree mortality and posing significant risks to global forest health. Since the mid-1980s, in the Western US, earlier snowmelt and associated warming have also been associated with an increase in length and severity of the wildfire season, or the most fire-prone time of the year. A 2019 study indicates that the increase in fire risk in California may be partially attributable to human-induced climate change.\nIn the summer of 1974–1975 (southern hemisphere), Australia suffered its worst recorded wildfire, when 15% of Australia's land mass suffered \"extensive fire damage\". Fires that summer burned up an estimated 117 million hectares (290 million acres; 1,170,000 square kilometres; 450,000 square miles). In Australia, the annual number of hot days (above 35 °C or 95 °F) and very hot days (above 40 °C or 104 °F) has increased significantly in many areas of the country since 1950. The country has always had bushfires but in 2019, the extent and ferocity of these fires increased dramatically. For the first time catastrophic bushfire conditions were declared for Greater Sydney. New South Wales and Queensland declared a state of emergency but fires were also burning in South Australia and Western Australia.\nIn 2019, extreme heat and dryness caused massive wildfires in Siberia, Alaska, Canary Islands, Australia, and in the Amazon rainforest. The fires in the latter were caused mainly by illegal logging. The smoke from the fires expanded over a huge territory including major cities, dramatically reducing air quality.\n\nAs of August 2020, the wildfires in that year were 13% worse than in 2019 due primarily to climate change, deforestation and agricultural burning. The Amazon rainforest's existence is threatened by fires. Record-breaking wildfires in 2021 occurred in Turkey, Greece and Russia, thought to be linked to climate change.\n\nCarbon dioxide and other emissions from fires\nThe carbon released from wildfires can add to greenhouse gas concentrations. Climate models do not yet fully reflect this feedback.\n\nWildfires release large amounts of carbon dioxide, black and brown carbon particles, and ozone precursors such as volatile organic compounds and nitrogen oxides (NOx) into the atmosphere. These emissions affect radiation, clouds, and climate on regional and even global scales. Wildfires also emit substantial amounts of semi-volatile organic species that can partition from the gas phase to form secondary organic aerosol (SOA) over hours to days after emission. In addition, the formation of the other pollutants as the air is transported can lead to harmful exposures for populations in regions far away from the wildfires. While direct emissions of harmful pollutants can affect first responders and residents, wildfire smoke can also be transported over long distances and impact air quality across local, regional, and global scales.The health effects of wildfire smoke, such as worsening cardiovascular and respiratory conditions, extend beyond immediate exposure, contributing to nearly 16,000 annual deaths, a number expected to rise to 30,000 by 2050. The economic impact is also significant, with projected costs reaching $240 billion annually by 2050, surpassing other climate-related damages.\nOver the past century, wildfires have accounted for 20–25% of global carbon emissions, the remainder from human activities. Global carbon emissions from wildfires through August 2020 equaled the average annual emissions of the European Union. In 2020, the carbon released by California's wildfires was significantly larger than the state's other carbon emissions.\nForest fires in Indonesia in 1997 were estimated to have released between 0.81 and 2.57 gigatonnes (0.89 and 2.83 billion short tons) of CO2 into the atmosphere, which is between 13–40% of the annual global carbon dioxide emissions from burning fossil fuels.\nIn June and July 2019, fires in the Arctic emitted more than 140 megatons of carbon dioxide, according to an analysis by CAMS. To put that into perspective this amounts to the same amount of carbon emitted by 36 million cars in a year. The recent wildfires and their massive CO2 emissions mean that it will be important to take them into consideration when implementing measures for reaching greenhouse gas reduction targets accorded with the Paris climate agreement. Due to the complex oxidative chemistry occurring during the transport of wildfire smoke in the atmosphere, the toxicity of emissions was indicated to increase over time.\nAtmospheric models suggest that these concentrations of sooty particles could increase absorption of incoming solar radiation during winter months by as much as 15%. The Amazon is estimated to hold around 90 billion tons of carbon. As of 2019, the earth's atmosphere has 415 parts per million of carbon, and the destruction of the Amazon would add about 38 parts per million.\nSome research has shown wildfire smoke can have a cooling effect.\nResearch in 2007 stated that black carbon in snow changed temperature three times more than atmospheric carbon dioxide. As much as 94 percent of Arctic warming may be caused by dark carbon on snow that initiates melting. The dark carbon comes from fossil fuels burning, wood and other biofuels, and forest fires. Melting can occur even at low concentrations of dark carbon (below five parts per billion).\n\nPrevention and mitigation\n\nWildfire prevention refers to the preemptive methods aimed at reducing the risk of fires as well as lessening its severity and spread. Prevention techniques aim to manage air quality, maintain ecological balances, protect resources, and to affect future fires. Prevention policies must consider the role that humans play in wildfires, since, for example, 95% of forest fires in Europe are related to human involvement.\nWildfire prevention programs around the world may employ techniques such as wildland fire use (WFU) and prescribed or controlled burns. Wildland fire use refers to any fire of natural causes that is monitored but allowed to burn. Controlled burns are fires ignited by government agencies under less dangerous weather conditions. Other objectives can include maintenance of healthy forests, rangelands, and wetlands, and support of ecosystem diversity.\n\nStrategies for wildfire prevention, detection, control and suppression have varied over the years. One common and inexpensive technique to reduce the risk of uncontrolled wildfires is controlled burning: intentionally igniting smaller less-intense fires to minimize the amount of flammable material available for a potential wildfire. Vegetation may be burned periodically to limit the accumulation of plants and other debris that may serve as fuel, while also maintaining high species diversity. While other people claim that controlled burns and a policy of allowing some wildfires to burn is the cheapest method and an ecologically appropriate policy for many forests, they tend not to take into account the economic value of resources that are consumed by the fire, especially merchantable timber. Some studies conclude that while fuels may also be removed by logging, such thinning treatments may not be effective at reducing fire severity under extreme weather conditions.\nBuilding codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure. Communities in the Philippines also maintain fire lines 5 to 10 meters (16 to 33 ft) wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather. Continued residential development in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism. The ecological benefits of fire are often overridden by the economic and safety benefits of protecting structures and human life.\n\nGoat grazing programs\nAs climate change drives more frequent and more intense wildfires, more effort is being given to mitigation of fire potential by active measures such as managing fire fuels (ground cover, weeds, small shrubs, coyote brush, etc). In Northern California, for example, goat herds have been used in many communities to reduce the amount of fire fuels on the outskirts of some communities. It is estimated that 60 to 80,000 goats were thus employed by 2024.\n\nDetection\n\nThe demand for timely, high-quality fire information has increased in recent years. Fast and effective detection is a key factor in wildfire fighting. Early detection efforts were focused on early response, accurate results in both daytime and nighttime, and the ability to prioritize fire danger. Fire lookout towers were used in the United States in the early 20th century and fires were reported using telephones, carrier pigeons, and heliographs. Aerial and land photography using instant cameras were used in the 1950s until infrared scanning was developed for fire detection in the 1960s. However, information analysis and delivery was often delayed by limitations in communication technology. Early satellite-derived fire analyses were hand-drawn on maps at a remote site and sent via overnight mail to the fire manager. During the Yellowstone fires of 1988, a data station was established in West Yellowstone, permitting the delivery of satellite-based fire information in approximately four hours.\nPublic hotlines, fire lookouts in towers, and ground and aerial patrols can be used as a means of early detection of forest fires. However, accurate human observation may be limited by operator fatigue, time of day, time of year, and geographic location. Electronic systems have gained popularity in recent years as a possible resolution to human operator error. These systems may be semi- or fully automated and employ systems based on the risk area and degree of human presence, as suggested by GIS data analyses. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via Global Positioning System (GPS) into a collective whole for near-realtime use by wireless Incident Command Centers.\n\nLocal sensor networks\nA small, high risk area that features thick vegetation, a strong human presence, or is close to a critical urban area can be monitored using a local sensor network. Detection systems may include wireless sensor networks that act as automated weather systems: detecting temperature, humidity, and smoke. These may be battery-powered, solar-powered, or tree-rechargeable: able to recharge their battery systems using the small electrical currents in plant material. Larger, medium-risk areas can be monitored by scanning towers that incorporate fixed cameras and sensors to detect smoke or additional factors such as the infrared signature of carbon dioxide produced by fires. Additional capabilities such as night vision, brightness detection, and color change detection may also be incorporated into sensor arrays.\nThe Department of Natural Resources signed a contract with PanoAI for the installation of 360 degree 'rapid detection' cameras around the Pacific northwest, which are mounted on cell towers and are capable of continuous monitoring of a 24-kilometre (15 mi) radius. Additionally, Sensaio Tech, based in Brazil and Toronto, has released a sensor device that continuously monitors 14 different variables common in forests, ranging from soil temperature to salinity. This information is connected live back to clients through dashboard visualizations, while mobile notifications are provided regarding dangerous levels.\n\nSatellite and aerial monitoring\n\nSatellite and aerial monitoring through the use of planes, helicopter, or UAVs can provide a wider view and may be sufficient to monitor very large, low risk areas. These more sophisticated systems employ GPS and aircraft-mounted infrared or high-resolution visible cameras to identify and target wildfires. Satellite-mounted sensors such as Envisat's Advanced Along Track Scanning Radiometer and European Remote-Sensing Satellite's Along-Track Scanning Radiometer can measure infrared radiation emitted by fires, identifying hot spots greater than 39 °C (102 °F). The National Oceanic and Atmospheric Administration's Hazard Mapping System combines remote-sensing data from satellite sources such as Geostationary Operational Environmental Satellite (GOES), Moderate-Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) for detection of fire and smoke plume locations. However, satellite detection is prone to offset errors, anywhere from 2 to 3 kilometers (1 to 2 mi) for MODIS and AVHRR data and up to 12 kilometers (7.5 mi) for GOES data. Satellites in geostationary orbits may become disabled, and satellites in polar orbits are often limited by their short window of observation time. Cloud cover and image resolution may also limit the effectiveness of satellite imagery. Global Forest Watch provides detailed daily updates on fire alerts.\nIn 2015 a new fire detection tool is in operation at the U.S. Department of Agriculture (USDA) Forest Service (USFS) which uses data from the Suomi National Polar-orbiting Partnership (NPP) satellite to detect smaller fires in more detail than previous space-based products. The high-resolution data is used with a computer model to predict how a fire will change direction based on weather and land conditions.\nIn 2014, an international campaign was organized in South Africa's Kruger National Park to validate fire detection products including the new VIIRS active fire data. In advance of that campaign, the Meraka Institute of the Council for Scientific and Industrial Research in Pretoria, South Africa, an early adopter of the VIIRS 375 m fire product, put it to use during several large wildfires in Kruger.\nSince 2021 NASA has provided active fire locations in near real-time via the Fire Information for Resource Management System (FIRMS).\nThe increased prevalence of wildfires has led to proposals deploy technologies based on artificial intelligence for early detection, prevention, and prediction of wildfires.\n\nSuppression\n\nWildfire suppression depends on the technologies available in the area in which the wildfire occurs. In less developed nations the techniques used can be as simple as throwing sand or beating the fire with sticks or palm fronds. In more advanced nations, the suppression methods vary due to increased technological capacity. Silver iodide can be used to encourage snow fall, while fire retardants and water can be dropped onto fires by unmanned aerial vehicles, planes, and helicopters. Complete fire suppression is no longer an expectation, but the majority of wildfires are often extinguished before they grow out of control. While more than 99% of the 10,000 new wildfires each year are contained, escaped wildfires under extreme weather conditions are difficult to suppress without a change in the weather. Wildfires in Canada and the US burn an average of 54,500 square kilometers (13,000,000 acres) per year.\nAbove all, fighting wildfires can become deadly. A wildfire's burning front may also change direction unexpectedly and jump across fire breaks. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire, which can make fires particularly dangerous. For example, during the 1949 Mann Gulch fire in Montana, United States, thirteen smokejumpers died when they lost their communication links, became disoriented, and were overtaken by the fire. In the Australian February 2009 Victorian bushfires, at least 173 people died and over 2,029 homes and 3,500 structures were lost when they became engulfed by wildfire.\n\nCosts of wildfire suppression\nThe suppression of wild fires takes up a large amount of a country's gross domestic product which directly affects the country's economy. While costs vary wildly from year to year, depending on the severity of each fire season, in the United States, local, state, federal and tribal agencies collectively spend tens of billions of dollars annually to suppress wildfires. In the United States, it was reported that approximately $6 billion was spent between 2004–2008 to suppress wildfires in the country. In California, the U.S. Forest Service spends about $200 million per year to suppress 98% of wildfires and up to $1 billion to suppress the other 2% of fires that escape initial attack and become large.\n\nWildland firefighting safety\n\nWildland fire fighters face several life-threatening hazards including heat stress, fatigue, smoke and dust, as well as the risk of other injuries such as burns, cuts and scrapes, animal bites, and even rhabdomyolysis. Between 2000 and 2016, more than 350 wildland firefighters died on-duty.\nEspecially in hot weather conditions, fires present the risk of heat stress, which can entail feeling heat, fatigue, weakness, vertigo, headache, or nausea. Heat stress can progress into heat strain, which entails physiological changes such as increased heart rate and core body temperature. This can lead to heat-related illnesses, such as heat rash, cramps, exhaustion or heat stroke. Various factors can contribute to the risks posed by heat stress, including strenuous work, personal risk factors such as age and fitness, dehydration, sleep deprivation, and burdensome personal protective equipment. Rest, cool water, and occasional breaks are crucial to mitigating the effects of heat stress.\nSmoke, ash, and debris can also pose serious respiratory hazards for wildland firefighters. The smoke and dust from wildfires can contain gases such as carbon monoxide, sulfur dioxide and formaldehyde, as well as particulates such as ash and silica. To reduce smoke exposure, wildfire fighting crews should, whenever possible, rotate firefighters through areas of heavy smoke, avoid downwind firefighting, use equipment rather than people in holding areas, and minimize mop-up. Camps and command posts should also be located upwind of wildfires. Protective clothing and equipment can also help minimize exposure to smoke and ash.\nFirefighters are also at risk of cardiac events including strokes and heart attacks. Firefighters should maintain good physical fitness. Fitness programs, medical screening and examination programs which include stress tes",
    "source": "wikipedia:Wildfire",
    "domain": "climate"
  },
  {
    "text": "A glacier (US: ; UK: or ) is a persistent body of natural ice, a form of\nrock, that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It slowly flows and deforms under stresses induced by gravity, undergoing both ductile and brittle deformation, and acquiring distinguishing surface features, such as crevasses and seracs. As a glacier moves, it abrades underlying rock and debris to create glacial landforms, such as cirques, moraines, and fjords. Although a glacier may flow into a body of water, and can include ice shelves and ice tongues, it originates only on land and is distinct from the much thinner sea ice and lake ice that form on the surface of freezing bodies of water.\nOn Earth, 99% of glacial ice is contained within vast ice sheets (also known as \"continental glaciers\") in the polar regions, but glaciers may be found in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand. Between latitudes 35°N and 35°S, glaciers occur only in the Himalayas, Andes, and a few high mountains in East Africa, Mexico, New Guinea and on Zard-Kuh in Iran. With more than 7,000 known glaciers, Pakistan has more glacial ice than any other country outside the polar regions. Glaciers cover about 10% of Earth's land surface. Continental glaciers cover nearly 13 million km2 (5 million sq mi) or about 98% of Antarctica's 13.2 million km2 (5.1 million sq mi), with an average thickness of ice 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers. The volume of glaciers, not including the ice sheets of Antarctica and Greenland, has been estimated at 170,000 km3.\nGlacial ice is the largest reservoir of fresh water on Earth, holding with ice sheets about 69% of the world's freshwater. Many glaciers from temperate, alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. However, within high-altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater.\nSince glacial mass is affected by long-term climatic changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level.\nA large piece of compressed ice, or a glacier, appears blue, as large quantities of water appear blue, because water molecules absorb other colors more efficiently than blue. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing the created ice's density.\n\nEtymology and terminology\nThe word glacier is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, and ultimately Latin glaciēs, meaning \"ice\". The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere.\n\nTypes\n\nClassification by size, shape and behavior\n\nGlaciers are categorized by their morphology, thermal characteristics, and behavior. Alpine glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, or alternatively, an alpine glacier or mountain glacier. A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have an area less than 50,000 km2 (19,000 sq mi) by definition.\nGlacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets or continental glaciers. Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of freshwater, enough that if both melted, global sea levels would rise by over 70 m (230 ft). Portions of an ice sheet or cap that extend into water are called ice shelves; they tend to be thin with limited slopes and reduced velocities. Narrow, fast-moving sections of an ice sheet are called ice streams. In Antarctica, many ice streams drain into large ice shelves. Some drain directly into the sea, often with an ice tongue, like Mertz Glacier.\nTidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica, Baffin, Devon, and Ellesmere Islands in Canada, Southeast Alaska, and the Northern and Southern Patagonian Ice Fields. As the ice reaches the sea, pieces break off or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by climate change than other glaciers.\n\nClassification by thermal state\n\nThermally, a temperate glacier is at a melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing threshold from the surface to its base, although the surface snowpack may experience seasonal melting. A subpolar glacier includes both temperate and polar ice, depending on the depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is often described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface and is thus frozen to the underlying substrate. A warm-based glacier is above or at freezing at the interface and is able to slide at this contact. This contrast is thought to a large extent to govern the ability of a glacier to effectively erode its bed, as sliding ice promotes plucking at rock from the surface below. Glaciers which are partly cold-based and partly warm-based are known as polythermal.\n\nFormation\n\nGlaciers form where the accumulation of snow and ice exceeds ablation. A glacier usually originates from a cirque landform (alternatively known as a corrie or as a cwm) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes) – which collects and compresses through gravity the snow that falls into it. This snow accumulates and refreezes, turning into névé (granular snow). Further crushing of the individual snowflakes and expelling the air from the snow turns it into firn and eventually \"glacial ice\". This glacial ice will fill the cirque until it \"overflows\" through a geological weakness or vacancy from the edge of the cirque called the \"lip\" or threshold. When the mass of snow and ice reaches sufficient thickness, it begins to move by a combination of surface slope, gravity, and pressure. On steeper slopes, this can occur with as little as 15 m (49 ft) of snow-ice.\nIn temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice or névé. Under the pressure of the layers of ice and snow above it, this granular snow fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacier ice is slightly more dense than ice formed from frozen water because glacier ice contains fewer trapped air bubbles.\n\nColor\nGlacial ice has a distinctive blue tint because it absorbs some red light due to an overtone of the infrared OH stretching mode of the water molecule. Liquid water appears blue for the same reason. The blue of glacier ice is sometimes misattributed to Rayleigh scattering of bubbles in the ice.\n\nStructure\n\nA glacier originates at a location called its glacier head and terminates at its glacier foot, snout, or terminus.\nGlaciers are broken into zones based on surface snowpack and melt conditions. The ablation zone is the region where there is a net loss in glacier mass. The upper part of a glacier, where accumulation exceeds ablation, is called the accumulation zone. The equilibrium line separates the ablation zone and the accumulation zone; it is the contour where the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. In general, the accumulation zone accounts for 60–70% of the glacier's surface area, more if the glacier calves icebergs. Ice in the accumulation zone is deep enough to exert a downward force that erodes underlying rock. After a glacier melts, it often leaves behind a bowl- or amphitheater-shaped depression that ranges in size from large basins like the Great Lakes to smaller mountain depressions known as cirques.\nThe accumulation zone can be subdivided based on its melt conditions.\n\nThe dry snow zone is a region where no melt occurs, even in the summer, and the snowpack remains dry.\nThe percolation zone is an area with some surface melt, causing meltwater to percolate into the snowpack. This zone is often marked by refrozen ice lenses, glands, and layers. The snowpack also never reaches the melting point.\nNear the equilibrium line on some glaciers, a superimposed ice zone develops. This zone is where meltwater refreezes as a cold layer in the glacier, forming a continuous mass of ice.\nThe wet snow zone is the region where all of the snow deposited since the end of the previous summer has been raised to 0 °C.\nThe health of a glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area is snow-covered at the end of the melt season, and they have a terminus with a vigorous flow.\nFollowing the Little Ice Age's end around 1850, glaciers around the Earth have retreated substantially. A slight cooling led to the advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous.\n\nStructural glaciology\nGlaciers are made of glacial ice, which is a type of rock, composed predominantly of the mineral Ice Ih, with minor inclusions of trapped gasses, sediments, and other debris frozen into the matrix. In geologic terms, glacial ice is a monomineralic metamorphic rock very close to its melting point, which accumulates predominantly through sedimentary processes, such as meteoric snowfall, but also involves igneous processes on a smaller scale, such melting and refreezing of ice.\nApproaches from structural geology can be used to describe and characterize glaciers. These approaches have been used to enhance the description and understanding of glacial processes by analogy to other geologic structures, and to improve the description and understanding of processes in larger geologic structures by analogy to glaciers. Examples include structural mapping of glacier flow units and deformation features to give interpretive context to ice shelf collapse, and examining the deformation styles and zones of a glacier as an analogue to an extensional allochthon.\n\nMotion\n\nGlaciers move downhill by the force of gravity and the internal deformation of ice. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between layers. When the amount of strain (deformation) is proportional to the stress being applied, ice will act as an elastic solid. Ice needs to be at least 30 m (98 ft) thick to even start flowing, but once its thickness exceeds about 50 m (160 ft), stress on the layer above will exceeds the inter-layer binding strength, and then it will move faster than the layer below. This means that small amounts of stress can result in a large amount of strain, causing the deformation to become a plastic flow rather than elastic. Then, the glacier will begin to deform under its own weight and flow across the landscape. According to the Glen–Nye flow law, the relationship between stress and strain, and thus the rate of internal flow, can be modeled as follows:\n\n \n \n \n Σ\n =\n k\n \n τ\n \n n\n \n \n ,\n \n \n \n {\\displaystyle \\Sigma =k\\tau ^{n},\\,}\n \n\nwhere: \n\n \n \n \n Σ\n \n \n \n {\\displaystyle \\Sigma \\,}\n \n = shear strain (flow) rate\n\n \n \n \n τ\n \n \n \n {\\displaystyle \\tau \\,}\n \n = stress\n\n \n \n \n n\n \n \n \n {\\displaystyle n\\,}\n \n = a constant between 2–4 (typically 3 for most glaciers)\n\n \n \n \n k\n \n \n \n {\\displaystyle k\\,}\n \n = a temperature-dependent constant\n\nThe lowest velocities are near the base of the glacier and along valley sides where friction acts against flow, causing the most deformation. Velocity increases inward toward the center line and upward, as the amount of deformation decreases. The highest flow velocities are found at the surface, representing the sum of the velocities of all the layers below.\nBecause ice can flow faster where it is thicker, the rate of glacier-induced erosion is directly proportional to the thickness of overlying ice. Consequently, pre-glacial low hollows will be deepened and pre-existing topography will be amplified by glacial action, while nunataks, which protrude above ice sheets, barely erode at all – erosion has been estimated as 5 m per 1.2 million years. This explains, for example, the deep profile of fjords, which can reach a kilometer in depth as ice is topographically steered into them. The extension of fjords inland increases the rate of ice sheet thinning since they are the principal conduits for draining ice sheets. It also makes the ice sheets more sensitive to changes in climate and the ocean.\nAlthough evidence in favor of glacial flow was known by the early 19th century, other theories of glacial motion were advanced, such as the idea that meltwater, refreezing inside glaciers, caused the glacier to dilate and extend its length. As it became clear that glaciers behaved to some degree as if the ice were a viscous fluid, it was argued that \"regelation\", or the melting and refreezing of ice at a temperature lowered by the pressure on the ice inside the glacier, was what allowed the ice to deform and flow. James Forbes came up with the essentially correct explanation in the 1840s, although it was several decades before it was fully accepted.\n\nFracture zone and cracks\n\nThe top 50 m (160 ft) of a glacier are rigid because they are under low pressure. This upper section is known as the fracture zone and moves mostly as a single unit over the plastic-flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in the fracture zone. Crevasses form because of differences in glacier velocity. If two rigid sections of a glacier move at different speeds or directions, shear forces cause them to break apart, opening a crevasse. Crevasses are seldom more than 46 m (150 ft) deep but, in some cases, can be at least 300 m (1,000 ft) deep. Beneath this point, the plasticity of the ice prevents the formation of cracks. Intersecting crevasses can create isolated peaks in the ice, called seracs.\n\nCrevasses can form in several different ways. Transverse crevasses are transverse to flow and form where steeper slopes cause a glacier to accelerate. Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally. Marginal crevasses form near the edge of the glacier, caused by the reduction in speed caused by friction of the valley walls. Marginal crevasses are largely transverse to flow. Moving glacier ice can sometimes separate from the stagnant ice above, forming a bergschrund. Bergschrunds resemble crevasses but are singular features at a glacier's margins. Crevasses make travel over glaciers hazardous, especially when they are hidden by fragile snow bridges.\nBelow the equilibrium line, glacial meltwater is concentrated in stream channels. Meltwater can pool in proglacial lakes on top of a glacier or descend into the depths of a glacier via moulins. Streams within or beneath a glacier flow in englacial or sub-glacial tunnels. These tunnels sometimes reemerge at the glacier's surface.\n\nSubglacial processes\n\nMost of the important processes controlling glacial motion occur in the ice-bed contact—even though it is only a few meters thick. The bed's temperature, roughness and softness define basal shear stress, which in turn defines whether movement of the glacier will be accommodated by motion in the sediments, or if it will be able to slide. A soft bed, with high porosity and low pore fluid pressure, allows the glacier to move by sediment sliding: the base of the glacier may even remain frozen to the bed, where the underlying sediment slips underneath it like a tube of toothpaste. A hard bed cannot deform in this way; therefore the only way for hard-based glaciers to move is by basal sliding, where meltwater forms between the ice and the bed itself. Whether a bed is hard or soft depends on the porosity and pore pressure; higher porosity decreases the sediment strength (thus increases the shear stress τB).\nPorosity may vary through a range of methods. \n\nMovement of the overlying glacier may cause the bed to undergo dilatancy; the resulting shape change reorganizes blocks. This reorganizes closely packed blocks (a little like neatly folded, tightly packed clothes in a suitcase) into a messy jumble (just as clothes never fit back in when thrown in in a disordered fashion). This increases the porosity. Unless water is added, this will necessarily reduce the pore pressure (as the pore fluids have more space to occupy).\nPressure may cause compaction and consolidation of underlying sediments. Since water is relatively incompressible, this is easier when the pore space is filled with vapor; any water must be removed to permit compression. In soils, this is an irreversible process.\nSediment degradation by abrasion and fracture decreases the size of particles, which tends to decrease pore space. However, the motion of the particles may disorder the sediment, with the opposite effect. These processes also generate heat.\nBed softness may vary in space or time, and changes dramatically from glacier to glacier. An important factor is the underlying geology; glacial speeds tend to differ more when they change bedrock than when the gradient changes. Further, bed roughness can also act to slow glacial motion. The roughness of the bed is a measure of how many boulders and obstacles protrude into the overlying ice. Ice flows around these obstacles by melting under the high pressure on their stoss side; the resultant meltwater is then forced into the cavity arising in their lee side, where it re-freezes.\nAs well as affecting the sediment stress, fluid pressure (pw) can affect the friction between the glacier and the bed. High fluid pressure provides a buoyancy force upwards on the glacier, reducing the friction at its base. The fluid pressure is compared to the ice overburden pressure, pi, given by ρgh. Under fast-flowing ice streams, these two pressures will be approximately equal, with an effective pressure (pi – pw) of 30 kPa; i.e. all of the weight of the ice is supported by the underlying water, and the glacier is afloat.\n\nBasal melting and sliding\n\nGlaciers may also move by basal sliding, where the base of the glacier is lubricated by the presence of liquid water, reducing basal shear stress and allowing the glacier to slide over the terrain on which it sits. Meltwater may be produced by pressure-induced melting, friction or geothermal heat. The more variable the amount of melting at surface of the glacier, the faster the ice will flow. Basal sliding is dominant in temperate or warm-based glaciers.\n\nτD = ρgh sin α\nwhere τD is the driving stress, and α the ice surface slope in radians.\nτB is the basal shear stress, a function of bed temperature and softness.\nτF, the shear stress, is the lower of τB and τD. It controls the rate of plastic flow.\nThe presence of basal meltwater depends on both bed temperature and other factors. For instance, the melting point of water decreases under pressure, meaning that water melts at a lower temperature under thicker glaciers. This acts as a \"double whammy\", because thicker glaciers have a lower heat conductance, meaning that the basal temperature is also likely to be higher. Bed temperature tends to vary in a cyclic fashion. A cool bed has a high strength, reducing the speed of the glacier. This increases the rate of accumulation, since newly fallen snow is not transported away. Consequently, the glacier thickens, with three consequences: firstly, the bed is better insulated, allowing greater retention of geothermal heat.\nSecondly, the increased pressure can facilitate melting. Most importantly, τD is increased. These factors will combine to accelerate the glacier. As friction increases with the square of velocity, faster motion will greatly increase frictional heating, with ensuing melting – which causes a positive feedback, increasing ice speed to a faster flow rate still: west Antarctic glaciers are known to reach velocities of up to a kilometer per year.\nEventually, the ice will be surging fast enough that it begins to thin, as accumulation cannot keep up with the transport. This thinning will increase the conductive heat loss, slowing the glacier and causing freezing. This freezing will slow the glacier further, often until it is stationary, whence the cycle can begin again.\n\n \nThe flow of water under the glacial surface can have a large effect on the motion of the glacier itself. Subglacial lakes contain significant amounts of water, which can move fast: cubic kilometers can be transported between lakes over the course of a couple of years. This motion is thought to occur in two main modes: pipe flow involves liquid water moving through pipe-like conduits, like a sub-glacial river; sheet flow involves motion of water in a thin layer. A switch between the two flow conditions may be associated with surging behavior. Indeed, the loss of sub-glacial water supply has been linked with the shut-down of ice movement in the Kamb ice stream. The subglacial motion of water is expressed in the surface topography of ice sheets, which slump down into vacated subglacial lakes.\n\nSpeed\n\nThe speed of glacial displacement is partly determined by friction. Friction makes the ice at the bottom of the glacier move more slowly than ice at the top. In alpine glaciers, friction is also generated at the valley's sidewalls, which slows the edges relative to the center.\nMean glacial speed varies greatly but is typically around 1 m (3 ft) per day. There may be no motion in stagnant areas; for example, in parts of Alaska, trees can establish themselves on surface sediment deposits. In other cases, glaciers can move as fast as 20–30 m (70–100 ft) per day, such as in Greenland's Jacobshavn Isbræ. Glacial speed is affected by factors such as slope, ice thickness, snowfall, longitudinal confinement, basal temperature, meltwater production, and bed hardness.\nA few glaciers have periods of very rapid advancement called surges. These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous movement state. These surges may be caused by the failure of the underlying bedrock, the pooling of meltwater at the base of the glacier — perhaps delivered from a supraglacial lake — or the simple accumulation of mass beyond a critical \"tipping point\". Temporary rates up to 90 m (300 ft) per day have occurred when increased temperature or overlying pressure caused bottom ice to melt and water to accumulate beneath a glacier.\nIn glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur. These are large scale earthquakes that have seismic magnitudes as high as 6.1. The number of glacial earthquakes in Greenland peaks every year in July, August, and September and increased rapidly in the 1990s and 2000s. In a study using data from January 1993 through October 2005, more events were detected every year since 2002, and twice as many events were recorded in 2005 as there were in any other year.\n\nOgives\n\nOgives or Forbes bands are alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces. They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals the annual movement of the glacier. Ogives are formed when ice from an icefall is severely broken up, increasing ablation surface area during summer. This creates a swale and space for snow accumulation in the winter, which in turn creates a ridge. Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives.\n\nGeography\n\nGlaciers are present on every continent and in approximately fifty countries, excluding those (Australia, South Africa) that have glaciers only on distant subantarctic island territories. Extensive glaciers are found in Antarctica, Argentina, Chile, Canada, Pakistan, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in the Andes, the Himalayas, the Rocky Mountains, the Caucasus, Scandinavian Mountains, and the Alps. Snezhnika glacier in Pirin Mountain, Bulgaria with a latitude of 41°46′09″ N is the southernmost glacial mass in Europe. Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period. In New Guinea, small, rapidly diminishing, glaciers are located on Puncak Jaya. Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya, and in the Rwenzori Mountains. Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and Jan Mayen to the far north, New Zealand and the subantarctic islands of Marion, Heard, Grande Terre (Kerguelen) and Bouvet. During glacial periods of the Quaternary, Taiwan, Hawaii on Mauna Kea and Tenerife also had large alpine glaciers, while the Faroe and Crozet Islands were completely glaciated.\nThe permanent snow cover necessary for glacier formation is affected by factors such as the degree of slope on the land, amount of snowfall and the winds. Glaciers can be found in all latitudes except from 20° to 27° north and south of the equator where the presence of the descending limb of the Hadley circulation lowers precipitation so much that with high insolation snow lines reach above 6,500 m (21,330 ft). Between 19˚N and 19˚S, however, precipitation is higher, and the mountains above 5,000 m (16,400 ft) usually have permanent snow.\n\nEven at high latitudes, glacier formation is not inevitable. Areas of the Arctic, such as Banks Island, and the McMurdo Dry Valleys in Antarctica are considered polar deserts where glaciers cannot form because they receive little snowfall despite the bitter cold. Cold air, unlike warm air, is unable to transport much water vapor. Even during glacial periods of the Quaternary, Manchuria, lowland Siberia, and central and northern Alaska, though extraordinarily cold, had such light snowfall that glaciers could not form.\nIn addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high (4,500 to 6,900 m or 14,800 to 22,600 ft) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This is because these peaks are located near or in the hyperarid Atacama Desert.\n\nGlacial geology\n\nErosion\n\nGlaciers erode terrain through two principal processes: plucking and abrasion.\nAs glaciers flow over bedrock, they soften and lift blocks of rock into the ice. This process, called plucking, is caused by subglacial water that penetrates fractures in the bedrock and subsequently freezes and expands. This expansion causes the ice to act as a lever that loosens the rock by lifting it. Thus, sediments of all sizes become part of the glacier's load. If a retreating glacier gains enough debris, it may become a rock glacier, like the Timpanogos Glacier in Utah.\n\nAbrasion occurs when the ice and its load of rock fragments slide over bedrock and function as sandpaper, smoothing and polishing the bedrock below. The pulverized rock this process produces is called rock flour and is made up of rock grains between 0.002 and 0.00625 mm in size. Abrasion leads to steeper valley walls and mountain slopes in alpine settings, which can cause avalanches and rock slides, which add even more material to the glacier. Glacial abrasion is commonly characterized by glacial striations. Glaciers produce these when they contain large boulders that carve long scratches in the bedrock. By mapping the direction of the striations, researchers can determine the direction of the glacier's movement. Similar to striations are chatter marks, lines of crescent-shape depressions in the rock underlying a glacier. They are formed by abrasion when boulders in the glacier are repeatedly caught and released as they are dragged along the bedrock.The rate of glacier erosion varies. Six factors control erosion rate:\nVelocity of glacial movement\nThickness of the ice\nShape, abundance and hardness of rock fragments contained in the ice at the bottom of the glacier\nRelative ease of erosion of the surface under the glacier\nThermal conditions at the glacier base\nPermeability and water pressure at the glacier base\nWhen the bedrock has frequent fractures on the surface, glacial erosion rates tend to increase as plucking is the main erosive force on the surface; when the bedrock has wide gaps between sporadic fractures, however, abrasion tends to be the dominant erosive form and glacial erosion rates become slow. Glaciers in lower latitudes tend to be much more erosive than glaciers in higher latitudes, because they have more meltwater reaching the glacial bas",
    "source": "wikipedia:Glacier",
    "domain": "climate"
  },
  {
    "text": "An ice age is a term describing periods of time when the reduction in the temperature of Earth's surface and atmosphere results in the presence or expansion of continental and polar ice sheets and alpine glaciers. The term is applied in several different senses to very long and comparatively short periods of cooling. Colder periods are called glacials or ice ages, and warmer periods are called interglacials.\nEarth's climate alternates between icehouse and greenhouse periods based on whether there are glaciers on the planet, and for most of Earth's history it has been in a greenhouse period with little or no permanent ice. Over the very long term, Earth is currently in an icehouse period called the Late Cenozoic Ice Age, which started 34 million years ago. There have been colder and warmer periods within this ice age, and the term is also applied to the Quaternary glaciation, which started 2.58 million years ago. Within this period, the Last Interglacial ended 115,000 years ago, and was followed by the Last Glacial Period (LGP), which gave way to the current warm Holocene, which started 11,700 years ago. The most severe cold period of the LGP was the Last Glacial Maximum, which reached its maximum between 26,000 and 20,000 years ago. The most recent glaciation was the Younger Dryas between 12,800 and 11,700 years ago.\n\nHistory of research\n\nIn 1742, Pierre Martel (1706–1767), an engineer and geographer living in Geneva, visited the valley of Chamonix in the Alps of Savoy. Two years later he published an account of his journey. He reported that the inhabitants of that valley attributed the dispersal of erratic boulders to the glaciers, saying that they had once extended much farther. Later similar explanations were reported from other regions of the Alps. In 1815 the carpenter and chamois hunter Jean-Pierre Perraudin (1767–1858) explained erratic boulders in the Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further. An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss-German geologist Jean de Charpentier (1786–1855) in 1834. Comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland and in Goethe's scientific work. Such explanations could also be found in other parts of the world. When the Bavarian naturalist Ernst von Bibra (1806–1878) visited the Chilean Andes in 1849–1850, the natives attributed fossil moraines to the former action of glaciers.\nMeanwhile, European scholars had begun to wonder what had caused the dispersal of erratic material. From the middle of the 18th century, some discussed ice as a means of transport. The Swedish mining expert Daniel Tilas (1712–1772) was, in 1742, the first person to suggest drifting sea ice was a cause of the presence of erratic boulders in the Scandinavian and Baltic regions. In 1795, the Scottish philosopher and gentleman naturalist, James Hutton (1726–1797), explained erratic boulders in the Alps by the action of glaciers. Two decades later, in 1818, the Swedish botanist Göran Wahlenberg (1780–1851) published his theory of a glaciation of the Scandinavian peninsula. He regarded glaciation as a regional phenomenon.\n\nOnly a few years later, the Danish-Norwegian geologist Jens Esmark (1762–1839) argued for a sequence of worldwide ice ages. In a paper published in 1824, Esmark proposed changes in climate as the cause of those glaciations. He attempted to show that they originated from changes in Earth's orbit. Esmark discovered the similarity between moraines near Haukalivatnet lake near sea level in Rogaland and moraines at branches of Jostedalsbreen. Esmark's discovery were later attributed to or appropriated by Theodor Kjerulf and Louis Agassiz.\nDuring the following years, Esmark's ideas were discussed and taken over in parts by Swedish, Scottish and German scientists. At the University of Edinburgh Robert Jameson (1774–1854) seemed to be relatively open to Esmark's ideas, as reviewed by Norwegian professor of glaciology Bjørn G. Andersen (1992). Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark. In Germany, Albrecht Reinhard Bernhardi (1797–1849), a geologist and professor of forestry at an academy in Dreissigacker (since incorporated in the southern Thuringian city of Meiningen), adopted Esmark's theory. In a paper published in 1832, Bernhardi speculated about the polar ice caps once reaching as far as the temperate zones of the globe.\nIn Val de Bagnes, a valley in the Swiss Alps, there was a long-held local belief that the valley had once been covered deep in ice, and in 1815 a local chamois hunter called Jean-Pierre Perraudin attempted to convert the geologist Jean de Charpentier to the idea, pointing to deep striations in the rocks and giant erratic boulders as evidence. Charpentier held the general view that these signs were caused by vast floods, and he rejected Perraudin's theory as absurd. In 1818 the engineer Ignatz Venetz joined Perraudin and Charpentier to examine a proglacial lake above the valley created by an ice dam as a result of the 1815 eruption of Mount Tambora, which threatened to cause a catastrophic flood when the dam broke. Perraudin attempted unsuccessfully to convert his companions to his theory, but when the dam finally broke, there were only minor erratics and no striations, and Venetz concluded that Perraudin was right and that only ice could have caused such major results. In 1821 he read a prize-winning paper on the theory to the Swiss Society, but it was not published until Charpentier, who had also become converted, published it with his own more widely read paper in 1834.\nIn the meantime, the German botanist Karl Friedrich Schimper (1803–1867) was studying mosses which were growing on erratic boulders in the alpine upland of Bavaria. He began to wonder where such masses of stone had come from. During the summer of 1835 he made some excursions to the Bavarian Alps. Schimper came to the conclusion that ice must have been the means of transport for the boulders in the alpine upland. In the winter of 1835–36 he held some lectures in Munich. Schimper then assumed that there must have been global times of obliteration (\"Verödungszeiten\") with a cold climate and frozen water. Schimper spent the summer months of 1836 at Devens, near Bex, in the Swiss Alps with his former university friend Louis Agassiz (1801–1873) and Jean de Charpentier. Schimper, Charpentier and possibly Venetz convinced Agassiz that there had been a time of glaciation. During the winter of 1836–37, Agassiz and Schimper developed the theory of a sequence of glaciations. They mainly drew upon the preceding works of Venetz, Charpentier and on their own fieldwork. Agassiz appears to have been already familiar with Bernhardi's paper at that time. At the beginning of 1837, Schimper coined the term \"ice age\" (\"Eiszeit\") for the period of the glaciers. In July 1837 Agassiz presented their synthesis before the annual meeting of the Swiss Society for Natural Research at Neuchâtel. The audience was very critical, and some were opposed to the new theory because it contradicted the established opinions on climatic history. Most contemporary scientists thought that Earth had been gradually cooling down since its birth as a molten globe.\nIn order to persuade the skeptics, Agassiz embarked on geological fieldwork. He published his book Study on Glaciers (\"Études sur les glaciers\") in 1840. Charpentier was put out by this, as he had also been preparing a book about the glaciation of the Alps. Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in-depth glacial research. As a result of personal quarrels, Agassiz had also omitted any mention of Schimper in his book.\nIt took several decades before the ice age theory was fully accepted by scientists. This happened on an international scale in the second half of the 1870s, following the work of James Croll, including the publication of Climate and Time, in Their Geological Relations in 1875, which provided a credible explanation for the causes of ice ages.\n\nEvidence\nThere are three main types of evidence for ice ages: geological, chemical, and paleontological.\nGeological evidence for ice ages comes in various forms, including rock scouring and scratching, glacial moraines, drumlins, valley cutting, and the deposition of till or tillites and glacial erratics. Successive glaciations tend to distort and erase the geological evidence for earlier glaciations, making it difficult to interpret. Furthermore, this evidence was difficult to date exactly; early theories assumed that the glacials were short compared to the long interglacials. The advent of sediment and ice cores revealed the true situation: glacials are long, interglacials short. It took some time for the current theory to be worked out.\nThe chemical evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks and ocean sediment cores. For the most recent glacial periods, ice cores provide climate proxies, both from the ice itself and from atmospheric samples provided by included bubbles of air. Because water containing lighter isotopes has a lower heat of evaporation, its proportion decreases with warmer conditions. This allows a temperature record to be constructed. This evidence can be confounded, however, by other factors recorded by isotope ratios.\nThe paleontological evidence consists of changes in the geographical distribution of fossils. During a glacial period, cold-adapted organisms spread into lower latitudes, and organisms that prefer warmer conditions become extinct or retreat into lower latitudes. This evidence is also difficult to interpret because it requires:\n\nsequences of sediments covering a long period of time, over a wide range of latitudes and which are easily correlated;\nancient organisms which survive for several million years without change and whose temperature preferences are easily diagnosed; and\nthe finding of the relevant fossils.\nDespite the difficulties, analysis of ice core and ocean sediment cores has provided a credible record of glacials and interglacials over the past few million years. These also confirm the linkage between ice ages and continental crust phenomena such as glacial moraines, drumlins, and glacial erratics. Hence the continental crust phenomena are accepted as good evidence of earlier ice ages when they are found in layers created much earlier than the time range for which ice cores and ocean sediment cores are available.\n\nMajor ice ages\n\nThere have been at least five major ice ages in Earth's history (the Huronian, Cryogenian, Andean-Saharan, late Paleozoic, and the latest Quaternary Ice Age). Outside these ages, Earth was previously thought to have been ice-free even in high latitudes; such periods are known as greenhouse periods. However, other studies dispute this, finding evidence of occasional glaciations at high latitudes even during apparent greenhouse periods.\n\nRocks from the earliest well-established ice age, called the Huronian, have been dated to around 2.4 to 2.1 billion years ago during the early Proterozoic Eon. Several hundreds of kilometers of the Huronian Supergroup are exposed 10 to 100 kilometers (6 to 62 mi) north of the north shore of Lake Huron, extending from near Sault Ste. Marie to Sudbury, northeast of Lake Huron, with giant layers of now-lithified till beds, dropstones, varves, outwash, and scoured basement rocks. Correlative Huronian deposits have been found near Marquette, Michigan, and correlation has been made with Paleoproterozoic glacial deposits from Western Australia. The Huronian ice age was caused by the elimination of atmospheric methane, a greenhouse gas, during the Great Oxygenation Event.\nThe next well-documented ice age, and probably the most severe of the last billion years, occurred from 720 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which glacial ice sheets reached the equator, possibly being ended by the accumulation of greenhouse gases such as CO2 produced by volcanoes. \"The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis, which are the two major sinks for CO2 at present.\" It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian explosion, though this model is recent and controversial.\nThe Andean-Saharan occurred from 460 to 420 million years ago, during the Late Ordovician and the Silurian period.\n\nThe evolution of land plants at the onset of the Devonian period caused a long term increase in planetary oxygen levels and reduction of CO2 levels, which resulted in the late Paleozoic icehouse. Its former name, the Karoo glaciation, was named after the glacial tills found in the Karoo region of South Africa. There were extensive polar ice caps at intervals from 360 to 260 million years ago in South Africa during the Carboniferous and early Permian periods. Correlatives are known from Argentina, also in the center of the ancient supercontinent Gondwanaland.\nAlthough the Mesozoic Era retained a greenhouse climate over its timespan and was previously assumed to have been entirely glaciation-free, more recent studies suggest that brief periods of glaciation occurred in both hemispheres during the Early Cretaceous. Geologic and palaeoclimatological records suggest the existence of glacial periods during the Valanginian, Hauterivian, and Aptian stages of the Early Cretaceous. Ice-rafted glacial dropstones indicate that in the Northern Hemisphere, ice sheets may have extended as far south as the Iberian Peninsula during the Hauterivian and Aptian. Although ice sheets largely disappeared from Earth for the rest of the period (potential reports from the Turonian, otherwise the warmest period of the Phanerozoic, are disputed), ice sheets and associated sea ice appear to have briefly returned to Antarctica near the very end of the Maastrichtian just prior to the Cretaceous-Paleogene extinction event.\nThe Quaternary Glaciation / Quaternary Ice Age started about 2.58 million years ago at the beginning of the Quaternary Period when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods, glacials or glacial advances, and interglacial periods, interglacials or glacial retreats. Earth is currently in an interglacial, and the last glacial period ended about 11,700 years ago. All that remains of the continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island.\nThe definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic (Eocene-Oligocene Boundary). The term Late Cenozoic Ice Age is used to include this early phase.\nIce ages can be further divided by location and time; for example, the names Riss (180,000–130,000 years bp) and Würm (70,000–10,000 years bp) refer specifically to glaciation in the Alpine region. The maximum extent of the ice is not maintained for the full interval. The scouring action of each glaciation tends to remove most of the evidence of prior ice sheets almost completely, except in regions where the later sheet does not achieve full coverage.\n\nGlacials and interglacials\n\nWithin the current glaciation, more temperate and more severe periods have occurred. The colder periods are called glacial periods, the warmer periods interglacials, such as the Eemian Stage. There is evidence that similar glacial cycles occurred in previous glaciations, including the Andean-Saharan and the late Paleozoic ice house. The glacial cycles of the late Paleozoic ice house are likely responsible for the deposition of cyclothems.\nGlacials are characterized by cooler and drier climates over most of Earth and large land and sea ice masses extending outward from the poles. Mountain glaciers in otherwise unglaciated areas extend to lower elevations due to a lower snow line. Sea levels drop due to the removal of large volumes of water above sea level in the icecaps. There is evidence that ocean circulation patterns are disrupted by glaciations. The glacials and interglacials coincide with changes in orbital forcing of climate due to Milankovitch cycles, which are periodic changes in Earth's orbit and the tilt of Earth's rotational axis.\nEarth has been in an interglacial period known as the Holocene for around 11,700 years, and an article in Nature in 2004 argues that it might be most analogous to a previous interglacial that lasted 28,000 years. Predicted changes in orbital forcing suggest that the next glacial period would begin at least 50,000 years from now. Moreover, anthropogenic forcing from increased greenhouse gases is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years.\n\nFeedback processes\nEach glacial period is subject to positive feedback mechanisms, which makes it more severe, and negative feedback which dampens the overall climate response to different types of forcing. In the case of Quaternary ice ages, Earth's high albedo from ice sheets and atmospheric dust as well as low concentrations of atmospheric CO2 contributed to cold glacial climates.\n\nPositive\nAn important form of feedback is provided by Earth's albedo, which is how much of the sun's energy is reflected rather than absorbed by Earth. Ice and snow increase Earth's albedo, while forests reduce its albedo. When the air temperature decreases, ice and snow fields grow, and they reduce forest cover. This continues until competition with a negative feedback mechanism forces the system to an equilibrium.\nOne theory is that when glaciers form, two things happen: the ice grinds rocks into dust, and the land becomes dry and arid. This allows winds to transport iron rich dust into the open ocean, where it acts as a fertilizer that causes massive algal blooms that pulls large amounts of CO2 out of the atmosphere. This in turn makes it even colder and causes the glaciers to grow more.\nIn 1956, Ewing and Donn hypothesized that an ice-free Arctic Ocean leads to increased snowfall at high latitudes. When low-temperature ice covers the Arctic Ocean there is little evaporation or sublimation and the polar regions are quite dry in terms of precipitation, comparable to the amount found in mid-latitude deserts. This low precipitation allows high-latitude snowfalls to melt during the summer. An ice-free Arctic Ocean absorbs solar radiation during the long summer days, and evaporates more water into the Arctic atmosphere. With higher precipitation, portions of this snow may not melt during the summer and so glacial ice can form at lower altitudes and more southerly latitudes, reducing the temperatures over land by increased albedo as noted above. Furthermore, under this hypothesis the lack of oceanic pack ice allows increased exchange of waters between the Arctic and the North Atlantic Oceans, warming the Arctic and cooling the North Atlantic. (Current projected consequences of global warming include a brief ice-free Arctic Ocean period by 2050.) Additional fresh water flowing into the North Atlantic during a warming cycle may also reduce the global ocean water circulation. Such a reduction (by reducing the effects of the Gulf Stream) would have a cooling effect on northern Europe, which in turn would lead to increased low-latitude snow retention during the summer. It has also been suggested that during an extensive glacial, glaciers may move through the Gulf of Saint Lawrence, extending into the North Atlantic Ocean far enough to block the Gulf Stream.\n\nNegative\nIce sheets that form during glaciations erode the land beneath them. This can reduce the land area above sea level and thus diminish the amount of space on which ice sheets can form. This mitigates the albedo feedback, as does the rise in sea level that accompanies the reduced area of ice sheets, since open ocean has a lower albedo than land.\nAnother negative feedback mechanism is the increased aridity occurring with glacial maxima, which reduces the precipitation available to maintain glaciation. The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances.\nAccording to research published in Nature Geoscience, human emissions of carbon dioxide (CO2) will defer the next glacial period. Researchers used data on Earth's orbit to find the historical warm interglacial period that looks most like the current one and from this have predicted that the next glacial period would usually begin within 1,500 years. They go on to predict that emissions have been so high that it will not.\n\nCauses\nThe causes of ice ages are not fully understood for either the large-scale ice age periods or the smaller ebb and flow of glacial–interglacial periods within an ice age. The consensus is that several factors are important: atmospheric composition, such as the concentrations of carbon dioxide and methane (the specific levels of the previously mentioned gases are now able to be seen with the new ice core samples from the European Project for Ice Coring in Antarctica (EPICA) Dome C in Antarctica over the past 800,000 years); changes in Earth's orbit around the Sun known as Milankovitch cycles; the motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on Earth's surface, which affect wind and ocean currents; variations in solar output; the orbital dynamics of the Earth–Moon system; the impact of relatively large meteorites and volcanism including eruptions of supervolcanoes.\nSome of these factors influence each other. For example, changes in Earth's atmospheric composition (especially the concentrations of greenhouse gases) may alter the climate, while climate change itself can change the atmospheric composition (for example by changing the rate at which weathering removes CO2).\nMaureen Raymo, William Ruddiman and others propose that the Tibetan and Colorado Plateaus are immense CO2 \"scrubbers\" with a capacity to remove enough CO2 from the global atmosphere to be a significant causal factor of the 40 million year Cenozoic Cooling trend. They further claim that approximately half of their uplift (and CO2 \"scrubbing\" capacity) occurred in the past 10 million years.\n\nChanges in Earth's atmosphere\nThere is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets, but it is difficult to establish cause and effect (see the notes above on the role of weathering). Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages, such as the movement of continents and volcanism.\nThe Snowball Earth hypothesis maintains that the severe freezing in the late Proterozoic was ended by an increase in CO2 levels in the atmosphere, mainly from volcanoes, and some supporters of Snowball Earth argue that it was caused in the first place by a reduction in atmospheric CO2. The hypothesis also warns of future Snowball Earths.\nIn 2009, further evidence was provided that changes in solar insolation provide the initial trigger for Earth to warm after an Ice Age, with secondary factors like increases in greenhouse gases accounting for the magnitude of the change.\n\nPosition of the continents\nThe geological record appears to show that ice ages start when the continents are in positions which block or reduce the flow of warm water from the equator to the poles and thus allow ice sheets to form. The ice sheets increase Earth's reflectivity and thus reduce the absorption of solar radiation. With less radiation absorbed the atmosphere cools; the cooling allows the ice sheets to grow, which further increases reflectivity in a positive feedback loop. The ice age continues until the reduction in weathering causes an increase in the greenhouse effect.\nThere are three main contributors from the layout of the continents that obstruct the movement of warm water to the poles:\n\nA continent sits on top of a pole, as Antarctica does today.\nA polar sea is almost land-locked, as the Arctic Ocean is today.\nA supercontinent covers most of the equator, as Rodinia did during the Cryogenian period.\nSince today's Earth has a continent over the South Pole and an almost land-locked ocean over the North Pole, geologists believe that Earth will continue to experience glacial periods in the geologically near future.\nSome scientists believe that the Himalayas are a major factor in the current ice age, because these mountains have increased Earth's total rainfall and therefore the rate at which carbon dioxide is washed out of the atmosphere, decreasing the greenhouse effect. The Himalayas' formation started about 70 million years ago when the Indo-Australian Plate collided with the Eurasian Plate, and the Himalayas are still rising by about 5 mm per year because the Indo-Australian plate is still moving at 67 mm/year. The history of the Himalayas broadly fits the long-term decrease in Earth's average temperature since the mid-Eocene, 40 million years ago.\n\nFluctuations in ocean currents\n\nAnother important contribution to ancient climate regimes is the variation of ocean currents, which are modified by continent position, sea levels and salinity, as well as other factors. They have the ability to cool (e.g. aiding the creation of Antarctic ice) and the ability to warm (e.g. giving the British Isles a temperate as opposed to a boreal climate). The closing of the Isthmus of Panama about 3 million years ago may have ushered in the present period of strong glaciation over North America by ending the exchange of water between the tropical Atlantic and Pacific Oceans.\nAnalyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations. During the last glacial period the sea-level fluctuated 20 to 30 metres (66 to 98 ft) as water was sequestered, primarily in the Northern Hemisphere ice sheets. When ice collected and the sea level dropped sufficiently, flow through the Bering Strait (the narrow strait between Siberia and Alaska is about 50 metres – 165 feet – deep today) was reduced, resulting in increased flow from the North Atlantic. This realigned the thermohaline circulation in the Atlantic, increasing heat transport into the Arctic, which melted the polar ice accumulation and reduced other continental ice sheets. The release of water raised sea levels again, restoring the ingress of colder water from the Pacific with an accompanying shift to northern hemisphere ice accumulation.\nAccording to a study published in Nature in 2021, all glacial periods of ice ages over the last 1.5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns, leading to more CO2 being pulled out of the atmosphere. The authors suggest that this process may be disrupted in the future as the Southern Ocean will become too warm for the icebergs to travel far enough to trigger these changes.\n\nUplift of the Tibetan plateau\nMatthias Kuhle's geological theory of Ice Age development was suggested by the existence of an ice sheet covering the Tibetan Plateau during the Ice Ages (Last Glacial Maximum?). According to Kuhle, the plate-tectonic uplift of Tibet past the snow-line has led to a surface of c. 2,400,000 square kilometres (930,000 sq mi) changing from bare land to ice with a 70% greater albedo. The reflection of energy into space resulted in a global cooling, triggering the Pleistocene Ice Age. Because this highland is at a subtropical latitude, with four to five times the insolation of high-latitude areas, what would be Earth's strongest heating surface has turned into a cooling surface.\nKuhle explains the interglacial periods by the 100,000-year cycle of radiation changes due to variations in Earth's orbit. This comparatively insignificant warming, when combined with the lowering of the Nordic inland ice areas and Tibet due to the weight of the superimposed ice-load, has led to the repeated complete thawing of the inland ice areas.\n\nVariations in Earth's orbit\n\nThe Milankovitch cycles are a set of cyclic variations in characteristics of Earth's orbit around the Sun. Each cycle has a different length, so at some times their effects reinforce each other and at other times they (partially) cancel each other.\nThere is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. The present ice age is the most studied and best understood, particularly the last 400,000 years, since this is the period covered by ice cores that record atmospheric composition and proxies for temperature and ice volume. Within this period, the match of glacial/interglacial frequencies to the Milanković orbital forcing periods is so close that orbital forcing is generally accepted. The combined effects of the changing distance to the Sun, the precession of Earth's axis, and the changing tilt of Earth's axis redistribute the sunlight received by Earth. Of particular importance are changes in the tilt of Earth's axis, which affect the intensity of seasons. For example, the amount of solar influx in July at 65 degrees north latitude varies by as much as 22% (from 450 W/m2 to 550 W/m2). It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter. Some believe that the strength of the orbital forcing is too small to tri",
    "source": "wikipedia:Ice age",
    "domain": "climate"
  },
  {
    "text": "The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about 85,133,000 square kilometers (32,870,000 sq mi). It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for separating the New World of the Americas (North America and South America) from the Old World of Afro-Eurasia (Africa, Asia, and Europe).\nThrough its separation of Afro-Eurasia from the Americas, the Atlantic Ocean has played a central role in the development of human society, globalization, and the histories of many nations. While the Norse were the first known humans to cross the Atlantic, it was the expedition of Christopher Columbus in 1492 that proved to be the most consequential. Columbus's expedition ushered in an age of exploration and colonization of the Americas by European powers, most notably Portugal, Spain, France, and the United Kingdom. From the 16th to 19th centuries, the Atlantic Ocean was the center of both an eponymous slave trade and the Columbian exchange while occasionally hosting naval battles. Such naval battles, as well as growing trade from regional American powers like the United States and Brazil, both increased in degree during the early 20th century. After World War II, major military operations became rarer, though notable postwar conflicts include the Cuban Missile Crisis and the Falklands War. The ocean remains a core component of trade around the world.\nThe Atlantic Ocean's temperatures vary by location. For example, the South Atlantic maintains warm temperatures year-round, as its basin countries are tropical. The North Atlantic maintains a temperate climate, as its basin countries are temperate and have seasons of extremely low temperatures and high temperatures.\nThe Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and the Americas to the west. As one component of the interconnected World Ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south. Other definitions describe the Atlantic as extending southward to Antarctica. The Atlantic Ocean is divided in two parts, the northern and southern Atlantic, by the Equator.\n\nNames\n\nThe oldest known mentions of an \"Atlantic\" sea come from Stesichorus around mid-sixth century BC (Sch. A. R. 1. 211): Atlantikôi pelágei (Ancient Greek: Ἀτλαντικῷ πελάγει, 'the Atlantic sea', etym. 'Sea of Atlas') and in The Histories of Herodotus around 450 BC (Hdt. 1.202.4): Atlantis thalassa (Ancient Greek: Ἀτλαντὶς θάλασσα, 'Sea of Atlas' or 'the Atlantic sea'), where the name refers to \"the sea beyond the pillars of Hercules\" (the Strait of Gibraltar), beyond the Atlas Mountains in Morocco and off the West African coast. In these uses, the name refers to Atlas, the Titan in Greek mythology, who supported the heavens and who later appeared as a frontispiece in medieval maps and atlases. \nEarly Greek sailors believed the Atlantic to be part of the Oceanus, the great sea or river that surrounds all land, mentioned in ancient Greek mythological literature such as the Iliad and Odyssey. This was in contrast to the enclosed seas well known to the Greeks, the Mediterranean and the Black Sea. The great ocean was believed to stretch around Africa, leading to the term \"Aethiopian Ocean\", derived from Ancient Ethiopia, applied to the southern Atlantic as late as the mid-19th century. \nDuring the Age of Discovery, the Atlantic was also known to English cartographers as the Great Western Ocean.\n\nThe pond is a humorous term often used by British and American speakers in reference to the northern Atlantic Ocean (an example of meiosis, ironic understatement). It is used mostly when referring to events or circumstances \"on this side of the pond\" or \"on the other side of the pond\" or \"across the pond\", emphasizing the connection and division between Britain and its former colonies, rather than to discuss the ocean itself. The term dates to 1640, first appearing in print in a pamphlet released during the reign of Charles I, and reproduced in 1869 in Nehemiah Wallington's Historical Notices of Events Occurring Chiefly in The Reign of Charles I, where \"great Pond\" is used in reference to the Atlantic Ocean by Francis Windebank, Charles I's Secretary of State.\n\nExtent and data\n\nThe International Hydrographic Organization (IHO) defined the limits of the oceans and seas in 1953, but some of these definitions have been revised since then and some are not recognized by various authorities, institutions, and countries, such as the CIA World Factbook, for example. Correspondingly, the extent and number of oceans and seas vary.\nThe Atlantic Ocean is bounded on the west by North and South America. It connects to the Arctic Ocean through the Labrador Sea, Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea with the northern divider passing through Iceland and Svalbard. To the east, the boundaries of the ocean proper are Europe and Africa: the Strait of Gibraltar (where it connects with the Mediterranean Sea – one of its marginal seas – and, in turn, the Black Sea, both of which also touch upon Asia).\nIn the southeast, the Atlantic merges into the Indian Ocean. The 20° East meridian, running south from Cape Agulhas to Antarctica defines its border. In the 1953 definition it extends south to Antarctica, while in later maps it is bounded at the 60° parallel by the Southern Ocean.\nThe Atlantic has irregular coasts indented by numerous bays, gulfs and seas. These include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, part of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea, almost all of the Scotia Sea, and other tributary water bodies. Including these marginal seas the coast line of the Atlantic measures 111,866 km (69,510 mi) compared to 135,663 km (84,297 mi) for the Pacific.\nIncluding its marginal seas, the Atlantic covers an area of 106,460,000 km2 (41,100,000 sq mi) or 23.5% of the global ocean and has a volume of 310,410,900 km3 (74,471,500 cu mi) or 23.3% of the total volume of the Earth's oceans. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 (31,570,000 sq mi) and has a volume of 305,811,900 km3 (73,368,200 cu mi). The North Atlantic covers 41,490,000 km2 (16,020,000 sq mi) (11.5%) and the South Atlantic 40,270,000 km2 (15,550,000 sq mi) (11.1%). The average depth is 3,646 m (11,962 ft) and the maximum depth, the Milwaukee Deep in the Puerto Rico Trench, is 8,376 m (27,480 ft).\n\nBathymetry\n\nThe bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge (MAR). It runs from 87°N or 300 km (190 mi) south of the North Pole to the subantarctic Bouvet Island at 54°S. Expeditions to explore the bathymertry of the Atlantic include the Challenger expedition and the German Meteor expedition; as of 2001, Columbia University's Lamont–Doherty Earth Observatory and the United States Navy Hydrographic Office conduct research on the ocean.\n\nMid-Atlantic Ridge\n\nThe MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2,000 m (6,600 ft) along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs fracture zone at 53°N. The MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other.\nThe MAR rises 2–3 km (1.2–1.9 mi) above the surrounding ocean floor and its rift valley is the divergent boundary between the North American and Eurasian plates in the North Atlantic and the South American and African plates in the South Atlantic. The MAR produces basaltic volcanoes in Eyjafjallajökull, Iceland, and pillow lava on the ocean floor. The depth of water at the apex of the ridge is less than 2,700 m (1,500 fathoms; 8,900 ft) in most places, while the bottom of the ridge is three times as deep.\nThe MAR is intersected by two perpendicular ridges: the Azores–Gibraltar transform fault, the boundary between the Nubian and Eurasian plates, intersects the MAR at the Azores triple junction, on either side of the Azores microplate, near the 40°N. A much vaguer, nameless boundary, between the North American and South American plates, intersects the MAR near or just north of the Fifteen-Twenty fracture zone, approximately at 16°N.\nIn the 1870s, the Challenger expedition discovered parts of what is now known as the Mid-Atlantic Ridge, or:\n\nAn elevated ridge rising to an average height of about 1,900 fathoms [3,500 m; 11,400 ft] below the surface traverses the basins of the North and South Atlantic in a meridianal direction from Cape Farewell, probably its far south at least as Gough Island, following roughly the outlines of the coasts of the Old and the New Worlds. The remainder of the ridge was discovered in the 1920s by the German Meteor expedition using echo-sounding equipment. The exploration of the MAR in the 1950s led to the general acceptance of seafloor spreading and plate tectonics.\nMost of the MAR runs under water but where it reaches the surfaces it has produced volcanic islands. While nine of these have collectively been nominated a World Heritage Site for their geological value, four of them are considered of \"Outstanding Universal Value\" based on their cultural and natural criteria: Þingvellir, Iceland; Landscape of the Pico Island Vineyard Culture, Portugal; Gough and Inaccessible Islands, United Kingdom; and Brazilian Atlantic Islands: Fernando de Noronha and Atol das Rocas Reserves, Brazil.\n\nOcean floor\n\nContinental shelves in the Atlantic are wide off Newfoundland, southernmost South America, and northeastern Europe.\nIn the western Atlantic carbonate platforms dominate large areas, for example, the Blake Plateau and Bermuda Rise.\nThe Atlantic is surrounded by passive margins except at a few locations where active margins form deep trenches: the Puerto Rico Trench (8,376 m or 27,480 ft maximum depth) in the western Atlantic and South Sandwich Trench (8,264 m or 27,113 ft) in the South Atlantic. There are numerous submarine canyons off northeastern North America, western Europe, and northwestern Africa. Some of these canyons extend along the continental rises and farther into the abyssal plains as deep-sea channels.\nIn 1922, a historic moment in cartography and oceanography occurred. The USS Stewart used a Navy Sonic Depth Finder to draw a continuous map across the bed of the Atlantic. This involved little guesswork because the idea of sonar is straightforward with pulses being sent from the vessel, which bounce off the ocean floor, then return to the vessel. The deep ocean floor is thought to be fairly flat with occasional deeps, abyssal plains, trenches, seamounts, basins, plateaus, canyons, and some guyots. Various shelves along the margins of the continents constitute about 11% of the bottom topography with few deep channels cut across the continental rise.\nThe mean depth between 60°N and 60°S is 3,730 m (12,240 ft), or close to the average for the global ocean, with a modal depth between 4,000 and 5,000 m (13,000 and 16,000 ft).\nIn the South Atlantic the Walvis Ridge and Rio Grande Rise form barriers to ocean currents.\nThe Laurentian Abyss is found off the eastern coast of Canada.\n\nWater characteristics\n\nSurface water temperatures, which vary with latitude, current systems, and season and reflect the latitudinal distribution of solar energy, range from below −2 °C (28 °F) to over 30 °C (86 °F). Maximum temperatures occur north of the equator, and minimum values are found in the polar regions. In the middle latitudes, the area of maximum temperature variations, values may vary by 7–8 °C (13–14 °F).\nFrom October to June the surface is usually covered with sea ice in the Labrador Sea, Denmark Strait, and Baltic Sea.\nThe Coriolis effect circulates North Atlantic water in a clockwise direction, whereas South Atlantic water circulates counter-clockwise. The south tides in the Atlantic Ocean are semi-diurnal; that is, two high tides occur every 24 lunar hours. In latitudes above 40° North some east–west oscillation, known as the North Atlantic oscillation, occurs.\n\nSalinity\nOn average, the Atlantic is the saltiest major ocean; surface water salinity in the open ocean ranges from 33 to 37 parts per thousand (3.3–3.7%) by mass and varies with latitude and season. Evaporation, precipitation, river inflow and sea ice melting influence surface salinity values. Although the lowest salinity values are just north of the equator (because of heavy tropical rainfall), in general, the lowest values are in the high latitudes and along coasts where large rivers enter. Maximum salinity values occur at about 25° north and south, in subtropical regions with low rainfall and high evaporation.\nThe high surface salinity in the Atlantic, on which the Atlantic thermohaline circulation is dependent, is maintained by two processes. The Agulhas Leakage/Rings brings salty Indian Ocean waters into the South Atlantic. While the \"Atmospheric Bridge\" evaporates subtropical Atlantic waters and exports it to the Pacific.\n\nWater masses\n\nThe Atlantic Ocean consists of four major, upper water masses with distinct temperature and salinity. The Atlantic subarctic upper water in the northernmost North Atlantic is the source for subarctic intermediate water and North Atlantic intermediate water. North Atlantic central water can be divided into the eastern and western North Atlantic central water since the western part is strongly affected by the Gulf Stream and therefore the upper layer is closer to underlying fresher subpolar intermediate water. The eastern water is saltier because of its proximity to Mediterranean water. North Atlantic central water flows into South Atlantic central water at 15°N.\nThere are five intermediate waters: four low-salinity waters formed at subpolar latitudes and one high-salinity formed through evaporation. Arctic intermediate water flows from the north to become the source for North Atlantic deep water, south of the Greenland-Scotland sill. These two intermediate waters have different salinity in the western and eastern basins. The wide range of salinities in the North Atlantic is caused by the asymmetry of the northern subtropical gyre and a large number of contributions from a wide range of sources: Labrador Sea, Norwegian-Greenland Sea, Mediterranean, and South Atlantic Intermediate Water.\nThe North Atlantic deep water (NADW) is a complex of four water masses, two that form by deep convection in the open ocean – classical and upper Labrador sea water – and two that form from the inflow of dense water across the Greenland-Iceland-Scotland sill – Denmark Strait and Iceland-Scotland overflow water. Along its path across Earth the composition of the NADW is affected by other water masses, especially Antarctic bottom water and Mediterranean overflow water.\nThe NADW is fed by a flow of warm shallow water into the northern North Atlantic which is responsible for the anomalous warm climate in Europe. Changes in the formation of NADW have been linked to global climate changes in the past. Since human-made substances were introduced into the environment, the path of the NADW can be traced throughout its course by measuring tritium and radiocarbon from nuclear weapon tests in the 1960s and CFCs.\n\nGyres\n\nThe clockwise warm-water North Atlantic Gyre occupies the northern Atlantic, and the counter-clockwise warm-water South Atlantic Gyre appears in the southern Atlantic.\nIn the North Atlantic, surface circulation is dominated by three inter-connected currents: the Gulf Stream which flows north-east from the North American coast at Cape Hatteras; the North Atlantic Current, a branch of the Gulf Stream which flows northward from the Grand Banks; and the Subpolar Front, an extension of the North Atlantic Current, a wide, vaguely defined region separating the subtropical gyre from the subpolar gyre. This system of currents transports warm water into the North Atlantic, without which temperatures in the North Atlantic and Europe would plunge dramatically.\n\nNorth of the North Atlantic Gyre, the cyclonic North Atlantic Subpolar Gyre plays a key role in climate variability. It is governed by ocean currents from marginal seas and regional topography, rather than being steered by wind, both in the deep ocean and at sea level.\nThe subpolar gyre forms an important part of the global thermohaline circulation. Its eastern portion includes eddying branches of the North Atlantic Current which transport warm, saline waters from the subtropics to the northeastern Atlantic. There this water is cooled during winter and forms return currents that merge along the eastern continental slope of Greenland where they form an intense (40–50 Sv) current which flows around the continental margins of the Labrador Sea. A third of this water becomes part of the deep portion of the North Atlantic Deep Water (NADW). The NADW, in turn, feeds the meridional overturning circulation (MOC), the northward heat transport of which is threatened by anthropogenic climate change. Large variations in the subpolar gyre on a decade-century scale, associated with the North Atlantic oscillation, are especially pronounced in Labrador Sea Water, the upper layers of the MOC.\nThe South Atlantic is dominated by the anti-cyclonic southern subtropical gyre. The South Atlantic Central Water originates in this gyre, while Antarctic Intermediate Water originates in the upper layers of the circumpolar region, near the Drake Passage and the Falkland Islands. Both these currents receive some contribution from the Indian Ocean. On the African east coast, the small cyclonic Angola Gyre lies embedded in the large subtropical gyre.\nThe southern subtropical gyre is partly masked by a wind-induced Ekman layer. The residence time of the gyre is 4.4–8.5 years. North Atlantic Deep Water flows southward below the thermocline of the subtropical gyre.\n\nSargasso Sea\n\nThe Sargasso Sea in the western North Atlantic can be defined as the area where two species of Sargassum (S. fluitans and natans) float, an area 4,000 km (2,500 mi) wide and encircled by the Gulf Stream, North Atlantic Drift, and North Equatorial Current. This population of seaweed probably originated from Tertiary ancestors on the European shores of the former Tethys Ocean and has, if so, maintained itself by vegetative growth, floating in the ocean for millions of years.\nOther species endemic to the Sargasso Sea include the sargassum fish, a predator with algae-like appendages which hovers motionless among the Sargassum. Fossils of similar fishes have been found in fossil bays of the former Tethys Ocean, in what is now the Carpathian region, that were similar to the Sargasso Sea. It is possible that the population in the Sargasso Sea migrated to the Atlantic as the Tethys closed at the end of the Miocene around 17 Ma. The origin of the Sargasso fauna and flora remained enigmatic for centuries. The fossils found in the Carpathians in the mid-20th century often called the \"quasi-Sargasso assemblage\", finally showed that this assemblage originated in the Carpathian Basin from where it migrated over Sicily to the central Atlantic where it evolved into modern species of the Sargasso Sea.\nThe location of the spawning ground for European eels remained unknown for decades. In the early 19th century it was discovered that the southern Sargasso Sea is the spawning ground for both the European and American eel and that the former migrate more than 5,000 km (3,100 mi) and the latter 2,000 km (1,200 mi). Ocean currents such as the Gulf Stream transport eel larvae from the Sargasso Sea to foraging areas in North America, Europe, and northern Africa. Recent but disputed research suggests that eels possibly use Earth's magnetic field to navigate through the ocean both as larvae and as adults.\n\nClimate\n\nThe climate is influenced by the temperatures of the surface waters and water currents as well as winds. Because of the ocean's great capacity to store and release heat, maritime climates are more moderate and have less extreme seasonal variations than inland climates. Precipitation can be approximated from coastal weather data and air temperature from water temperatures.\nThe oceans are the major source of atmospheric moisture that is obtained through evaporation. Climatic zones vary with latitude; the warmest zones stretch across the Atlantic north of the equator. The coldest zones are in high latitudes, with the coldest regions corresponding to the areas covered by sea ice. Ocean currents influence the climate by transporting warm and cold waters to other regions. The winds that are cooled or warmed when blowing over these currents influence adjacent land areas.\nThe Gulf Stream and its northern extension towards Europe, the North Atlantic Drift is thought to have at least some influence on climate. For example, the Gulf Stream helps moderate winter temperatures along the coastline of southeastern North America, keeping it warmer in winter along the coast than inland areas. The Gulf Stream also keeps extreme temperatures from occurring on the Florida Peninsula. In the higher latitudes, the North Atlantic Drift, warms the atmosphere over the oceans, keeping the British Isles and northwestern Europe mild and cloudy, and not severely cold in winter, like other locations at the same high latitude. The cold water currents contribute to heavy fog off the coast of eastern Canada (the Grand Banks of Newfoundland area) and Africa's northwestern coast. In general, winds transport moisture and air over land areas.\n\nNatural hazards\n\nEvery winter, the Icelandic Low produces frequent storms. Icebergs are common from early February to the end of July across the shipping lanes near the Grand Banks of Newfoundland. The ice season is longer in the polar regions, but there is little shipping in those areas.\nHurricanes are a hazard in the western parts of the North Atlantic during the summer and autumn. Due to a consistently strong wind shear and a weak Intertropical Convergence Zone, South Atlantic tropical cyclones are rare.\n\nGeology and plate tectonics\nThe Atlantic Ocean is underlain mostly by dense mafic oceanic crust made up of basalt and gabbro and overlain by fine clay, silt and siliceous ooze on the abyssal plain. The continental margins and continental shelf mark lower density, but greater thickness felsic continental rock that is often much older than that of the seafloor. The oldest oceanic crust in the Atlantic is up to 145 million years and is situated off the west coast of Africa and the east coast of North America, or on either side of the South Atlantic.\nIn many places, the continental shelf and continental slope are covered in thick sedimentary layers. For instance, on the North American side of the ocean, large carbonate deposits formed in warm shallow waters such as Florida and the Bahamas, while coarse river outwash sands and silt are common in shallow shelf areas like the Georges Bank. Coarse sand, boulders, and rocks were transported into some areas, such as off the coast of Nova Scotia or the Gulf of Maine during the Pleistocene ice ages.\n\nCentral Atlantic\n\nThe break-up of Pangaea began in the central Atlantic, between North America and Northwest Africa, where rift basins opened during the Late Triassic and Early Jurassic. This period also saw the first stages of the uplift of the Atlas Mountains. The exact timing is controversial with estimates ranging from 200 to 170 Ma.\nThe opening of the Atlantic Ocean coincided with the initial break-up of the supercontinent Pangaea, both of which were initiated by the eruption of the Central Atlantic Magmatic Province (CAMP), one of the most extensive and voluminous large igneous provinces in Earth's history associated with the Triassic–Jurassic extinction event, one of Earth's major extinction events.\nTheoliitic dikes, sills, and lava flows from the CAMP eruption at 200 Ma have been found in West Africa, eastern North America, and northern South America. The extent of the volcanism has been estimated to 4.5×106 km2 (1.7×106 sq mi) of which 2.5×106 km2 (9.7×105 sq mi) covered what is now northern and central Brazil.\nThe formation of the Central American Isthmus closed the Central American Seaway at the end of the Pliocene 2.8 Ma ago. The formation of the isthmus resulted in the migration and extinction of many land-living animals, known as the Great American Interchange, but the closure of the seaway resulted in a \"Great American Schism\" as it affected ocean currents, salinity, and temperatures in both the Atlantic and Pacific. Marine organisms on both sides of the isthmus became isolated and either diverged or went extinct.\n\nNorth Atlantic\n\nGeologically, the North Atlantic is the area delimited to the south by two conjugate margins, Newfoundland and Iberia, and to the north by the Arctic Eurasian Basin. The opening of the North Atlantic closely followed the margins of its predecessor, the Iapetus Ocean, and spread from the central Atlantic in six stages: Iberia–Newfoundland, Porcupine–North America, Eurasia–Greenland, Eurasia–North America. Active and inactive spreading systems in this area are marked by the interaction with the Iceland hotspot.\nSeafloor spreading led to the extension of the crust and the formation of troughs and sedimentary basins. The Rockall Trough opened between 105 and 84 million years ago although the rift failed along with one leading into the Bay of Biscay.\nSpreading began opening the Labrador Sea around 61 million years ago, continuing until 36 million years ago. Geologists distinguish two magmatic phases. One from 62 to 58 million years ago predates the separation of Greenland from northern Europe while the second from 56 to 52 million years ago happened as the separation occurred.\nIceland began to form 62 million years ago due to a particularly concentrated mantle plume. Large quantities of basalt erupted at this time period are found on Baffin Island, Greenland, the Faroe Islands, and Scotland, with ash falls in Western Europe acting as a stratigraphic marker. The opening of the North Atlantic caused a significant uplift of continental crust along the coast. For instance, despite 7 km thick basalt, Gunnbjorn Field in East Greenland is the highest point on the island, elevated enough that it exposes older Mesozoic sedimentary rocks at its base, similar to old lava fields above sedimentary rocks in the uplifted Hebrides of western Scotland.\nThe North Atlantic Ocean contains about 810 seamounts, most of them situated along the Mid-Atlantic Ridge. The OSPAR database (Convention for the Protection of the Marine Environment of the North-East Atlantic) mentions 104 seamounts: 74 within national exclusive economic zones. Of these seamounts, 46 are located close to the Iberian Peninsula.\n\nSouth Atlantic\n\nWest Gondwana (South America and Africa) broke up in the Early Cretaceous to form the South Atlantic. The apparent fit between the coastlines of the two continents was noted on the first maps that included the South Atlantic and it was also the subject of the first computer-assisted plate tectonic reconstructions in 1965. This magnificent fit, however, has since then proven problematic and later reconstructions have introduced various deformation zones along the shorelines to accommodate the northward-propagating break-up. Intra-continental rifts and deformations have also been introduced to subdivide both continental plates into sub-plates.\nGeologically, the South Atlantic can be divided into four segments: equatorial segment, from 10°N to the Romanche fracture zone (RFZ); central segment, from RFZ to Florianopolis fracture zone (FFZ, north of Walvis Ridge and Rio Grande Rise); southern segment, from FFZ to the Agulhas–Falkland fracture zone (AFFZ); and Falkland segment, south of AFFZ.\nIn the southern segment the Early Cretaceous (133–130 Ma) intensive magmatism of the Paraná–Etendeka Large Igneous Province produced by the Tristan hotspot resulted in an estimated volume of 1.5×106 to 2.0×106 km3 (3.6×105 to 4.8×105 cu mi). It covered an area of 1.2×106 to 1.6×106 km2 (4.6×105 to 6.2×105 sq mi) in Brazil, Paraguay, and Uruguay and 0.8×105 km2 (3.1×104 sq mi) in Africa. Dyke swarms in Brazil, Angola, eastern Paraguay, and Namibia, however, suggest the LIP originally covered a much larger area and also indicate failed rifts in all these areas. Associated offshore basaltic flows reach as far south as the Falkland Islands and South Africa. Traces of magmatism in both offshore and onshore basins in the central and southern segments have been dated to 147–49 Ma with two peaks between 143 and 121 Ma and 90–60 Ma.\nIn the Falkland segment rifting began with dextral movements between the Patagonia and Colorado sub-plates between the Early Jurassic (190 Ma) and the Early Cretaceous (126.7 Ma). Around 150 Ma sea-floor spreading propagated northward into the southern segment. No later than 130 Ma rifting had reached the Walvis Ridge–Rio Grande Rise.\nIn the central segment, rifting started to break Africa in two by opening the Benue Trough around 118 Ma. Rifting in the central segment, however, coincided with the Cretaceous Normal Superchron (also known as the Cretaceous quiet period), a 40 Ma period without magnetic reversals, which makes it difficult to date sea-floor spreading in this segment.\nThe equatorial segment is the last phase of the break-up, but, because it is located on the Equator, magnetic anomalies cannot be used for dating. Various estimates date the propagation of seafloor spreading in this segment and consequent opening of the Equatorial Atlantic Gatew",
    "source": "wikipedia:Atlantic Ocean",
    "domain": "climate"
  },
  {
    "text": "An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, shoreline configurations, and interactions with other currents influence a current's direction and strength. Ocean currents move both horizontally, on scales that can span entire oceans, as well as vertically, with vertical currents (upwelling and downwelling) playing an important role in the movement of nutrients and gases, such as carbon dioxide, between the surface and the deep ocean. \nOcean currents are classified by temperature as either warm currents or cold currents. They are also classified by their velocity, dimension, and direction as either drifts, currents, or streams. Drifts, such as the North Atlantic Drift Current, involve the forward movement of surface ocean water under the influence of the prevailing wind. Currents, such as the Labrador Current, \ninvolve the movement of oceanic water in a more definite direction at a greater velocity than drifts. Streams, such as the Gulf Stream, involve movement of larger masses of ocean water with greater velocity than drifts or currents.\nOcean currents are patterns of water movement that influence climate zones and weather patterns around the world. They are primarily driven by winds and by seawater density, although many other factors influence them, including the shape and configuration of the oceanic basin they flow through. The two basic types of currents – surface and deep-water currents – help define the character and flow of ocean waters across the planet.\nOcean currents flow for great distances, and together they create the global conveyor belt, which plays a dominant role in determining the climate of many of Earth's regions. More specifically, ocean currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Perhaps the most striking example is the Gulf Stream, which, together with its extension the North Atlantic Drift, makes northwest Europe much more temperate for its high latitude than other areas at the same latitude. Another example is Lima, Peru, whose cooler subtropical climate contrasts with that of its surrounding tropical latitudes because of the Humboldt Current.\nThe largest ocean current is the Antarctic Circumpolar Current (ACC), a wind-driven current which flows clockwise uninterrupted around Antarctica. The ACC connects all the oceanic basins together, and also provides a link between the atmosphere and the deep ocean due to the way water upwells and downwells on either side of it.\n\nCauses\n\nOcean currents are driven by the wind, by the gravitational pull of the Moon in the form of tides, and by the effects of variations in water density. Ocean dynamics define and describe the motion of water within the oceans.\nOcean temperature and motion fields can be separated into three distinct layers: mixed (surface) layer, upper ocean (above the thermocline), and deep ocean. Ocean currents are measured in units of sverdrup (Sv), where 1 Sv is equivalent to a volume flow rate of 1,000,000 m3 (35,000,000 ft3) per second.\nThere are two main types of currents, surface currents and deep-water currents. Generally surface currents are driven by wind systems and deep-water currents are driven by differences in water density due to variations in water temperature and salinity.\n\nWind-driven circulation\nSurface oceanic currents are driven by wind currents, the large scale prevailing winds drive major persistent ocean currents, and seasonal or occasional winds drive currents of similar persistence to the winds that drive them, and the Coriolis effect plays a major role in their development. The Ekman spiral velocity distribution results in the currents flowing at an angle to the driving winds, and they develop typical clockwise spirals in the Northern Hemisphere and counter-clockwise rotation in the Southern Hemisphere.\nIn addition, the areas of surface ocean currents move somewhat with the seasons; this is most notable in equatorial currents.\nDeep ocean basins generally have a non-symmetric surface current, in that the eastern equator-ward flowing branch is broad and diffuse whereas the pole-ward flowing western boundary current is relatively narrow.\n\nThermohaline circulation\n\nLarge scale currents are driven by gradients in water density, which in turn depend on variations in temperature and salinity. This thermohaline circulation is also known as the ocean's conveyor belt. Where significant vertical movement of ocean currents is observed, this is known as upwelling and downwelling. The adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of seawater.\nThe thermohaline circulation is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of around 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. On their journey, the water masses transport both energy (in the form of heat) and matter (solids, dissolved substances and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is imprecisely used to refer to the meridional overturning circulation, (MOC).\nSince the 2000s an international program called Argo has been mapping the temperature and salinity structure of the ocean with a fleet of automated platforms that float with the ocean currents. The information gathered will help explain the role the oceans play in the Earth's climate.\n\nEffects on climate and ecology\nOcean currents affect temperatures throughout the world. For example, the ocean current that brings warm water up the north Atlantic to northwest Europe also cumulatively and slowly blocks ice from forming along the seashores, which would also block ships from entering and exiting inland waterways and seaports, hence ocean currents play a decisive role in influencing the climates of regions through which they flow. Ocean currents are important in the study of marine debris.\n\nUpwellings and cold ocean water currents flowing from polar and sub-polar regions bring in nutrients that support plankton growth, which are crucial prey items for several key species in marine ecosystems.\nOcean currents are also important in the dispersal and distribution of many organisms, including those with pelagic egg or larval stages. An example is the life-cycle of the European Eel. Terrestrial species, for example tortoises and lizards, can be carried on floating debris by currents to colonise new terrestrial areas and islands.\n\nOcean currents and climate change\nThe continued rise of atmospheric temperatures is anticipated to have various effects on the strength of surface ocean currents, wind-driven circulation and dispersal patterns. Ocean currents play a significant role in influencing climate, and shifts in climate in turn impact ocean currents.\n\nOver the last century, reconstructed sea surface temperature data reveal that western boundary currents are heating at double the rate of the global average. These observations indicate that the western boundary currents are likely intensifying due to this change in temperature, and may continue to grow stronger in the near future. There is evidence that surface warming due to anthropogenic climate change has accelerated upper ocean currents in 77% of the global ocean. Specifically, increased vertical stratification due to surface warming intensifies upper ocean currents, while changes in horizontal density gradients caused by differential warming across different ocean regions results in the acceleration of surface zonal currents.\nThere are suggestions that the Atlantic meridional overturning circulation (AMOC) is in danger of collapsing due to climate change, which would have extreme impacts on the climate of northern Europe and more widely, although this topic is controversial and remains an active area of research. The \"State of the cryosphere\" report, dedicates significant space to AMOC, saying it may be en route to collapse because of ice melt and water warming. In the same time, the Antarctic Circumpolar Current (ACC) is also slowing down and is expected to lose 20% of its power by the year 2050, \"with widespread impacts on ocean circulation and climate\". UNESCO mentions that the report in the first time \"notes a growing scientific consensus that melting Greenland and Antarctic ice sheets, among other factors, may be slowing important ocean currents at both poles, with potentially dire consequences for a much colder northern Europe and greater sea-level rise along the U.S. East Coast.\"\nIn addition to water surface temperatures, the wind systems are a crucial determinant of ocean currents. Wind wave systems influence oceanic heat exchange, the condition of the sea surface, and can alter ocean currents. In the North Atlantic, equatorial Pacific, and Southern Ocean, increased wind speeds as well as significant wave heights have been attributed to climate change and natural processes combined. In the East Australian Current, global warming has also been accredited to increased wind stress curl, which intensifies these currents, and may even indirectly increase sea levels, due to the additional warming created by stronger currents.\nAs ocean circulation changes due to climate, typical distribution patterns are also changing. The dispersal patterns of marine organisms depend on oceanographic conditions, which as a result, influence the biological composition of oceans. Due to the patchiness of the natural ecological world, dispersal is a species survival mechanism for various organisms. With strengthened boundary currents moving toward the poles, it is expected that some marine species will be redirected to the poles and greater depths. The strengthening or weakening of typical dispersal pathways by increased temperatures are expected to not only impact the survival of native marine species due to inability to replenish their meta populations but also may increase the prevalence of invasive species. In Japanese corals and macroalgae, the unusual dispersal pattern of organisms toward the poles may destabilize native species.\n\nEconomic importance\nKnowledge of surface ocean currents is essential in reducing costs of shipping, since traveling with them reduces fuel costs. In the wind powered sailing-ship era, knowledge of wind patterns and ocean currents was even more essential. Using ocean currents to help their ships into harbor and using currents such as the gulf stream to get back home. The lack of understanding of ocean currents during that time period is hypothesized to be one of the contributing factors to exploration failure. The Gulf Stream and the Canary current keep western European countries warmer and less variable, while at the same latitude North America's weather was colder. A good example of this is the Agulhas Current (down along eastern Africa), which long prevented sailors from reaching India.\nIn recent times, around-the-world sailing competitors make good use of surface currents to build and maintain speed.\nOcean currents can also be used for marine power generation, with areas of Japan, Florida and Hawaii being considered for test projects. The utilization of currents today can still impact global trade, it can reduce the cost and emissions of shipping vessels. \n\nOcean currents can also impact the fishing industry, examples of this include the Tsugaru, Oyashio and Kuroshio currents all of which influence the western North Pacific temperature, which has been shown to be a habitat predictor for the Skipjack tuna. It has also been shown that it is not just local currents that can affect a country's economy, but neighboring currents can influence the viability of local fishing industries.\n\nDistribution\n\nCurrents of the Arctic Ocean\n\nBaffin Island Current – Arctic Ocean current\nBeaufort Gyre – Wind-driven ocean current in the Arctic Ocean polar region\nEast Greenland Current – Current from Fram Strait to Cape Farewell off the eastern coat of Greenland\nEast Iceland Current – Cold water ocean current that forms as a branch of the East Greenland Current\nLabrador Current – Western North Atlantic Ocean current\nNorth Icelandic Jet – Deep-reaching current that flows along the continental slope of Iceland\nNorwegian Current – Current that flows northeasterly along the Atlantic coast of Norway\nTranspolar Drift Stream – Current in the Arctic Ocean\nWest Greenland Current – Weak cold water current that flows to the north along the west coast of Greenland\nWest Spitsbergen Current – Warm, salty current that runs poleward just west of Spitsbergen\nCurrents of the Atlantic Ocean\n\nAngola Current – Temporary ocean surface current\nAntilles Current – Ocean current\nAtlantic meridional overturning circulation – System of surface and deep currents in the Atlantic Ocean\nAzores Current – Ocean current in the North Atlantic Ocean\nBenguela Current – Ocean current in the South Atlantic\nBrazil Current – Water current along Brazil's southern coast\nCanary Current – Wind-driven surface current that is part of the North Atlantic Gyre\nCape Horn Current – Cold water current that flows west-to-east around Cape Horn\nCaribbean Current – Atlantic Ocean current\nEast Greenland Current – Current from Fram Strait to Cape Farewell off the eastern coat of Greenland\nEast Iceland Current – Cold water ocean current that forms as a branch of the East Greenland Current\nEquatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans\nFalkland Current – Northward cold water Atlantic Ocean current\nFlorida Current – Thermal ocean current\nGuinea Current – Atlantic warm-water current off West Africa\nGulf Stream – Warm Atlantic Ocean current\nIrminger Current\nLabrador Current – Western North Atlantic Ocean current\nLomonosov Current – Deep current in the Atlantic Ocean. from the coast of Brazil to the Gulf of Guinea\nLoop Current – Ocean current between Cuba and Yucatán Peninsula\nNorth Atlantic Current – Current of the Atlantic Ocean\nNorth Brazil Current – North Atlantic ocean current\nNorth Equatorial Current – Current in the Pacific and Atlantic Oceans\nNorwegian Current – Current that flows northeasterly along the Atlantic coast of Norway\nPortugal Current – Weak ocean current that flows south along the coast of Portugal\nSouth Atlantic Current – Eastward ocean current, fed by the Brazil Current\nSouth Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean\nWest Greenland Current – Weak cold water current that flows to the north along the west coast of Greenland\nWest Spitsbergen Current – Warm, salty current that runs poleward just west of Spitsbergen\nCurrents of the Indian Ocean\n\nAgulhas Current – Southwest Indian Ocean current off Africa's east coast\nAgulhas Return Current – Ocean current in the southern Indian Ocean\nEast Madagascar Current – Oceanic flow feature near Madagascar\nEquatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans\nIndian Monsoon Current – Seasonally-varying ocean current regime in the northern Indian Ocean\nIndonesian Throughflow – Ocean current\nLeeuwin Current – Ocean current off Western Australia\nMadagascar Current – Ocean current in the West Indian Ocean\nMozambique Current – Warm ocean current in the Indian Ocean\nNorth Madagascar Current – Ocean current near Madagascar that flows into the South Equatorial Current\nSomali Current – Boundary current in the Indian Ocean\nSouth Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean\nSouthwest Madagascar Coastal Current – Warm poleward ocean current flowing in the south-west of Madagascar\nWest Australian Current – Cool oceanic current\nCurrents of the Pacific Ocean\n\nAlaska Current – Warm-water current west of North America\nAleutian Current – Eastward-flowing ocean current which lies north of the North Pacific Current;\nCalifornia Current – Pacific Ocean current\nCape Horn Current – Cold water current that flows west-to-east around Cape Horn\nCromwell Current – Eastward-flowing subsurface current that extends along the equator in the Pacific Ocean\nDavidson Current – Countercurrent of the Pacific Ocean\nEast Australian Current – Currents of the Pacific Ocean\nEast Korea Warm Current – Ocean current in the Sea of Japan\nEquatorial Counter Current – Shallow eastward flowing current found in the Atlantic, Indian, and Pacific Oceans\nHumboldt Current – Current of the Pacific Ocean\nIndonesian Throughflow – Ocean current\nKamchatka Current – Pacific Ocean current\nKuroshio Current – North-flowing current in the northwest Pacific Ocean\nMindanao Current – Narrow, southward-flowing ocean current along the southeastern coast of the Philippines\nMindanao Eddy – Semi-permanent cold-ring ocean eddy near the Philippines\nNorth Equatorial Current – Current in the Pacific and Atlantic Oceans\nNorth Korea Cold Current – Cold water current in the Sea of Japan\nNorth Pacific Current – Ocean current, Japan to British Columbia\nOyashio Current – Cold subarctic ocean current in the Pacific Ocean\nSouth Equatorial Current – Ocean current in the Pacific, Atlantic, and Indian Ocean\nSubtropical Countercurrent – Narrow eastward ocean current in the central North Pacific Ocean\nTasman Front – Pacific Ocean current\nTasman Outflow – Deepwater current that flows from the Pacific Ocean past Tasmania into the Indian Ocean\nCurrents of the Southern Ocean\n\nAntarctic Circumpolar Current – Ocean current that flows clockwise from west to east around Antarctica\nTasman Outflow – Deepwater current that flows from the Pacific Ocean past Tasmania into the Indian Ocean\nKerguelen deep western boundary current\nOceanic gyres\n\nBeaufort Gyre – Wind-driven ocean current in the Arctic Ocean polar region\nIndian Ocean Gyre – Major oceanic gyre in the Indian Ocean\nNorth Atlantic Gyre – Major circular system of ocean currents\nNorth Pacific Gyre – Major circulating system of ocean currents\nRoss Gyre – Circulating system of ocean currents in the Ross Sea\nSouth Atlantic Gyre – Subtropical gyre in the south Atlantic Ocean\nSouth Pacific Gyre – Major circulating system of ocean currents\nWeddell Gyre – One of two gyres within the Southern Ocean\n\nSee also\n\nCurrentology – Science that studies the internal movements of water masses\nDeep ocean water – Cold, salty water deep below the surface of Earth's oceans\nFish migration – Movement of fishes from one part of a water body to another on a regular basis\nGeostrophic current – Oceanic flow in which the pressure gradient force is balanced by the Coriolis effect\nLatitude of the Gulf Stream and the Gulf Stream north wall index\nList of ocean circulation models\nMarine habitats § Ocean currents\nMarine current power – Extraction of power from ocean currents\nOcean gyre – Any large system of circulating ocean surface currents\nPhysical oceanography – Study of physical conditions and processes within the ocean\nSubsurface ocean current – Oceanic currents that flow beneath surface currents\nThermohaline circulation – Part of large-scale ocean circulation\nTidal current – Flow of water induced by astronomical gravitational effects\nVolta do mar – Archaic navigational technique\n\nReferences\n\nFurther reading\nHansen, B.; Østerhus, S; Quadfasel, D; Turrell, W (2004). \"Already the day after tomorrow?\". Science. 305 (5686): 953–954. doi:10.1126/science.1100085. PMID 15310882. S2CID 12968045.\nKerr, Richard A. (2004). \"A slowing cog in the North Atlantic ocean's climate machine\". Science. 304 (5669): 371–372. doi:10.1126/science.304.5669.371a. PMID 15087513. S2CID 42150417.\nMunday, Phillip L.; Jones, Geoffrey P.; Pratchett, Morgan S.; Williams, Ashley J. (2008). \"Climate change and the future for coral reef fishes\". Fish and Fisheries. 9 (3): 261–285. Bibcode:2008AqFF....9..261M. doi:10.1111/j.1467-2979.2008.00281.x.\nRahmstorf, S. (2003). \"Thermohaline circulation: The current climate\". Nature. 421 (6924): 699. Bibcode:2003Natur.421..699R. doi:10.1038/421699a. PMID 12610602. S2CID 4414604.\nRoemmich, D. (2007). \"Physical oceanography: Super spin in the southern seas\". Nature. 449 (7158): 34–35. Bibcode:2007Natur.449...34R. doi:10.1038/449034a. PMID 17805284. S2CID 2951110.\n\nExternal links\n\nCurrent global map of sea surface currents",
    "source": "wikipedia:Ocean current",
    "domain": "climate"
  },
  {
    "text": "The Paris Agreement (also called the Paris Accords or Paris Climate Accords) is an international treaty on climate change that was signed in 2016. The treaty covers climate change mitigation, adaptation, and finance. The Paris Agreement was negotiated by 196 parties at the 2015 United Nations Climate Change Conference near Paris, France. As of January 2026, 194 members of the United Nations Framework Convention on Climate Change (UNFCCC) are parties to the agreement. Of the three UNFCCC member states which have not ratified the agreement, the only major emitter is Iran. The United States, the second largest emitter, withdrew from the agreement in 2020, rejoined in 2021, and withdrew again in 2026.\nThe Paris Agreement has a long-term temperature goal which is to keep the rise in global surface temperature to well below 2 °C (3.6 °F) above pre-industrial levels. The treaty also states that preferably the limit of the increase should only be 1.5 °C (2.7 °F). These limits are defined as averages of the global temperature as measured over many years. \nThe lower the temperature increase, the smaller the effects of climate change can be expected. To achieve this temperature goal, greenhouse gas emissions should be reduced as soon as, and by as much as, possible. They should even reach net zero by the middle of the 21st century. To stay below 1.5 °C of global warming, emissions need to be cut by roughly 50% by 2030. This figure takes into account each country's documented pledges. After the Paris Agreement was signed, global emissions continued to rise rather than fall. 2024 was the hottest year on record, with a rise of more than 1.5 °C in global average temperature. \nThe treaty aims to help countries adapt to climate change effects, and mobilize enough finance. Under the agreement, each country must determine, plan, and regularly report on its contributions. No mechanism forces a country to set specific emissions targets, but each target should go beyond previous targets. In contrast to the 1997 Kyoto Protocol, the distinction between developed and developing countries is blurred, so that the latter also have to submit plans for emission reductions.\nThe Paris Agreement was opened for signature on 22 April 2016 (Earth Day) at a ceremony inside the UN Headquarters in New York. After the European Union ratified the agreement, sufficient countries had ratified the agreement responsible for enough of the world's greenhouse gases for the agreement to enter into force on 4 November 2016.\nWorld leaders have lauded the agreement. However, there is debate about its effectiveness, with some environmentalists and analysts criticizing it for not being strict enough. While pledges under the Paris Agreement are insufficient for reaching the set temperature goals, there is a mechanism of increased ambition. The Paris Agreement has been successfully used in climate litigation in the late 2010s forcing countries and oil companies to strengthen climate action.\n\nAims\nThe aim of the agreement, as described in Article 2, is to have a stronger response to the danger of climate change; it seeks to enhance the implementation of the United Nations Framework Convention on Climate Change through:\n\n(a) Holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change;\n(b) Increasing the ability to adapt to the adverse impacts of climate change and foster climate resilience and low greenhouse gas emissions development, in a manner that does not threaten food production;\n\n(c) Making finance flows consistent with a pathway towards low greenhouse gas emissions and climate-resilient development.\nCountries furthermore aim to reach \"global peaking of greenhouse gas emissions as soon as possible.\"\n\nDevelopment\n\nLead-up\nThe UN Framework Convention on Climate Change (UNFCCC), adopted at the 1992 Earth Summit is one of the first international treaties on the topic. It stipulates that parties should meet regularly to address climate change, at the Conference of Parties or COP. It forms the foundation to future climate agreements.\nThe Kyoto Protocol, adopted in 1997, regulated greenhouse gas reductions for a limited set of countries from 2008 to 2012. The protocol was extended until 2020 with the Doha Amendment in 2012. The United States decided not to ratify the protocol, mainly because of its legally-binding nature. This, and distributional conflict, led to failures of subsequent international climate negotiations. The 2009 negotiations were intended to produce a successor treaty of Kyoto, but the negotiations collapsed and the resulting Copenhagen Accord was not legally binding and did not get adopted universally.\nThe accord did lay the framework for bottom-up approach of the Paris Agreement. Under the leadership of UNFCCC executive secretary Christiana Figueres, negotiation regained momentum after Copenhagen's failure. During the 2011 United Nations Climate Change Conference, the Durban Platform was established to negotiate a legal instrument governing climate change mitigation measures from 2020. The platform had a mandate to be informed by the Fifth Assessment Report of the IPCC and the work of the subsidiary bodies of the UNFCCC. The resulting agreement was to be adopted in 2015.\n\nNegotiations and adoption\n\nNegotiations in Paris took place over a two-week span, and continued throughout the three final nights. Various drafts and proposals had been debated and streamlined in the preceding year. According to one commentator two ways in which the French increased the likelihood of success were: firstly to ensure that Intended Nationally Determined Contributions (INDCs) were completed before the start of the negotiations, and secondly to invite leaders just for the beginning of the conference.\nThe negotiations almost failed because of a single word when the US legal team realized at the last minute that \"shall\" had been approved, rather than \"should\", meaning that developed countries would have been legally obliged to cut emissions: the French solved the problem by changing it as a \"typographical error\". At the conclusion of COP21 (the 21st meeting of the Conference of the Parties), on 12 December 2015, the final wording of the Paris Agreement was adopted by consensus by the 195 UNFCCC participating member states and the European Union. Nicaragua indicated they had wanted to object to the adoption as they denounced the weakness of the agreement, but were not given a chance. In the agreement the members promised to reduce their carbon output \"as soon as possible\" and to do their best to keep global warming \"to well below 2 degrees C\" (3.6 °F).\n\nSigning and entry into force\nThe Paris Agreement was open for signature by states and regional economic integration organizations that are parties to the UNFCCC (the convention) from 22 April 2016 to 21 April 2017 at the UN Headquarters in New York. Signing of the agreement is the first step towards ratification, but it is possible to accede to the agreement without signing. It binds parties to not act in contravention of the goal of the treaty. On 1 April 2016, the United States and China, which represent almost 40% of global emissions confirmed they would sign the Paris Climate Agreement. The agreement was signed by 175 parties (174 states and the European Union) on the first day it was opened for signature. As of January 2026, 194 states and the European Union have signed the agreement.\n\nThe agreement would enter into force (and thus become fully effective) if 55 countries that produce at least 55% of the world's greenhouse gas emissions (according to a list produced in 2015) ratify or otherwise join the treaty. Alternative ways to join the treaty are acceptance, approval or accession. The first two are typically used when a head of state is not necessary to bind a country to a treaty, whereas the latter typically happens when a country joins a treaty already in force. After ratification by the European Union, the agreement obtained enough parties to enter into effect on 4 November 2016.\nBoth the EU and its member states are individually responsible for ratifying the Paris Agreement. A strong preference was reported that the EU and its 28 member states ratify at the same time to ensure that they do not engage themselves to fulfilling obligations that strictly belong to the other, and there were fears by observers that disagreement over each member state's share of the EU-wide reduction target, as well as Britain's vote to leave the EU might delay the Paris pact. However, the EU deposited its instruments of ratification on 5 October 2016, along with seven EU member states.\n\nParties\n\nCountries that have ratified or acceded\nThe EU and 194 states, totalling over 98% of greenhouse gas emissions, have ratified or acceded to the agreement. The only countries which have not ratified are some greenhouse gas emitters in the Middle East: Iran with 2% of the world total being the largest. Libya and Yemen have also not ratified the agreement. Eritrea is the latest country to ratify the agreement, on 7 February 2023.\nArticle 28 enables parties to withdraw from the agreement after sending a withdrawal notification to the depositary. Notice can be given no earlier than three years after the agreement goes into force for the country. Withdrawal is effective one year after the depositary is notified.\n\nUnited States withdrawal, readmittance, and rewithdrawal\n\nOn 4 August 2017, the Trump administration delivered an official notice to the United Nations that the United States, the second largest emitter of greenhouse gases after China, intended to withdraw from the Paris Agreement as soon as it was eligible to do so. The notice of withdrawal could not be submitted until the agreement was in force for three years for the US, on 4 November 2019. The U.S. government deposited the notification with the secretary-general of the United Nations and officially withdrew one year later on 4 November 2020. \nPresident Joe Biden signed an executive order on his first day in office, 20 January 2021, to re-admit the United States into the Paris Agreement. Following the 30-day period set by Article 21.3, the U.S. was readmitted to the agreement. United States climate envoy John Kerry took part in virtual events, saying that the US would \"earn its way back\" into legitimacy in the Paris process. United Nations secretary-general António Guterres welcomed the return of the United States as restoring the \"missing link that weakened the whole\".\nOn 20 January 2025, President Donald Trump signed an executive order again withdrawing the U.S. from the agreement. The withdrawal went into effect on 27 January 2026.\n\nContent\n\nStructure\nThe Paris Agreement is a short agreement with 16 introductory paragraphs and 29 articles. It contains procedural articles (covering, for example, the criteria for its entry into force) and operational articles (covering, for example, mitigation, adaptation and finance). It is a binding agreement, but many of its articles do not imply obligations or are there to facilitate international collaboration. It covers most greenhouse gas emissions, but does not apply to international aviation and shipping, which fall under the responsibility of the International Civil Aviation Organization and the International Maritime Organization, respectively.\nThe Paris Agreement has been described as having a bottom-up structure, as its core pledge and review mechanism allows nations to set their own nationally determined contributions (NDCs), rather than having targets imposed top down. Unlike its predecessor, the Kyoto Protocol, which sets commitment targets that have legal force, the Paris Agreement, with its emphasis on consensus building, allows for voluntary and nationally determined targets. The specific climate goals are thus politically encouraged, rather than legally bound. Only the processes governing the reporting and review of these goals are mandated under international law. This structure is especially notable for the United States – because there are no legal mitigation or finance targets, the agreement is considered an \"executive agreement rather than a treaty\". Because the UNFCCC treaty of 1992 received the consent of the US Senate, this new agreement does not require further legislation.\nAnother key difference between the Paris Agreement and the Kyoto Protocol is their scope. The Kyoto Protocol differentiated between Annex-I, richer countries with a historical responsibility for climate change, and non-Annex-I countries, but this division is blurred in the Paris Agreement as all parties are required to submit emissions reduction plans. The Paris Agreement still emphasizes the principle of Common but Differentiated Responsibility and Respective Capabilities – the acknowledgement that different nations have different capacities and duties to climate action – but it does not provide a specific division between developed and developing nations.\n\nNationally determined contributions\n\nCountries determine themselves what contributions they should make to achieve the aims of the treaty. As such, these plans are called nationally determined contributions (NDCs). Article 3 requires NDCs to be \"ambitious efforts\" towards \"achieving the purpose of this Agreement\" and to \"represent a progression over time\". The contributions should be set every five years and are to be registered by the UNFCCC Secretariat. Each further ambition should be more ambitious than the previous one, known as the principle of progression. Countries can cooperate and pool their nationally determined contributions. The Intended Nationally Determined Contributions pledged during the 2015 Climate Change Conference are converted to NDCs when a country ratifies the Paris Agreement, unless they submit an update.\nThe Paris Agreement does not prescribe the exact nature of the NDCs. At a minimum, they should contain mitigation provisions, but they may also contain pledges on adaptation, finance, technology transfer, capacity building and transparency. Some of the pledges in the NDCs are unconditional, but others are conditional on outside factors such as getting finance and technical support, the ambition from other parties or the details of rules of the Paris Agreement that are yet to be set. Most NDCs have a conditional component.\nWhile the NDCs themselves are not binding, the procedures surrounding them are. These procedures include the obligation to prepare, communicate and maintain successive NDCs, set a new one every five years, and provide information about the implementation. There is no mechanism to force a country to set a NDC target by a specific date, nor to meet their targets. There will be only a name and shame system or as János Pásztor, the former U.N. assistant secretary-general on climate change, stated, a \"name and encourage\" plan.\n\nGlobal stocktake\nUnder the Paris Agreement, countries must increase their ambition every five years. To facilitate this, the agreement established the Global Stocktake, which assesses progress, with the first evaluation in 2023. The outcome is to be used as input for new nationally determined contributions of parties. The Talanoa Dialogue in 2018 was seen as an example for the global stocktake. After a year of discussion, a report was published and there was a call for action, but countries did not increase ambition afterwards.\nThe stocktake works as part of the Paris Agreement's effort to create a \"ratcheting up\" of ambition in emissions cuts. Because analysts agreed in 2014 that the NDCs would not limit rising temperatures below 2 °C, the global stocktake reconvenes parties to assess how their new NDCs must evolve so that they continually reflect a country's \"highest possible ambition\". While ratcheting up the ambition of NDCs is a major aim of the global stocktake, it assesses efforts beyond mitigation. The five-year reviews will also evaluate adaptation, climate finance provisions, and technology development and transfer.\nOn 30 November 2023, the United Nations Climate Change Conference (COP28) commenced in Dubai with renewed calls for amplified efforts towards climate action.\n\nMitigation provisions and carbon markets\nArticle 6 has been flagged as containing some of the key provisions of the Paris Agreement. Broadly, it outlines the cooperative approaches that parties can take in achieving their nationally determined carbon emissions reductions. In doing so, it helps establish the Paris Agreement as a framework for a global carbon market. Article 6 is the only important part of the agreement yet to be resolved; negotiations in 2019 did not produce a result. The topic was settled during the 2021 COP26 in Glasgow. A mechanism, the \"corresponding adjustment\", was established to avoid double counting for emission offsets.\n\nLinkage of carbon trading systems and ITMOs\n\nParagraphs 6.2 and 6.3 establish a framework to govern the international transfer of mitigation outcomes (ITMOs). The agreement recognizes the rights of parties to use emissions reductions outside of their own borders toward their NDC, in a system of carbon accounting and trading. This provision requires the \"linkage\" of carbon emissions trading systems – because measured emissions reductions must avoid \"double counting\", transferred mitigation outcomes must be recorded as a gain of emission units for one party and a reduction of emission units for the other, a so-called \"corresponding adjustment\". Because the NDCs, and domestic carbon trading schemes, are heterogeneous, the ITMOs will provide a format for global linkage under the auspices of the UNFCCC. The provision thus also creates a pressure for countries to adopt emissions management systems – if a country wants to use more cost-effective cooperative approaches to achieve their NDCs, they will have to monitor carbon units for their economies.\nSo far, as the only country who wants to buy ITMOs, Switzerland has signed deals regarding ITMO tradings with Peru, Ghana, Senegal, Georgia, Dominica, Vanuatu, Thailand and Ukraine.\n\nSustainable Development Mechanism\nParagraphs 6.4–6.7 establish a mechanism \"to contribute to the mitigation of greenhouse gases and support sustainable development\". Though there is no official name for the mechanism as yet, it has been referred to as the Sustainable Development Mechanism or SDM. The SDM is considered to be the successor to the Clean Development Mechanism, a mechanism under the Kyoto Protocol by which parties could collaboratively pursue emissions reductions.\nThe SDM is set to largely resemble the Clean Development Mechanism, with the dual goal of contributing to global GHG emissions reductions and supporting sustainable development. Though the structure and processes governing the SDM are not yet determined, certain similarities and differences from the Clean Development Mechanisms have become clear. A key difference is that the SDM will be available to all parties as opposed to only Annex-I parties, making it much wider in scope.\nThe Clean Development Mechanism of the Kyoto Protocol was criticized for failing to produce either meaningful emissions reductions or sustainable development benefits in most instances. and for its complexity. It is possible that the SDM will see difficulties.\n\nClimate change adaptation provisions\nClimate change adaptation received more focus in Paris negotiations than in previous climate treaties. Collective, long-term adaptation goals are included in the agreement, and countries must report on their adaptation actions, making it a parallel component with mitigation. The adaptation goals focus on enhancing adaptive capacity, increasing resilience, and limiting vulnerability.\n\nImplementation\nThe Paris Agreement is implemented via national policy. It would involve improvements to energy efficiency to decrease the energy intensity of the global economy. Implementation also requires fossil fuel burning to be cut back and the share of sustainable energy to grow rapidly. Emissions are being reduced rapidly in the electricity sector, but not in the building, transport and heating sector. Some industries are difficult to decarbonize, and for those carbon dioxide removal may be necessary to achieve net zero emissions. In a report released in 2022 the IPCC promotes the need for innovation and technological changes in combination with consumption and production behavioral changes to meet Paris Agreement objectives.\nTo stay below 1.5 °C of global warming, emissions need to be cut by roughly 50% by 2030. This is an aggregate of each country's nationally determined contributions. By mid-century, CO2 emissions would need to be cut to zero, and total greenhouse gases would need to be net zero just after mid-century.\nThere are barriers to implementing the agreement. Some countries struggle to attract the finance necessary for investments in decarbonization. Climate finance is fragmented, further complicating investments. Another issue is the lack of capabilities in government and other institutions to implement policy. Clean technology and knowledge is often not transferred to countries or places that need it. In December 2020, the former chair of the COP 21, Laurent Fabius, argued that the implementation of the Paris Agreement could be bolstered by the adoption of a Global Pact for the Environment. The latter would define the environmental rights and duties of states, individuals and businesses.\n\nSpecific topics of concern\n\nEffectiveness\n\nThe effectiveness of the Paris Agreement to reach its climate goals is under debate, with most experts saying it is insufficient for its more ambitious goal of keeping global temperature rise under 1.5 °C. Many of the exact provisions of the Paris Agreement have yet to be straightened out, so that it may be too early to judge effectiveness. According to the 2020 United Nations Environment Programme (UNEP), with the current climate commitments of the Paris Agreement, global mean temperatures will likely rise by more than 3 °C by the end of the 21st century. Newer net zero commitments were not included in the Nationally Determined Contributions, and may bring down temperatures by a further 0.5 °C.\nWith initial pledges by countries inadequate, faster and more expensive future mitigation would be needed to still reach the targets. Furthermore, there is a gap between pledges by countries in their NDCs and implementation of these pledges; one third of the emission gap between the lowest-costs and actual reductions in emissions would be closed by implementing existing pledges. A pair of studies in Nature found that as of 2017 none of the major industrialized nations were implementing the policies they had pledged, and none met their pledged emission reduction targets, and even if they had, the sum of all member pledges (as of 2016) would not keep global temperature rise \"well below 2°C\".\nIn 2021, a study using a probabilistic model concluded that the rates of emissions reductions would have to increase by 80% beyond NDCs to likely meet the 2 °C upper target of the Paris Agreement, that the probabilities of major emitters meeting their NDCs without such an increase is very low. It estimated that with current trends the probability of staying below 2 °C of warming is 5–26% if NDCs were met and continued post-2030 by all signatories.\nAs of 2020, there is little scientific literature on the topics of the effectiveness of the Paris Agreement on capacity building and adaptation, even though they feature prominently in the Paris Agreement. The literature available is mostly mixed in its conclusions about loss and damage, and adaptation.\nAccording to the stocktake report, the agreement has a significant effect: while in 2010 the expected temperature rise by 2100 was 3.7–4.8 °C, at COP 27 it was 2.4–2.6 °C and if all countries will fulfill their long-term pledges even 1.7–2.1 °C. Despite it, the world is still very far from reaching the aim of the agreement: limiting temperature rise to 1.5 degrees. For doing this, emissions must peak by 2025. Recent work – on the basis of the first single calendar year in 2024 with an average temperature above 1.5 degrees Celsius – indicates that most probably Earth has already entered the 20-year period that will reach an average warming of 1.5 degrees Celsius. Furthermore, it has been suggested that the global mean temperature may have already passed the 1.5 degrees Celsius level in 2024.\nThe Paris Agreement also seemed to have influenced the focus of the following IPCC reports. Before the Paris Agreement was settled, the IPCC assessment reports focused roughly in equal proportions on temperatures above and below 2 °C. However, in the 6th assessment report, after the Paris Engagement was reached, slightly less than 20% of the temperature mentions are above 2 °C and almost 50% focus on 1.5 °C alone.\n\nFulfillment of requirements\n\nIn September 2021, the Climate Action Tracker estimated that, with current policies, global emissions will double above the 2030 target level. The gap is 20–23 Gt CO2e. Countries such as Iran, Russia, Saudi Arabia, Singapore, and Thailand have been criticised of not doing enough to meet the requirements of the agreement, and are on track to achieve a 4 °C warming of the planet if current policies are implemented more widely. Of the world's countries, only the Gambia's emissions are at the level required by the Paris Agreement. Models predicted that if the necessary measures were not implemented by autumn 2021, the global average temperature would rise by 2.9 °C. With the implementation of the Paris Agreement pledges, the average temperature would rise by 2.4 °C, and with every zero emission target reached, the average temperature would rise by 2.0 °C.\nThe Production Gap 2021 report states that world governments still plan to produce 110% more fossil fuels in 2030 (including 240% more coal, 57% more oil and 71% more gas) than the 1.5 degree limit.\nIn September 2023 the first global stocktake report about the implementation of the agreement was released. According to the report contrarily to expectations, the agreement has a significant effect: while in 2010 the expected temperature rise by 2100 was 3.7–4.8 °C, at COP 27 it was 2.4–2.6 °C and if all countries will fulfill their long-term pledges 1.7–2.1 °C. However, the world remains very far from limiting warming to 1.5 degrees. To meet this benchmark, global emissions must peak by 2025, and although emissions have peaked in some countries, global emissions have not.\n\nEnsuring finance\n\nDeveloped countries reaffirmed the commitment to mobilize $100 billion a year in climate finance by 2020, and agreed to continue mobilising finance at this level until 2025. The money is for supporting mitigation and adaptation in developing countries. It includes finance for the Green Climate Fund, which is a part of the UNFCCC, but also for a variety of other public and private pledges. The Paris Agreement states that a new commitment of at least $100 billion per year has to be agreed before 2025.\nThough both mitigation and adaptation require increased climate financing, adaptation has typically received lower levels of support and has mobilized less action from the private sector. A report by the OECD found that 16% of global climate finance was directed toward climate adaptation in 2013–2014, compared to 77% for mitigation. The Paris Agreement called for a balance of climate finance between adaptation and mitigation, and specifically increasing adaptation support for parties most vulnerable to the effects of climate change, including Least developed countries and Small Island Developing States. The agreement also reminds parties of the importance of public grants, because adaptation measures receive less investment from the public sector.\nIn 2015, twenty multilateral development banks (MDBs) and members of the International Development Finance Club introduced five principles to maintain widespread climate action in their investments: commitment to climate strategies, managing climate risks, promoting climate smart objectives, improving climate performance and accounting for their own actions. As of January 2020, the number of members abiding by these principles grew to 44.\nSome specific outcomes of the elevated attention to adaptation financing in Paris include the G7 countries' announcement to provide US$420 million for climate risk insurance, and the launching of a Climate Risk and Early Warning Systems (CREWS) Initiative. The largest donors to multilateral climate funds, which includes the Green Climate Fund, are the United States, the United Kingdom, Japan, Germany, France and Sweden.\n\nLoss and damage\n\nIt is not possible to adapt to all effects of climate change: even in the case of optimal adaptation, severe damage may still occur. The Paris Agreement recognizes loss and damage of this kind. Loss and damage can stem from extreme weather events, or from slow-onset events such as the loss of land to sea level rise for low-lying islands. Previous climate agreements classified loss and damage as a subset of adaptation.\nThe push to address loss and damage as a distinct issue in the Paris Agreement came from the Alliance of Small Island States and the Least Developed Countries, whose economies and livelihoods are most vulnerable to the negative effects of climate change. The Warsaw Mechanism, established two years earlier during COP19 and set to expire in 2016, categorizes loss and damage as a subset of adaptation, which was unpopular with many countries. It is recognized as a separate pillar of the Paris Agreement. The United States argued against this, possibly worried that classifying the issue as separate from adaptation would create yet anoth",
    "source": "wikipedia:Paris Agreement",
    "domain": "climate"
  },
  {
    "text": "The Kyoto Protocol (Japanese: 京都議定書, Hepburn: Kyōto Giteisho) was an international treaty which extended the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits state parties to reduce greenhouse gas emissions, based on the scientific consensus that global warming is occurring and that human-made CO2 emissions are driving it. The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force on 16 February 2005. There were 192 parties (Canada withdrew from the protocol, effective December 2012) to the Protocol in 2020.\nThe Kyoto Protocol implemented the objective of the UNFCCC to reduce the onset of global warming by reducing greenhouse gas concentrations in the atmosphere to \"a level that would prevent dangerous anthropogenic interference with the climate system\" (Article 2). The Kyoto Protocol applied to the seven greenhouse gases listed in Annex A: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3). Nitrogen trifluoride was added for the second compliance period during the Doha Round.\nThe Protocol was based on the principle of common but differentiated responsibilities: it acknowledged that individual countries have different capabilities in combating climate change, owing to economic development, and therefore placed the obligation to reduce current emissions on developed countries on the basis that they are historically responsible for the current levels of greenhouse gases in the atmosphere.\nThe Protocol's first commitment period started in 2008 and ended in 2012. All 36 countries that fully participated in the first commitment period complied with the Protocol. However, nine countries had to resort to the flexibility mechanisms by funding emission reductions in other countries because their national emissions were slightly greater than their targets. The 2008 financial crisis reduced emissions. The greatest emission reductions were seen in the former Eastern Bloc countries because the dissolution of the Soviet Union reduced their emissions in the early 1990s. Even though the 36 developed countries reduced their emissions, the global emissions increased by 32% from 1990 to 2010.\nA second commitment period was agreed to in 2012 to extend the agreement to 2020, known as the Doha Amendment to the Kyoto Protocol, in which 37 countries had binding targets: Australia, the European Union (and its then 28 member states, now 27), Belarus, Iceland, Kazakhstan, Liechtenstein, Norway, Switzerland, and Ukraine. Belarus, Kazakhstan, and Ukraine stated that they may withdraw from the Kyoto Protocol or not put into legal force the Amendment with second round targets. Japan, New Zealand, and Russia had participated in Kyoto's first-round but did not take on new targets in the second commitment period. Other developed countries without second-round targets were Canada (which withdrew from the Kyoto Protocol in 2012) and the United States (which did not ratify). If they were to remain as a part of the protocol, Canadian politicians claimed Canada would be hit with a $14 billion fine, which would be devastating to their economy, hence the reluctant decision to exit. As of October 2020, 147 states had accepted the Doha Amendment. It entered into force on 31 December 2020, following its acceptance by the mandated minimum of at least 144 states, although the second commitment period ended on the same day. Of the 37 parties with binding commitments, 34 had ratified.\nNegotiations were held in the framework of the yearly UNFCCC Climate Change Conferences on measures to be taken after the second commitment period ended in 2020. This resulted in the 2015 adoption of the Paris Agreement, which is a separate instrument under the UNFCCC rather than an amendment of the Kyoto Protocol.\n\nChronology\n\n1992 – The UN Conference on the Environment and Development is held in Rio de Janeiro. It results in the Framework Convention on Climate Change (UNFCCC) among other agreements.\n1995 – Parties to the UNFCCC meet in Berlin (the 1st Conference of Parties (COP) to the UNFCCC) to outline specific targets on emissions.\n1997 – In December the parties conclude the Kyoto Protocol in Kyoto, Japan, in which they agree to the broad outlines of emissions targets.\n2004 – Russia and Canada ratify the Kyoto Protocol to the UNFCCC bringing the treaty into effect on 16 February 2005.\n2011 – Canada became the first signatory to announce its withdrawal from the Kyoto Protocol.\n2012 – On 31 December 2012, the first commitment period under the Protocol expired.\nThe official meeting of all states party to the Kyoto Protocol is the annual Conference of the Parties (COP) to the United Nations Framework Convention on Climate Change (UNFCCC). The first conference was held in 1995 in Berlin (COP 1). The first Meeting of Parties of the Kyoto Protocol (CMP) was held in 2005 in conjunction with COP 11.\n\nObjectives\n\nThe main goal of the Kyoto Protocol was to control emissions of the main anthropogenic (human-emitted) greenhouse gases (GHGs) in ways that reflect underlying national differences in GHG emissions, wealth, and capacity to make the reductions. The treaty follows the main principles agreed in the original 1992 UN Framework Convention. According to the treaty, in 2012, Annex I Parties who have ratified the treaty must have fulfilled their obligations of greenhouse gas emissions limitations established for the Kyoto Protocol's first commitment period (2008–2012). These emissions limitation commitments are listed in Annex B of the Protocol.\nThe Kyoto Protocol's first round commitments are the first detailed step taken within the UN Framework Convention on Climate Change. The Protocol establishes a structure of rolling emission reduction commitment periods. It set a timetable starting in 2006 for negotiations to establish emission reduction commitments for a second commitment period. The first period emission reduction commitments expired on 31 December 2012.\nThe first-round Kyoto emissions limitation commitments were not sufficient to stabilize the atmospheric concentration of GHGs. Stabilization of atmospheric GHG concentrations will require further emissions reductions after the end of the first-round Kyoto commitment period in 2012.\nThe ultimate objective of the UNFCCC is the \"stabilization of greenhouse gas concentrations in the atmosphere at a level that would stop dangerous anthropogenic interference with the climate system.\" Even if Annex I Parties succeed in meeting their first-round commitments, much greater emission reductions will be required in future to stabilize atmospheric GHG concentrations.\nFor each of the different anthropogenic GHGs, different levels of emissions reductions would be required to meet the objective of stabilizing atmospheric concentrations. Carbon dioxide (CO2) is the most important anthropogenic GHG. Stabilizing the concentration of CO2 in the atmosphere would ultimately require the effective elimination of anthropogenic CO2 emissions.\nTo achieve stabilization, global GHG emissions must peak, then decline. The lower the desired stabilization level, the sooner this peak and decline must occur. For a given stabilization level, larger emissions reductions in the near term allow for less stringent emissions reductions later. On the other hand, less stringent near term emissions reductions would, for a given stabilization level, require more stringent emissions reductions later on.\nThe first period Kyoto emissions limitations can be viewed as a first-step towards achieving atmospheric stabilization of GHGs. In this sense, the first period Kyoto commitments may affect what future atmospheric stabilization level can be achieved.\n\nPrincipal concepts\nSome of the principal concepts of the Kyoto Protocol are:\n\nBinding commitments for the Annex I Parties. The main feature of the Protocol is that it established legally binding commitments to reduce emissions of greenhouse gases for Annex I Parties. The commitments were based on the Berlin Mandate, which was a part of UNFCCC negotiations leading up to the Protocol.\nImplementation. In order to meet the objectives of the Protocol, Annex I Parties are required to prepare policies and measures for the reduction of greenhouse gases in their respective countries. In addition, they are required to increase the absorption of these gases and utilize all mechanisms available, such as joint implementation, the clean development mechanism and emissions trading, in order to be rewarded with credits that would allow more greenhouse gas emissions at home.\nMinimizing Impacts on Developing Countries by establishing an adaptation fund for climate change.\nAccounting, Reporting and Review in order to ensure the integrity of the Protocol.\nCompliance. Establishing a Compliance Committee to enforce compliance with the commitments under the Protocol.\n\nFlexibility mechanisms\nThe Protocol defines three \"Flexibility Mechanisms\" that can be used by Annex I Parties in meeting their emission limitation commitments. The flexibility mechanisms are International Emissions Trading (IET), the Clean Development Mechanism (CDM), and Joint Implementation (JI). IET allows Annex I Parties to \"trade\" their emissions (Assigned Amount Units, AAUs, or \"allowances\" for short).\nThe economic basis for providing this flexibility is that the marginal cost of reducing (or abating) emissions differs among countries. \"Marginal cost\" is the cost of abating the last tonne of CO2-eq for an Annex I/non-Annex I Party. At the time of the original Kyoto targets, studies suggested that the flexibility mechanisms could reduce the overall (aggregate) cost of meeting the targets. Studies also showed that national losses in Annex I gross domestic product (GDP) could be reduced by the use of the flexibility mechanisms.\nThe CDM and JI are called \"project-based mechanisms\", in that they generate emission reductions from projects. The difference between IET and the project-based mechanisms is that IET is based on the setting of a quantitative restriction of emissions, while the CDM and JI are based on the idea of \"production\" of emission reductions. The CDM is designed to encourage production of emission reductions in non-Annex I Parties, while JI encourages production of emission reductions in Annex I Parties.\nThe production of emission reductions generated by the CDM and JI can be used by Annex I Parties in meeting their emission limitation commitments. The emission reductions produced by the CDM and JI are both measured against a hypothetical baseline of emissions that would have occurred in the absence of a particular emission reduction project. The emission reductions produced by the CDM are called Certified emission reductions (CERs); reductions produced by JI are called emission reduction units (ERUs). The reductions are called \"credits\" because they are emission reductions credited against a hypothetical baseline of emissions.\nOnly emission reduction projects that do not involve using nuclear energy are eligible for accreditation under the CDM, in order to prevent nuclear technology exports from becoming the default route for obtaining credits under the CDM.\nEach Annex I country is required to submit an annual report of inventories of all anthropogenic greenhouse gas emissions from sources and removals from sinks under UNFCCC and the Kyoto Protocol. These countries nominate a person (called a \"designated national authority\") to create and manage its greenhouse gas inventory. Virtually all of the non-Annex I countries have also established a designated national authority to manage their Kyoto obligations, specifically the \"CDM process\". This determines which GHG projects they wish to propose for accreditation by the CDM Executive Board.\n\nInternational emissions trading\n\nIntergovernmental emissions trading\nThe design of the European Union Emissions Trading Scheme (EU ETS) implicitly allows for trade of national Kyoto obligations to occur between participating countries. The Carbon Trust found that other than the trading that occurs as part of the EU ETS, no intergovernmental emissions trading had taken place.\nOne of the environmental problems with IET is the large surplus of allowances that are available. Russia, Ukraine, and the new EU-12 member states (the Kyoto Parties Annex I Economies-in-Transition, abbreviated \"EIT\": Belarus, Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Russia, Slovakia, Slovenia, and Ukraine) have a surplus of allowances, while many OECD countries have a deficit. Some of the EITs with a surplus regard it as potential compensation for the trauma of their economic restructuring. When the Kyoto treaty was negotiated, it was recognized that emissions targets for the EITs might lead to them having an excess number of allowances. This excess of allowances were viewed by the EITs as \"headroom\" to grow their economies. The surplus has, however, also been referred to by some as \"hot air\", a term which Russia (a country with an estimated surplus of 3.1 billion tonnes of carbon dioxide equivalent allowances) views as \"quite offensive\".\nOECD countries with a deficit could meet their Kyoto commitments by buying allowances from transition countries with a surplus. Unless other commitments were made to reduce the total surplus in allowances, such trade would not actually result in emissions being reduced (see also the section below on the Green Investment Scheme).\n\n\"Green Investment Schemes\"\nThe \"Green Investment Scheme\" (GIS) is a plan for achieving environmental benefits from trading surplus allowances (AAUs) under the Kyoto Protocol. The Green Investment Scheme (GIS), a mechanism in the framework of International Emissions Trading (IET), is designed to achieve greater flexibility in reaching the targets of the Kyoto Protocol while preserving environmental integrity of IET. However, using the GIS is not required under the Kyoto Protocol, and there is no official definition of the term.\nUnder the GIS a party to the protocol expecting that the development of its economy will not exhaust its Kyoto quota, can sell the excess of its Kyoto quota units (AAUs) to another party. The proceeds from the AAU sales should be \"greened\", i.e. channelled to the development and implementation of the projects either acquiring the greenhouse gases emission reductions (hard greening) or building up the necessary framework for this process (soft greening).\n\nTrade in AAUs\nLatvia was one of the front-runners of GISs. World Bank (2011) reported that Latvia has stopped offering AAU sales because of low AAU prices. In 2010, Estonia was the preferred source for AAU buyers, followed by the Czech Republic and Poland.\nJapan's national policy to meet their Kyoto target includes the purchase of AAUs sold under GISs. In 2010, Japan and Japanese firms were the main buyers of AAUs. In terms of the international carbon market, trade in AAUs are a small proportion of overall market value. In 2010, 97% of trade in the international carbon market was driven by the European Union Emission Trading Scheme (EU ETS).\n\nClean Development Mechanism\nBetween 2001, which was the first year Clean Development Mechanism (CDM) projects could be registered, and 2012, the end of the first Kyoto commitment period, the CDM is expected to produce some 1.5 billion tons of carbon dioxide equivalent (CO2e) in emission reductions. Most of these reductions are through renewable energy commercialisation, energy efficiency, and fuel switching (World Bank, 2010, p. 262). By 2012, the largest potential for production of CERs are estimated in China (52% of total CERs) and India (16%). CERs produced in Latin America and the Caribbean make up 15% of the potential total, with Brazil as the largest producer in the region (7%).\n\nJoint Implementation\nThe formal crediting period for Joint Implementation (JI) was aligned with the first commitment period of the Kyoto Protocol, and did not start until January 2008 (Carbon Trust, 2009, p. 20). In November 2008, only 22 JI projects had been officially approved and registered. The total projected emission savings from JI by 2012 are about one tenth that of the CDM. Russia accounts for about two-thirds of these savings, with the remainder divided up roughly equally between Ukraine and the EU's New Member States. Emission savings include cuts in methane, HFC, and N2O emissions.\n\nDetails of the agreement\nThe agreement is a protocol to the United Nations Framework Convention on Climate Change (UNFCCC) adopted at the Earth Summit in Rio de Janeiro in 1992, which did not set any legally binding limitations on emissions or enforcement mechanisms. Only Parties to the UNFCCC can become Parties to the Kyoto Protocol. The Kyoto Protocol was adopted at the third session of the Conference of Parties to the UNFCCC in 1997 in Kyoto, Japan.\nNational emission targets specified in the Kyoto Protocol exclude international aviation and shipping. Kyoto Parties can use land use, land use change, and forestry (LULUCF) in meeting their targets. LULUCF activities are also called \"sink\" activities. Changes in sinks and land use can have an effect on the climate, and indeed the Intergovernmental Panel on Climate Change's Special Report on Land use, land-use change, and forestry estimates that since 1750 a third of global warming has been caused by land use change. Particular criteria apply to the definition of forestry under the Kyoto Protocol.\nForest management, cropland management, grazing land management, and revegetation are all eligible LULUCF activities under the Protocol. Annex I Parties use of forest management in meeting their targets is capped.\n\nFirst commitment period: 2008–2012\nUnder the Kyoto Protocol, 37 industrialized countries and the European Community (the European Union-15, made up of 15 states at the time of the Kyoto negotiations) commit themselves to binding targets for GHG emissions. The targets apply to the four greenhouse gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulphur hexafluoride (SF6), and two groups of gases, hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). The six GHG are translated into CO2 equivalents in determining reductions in emissions. These reduction targets are in addition to the industrial gases, chlorofluorocarbons, or CFCs, which are dealt with under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer.\nUnder the Protocol, only the Annex I Parties have committed themselves to national or joint reduction targets (formally called \"quantified emission limitation and reduction objectives\" (QELRO) – Article 4.1). Parties to the Kyoto Protocol not listed in Annex I of the convention (the non-Annex I Parties) are mostly low-income developing countries, and may participate in the Kyoto Protocol through the Clean Development Mechanism (explained below).\nThe emissions limitations of Annex I Parties varies between different Parties. Some Parties have emissions limitations reduce below the base year level, some have limitations at the base year level (no permitted increase above the base year level), while others have limitations above the base year level.\nEmission limits do not include emissions by international aviation and shipping. Although Belarus and Turkey are listed in the convention's Annex I, they do not have emissions targets as they were not Annex I Parties when the Protocol was adopted. Kazakhstan does not have a target, but has declared that it wishes to become an Annex I Party to the convention.\n\nFor most state parties, 1990 is the base year for the national GHG inventory and the calculation of the assigned amount. However, five state parties have an alternative base year:\n\nBulgaria: 1988;\nHungary: the average of the years 1985–1987;\nPoland: 1988;\nRomania: 1989;\nSlovenia: 1986.\nAnnex I Parties can use a range of sophisticated \"flexibility\" mechanisms (see below) to meet their targets. Annex I Parties can achieve their targets by allocating reduced annual allowances to major operators within their borders, or by allowing these operators to exceed their allocations by offsetting any excess through a mechanism that is agreed by all the parties to the UNFCCC, such as by buying emission allowances from other operators which have excess emissions credits.\n\nNegotiations\n\nArticle 4.2 of the UNFCCC commits industrialized countries to \"[take] the lead\" in reducing emissions. The initial aim was for industrialized countries to stabilize their emissions at 1990 levels by 2000. The failure of key industrialized countries to move in this direction was a principal reason why Kyoto moved to binding commitments.\nAt the first UNFCCC Conference of the Parties in Berlin, the G77 was able to push for a mandate (the \"Berlin mandate\") where it was recognized that:\n\ndeveloped nations had contributed most to the then-current concentrations of GHGs in the atmosphere (see Greenhouse gas emissions).\ndeveloping country emissions per-capita (i.e., average emissions per head of population) were still relatively low.\nand that the share of global emissions from developing countries would grow to meet their development needs.\nDuring negotiations, the G-77 represented 133 developing countries. China was not a member of the group but an associate. It has since become a member.\nThe Berlin mandate was recognized in the Kyoto Protocol in that developing countries were not subject to emission reduction commitments in the first Kyoto commitment period. However, the large potential for growth in developing country emissions made negotiations on this issue tense. In the final agreement, the Clean Development Mechanism was designed to limit emissions in developing countries, but in such a way that developing countries do not bear the costs for limiting emissions. The general assumption was that developing countries would face quantitative commitments in later commitment periods, and at the same time, developed countries would meet their first round commitments.\n\nEmissions cuts\n\nThere were multiple emissions cuts proposed by UNFCCC parties during negotiations. The G77 and China were in favour of strong uniform emission cuts across the developed world. The US originally proposed for the second round of negotiations on Kyoto commitments to follow the negotiations of the first. In the end, negotiations on the second period were set to open no later than 2005. Countries over-achieving in their first period commitments can \"bank\" their unused allowances for use in the subsequent period.\nThe EU initially argued for only three GHGs to be included – CO2, CH4, and N2O – with other gases such as HFCs regulated separately. The EU also wanted to have a \"bubble\" commitment, whereby it could make a collective commitment that allowed some EU members to increase their emissions, while others cut theirs.\nThe most vulnerable nations – the Alliance of Small Island States (AOSIS) – pushed for deep uniform cuts by developed nations, with the goal of having emissions reduced to the greatest possible extent. Countries that had supported differentiation of targets had different ideas as to how it should be calculated, and many different indicators were proposed. Two examples include differentiation of targets based on gross domestic product (GDP), and differentiation based on energy intensity (energy use per unit of economic output).\nThe final targets negotiated in the Protocol are the result of last minute political compromises. The targets closely match those decided by Argentinian Raul Estrada, the diplomat who chaired the negotiations. The numbers given to each Party by Chairman Estrada were based on targets already pledged by Parties, information received on latest negotiating positions, and the goal of achieving the strongest possible environmental outcome. The final targets are weaker than those proposed by some Parties, e.g., the Alliance of Small Island States and the G-77 and China, but stronger than the targets proposed by others, e.g., Canada and the United States.\n\nRelation to temperature targets\nAt the 16th Conference of the Parties held in 2010, Parties to the UNFCCC agreed that future global warming should be limited below 2°C relative to the pre-industrial temperature level. One of the stabilization levels discussed in relation to this temperature target is to hold atmospheric concentrations of GHGs at 450 parts per million (ppm) CO2- eq. Stabilization at 450 ppm could be associated with a 26 to 78% risk of exceeding the 2 °C target.\nScenarios assessed by Gupta et al. (2007) suggest that Annex I emissions would need to be 25% to 40% below 1990 levels by 2020, and 80% to 95% below 1990 levels by 2050. The only Annex I Parties to have made voluntary pledges in line with this are Japan (25% below 1990 levels by 2020) and Norway (30–40% below 1990 levels by 2020).\nGupta et al. (2007) also looked at what 450 ppm scenarios projected for non-Annex I Parties. Projections indicated that by 2020, non-Annex I emissions in several regions (Latin America, the Middle East, East Asia, and centrally planned Asia) would need to be substantially reduced below \"business-as-usual\". \"Business-as-usual\" are projected non-Annex I emissions in the absence of any new policies to control emissions. Projections indicated that by 2050, emissions in all non-Annex I regions would need to be substantially reduced below \"business-as-usual\".\n\nFinancial commitments\nThe Protocol also reaffirms the principle that developed countries have to pay billions of dollars, and supply technology to other countries for climate-related studies and projects. The principle was originally agreed in UNFCCC. One such project is The Adaptation Fund, which has been established by the Parties to the Kyoto Protocol of the UN Framework Convention on Climate Change to finance concrete adaptation projects and programmes in developing countries that are Parties to the Kyoto Protocol.\n\nImplementation provisions\nThe protocol left several issues open to be decided later by the sixth Conference of Parties COP6 of the UNFCCC, which attempted to resolve these issues at its meeting in the Hague in late 2000, but it was unable to reach an agreement due to disputes between the European Union (who favoured a tougher implementation) and the United States, Canada, Japan and Australia (who wanted the agreement to be less demanding and more flexible).\nIn 2001, a continuation of the previous meeting (COP6-bis) was held in Bonn, where the required decisions were adopted. After some concessions, the supporters of the protocol (led by the European Union) managed to secure the agreement of Japan and Russia by allowing more use of carbon dioxide sinks.\nCOP7 was held from 29 October 2001 through 9 November 2001 in Marrakesh to establish the final details of the protocol.\nThe first Meeting of the Parties to the Kyoto Protocol (MOP1) was held in Montreal from 28 November to 9 December 2005, along with the 11th conference of the Parties to the UNFCCC (COP11). See United Nations Climate Change Conference.\nDuring COP13 in Bali, 36 developed Contact Group countries (plus the EU as a party in the European Union) agreed to a 10% emissions increase for Iceland; but, since the EU's member states each have individual obligations, much larger increases (up to 27%) are allowed for some of the less developed EU countries (see below § Increase in greenhouse gas emission since 1990). Reduction limitations expired in 2013.\n\nMechanism of compliance\nThe protocol defines a mechanism of \"compliance\" as a \"monitoring compliance with the commitments and penalties for non-compliance.\" According to Grubb (2003), the explicit consequences of non-compliance of the treaty are weak compared to domestic law. Yet, the compliance section of the treaty was highly contested in the Marrakesh Accords.\n\nMonitoring emissions\nMonitoring emissions in international agreements is tough as in international law, there is no police power, creating the incentive for states to find 'ways around' monitoring. The Kyoto Protocol regulated six sinks and sources of Gases. Carbon dioxide, Methane, Nirous oxide, Hydroflurocarbons, Sulfur hexafluouride and Perfluorocarbons. Monitoring these gases can become quite a challenge. Methane can be monitored and measured from irrigated rice fields and can be measured by the seedling growing up to harvest. Future implications state that this can be affected by more cost effective ways to control emissions as changes in types of fertilizer can reduce emissions by 50%. In addition to this, many countries are unable to monitor certain ways of carbon absorption through trees and soils to an accurate level.\n\nEnforcing emission cuts\nIf the enforcement branch determines that an Annex I country is not in compliance with its emissions limitation, then that country is required to make up the difference during the second commitment period plus an additional 30%. In addition, that country will be suspended from making transfers under an emissions trading program.\n\nRatification process\n\nCountries that ratified the Protocol\nThe Protocol was adopted by COP 3 of UNFCCC on 11 December 1997 in Kyoto, Japan. It was opened on 16 March 1998 for signature during one year by parties to UNFCCC, when it was signed Antigua and Barbuda, Argentina, the Maldives, Samoa, St. Lucia and Switzerland. At the end of the signature period, 82 countries and the European Community had signed. Ratification (which is required to become a party to the Protocol) started on 17 September with ratification by Fiji. Countries that did not sign acceded to the convention, which has the same legal effect.\nArticle 25 of the Protocol specifies that the Protocol enters into force \"on the ninetieth day after the date on which not less than 55 Parties to the Convention, incorporating Parties included in Annex I ",
    "source": "wikipedia:Kyoto Protocol",
    "domain": "climate"
  },
  {
    "text": "A carbon tax is a tax levied on the carbon emissions from producing goods and services. Carbon taxes are intended to make visible the hidden social costs of carbon emissions. They are designed to reduce greenhouse gas emissions by essentially increasing the price of fossil fuels. This both decreases demand for goods and services that produce high emissions and incentivizes making them less carbon-intensive. When a fossil fuel such as coal, petroleum, or natural gas is burned, most or all of its carbon is converted to CO2. Greenhouse gas emissions cause climate change. This negative externality can be reduced by taxing carbon content at any point in the product cycle.\nA carbon tax as well as carbon emission trading is used within the carbon price concept. Two common economic alternatives to carbon taxes are tradable permits with carbon credits and subsidies. In its simplest form, a carbon tax covers only CO2 emissions. It could also cover other greenhouse gases, such as methane or nitrous oxide, by taxing such emissions based on their CO2-equivalent global warming potential. Research shows that carbon taxes do often reduce emissions. Many economists argue that carbon taxes are the most efficient (lowest cost) way to tackle climate change. As of 2019, carbon taxes have either been implemented or are scheduled for implementation in 25 countries. 46 countries have put some form of price on carbon, either through carbon taxes or carbon emission trading schemes.\n\nSome experts observe that a carbon tax can negatively affect public welfare, tending to hit low- and middle-income households the hardest and making their necessities more expensive (for instance, the tax might drive up prices for, say, petrol and electricity). Alternatively, the tax can be too conservative, making \"comparatively small dents in overall emissions\". To make carbon taxes fairer, policymakers can try to redistribute the revenue generated from carbon taxes to low-income groups by various fiscal means. Such a policy initiative becomes a carbon fee and dividend, rather than a plain tax.\n\nPurpose\n\nCarbon dioxide is one of several heat-trapping greenhouse gases (others include methane and water vapor) emitted as a result of human activities. The scientific consensus is that human-induced greenhouse gas emissions are the primary cause of climate change, and that carbon dioxide is the most important of the anthropogenic greenhouse gases. Worldwide, 27 billion tonnes of carbon dioxide are produced by human activity annually. The physical effect of CO2 in the atmosphere can be measured as a change in the Earth-atmosphere system's energy balance – the radiative forcing of CO2.\nDifferent greenhouse gases have different physical properties: the global warming potential is an internationally accepted scale of equivalence for other greenhouse gases in units of tonnes of carbon dioxide equivalent. Carbon taxes are designed to reduce greenhouse gas emissions by increasing prices of the fossil fuels that emit them when burned. This both decreases demand for goods and services that produce high emissions and incentivizes making them less carbon-intensive.\n\nEconomic theory\n\nHistory and Rationale\nA carbon tax is a form of pollution tax. David Gordon Wilson first proposed this type of tax in 1973. Unlike classic command and control regulations, which explicitly limit or prohibit emissions by each individual polluter, a carbon tax aims to allow market forces to determine the most efficient way to reduce pollution. A carbon tax is an indirect tax—a tax on a transaction—as opposed to a direct tax, which taxes income. Carbon taxes are price instruments since they set a price rather than an emission limit.\nIn addition to creating incentives for energy conservation, a carbon tax puts renewable energy such as wind, solar and geothermal on a more competitive footing. In economic theory, pollution is considered a negative externality, a negative effect on a third party not directly involved in a transaction, and is a type of market failure. To confront the issue, economist Arthur Pigou proposed taxing the goods (in this case hydrocarbon fuels), that were the source of the externality (CO2) so as to accurately reflect the cost of the goods to society, thereby internalizing the production costs. A tax on a negative externality is called a Pigovian tax, which should equal the cost.\nWithin Pigou's framework, the changes involved are marginal, and the size of the externality is assumed to be small enough not to distort the economy. Climate change is claimed to result in catastrophe (non-marginal) changes. \"Non-marginal\" means that the impact could significantly reduce the growth rate in income and welfare. The amount of resources that should be devoted to climate change mitigation is controversial. Policies designed to reduce carbon emissions could have a non-marginal impact, but are asserted to not be catastrophic.\n\nDesign\nThe design of a carbon tax involves two primary factors: the level of the tax, and the use of the revenue. The former is based on the social cost of carbon (SCC), which attempts to calculate the numeric cost of the externalities of carbon pollution. The precise number is the subject of debate in environmental and policy circles. A higher SCC corresponds with a higher evaluation of the costs of carbon pollution on society. Stanford University scientists have estimated the social cost of carbon to be upwards of $200 per ton. More conservative estimates pin the cost at around $50.\nThe use of the revenue is another subject of debate in carbon tax proposals. A government may use revenue to increase its discretionary spending, or address deficits. However, such proposals often run the risk of being regressive, and sparking backlash among the public due to an increased cost of energy associated with such taxes. To avoid this and increase the popularity of a carbon tax, a government may make the carbon tax revenue-neutral. This can be done by reducing income tax proportionate to the level of the carbon tax, or by returning carbon tax revenues to citizens as a dividend.\n\nCarbon leakage\nCarbon leakage happens when the regulation of emissions in one country/sector pushes those emissions to other places with less regulation. Leakage effects can be both negative (i.e., increasing the effectiveness of reducing overall emissions) and positive (reducing the effectiveness of reducing overall emissions). Negative leakages, which are desirable, can be referred to as \"spill-over\".\nAccording to one study, short-term leakage effects need to be judged against long-term effects. A policy that, for example, establishes carbon taxes only in developed countries might leak emissions to developing countries. However, a desirable negative leakage could occur due to reduced demand for coal, oil, and gas in developed countries, lowering prices. This could allow developing countries to replace coal with oil or gas, lowering emissions. In the long-run, however, if less polluting technologies are delayed, this substitution might have no long-term benefit. Carbon leakage is central to climate policy, given the 2030 Energy and Climate Framework and the review of the European Union's third carbon leakage list.\n\nCarbon tariff\n\nImpacts\n\nPositive impacts\nResearch shows that carbon taxes effectively reduce greenhouse gas emissions. Most economists assert that carbon taxes are the most efficient and effective way to curb climate change, with the least adverse economic effects. One study found that Sweden's carbon tax successfully reduced carbon dioxide emissions from transport by 11%. A 2015 British Columbia study found that the taxes reduced greenhouse gas emissions by 5–15% while having negligible overall economic effects. A 2017 British Columbia study found that industries on the whole benefited from the tax and \"small but statistically significant 0.74 percent annual increases in employment\" but that carbon-intensive and trade-sensitive industries were adversely affected. A 2020 study of carbon taxes in wealthy democracies showed that carbon taxes had not limited economic growth. Carbon taxes also appear to not adversely affect employment or GDP growth in Europe. Their economic impact ranges from zero to modest positive.\n\nNegative impacts and trade-offs\nA number of studies have found that in the absence of an increase in social benefits and tax credits, a carbon tax would hit poor households harder than rich households. Gilbert E. Metcalf disputed that carbon taxes would be regressive in the US. Carbon taxes can increase electricity prices. There is a debate about the relation between carbon pricing (like carbon emission trading and carbon tax) and climate justice. Carbon pricing can be adjusted to some principles of climate justice like polluters pay. Many proponents of climate justice object to carbon pricing. To close the gap between the two concepts, carbon pricing could put a cap on emissions, remove pollution from underserved communities, and justly divide revenues.\n\nSupport and opposition\nSince carbon taxation was first proposed, numerous economists have described its strengths as a means of reducing CO2 pollution. This tax has been praised as \"a far better way to control pollution than the present method of specific regulation.\" It has also been lauded for its market based simplicity. This includes a description as \"the most efficient way to guide the decisions of producers and consumers\", since \"carbon emissions have an 'unpriced' societal cost in terms of their deleterious effects on the earth's climate.\"\nSince 2019 over 3,500 U.S. economists have signed The Economists' Statement on Carbon Dividends. This statement describes the benefits of a U.S. carbon tax along with suggestions for how it could be developed. One recommendation is to return revenues generated by a tax to the general public. The statement was originally signed by 45 Nobel Prize winning economists, former chairs of the Federal Reserve, former chairs of the Council of Economic Advisers, and former secretaries of the Treasury Department. It has been recognized as a historic example of consensus amongst economists. Ben Ho, professor of economics at Vassar College, has argued that \"while carbon taxes are part of the optimal portfolio of policies to fight climate change, they are not the most important part.\"\nCarbon taxes have been opposed by a substantial proportion of the public. They have also been rejected in several elections, and in some cases reversed as opposition increased. One response has been to specifically allocate carbon tax revenues back to the public in order to garner support. Citizens' Climate Lobby is an international organization with over 500 chapters. It advocates for carbon tax legislation in the form of a progressive fee and dividend structure. NASA climatologist James E. Hansen has also spoken in favor of a revenue neutral carbon fee.\n\nPublic perception\nIn some instances knowledge about how carbon tax revenues are used can affect public support. Dedicating revenues to climate projects and compensating low income housing have been found to be popular uses of revenue. However, providing information about specific revenue uses in countries that have implemented carbon taxes has been shown to have limited effectiveness in increasing public support. A 2021 poll conducted by GlobeScan on 31 countries and territories found that 62 percent on average are supportive of a carbon tax, while only 33 percent are opposed to a carbon tax. In 28 of the 31 countries and territories listed in the poll, a majority of their populations are supportive of a carbon tax.\n\nAlternatives\n\nCarbon emission trading\n\nCarbon emission trading (also called cap and trade) is another approach. Emission levels are limited and emission permits traded among emitters. The permits can be issued via government auctions or offered without charge based on existing emissions (grandfathering). Auctions raise revenues that can be used to reduce other taxes or to fund government programs. Variations include setting price-floor and/or price-ceiling for permits. A carbon tax can be combined with trading. A cap with grandfathered permits can have an efficiency advantage since it applies to all industries. Cap and trade provides an equal incentive for all producers at the margin to reduce their emissions. This is an advantage over a tax that exempts or has reduced rates for certain sectors.\nBoth carbon taxes and trading systems aim to reduce emissions by creating a price for emitting CO2. In the absence of uncertainty both systems will result in the efficient market quantity and price of CO2. When the environmental damage and therefore the appropriate tax of each unit of CO2 cannot be accurately calculated, a permit system may be more advantageous. In the case of uncertainty regarding the costs of CO2 abatement for firms, a tax is preferable. Permit systems regulate total emissions. In practice the limit has often been set so high that permit prices are not significant. In the first phase of the European Union Emissions Trading System, firms reduced their emissions to their allotted quantity without the purchase of any additional permits. This drove permit prices to nearly zero two years later, crashing the system and requiring reforms that would eventually appear in EUETS Phase 3.\nThe distinction between carbon taxes and permit systems can get blurred when hybrid systems are allowed. A hybrid sets limits on price movements, potentially softening the cap. When the price gets too high, the issuing authority issues additional permits at that price. A price floor may be breached when emissions are so low that no one needs to buy a permit. Economist Gilbert Metcalf has proposed such a system, the Emissions Assurance Mechanism, and the idea, in principle, has been adopted by the Climate Leadership Council. James E. Hansen argued in 2009 that emissions trading would only make money for banks and hedge funds and allow business-as-usual for the chief carbon-emitting industries.\n\nCarbon offsets and credits\n\nOther types of taxes\n\nTwo related taxes are emissions taxes and energy taxes. An emissions tax on greenhouse gas emissions requires individual emitters to pay a fee, charge, or tax for every tonne of greenhouse gas, while an energy tax is applied to the fuels themselves. In terms of climate change mitigation, a carbon tax is not a perfect substitute for an emissions tax. For example, a carbon tax encourages reduced fuel use, but it does not encourage emissions reduction such as carbon capture and storage. Energy taxes increase the price of energy regardless of emissions.\nAn ad valorem energy tax is levied according to the energy content of a fuel or the value of an energy product, which may or may not be consistent with the emitted greenhouse gas amounts and their respective global warming potentials. Studies indicate that to reduce emissions by a certain amount, ad valorem energy taxes would be more costly than carbon taxes. However, although greenhouse gas emissions are an externality, using energy services may result in other negative externalities, e.g., air pollution not covered by the carbon tax (such as ammonia or fine particles). A combined carbon-energy tax may therefore be better at reducing air pollution than a carbon tax alone.\nAny of these taxes can be combined with a rebate, where the money collected by the tax is returned to qualifying parties, taxing heavy emitters and subsidizing those that emit less carbon. Because carbon taxes only target carbon dioxide, they do not target other greenhouse gasses, such as methane, which have a greater warming potential.\n\nPetroleum (gasoline, diesel, jet fuel) taxes\nMany countries tax fuel directly; for example, the UK imposes a hydrocarbon oil duty directly on vehicle hydrocarbon oils, including petrol and diesel fuel. While a direct tax sends a clear signal to the consumer, its efficiency at influencing consumers' fuel use has been challenged for reasons including:\n\nPossible delays of a decade or more as inefficient vehicles are replaced by newer models and the older models filter through the fleet.\nPolitical pressures that deter policymakers from increasing taxes.\nLimited relationship between consumer decisions on fuel economy and fuel prices. Other efforts, such as fuel efficiency standards, or changing income tax rules on taxable benefits, may be more effective.\nThe historical use of fuel taxes as a source of general revenue, given fuel's low price elasticity, which allows higher rates without reducing fuel volumes. In these circumstances, the policy rational may be unclear.\nVehicle fuel taxes may reduce the \"rebound effect\" that occurs when vehicle efficiency improves. Consumers may make additional journeys or purchase heavier and more powerful vehicles, offsetting the efficiency gains.\n\nComparison of alternatives\nA 2018 survey of leading economists found that 58% of the surveyed economists agreed with the assertion, \"Carbon taxes are a better way to implement climate policy than cap-and-trade,\" 31% stated that they had no opinion or that it was uncertain, but none of the respondents disagreed.\nIn a review study in 1996 the authors concluded that the choice between an international quota (cap) system, or an international carbon tax, remained ambiguous. Another study in 2012 compared a carbon tax, emissions trading, and command-and-control regulation at the industry level, concluding that market-based mechanisms would perform better than emission standards in achieving emission targets without affecting industrial production.\n\nImplementation\n\nBoth energy and carbon taxes have been implemented in response to commitments under the United Nations Framework Convention on Climate Change. In most cases the tax is implemented in combination with exemptions. Indirect carbon prices, such as fuel taxes, are much more common than carbon taxes. In 2021, OECD reported that 67 of the 71 countries it assessed had some form of fuel tax. Only 39 had carbon taxes or ETSs. However, the use of carbon taxes is growing more quickly. In addition, several countries plan to further strengthen existing carbon taxes in the coming years, including Singapore, Canada and South Africa.\nCurrent carbon price policies, including carbon taxes, are still considered insufficient to create the kinds of changes in emissions that would be consistent with Paris Agreement goals. The International Monetary Fund, OECD, and others have stated that current fossil fuel prices generally fail to reflect environmental impacts.\n\nEurope\n\nIn Europe, many countries have imposed energy taxes or energy taxes based partly on carbon content. These include Denmark, Finland, Germany, Ireland, Italy, the Netherlands, Norway, Slovenia, Sweden, Switzerland, and the UK. None of these countries have been able to introduce a uniform carbon tax for fuels in all sectors. Denmark is the first country to include livestock emissions in their carbon tax system.\nDuring the 1990s, a carbon/energy tax was proposed at the EU level but failed due to industrial lobbying. In 2010, the European Commission considered implementing a pan-European minimum tax on pollution permits purchased under the European Union Greenhouse Gas Emissions Trading Scheme (EU ETS) in which the proposed new tax would be calculated in terms of carbon content. The suggested rate of €4 to €30 per tonne of CO2.\n\nAmericas\n\nCosta Rica\nIn 1997, Costa Rica imposed a 3.5 percent carbon tax on hydrocarbon fuels. A portion of the proceeds go to the \"Payment for Environmental Services\" (PSA) program which gives incentives to property owners to practice sustainable development and forest conservation. Approximately 11% of Costa Rica's national territory is protected by the plan. The program now pays out roughly $15 million a year to around 8,000 property owners.\n\nCanada\n\nIn the 2008 Canadian federal election, a carbon tax proposed by Liberal Party leader Stéphane Dion, known as the Green Shift, became a central issue. It would have been revenue-neutral, balancing increased taxation on carbon with rebates. However, it proved to be unpopular and contributed to the Liberal Party's defeat, earning the lowest vote share since Confederation. The Conservative party won the election by promising to \"develop and implement a North American-wide cap-and-trade system for greenhouse gases and air pollution, with implementation to occur between 2012 and 2015\".\nIn 2018, Canada enacted a revenue-neutral carbon levy starting in 2019, fulfilling Prime Minister Justin Trudeau's campaign pledge. The Greenhouse Gas Pollution Pricing Act applies only to provinces without provincial adequate carbon pricing. As of September 2020, seven of thirteen Canadian provinces and territories use the federal carbon tax while three have developed their own carbon tax programs. In December 2020, the federal government released an updated plan with a CA$15 per tonne per year increase in the carbon pricing, reaching CA$95 per tonne in 2025 and CA$170 per tonne in 2030. Quebec became the first province to introduce a carbon tax. The tax was to be imposed on energy producers starting 1 October 2007, with revenue collected used for energy-efficiency programs. The tax rate for gasoline is $CDN0.008 per liter, or about CA$3.50 per tonne of CO2 equivalent.\nThe Liberal government claimed 80% of Canadians were receiving more money back via a carbon rebate but the tax was unpopular with many Canadians and became a political issue. In 2023, the Official Opposition refused to support a free trade bill between Canada and the Ukraine that added a new environmental chapter to \"promote carbon pricing\". Liberal Trade Minister Mary Ng stated, \"We should applaud the Ukrainians for being able to negotiate an agreement and also fight climate change.\" Liberal House leader Karina Gould, argued the Tories were \"abandoning Ukraine and not taking climate change seriously\", and accused them of \"American-style, right-wing politics\". Pierre Poilievre, the leader of the Opposition, called the carbon tax stipulation \"cruel\" and stated, \"It is disgusting, that Trudeau’s ideological obsession with taxing working-class people, seniors and suffering families has come ahead of what should have been a free trade agreement.\"\nBy the end of 2024, opinion polls showed the ruling Trudeau Liberals were 20 points behind the Conservative Party of Canada, which was using the slogan \"Axe the Tax\" in their platform. Many Liberals, worried about projected losses in the 2025 federal election, pushed for Justin Trudeau to resign, which he eventually announced on January 6, 2025. The party former Governor of the Bank of Canada, Mark Carney, and within a few hours of being sworn in as Canada's 24th prime minister on March 14, 2025, Carney signed a declaration ending the consumer carbon tax and the rebate. Carney stated in his platform that \"further measures to make up for the lost impact of the consumer carbon tax\" would be implemented. Alberta Premier Danielle Smith warned of forthcoming increased industrial carbon taxes, which would be passed onto consumers without a rebate program in effect.\n\nUnited States\n\nA national carbon tax in the U.S. has been repeatedly proposed, but never enacted. For instance, on 23 July 2018, Representative Carlos Curbelo (R-FL) introduced H.R. 6463, the \"Market Choice Act\", a proposal for a carbon tax in which revenue is used to bolster American infrastructure and environmental solutions. The bill was introduced in the House of Representatives, but did not become law.\nA number of organizations are currently advancing national carbon tax proposals. To address concerns from conservatives that a carbon tax would grow government and increase cost of living, recent proposals have centered around revenue-neutrality. The Citizens' Climate Lobby (CCL), republicEn (formerly E&EI), the Climate Leadership Council (CLC), and Americans for Carbon Dividends (AFCD) support a revenue-neutral carbon tax with a border adjustment. The latter two organizations advocate for a specific framework called the Baker-Shultz Carbon Dividends Plan, which has gained national bipartisan traction since its announcement in 2017. The central principle is a gradually rising carbon tax in which all revenues are rebated as equal dividends to the American people. This plan is co-authored by and named after Republican elder-statesmen James Baker and George Shultz. It is also supported by companies including Microsoft, Pepsico, First Solar, American Wind Energy Association, Exxon Mobil, BP, and General Motors.\n\nSee also\n\nReferences",
    "source": "wikipedia:Carbon tax",
    "domain": "climate"
  },
  {
    "text": "Emissions trading is a market-oriented approach to controlling pollution by providing economic incentives for reducing the emissions of pollutants. The concept is also known as cap and trade (CAT) or emissions trading scheme (ETS). One prominent example is carbon emission trading for CO2 and other greenhouse gases which is a tool for climate change mitigation. Other schemes include sulfur dioxide and other pollutants.\nIn an emissions trading scheme, a central authority or governmental body allocates or sells a limited number (a \"cap\") of permits that allow a discharge of a specific quantity of a specific pollutant over a set time period. Polluters are required to hold permits in amount equal to their emissions. Polluters that want to increase their emissions must buy permits from others willing to sell them.\nEmissions trading is a type of flexible environmental regulation that allows organizations and markets to decide how best to meet policy targets. This is in contrast to command-and-control environmental regulations such as best available technology (BAT) standards and government subsidies.\n\nIntroduction\n\nPollution is a prime example of a market externality. An externality is an effect of some activity on an entity (such as a person) that is not party to a market transaction related to that activity. Emissions trading is a market-based approach to address pollution. The overall goal of an emissions trading plan is to minimize the cost of meeting a set emissions target.\nIn an emissions trading system, the government sets an overall limit on emissions, and defines permits (also called allowances), or limited authorizations to emit, up to the level of the overall limit. The government may sell the permits, but in many existing schemes, it gives permits to participants (regulated polluters) equal to each participant's baseline emissions. The baseline is determined by reference to the participant's historical emissions. To demonstrate compliance, a participant must hold permits at least equal to the quantity of pollution it actually emitted during the time period. If every participant complies, the total pollution emitted will be at most equal to the sum of individual limits. Because permits can be bought and sold, a participant can choose either to use its permits exactly (by reducing its own emissions); or to emit less than its permits, and perhaps sell the excess permits; or to emit more than its permits, and buy permits from other participants. In effect, the buyer pays a charge for polluting, while the seller gains a reward for having reduced emissions.\nEmissions Trading results in the incorporation of economic costs into the costs of production which incentivizes corporations to consider investment returns and capital expenditure decisions with a model that includes the price of carbon and greenhouse gases (GHG).\nIn many schemes, organizations which do not pollute (and therefore have no obligations) may also trade permits and financial derivatives of permits.\nIn some schemes, participants can bank allowances to use in future periods. In some schemes, a proportion of all traded permits must be retired periodically, causing a net reduction in emissions over time. Thus, environmental groups may buy and retire permits, driving up the price of the remaining permits according to the law of demand. In most schemes, permit owners can donate permits to a nonprofit entity and receive a tax deductions. Usually, the government lowers the overall limit over time, with an aim towards a national emissions reduction target.\nThere are active trading programs in several air pollutants. An earlier application was the US national market to reduce acid rain. The United States now has several regional markets in nitrogen oxides.\n\nHistory\nThe efficiency of what later was to be called the \"cap-and-trade\" approach to air pollution abatement was first demonstrated in a series of micro-economic computer simulation studies between 1967 and 1970 for the National Air Pollution Control Administration (predecessor to the United States Environmental Protection Agency's Office of Air and Radiation) by Ellison Burton and William Sanjour. These studies used mathematical models of several cities and their emission sources in order to compare the cost and effectiveness of various control strategies. Each abatement strategy was compared with the \"least-cost solution\" produced by a computer optimization program to identify the least-costly combination of source reductions in order to achieve a given abatement goal. In each case it was found that the least-cost solution was dramatically less costly than the same amount of pollution reduction produced by any conventional abatement strategy. Burton and later Sanjour along with Edward H. Pechan continued improving and advancing these computer models at the newly created U.S. Environmental Protection Agency. The agency introduced the concept of computer modeling with least-cost abatement strategies (i.e., emissions trading) in its 1972 annual report to Congress on the cost of clean air. This led to the concept of \"cap and trade\" as a means of achieving the \"least-cost solution\" for a given level of abatement.\nThe development of emissions trading over the course of its history can be divided into four phases:\n\nGestation: Theoretical articulation of the instrument (by Coase, Crocker, Dales, Montgomery etc.) and, independent of the former, tinkering with \"flexible regulation\" at the US Environmental Protection Agency.\nProof of Principle: First developments towards trading of emission certificates based on the \"offset-mechanism\" taken up in Clean Air Act in 1977. A company could get allowance from the Act on a greater amount of emission when it paid another company to reduce the same pollutant.\nPrototype: Launching of a first \"cap-and-trade\" system as part of the US Acid Rain Program in Title IV of the 1990 Clean Air Act, officially announced as a paradigm shift in environmental policy, as prepared by \"Project 88\", a network-building effort to bring together environmental and industrial interests in the US.\nRegime formation: branching out from the US clean air policy to global climate policy, and from there to the European Union, along with the expectation of an emerging global carbon market and the formation of the \"carbon industry\".\nIn the United States, the acid rain related emission trading system was principally conceived by C. Boyden Gray, a G.H.W. Bush administration attorney. Gray worked with the Environmental Defense Fund (EDF), who worked with the EPA to write the bill that became law as part of the Clean Air Act of 1990. The new emissions cap on NOx and SO2 gases took effect in 1995, and according to Smithsonian magazine, those acid rain emissions dropped 3 million tons that year.\n\nEconomics\n\nIt is possible for a country to reduce emissions using a command-and-control approach, such as regulation, direct and indirect taxes. The cost of that approach differs between countries because the Marginal Abatement Cost Curve (MAC)—the cost of eliminating an additional unit of pollution—differs by country.\n\nCoase model\nCoase (1960) argued that social costs could be accounted for by negotiating property rights according to a particular objective. Coase's model assumes perfectly operating markets and equal bargaining power among those arguing for property rights. \nIn Coase's model, efficiency, i.e., achieving a given reduction in emissions at lowest cost, is promoted by the market system. This can also be looked at from the perspective of having the greatest flexibility to reduce emissions. Flexibility is desirable because the marginal costs, that is to say, the incremental costs of reducing emissions, varies among countries. Emissions trading allows emission reductions to be first made in locations where the marginal costs of abatement are lowest (Bashmakov et al., 2001). Over time, efficiency can also be promoted by allowing \"banking\" of permits (Goldemberg et al., 1996, p. 30). This allows polluters to reduce emissions at a time when it is most efficient to do so.\n\nEquity\nOne of the advantages of Coase's model is that it suggests that fairness (equity) can be addressed in the distribution of property rights, and that regardless of how these property rights are assigned, the market will produce the most efficient outcome. In reality, according to the held view, markets are not perfect, and it is therefore possible that a trade-off will occur between equity and efficiency (Halsnæs et al., 2007).\n\nTrading\nIn an emissions trading system, permits may be traded by emitters who are liable to hold a sufficient number of permits in system. Some analysts argue that allowing others to participate in trading, e.g., private brokerage firms, can allow for better management of risk in the system, e.g., to variations in permit prices (Bashmakov et al., 2001). It may also improve the efficiency of system. According to Bashmakov et al. (2001), regulation of these other entities may be necessary, as is done in other financial markets, e.g., to prevent abuses of the system, such as insider trading.\n\nIncentives and allocation\nEmissions trading gives polluters an incentive to reduce their emissions. However, there are possible perverse incentives that can exist in emissions trading. Allocating permits on the basis of past emissions (\"grandfathering\") can result in firms having an incentive to maintain emissions. For example, a firm that reduced its emissions would receive fewer permits in the future (IMF, 2008, pp. 25–26). There are costs that emitters do face, e.g., the costs of the fuel being used, but there are other costs that are not necessarily included in the price of a good or service. These other costs are called external costs (Halsnæs et al., 2007). This problem can also be criticized on ethical grounds, since the polluter is being paid to reduce emissions (Goldemberg et al., 1996, p. 38). On the other hand, a permit system where permits are auctioned rather than given away, provides the government with revenues. These revenues might be used to improve the efficiency of overall climate policy, e.g., by funding energy efficiency programs (ACEEE 2019) or reductions in distortionary taxes (Fisher et al., 1996, p. 417).\nIn Coase's model of social costs, either choice (grandfathering or auctioning) leads to efficiency. In reality, grandfathering subsidizes polluters, meaning that polluting industries may be kept in business longer than would otherwise occur. Grandfathering may also reduce the rate of technological improvement towards less polluting technologies (Fisher et al., 1996, p. 417).\nWilliam Nordhaus argues that allocations cost the economy as they cause the under utilization an efficient form of taxation. Nordhaus argues that normal income, goods or service taxes distort efficient investment and consumption, so by using pollution taxes to generate revenue an emissions scheme can increase the efficiency of the economy.\nForm of allocation\nThe economist Ross Garnaut states that permits allocated to existing emitters by 'grandfathering' are not 'free'. As the permits are scarce they have value and the benefit of that value is acquired in full by the emitter. The cost is imposed elsewhere in the economy, typically on consumers who cannot pass on the costs.\n\nMarket and least-cost\nSome economists have urged the use of market-based instruments such as emissions trading to address environmental problems instead of prescriptive \"command-and-control\" regulation. Command and control regulation is criticized for being insensitive to geographical and technological differences, and therefore inefficient; however, this is not always so, as shown by the WWII rationing program in the U.S. in which local and regional boards made adjustments for these differences.\nAfter an emissions limit has been set by a government political process, individual companies are free to choose how or whether to reduce their emissions. Failure to report emissions and surrender emission permits is often punishable by a further government regulatory mechanism, such as a fine that increases costs of production. Firms will choose the least-cost way to comply with the pollution regulation, which will lead to reductions where the least expensive solutions exist, while allowing emissions that are more expensive to reduce.\nUnder an emissions trading system, each regulated polluter has flexibility to use the most cost-effective combination of buying or selling emission permits, reducing its emissions by installing cleaner technology, or reducing its emissions by reducing production. The most cost-effective strategy depends on the polluter's marginal abatement cost and the market price of permits. In theory, a polluter's decisions should lead to an economically efficient allocation of reductions among polluters, and lower compliance costs for individual firms and for the economy overall, compared to command-and-control mechanisms.\n\nMeasuring, reporting, verification and enforcement\n\nIn some industrial processes, emissions can be physically measured by inserting sensors and flowmeters in chimneys and stacks, but many types of activity rely on theoretical calculations instead of measurement. Depending on local legislation, measurements may require additional checks and verification by government or third party auditors, prior or post submission to the local regulator.\nEnforcement methods include fines and sanctions for polluters that have exceeded their allowances. Concerns include the cost of MRV and enforcement, and the risk that facilities may lie about actual emissions.\n\nPollution markets\nAn emission license directly confers a right to emit pollutants up to a certain rate.\nIn contrast, a pollution license for a given location confers the right to emit pollutants at a rate which will cause no more than a specified increase at the pollution-level. For concreteness, consider the following model.\n\nThere are \n \n \n \n n\n \n \n {\\displaystyle n}\n \n agents each of which emits \n \n \n \n \n e\n \n i\n \n \n \n \n {\\displaystyle e_{i}}\n \n pollutants.\nThere are \n \n \n \n m\n \n \n {\\displaystyle m}\n \n locations each of which suffers pollution \n \n \n \n \n q\n \n i\n \n \n \n \n {\\displaystyle q_{i}}\n \n.\nThe pollution is a linear combination of the emissions. The relation between \n \n \n \n e\n \n \n {\\displaystyle e}\n \n and \n \n \n \n q\n \n \n {\\displaystyle q}\n \n is given by a diffusion matrix \n \n \n \n H\n \n \n {\\displaystyle H}\n \n, such that: \n \n \n \n q\n =\n H\n ⋅\n e\n \n \n {\\displaystyle q=H\\cdot e}\n \n.\nAs an example, consider three countries along a river (as in the fair river sharing setting).\n\nPollution in the upstream country is determined only by the emission of the upstream country: \n \n \n \n \n q\n \n 1\n \n \n =\n \n e\n \n 1\n \n \n \n \n {\\displaystyle q_{1}=e_{1}}\n \n.\nPollution in the middle country is determined by its own emission and by the emission of country 1: \n \n \n \n \n q\n \n 2\n \n \n =\n \n e\n \n 1\n \n \n +\n \n e\n \n 2\n \n \n \n \n {\\displaystyle q_{2}=e_{1}+e_{2}}\n \n.\nPollution in the downstream country is the sum of all emissions: \n \n \n \n \n q\n \n 3\n \n \n =\n \n e\n \n 1\n \n \n +\n \n e\n \n 2\n \n \n +\n \n e\n \n 3\n \n \n \n \n {\\displaystyle q_{3}=e_{1}+e_{2}+e_{3}}\n \n.\nSo the matrix \n \n \n \n H\n \n \n {\\displaystyle H}\n \n in this case is a triangular matrix of ones.\nEach pollution-license for location \n \n \n \n i\n \n \n {\\displaystyle i}\n \n permits its holder to emit pollutants that will cause at most this level of pollution at location \n \n \n \n i\n \n \n {\\displaystyle i}\n \n. Therefore, a polluter that affects water quality at a number of points has to hold a portfolio of licenses covering all relevant monitoring-points. In the above example, if country 2 wants to emit a unit of pollutant, it should purchase two permits: one for location 2 and one for location 3.\nMontgomery shows that, while both markets lead to efficient license allocation, the market in pollution-licenses is more widely applicable than the market in emission-licenses.\n\nInternational emissions trading\n\nThe nature of the pollutant plays a very important role when policy-makers decide which framework should be used to control pollution. CO2 acts globally, thus its impact on the environment is generally similar wherever in the globe it is released. So the location of the originator of the emissions does not matter from an environmental standpoint.\nThe policy framework is different for regional pollutants (e.g. SO2 and NOx, and also mercury) because the impact of these pollutants may differ by location. The same amount of a regional pollutant can exert a very high impact in some locations and a low impact in other locations, so it matters where the pollutant is released. This is known as the Hot Spot problem.\nA Lagrange framework is commonly used to determine the least cost of achieving an objective, in this case the total reduction in emissions required in a year. In some cases, it is possible to use the Lagrange optimization framework to determine the required reductions for each country (based on their MAC) so that the total cost of reduction is minimized. In such a scenario, the Lagrange multiplier represents the market allowance price (P) of a pollutant, such as the current market price of emission permits in Europe and the US.\nCountries face the permit market price that exists in the market that day, so they are able to make individual decisions that would minimize their costs while at the same time achieving regulatory compliance. This is also another version of the Equi-Marginal Principle, commonly used in economics to choose the most economically efficient decision.\n\nPrices versus quantities, and the safety valve\n\nThere has been longstanding debate on the relative merits of price versus quantity instruments to achieve emission reductions.\nAn emission cap and permit trading system is a quantity instrument because it fixes the overall emission level (quantity) and allows the price to vary. Uncertainty in future supply and demand conditions (market volatility) coupled with a fixed number of pollution permits creates an uncertainty in the future price of pollution permits, and the industry must accordingly bear the cost of adapting to these volatile market conditions. The burden of a volatile market thus lies with the industry rather than the controlling agency, which is generally more efficient. However, under volatile market conditions, the ability of the controlling agency to alter the caps will translate into an ability to pick \"winners and losers\" and thus presents an opportunity for corruption.\nIn contrast, an emission tax is a price instrument because it fixes the price while the emission level is allowed to vary according to economic activity. A major drawback of an emission tax is that the environmental outcome (e.g. a limit on the amount of emissions) is not guaranteed. On one hand, a tax will remove capital from the industry, suppressing possibly useful economic activity, but conversely, the polluter will not need to hedge as much against future uncertainty since the amount of tax will track with profits. The burden of a volatile market will be borne by the controlling (taxing) agency rather than the industry itself, which is generally less efficient. An advantage is that, given a uniform tax rate and a volatile market, the taxing entity will not be in a position to pick \"winners and losers\" and the opportunity for corruption will be less.\nAssuming no corruption and assuming that the controlling agency and the industry are equally efficient at adapting to volatile market conditions, the best choice depends on the sensitivity of the costs of emission reduction, compared to the sensitivity of the benefits (i.e., climate damage avoided by a reduction) when the level of emission control is varied.\nA third option, known as a safety valve, is a hybrid of the price and quantity instruments. The system is essentially an emission cap and permit trading system but the maximum (or minimum) permit price is capped. Emitters have the choice of either obtaining permits in the marketplace or buying them from the government at a specified trigger price (which could be adjusted over time). The system is sometimes recommended as a way of overcoming the fundamental disadvantages of both systems by giving governments the flexibility to adjust the system as new information comes to light. It can be shown that by setting the trigger price high enough, or the number of permits low enough, the safety valve can be used to mimic either a pure quantity or pure price mechanism.\n\nComparison with other methods of emission reduction\nCap and trade is the textbook example of an emissions trading program. Other market-based approaches include baseline-and-credit, and pollution tax. They all put a price on pollution (for example, see carbon price), and so provide an economic incentive to reduce pollution beginning with the lowest-cost opportunities. By contrast, in a command-and-control approach, a central authority designates pollution levels each facility is allowed to emit. Cap and trade essentially functions as a tax where the tax rate is variable based on the relative cost of abatement per unit, and the tax base is variable based on the amount of abatement needed.\n\nBaseline and credit\nIn a baseline and credit program, polluters can create permits, called credits or offsets, by reducing their emissions below a baseline level, which is often the historical emissions level from a designated past year. Such credits can be bought by polluters that have a regulatory limit.\n\nPollution tax\n\nEmissions fees or environmental tax is a surcharge on the pollution created while producing goods and services. For example, a carbon tax is a tax on the carbon content of fossil fuels that aims to discourage their use and thereby reduce carbon dioxide emissions. The two approaches are overlapping sets of policy designs. Both can have a range of scopes, points of regulation, and price schedules. They can be fair or unfair, depending on how the revenue is used. Both have the effect of increasing the price of goods (such as fossil fuels) to consumers. A comprehensive, upstream, auctioned cap-and-trade system is very similar to a comprehensive, upstream carbon tax. Yet, many commentators sharply contrast the two approaches.\nThe main difference is what is defined and what derived. A tax is a price control, while a cap-and-trade system is a quantity control instrument. That is, a tax is a unit price for pollution that is set by authorities, and the market determines the quantity emitted; in cap and trade, authorities determine the amount of pollution, and the market determines the price. This difference affects a number of criteria.\nResponsiveness to inflation: Cap-and-trade has the advantage that it adjusts to inflation (changes to overall prices) automatically, while emissions fees must be changed by regulators.\nResponsiveness to cost changes: It is not clear which approach is better. It is possible to combine the two into a safety valve price: a price set by regulators, at which polluters can buy additional permits beyond the cap.\nResponsiveness to recessions: This point is closely related to responsiveness to cost changes, because recessions cause a drop in demand. Under cap and trade, the emissions cost automatically decreases, so a cap-and-trade scheme adds another automatic stabilizer to the economy—in effect, an automatic fiscal stimulus. However, a lower pollution price also results in reduced efforts to reduce pollution. If the government is able to stimulate the economy regardless of the cap-and-trade scheme, an excessively low price causes a missed opportunity to cut emissions faster than planned. Instead, it might be better to have a price floor (a tax). This is especially true when cutting pollution is urgent, as with greenhouse gas emissions. A price floor also provides certainty and stability for investment in emissions reductions: recent experience from the UK shows that nuclear power operators are reluctant to invest on \"un-subsidized\" terms unless there is a guaranteed price floor for carbon (which the EU emissions trading scheme does not presently provide).\nResponsiveness to uncertainty: As with cost changes, in a world of uncertainty, it is not clear whether emissions fees or cap-and-trade systems are more efficient—it depends on how fast the marginal social benefits of reducing pollution fall with the amount of cleanup (e.g., whether inelastic or elastic marginal social benefit schedule).\nOther: The magnitude of the tax will depend on how sensitive the supply of emissions is to the price. The permit price of cap-and-trade will depend on the pollutant market. A tax generates government revenue, but full-auctioned emissions permits can do the same. A similar upstream cap-and-trade system could be implemented. An upstream carbon tax might be the simplest to administer. Setting up a complex cap-and-trade arrangement that is comprehensive has high institutional needs.\n\nCommand-and-control regulation\nCommand and control is a system of regulation that prescribes emission limits and compliance methods for each facility or source. It is the traditional approach to reducing air pollution.\nCommand-and-control regulations are more rigid than incentive-based approaches such as pollution fees and cap and trade. An example of this is a performance standard which sets an emissions goal for each polluter that is fixed and, therefore, the burden of reducing pollution cannot be shifted to the firms that can achieve it more cheaply. As a result, performance standards are likely to be more costly overall. The additional costs would be passed to end consumers.\n\nTrading systems\n\nApart from the dynamic development in carbon emission trading, other pollutants have also been targeted.\n\nUnited States\n\nSulfur dioxide\n\nAn early example of an emission trading system has been the sulfur dioxide (SO2) trading system under the framework of the Acid Rain Program of the 1990 Clean Air Act in the U.S. Under the program, which is essentially a cap-and-trade emissions trading system, SO2 emissions were reduced by 50% from 1980 levels by 2007. Some experts argue that the cap-and-trade system of SO2 emissions reduction has reduced the cost of controlling acid rain by as much as 80% versus source-by-source reduction. The SO2 program was challenged in 2004, which set in motion a series of events that led to the 2011 Cross-State Air Pollution Rule (CSAPR). Under the CSAPR, the national SO2 trading program was replaced by four separate trading groups for SO2 and NOx.\nSO2 emissions from Acid Rain Program sources have fallen from 17.3 million tons in 1980 to about 7.6 million tons in 2008, a decrease in emissions of 56 percent. A 2014 EPA analysis estimated that implementation of the Acid Rain Program avoided between 20,000 and 50,000 incidences of premature mortality annually due to reductions of ambient PM2.5 concentrations, and between 430 and 2,000 incidences annually due to reductions of ground-level ozone.\n\nNitrogen oxides\nIn 2003, the Environmental Protection Agency (EPA) began to administer the NOx Budget Trading Program (NBP) under the NOx State Implementation Plan (also known as the \"NOx SIP Call\"). The NOx Budget Trading Program was a market-based cap and trade program created to reduce emissions of nitrogen oxides (NOx) from power plants and other large combustion sources in the eastern United States. NOx is a prime ingredient in the formation of ground-level ozone (smog), a pervasive air pollution problem in many areas of the eastern United States. The NBP was designed to reduce NOx emissions during the warm summer months, referred to as the ozone season, when ground-level ozone concentrations are highest. In March 2008, EPA again strengthened the 8-hour ozone standard to 0.075 parts per million (ppm) from its previous 0.08 ppm.\nOzone season NOx emissions decreased by 43 percent between 2003 and 2008, even while energy demand remained essentially flat during the same period. CAIR will result in $85 billion to $100 billion in health benefits and nearly $2 billion in visibility benefits per year by 2015 and will substantially reduce premature mortality in the eastern United States.\nNOx reductions due to the NOx Budget Trading Program have led to improvements in ozone and PM2.5, saving an estimated 580 to 1,800 lives in 2008.\nA 2017 study in the American Economic Review found that the NOx Budget Trading Program decreased NOx emissions and ambient ozone concentrations. The program reduced expenditures on medicine by about 1.5% ($800 million annually) and reduced the mortality rate by up to 0.5% (2,200 fewer premature deaths, mainly among individuals 75 and older).\n\nVolatile organic compounds\n\nIn the United States the Environmental Protection Agency (EPA) classifies Volatile Organic Compounds (VOCs) as gases emitted from certain solids and liquids that may have adverse health effects. These VOCs include a variety of chemicals that are emitted from a variety of different products. These include products such as gasoline, perfumes, hair spray, fabric cleaners, PVC, and refrigerants; all of which can contain chemicals such as benzene, acetone, methylene chloride, freons, formaldehyde.\nVOCs are also monitored by the United States Geological Survey for its presence in groundwater supply. The USGS concluded that many of the nations aquifers are at risk to low-level VOC contamination. The common symptoms of short levels of exposure to VOCs include headaches, nausea, and eye irritation. If exposed for an extended period of time the symptoms include cancer and damage to the central nervous system.\n\nChina\nIn an effort to reverse the adverse consequences of air pollution, in 2006, China started to consider a national pollution permit trading system in order to use market-based mechanisms to incentivize companies to cut pollution. This has been based on a previous",
    "source": "wikipedia:Emissions trading",
    "domain": "climate"
  },
  {
    "text": "The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations (UN). Its job is to \"provide governments at all levels with scientific information that they can use to develop climate policies\". The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) set up the IPCC in 1988. The UN endorsed the creation of the IPCC later that year. It has a secretariat in Geneva, Switzerland, hosted by the WMO. It has 195 member states who govern the IPCC. The member states elect a bureau of scientists to serve through an assessment cycle. A cycle is usually six to seven years. The bureau selects experts in their fields to prepare IPCC reports. \nThere is a formal nomination process by governments and observer organizations to find these experts. The IPCC has three working groups and a task force, which carry out its scientific work.\nThe IPCC informs governments about the state of knowledge of climate change. It does this by examining all the relevant scientific literature on the subject. This includes the natural, economic and social impacts and risks. It also covers possible response options. The IPCC does not conduct its own original research. It aims to be objective and comprehensive. Thousands of scientists and other experts volunteer to review the publications. They compile key findings into \"Assessment Reports\" for policymakers and the general public; Experts have described this work as the biggest peer review process in the scientific community. The IPCC was the first of three global science policy panels to be established, followed by and IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services), established in 2012 and the Intergovernmental Science-Policy Panel on Chemicals, Waste and Pollution (ISPCWP) established in 2025. \nLeading climate scientists and all member governments endorse the IPCC's findings. This underscores that the IPCC is a well-respected authority on climate change. Governments, civil society organizations, and the media regularly quote from the panel's reports. IPCC reports play a key role in the annual climate negotiations held by the United Nations Framework Convention on Climate Change (UNFCCC). The IPCC Fifth Assessment Report was an important influence on the landmark Paris Agreement in 2015. The IPCC shared the 2007 Nobel Peace Prize with Al Gore for contributions to the understanding of climate change.\nThe seventh assessment cycle of the IPCC began in 2023. In August 2021, the IPCC published its Working Group I contribution to the Sixth Assessment Report on the physical science basis of climate change. The Guardian described this report as the \"starkest warning yet\" of \"major inevitable and irreversible climate changes\". Many newspapers around the world echoed this theme. In February 2022, the IPCC released its Working Group II report on impacts and adaptation. It published Working Group III's \"mitigation of climate change\" contribution to the Sixth Assessment in April 2022. \nThe Sixth Assessment Report concluded with a Synthesis Report in March 2023.\nDuring the period of the Sixth Assessment Report, the IPCC released three special reports. The first and most influential was the Special Report on Global Warming of 1.5°C in 2018. In 2019 the Special Report on Climate Change and Land, and the Special Report on the Ocean and Cryosphere in a Changing Climate came out. The IPCC also updated its methodologies in 2019. So the sixth assessment cycle was the most ambitious in the IPCC's history.\nIn January 2026, United States president Donald Trump announced that the United States would withdraw from the organization.\n\nOrigins\nThe predecessor of the IPCC was the Advisory Group on Greenhouse Gases (AGGG). Three organizations set up the AGGG in 1986. These were the International Council of Scientific Unions, the United Nations Environment Programme (UNEP), and the World Meteorological Organization (WMO). The AGGG reviewed scientific research on greenhouse gases. It also studied increases in greenhouse gases. Climate science was becoming more complicated and covering more disciplines. This small group of scientists lacked the resources to cover climate science.\nThe United States Environmental Protection Agency sought an international convention to restrict greenhouse gas emissions. The Reagan administration worried that independent scientists would have too much influence. The WMO and UNEP therefore created the IPCC as an intergovernmental body in 1988. Scientists take part in the IPCC as both experts and government representatives. The IPCC produces reports backed by all leading relevant scientists. Member governments must also endorse the reports by consensus agreement. So the IPCC is both a scientific body and an organization of governments. Its job is to tell governments what scientists know about climate change. It also examines the impacts of climate change and options for dealing with it. The IPCC does this by assessing peer-reviewed scientific literature.\nThe United Nations endorsed the creation of the IPCC in 1988. The General Assembly resolution noted that human activity could change the climate. This could lead to severe economic and social consequences. It said increasing concentrations of greenhouse gases could warm the planet. This would cause the sea level to rise. The effects on humanity would be disastrous if timely steps were not taken.\n\nOrganization\n\nWay of working\nThe IPCC does not conduct original research. It produces comprehensive assessments on the state of knowledge of climate change. It prepares reports on special topics relevant to climate change. It also produces methodologies. These methodologies help countries estimate their greenhouse gas emissions and removals through sinks. Its assessments build on previous reports and scientific publications. Throughout six assessments the reports reflect the growing evidence for a changing climate. And they show how this is due to human activity.\n\nRules and governing principles\nThe IPCC has adopted its rules of procedure in the \"Principles Governing IPCC Work\". These state that the IPCC will assess:\n\nthe risk of climate change caused by human activities,\nits potential impacts, and\npossible options for prevention.\nUnder IPCC rules its assessments are comprehensive, objective, open, and transparent. They cover all the information relevant to the scientific understanding of climate change. This draws on scientific, technical, and socioeconomic information. IPCC reports must be neutral regarding policy recommendations. However, they may address the objective factors relevant to enacting policies.\n\nStructure\nThe IPCC has the following structure:\n\nIPCC Panel: Meets in plenary session about twice a year. It may meet more often for the approval of reports. It controls the IPCC's structure, procedures, work programme, and budget. It accepts and approves IPCC reports. The Panel is the IPCC corporate entity.\nChair: Elected by the Panel. Chairs the Bureau and other bodies. Represents the organization.\nBureau: Elected by the Panel. It currently has 34 members from different geographic regions. Besides the Chair and three IPCC Vice-Chairs, they provide the leadership for the IPCC's three Working Groups and Task Force. It provides guidance to the Panel on the scientific and technical aspects of its work.\nWorking Groups: Each has two Co-Chairs, one from a developed and one from a developing country. A technical support unit supports each Working Group. Working Group sessions approve the Summary for Policymakers of assessment and special reports. Each Working Group has a Bureau. This consists of its Co-Chairs and Vice-Chairs, who are also members of the IPCC Bureau.\nWorking Group I: Assesses scientific aspects of the climate system and climate change. Co-Chairs: Robert Vautard (France) and Xiaoye Zhang (China)\nWorking Group II: Assesses the impacts of climate change on human and natural systems. Assesses adaptation options. Co-Chairs: Bart van den Hurk (Netherlands) and Winston Chow (Singapore)\nWorking Group III: Assesses how to stop climate change by limiting greenhouse gas emissions. (Known as \"mitigation\".) Co-Chairs: Katherine Calvin (United States) and Joy Jacqueline Pereira (Malaysia)\nTask Force on National Greenhouse Gas Inventories. Develops methodologies for estimating greenhouse gas emissions. Co-Chairs: Takeshi Enoki (Japan) and Mazhar Hayat (Pakistan)\nTask Force Bureau: Consists of two Co-Chairs, who are also members of the IPCC Bureau, and 12 members.\nExecutive Committee: Consists of the Chair, IPCC Vice-Chairs and the Co-Chairs of the Working Groups and Task Force. It addresses urgent issues that arise between sessions of the Panel.\nSecretariat: Administers activities, supports the Chair and Bureau, point of contact for governments. Supported by UNEP and the WMO.\n\nChair\nThe chair of the IPCC is British energy scientist Jim Skea, who is hosted by the International Institute for Environment and Development. Skea has served since 28 July 2023 with the election of the new IPCC Bureau. His predecessor was Korean economist Hoesung Lee, elected in 2015. The previous chairs were Rajendra K. Pachauri, elected in 2002, Robert Watson, elected in 1997, and Bert Bolin, elected in 1988.\n\nPanel\nThe Panel consists of representatives appointed by governments. They take part in plenary sessions of the IPCC and its Working Groups. Non-governmental and intergovernmental organizations may attend as observers. Meetings of IPCC bodies are by invitation only. About 500 people from 130 countries attended the 48th Session of the Panel in Incheon, Republic of Korea. This took place in October 2018. They included 290 government officials and 60 representatives of observer organizations. The opening ceremonies of sessions of the Panel and of Lead Author Meetings are open to media. Otherwise, IPCC meetings are closed.\n\nFunding\nThe IPCC receives funding through a dedicated trust fund. UNEP and the WMO established the fund in 1989. The trust fund receives annual financial contributions from member governments. The WMO, UNEP, and other organizations also contribute. Payments are voluntary and there is no set amount required. The WMO covers the operating costs of the secretariat. It also sets the IPCC's financial regulations and rules. The Panel sets the annual budget.\nIn 2021, the IPCC's annual budget amounts to approximately six million euros, financed by the 195 UN Member states, who contribute \"independently and voluntarily\". In 2021, the countries giving the most money include the United States, Japan, France, Germany and Norway. Other countries, often developing ones, give an \"in-kind contribution, by hosting IPCC meetings\". In 2022, this budget was a little less than eight million euros.\n\nList of all reports\n\nActivities other than report preparation\nThe IPCC bases its work on the decisions of the WMO and UNEP, which established the IPCC. It also supports the work of the UNFCCC. The main work of the IPCC is to prepare assessments and other reports. It also supports other activities such as the Data Distribution Centre. This helps manage data related to IPCC reports.\nThe IPCC has a \"Gender Policy and Implementation Plan\" to pay attention to gender in its work. It aims to carry out its work inclusively and respectfully. The IPCC aims for balance in participation in IPCC work. This should offer all participants equal opportunity.\n\nCommunications and dissemination activities\nThe IPCC enhanced its communications activities for the Fifth Assessment Report. For instance, it made the approved report and press release available to registered media under embargo before the release. And it expanded its outreach activities with an outreach calendar. The IPCC held an Expert Meeting on Communication in February 2016, at the start of the Sixth Assessment Report cycle. Members of the old and new Bureaus worked with communications experts and practitioners at this meeting. This meeting produced a series of recommendations. The IPCC adopted many of them. One was to bring people with communications expertise into the Working Group Technical Support Units. Another was to consider communication questions early on in the preparation of reports.\nFollowing these steps in communications, the IPCC saw a significant increase in media coverage of its reports. This was particularly the case with the Special Report on Global Warming of 1.5 °C in 2018 and Climate Change 2021: The Physical Science Basis, the Working Group I contribution to the Sixth Assessment Report, in 2021. There was also much greater public interest, reflected in the youth and other movements that emerged in 2018.\nIPCC reports are important for public awareness of climate change and related policymaking. This has led to several academic studies of IPCC communications, for example in 2021.\n\nArchiving\nThe IPCC archives its reports and electronic files on its website. They include the review comments on drafts of reports. The Environmental Science and Public Policy Archives in the Harvard Library also archives them.\n\nAssessment reports\n\nBetween 1990 and 2023, the IPCC published six comprehensive assessment reports reviewing the latest climate science. The IPCC has also produced 14 special reports on particular topics. Each assessment report has four parts. These are a contribution from each of the three working groups, plus a synthesis report. The synthesis report integrates the working group contributions. It also integrates any special reports produced in that assessment cycle.\n\nReview process of scientific literature\nThe IPCC does not carry out research. It does not monitor climate-related data. The reports by IPCC assess scientific papers and independent results from other scientific bodies. The IPCC sets a deadline for publication of scientific papers that a report will cover. That report will not include new information that emerges after this deadline. However, there is a steady evolution of key findings and levels of scientific confidence from one assessment report to the next. Each IPCC report notes areas where the science has improved since the previous report. It also notes areas that would benefit from further research.\nThe First Assessment Report was published in 1990 and received an update in 1992. In intervals of about six years, new editions of IPCC Assessment Report followed.\n\nSelection and role of authors\nThe focal points of the Member states — the individual appointed by each state to liaise with the IPCC — and the observer organizations submit to the IPCC Bureau a list of personalities, which they have freely constituted. The Bureau (more precisely, the co-chairs of the relevant working group, with the help of its technical support unit) uses these lists as a basis for appointing authors while retaining the possibility of appointing people who are not on the list, primarily based on scientific excellence and diversity of viewpoints, and to a lesser extent by ensuring geographical diversity, experience within the IPCC and gender. Authors may include, in addition to researchers, personalities from the private sector and experts from NGOs.\nThe IPCC Bureau or Working Group Bureau selects the authors of the reports from government nominations. Lead authors of IPCC reports assess the available information about climate change based on published sources. According to IPCC guidelines, authors should give priority to peer-reviewed sources. Authors may refer to non-peer-reviewed sources (\"grey literature\"), if they are of sufficient quality. These could include reports from government agencies and non-governmental organizations. Industry journals and model results are other examples of non-peer-reviewed sources.\nAuthors prepare drafts of a full report divided into chapters. They also prepare a technical summary of the report, and a summary for policymakers.\nEach chapter has many authors to write and edit the material. A typical chapter has two coordinating lead authors, ten to fifteen lead authors, and a larger number of contributing authors. The coordinating lead authors assemble the contributions of the other authors. They ensure that contributions meet stylistic and formatting requirements. They report to the Working Group co-chairs. Lead authors write sections of chapters. They invite contributing authors to prepare text, graphs, or data for inclusion. Review editors must ensure that authors respond to comments received during the two stages of drafts review: the first is only open to external experts and researchers, while the second is also open to government representatives.\nThe Bureau aims for a range of views, expertise, and geographical representation in its choice of authors. This ensures the author team includes experts from both developing and developed countries. The Bureau also seeks a balance between male and female authors. It aims for a balance between those who have worked previously on IPCC reports and those new to the process.\nScientists who work as authors on IPCC reports do not receive any compensation for this work, and all work voluntarily. They depend on the salaries they receive from their home institutions or other work. The work is labour-intensive with a big time commitment. It can disrupt participating scientists' research. This has led to concern that the IPCC process may discourage qualified scientists from participating. More than 3,000 authors (coordinating lead authors, lead authors, review editors) have participated in the drafting of IPCC reports since its creation.\n\nReview process for assessment reports\nExpert reviewers comment at different stages on the drafts. Reviewers come from member governments and IPCC observers. Also, anyone may become an IPCC reviewer by stating they have the relevant expertise.\nThere are generally three stages in the review process. First comes an expert review of the first draft of the chapters. The next stage is a review by governments and experts of the revised draft of the chapters and the first draft of the Summary for Policymakers. The third stage is a government review of the revised Summary for Policymakers. Review comments and author responses remain in an open archive for at least five years. Finally, government representatives together with the authors review the Summary for Policymakers. They go through the Summary for Policymakers line by line to ensure it is a good summary of the underlying report. This final review of the Summary of Policymakers takes place at sessions of the responsible working group or of the Panel.\nThere are several types of endorsement that documents receive:\n\nApproval - Material has been subject to detailed, line-by-line discussion and agreement. (The relevant Working Groups approve Working Group Summaries for Policymakers. The Panel approves the Synthesis Report Summary for Policymakers.)\nAdoption - Endorsed section by section (not line by line). (The Panel adopts the full IPCC Synthesis Report. It also adopts Overview Chapters of Methodology Reports.)\nAcceptance - Not been subject to line-by-line discussion and agreement. But it presents a comprehensive, objective, and balanced view of the subject matter. (Working Groups accept their reports. The Panel accepts Working Group Summaries for Policymakers after working group approval. The Panel accepts Methodology Reports.)\n\nKey findings and impacts\n\nAssessment reports one to five (1990 to 2014)\n\nThe IPCC's First Assessment Report (FAR) appeared in 1990. The report gave a broad overview of climate change science. It discussed uncertainties and provided evidence of warming. The authors said they are certain that greenhouse gases are increasing in the atmosphere because of human activity. This is resulting in more warming of the Earth's surface. The report led to the establishment of the United Nations Framework Convention on Climate Change (UNFCCC).\nThe Second Assessment Report (SAR), was published in 1995. It strengthened the findings of the First Assessment Report. The evidence suggests that there is a discernible human influence on the global climate, it said. The Second Assessment Report provided important material for the negotiations leading to the UNFCCC's Kyoto Protocol.\nThe Third Assessment Report (TAR) was completed in 2001. It found more evidence that most of the global warming seen over the previous 50 years was due to human activity. The report includes a graph reconstructing global temperature since the year 1000. The sharp rise in temperature in recent years gave it the name \"hockey stick\". This became a powerful image of how temperature is soaring with climate change. The report also shows how adaptation to the effects of climate change can reduce some of its ill effects.\nThe IPCC's Fourth Assessment Report (AR4) was published in 2007. It gives much greater certainty about climate change. It states: \"Warming of the climate system is unequivocal...\" The report helped make people around the world aware of climate change. The IPCC shared the Nobel Peace Prize in the year of the report's publication for this work (see below).\nThe Fifth Assessment Report (AR5) was published in 2013 and 2014. This report again stated the fact of climate change. It warned of the dangerous risks. And it emphasizes how the world can counter climate change. Three key findings were for example: Firstly, human influence on the climate system is clear. Secondly, the more we disrupt our climate, the more we risk severe, pervasive, and irreversible impacts. And thirdly, we have the means to limit climate change and build a more prosperous, sustainable future. The report's findings were the scientific foundation of the UNFCCC's 2015 Paris Agreement.\n\nSixth assessment report (2021/2022)\nThe IPCC's most recent report is the Sixth Assessment Report (AR6). The first three installments of AR6 appeared in 2021 and 2022. The final synthesis report was completed in March 2023.\nThe IPCC published the Working Group I report, Climate Change 2021: The Physical Science Basis, in August 2021. It confirms that the climate is already changing in every region. Many of these changes have not been seen in thousands of years. Many of them such as sea-level rise are irreversible over hundreds of thousands of years. Strong reductions in greenhouse gas emissions would limit climate change. But it could take 20–30 years for the climate to stabilize. This report attracted enormous media and public attention. U.N. Secretary-General António Guterres described it as \"code red for humanity\".\nThe IPCC published the Working Group II report, Climate Change 2022: Impacts, Adaptation and Vulnerability, in February 2022. Climate change due to human activities is already affecting the lives of billions of people, it said. It is disrupting nature. The world faces unavoidable hazards over the next two decades even with global warming of 1.5 °C, it said.\nThe IPCC published the Working Group III report, Climate Change 2022: Mitigation of Climate Change, in April 2022. It will be impossible to limit warming to 1.5 °C without immediate and deep cuts in greenhouse gas emissions. It is still possible to halve emissions by 2050, it said.\n\nOther reports\n\nSpecial reports\nThe IPCC also publishes other types of reports. It produces Special Reports on topics proposed by governments or observer organizations. Between 1994 and 2019 the IPCC published 14 special reports. Now usually more than one working group cooperates to produce a special report. The preparation and approval process is the same as for assessment reports.\n\nSpecial reports in 2011\nDuring the fifth assessment cycle, the IPCC produced two special reports. It completed the Special Report on Renewable Energy Sources and Climate Change Mitigation in 2011. Working Group III prepared this report. The report examined options to use different types of renewable energy to replace fossil fuels. The report noted that the cost of most renewable technologies had fallen. It was likely to fall even more with further advances in technology. It said renewables could increase access to energy. The report reviewed 164 scenarios that examine how renewables could help stop climate change. In more than half of these scenarios, renewables would contribute more than 27% of the primary energy supply in the mid-century. This would be more than double the 13% share in 2008. In the scenarios with the highest shares for renewable energy, it will contribute 77% by 2050.\nLater in 2011, the IPCC released the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. This was a collaboration between Working Groups I and II. It was the first time two IPCC working groups worked together on a special report. The report shows how climate change has contributed to changes in extreme weather. And it shows how policies to avoid and prepare for extreme weather events can reduce their impact. In the same way, policies to respond to events and recover from them can make societies more resilient.\n\nSpecial reports 2018–2019\nDuring the sixth assessment cycle, the IPCC produced three special reports. This made it the most ambitious cycle in IPCC history. The UNFCCC set a goal of keeping global warming well below 2 °C (36 °F) while trying to hold it at 1.5 °C (34.7 °F), when it reached the Paris Agreement at COP21 in 2015. But at the time there was little understanding of what warming of 1.5 °C meant. There was little scientific research explaining how the impacts of 1.5 °C would differ from 2 °C. And there was little understanding about how to keep warming to 1.5 °C. So the UNFCCC invited the IPCC to prepare a report on global warming of 1.5 °C. The IPCC subsequently released the Special Report on Global Warming of 1.5 °C (SR15) in 2018. The report showed that it was possible to keep warming below 1.5 °C during the 21st century. But this would mean deep cuts in emissions. It would also mean rapid, far-reaching changes in all aspects of society. The report showed warming of 2 °C would have much more severe impacts than 1.5 °C. In other words: every bit of warming matters. SR15 had an unprecedented impact on an IPCC report in the media and with the public. It put the 1.5 °C target at the centre of climate activism.\nIn 2019 the IPCC released two more special reports that examine different parts of the climate system. The Special Report on Climate Change and Land examined how the way we use land affects the climate. It looked at emissions from activities such as farming and forestry rather than from energy and transport. It also looked at how climate change is affecting land. All three IPCC working groups and its Task Force on National Greenhouse Gas Inventories collaborated on the report. The report found that climate change is adding to the pressures we are putting on the land we use to live on and grow our food. It will only be possible to keep warming well below 2 °C if we reduce emissions from all sectors including land and food, it said.\nThe Special Report on the Ocean and Cryosphere in a Changing Climate examined how the ocean and frozen parts of the planet interact with climate change. (The cryosphere includes frozen systems such as ice sheets, glaciers, and permafrost.) IPCC Working Groups I and II prepared the report. The report highlighted the need to tackle unprecedented changes in the ocean and cryosphere. It also showed how adaptation could help sustainable development.\n\nMethodology Reports\nThe IPCC has a National Greenhouse Gas Inventories Programme. It develops methodologies and software for countries to report their greenhouse gas emissions. The IPCC's Task Force on National Greenhouse Gas Inventories (TFI) has managed the program since 1998. Japan's Institute for Global Environmental Strategies hosts the TFI's Technical Support Unit.\n\nRevised 1996 IPCC Guidelines\nThe IPCC released its first Methodology Report, the IPCC Guidelines for National Greenhouse Gas Inventories, in 1994. The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories updated this report. Two \"good practice reports\" complete these guidelines. These are the Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories and Good Practice Guidance for Land Use, Land-Use Change and Forestry. Parties to the UNFCCC and its Kyoto Protocol use the 1996 guidelines and two good practice reports for their annual submissions of inventories.\n\n2006 IPCC Guidelines\nThe 2006 IPCC Guidelines for National Greenhouse Gas Inventories further update these methodologies. They include a large number of \"default emission factors\". These are factors to estimate the amount of emissions for an activity. The IPCC prepared this new version of the guidelines at the request of the UNFCCC. The UNFCCC accepted them for use at its 2013 Climate Change Conference, COP19, in Warsaw. The IPCC added further material in its 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.\nThe TFI has started preparations for a methodology report on short-lived climate forcers (SLCFs). It will complete this report in the next assessment cycle, the seventh.\n\nChallenges and controversies\nIPCC reports also attract criticism. Criticisms come from both people who say the reports exaggerate the risks and people who say they understate them. The IPCC consensus approach has faced internal and external challenges.\n\nConservative nature of IPCC reports\nSome critics have argued that IPCC reports tend to be too conservative in their assessments of climate risk. In 2012, it was reported that the IPCC has been criticized by some scientists, who argue that the reports consistently underestimate the pace and impacts of global warming. As a result, they believe this leads to findings that are the \"lowest common denominator\". Similar claims have also been made by scientists who found that for the last sev",
    "source": "wikipedia:Intergovernmental Panel on Climate Change",
    "domain": "climate"
  },
  {
    "text": "A carbon credit is a tradable instrument (typically a virtual certificate) that conveys a claim to have avoided greenhouse gas (GHG) emissions or to have enhanced removal of GHG from the atmosphere. One carbon credit represents the avoided or enhanced removal of one metric ton of carbon dioxide or its carbon dioxide-equivalent (CO2e).\nCarbon offsetting is the practice of using carbon credits to offset or counter an entity's greenhouse gas inventory emissions in line with reporting programs or institutional emissions targets/goals. Carbon credit trading mechanisms (i.e., crediting programs), enable project developers to implement projects that mitigate GHGs and receive carbon credits which can be sold to interested buyers who may use the credits to claim they have offset their inventory GHG emissions. Similar to \"offsetting\", carbon credits that are permitted as compliance instruments within regulatory compliance markets (e.g., The European Union Emission Trading Scheme or the California Cap-n-Trade program) can be used by regulated entities to report lower emissions and achieve compliance status (with limitations around their use that vary by compliance program). Aside from \"offsetting\", carbon credits can also be used to make contributions toward global net zero GHG-level targets. It is an individual buyer's choice how to use, or \"retire\", the carbon credit.\nProjects entail mitigation actions that avoid or enhance the removal of GHG emissions. Projects are implemented in line with the standards of crediting programs, including their methodologies, rules, and requirements. Methodologies are approved for each specific project type (e.g., tree planting, mangrove restoration, early retirement of coal powerplants). Provided a project fulfills all of the requirements and provisions of a crediting program, it will be issued credits that can be sold to buyers. Each crediting program typically has its own carbon credit 'label' such as CDM's Certified Emission Reductions (CERs), Article 6.4 Mechanism Emission Reductions (A6.4ERs), VCS' Verified Emission Reductions (VERs), ACR's Emission Reduction Tonnes, Climate Action Reserves' Climate Reserve Tonnes (CRTs), etc.\nHundreds of GHG mitigation project types exist and have approved methodologies with established crediting programs. The program that defined the first phase of carbon market development, the Clean Development Mechanism (CDM) provides a summary booklet of its many approved methodologies. But each crediting program has its own list of approved methodologies, for example unless explicitly stated, an ACR approved methodology could not be used by someone trying to work through Verra's Verified Carbon Standard. Carbon credits are a form of carbon pricing, along with carbon taxes, and Carbon Border Adjustment Mechanisms (CBAM). Carbon credits are intended to be fungible across different markets, but some compliance markets and reporting programs limit eligibility to specified carbon credit types or characteristics (e.g., vintage, project origin, project type).\n\nCredit quality\n\"The originating idea behind a carbon credit is that it can substitute for reductions that a buyer could have made to their own emissions (i.e., compensation use). For this to be true, the world must be at least as well off when a carbon credit is used as it would have been if the buyer had reduced their own carbon footprint. The \"quality\" of a carbon credit refers to the level of confidence that the use of the credit will fulfill this basic principle.\"\nCarbon credits and crediting programs have come under increased scrutiny following the rigorous assessment of credit quality and many investigative journalism articles, which have identified significant quality, or environmental integrity, concerns related to credit's avoided emissions or enhanced removals claims. The Australia Institute highlights 23 instances where carbon crediting programs were found to have significant shortcomings. These include claims of overestimated carbon sequestration, double-counting of credits, and the failure of projects to provide \"additional\" environmental benefits beyond what would have occurred in the absence of the project. Many enhanced removal projects have received criticism as greenwashing because they overstated their ability to sequester carbon, with some projects being shown to actually increase overall emissions.\nThe essential elements of carbon credit quality can be distilled to five criteria. Higher-quality carbon credits are those associated with avoided emissions or enhanced removals that are:\n\nAdditional\nRobustly quantified\nPermanent\nNot claimed by another entity\nNot associated with significant social or environmental harms\nCarbon credit quality is possible to assess and in response to the growing concerns related to credit quality, many credit ratings initiatives began to form around 2020 to aid buyers and crediting programs in discerning high-quality from low-quality projects and to make improvements to crediting methodologies so that future credits will only be issued if they meet more rigorous requirements. These credit ratings initiatives have taken the form of open access resources like OffsetGuide.org, labeling initiatives like the Integrity Council for the Voluntary Carbon Market that works to assess methodologies and determine if they meet the threshold of quality (determined by applying an assessment framework) to receive the Core Carbon Principle (CCP) label or not, or the Carbon Credit Quality Initiative which conducts deep analysis (an exhaustive assessment framework) and assigns a score of 1-5 representing the holistic quality of a methodology. For profit credit ratings companies have also sprung up that provide quality ratings for individual projects by reviewing their project documents.\n\nThe Paris Agreement crediting mechanism\nThrough international climate negotiations led by the UNFCCC, the Paris Agreement was agreed to in 2015 and included provisions for carbon crediting to be a mechanism that could be used to aid countries in meeting their Nationally Determined Contributions (NDCs). At COP27, negotiators agreed to define credits issued under Article 6 of the Paris Agreement as \"mitigation contributions\" toward a country's NDC fulfillment. Article 6 of the Paris Agreement includes three mechanisms for \"voluntary cooperation\" between countries toward climate goals, including carbon credit markets. Article 6.2 enabled countries to directly trade carbon credits through the development of bilateral crediting mechanisms (i.e., bilateral crediting programs). Article 6.4 established a new international crediting program that supplants the CDM program. The third option is Article 6.8, which enables non-credit generating cooperation (and is not relevant to this article). These provisions allow for mechanisms (excluding Article 6.8) to be developed to enable carbon credits to aid countries in meeting their Nationally Determined Contributions (NDC) commitments to achieve the goals of the Paris Agreement. Article 6.4, also referred to as the Paris Agreement Crediting Mechanism (PACM), and is supplanting the CDM but seeks to respond to quality concerns raised by researchers and the media by enhancing the quality of credits and raise the standard of rigor for the entire market. CDM projects may transition to become PACM projects if they meet the eligibility requirements and the Article 6.4 Methodology Panel is reviewing CDM (and other submitted methodologies) to determine if they meet the more rigorous standards of the PACM standard documents to be adopted by PACM to guide project development.\n\nProject types\nSome include forestry projects that avoid logging and plant saplings, renewable energy projects such as wind farms, biomass energy, biogas digesters, hydroelectric dams, as well as energy efficiency projects. Further projects include carbon dioxide removal projects, carbon capture and storage projects, and the elimination of methane emissions in various settings such as landfills.\n\nCommon terms\nForward crediting, is typically regarded as a risky practice that leads to lower-quality credits. Forward crediting is a process where credits are issued for projected avoided emissions or enhanced removals, which can be claimed by buyers even before the reduction activities have occurred.\nThe vintage of a carbon credit is the year in which a carbon credit was issued by a crediting program, which usually corresponds to the year in which a third party auditor reviews the project — generates the carbon offset credit is known as the vintage.\nA registry is a core function of a carbon crediting program. Through a typically publicly accessible registry, carbon credits are tracked for their ownership and retirement. Registries may contain project information such as project status, project documents, credits generated, ownership, sale, and retirement.\n\nHistory\nIn 1977, major amendments to the US Clean Air Act created one of the first tradable emission offset mechanisms, allowing permitted facilities to increase emissions in exchange for paying another company to reduce its emissions of the same pollutant by a greater amount. The 1990 amendments to that same law established the Acid Rain Trading Program, which introduced the concept of a cap and trade system, which allowed companies to buy and sell offsets created by other companies that invested in emission reduction projects subject to an overall limit on emissions. In the 1990s, regulatory frameworks for the US Clean Water Act enabled mitigation banking and wetlands offsetting, which set the procedural and conceptual precedent for carbon offsetting.\nIn 1997, the original international compliance carbon markets emerged from the Kyoto Protocol, which established three mechanisms that enable countries or operators in developed countries to acquire offset credits. One mechanism was the Clean Development Mechanism (CDM), which expanded the concept of carbon emissions trading to a global scale, focusing on the major greenhouse gases that cause climate change: carbon dioxide (CO2), methane, nitrous oxide (N2O), perfluorocarbons, hydrofluorocarbons, and sulfur hexafluoride. The Kyoto Protocol was to expire in 2020, to be superseded by the Paris Agreement. Countries are still determining the role of carbon offsets in the Paris Agreement through international negotiations on the agreement's Article 6.\nIn November 2024, after years of deadlock, governments attending the COP29 conference in Baku, Azerbaijan agreed to rules on creating, trading and registering emission reductions and removals as carbon credits that higher-emission countries can buy, thus providing funding for low-emission technologies.\n\nEconomics\nThe economics behind programs such as the Kyoto Protocol was that the marginal cost of reducing emissions would differ among countries. Studies suggested that the flexibility mechanisms could reduce the overall cost of meeting the targets. Offset and credit programs have been identified as a way for countries to meet their NDC commitments and achieve the goals of the Paris agreement at a lower cost. They may also help close the emissions gap identified in annual UNEP reports.\nThere is a diverse range of sources of supply and demand as well as trading frameworks that drive offset and credit markets. Demand for offsets and credits derives from a range of compliance obligations, arising from international agreements, national laws, as well as voluntary commitments that companies and governments have adopted. Voluntary carbon markets usually consist of private entities purchasing carbon offset credits to meet voluntary greenhouse gas reduction commitments. In some cases, non-covered participants in an ETS may purchase credits as an alternative to purchasing offsets in a voluntary market.\nThese programs also have other positive externalities, or co-benefits, which include better air quality, increased biodiversity, and water and soil protection; community employment opportunities, energy access, and gender equality; and job creation, education opportunities, and technology transfer. Some certification programs have tools and research products to help quantify these benefits.\nPrices for offsets and credits vary widely, reflecting the uncertainty associated with verifying the indirect value of carbon offsets. At the same time, uncertainty has caused some companies to become more skeptical about buying offsets .\n\nEmissions trading systems\n\nEmissions trading are now an important element of regulatory programs to control pollution, including GHG emissions. GHG emission trading programs exist at the sub-national, national, and international level. Under these programs, there is a cap on emissions. Sources of emissions have the flexibility to find and apply the lowest-cost methods for reducing pollution. A central authority or government body usually allocates or sells a limited number (a \"cap\") of permits. These permit a discharge of a specific quantity of a specific pollutant over a set time period. Polluters are required to hold permits in amounts equal to their emissions. Those that want to increase their emissions must buy permits from others willing to sell them. These programs have been applied to greenhouse gases for several reasons. Their warming effects are the same regardless of where they are emitted. The costs of reducing emissions vary widely by source. The cap ensures that the environmental goal is attained.\n\nRegulations and schemes\nAs of 2022, 68 carbon pricing programs were in place or scheduled to be created globally. International programs include the Clean Development Mechanism, Article 6 of the Paris Agreement, and CORSIA. National programs include ETS systems such as the European Union Emissions Trading System (EU-ETS) and the California Cap and Trade Program. Eligible credits in these programs may include credits that international or independent crediting systems have issued. There are also standards and crediting mechanisms that independent, nongovernmental entities such as Verra and Gold Standard manage.\n\nKyoto Protocol\nUnder the Clean Development Mechanism, a developed country can sponsor a greenhouse gas reduction project in a developing country, where the costs of greenhouse gas reduction activities are usually much lower. The developed country receives credits for meeting its emission reduction targets known as Certified Emission Reductions (CERs), while the developing country receives capital investment and clean technology or beneficial change in land use. Under Joint Implementation, a developed country with relatively high domestic costs of emission reduction would set up a project in another developed country. Offset credits under this program are designated as Emission Reduction Units.\nThe International Emissions Trading program enables countries to trade in the international carbon credit market to cover their shortfall in assigned amount units. Countries with surplus units can sell them to countries that are exceeding their emission targets under Annex B of the Kyoto Protocol.\nNuclear energy projects are not eligible for credits under these programs. Country-specific designated national authorities approve projects under the CDM.\n\nParis Agreement Article 6 mechanisms\n\nArticle 6 of the Paris Agreement continues to support offset and credit programs between countries, including CDM projects from the Kyoto Protocol. Programs now occur to help achieve emission reduction targets set out in each country's nationally determined contribution (NDC).\n\nThe ITMO system requires \"corresponding adjustments\" to avoid double counting of emission reductions. Double-counting occurs if both the host country and purchasing country count the reduction towards their target. If the receiving country uses ITMOs towards its NDC, the host country must discount those reductions from its emissions budget by adding and reporting that higher total in its biennial reporting. Otherwise Article 6.2 gives countries a lot of flexibility in how they can create trading agreements.\nThe supervisory board under Article 6.4 is responsible for approving methodologies, setting guidance, and implementing procedures. The preparation work for this is expected to last until the end of 2023. ER credits issued will fall by 2% to ensure that the program as a whole results in an overall Mitigation of Global Emissions. An additional 5% reduction of ERs will go to a fund to finance adaptation. Administrative fees for program management are still under discussion.\nCDM projects may transition to the Article 6.4 program subject to approval by the country hosting the project, and if the project meets the new rules, with certain exceptions for rules on methodologies. Projects can generally continue to use the same CDM methodologies through 2025. From 2026 on, they must meet all Article 6 requirements. Up to 2.8 billion credits could potentially become eligible for issuance under Article 6.4 if all CDM projects transition.\nArticle 6 does not directly regulate the voluntary carbon markets. In principle, it is possible to issue and purchase carbon offsets without reference to Article 6. It is possible that a multi-tier system could emerge with different types of offsets and credits available for investors. Companies may be able to purchase 'adjusted credits' that eliminate the risk of double counting. These may be seen as more valuable if they support science-based targets and net-zero emissions. Other non-adjusted offsets and credits could support claims for other environmental or social indicators. They could also support emission reductions that are seen as less valuable in terms of these goals. Uncertainty remains around Article 6's effects on future voluntary carbon markets. There is also uncertainty about what investors could claim by purchasing various types of carbon credits.\n\nREDD+\nREDD+ is a UNFCCC framework, largely addressed at tropical regions in developing countries, that is designed to compensate countries for not clearing or degrading their forests, or for enhancing forest carbon stocks. It aims to create financial value for carbon stored in forests, using the concept of results-based payments. REDD+ also promotes co-benefits from reducing deforestation such as biodiversity. It was introduced in its basic form at COP11 in 2005 and has grown into a broad policy initiative to address deforestation and forest degradation.\nIn 2015, REDD+ was incorporated into Article 5 of the Paris Agreement. REDD+ initiatives typically compensate developing countries or their regional administrations for reducing their emissions from deforestation and forest degradation. It consists of several stages: One, achieving REDD+ readiness; two, formalizing an agreement for financing; three, measuring, reporting, and verifying results; and four, receiving results-based payments.\nOver 50 countries have national REDD+ initiatives. REDD+ is also taking place through provincial and district governments and at the local level through private landowners. As of 2020, there were over 400 ongoing REDD+ projects globally. Brazil and Colombia account for the largest amount of REDD+ project land area.\n\nCORSIA\nThe Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is a global, market-based program to reduce emissions from international aviation. It aims to allow credits and offsets for emissions that cannot be reduced by technology and operational improvements or sustainable aviation fuels. To ensure the environmental integrity of these offsets, the program has developed a list of eligible offsets that can be used. Operating principles are similar to those under existing trading mechanisms and carbon offset certification standards. CORSIA was applied to international aviation since January 2019. At that point all airlines had been required to report their CO2 emissions on an annual basis. International flights must undertake offsetting under CORSIA since January 2021.\n\nMarkets\nCompliance market credits account for most of the offset and credit market today. Trading on voluntary carbon markets was 300 MtCO2e in 2021. By comparison, the compliance carbon market trading volume was 12 GtCO2e, and global greenhouse gas emissions in 2019 were 59 GtCO2e.\nCurrently several exchanges trade in carbon credits and allowances covering both spot and futures markets. These include the Chicago Mercantile Exchange, CTX Global, the European Energy Exchange, Global Carbon Credit Exchange gCCEx, Intercontinental Exchange, MexiCO2, NASDAQ OMX Commodities Europe and Xpansiv. Many companies now engage in emissions abatement, offsetting, and sequestration programs, which generate credits that can be sold on an exchange.\nAt the start of 2022 there were 25 operational emissions trading systems around the world. They are in jurisdictions representing 55% of global GDP. These systems cover 17% of global emissions. The European Union Emissions Trading System (EU-ETS) is the second largest trading system in the world after the Chinese national carbon trading scheme. It covers over 40% of European GHG emissions. California's cap-and-trade program covers about 85% of statewide GHG emissions.\n\nVoluntary carbon markets and certification programs\nVoluntary carbon markets (VCM) are largely unregulated markets where carbon offsets are traded by corporations, individuals and organizations that are under no legal obligation to make emission cuts. In voluntary carbon markets, companies or individuals use carbon offsets to meet the goals they set themselves for reducing emissions. Credits are issued under independent crediting standards. Some entities also purchase them under international or domestic crediting mechanisms. National and subnational programs have been increasing in popularity.\nMany different groups exist within the voluntary carbon market, including developers, brokers, auditors, and buyers. Certification programs for VCMs establish accounting standards, project eligibility requirements, and monitoring, reporting and verification (MRV) procedures for credit and offset projects. They include the Verified Carbon Standard issued by Verra, the Gold Standard, the Global Carbon Council based in Qatar, the Climate Action Reserve, the American Carbon Registry, and Plan Vivo. Puro Standard, the first standard for engineered carbon removal, is verified by DNV GL. Isometric was the first carbon registry to issue credits for enhanced weathering carbon removal. There are also some additional standards for validating co-benefits, including the Climate, Community and Biodiversity Standard (CCB Standard), also issued by Verra, and the Social Carbon Standard, issued by the Ecologica Institute. The Integrity Council for the Voluntary Carbon Market (ICVCM) publishes the Core Carbon Principles (CCPs) as a benchmark for carbon credit integrity and assesses carbon crediting programs to determine whether they are \"CCP-Eligible\".\nThe voluntary carbon markets currently represent less than 1% of the reductions pledged in country NDCs by 2030. It represents an even smaller portion of the reductions needed to achieve the 1.5 °C Paris temperature goal pathway in 2030. However, the VCM is growing significantly. Between 2017 and 2021, both the issuance and retirement of VCM carbon offsets more than tripled. Some predictions call for global VCM demand to increase 15-fold between 2021 and 2030, and 100 times by 2050. Carbon removal projects such as forestry and carbon capture and storage are expected to have a larger share of this market in the future, compared to renewable energy projects. However, there is evidence that large companies are becoming more reluctant to use VCM offsets and credits because of a complex web of standards, despite an increased focus on net zero emissions goals.\n\nDetermining value\nIn 2022 voluntary carbon market (VCM) prices ranged from $8 to $30 per tonne of CO2e for the most common types of offset projects. Several factors can affect these prices. The costs of developing a project are a significant factor. Those tied to projects that can sequester carbon have recently been selling at a premium compared to other projects such as renewable energy or energy efficiency. Projects that sequester carbon are also called Nature-Based Solutions. Projects with additional social and environmental benefits can command a higher price. This reflects the value of the co-benefits and the perceived value of association with these projects. Credits from a reputable organization may command a higher price. Some credits located in developed countries may be priced higher. One reason could be that companies prefer to back projects closer to their business sites. Conversely, carbon credits with older vintages tend to be valued lower on the market.\nPrices on the compliance market are generally higher. They vary based on geography, with EU and UK ETS credits trading at higher prices than those in the US in 2022. Lower prices on the VCM are in part due to an excess of supply in relation to demand. Some types of offsets are able to be created at very low costs under present standards. Without this surplus, current VCM prices could be at least $10/tCO2e higher.\nSome pricing forecasts predict VCM prices could increase to as much as $47–$210 per tonne by 2050. There could be an even higher spike in the short term in certain scenarios. A major factor in future price models is the extent to which programs that support more permanent removals can influence future global climate policy. This could limit the supply of approvable offsets, and thereby raise prices.\nDemand for VCM offsets is expected to increase five to ten-fold over the next decade as more companies adopt Net Zero climate commitments. This could benefit both markets and progress on reducing GHG emissions. If carbon offset prices remain significantly below these forecast levels, companies could be open to criticisms of greenwashing. This is because some might claim credit for emission reduction projects that would have been undertaken anyway. At prices of $100/tCO2e, a variety of carbon removal technologies could deliver around 2 GtCO2e per year of annual emission reductions between now and 2050. These technologies include reducing deforestation, forest restoration, CCS, BECCs and renewables in least developed countries. In addition, as the cost of using offsets and credits rises, investments in reducing supply chain emissions will become more attractive.\n\nVerified Carbon Standard by Verra\n\nVerra was developed in 2005. It is a widely used voluntary carbon standard, which also offers specific methodologies for REDD+ projects. As of 2020, there had been over 1,500 certified VCS projects covering energy, transport, waste, forestry, and other sectors. In 2021, Verra issued 300 MtCO2e worth of offset credits for 110 projects. Verra is the program of choice for most of the forest credits in the voluntary market, and almost all REDD+ projects.\n\nGold Standard\n\nThe Gold Standard was developed in 2003 by the World Wide Fund for Nature (WWF) in consultation with an independent standards advisory board. Projects are open to any non-government, community-based organization. Allowable categories include renewable energy supply, energy efficiency, afforestation, reforestation, and agriculture. The program also promotes the Sustainable Developments Goals. Projects must meet at least three of those goals besides reducing GHG emissions. Projects must make a net-positive contribution to the economic, environmental and social welfare of the local population. Program monitoring requirements help determine this.\n\nTypes of offset projects\nA variety of projects can be used to reduce GHG emissions and thus to generate carbon offsets and credits. These can include land use improvement, methane capture, biomass sequestration, renewable energy, or industrial energy efficiency. They also include reducing methane, reforestation and switching fuel, for example to carbon-neutral and carbon-negative fuels. The CDM identifies over 200 types of projects suitable for generating carbon offsets and credits. An example of land use improvement is better forest management.\nOffset certification and carbon trading programs vary by how much they consider specific projects eligible for offsets or credits. The European Union Emission Trading System considers nuclear energy projects, afforestation or reforestation activities, and projects involving destruction of industrial gases ineligible. Industrial gases include HFC-23 and N2O.\n\nRenewable energy\nRenewable energy projects can include hydroelectric, wind, photovoltaic solar, solar hot water, biomass power, and heat production. These types of projects help societies move from electricity and heating based on fossil fuels towards forms of energy that are less carbon-intensive. However, they may not qualify as offset projects. This is because it is difficult or impossible to determine their additionality. They usually generate revenue. And they usually involve subsidies or other complex financial arrangements. This can make them ineligible under many offset and credit programs.\n\nMethane collection and combustion\nMethane is a potent greenhouse gas. It is most often emitted from landfills, livestock, and from coal mining. Methane projects can produce carbon offsets through the capture of methane for energy production. Examples include the combustion or containment of methane generated by farm animals by use of an anaerobic digester, in landfills, or from other industrial waste.\n\nEnergy efficiency\n\nCarbon offsets that fund renewable energy projects help lower the carbon intensity of energy supply. Energy conservation projects seek to reduce the overall demand for energy. Carbon offsets in this category fund projects of three main types.\nCogeneration plants generate both electricity and heat from the sa",
    "source": "wikipedia:Carbon offset",
    "domain": "climate"
  },
  {
    "text": "A carbon footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO2-equivalent) per unit of comparison. Such units can be for example tonnes CO2-eq per year, per kilogram of protein for consumption, per kilometer travelled, per piece of clothing and so forth. A product's carbon footprint includes the emissions for the entire life cycle. These run from the production along the supply chain to its final consumption and disposal.\nSimilarly, an organization's carbon footprint includes the direct as well as the indirect emissions that it causes. The Greenhouse Gas Protocol (for carbon accounting of organizations) calls these Scope 1, 2 and 3 emissions. There are several methodologies and online tools to calculate the carbon footprint. They depend on whether the focus is on a country, organization, product or individual person. For example, the carbon footprint of a product could help consumers decide which product to buy if they want to be climate aware. For climate change mitigation activities, the carbon footprint can help distinguish those economic activities with a high footprint from those with a low footprint. So the carbon footprint concept allows everyone to make comparisons between the climate impacts of individuals, products, companies and countries. It also helps people devise strategies and priorities for reducing the carbon footprint.\nThe carbon dioxide equivalent (CO2eq) emissions per unit of comparison is a suitable way to express a carbon footprint. This sums up all the greenhouse gas emissions. It includes all greenhouse gases, not just carbon dioxide. And it looks at emissions from economic activities, events, organizations and services. In some definitions, only the carbon dioxide emissions are taken into account. These do not include other greenhouse gases, such as methane and nitrous oxide.\nVarious methods to calculate the carbon footprint exist, and these may differ somewhat for different entities. For organizations it is common practice to use the Greenhouse Gas Protocol. It includes three carbon emission scopes. Scope 1 refers to direct carbon emissions. Scope 2 and 3 refer to indirect carbon emissions. Scope 3 emissions are those indirect emissions that result from the activities of an organization but come from sources which they do not own or control.\nFor countries it is common to use consumption-based emissions accounting to calculate their carbon footprint for a given year. Consumption-based accounting using input-output analysis backed by super-computing makes it possible to analyse global supply chains. Countries also prepare national GHG inventories for the UNFCCC. The GHG emissions listed in those national inventories are only from activities in the country itself. This approach is called territorial-based accounting or production-based accounting. It does not take into account production of goods and services imported on behalf of residents. Consumption-based accounting does reflect emissions from goods and services imported from other countries.\nConsumption-based accounting is therefore more comprehensive. This comprehensive carbon footprint reporting including Scope 3 emissions deals with gaps in current systems. Countries' GHG inventories for the UNFCCC do not include international transport. Comprehensive carbon footprint reporting looks at the final demand for emissions, to where the consumption of the goods and services takes place.\n\nDefinition\n\nA formal definition of carbon footprint is as follows: \"A measure of the total amount of carbon dioxide (CO2) and methane (CH4) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent using the relevant 100-year global warming potential (GWP100).\"\nScientists report carbon footprints in terms of equivalents of tonnes of CO2 emissions (CO2-equivalent). They may report them per year, per person, per kilogram of protein, per kilometer travelled, and so on.\nIn the definition of carbon footprint, some scientists include only CO2. But more commonly they include several of the notable greenhouse gases. They can compare various greenhouse gases by using carbon dioxide equivalents over a relevant time scale, like 100 years. Some organizations use the term greenhouse gas footprint or climate footprint to emphasize that all greenhouse gases are included, not just carbon dioxide.\nThe Greenhouse Gas Protocol includes all of the most important greenhouse gases. \"The standard covers the accounting and reporting of seven greenhouse gases covered by the Kyoto Protocol – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PCFs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3).\"\nIn comparison, the IPCC definition of carbon footprint in 2022 covers only carbon dioxide. It defines the carbon footprint as the \"measure of the exclusive total amount of emissions of carbon dioxide (CO2) that is directly and indirectly caused by an activity or is accumulated over the lifecycle stages of a product.\" The IPCC report's authors adopted the same definition that had been proposed in 2007 in the UK. That publication included only carbon dioxide in the definition of carbon footprint. It justified this with the argument that other greenhouse gases were more difficult to quantify. This is because of their differing global warming potentials. They also stated that an inclusion of all greenhouse gases would make the carbon footprint indicator less practical. But there are disadvantages to this approach. One disadvantage of not including methane is that some products or sectors that have a high methane footprint such as livestock appear less harmful for the climate than they actually are.\n\nTypes of greenhouse gas emissions\n\nThe greenhouse gas protocol is a set of standards for tracking greenhouse gas emissions. The standards divide emissions into three scopes (Scope 1, 2 and 3) within the value chain. Greenhouse gas emissions caused directly by the organization such as by burning fossil fuels are referred to as Scope 1. Emissions caused indirectly by an organization, such as by purchasing secondary energy sources like electricity, heat, cooling or steam are called Scope 2. Lastly, indirect emissions associated with upstream or downstream processes are called Scope 3.\n\nDirect carbon emissions (Scope 1)\nDirect or Scope 1 carbon emissions come from sources on the site that is producing a product or delivering a service. An example for industry would be the emissions from burning a fuel on site. On the individual level, emissions from personal vehicles or gas-burning stoves are Scope 1.\n\nIndirect carbon emissions (Scope 2)\nIndirect carbon emissions are emissions from sources upstream or downstream from the process being studied. They are also known as Scope 2 or Scope 3 emissions.\nScope 2 emissions are the indirect emissions related to purchasing electricity, heat, or steam used on site. Examples of upstream carbon emissions include transportation of materials and fuels, any energy used outside of the production facility, and waste produced outside the production facility. Examples of downstream carbon emissions include any end-of-life process or treatments, product and waste transportation, and emissions associated with selling the product. The GHG Protocol says it is important to calculate upstream and downstream emissions. There could be some double counting. This is because upstream emissions of one person's consumption patterns could be someone else's downstream emissions\n\nOther indirect carbon emissions (Scope 3)\nScope 3 emissions are all other indirect emissions derived from the activities of an organization. But they are from sources they do not own or control. The GHG Protocol's Corporate Value Chain (Scope 3) Accounting and Reporting Standard allows companies to assess their entire value chain emissions impact and identify where to focus reduction activities.\nScope 3 emission sources include emissions from suppliers and product users. These are also known as the value chain. Transportation of good, and other indirect emissions are also part of this scope. In 2022 about 30% of US companies reported Scope 3 emissions. The International Sustainability Standards Board is developing a recommendation to include Scope 3 emissions in all GHG reporting.\n\nPurpose and strengths\n\nThe current rise in global average temperature is more rapid than previous changes. It is primarily caused by humans burning fossil fuels. The increase in greenhouse gases in the atmosphere is also due to deforestation and agricultural and industrial practices. These include cement production. The two most notable greenhouse gases are carbon dioxide and methane. Greenhouse gas emissions, and hence humanity's carbon footprint, have been increasing during the 21st century. The Paris Agreement aims to reduce greenhouse gas emissions enough to limit the rise in global temperature to no more than 1.5 °C above pre-industrial levels.\nThe carbon footprint concept makes comparisons between the climate impacts of individuals, products, companies and countries. A carbon footprint label on products could enable consumers to choose products with a lower carbon footprint if they want to help limit climate change. For meat products, as an example, such a label could make it clear that beef has a higher carbon footprint than chicken.\nUnderstanding the size of an organization's carbon footprint makes it possible to devise a strategy to reduce it. For most businesses the vast majority of emissions do not come from activities on site, known as Scope 1, or from energy supplied to the organization, known as Scope 2, but from Scope 3 emissions, the extended upstream and downstream supply chain. Therefore, ignoring Scope 3 emissions makes it impossible to detect all emissions of importance, which limits options for mitigation. Large companies in sectors such as clothing or automobiles would need to examine more than 100,000 supply chain pathways to fully report their carbon footprints.\nThe importance of displacement of carbon emissions has been known for some years. Scientists also call this carbon leakage. The idea of a carbon footprint addresses concerns of carbon leakage which the Paris Agreement does not cover. Carbon leakage occurs when importing countries outsource production to exporting countries. The outsourcing countries are often rich countries while the exporters are often low-income countries. Countries can make it appear that their GHG emissions are falling by moving \"dirty\" industries abroad, even if their emissions could be increasing when looked at from a consumption perspective.\nCarbon leakage and related international trade have a range of environmental impacts. These include increased air pollution, water scarcity, biodiversity loss, raw material usage, and energy depletion.\nScholars have argued in favour of using both consumption-based and production-based accounting. This helps establish shared producer and consumer responsibility. Currently countries report on their annual GHG inventory to the UNFCCC based on their territorial emissions. This is known as the territorial-based or production-based approach. Including consumption-based calculations in the UNFCCC reporting requirements would help close loopholes by addressing the challenge of carbon leakage.\nThe Paris Agreement currently does not require countries to include in their national totals GHG emissions associated with international transport. These emissions are reported separately. They are not subject to the limitation and reduction commitments of Annex 1 Parties under the Climate Convention and Kyoto Protocol. The carbon footprint methodology includes GHG emissions associated with international transport, thereby assigning emissions caused by international trade to the importing country.\n\nUnderlying concepts for calculations\nThe calculation of the carbon footprint of a product, service or sector requires expert knowledge and careful examination of what is to be included. Carbon footprints can be calculated at different scales. They can apply to whole countries, cities, neighborhoods and also sectors, companies and products. Several free online carbon footprint calculators exist to calculate personal carbon footprints.\nSoftware such as the \"Scope 3 Evaluator\" can help companies report emissions throughout their value chain. The software tools can help consultants and researchers to model global sustainability footprints. In each situation there are a number of questions that need to be answered. These include which activities are linked to which emissions, and which proportion should be attributed to which company. Software is essential for company management. But there is a need for new ways of enterprise resource planning to improve corporate sustainability performance.\nTo achieve 95% carbon footprint coverage, it would be necessary to assess 12 million individual supply-chain contributions. This is based on analyzing 12 sectoral case studies. The Scope 3 calculations can be made easier using input-output analysis. This is a technique originally developed by Nobel Prize-winning economist Wassily Leontief.\n\nConsumption-based emission accounting based on input-output analysis\n\nConsumption-based emission accounting traces the impacts of demand for goods and services along the global supply chain to the end-consumer. It is also called consumption-based carbon accounting. In contrast, a production-based approach to calculating GHG emissions is not a carbon footprint analysis. This approach is also called a territorial-based approach. The production-based approach includes only impacts physically produced in the country in question. Consumption-based accounting redistributes the emissions from production-based accounting. It considers that emissions in another country are necessary for the home country's consumption bundle.\nConsumer-based accounting is based on input-output analysis. It is used at the highest levels for any economic research question related to environmental or social impacts. Analysis of global supply chains is possible using consumption-based accounting with input-output analysis assisted by super-computing capacity.\nLeontief created Input-output analysis (IO) to demonstrate the relationship between consumption and production in an economy. It incorporates the entire supply chain. It uses input-output tables from countries' national accounts. It also uses international data such as UN Comtrade and Eurostat. Input-output analysis has been extended globally to multi-regional input-output analysis (MRIO). Innovations and technology enabling the analysis of billions of supply chains made this possible. Standards set by the United Nations underpin this analysis. The analysis enables a Structural Path Analysis. This scans and ranks the top supply chain nodes and paths. It conveniently lists hotspots for urgent action. Input-output analysis has increased in popularity because of its ability to examine global value chains.\n\nCombination with life cycle analysis (LCA)\n\nLife cycle assessment (LCA) is a methodology for assessing all environmental impacts associated with the life cycle of a commercial product, process, or service. It is not limited to the greenhouse gas emissions. It is also called life cycle analysis. It includes water pollution, air pollution, ecotoxicity and similar types of pollution. Some widely recognized procedures for LCA are included in the ISO 14000 series of environmental management standards. A standard called ISO 14040:2006 provides the framework for conducting an LCA study. ISO 14060 family of standards provides further sophisticated tools. Also the latest standard, ISO 14064:2018 has the right set of tools that will help reduce Carbon Emissions in Corporations. These are used to quantify, monitor, report and validate or verify GHG emissions and removals.\nGreenhouse gas product life cycle assessments can also comply with specifications such as Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.\nAn advantage of LCA is the high level of detail that can be obtained on-site or by liaising with suppliers. However, LCA has been hampered by the artificial construction of a boundary after which no further impacts of upstream suppliers are considered. This can introduce significant truncation errors. LCA has been combined with input-output analysis. This enables on-site detailed knowledge to be incorporated. IO connects to global economic databases to incorporate the entire supply chain.\n\nProblems\n\nShifting responsibility from corporations to individuals\nCritics argue that the original aim of promoting the personal carbon footprint concept was to shift responsibility away from corporations and institutions and on to personal lifestyle choices. The fossil fuel company BP ran a large advertising campaign for the personal carbon footprint in 2004 which helped popularize this concept. This strategy, employed by many major fossil fuel companies, has been criticized for trying to shift the blame for negative consequences of those industries on to individual choices.\nGeoffrey Supran and Naomi Oreskes of Harvard University argue that concepts such as carbon footprints \"hamstring us, and they put blinders on us, to the systemic nature of the climate crisis and the importance of taking collective action to address the problem\".\nWhile the focus on individual behaviour has shaped public discourse, scientific assessments emphasize that this approach alone is insufficient. The IPCC notes that individual behavioural changes alone are insufficient to achieve deep emission reductions. In its Sixth Assessment Report (2023), the IPCC stated that \"Demand-side measures and new ways of end-use service provision can reduce global GHG emissions in end-use sectors by 40–70% by 2050 compared to baseline scenarios\" This highlights the need to combine lifestyle changes with systemic transitions—such as clean energy systems, electrification of transport and heating, and collective infrastructure solutions—to effectively address climate change. Reducing emissions through behaviour is important, but eliminating combustion altogether through systemic change is critical to long-term climate goals.\n\nRelationship with other environmental impacts\nA focus on carbon footprints can lead people to ignore or even exacerbate other related environmental issues of concern. These include biodiversity loss, ecotoxicity, and habitat destruction. It may not be easy to measure these other human impacts on the environment with a single indicator like the carbon footprint. Consumers may think that the carbon footprint is a proxy for environmental impact. In many cases this is not correct. There can be trade-offs between reducing carbon footprint and environmental protection goals. One example is the use of biofuel, a renewable energy source that can reduce the carbon footprint of the energy supply but can also pose ecological challenges during its production. This is because it is often produced in monocultures with ample use of fertilizers and pesticides. Another example is offshore wind parks, which could have unintended impacts on marine ecosystems.\nThe carbon footprint analysis solely focuses on greenhouse gas emissions, unlike a life-cycle assessment which is much broader and looks at all environmental impacts. Therefore, it is useful to stress in communication activities that the carbon footprint is just one in a family of indicators (e.g. ecological footprint, water footprint, land footprint, and material footprint), and should not be looked at in isolation. In fact, carbon footprint can be treated as one component of ecological footprint.\nThe \"Sustainable Consumption and Production Hotspot Analysis Tool\" (SCP-HAT) is a tool to place carbon footprint analysis into a wider perspective. It includes a number of socio-economic and environmental indicators. It offers calculations that are either consumption-based, following the carbon footprint approach, or production-based. The database of the SCP-HAT tool is underpinned by input–output analysis. This means it includes Scope 3 emissions. The IO methodology is also governed by UN standards. It is based on input-output tables of countries' national accounts and international trade data such as UN Comtrade, and therefore it is comparable worldwide.\n\nDiffering boundaries for calculations\nThe term carbon footprint has been applied to limited calculations that do not include Scope 3 emissions or the entire supply chain. This can lead to claims of misleading customers with regards to the real carbon footprints of companies or products.\n\nReported values\n\nGreenhouse gas emissions overview\n\nBy products\n\nThe Carbon Trust has worked with UK manufacturers to produce \"thousands of carbon footprint assessments\". As of 2014 the Carbon Trust state they have measured 28,000 certifiable product carbon footprints. This NGO has also developed a labelling scheme which \"supports informed consumer choices and business procurement decisions\".\n\nFood\nPlant-based foods tend to have a lower carbon footprint than meat and dairy. In many cases a much smaller footprint. This holds true when comparing the footprint of foods in terms of their weight, protein content or calories. The protein output of peas and beef provides an example. Producing 100 grams of protein from peas emits just 0.4 kilograms of carbon dioxide equivalents (CO2eq). To get the same amount of protein from beef, emissions would be nearly 90 times higher, at 35 kgCO2eq. Only a small fraction of the carbon footprint of food comes from transport and packaging. Most of it comes from processes on the farm, or from land use change. This means the choice of what to eat has a larger potential to reduce carbon footprint than how far the food has traveled, or how much packaging it is wrapped in.\n\nBy sector\n\nThe IPCC Sixth Assessment Report found that global GHG emissions have continued to rise across all sectors. Global consumption was the main cause. The most rapid growth was in transport and industry. A key driver of global carbon emissions is affluence. The IPCC noted that the wealthiest 10% in the world contribute between about one third to one half (36%–45%) of global GHG emissions. Researchers have previously found that affluence is the key driver of carbon emissions. It has a bigger impact than population growth. And it counters the effects of technological developments. Continued economic growth mirrors the increasing trend in material extraction and GHG emissions. \"Industrial emissions have been growing faster since 2000 than emissions in any other sector, driven by increased basic materials extraction and production,\" the IPCC said.\n\nTransport\nThere can be wide variations in emissions for transport of people. This is due to various factors. They include the length of the trip, the source of electricity in the local grid and the occupancy of public transport. In the case of driving the type of vehicle and number of passengers are factors. Over short to medium distances, walking or cycling are nearly always the lowest carbon way to travel. The carbon footprint of cycling one kilometer is usually in the range of 16 to 50 grams CO2eq per km. For moderate or long distances, trains nearly always have a lower carbon footprint than other options.\n\nBy organization\n\nCarbon accounting\n\nBy country\n\nCO2 emissions of countries are typically measured on the basis of production. This accounting method is sometimes referred to as territorial emissions. Countries use it when they report their emissions, and set domestic and international targets such as Nationally Determined Contributions. Consumption-based emissions on the other hand are adjusted for trade. To calculate consumption-based emissions analysts have to track which goods are traded across the world. Whenever a product is imported, all CO2 emissions that were emitted in the production of that product are included. Consumption-based emissions reflect the lifestyle choices of a country's citizens.\nAccording to the World Bank, the global average carbon footprint in 2014 was about 5 tonnes of CO2 per person, measured on a production basis. The EU average for 2007 was about 13.8 tonnes CO2e per person. For the USA, Luxembourg and Australia it was over 25 tonnes CO2e per person. In 2017, the average for the USA was about 20 metric tonnes CO2e per person. This is one of the highest per capita figures in the world.\nThe footprints per capita of countries in Africa and India were well below average. Assuming a global population of around 9–10 billion by 2050, a carbon footprint of about 2–2.5 tonnes CO2e per capita is needed to stay within a 2 °C target. These carbon footprint calculations are based on a consumption-based approach using a Multi-Regional Input-Output (MRIO) database. This database accounts for all greenhouse gas (GHG) emissions in the global supply chain and allocates them to the final consumer of the purchased commodities.\n\nReducing the carbon footprint\n\nClimate change mitigation\nEfforts to reduce the carbon footprint of products, services, and organizations help limit climate change. Such activities are called climate change mitigation.\n\nReducing industry's carbon footprint\n\nCarbon offsetting can reduce a company's overall carbon footprint by providing it with a carbon credit. This compensates the company for carbon dioxide emissions by recognizing an equivalent reduction of carbon dioxide in the atmosphere. Reforestation, or restocking existing forests that have previously been depleted, is an example of carbon offsetting.\nA carbon footprint study can identify specific and critical areas for improvement. It uses input-output analysis and scrutinizes the entire supply chain. Such an analysis could be used to eliminate the supply chains with the highest greenhouse gas emissions.\n\nHistory\nThe term carbon footprint was first used in a BBC vegetarian food magazine in 1999, though the broader concept of ecological footprint, which encompasses the carbon footprint, had been used since at least 1992, as also chronicled by journalist William Safire in the New York Times.\nIn 2005, fossil fuel company BP hired the large advertising campaign Ogilvy to popularize the idea of a carbon footprint for individuals. The campaign instructed people to calculate their personal footprints and provided ways for people to \"go on a low-carbon diet\".\nThe carbon footprint is derived from the ecological footprint, which encompasses carbon emissions. The carbon footprint follows the logic of ecological footprint accounting, which tracks the resource use embodied in consumption, whether it is a product, an individual, a city, or a country. While in the ecological footprint, carbon emissions are translated into areas needed to absorb the carbon emissions, the carbon footprint on its own is expressed in the weight of carbon emissions per time unit. William Rees wrote the first academic publication about ecological footprints in 1992. Other related concepts from the 1990s are the \"ecological backpack\" and material input per unit of service (MIPS).\n\nTrends and similar concepts\nThe International Sustainability Standards Board (ISSB) aims to bring global, rigorous oversight to carbon footprint reporting. It was formed out of the International Financial Reporting Standards. It will require companies to report on their Scope 3 emissions. The ISSB has taken on board criticisms of other initiatives in its aims for universality. It consolidates the Carbon Disclosure Standards Board, the Sustainability Accounting Standards Board and the Value Reporting Foundation. It complements the Global Reporting Initiative. It is influenced by the Task Force on Climate-Related Financial Disclosures. As of early 2023, Great Britain and Nigeria were preparing to adopt these standards.\nThe concept of total equivalent warming impact (TEWI) is the most used index for carbon dioxide equivalent (CO2) emissions calculation in air conditioning and refrigeration sectors by including both the direct and indirect contributions since it evaluates the emissions caused by the operating lifetime of systems. The Expanded Total Equivalent Warming Impact method has been used for an accurate evaluation of refrigerators emissions.\n\nSee also\n\nCarbon emission\nCarbon intensity\nCarbon neutrality\nEcological footprint\nEmbedded emissions\nFood miles\nGreenhouse gas inventory\nIndividual action on climate change\nLife-cycle greenhouse gas emissions of energy sources\nZero-carbon city\n\nReferences\n\nExternal links\nThe GHG Protocol",
    "source": "wikipedia:Carbon footprint",
    "domain": "climate"
  },
  {
    "text": "Sustainable development is an approach to growth and human development that aims to meet the needs of the present without compromising the ability of future generations to meet their own needs. The aim is to have a society where living conditions and resources meet human needs without undermining planetary integrity. Sustainable development aims to balance the needs of the economy, environment, and society. Equitable health access is a pillar of social sustainability. The Brundtland Report, published in 1987, helped to make the concept of sustainable development better known.\nSustainable development overlaps with the idea of sustainability which is a normative concept. UNESCO formulated a distinction between the two concepts as follows: \"Sustainability is often thought of as a long-term goal (i.e. a more sustainable world), while sustainable development refers to the many processes and pathways to achieve it.\"\nThe Rio Process that began at the 1992 Earth Summit in Rio de Janeiro has placed the concept of sustainable development on the international agenda. Sustainable development is the foundational concept of the Sustainable Development Goals (SDGs). These global goals for the year 2030 were adopted in 2015 by the United Nations General Assembly (UNGA). They address the global challenges, including poverty, climate change, biodiversity loss, and peace.\n\nThere are some problems with the concept of sustainable development. Some scholars say it is an oxymoron because according to them, development is inherently unsustainable. Other commentators are disappointed in the lack of progress that has been achieved so far. Scholars have stated that \"sustainable development\" is open-ended, ambiguous, and incoherent, so it can be easily appropriated. Furthermore, while digitalization is often promoted as a tool for sustainable development, recent scholarly analysis has introduced a more complex view, indicating that the rapid reliance on digital technologies can have a negative overall impact on environmental sustainability, despite positive influences on economic and social development aspects. Therefore, it is important that there is increased funding for research on sustainability in order to better understand sustainable development and address its vagueness and shortcomings.\n\nDefinition\nIn 1987, the United Nations World Commission on Environment and Development released the report Our Common Future, commonly called the Brundtland Report. The report included a definition of \"sustainable development\" which is now widely used:\n\nSustainable development is a development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It contains two key concepts within it:\nThe concept of 'needs', in particular, the essential needs of the world's poor, to which overriding priority should be given; and\nThe idea of limitations imposed by the state of technology and social organization on the environment's ability to meet present and future needs.Sustainable development thus tries to find a balance between economic development, environmental protection, and social well-being.\nScholars note that sustainable development is understood in many different ways. They also highlight inconsistencies in the current market-driven system of social, economic and political organization. Efforts toward global sustainability must consider the diverse challenges, conditions, and choices that affect prospects and prosperity for all, everywhere.\nSustainability means different things to different people, and the concept of sustainable development has led to a diversity of discourses that legitimize competing sociopolitical projects.\n\nDevelopment of the concept\n\nSustainable development has its roots in ideas regarding sustainable forest management, which were developed in Europe during the 17th and 18th centuries. In response to a growing awareness of the depletion of timber resources in England, John Evelyn argued, in his 1662 essay Sylva, that \"sowing and planting of trees had to be regarded as a national duty of every landowner, in order to stop the destructive over- exploitation of natural resources.\" In 1713, Hans Carl von Carlowitz, a senior mining administrator in the service of Elector Frederick Augustus I of Saxony published Sylvicultura economics, a 400-page work on forestry. Building upon the ideas of Evelyn and French minister Jean-Baptiste Colbert, von Carlowitz developed the concept of managing forests for sustained yield. His work influenced others, including Alexander von Humboldt and Georg Ludwig Hartig, eventually leading to the development of the science of forestry. This, in turn, influenced people like Gifford Pinchot, the first head of the US Forest Service, whose approach to forest management was driven by the idea of wise use of resources, and Aldo Leopold whose land ethic was influential in the development of the environmental movement in the 1960s.\nFollowing the publication of Rachel Carson's Silent Spring in 1962, the developing environmental movement drew attention to the relationship between economic growth and environmental degradation. Kenneth E. Boulding, in his influential 1966 essay The Economics of the Coming Spaceship Earth, identified the need for the economic system to fit itself to the ecological system with its limited pools of resources. Another milestone was the 1968 article by Garrett Hardin that popularized the term \"tragedy of the commons\".\nThe direct linking of sustainability and development in a contemporary sense can be traced to the early 1970s. \"Strategy of Progress\", a 1972 book (in German) by Ernst Basler, explained how the long-acknowledged sustainability concept of preserving forests for future wood production can be directly transferred to the broader importance of preserving environmental resources to sustain the world for future generations. That same year, the interrelationship of environment and development was formally demonstrated in a systems dynamic simulation model reported in the classic report on Limits to Growth. This was commissioned by the Club of Rome and written by a group of scientists led by Dennis and Donella Meadows of the Massachusetts Institute of Technology. Describing the desirable \"state of global equilibrium\", the authors wrote: \"We are searching for a model output that represents a world system that is sustainable without sudden and uncontrolled collapse and capable of satisfying the basic material requirements of all of its people.\" The year 1972 also saw the publication of the influential book, A Blueprint for Survival.\nIn 1975, an MIT research group prepared ten days of hearings on \"Growth and Its Implication for the Future\" for the US Congress, the first hearings ever held on sustainable development.\nIn 1980, the International Union for Conservation of Nature published a world conservation strategy that included one of the first references to sustainable development as a global priority and introduced the term \"sustainable development\". Two years later, the United Nations World Charter for Nature raised five principles of conservation by which human conduct affecting nature is to be guided and judged.\nSince the Brundtland Report, the concept of sustainable development has developed beyond the initial intergenerational framework to focus more on the goal of \"socially inclusive and environmentally sustainable economic growth\". In 1992, the UN Conference on Environment and Development published the Earth Charter, which outlines the building of a just, sustainable, and peaceful global society in the 21st century. The action plan Agenda 21 for sustainable development identified information, integration, and participation as key building blocks to help countries achieve development that recognizes these interdependent pillars. Furthermore, Agenda 21 emphasizes that broad public participation in decision-making is a fundamental prerequisite for achieving sustainable development.\nThe Rio Protocol was a huge leap forward: for the first time, the world agreed on a sustainability agenda. In fact, a global consensus was facilitated by neglecting concrete goals and operational details.\nWhilst the discussions about (or discourse of) sustainable development are highly influential in global and national governance frameworks, its meaning and operationalization are context-dependent and have evolved over time. This evolution can for example be seen in the transition from the Millennium Development Goals (years 2000 to 2015) to the Sustainable Development Goals (years 2015 to 2030).\n\nGlobal governance framework\nThe most comprehensive global governance framework for sustainable development is the 2030 Agenda for Sustainable Development with its 17 Sustainable Development Goals (SDGs). This agenda was a follow-up to the Millennium Declaration from the year 2000 with its eight Millennium Development Goals (MDGs), the first comprehensive global governance framework for sustainable development. The SDGs have concrete targets (unlike the results from the Rio Process) but no methods for sanctions. They contain goals, targets and indicators for example in the areas of poverty reduction, environmental protection, human prosperity and peace.\nScholars who are investigating global environmental governance have identified a set of discourses within the public space that mostly convey four sustainability frames: mainstream sustainability, progressive sustainability, a limits discourse, and radical sustainability. First, mainstream sustainability is a conservative approach on both economic and political terms. Second, progressive sustainability is an economically conservative, yet politically reformist approach. Under this framing, sustainable development is still centered on economic growth but human well-being and development can only be achieved through a redistribution of power to even out inequalities between developed and developing countries. Third, a limits discourse is an economically reformist, yet politically conservative approach to sustainability. Fourth, radical sustainability is a transformative approach seeking to break with existing global economic and political structures.\n\nRelated concepts\n\nSustainability\n\nDimensions\n\nSustainable development, like sustainability, is regarded to have three dimensions: the environment, economy and society. The idea is that a good balance between the three dimensions should be achieved. Instead of calling them dimensions, other terms commonly used are pillars, domains, aspects, spheres.\n\nPathways\n\nSix interdependent capacities are deemed to be necessary for the successful pursuit of sustainable development. These are the capacities to measure progress towards sustainable development; promote equity within and between generations; adapt to shocks and surprises; transform the system onto more sustainable development pathways; link knowledge with action for sustainability; and to devise governance arrangements that allow people to work together.\nDuring the MDG era (year 2000 to 2015), the key objective of sustainable development was poverty reduction to be reached through economic growth and participation in the global trade system. The SDGs take a much more comprehensive approach to sustainable development than the MDGs did. They offer a more people-centered development agenda. Out of the 17 SDGs, for example, 11 goals contain targets related to equity, equality or inclusion, and SDG 10 is solely devoted to addressing inequality within and among countries.\n\nImproving on environmental sustainability\n An unsustainable situation occurs when natural capital (the total of nature's resources) is used up faster than it can be replenished. Sustainability requires that human activity only uses nature's resources at a rate at which they can be replenished naturally. The concept of sustainable development is intertwined with the concept of carrying capacity. Theoretically, the long-term result of environmental degradation is the inability to sustain human life.\nImportant operational principles of sustainable development were published by Herman Daly in 1990: renewable resources should provide a sustainable yield (the rate of harvest should not exceed the rate of regeneration); for non-renewable resources there should be equivalent development of renewable substitutes; waste generation should not exceed the assimilative capacity of the environment.\nIn 2019, a summary for policymakers of the largest, most comprehensive study to date of biodiversity and ecosystem services was published by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. It recommended that human civilization will need a transformative change, including sustainable agriculture, reductions in consumption and waste, fishing quotas and collaborative water management.\n\nEnvironmental problems associated with industrial agriculture and agribusiness are now being addressed through approaches such as sustainable agriculture, organic farming and more sustainable business practices. At the local level there are various movements working towards sustainable food systems which may include less meat consumption, local food production, slow food, sustainable gardening, and organic gardening. The environmental effects of different dietary patterns depend on many factors, including the proportion of animal and plant foods consumed and the method of food production. \nAs global population and affluence have increased, so has the use of various materials increased in volume, diversity, and distance transported. By 2050, humanity could consume an estimated 140 billion tons of minerals, ores, fossil fuels and biomass per year (three times its current amount) unless the economic growth rate is decoupled from the rate of natural resource consumption.\nSustainable use of materials has targeted the idea of dematerialization, converting the linear path of materials (extraction, use, disposal in landfill) to a circular material flow that reuses materials as much as possible, much like the cycling and reuse of waste in nature. This way of thinking is expressed in the concept of circular economy, which employs reuse, sharing, repair, refurbishment, remanufacturing and recycling to create a closed-loop system, minimizing the use of resource inputs and the creation of waste, pollution and carbon emissions. The European Commission has adopted an ambitious Circular Economy Action Plan in 2020, which aims at making sustainable products the norm in the EU.\n\nImproving on economic and social aspects\n\nIt has been suggested that because of the rural poverty and overexploitation, environmental resources should be treated as important economic assets, called natural capital. Economic development has traditionally required a growth in the gross domestic product. This model of unlimited personal and GDP growth may be over. Sustainable development may involve improvements in the quality of life for many but may necessitate a decrease in resource consumption. \"Growth\" generally ignores the direct effect that the environment may have on social welfare, whereas \"development\" takes it into account.\nAs early as the 1970s, the concept of sustainability was used to describe an economy \"in equilibrium with basic ecological support systems\". Scientists in many fields have highlighted The Limits to Growth, and economists have presented alternatives, for example a 'steady-state economy', to address concerns over the impacts of expanding human development on the planet. In 1987, the economist Edward Barbier published the study The Concept of Sustainable Economic Development, where he recognized that goals of environmental conservation and economic development are not conflicting and can be reinforcing each other.\nA World Bank study from 1999 concluded that based on the theory of genuine savings (defined as \"traditional net savings less the value of resource depletion and environmental degradation plus the value of investment in human capital\"), policymakers have many possible interventions to increase sustainability, in macroeconomics or purely environmental. Several studies have noted that efficient policies for renewable energy and pollution are compatible with increasing human welfare, eventually reaching a golden-rule steady state.\nA meta review in 2002 looked at environmental and economic valuations and found a \"lack of concrete understanding of what \"sustainability policies\" might entail in practice\". A study concluded in 2007 that knowledge, manufactured and human capital (health and education) has not compensated for the degradation of natural capital in many parts of the world. It has been suggested that intergenerational equity can be incorporated into a sustainable development and decision making, as has become common in economic valuations of climate economics.\nThe World Business Council for Sustainable Development published a Vision 2050 document in 2021 to show \"How business can lead the transformations the world needs\". The vision states that \"we envision a world in which 9+billion people can live well, within planetary boundaries, by 2050.\" This report was highlighted by The Guardian as \"the largest concerted corporate sustainability action plan to date – include reversing the damage done to ecosystems, addressing rising greenhouse gas emissions and ensuring societies move to sustainable agriculture.\"\n\nBarriers\n\nAssessments and reactions\n\nThe concept of sustainable development has been and still is, subject to criticism, including the question of what is to be sustained in sustainable development. It has been argued that there is no such thing as sustainable use of a non-renewable resource, since any positive rate of exploitation will eventually lead to the exhaustion of earth's finite stock; this perspective renders the Industrial Revolution as a whole unsustainable.\nThe sustainable development debate is based on the assumption that societies need to manage three types of capital (economic, social, and natural), which may be non-substitutable and whose consumption might be irreversible. Natural capital can not necessarily be substituted by economic capital. While it is possible that we can find ways to replace some natural resources, it is much less likely that they will ever be able to replace ecosystem services, such as the protection provided by the ozone layer, or the climate stabilizing function of the Amazonian forest.\nThe concept of sustainable development has been criticized from different angles. While some see it as paradoxical (or an oxymoron) and regard development as inherently unsustainable, others are disappointed in the lack of progress that has been achieved so far. Part of the problem is that \"development\" itself is not consistently defined.\nThe vagueness of the Brundtland definition of sustainable development has been criticized as follows: The definition has \"opened up the possibility of downplaying sustainability. Hence, governments spread the message that we can have it all at the same time, i.e. economic growth, prospering societies and a healthy environment. No new ethic is required. This so-called weak version of sustainability is popular among governments, and businesses, but profoundly wrong and not even weak, as there is no alternative to preserving the earth's ecological integrity.\"\nScholars have stated that sustainable development is open-ended, much critiqued as ambiguous, incoherent, and therefore easily appropriated.\n\nSociety and culture\n\nSustainable development goals\nSustainable development is the foundational concept of the Sustainable Development Goals (SDGs). Policies to achieve the SDGs are meant to cohere around this concept.\n\nEducation for sustainable development\nEducation for sustainable development (ESD) is a term officially used by the United Nations. It is defined as education practices that encourage changes in knowledge, skills, values, and attitudes to enable a more sustainable and just society for humanity. ESD aims to empower and equip current and future generations to meet their needs using a balanced and integrated approach to sustainable development's economic, social, and environmental dimensions.\nAgenda 21 was the first international document that identified education as an essential tool for achieving sustainable development and highlighted areas of action for education. ESD is a component of measurement in an indicator for Sustainable Development Goal 12 (SDG) for \"responsible consumption and production\". SDG 12 has 11 targets, and target 12.8 is \"By 2030, ensure that people everywhere have the relevant information and awareness for sustainable development and lifestyles in harmony with nature.\" 20 years after the Agenda 21 document was declared, the 'Future we want' document was proclaimed in the Rio+20 UN Conference on Sustainable Development, stating that \"We resolve to promote education for sustainable development and to integrate sustainable development more actively into education beyond the Decade of Education for Sustainable Development.\"\nOne version of education for Sustainable Development recognizes modern-day environmental challenges. It seeks to define new ways to adjust to a changing biosphere, as well as engage individuals to address societal issues that come with them. In the International Encyclopedia of Education, this approach to education is seen as an attempt to \"shift consciousness toward an ethics of life-giving relationships that respects the interconnectedness of man to his natural world\" to equip future members of society with environmental awareness and a sense of responsibility to sustainability.\nFor UNESCO, education for sustainable development involves:\n\nintegrating key sustainable development issues into teaching and learning. This may include, for example, instruction about climate change, disaster risk reduction, biodiversity, and poverty reduction and sustainable consumption. It also requires participatory teaching and learning methods that motivate and empower learners to change their behaviours and take action for sustainable development. ESD consequently promotes competencies like critical thinking, imagining future scenarios and making decisions in a collaborative way.\nThe Thessaloniki Declaration, presented at the \"International Conference on Environment and Society: Education and Public Awareness for Sustainability\" by UNESCO and the Government of Greece (December 1997), highlights the importance of sustainability not only with regards to the natural environment, but also with \"poverty, health, food security, democracy, human rights, and peace\".\n\nSee also\n\nDigital public goods – Digital good that is non-excludable and non-rival\nList of sustainability topics\nOutline of sustainability – Overview of and topical guide to sustainability\nPolicy coherence for development – Approach in development assistance\nSustainability measurement – Quantitbasis for the informed management of sustainability\nSustainability strategies – Mechanisms to foster sustainabilityPages displaying short descriptions of redirect targets\nSustainable remediation – Mode of approaching potentially contaminated land and groundwater\nUnited Nations Decade of Education for Sustainable Development\n\nReferences\n\nExternal links\n\nSustainable Development Knowledge Platform of the UN\nSustainable Development Solutions Network",
    "source": "wikipedia:Sustainable development",
    "domain": "climate"
  },
  {
    "text": "Environmental policy is the pledge by governments or organizations to adopt laws, regulations, and other policy tools aimed at addressing environmental issues. These typically involve air and water pollution, waste management, ecosystem protection, biodiversity conservation, management of natural resources, and safeguarding wildlife and endangered species\nFor example, concerning environmental policy, the implementation of an eco-energy-oriented policy at a global level to address the issue of climate change could be addressed.\nPolicies concerning energy or regulation of toxic substances including pesticides and many types of industrial waste are part of the topic of environmental policy. This policy can be deliberately taken to influence human activities and thereby prevent undesirable effects on the biophysical environment and natural resources, as well as to make sure that changes in the environment do not have unacceptable effects on humans.\n\nDefinition\nOne way is to describe environmental policy is that it comprises two major terms: environment and policy. Environment refers to the physical ecosystems, but can also take into consideration the social dimension (quality of life, health) and an economic dimension (resource management, biodiversity). Policy can be defined as a \"course of action or principle adopted or proposed by a government, party, business or individual\". Thus, environmental policy tends to focus on problems arising from human impact on the environment, which is important to human society by having a (negative) impact on human values. Such human values are often labeled as good health or the 'clean and green' environment. In practice, policy analysts provide a wide variety of types of information to the public decision-making process.\nThe concept of environmental policy was first used in the 1960s to recognise that all environmental problems, like the environment itself, are interconnected. Addressing environmental problems effectively (such as air, water, and soil pollution) requires looking at their connections and underlying and common sources, and how policies addressing particular problems can have spill-over effects on other problems and policies. \"The environment\" thus became a focus for public policy and environmental policy the term to refer to the way environmental issues were addressed more or less comprehensively.\nEnvironmental issues typically addressed by environmental policy include (but are not limited to) air and water pollution, waste management, ecosystem management, biodiversity protection, the protection of natural resources, wildlife and endangered species, and the management of these natural resources for future generations. Relatively recently, environmental policy has also attended to the communication of environmental issues. Environmental policies often address issues in one of three dimensions of the environment: ecological (for instance, policies aimed at protecting a particular species or natural areas), resource (for instance, related to energy, land, water), and the human environment (the environment modified or shaped by humans, for instance, urban planning, pollution). Environmental policy-making is often highly fragmented, although environmental policy analysts have long pointed out the need for the development of more comprehensive and integrated environmental policies.\nIn contrast to environmental policy, ecological policy addresses issues that focus on achieving benefits (both monetary and non monetary) from the non human ecological world. Broadly included in ecological policy is natural resource management (fisheries, forestry, wildlife, range, biodiversity, and at-risk species). This specialized area of policy possesses its own distinctive features.\n\nHistory\nAs documented by environmental historians, human societies have always impacted their environment, often with adverse consequences for themselves and the rest of nature. Their failure to (timely) recognise and address these problems has been a contributing factor to their decline and collapse. \nConcerns about pollution and its threat to humans as well as nature has provided major stimulus for the development of environmental policies. In 1863, in the United Kingdom, health problems arising from the release of harmful chemicals led to the adoption of the Alkali Act and the creation of the Alkali Inspectorate. In 1956, the Clean Air Act 1956 was adopted in the wake of London's Great Smog of 1952 that is believed to have killed 12,000 people. Concerns about the effects of pollution fuelled notably by the publication, in 1962, of Rachel Carson's Silent Spring, sparked the beginning of the modern environmental movement. It also marked the start of \"the environment\" becoming a concern of public policy, as pointed out by Caldwell in 1963. These growing concerns, as well as the growing publicity about environmental problems and accidents, forced governments to introduce or strengthen laws and policies aimed at enhancing environmental protection.\nThe Post-war era resulted in the 'Great Acceleration', which saw a dramatic increase in industrialization, agriculture, and consumption of resources leading to a new geological era of environmental deficit. The development of environmentalism in the United Kingdom emerged in this period following the great London smog of 1952 and the Torrey Canyon oil spill of 1967. This is reflected by the emergence of Green politics in the Western world beginning in the 1970s. \nEarth Day founder Gaylord Nelson, then a U.S. Senator from Wisconsin, after witnessing the ravages of the 1969 massive oil spill in Santa Barbara, California, became famous for his environmental work. Administrator Ruckelshaus was confirmed by the Senate on December 2, 1970, which is the traditional date used as the birth of the United States Environmental Protection Agency (EPA). Five months earlier, in July 1970, President Nixon had signed Reorganization Plan No. 3 calling for the establishment of EPA. At the time, environmental policy was a bipartisan issue and the efforts of the United States of America made it an early environmental leader. During this period, legislation was passed to regulate pollutants that go into the air, water tables, and solid waste disposal. President Nixon signed the Clean Air Act in 1970.\nIn many countries, governments created environment ministries, departments or agencies, and appointed ministers of or for the environment. The world's first minister of the environment was the British Politician Peter Walker from the Conservative Party in 1970.\nIn the European Union, the very first Environmental Action Programme was adopted by national government representatives in July 1973 during the first meeting of the Council of Environmental Ministers. Since then an increasingly dense network of legislation has developed, which now extends to all areas of environmental protection including air pollution control, water protection and waste policy but also nature conservation and the control of chemicals, biotechnology and other industrial risks. EU environmental policy has thus become a core area of European politics.\nDespite commonalities between countries in the development of environmental policies and institutions, they have also adopted different approaches in this area. In the 1970s, the field of Comparative Environmental Politics and Policy emerged to compare the environmental policies and institutions of countries aimed at explaining differences and similarities.\nAlthough particular environmental problems like soil erosion, growing resource scarcity, air and water pollution increasingly became the subject of concern and government regulation in the 19th century, these were seen and addressed as separate issues. The shortcomings of this reactive and fragmented approach received growing recognition during the 1960s and early 1970s, the first wave of environmentalism. This was reflected in the creation, in many countries, of environmental agencies, policies and legislation with the aim of taking a more comprehensive and integrated approach to environmental issues. In 1972, the need for this was also recognised at the international level at the United Nations Conference on the Human Environment, which led to the creation of the United Nations Environment Programme. Notably, the 1972 United Nations Conference on the Human Environment in Stockholm marked the entry of environmental politics into the international agenda, giving rise to new environmental political thought and its incorporation into policymaking. Since then, environmentalism has taken shape as its own political ideology and has had numerous variations, from more radical theories like 'deep ecology' which seeks to prioritize environmental needs to more reformist ideologies which view environmental damage as an externality. \n\nRationale\nGrowing environmental awareness and concern provided the main rationale for the adoption of environmental policies and institutions by governments. Environmental protection became a focus of public policy.\nThis rationale for environmental policy is broader than that provided by some interpretations based on economic theories. The rationale for governmental involvement in the environment is often attributed to market failure in the form of forces beyond the control of one person, including the free rider problem and the tragedy of the commons. An example of an externality is when a factory produces waste pollution which may be discharged into a river, ultimately contaminating water. The cost of such action is paid by society at large when they must clean the water before drinking it and is external to the costs of the polluter. The free rider problem occurs when the private marginal cost of taking action to protect the environment is greater than the private marginal benefit, but the social marginal cost is less than the social marginal benefit. The tragedy of the commons is the condition that, because no one person owns the commons, each individual has an incentive to utilize common resources as much as possible. Without governmental involvement, the commons is overused. Examples of tragedies of the commons are overfishing and overgrazing.\nThe \"market failure\" rationale for environmental policy has been criticised for its implicit assumptions about the drivers of human behaviour, which are considered to be rooted in the idea that societies are nothing but collections of self-interested \"utility-maximising\" individuals. As Elinor Ostrom has demonstrated, this is not supported by evidence on how societies actually make resource decisions. The market-failure theory also assumes that \"markets\" have, or should have precedence over governments in collective decision-making, which is an ideological position that was challenged by Karl Polanyi whose historical analysis shows how the idea of a self-regulating market was politically created. He added that \"Such an institution could not exist for any length of time without annihilating the human and natural substance of society.\"\nBy contrast, ecological economists argue that economic policies should be developed within a theoretical framework that recognises the biophysical reality. The economic system is a sub-system of the biophysical environmental system on which humans and other species depend for their well-being and survival. The need for grounding environmental policy on ecological principles has also been recognised by many environmental policy analysts, sometimes under the label of ecological rationality and/or environmental integration. From this perspective, political, economic, and other systems, as well as policies, need to be \"greened\" to make them ecologically rational.\n\nPolicy approaches\n\nInstruments\nIn practice, governments have adopted a wide range of approaches to the development and implementation of environmental policies. To a large extent, differences in approaches have been influenced and shaped by the particular political, economic and social context of a country or polity (like the European Union or the United Nations). The differences in approaches, the reasons behind them, and their results have been the subject of research in the fields of comparative environmental politics and policy. But the study of problems and issues associated with environmental policy development has also been influenced by general public policy theories and analyses. Contributions on this front have been influenced by different academic disciplines, notably economics, public policy, and environmental studies, but also by political-ideological views, politics, and economic interests, among others through \"think tanks\". Thus, the design of environmental policy and the choice of policy instruments is always political and not just a matter determined by technical and efficiency considerations advanced by scientists, economists or other experts. As Majone has argued: \"Policy instruments are seldom ideologically neutral\" and \"cannot be neatly separated from goals.\" The choice of policy instruments always occurs in a political context. Differences in ideological preferences of governments and political actors, and in national policy styles, have been argued to strongly influence a government's approach to policy design, including the choice of instruments.\nAlthough many different policy instruments can be identified, and many ways of classifying them have been put forward, very broadly, a minimalist approach distinguishes three kinds or categories of policy instruments: regulation, economic instruments, and normative or \"hortatory\" approaches. These have also been referred to as \"sticks, carrots and sermons\". Vedung, based on Majone's classification of power, argues that the main difference underlying these categories is the degree of coercion (authoritative force) involved.\n\nRegulation\nRegulation has been a traditional and predominant approach to policymaking in many policy areas and countries. It relies foremost on adopting rules (often backed up by legislation), to prohibit, impose or circumscribe human behaviour and practices. In the environmental policy area, this includes, for instance, the imposition of limits or standards for air and water pollution, car emissions, the regulation or banning of the use of hazardous substances, the phasing out of ozone-depleting substances, waste disposal, and laws to protect endangered species and natural areas.\nRegulation is often derogatorily referred to by detractors as a top-down, \"command and control\" approach as it leaves target groups with little if any control over the way(s) environmental activities or goals must be pursued. Since the 1980s, with the rise of neoliberalism in many countries and the associated redefinition of the role of the state (centred on the notion of governance rather than government), regulation has been touted as ineffective and inefficient, sparking a move toward deregulation and the adoption by many governments of \"new\" policy instruments, notably market instruments and voluntary agreements, also in the realm of environmental policy.\n\nEconomic instruments\nEconomic instruments involve the imposition or use of economic incentives, including (environmental) taxes, tax exemptions, fees, subsidies, and the creation of markets and rights for trading in substances, pollutants, resources, or activities, such as for SO2, CO2 (carbon or greenhouse gas emissions), water, and tradeable fisheries quota. They are based on the assumption that behaviour and practices are foremost driven by rationality, self-interest and economic considerations and that these motivations can be harnessed for environmental purposes. Decision-making studies cast doubt on these premises. Often, decisions are reached based on irrational influences, unconscious biases, illogical assumptions, and the desire to avoid or create ambiguity and uncertainty.\nMarket-based policy instruments also have their supporters and detractors. Among the detractors, for example, some environmentalists contend that a more radical, overarching approach is needed than a set of specific initiatives, to deal with climate change. For example, energy efficiency measures may actually increase energy consumption in the absence of a cap on fossil fuel use, as people might drive more fuel-efficient cars. To combat this result, Aubrey Meyer calls for a 'framework-based market' of Contraction and Convergence. The Cap and Share and the Sky Trust are proposals based on the idea. In the case of corporations, it is assumed that such tools make it financially rewarding to engage in efficient environmental management that also improves business and organizational performance They also encourage businesses to become more transparent about their environmental performance by publishing data and reporting.\nFor economic instruments to function, some form(s) of regulation are needed that involve policy design, for instance, related to the choice and level of taxation, who pays, who qualifies for rights or permits, and the rules on which trading, and a \"market\" depend for their functioning. For example, the implementation of greener public purchasing programs relies on a combination of regulation and economic incentives.\n\nNormative (\"hortatory\") instruments\nNormative (\"hortatory\") instruments (\"sermons\") rely on persuasion and information. They include, among others, campaigns aimed at raising public awareness and enhancing knowledge of environmental problems, calls upon people to change their behaviour and practices (like taking up recycling, reducing waste, the use of water and energy, and using public transport), and voluntary agreements between governments and businesses. They share the aim of encouraging people to do \"the right thing\", to change their behaviour and practices, and to accept individual or group responsibility for addressing issues. Agreements between the government and private firms and commitments made by firms independent of government requirements are examples of voluntary environmental measures.\nEnvironmental Impact Assessment is a tool that relies foremost on the gathering of knowledge and information about (potential) environmental effects. It originated in the United States but has been adopted in many countries to analyse and assess the potential impacts of projects. Usually undertaken by experts, it is based on the assumption that an objective assessment of effects is possible, and that the knowledge generated will persuade decision-makers to make changes to proposals to mitigate or prevent adverse environmental effects. How EIA rules and processes are designed and implemented depends on regulation and is influenced by the political context. Eccleston and March argue that although policymakers normally have access to reasonably accurate environmental information, political and economic factors are important and often lead to policy decisions that rank environmental priorities of secondary importance.[Reference needed]\nThe effectiveness of hortatory instruments has also been under debate. Policies relying foremost on such instruments may amount to little more than symbolic policies, implying that governments have little or no intention to effectively address an issue while creating the impression of taking it seriously. Such policies rely more on rhetoric than action. In the environmental realm, sustainable development policies or strategies are often used for this purpose if these are not translated into clear and specific objectives, timeframes and measures. Yet, hortatory policy instruments are often preferred by governments and other actors as they are seen as a way of recognising and sharing collective responsibility, possibly avoiding the need for regulation and/or economic instruments. They are thus often used as a first step towards addressing environmental problems. However, these tools are often combined with some form of legislation and regulation, for instance, in the case of labelling of consumer products (product information), waste disposal and recycling.\n\nComparison of instruments\nThere has been much debate about the relative merits of the various kinds of policy instruments. Market instruments are often held up and used as a more efficient and cost-effective, alternative to regulation. Yet, many analysts have pointed out that regulation, economic incentives, \"market\" instruments, and environmental taxation and subsidies can achieve the same results. For instance, as Kemp and Pontoglio argue, policy instruments cannot be usefully ranked with regard to their effects on eco-innovation, \"the often expressed view that market-based approaches such as pollution taxes and emission trading systems are better for promoting eco-innovation is not brought out by the case study literature or by survey analysis\", and there is actually more evidence that regulations stimulate radical innovation more than market-based instruments. It has also been argued that If the government can anticipate new technology or is able to react to it optimally, regulatory policies by virtue of administered prices (taxes) and policies by setting quantities (issuing tradable permits) are (almost) equivalent. More generally, the performance of economic instruments in dealing with environmental problems has been a mixed bag, referred to by Hahn as \"not very impressive\", and has led Tietenberg to conclude that they are \"no panacea\".\nDifferent instruments are sometimes combined in a policy mix to address a particular environmental problem. Since environmental issues have many aspects, several policy instruments may be required to adequately address each one. Ideally, government policies are carefully formulated so that the individual measures do not undermine one another or create a rigid and cost-ineffective framework. Overlapping policies result in unnecessary administrative costs, increasing the cost of implementation. To help governments realize their policy goals, the OECD Environment Directorate, for example, collects data on the efficiency and consequences of environmental policies implemented by the national governments. Their website provides a database detailing countries' experiences with their environmental policies. The United Nations Economic Commission for Europe, through UNECE, and the OECD's Environmental Performance Reviews, evaluate progress made by its member countries in improving their environmental policies.\nHowever, although regulation, taxation and market instruments can be equally (in-) effective, they may differ significantly in the allocation and distribution of (potential) costs and benefits, with the allocation of tradeable (\"property\") rights potentially generating significant profits to those who receive such rights. They are, therefore, generally much preferred by affected resource users and industries, which explains their popularity since the rise of neoliberalism. This has led analysts to point out that there are many other important aspects to the choice of policy instruments than their efficiency and cost-effectiveness, such as distributional, ethical and political aspects, and their appropriateness for addressing environmental problems.\n\nPolicy analysis\nHow environmental policies are made, how effective they are, and how they can or should be improved, has become the subject of considerable research and debate. In the academic realm, these questions are commonly addressed under the label of environmental policy analysis.\nEnvironmental policy analysis is a broad field comprising different approaches to explaining and developing environmental policy. The first type has been referred to in the policy literature as the analysis of policy and the second as the analysis for policy. Many approaches are derived from the broader field of public policy analysis which emerged as a scientific enterprise after WWII. While policy analysis as a decision-making tool continued to be applied in the business sector, the study of public policy, defined broadly as \"What governments do, why they do it, and what difference it makes, became an important strand in political science. This variety, which has been classified into analycentric, policy process, and meta-policy categories, has also manifested itself in the area of environmental policy analysis which developed since the 1960s.\n\nThe analycentric or rational approach\nThe analycentric approach to environmental policy analysis, which focuses on particular issues and uses mostly quantitative methods to identify \"optimal\" (cost-effective or efficient) solutions, has been the prevalent way to address environmental problems, both by governments and businesses. It is also often depicted as the rational or scientific approach to and for policy development. While scientific analyses and (preferably) quantitative data provide knowledge of the more immediate sources or causes of environmental problems, such as forms of pollution and climate change, policy prescriptions are based on setting goals, objectives and targets and the identification of the most cost-effective and efficient means by assessing alternative options. Technological innovation, more efficient management, and economic instruments such as cost-benefit analysis, environmental taxes, and tradeable permit schemes (market creation) have been among the preferred means in this approach.\nThe analycentric or rational approach has been critiqued on various grounds. First, it assumes that there is adequate knowledge and agreement on the causes of problems and the goals to be achieved. Second, the approach (for policy) ignores the way policies are developed in (political) practice. Third, the preferred means are often based on questionable assumptions notably about human behaviour. Many of the limitations of the rational approach were already acknowledged by an early proponent, Herbert Simon, who argued that \"limited rationality\" provided a more realistic basis for decision-making. This view has also been expressed by advocates of more comprehensive and integrated environmental policy development, who argued that looking at problems in isolation (on a one-by-one basis) ignores the linkages between environmental problems and their causes. In the late 1980s, \"green planning\" and the adoption of sustainable development strategies, in particular, received support in academic circles and among many governments as rational, goal-based policy approaches aimed at overcoming the limitations of the fragmented analycentric approach.\n\nThe policy process approach\nThe policy process approach emphasises the role and importance of politics and power in policy development. It aims foremost at better understanding how policies are made and put into practice. It commonly involves identifying a variable number of steps, including problem definition and agenda setting, the formulation and selection of policy options, implementation, and evaluation. These are conceived as being parts of a policy cycle, as existing policies are reviewed and changed for political reasons and/or because they are deemed to be unsatisfactory. The various stages have become the focus of much research, generating insights into why and how policies have been developed and implemented, with variable outcomes and effectiveness. These studies show that policy development is more about the role of and interplay between conflicting interests than the result of rational analysis and finding and adopting (optimal) solutions to problems. One of the main schools of thought on this front is that of incrementalism, which argues that policy change often occurs in small steps that accommodate conflicting interests.\nPolicy process analysis has also been applied to environmental policy in its different stages. It has been used, for instance, to clarify why environmental issues have had difficulty reaching or staying on the public and political agendas. More recently, research has revealed the role and power of businesses, notably the oil industry, in downplaying the risks associated with climate change or \"climate change denial.\" \"Think tanks\" and the media have been used to sow scepticism about the science behind environmental and other problems, to redefine issues, and to avert policies that threaten the interests of businesses.\nPolicy process analyses also include studies of the variety of actors and their influence on government decision-making. Although pluralism, the idea that not one group dominates all decision-making in modern societies, has long been the prevailing school of thought in political science, it has been contested by elite theories that assign predominant power to elites in different areas or sectors of decision-making. To what extent environmental groups have had influence on government decisions and policies continues to be a subject of debate. Some argue that Non-Governmental organizations have the greatest influence on environmental policies. These days, many countries are facing huge environmental, social, and economic impacts of rapid population growth, development, and natural resource constraints. As NGOs try to help countries to tackle these issues more successfully, a lack of understanding about their role in civil society and the public perception that the government alone is responsible for the well-being of its citizens and residents makes NGOs tasks more difficult to achieve. NGOs such as Greenpeace and World Wildlife Fund can help tackling issues by conducting research to facilitate policy development, building institutional capacity, and facilitating independent dialogue with civil society to help people live more sustainable lifestyles. The need for a legal framework to recognize NGOs and enable them to access more diverse funding sources, high-level support/endorsement from local figureheads, and engaging NGOs in policy development and implementation is more important as e",
    "source": "wikipedia:Environmental policy",
    "domain": "climate"
  },
  {
    "text": "Air pollution is the presence of substances in the air that are harmful to humans, other living beings or the environment. Pollutants can be gases, like ozone or nitrogen oxides, or small particles like soot and dust. Both outdoor and indoor air can be polluted.\nOutdoor air pollution comes from burning fossil fuels for electricity and transport, wildfires, some industrial processes, waste management, demolition and agriculture. Indoor air pollution is often from burning firewood or agricultural waste for cooking and heating. Other sources of air pollution include dust storms and volcanic eruptions. Many sources of local air pollution, especially burning fossil fuels, also release greenhouse gases that cause global warming. However, air pollution may limit warming locally.\nAir pollution kills 7 or 8 million people each year. It is a significant risk factor for a number of diseases, including stroke, heart disease, chronic obstructive pulmonary disease (COPD), asthma, coronavirus and lung cancer. Particulate matter is the most deadly, both for indoor and outdoor air pollution. Ozone affects crops, and forests are damaged by the pollution that causes acid rain. Overall, the World Bank has estimated that welfare losses (premature deaths) and productivity losses (lost labor) caused by air pollution cost the world economy over $8 trillion per year.\nVarious technologies and strategies reduce air pollution. Key approaches include clean cookers, fire protection, improved waste management, dust control, industrial scrubbers, electric vehicles and renewable energy. National air quality laws have often been effective, notably the 1956 Clean Air Act in Britain and the 1963 US Clean Air Act. International efforts have had mixed results: the Montreal Protocol almost eliminated harmful ozone-depleting chemicals, while international action on climate change has been less successful.\n\nSources\n\nHuman sources\n\nIndustry and construction\n\nBurning fuel to generate electricity causes air pollution; lignite and coal produce the most air pollution, followed by oil, and then by fossil gas and biomass. Methane leaks are common in oil and gas production, and oil refineries emit a wide range of pollutants. Some hazardous air pollutants are produced in plastic and rubber production, whereas chloroform can be produced during water chlorination, and arsenic is found in the mining industry. Many polluting industries have been pushed out of richer nations, and China too has started to push its most polluting industries out of the country.\nConstruction and demolition produces dust, but also other pollutants. The direct particles from construction and demolition are relatively coarse. Construction also has an indirect impact on air quality, as cement production is one of the main sources of particle pollution. Though banned in many countries, asbestos persists in older buildings, where it poses a risk of lung disease when disturbed. Building materials including carpeting and plywood emit formaldehyde, a gas which can cause difficulty breathing and nausea.\n\nTransportation\n\nRoad vehicles produce a significant amount of all air pollution. For instance, they may be responsible for a third to half of all nitrogen dioxide emissions, and are a major cause of climate change. Vehicles with petrol and diesel engines produce about half of their emissions from their exhaust gas, and the other half from non-exhaust emissions (tire and brake wear and erosion or disturbance of the road surface); electric vehicles produce no tailpipe emissions, but still produce the other emissions. Diesel trains, ships, and planes also cause air pollution.\n\nAgriculture and waste\n\nAgricultural emissions, both from crops and from animal agriculture, contribute substantially to air pollution. For instance, methane is emitted by the digestion of food by cattle, causing ground-level ozone. Agriculture is also a major source of ammonia, which can form fine particulate matter. Practices like slash-and-burn in forests like the Amazon cause large air pollution alongside deforestation.\nOpen dumps of waste are a common source of air pollution in low-income countries. They can be a source of toxins and can promote the growth of microbes that pollute water and air. Through open burning of waste—whether self-ignited or burned on purpose—soot, methane, and other pollutants are released. Organic waste in landfills itself also produces methane as it decomposes. Globally, a quarter of solid waste is not collected and another quarter is not disposed of properly.\n\nHousehold sources\n\nAs of 2023, more than 2.3 billion people in developing countries rely on burning polluting fuels such as firewood, agricultural waste, dry dung, coal, or charcoal for cooking, which causes harmful household air pollution. Kerosene, another polluting fuel, is used in many countries for lighting and sometimes for space heating or cooking. Globally, 12% of outdoor fine particle pollution comes from household cooking. Health effects are concentrated among women, who are likely to be responsible for cooking, and young children.\nGas stoves for cooking contribute to indoor air pollution by emitting NO2, benzene, and carbon monoxide. Toasters can produce particulate pollution. Similarly, heating systems such as furnaces and other types of fuel-burning heating devices release pollutants into the air. In some developed countries, including the UK and Sydney, Australia, wood stoves are the major source of particulate pollution in urban areas. Wood stoves can also emit carbon monoxide and NOx.\nOther sources of indoor air pollution are building materials, biological material and tobacco smoke. Biological material, such as dander, house dust mite, mold and pollen, can come from humans, animals or plants. Some of this material can trigger allergies, such as allergic rhinitis. Fumes from pesticides, paints, cleaning products and personal care products can be substantial, and make up an increasing share of outdoor and indoor air pollution as transportation is getting cleaner.\n\nNatural sources\n\nDust from desert can cause poor air quality far from its source. For instance, dust from the Gobi Desert in China and Mongolia can reach Hawaii, and dust from the Sahara reaches the Amazon rainforest in South America.\nRadon is a radioactive gas that can build up in buildings from the soil. It can cause lung cancer, especially in smokers. Levels are generally low, but can be elevated in buildings with \"leaky\" foundations or areas with soils rich in uranium. Volcanic eruptions can be a large source of sulfur dioxide and also produce particle pollution.\nVegetation can emit gases that contribute to ozone formation and particle pollution. This is especially true in warmer climates and during the growth season. These gases react with human pollution sources to produce a seasonal haze. Black gum, poplar, oak and willow emit gases that can raise ozone levels up to eight times more than low-impact tree species. Wildfires, which have become more severe and more common due to climate change, release fine particles. They are a major source of air pollution.\n\nMajor pollutants\n\nAir pollutants can be tiny solid or liquid particles dispersed in the air (called aerosols), or gases. Pollutants are classified as primary or secondary. Primary pollutants are produced directly by a source and remain in the same chemical form after they have been emitted into the atmosphere. Examples include carbon monoxide gas from car exhausts and sulfur dioxide from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react with each other or with other parts of the atmosphere. Ground-level ozone is one example of a secondary pollutant. Some pollutants may be both primary and secondary — both are emitted directly and formed from other primary pollutants.\n\nAmmonia\nAmmonia (NH3) is emitted mainly by overuse of synthetic nitrogen fertilizers on farmland, and from manure and urine from livestock. At typical concentrations in the air, it is not harmful to health directly. However, ammonia can react with other pollutants in the air to form ammonium sulfate or nitrate salts, contributing to particulate matter pollution. Furthermore, when ammonia is deposited onto the soil, it can harm ecosystems via eutrophication.\n\nCarbon dioxide\nCarbon dioxide (CO2) is mainly emitted by the burning of fossil fuels. CO2 is sometimes called an air pollutant, because it is the main greenhouse gas responsible for climate change. Although the World Health Organization recognizes CO2 as a climate pollutant, it does not include the gas in its Air Quality Guidelines or set recommended targets for it. This question of terminology has practical consequences, for example, in determining whether the U.S. Clean Air Act (which is designed to improve air quality) is deemed to regulate CO2 emissions. The Inflation Reduction Act of 2022 amended the Clean Air Act to define CO2 from fossil fuel burning explicitly as an air pollutant.\n\nCarbon monoxide\nCarbon monoxide (CO) is a colorless, odorless, and toxic gas. It is a product of combustion of fuel such as natural gas, coal, or wood. In the past, emissions from vehicles were the main source of CO, but modern vehicles do not emit much of it. Now, wildfires and bonfires are the main source of outdoors CO. Indoors, CO is a larger problem and mainly comes from cooking and heating. In poorly ventilated spaces, CO can accumulate to dangerous levels, and exposure may cause people to lose consciousness and die. When CO is destroyed in the atmosphere, it can raise levels of CO2 and CH4.\n\nGround-level ozone\n\nGround-level ozone (O3) is mostly created when NOx and volatile organic compounds mix in the presence of sunlight. It can also form from carbon monoxide or methane. Due to the influence of temperature and sunlight on this reaction, high ozone levels are most common on hot summer afternoons. It is the main gas in photochemical smog.\nO3 can be harmful to human health, but also to some materials, forests, plants, and crops. Smog is a particular problem in big cities where it cannot easily be transported away by wind (e.g. cities built in valleys surrounded by mountains). When ground-level ozone is produced, it can linger in the air for days or weeks, and therefore be transported far from where it was first formed.\n\nNitrogen oxides\n\nNitrogen oxides (NOx), particularly nitric oxide (NO), are mostly created by the burning of fossil fuels, and in lesser amounts by lightning. Nitrogen dioxide (NO2) is formed from NO in a reaction with other atmospheric gases. NO and NO2 can form acid rain, can form into a haze, and can cause nutrient pollution in water. NO2 is a reddish-brown toxic gas with a strong odor, whereas NO is odorless and colorless.\n\nParticulate matter\nParticulate matter (PM), also known as particle pollution, includes all airborne substances that are not gases. It is a mix of microscopic solid particles or droplets suspended in a gas. \nParticulate matter can contain a large variety of materials and chemical compounds including toxic substances, which can vary strongly in size. Coarse PM (PM10) is 10 micrometer (μm) or smaller in diameter, fine PM (PM2.5) is smaller than 2.5 μm, and ultrafine particles are 0.1 μm or smaller. Smaller particles pose more risk to health, as they can reach the bloodstream. A definitive link between fine particulate pollution and higher death rates in urban areas was established by the Harvard Six Cities study, published in 1993.\nSea spray, wildfires, volcanoes and dust storms are the main natural sources of PM. Meanwhile, human sources include the burning of biomass and fossil fuels, as well as road emissions and dust resuspension. Human PM is usually finer than natural PM. Most particulate matter is formed in the atmosphere from precursor gases. For instance, sulfate comes from SO2, nitrate from NO2, and ammonium is formed from ammonia. Soot on the other hand is directly emitted from combustion, and consists of black carbon and organic compounds. Particulate matter can have a cooling effect locally on the climate, as it reflects sunlight away from Earth's surface.\n\nSulfur dioxide\nSulfur dioxide (SO2), an acidic and corrosive gas, is produced mostly by burning crude oil and coal. These fossil fuels often contain sulfur compounds, and their combustion generates sulfur dioxide. In Europe and North America, SO2 is mostly found in areas with significant shipping and industry, as road traffic fuels are regulated. Smaller amounts of SO2 are released from smelting and volcanoes.\nHigh concentrations of SO2 in the air generally also lead to the formation of other sulfur oxides (SOx). SOx can react with other compounds in the atmosphere to form small particles and contribute to particulate matter pollution. At high concentrations, gaseous SOx can harm plants by damaging leafs and decreasing growth. Further oxidation of SO2, mostly taking place in cloud droplets, forms sulfuric acid (H2SO4), which is one of the components of acid rain.\n\nVolatile organic compounds\nVolatile organic compounds (VOCs) are a class of carbon-based chemicals that exist as gases at room temperature, found both indoors and outdoors. They can cause photochemical smog and form aerosols impacting climate. The group includes methane, acetone, and toluene. Some can cause cancer, such as butadiene and benzene, with benzene being released from cigarette smoking. Methane is a greenhouse gas and the second-largest driver of global warming. Other VOCs contribute to climate warming because they help form ground-level ozone, a greenhouse gas.\n\nOther pollutants\nSome heavy metals can be bad for health. For instance, lead exposure can lead to learning disabilities in children. In the atmosphere, heavy metals can exist in different states, such as particles or gases. One of the forms of chromium can cause cancer. Mercury is harmful both as an element and in an organic compound. In the atmosphere, it comes mostly from cement production, coal burning, and incinerators.\nPersistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation. They persist in the environment, are capable of long-range transmission, bioaccumulate in humans and animals, and biomagnify in food chains. The Stockholm Convention on Persistent Organic Pollutants identified pesticides and other POPs of concern. These include dioxins and furans which are created by waste combustion. POPs are usually either semi-volatile (gaseous only at higher temperatures) or non-volatile (emitted as particles). The harmful effects of the pesticide DDT, a POP, were popularized by Rachel Carson's 1962 book Silent Spring. PFASs and polycyclic aromatic hydrocarbons (PAHs) are other examples of POPs.\nChlorofluorocarbons (CFCs) are a group of compounds which harm the ozone layer. They were widely used in aerosol sprays, refrigerants, and fire suppression. Due to their chemical stability, CFCs persist in the atmosphere and eventually reach the stratosphere (the upper atmosphere). There, they break down under the impact of UV light, which releases chlorine. This in turn reacts with ozone, destroying it. As the ozone layer blocks harmful UV radiation from reaching the Earth's surface, its depletion leads to health risks such as skin ageing and skin cancer.\n\nExposure\nExposure to air pollution varies widely across the world and across groups. Children, for example, are more exposed because they breathe more rapidly than adults and closer to the ground, where pollution from vehicle exhaust and dust is more concentrated. Similarly, people engaging in strenuous exercise inhale more pollutants than those at rest. People can reduce their exposure by wearing high-quality face masks or by using air purifiers.\nFor some pollutants, low exposure can be seen as safe, whereas other pollutants have negative health effects even at low levels. As evidence has grown that even very low levels of air pollutants hurt human health, the WHO halved its recommended safe limit for particulate matter from 10 μg/m3 to 5 μg/m3 in 2021. Under the new guideline, nearly the entire global population—97%—is classified as exposed to unsafe levels of fine particles (PM2.5). The new limit for nitrogen dioxide (NO2) became 75% lower. For all pollutants together, the World Health Organization concluded that 99% of the world population is exposed to harmful air pollution.\nFor some pollutants such as black carbon, traffic related exposures may dominate total exposure despite short exposure times, since high concentrations coincide with proximity to major roads or participation in (motorized) traffic. A large portion of total daily exposure occurs as short peaks of high concentrations.\n\nBy socioeconomic group\n\nWhile air pollution affects a variety of populations, some groups are more exposed. In many regions, there are disparities in exposure to pollution by race and income. This is especially true in countries with high inequalities in incomes and healthcare, such as the United States. Polluting industries and roads are more likely to be placed in poorer communities, and people in these communities are more likely to work outdoors, leading to additional exposure. Residents in public housing, who are generally low-income and cannot easily move to healthier neighborhoods, are highly affected by nearby refineries and chemical plants. Additionally, lower-income communities more often perform polluting activities, such as using solid biofuels for cooking. In the United States, Blacks and Latinos generally face more pollution than Whites and Asians.\n\nBy geographic area\n\nExposure to outdoor air pollution is worst in lower-middle income countries in line with the environmental Kuznets curve, which postulates that pollution is worst in economies that rely on manufacturing but have not yet been able to prioritize environmental regulation. Indoor air pollution is worst in low-income countries, in particularly south-east Asia, the western Pacific, and Africa.\nOutdoor air pollution is usually concentrated in densely populated metropolitan areas. Urbanization leads to a rapid rise in premature mortality due to air pollution in fast-growing tropical cities. Indoor air pollution on the other hand is most common in rural areas, which may lack access to clean cooking fuels.\nA map published in 2025 by Climate TRACE indicates that PM2.5 (fine particles) and other toxins are released near the homes of about 1.6 billion people, about 900 million of whom are in the path of \"super-emitting\" facilities such as power plants, refineries, ports, and mines.\n\nHealth effects\n\nAir pollution is an important risk factor for various diseases, such as COPD (a common lung disease), stroke, heart disease, lung cancer, and pneumonia. Indoor air pollution is also associated with cataract. According to the WHO, 99% of the world's population lives in areas with air pollution that exceeds WHO recommended levels. Even at very low levels (under the World Health Organization recommended levels), fine particulates can continue to cause harm. \nPollutants strongly linked to ill health include particulate matter, carbon monoxide, nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2). Fine particulates are especially damaging, as they can enter the bloodstream via the lungs and reach other organs. Air pollution causes disease by driving inflammation and oxidative stress, suppressing the immune system, and by damaging DNA.\nPeople living in poverty, babies, and older people are disproportionately affected by air pollution; pregnancy is also more risky when exposed to air pollution. Communities with a low socioeconomic status and minority groups are more vulnerable to pollution than more privileged communities. Lower-income groups might for instance have less access to healthcare. \n\nMortality\n\nEstimates of deaths due to air pollution vary. The 2024 Global Burden of Disease Study estimates that air pollution contributed to 8.1 million deaths in 2021, which is more than 1 in 8 deaths. Outdoor particulate pollution (PM2.5) was the largest cause of death (4.7 million), followed by indoor particulate pollution (3.1 million) and ozone (0.5 million).\nThe World Health Organization estimates that 6.7 million people die from air pollution each year, 4.2 million due to outdoor air pollution. Roughly 68% of outdoor air pollution-related premature deaths were due to coronary heart disease and stroke, 14% due to COPD, and 14% due to lung infections (lower respiratory tract infections).\nA study published in 2019 estimated that, for 2015, the number was around 8.8 million, with 5.5 million of these premature deaths due to air pollution from human sources. The global mean loss of life expectancy from air pollution in 2015 was 2.9 years, substantially more than, for example, 0.3 years from all forms of direct violence.\n\nBy region\nRegional deaths due to air pollution depend not only on the regional exposure, but also on how large and how old the population is, and the health of people overall.\nIn some countries, more than 20% of deaths are attributed to air pollution (e.g. China, Nepal, Bangladesh, Laos, and North Korea). In South America, around 4% of deaths are from air pollution, while in countries such as Australia, Canada, and the US, this number is under 3%.\nIn absolute number, India and China have the higher number of deaths from air pollution. In India, it contributed to 2.1 million deaths in 2021, whereas China saw 2.4 million deaths. Annual premature European deaths from air pollution are estimated at 416,000 to 800,000. The UK saw some 17,000 deaths in 2021 due to air pollution and the US saw 64,000. Nigeria, Indonesia and Pakistan each saw over 200,000 deaths resulting from air pollution.\n\nBy source\n\nThe burning of fossil fuels is the largest source of air pollution deaths. There are estimated 4.5 million annual premature deaths worldwide due to pollutants released by high-emission power stations and vehicle exhausts. PM2.5 formed from emissions from coal-fired power plants could be more harmful than other types of fine particulate matter.\nThe World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million annual deaths. The Global Burden of Disease study estimated the number of deaths in 2021 at 3.1 million.\n\nCardiovascular disease\nThere is strong evidence that air pollution increases the risk of cardiovascular disease, including stroke, high blood pressure, and coronary heart disease. According to the Global Burden of Disease Study, air pollution is responsible for 27% of deaths from strokes worldwide and 28% of coronary heart disease. The risks are highest in regions with higher air pollution (e.g. Asia), for elderly and for people who are overweight.\nAir pollution is a leading risk factor for stroke, particularly in developing countries where pollutant levels are highest. A systematic analysis of 17 different risk factors in 188 countries found air pollution is associated with nearly one in three strokes (29%) worldwide (34% of strokes in developing countries versus 10% in developed countries). The mechanisms linking air pollution to increased cardiovascular mortality are not fully understood, but likely include systemic inflammation and oxidative stress.\n\nLung disease\nAir pollution is associated with increased development, hospitalization, mortality, and COPD (chronic obstructive pulmonary disease). COPD is a common disease which causes restricted airflow and breathing difficulties, and is the fourth-largest cause of death globally. Nearly half of global COPD deaths are due to air pollution. Fine particles (PM2.5) and NO2 are associated with increased risk of developing COPD. In children, air pollution can hinder lung development, which may increase their susceptibility to COPD later in life.\nAir pollution is further associated with increased risk of asthma and worsening of symptoms, and this effect seems stronger in children. For adults, fine particles (PM2.5) or NO2 seem linked to asthma onset too. Short-term exposure to ozone makes asthma worse in children. There is limited evidence on (almost) fatal asthma attacks in children: ground-level ozone and PM2.5 seem to increase its risk.\n\nCancer\n\nAround 265,000 lung cancer deaths were attributed globally in 2019 to exposure to fine particulate matter (PM2.5) suspended in the air. Exposure to indoor air pollution, including radon, caused another 170,000 lung cancer deaths. Lung cancer was also more common among people exposed to NO2 and black carbon.\nOutdoor air pollution may increase risk of other types of cancer too, but the evidence is not as clear as for lung cancer. For example, there may be a relationship between kidney cancer and PM2.5 and NO2 levels. Household air pollution – from cooking with solid fuels, but also from radon in building material – has been associated with cervical, oral, and esophageal cancer.\n\nPregnancy and children\nStillbirths, miscarriages, and birth defects are all more likely when the mother is exposed to air pollution during pregnancy. Exposure to air pollution also raises the chance that a baby has a low birth weight. The impacts might be due to pollutants directly impacting the placenta or fetus, or indirectly via the mother's health (as air pollution can cause systemic inflammation and oxidative stress).\nOver a third of preterm births were associated with air pollution in 2021 globally. It causes more than half a million newborn deaths, a quarter of overall deaths. The source of PM2.5 differs greatly by region. In South and East Asia, pregnant women are frequently exposed to indoor air pollution because of wood and other biomass fuels being used for cooking, which are responsible for more than 80% of regional pollution. In the Middle East, North Africa, and West sub-Saharan Africa, fine PM comes from natural sources, such as dust storms.\nFor data including older children, polluted air resulted in the death of over 700,000 children in 2021 (709,000 under 5 years of age and 16,600 aged 5–14 years). Children in low- or middle-income countries are exposed to higher levels of fine particulate matter than those in high income countries. Further health effects of air pollution on children include asthma, pneumonia, and lower respiratory tract infections. There is possibly a link between exposure to air pollution during pregnancy and after birth and autism in children. \nMany of these relationships could previously only be described as correlations, as study designs that demonstrate causation are difficult or impossible to conduct in environmental medicine. This would require a randomized controlled trial. Scientists at BIPS in Bremen were able to demonstrate a causal relationship for at least some health problems (e.g. diabetes and high blood pressure) using a special study design.\n\nBrain health\n\nAir pollution is linked to various diseases of the brain. It increases the risk of dementia.\nIndoor air pollution exposure during childhood may negatively affect cognitive function and neurodevelopment. Prenatal exposure may also affect neurodevelopment. Exposure to air pollution may contribute to neurodegenerative diseases such as Parkinson's disease. \nExposure to air pollution may also drive mental health issues, such as depression and anxiety. In particular, air pollution from the use of solid fuels was associated with a higher depression risk. Depression risk and suicide was more strongly linked to finer particulate matter (PM2.5), compared to coarser particles (PM10). The association was strongest for people over the age of 65.\nProblems with thinking (cognitive issues) are also associated with air pollution. In people over the age of 40, both NOx and PM2.5 have been linked to general cognitive problems. PM2.5 was also associated with reduced verbal fluency (for instance, number of animals one can list in a minute) and worse executive functions (like attention and working memory). Similarly, children tended to fare worse in tests involving working memory when there was NOx, PM2.5, or PM10 pollution.\n\nPhysical activity\nThe health benefits of physical exercise may be modulated by air quality. A 2025 cross-national study involving 1.5 million adults demonstrated that high levels of ambient fine particulate matter (PM 2.5 μg/m³) can significantly diminish the protective effects of leisure-time physical activity against all-cause and cause-specific mortality.\nThe study identified a critical threshold of 25 μg/m³ exposure; below this annual average concentration, regular exercise reduced all-cause mortality by approximately 30%. However, this benefit was halved (to 12–15%) when concentrations exceeded 25 μg/m³ exposure.\n\nSocial and environmental impacts\n\nAcid rain\n\nNaturally, water in the atmosphere is slightly acidic. Some pollutants can form strong acids, making rainwater much more acidic. Key acids that cause acid rain are nitric acid (HNO3), sulfuric acid (H2SO4) and hydrochloric acid (HCl). HCl comes from coal combustion. H2SO4 forms from SO2, which comes from the burning of coal and oil and from some industrial processes like smelting. HNO3 forms from NO2, which is formed during high-temperature combustion. The term acid rain not only refers to rain, but also to pollution from hail, fog, and snow.\nAcid rain caused substantial damage in the 1970s, including lake acidification and forest diebacks in Northern Europe. Due to the changed acidity in water bodies and soils, essential nutrients such as magnesium and calcium became soluble and could be washed away. Other elements, such as aluminium, which were toxic to vegetation, became available for the roots to absorb. Acid rain also impacts buildings and statues made of specific stones (e.g. marble, calcite or freestone), as the stone reacts chemically with the acid in the water and erodes.\n\nWater and soil pollution",
    "source": "wikipedia:Air pollution",
    "domain": "climate"
  },
  {
    "text": "Renewable energy (also called green energy) is energy made from renewable natural resources that are replenished on a human timescale. The most widely used renewable energy types are solar energy, wind power, and hydropower. Bioenergy and geothermal power are also significant in some countries. Renewable energy installations can be large or small and are suited for both urban and rural areas. Renewable energy is often deployed together with further electrification. This has several benefits: electricity can move heat and vehicles efficiently and is clean at the point of consumption. Variable renewable energy sources are those that have a fluctuating nature, such as wind power and solar power. In contrast, controllable renewable energy sources include dammed hydroelectricity, bioenergy, or geothermal power.\n\nRenewable energy systems have rapidly become more efficient and cheaper over the past 30 years. A large majority of newly installed worldwide electricity capacity is now renewable. Renewable energy sources, such as solar and wind power, have seen significant cost reductions over the past decade, making them more competitive with traditional fossil fuels. In some geographic localities, photovoltaic solar or onshore wind is the cheapest new-build electricity. From 2011 to 2021, renewable energy grew from 20% to 28% of the global electricity supply. Power from the sun and wind accounted for most of this increase, growing from a combined 2% to 10%. Use of fossil energy shrank from 68% to 62%. In 2024, renewables accounted for over 30% of global electricity generation and are projected to reach over 45% by 2030. Many countries already have renewables contributing more than 20% of their total energy supply, with some generating over half or even all their electricity from renewable sources.\nThe main motivation to use renewable energy instead of fossil fuels is to reduce greenhouse gas emissions, which cause climate change. In general, renewable energy sources pollute much less than fossil fuels. Renewables also cause much less air pollution than fossil fuels, improving public health, and are less noisy. The International Energy Agency estimates that to achieve net zero emissions by 2050, 90% of global electricity will need to be generated by renewables. The current pace of renewable expansion remains far from this required rate globally, including in major economies with high financial capacities such as the G7 and the EU.\nThe deployment of renewable energy still faces obstacles, especially fossil fuel subsidies, lobbying by incumbent power providers, and local opposition to the use of land for renewable installations. Like all mining, the extraction of minerals required for many renewable energy technologies also results in environmental damage.\nSome also consider nuclear power a renewable power source, although this is controversial, as nuclear energy requires mining uranium, a nonrenewable resource.\n\nOverview\n\nDefinition\nRenewable energy is usually understood as energy harnessed from continuously occurring natural phenomena. The International Energy Agency defines it as \"energy derived from natural processes that are replenished at a faster rate than they are consumed\". Solar power, wind power, hydroelectricity, geothermal energy, and biomass are widely agreed to be the main types of renewable energy. Renewable energy often displaces conventional fuels in four areas: electricity generation, hot water/space heating, transportation, and rural (off-grid) energy services.\nAlthough almost all forms of renewable energy cause much fewer carbon emissions than fossil fuels, the term is not synonymous with low-carbon energy. Some non-renewable sources of energy, such as nuclear power,generate almost no emissions, while some renewable energy sources can be very carbon-intensive, such as the burning of biomass if it is not offset by planting new plants. Renewable energy is also distinct from sustainable energy, a more abstract concept that seeks to group energy sources based on their overall permanent impact on future generations of humans. For example, biomass is often associated with unsustainable deforestation.\n\nRole in addressing climate change\nAs part of the global effort to limit climate change, most countries have committed to net zero greenhouse gas emissions. In practice, this means phasing out fossil fuels and replacing them with low-emissions energy sources. This much needed process, coined as \"low-carbon substitutions\" in contrast to other transition processes including energy additions, needs to be accelerated multiple times in order to successfully mitigate climate change. At the 2023 United Nations Climate Change Conference, around three-quarters of the world's countries set a goal of tripling renewable energy capacity by 2030. The European Union aims to generate 40% of its electricity from renewables by the same year.\n\nOther benefits\n\nRenewable energy is more evenly distributed around the world than fossil fuels, which are concentrated in a limited number of countries. It also brings health benefits by reducing air pollution caused by the burning of fossil fuels. The potential worldwide savings in health care costs have been estimated at trillions of dollars annually.\n\nIntermittency\n\nThe two most important forms of renewable energy, solar and wind, are intermittent energy sources: they are not available constantly, resulting in lower capacity factors. In contrast, fossil fuel power plants, nuclear power plants and hydropower are usually able to produce precisely the amount of energy an electricity grid requires at a given time. Solar energy can only be captured during the day, and ideally in cloudless conditions. Wind power generation can vary significantly not only day-to-day, but even month-to-month. This poses a challenge when transitioning away from fossil fuels: energy demand will often be higher or lower than what renewables can provide.\nIn the medium-term, this variability may require keeping some gas-fired power plants or other dispatchable generation on standby until there is enough energy storage, demand response, grid improvement, or base load power from non-intermittent sources. In the long-term, energy storage is an important way of dealing with intermittency. Using diversified renewable energy sources and smart grids can also help flatten supply and demand.\nSector coupling of the power generation sector with other sectors may increase flexibility: for example the transport sector can be coupled by charging electric vehicles and sending electricity from vehicle to grid. Similarly the industry sector can be coupled by hydrogen produced by electrolysis, and the buildings sector by thermal energy storage for space heating and cooling.\nBuilding overcapacity for wind and solar generation can help ensure sufficient electricity production even during poor weather. In optimal weather, it may be necessary to curtail energy generation if it is not possible to use or store excess electricity.\n\nElectrical energy storage\n\nElectrical energy storage is a collection of methods used to store electrical energy. Electrical energy is stored during times when production (especially from intermittent sources such as wind power, tidal power, solar power) exceeds consumption, and returned to the grid when production falls below consumption. Pumped-storage hydroelectricity accounts for more than 85% of all grid power storage. Batteries are increasingly being deployed for storage and grid ancillary services and for domestic storage. Green hydrogen is a more economical means of long-term renewable energy storage, in terms of capital expenditures compared to pumped hydroelectric or batteries.\n\nEnergy supply security\nTwo main renewable energy sources - solar power and wind power - are usually deployed in distributed generation architecture, which offers specific benefits and comes with specific risks. Notable risks are associated with centralisation of 90% of the supply chains in a single country (China) in the photovoltaic sector. Mass-scale installation of photovoltaic power inverters with remote control, security vulnerabilities and backdoors results in cyberattacks that can disable generation from millions of physically decentralised panels, resulting in disappearance of hundreds of gigawatts of installed power from the grid in one moment. Similar attacks have targeted wind power farms through vulnerabilities in their remote control and monitoring systems. The European NIS2 directive partially responds to these challenges by extending the scope of cybersecurity regulations to the energy generation market. Recent analyses indicate that global solar photovoltaic capacity surpassed 1 terawatt in 2024, providing about 6–7% of global electricity supply. Renewable energy infrastructure is also increasingly vulnerable to extreme weather events linked to climate change, such as heat waves, wildfires, severe storms, and flooding. Solar farms can experience reduced output during prolonged heat or smoke conditions, while wind turbines may require shutdowns during high-wind events or face damage from icing or wave action. These climate-related stresses can threaten the continuity of electricity supply in regions with high shares of variable renewables. As a result, governments and grid operators are adopting climate-resilience standards, hardening infrastructure, and developing emergency-response protocols to maintain energy security under more frequent and severe weather conditions.\n\nMainstream technologies\n\nSolar energy\n\nSolar power produced around 1.3 terrawatt-hours (TWh) worldwide in 2022, representing 4.6% of the world's electricity. Almost all of this growth has happened since 2010. Solar energy can be harnessed anywhere that receives sunlight; however, the amount of solar energy that can be harnessed for electricity generation is influenced by weather conditions, geographic location and time of day.\nThere are two mainstream ways of harnessing solar energy: solar thermal, which converts solar energy into heat; and photovoltaics (PV), which converts it into electricity. PV is far more widespread, accounting for around two thirds of the global solar energy capacity as of 2022. It is also growing at a much faster rate, with 170 GW newly installed capacity in 2021, compared to 25 GW of solar thermal.\nPassive solar refers to a range of construction strategies and technologies that aim to optimize the distribution of solar heat in a building. Examples include solar chimneys, orienting a building to the sun, using construction materials that can store heat, and designing spaces that naturally circulate air.\nFrom 2020 to 2022, solar technology investments almost doubled from USD 162 billion to USD 308 billion, driven by the sector's increasing maturity and cost reductions, particularly in solar photovoltaic (PV), which accounted for 90% of total investments. China and the United States were the main recipients, collectively making up about half of all solar investments since 2013. Despite reductions in Japan and India due to policy changes and COVID-19, growth in China, the United States, and a significant increase from Vietnam's feed-in tariff program offset these declines. Globally, the solar sector added 714 gigawatts (GW) of solar PV and concentrated solar power (CSP) capacity between 2013 and 2021, with a notable rise in large-scale solar heating installations in 2021, especially in China, Europe, Turkey, and Mexico. In 2023, global solar power capacity grew by nearly 30%, driven by falling panel prices and expanded government incentives worldwide.\n\nPhotovoltaics\n\nA photovoltaic system, consisting of solar cells assembled into panels, converts light into electrical direct current via the photoelectric effect. \nPV systems range from small, residential and commercial rooftop or building integrated installations, to large utility-scale photovoltaic power station. A household's solar panels can either be used for just that household or, if connected to an electrical grid, can be aggregated with millions of others.\nThe first utility-scale solar power plant was built in 1982 in Hesperia, California by ARCO. The plant was not profitable and was sold eight years later. However, over the following decades, PV cells became significantly more efficient and cheaper. As a result, PV adoption has grown exponentially since 2010. Global capacity increased from 230 GW at the end of 2015 to 890 GW in 2021. PV grew fastest in China between 2016 and 2021, adding 560 GW, more than all advanced economies combined. Four of the ten biggest solar power stations are in China, including the biggest, Golmud Solar Park in China.\nSolar panels are recycled to reduce electronic waste and create a source for materials that would otherwise need to be mined, but such business is still small and work is ongoing to improve and scale-up the process.\n\nSolar thermal\n\nUnlike photovoltaic cells that convert sunlight directly into electricity, solar thermal systems convert it into heat. They use mirrors or lenses to concentrate sunlight onto a receiver, which in turn heats a water reservoir. The heated water can then be used in homes. The advantage of solar thermal is that the heated water can be stored until it is needed, eliminating the need for a separate energy storage system. Solar thermal power can also be converted to electricity by using the steam generated from the heated water to drive a turbine connected to a generator. However, because generating electricity this way is much more expensive than photovoltaic power plants, there are very few in use today.\n\nFloatovoltaics\n\nFloatovoltiacs, or floating solar panels, are solar panels floating on bodies of water. There are both positive and negative points to this. Some positive points are increased efficiency and price decrease of water space compared to land space. A negative point is that making floating solar panels could be more expensive.\n\nAgrivoltaics\n\nAgrivoltaics is where there is simultaneous use of land for energy production and agriculture. There are again both positive and negative points. A positive viewpoint is there is a better use of land, which leads to lower land costs. A negative viewpoint is it the plants grown underneath would have to be plants that can grow well under shade, such as Polka Dot Plant, Pineapple Sage, and Begonia. Agrivoltaics not only optimizes land use and reduces costs by enabling dual revenue streams from both energy production and agriculture, but it can also help moderate temperatures beneath the panels, potentially reducing water loss and improving microclimates for crop growth. However, careful design and crop selection are crucial, as the shading effect may limit the types of plants that can thrive, necessitating the use of shade-tolerant species and innovative management practices.\n\nWind power\n\nHumans have harnessed wind energy since at least 3500 BC. Until the 20th century, it was primarily used to power ships, windmills and water pumps. Today, the vast majority of wind power is used to generate electricity using wind turbines. Modern utility-scale wind turbines range from around 600 kW to 9 MW of rated power. The power available from the wind is a function of the cube of the wind speed, so as wind speed increases, power output increases up to the maximum output for the particular turbine. Areas where winds are stronger and more constant, such as offshore and high-altitude sites, are preferred locations for wind farms.\nWind-generated electricity met nearly 4% of global electricity demand in 2015, with nearly 63 GW of new wind power capacity installed. Wind energy was the leading source of new capacity in Europe, the US and Canada, and the second largest in China. In Denmark, wind energy met more than 40% of its electricity demand while Ireland, Portugal and Spain each met nearly 20%.\nGlobally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand, assuming all practical barriers needed were overcome. This would require wind turbines to be installed over large areas, particularly in areas of higher wind resources, such as offshore, and likely also industrial use of new types of VAWT turbines in addition to the horizontal axis units currently in use. As offshore wind speeds average ~90% greater than that of land, offshore resources can contribute substantially more energy than land-stationed turbines.\nInvestments in wind technologies reached USD 161 billion in 2020, with onshore wind dominating at 80% of total investments from 2013 to 2022. Offshore wind investments nearly doubled to USD 41 billion between 2019 and 2020, primarily due to policy incentives in China and expansion in Europe. Global wind capacity increased by 557 GW between 2013 and 2021, with capacity additions increasing by an average of 19% each year.\n\nHydropower\n\nSince water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. Water can generate electricity with a conversion efficiency of about 90%, which is the highest rate in renewable energy. There are many forms of water energy:\n\nHistorically, hydroelectric power came from constructing large hydroelectric dams and reservoirs, which are still popular in developing countries. The largest of them are the Three Gorges Dam (2003) in China and the Itaipu Dam (1984) built by Brazil and Paraguay.\nSmall hydro systems are hydroelectric power installations that typically produce up to 50 MW of power. They are often used on small rivers or as a low-impact development on larger rivers. China is the largest producer of hydroelectricity in the world and has more than 45,000 small hydro installations.\nRun-of-the-river hydroelectricity plants derive energy from rivers without the creation of a large reservoir. The water is typically conveyed along the side of the river valley (using channels, pipes or tunnels) until it is high above the valley floor, whereupon it can be allowed to fall through a penstock to drive a turbine. A run-of-river plant may still produce a large amount of electricity, such as the Chief Joseph Dam on the Columbia River in the United States. However many run-of-the-river hydro power plants are micro hydro or pico hydro plants.\nMuch hydropower is flexible, thus complementing wind and solar, as it not intermittent. In 2021, the world renewable hydropower capacity was 1,360 GW. Only a third of the world's estimated hydroelectric potential of 14,000 TWh/year has been developed. New hydropower projects face opposition from local communities due to their large impact, including relocation of communities and flooding of wildlife habitats and farming land. High cost and lead times from permission process, including environmental and risk assessments, with lack of environmental and social acceptance are therefore the primary challenges for new developments. It is popular to repower old dams thereby increasing their efficiency and capacity as well as quicker responsiveness on the grid. Where circumstances permit existing dams such as the Russell Dam built in 1985 may be updated with \"pump back\" facilities for pumped-storage which is useful for peak loads or to support intermittent wind and solar power. Because dispatchable power is more valuable than VRE countries with large hydroelectric developments such as Canada and Norway are spending billions to expand their grids to trade with neighboring countries having limited hydro.\n\nBioenergy\n\nBiomass is biological material derived from living, or recently living organisms. Most commonly, it refers to plants or plant-derived materials. As an energy source, biomass can either be used directly via combustion to produce heat, or converted to a more energy-dense biofuel like ethanol. Wood is the most significant biomass energy source as of 2012 and is usually sourced from a trees cleared for silvicultural reasons or fire prevention. Municipal wood waste – for instance, construction materials or sawdust – is also often burned for energy. The biggest per-capita producers of wood-based bioenergy are heavily forested countries like Finland, Sweden, Estonia, Austria, and Denmark.\nBioenergy can be environmentally destructive if old-growth forests are cleared to make way for crop production. In particular, demand for palm oil to produce biodiesel has contributed to the deforestation of tropical rainforests in Brazil and Indonesia. In addition, burning biomass still produces carbon emissions, although much less than fossil fuels (39 grams of CO2 per megajoule of energy, compared to 75 g/MJ for fossil fuels).\nSome biomass sources are unsustainable at current rates of exploitation (as of 2017). \n\nBiofuel\n\nBiofuels are primarily used in transportation, providing 3.5% of the world's transport energy demand in 2022, up from 2.7% in 2010. Biojet is expected to be important for short-term reduction of carbon dioxide emissions from long-haul flights.\n\nAside from wood, the major sources of bioenergy are bioethanol and biodiesel. Bioethanol is usually produced by fermenting the sugar components of crops like sugarcane and maize, while biodiesel is mostly made from oils extracted from plants, such as soybean oil and corn oil. Most of the crops used to produce bioethanol and biodiesel are grown specifically for this purpose, although used cooking oil accounted for 14% of the oil used to produce biodiesel as of 2015. The biomass used to produce biofuels varies by region. Maize is the major feedstock in the United States, while sugarcane dominates in Brazil. In the European Union, where biodiesel is more common than bioethanol, rapeseed oil and palm oil are the main feedstocks. China, although it produces comparatively much less biofuel, uses mostly corn and wheat. In many countries, biofuels are either subsidized or mandated to be included in fuel mixtures.\n\nThere are many other sources of bioenergy that are more niche, or not yet viable at large scales. For instance, bioethanol could be produced from the cellulosic parts of crops, rather than only the seed as is common today. Sweet sorghum may be a promising alternative source of bioethanol, due to its tolerance of a wide range of climates. Cow dung can be converted into methane. There is also a great deal of research involving algal fuel, which is attractive because algae is a non-food resource, grows around 20 times faster than most food crops, and can be grown almost anywhere. \n\nGeothermal energy\n\nGeothermal energy is thermal energy (heat) extracted from the Earth's crust. It originates from several different sources, of which the most significant is slow radioactive decay of minerals contained in the Earth's interior, as well as some leftover heat from the formation of the Earth. Some of the heat is generated near the Earth's surface in the crust, but some also flows from deep within the Earth from the mantle and core. Geothermal energy extraction is viable mostly in countries located on tectonic plate edges, where the Earth's hot mantle is more exposed. As of 2023, the United States has by far the most geothermal capacity (2.7 GW, or less than 0.2% of the country's total energy capacity), followed by Indonesia and the Philippines. Global capacity in 2022 was 15 GW.\nGeothermal energy can be either used directly to heat homes, as is common in Iceland where almost all of its energy is renewable, or to generate electricity. Iceland is a global leader in renewable energy, relying almost entirely on its abundant geothermal and hydroelectric resources derived from volcanic activity and glaciers. At smaller scales, geothermal power can be generated with geothermal heat pumps, which can extract heat from ground temperatures of under 30 °C (86 °F), allowing them to be used at relatively shallow depths of a few meters. Electricity generation requires large plants and ground temperatures of at least 150 °C (302 °F). In some countries, electricity produced from geothermal energy accounts for a large portion of the total, such as Kenya (43%) and Indonesia (5%).\nTechnical advances may eventually make geothermal power more widely available. For example, enhanced geothermal systems involve drilling around 10 kilometres (6.2 mi) into the Earth, breaking apart hot rocks and extracting the heat using water. In theory, this type of geothermal energy extraction could be done anywhere on Earth.\n\nEmerging technologies\nThere are also other renewable energy technologies that are still under development, including enhanced geothermal systems, concentrated solar power, cellulosic ethanol, piezoelectricity, and marine energy. These technologies are not yet widely demonstrated or have limited commercialization. Some may have potential comparable to other renewable energy technologies, but still depend on further breakthroughs from research, development and engineering.\n\nEnhanced geothermal systems\n\nEnhanced geothermal systems (EGS) are a new type of geothermal power which does not require natural hot water reservoirs or steam to generate power. Most of the underground heat within drilling reach is trapped in solid rocks, not in water. EGS technologies use hydraulic fracturing to break apart these rocks and release the heat they contain, which is then harvested by pumping water into the ground. The process is sometimes known as \"hot dry rock\" (HDR). Unlike conventional geothermal energy extraction, EGS may be feasible anywhere in the world, depending on the cost of drilling. EGS projects have so far primarily been limited to demonstration plants, as the technology is capital-intensive due to the high cost of drilling.\n\nSand battery\nSand batteries are large tanks filled with soapstone that absorb heat. Excess heat energy from renewable energy is piped into the tank and then energy is discharged as boiling water, steam, or heated air. Finland is using this technology in Pornainen as Polar Night Energy built a 1MW sand battery that can store up to 100 MWh that went online in 2025.\n\nPiezoelectricity\nPiezoelectricity is the conversion of existing mechanical stress or vibration (classical mechanics) into an electrical charge without consuming or depleting a fuel source. Piezotronics enables the interaction of piezoelectric and semiconducting behaviors to modulate energy barriers at contact surface, thereby controlling charge carrier transport. Since the introduction of nanogenerators, the efficiency of microscale energy harvesting has improved. For instance, nanogenerators typically consist of piezoelectric nanowires; as these wires bend or compress, the applied mechanical stress causes the ions within the material's crystal lattice to shift their positions. This shift disrupts the nanowire's charge symmetry which causes an instantaneous charge polarization (separation of positive and negative charges) across the nanowire's ends. Once polarized, electrons are freed from the attached electrode which generates usable alternating current (AC) electricity that can energize low-power sensors. Piezoelectric microelectromechanical systems (piezoMEMS), such as actuators for artificial organs and pacemakers or micropumps for drug delivery and reagent transfers, are vital for medical purposes and energy harvesting. Furthermore, specialized components like piezoelectric resonators and quartz crystal oscillators are used to regulate electrical circuit frequencies.\n\nMarine energy\n\nMarine energy (also sometimes referred to as ocean energy) is the energy carried by ocean waves, tides, salinity, and ocean temperature differences. Technologies to harness the energy of moving water include wave power, marine current power, and tidal power. Reverse electrodialysis (RED) is a technology for generating electricity by mixing fresh water and salty sea water in large power cells. Most marine energy harvesting technologies are still at low technology readiness levels and not used at large scales. Tidal energy is generally considered the most mature, but has not seen wide deployment. The world's largest tidal power station is on Sihwa Lake, South Korea, which produces around 550 gigawatt-hours of electricity per year.\n\nEarth infrared thermal radiation\nEarth emits roughly 1017 W of infrared thermal radiation that flows toward the cold outer space. Solar energy hits the surface and atmosphere of the earth and produces heat. Using various theorized devices like emissive energy harvester (EEH) or thermoradiative diode, this energy flow can be converted into electricity. In theory, this technology can be used during nighttime.\n\nOthers\n\nAlgae fuels\n\nProducing liquid fuels from oil-rich (fat-rich) varieties of algae is an ongoing research topic. Various microalgae grown in open or closed systems are being tried including some systems that can be set up in brownfield and desert lands.\n\nSpace-based solar power\n\nThere have been numerous proposals for space-based solar power, in which very large satellites with photovoltaic panels would be equipped with microwave transmitters to beam power back to terrestrial receivers. A 2024 study by the NASA Office of Science and Technology Policy examined the concept and concluded that with current and near-future technologies it would be economically uncompetitive.\n\nWater vapor\nCollection of static electricity charges from water droplets on metal surfaces is an experimental technology that would be especially useful in low-income countries with relative air humidity over 60%.\n\nNuclear energy\nBreeder reactors could, in principle, depending on the fuel cycle employed, extract almost all of the energy contained in uranium or thorium, decreasing fuel requirements by a factor of 100 compared to widely used once-through light water reactors, which extract less than 1% of the energy in the actinide metal (uranium or thorium) mined from th",
    "source": "wikipedia:Renewable energy",
    "domain": "climate"
  },
  {
    "text": "Solar energy is the radiant energy from the Sun's light and heat, which can be harnessed using a range of technologies such as solar electricity, solar thermal energy (including solar water heating) and solar architecture. It is an essential source of renewable energy, and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power, and solar water heating to harness the energy. Passive solar techniques include designing a building for better daylighting, selecting materials with favorable thermal mass or light-dispersing properties, and organizing spaces that naturally circulate air.\nIn 2011, the International Energy Agency said that \"the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries' energy security through reliance on an indigenous, inexhaustible, and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating global warming .... these advantages are global\".\n\nPotential\n\nThe Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest, 122 PW, is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Most of the world's population live in areas with insolation levels of 150–300 watts/m2, or 3.5–7.0 kWh/m2 per day.\nSolar radiation is absorbed by the Earth's land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anticyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis, green plants convert solar energy into chemically stored energy, which produces food, wood and the biomass from which fossil fuels are derived.\nThe total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 122 PW·year = 3,850,000 exajoules (EJ) per year. In 2002 (2019), this was more energy in one hour (one hour and 25 minutes) than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass.\n\nThe potential solar energy that could be used by humans differs from the amount of solar energy present near the surface of the planet because factors such as geography, time variation, cloud cover, and the land available to humans limit the amount of solar energy that we can acquire. In 2021, Carbon Tracker Initiative estimated the land area needed to generate all our energy from solar alone was 450,000 km2 — or about the same as the area of Sweden, or the area of Morocco, or the area of California (0.3% of the Earth's total land area).\nSolar technologies are categorized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on the distance from the Equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all types of renewable energy, other than geothermal power and tidal power, are derived either directly or indirectly from the Sun.\nActive solar techniques use photovoltaics, concentrated solar power, solar thermal collectors, pumps, and fans to convert sunlight into useful output. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternative resources and are generally considered demand-side technologies.\nIn 2000, the United Nations Development Programme, UN Department of Economic and Social Affairs, and World Energy Council published an estimate of the potential solar energy that could be used by humans each year. This took into account factors such as insolation, cloud cover, and the land that is usable by humans. It was stated that solar energy has a global potential of 1,600 to 49,800 exajoules (4.4×1014 to 1.4×1016 kWh) per year (see table below).\n\nThermal energy\n\nSolar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.\n\nEarly commercial adaptation\nIn 1878, at the Universal Exposition in Paris, Augustin Mouchot successfully demonstrated a solar steam engine but could not continue development because of cheap coal and other factors.\n\nIn 1897, Frank Shuman, a US inventor, engineer and solar energy pioneer built a small demonstration solar engine that worked by reflecting solar energy onto square boxes filled with ether, which has a lower boiling point than water and were fitted internally with black pipes which in turn powered a steam engine. In 1908 Shuman formed the Sun Power Company with the intent of building larger solar power plants. He, along with his technical advisor A.S.E. Ackermann and British physicist Sir Charles Vernon Boys, developed an improved system using mirrors to reflect solar energy upon collector boxes, increasing heating capacity to the extent that water could now be used instead of ether. Shuman then constructed a full-scale steam engine powered by low-pressure water, enabling him to patent the entire solar engine system by 1912.\nShuman built the world's first solar thermal power station in Maadi, Egypt, between 1912 and 1913. His plant used parabolic troughs to power a 45–52 kilowatts (60–70 hp) engine that pumped more than 22,000 litres (4,800 imp gal; 5,800 US gal) of water per minute from the Nile River to adjacent cotton fields. Although the outbreak of World War I and the discovery of cheap oil in the 1930s discouraged the advancement of solar energy, Shuman's vision, and basic design were resurrected in the 1970s with a new wave of interest in solar thermal energy. In 1916 Shuman was quoted in the media advocating solar energy's utilization, saying:\n\nWe have proved the commercial profit of sun power in the tropics and have more particularly proved that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the Sun.\n\nWater heating\n\nSolar hot water systems use sunlight to heat water. In middle geographical latitudes (between 40 degrees north and 40 degrees south), 60 to 70% of the domestic hot water use, with water temperatures up to 60 °C (140 °F), can be provided by solar heating systems. The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.\nAs of 2015, the total installed capacity of solar hot water systems was approximately 436 thermal gigawatt (GWth), and China is the world leader in their deployment with 309 GWth installed, taken up 71% of the market. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada, and Australia, heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GWth as of 2005.\n\nHeating, cooling and ventilation\n\nIn the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ/yr) of the energy used in commercial buildings and nearly 50% (10.1 EJ/yr) of the energy used in residential buildings. Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy. Use of solar for heating can roughly be divided into passive solar concepts and active solar concepts, depending on whether active elements such as sun tracking and solar concentrator optics are used.\n\nThermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement, and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However, they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, daylighting, and shading conditions. When duly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.\nA solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated, causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses.\nDeciduous trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building in the northern hemisphere or the northern side in the southern hemisphere, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating. In climates with significant heating loads, deciduous trees should not be planted on the Equator-facing side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain.\n\nCooking\n\nSolar cookers use sunlight for cooking, drying, and pasteurization. They can be grouped into three broad categories: box cookers, panel cookers, and reflector cookers. The simplest solar cooker is the box cooker first built by Horace de Saussure in 1767. A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150 °C (194–302 °F). Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315 °C (599 °F) and above but require direct light to function properly and must be repositioned to track the Sun.\n\nProcess heat\n\nSolar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the Solar Total Energy Project (STEP) in Shenandoah, Georgia, US where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. This grid-connected cogeneration system provided 400 kW of electricity plus thermal energy in the form of 401 kW steam and 468 kW chilled water and had a one-hour peak load thermal storage. Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from seawater is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams.\nClothes lines, clotheshorses, and clothes racks dry clothes through evaporation by wind and sunlight without consuming electricity or gas. In some states of the United States legislation protects the \"right to dry\" clothes. Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22 °C (40 °F) and deliver outlet temperatures of 45–60 °C (113–140 °F). The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative than glazed collection systems. As of 2003, over 80 systems with a combined collector area of 35,000 square metres (380,000 sq ft) had been installed worldwide, including an 860 m2 (9,300 sq ft) collector in Costa Rica used for drying coffee beans and a 1,300 m2 (14,000 sq ft) collector in Coimbatore, India, used for drying marigolds.\n\nWater treatment\n\nSolar distillation can be used to make saline or brackish water potable. The first recorded instance of this was by 16th-century Arab alchemists. A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas. The plant, which had solar collection area of 4,700 m2 (51,000 sq ft), could produce up to 22,700 L (5,000 imp gal; 6,000 US gal) per day and operate for 40 years. Individual still designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect. These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications.\nSolar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. It is recommended by the World Health Organization as a viable method for household water treatment and safe storage. Over two million people in developing countries use this method for their daily drinking water.\nSolar energy may be used in a water stabilization pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consume carbon dioxide in photosynthesis, although algae may produce toxic chemicals that make the water unusable.\n\nMolten salt technology\nMolten salt can be employed as a thermal energy storage method to retain thermal energy collected by a solar tower or solar trough of a concentrated solar power plant so that it can be used to generate electricity in bad weather or at night. It was demonstrated in the Solar Two project from 1995 to 1999. The system is predicted to have an annual efficiency of 99%, a reference to the energy retained by storing heat before turning it into electricity, versus converting heat directly into electricity. The molten salt mixtures vary. The most extended mixture contains sodium nitrate, potassium nitrate and calcium nitrate. It is non-flammable and non-toxic, and has already been used in the chemical and metals industries as a heat-transport fluid. Hence, experience with such systems exists in non-solar applications.\nThe salt melts at 131 °C (268 °F). It is kept liquid at 288 °C (550 °F) in an insulated \"cold\" storage tank. The liquid salt is pumped through panels in a solar collector where the focused irradiance heats it to 566 °C (1,051 °F). It is then sent to a hot storage tank. This is so well insulated that the thermal energy can be usefully stored for up to a week.\nWhen electricity is needed, the hot salt is pumped to a conventional steam-generator to produce superheated steam for a turbine/generator as used in any conventional coal, oil, or nuclear power plant. A 100-megawatt turbine would need a tank about 9.1 metres (30 ft) tall and 24 metres (79 ft) in diameter to drive it for four hours by this design.\nSeveral parabolic trough power plants in Spain and solar power tower developer SolarReserve use this thermal energy storage concept. The Solana Generating Station in the U.S. has six hours of storage by molten salt. In Chile, The Cerro Dominador power plant has a 110 MW solar-thermal tower, the heat is transferred to molten salts.\nThe molten salts then transfer their heat in a heat exchanger to water, generating superheated steam, which feeds a turbine that transforms the kinetic energy of the steam into electric energy using the Rankine cycle. In this way, the Cerro Dominador plant is capable of generating around 110 MW of power.\nThe plant has an advanced storage system enabling it to generate electricity for up to 17.5 hours without direct solar radiation, which allows it to provide a stable electricity supply without interruptions if required. The Project secured up to 950 GW·h per year sale. Another project is the María Elena plant is a 400 MW thermo-solar complex in the northern Chilean region of Antofagasta employing molten salt technology.\n\nElectricity production\n\nConcentrated solar power\n\nConcentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the solar tower collectors, the concentrating linear Fresnel reflector, and the Stirling dish. Various techniques are used to track the Sun and focus light. In all of these systems, a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage. Designs need to account for the risk of a dust storm, hail, or another extreme weather event that can damage the fine glass surfaces of solar power plants. Metal grills would allow a high percentage of sunlight to enter the mirrors and solar panels while also preventing most damage.\n\nArchitecture and urban planning\n\nSunlight has influenced building design since the beginning of architectural history. Advanced solar architecture and urban planning methods were first employed by the Greeks and Chinese, who oriented their buildings toward the south to provide light and warmth.\nThe common features of passive solar architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and thermal mass. When these features are tailored to the local climate and environment, they can produce well-lit spaces that stay in a comfortable temperature range. Socrates' Megaron House is a classic example of passive solar design. The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integrated solar design package. Active solar equipment such as pumps, fans, and switchable windows can complement passive design and improve system performance.\nUrban heat islands (UHI) are metropolitan areas with higher temperatures than that of the surrounding environment. The higher temperatures result from increased absorption of solar energy by urban materials such as asphalt and concrete, which have lower albedos and higher heat capacities than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and to plant trees in the area. Using these methods, a hypothetical \"cool communities\" program in Los Angeles has projected that urban temperatures could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated total annual benefits of US$530 million from reduced air-conditioning costs and healthcare savings.\n\nAgriculture and horticulture\n\nAgriculture and horticulture seek to optimize the capture of solar energy to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields. While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the Little Ice Age, French and English farmers employed fruit walls to maximize the collection of solar energy. These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier even suggested using a tracking mechanism which could pivot to follow the Sun. Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure. More recently the technology has been embraced by vintners, who use the energy generated by solar panels to power grape presses.\nGreenhouses convert solar light to heat, enabling year-round production and the growth (in enclosed environments) of specialty crops and other plants not naturally suited to the local climate. Primitive greenhouses were first used during Roman times to produce cucumbers year-round for the Roman emperor Tiberius. The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad. Greenhouses remain an important part of horticulture today. Plastic transparent materials have also been used to similar effect in polytunnels and row covers.\n\nTransport\n\nDevelopment of a solar-powered car has been an engineering goal since the 1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877 mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph).\nThe North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles.\nSome vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.\nIn 1975, the first practical solar boat was constructed in England. By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. In 1996, Kenichi Horie made the first solar-powered crossing of the Pacific Ocean, and the Sun21 catamaran made the first solar-powered crossing of the Atlantic Ocean in the winter of 2006–2007. There were plans to circumnavigate the globe in 2010.\nIn 1974, the unmanned AstroFlight Sunrise airplane made the first solar flight. On 29 April 1979, the Solar Riser made the first flight in a solar-powered, fully controlled, man-carrying flying machine, reaching an altitude of 40 ft (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger which crossed the English Channel in July 1981. In 1990 Eric Scott Raymond in 21 hops flew from California to North Carolina using solar power. Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,864 ft) in 2001. The Zephyr, developed by BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights were envisioned by 2010. From March 2015 to July 2016, Solar Impulse, an electric aircraft, successfully circumnavigated the globe. It is a single-seat plane powered by solar cells and capable of taking off under its own power. The design allows the aircraft to remain airborne for several days.\nA solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands, causing an upward buoyancy force, much like an artificially heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.\n\nSquad Solar vehicle\n\nThe Squad Solar is a Neighborhood Electric Vehicle that has a solar roof and can be plugged into a normal 120 volt outlet to be charged.\n\nFuel production\n\nSolar chemical processes use solar energy to drive chemical reactions. These processes offset energy that would otherwise come from a fossil fuel source and can also convert solar energy into storable and transportable fuels. Solar induced chemical reactions can be divided into thermochemical or photochemical. A variety of fuels can be produced by artificial photosynthesis. The multielectron catalytic chemistry involved in making carbon-based fuels (such as methanol) from reduction of carbon dioxide is challenging; a feasible alternative is hydrogen production from protons, though use of water as the source of electrons (as plants do) requires mastering the multielectron oxidation of two water molecules to molecular oxygen. Some have envisaged working solar fuel plants in coastal metropolitan areas by 2050 – the splitting of seawater providing hydrogen to be run through adjacent fuel-cell electric power plants and the pure water by-product going directly into the municipal water system. In addition, chemical energy storage is another solution to solar energy storage.\nHydrogen production technologies have been a significant area of solar chemical research since the 1970s. Aside from electrolysis driven by photovoltaic or photochemical cells, several thermochemical processes have also been explored. One such route uses concentrators to split water into oxygen and hydrogen at high temperatures (2,300–2,600 °C or 4,200–4,700 °F). Another approach uses the heat from solar concentrators to drive the steam reformation of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods. Thermochemical cycles characterized by the decomposition and regeneration of reactants present another avenue for hydrogen production. The Solzinc process under development at the Weizmann Institute of Science uses a 1 MW solar furnace to decompose zinc oxide (ZnO) at temperatures above 1,200 °C (2,200 °F). This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.\n\nEnergy storage methods\n\nThermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or interseasonal durations. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.\nPhase change materials such as paraffin wax and Glauber's salt are another thermal storage medium. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C or 147 °F). The \"Dover House\" (in Dover, Massachusetts) was the first to use a Glauber's salt heating system, in 1948. Solar energy can also be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity, and can deliver heat at temperatures compatible with conventional power systems. The Solar Two project used this method of energy storage, allowing it to store 1.44 terajoules (400,000 kWh) in its 68 m3 storage tank with an annual storage efficiency of about 99%.\nOff-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid, while standard grid electricity can be used to meet shortfalls. Net metering programs give household systems credit for any electricity they deliver to the grid. This is handled by 'rolling back' the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility then rolls over the kilowatt-hour credit to the next month. Other approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter. Most standard meters accurately measure in both directions, making a second meter unnecessary.\nPumped-storage hydroelectricity stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water, with the pump becoming a hydroelectric power generator.\n\nDevelopment, deployment and economics\n\nBeginning with the surge in coal use, which accompanied the Industrial Revolution, energy consumption steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum.\nThe 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world. It brought renewed attention to developing solar technologies. Depl",
    "source": "wikipedia:Solar energy",
    "domain": "climate"
  },
  {
    "text": "Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity generation.\nToday, wind power is generated almost completely using wind turbines, generally grouped into wind farms and connected to the electrical grid.\nIn 2024, wind supplied about 2,500 TWh of electricity, which was over 8% of world electricity. With about 100 GW added during 2021, mostly in China and the United States, global installed wind power capacity exceeded 800 GW. 30 countries generated more than a tenth of their electricity from wind power in 2024 and wind generation has nearly tripled since 2015. To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster – by over 1% of electricity generation per year.\nWind power is a sustainable, renewable energy source, and has a much smaller impact on the environment than burning fossil fuels. Wind power is variable, so it needs energy storage or other dispatchable generation energy sources to attain a reliable supply of electricity. Land-based (onshore) wind farms have a greater visual impact on the landscape than most other power stations per energy produced. Wind farms sited offshore have less visual impact and have higher capacity factors, although they are generally more expensive. Offshore wind power currently has a share of about 10% of new installations.\nWind power is one of the lowest-cost electricity sources per unit of energy produced. \nIn many locations, new onshore wind farms are cheaper than new coal or gas plants.\nRegions in the higher northern and southern latitudes have the highest potential for wind power. In most regions, wind power generation is higher in nighttime, and in winter when solar power output is low. So combinations of wind and solar power are suitable in many countries.\n\nWind energy resources\n\nWind is air movement in the Earth's atmosphere. In a unit of time, say 1 second, the volume of air that had passed an area \n \n \n \n A\n \n \n {\\displaystyle A}\n \n is \n \n \n \n A\n v\n \n \n {\\displaystyle Av}\n \n. If the air density is \n \n \n \n ρ\n \n \n {\\displaystyle \\rho }\n \n, the flow rate of this volume of air is \n \n \n \n \n \n \n M\n \n Δ\n t\n \n \n \n \n =\n ρ\n A\n v\n \n \n {\\displaystyle {\\tfrac {M}{\\Delta t}}=\\rho Av}\n \n, and the power transfer, or energy transfer per second is \n \n \n \n P\n =\n \n \n \n 1\n 2\n \n \n \n \n \n \n M\n \n Δ\n t\n \n \n \n \n \n v\n \n 2\n \n \n =\n \n \n \n 1\n 2\n \n \n \n ρ\n A\n \n v\n \n 3\n \n \n \n \n {\\displaystyle P={\\tfrac {1}{2}}{\\tfrac {M}{\\Delta t}}v^{2}={\\tfrac {1}{2}}\\rho Av^{3}}\n \n. Wind power is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Change of wind speed by a factor of 2.1544 increases the wind power by one order of magnitude (multiply by 10).\nThe global wind kinetic energy averaged approximately 1.50 MJ/m2 over the period from 1979 to 2010, 1.31 MJ/m2 in the Northern Hemisphere with 1.70 MJ/m2 in the Southern Hemisphere. The atmosphere acts as a thermal engine, absorbing heat at higher temperatures, releasing heat at lower temperatures. The process is responsible for the production of wind kinetic energy at a rate of 2.46 W/m2 thus sustaining the circulation of the atmosphere against friction.\nThrough wind resource assessment, it is possible to estimate wind power potential globally, by country or region, or for a specific site. The Global Wind Atlas provided by the Technical University of Denmark in partnership with the World Bank provides a global assessment of wind power potential.\nUnlike 'static' wind resource atlases which average estimates of wind speed and power density across multiple years, tools such as Renewables.ninja provide time-varying simulations of wind speed and power output from different wind turbine models at an hourly resolution. More detailed, site-specific assessments of wind resource potential can be obtained from specialist commercial providers, and many of the larger wind developers have in-house modeling capabilities.\nThe total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there.\nTo assess prospective wind power sites, a probability distribution function is often fit to the observed wind speed data. Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly/ten-minute wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.\n\nWind farms\n\nA wind farm is a group of wind turbines in the same location. A large wind farm may consist of several hundred individual wind turbines distributed over an extended area. The land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore. Almost all large wind turbines have the same design — a horizontal axis wind turbine having an upwind rotor with 3 blades, attached to a nacelle on top of a tall tubular tower.\nIn a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV) power collection system and communications network. In general, a distance of 7D (7 times the rotor diameter of the wind turbine) is set between each turbine in a fully developed wind farm. At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.\n\nGenerator characteristics and stability\nMost modern turbines use variable speed generators combined with either a partial or full-scale power converter between the turbine generator and the collector system, which generally have more desirable properties for grid interconnection and have low-voltage ride-through capabilities. Modern turbines use either doubly fed electric machines with partial-scale converters or squirrel-cage induction generators or synchronous generators (both permanently and electrically excited) with full-scale converters. Black start is possible and is being further developed for places (such as Iowa) which generate most of their electricity from wind.\nTransmission system operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include the power factor, the constancy of frequency, and the dynamic behaviour of the wind farm turbines during a system fault.\n\nOffshore wind power\n\nOffshore wind power is wind farms in large bodies of water, usually the sea. These installations can use the more frequent and powerful winds that are available in these locations and have less visual impact on the landscape than land-based projects. However, the construction and maintenance costs are considerably higher.\nAs of November 2021, the Hornsea Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 1,218 MW.\n\nCollection and transmission network\nNear offshore wind farms may be connected by AC and far offshore by HVDC.\nWind power resources are not always located near areas with a high population density. As transmission lines become longer, the losses associated with power transmission increase, as modes of losses at lower lengths are exacerbated and new modes of losses are no longer negligible as the length is increased; making it harder to transport large loads over large distances.\nWhen the transmission capacity does not meet the generation capacity, wind farms are forced to produce below their full potential or stop running altogether, in a process known as curtailment. While this leads to potential renewable generation left untapped, it prevents possible grid overload or risk to reliable service.\nOne of the major challenges to wind power grid integration in some countries is developing new transmission lines to carry power from wind farms, which are often in remote lowly populated areas due to availability of wind, to high load locations where population density is higher. Any existing transmission lines in remote locations may not have been designed for the transport of large amounts of energy. In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power, whether offshore or onshore. A possible future option may be to interconnect widely dispersed geographic areas with an HVDC super grid.\n\nWind power capacity and production\n\nIn 2024, wind supplied over 2,494 TWh of electricity, which was 8.1% of world electricity.\n\nGrowth trends\n\nTo help meet the Paris Agreement's goals to limit climate change, analysts say it should expand much faster than it currently is – by over 1% of electricity generation per year. Expansion of wind power is being hindered by fossil fuel subsidies.\nThe actual amount of electric power that wind can generate is calculated by multiplying the nameplate capacity by the capacity factor, which varies according to equipment and location. Estimates of the capacity factors for wind installations are in the range of 35% to 44%.\n\nCapacity factor\nSince wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Online data is available for some locations, and the capacity factor can be calculated from the yearly output.\n\nPenetration\n\nWind energy penetration is the fraction of energy produced by wind compared with the total generation. Wind power's share of worldwide electricity usage in 2021 was almost 7%, up from 3.5% in 2015.\nThere is no generally accepted maximum level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for energy storage, demand management, and other factors. An interconnected electric power grid will already include reserve generating and transmission capacity to allow for equipment failures. This reserve capacity can also serve to compensate for the varying power generation produced by wind stations. Studies have indicated that 20% of the total annual electrical energy consumption may be incorporated with minimal difficulty. These studies have been for locations with geographically dispersed wind farms, some degree of dispatchable energy or hydropower with storage capacity, demand management, and interconnected to a large grid area enabling the export of electric power when needed. Electrical utilities continue to study the effects of large-scale penetration of wind generation on system stability.\nA wind energy penetration figure can be specified for different duration of time but is often quoted annually. To generate almost all electricity from wind annually requires substantial interconnection to other systems, for example some wind power in Scotland is sent to the rest of the British grid. On a monthly, weekly, daily, or hourly basis—or less—wind might supply as much as or more than 100% of current use, with the rest stored, exported or curtailed. The seasonal industry might then take advantage of high wind and low usage times such as at night when wind output can exceed normal demand. Such industry might include the production of silicon, aluminum, steel, or natural gas, and hydrogen, and using future long-term storage to facilitate 100% energy from variable renewable energy. Homes and businesses can also be programmed to vary electricity demand, for example by remotely turning up water heater thermostats.\n\nVariability\n\nWind power is variable, and during low wind periods, it may need to be replaced by other power sources. Transmission networks presently cope with outages of other generation plants and daily changes in electrical demand, but the variability of intermittent power sources such as wind power is more frequent than those of conventional power generation plants which, when scheduled to be operating, may be able to deliver their nameplate capacity around 95% of the time.\nElectric power generated from wind power can be highly variable at several different timescales: hourly, daily, or seasonally. Annual variation also exists but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, storage solutions, or system interconnection with HVDC cables.\nFluctuations in load and allowance for the failure of large fossil-fuel generating units require operating reserve capacity, which can be increased to compensate for the variability of wind generation.\nUtility-scale batteries are often used to balance hourly and shorter timescale variation, but car batteries may gain ground from the mid-2020s. Wind power advocates argue that periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness, or interlinking with HVDC.\nThe combination of diversifying variable renewables by type and location, forecasting their variation, and integrating them with dispatchable renewables, flexible fueled generators, and demand response can create a power system that has the potential to meet power supply needs reliably. Integrating ever-higher levels of renewables is being successfully demonstrated in the real world.\n\nSolar power tends to be complementary to wind. On daily to weekly timescales, high-pressure areas tend to bring clear skies and low surface winds, whereas low-pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter. Thus the seasonal variation of wind and solar power tend to cancel each other somewhat. Wind hybrid power systems are becoming more popular.\n\nPredictability\n\nFor any particular generator, there is an 80% chance that wind output will change less than 10% in an hour and a 40% chance that it will change 10% or more in 5 hours.\nIn summer 2021, wind power in the United Kingdom fell due to the lowest winds in seventy years, In the future, smoothing peaks by producing green hydrogen may help when wind has a larger share of generation.\nWhile the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable and more predictable. Weather forecasting permits the electric-power network to be readied for the predictable variations in production that occur.\nIt is thought that the most reliable low-carbon electricity systems will include a large share of wind power.\n\nEnergy storage\n\nTypically, conventional hydroelectricity complements wind power very well. When the wind is blowing strongly, nearby hydroelectric stations can temporarily hold back their water. When the wind drops they can, provided they have the generation capacity, rapidly increase production to compensate. This gives a very even overall power supply and virtually no loss of energy and uses no more water.\nAlternatively, where a suitable head of water is not available, pumped-storage hydroelectricity or other forms of grid energy storage such as compressed air energy storage and thermal energy storage can store energy developed by high-wind periods and release it when needed. The type of storage needed depends on the wind penetration level – low penetration requires daily storage, and high penetration requires both short- and long-term storage – as long as a month or more. Stored energy increases the economic value of wind energy since it can be shifted to displace higher-cost generation during peak demand periods. The potential revenue from this arbitrage can offset the cost and losses of storage. Although pumped-storage power systems are only about 75% efficient and have high installation costs, their low running costs and ability to reduce the required electrical base-load can save both fuel and total electrical generation costs.\n\nEnergy payback\nThe energy needed to build a wind farm divided into the total output over its life, Energy Return on Energy Invested, of wind power varies, but averages about 20–25. Thus, the energy payback time is typically around a year.\n\nEconomics\n\nOnshore wind is an inexpensive source of electric power, cheaper than coal plants and new gas plants. According to BusinessGreen, wind turbines reached grid parity (the point at which the cost of wind power matches traditional sources) in some areas of Europe in the mid-2000s, and in the US around the same time. Falling prices continue to drive the Levelized cost down and it has been suggested that it has reached general grid parity in Europe in 2010, and will reach the same point in the US around 2016 due to an expected reduction in capital costs of about 12%. In 2021, the CEO of Siemens Gamesa warned that increased demand for low-cost wind turbines combined with high input costs and high costs of steel result in increased pressure on the manufacturers and decreasing profit margins.\nNorthern Eurasia, Canada, some parts of the United States, and Patagonia in Argentina are the best areas for onshore wind: whereas in other parts of the world solar power, or a combination of wind and solar, tend to be cheaper.\n\nElectric power cost and trends\n\nWind power is capital intensive but has no fuel costs. The price of wind power is therefore much more stable than the volatile prices of fossil fuel sources. However, the estimated average cost per unit of electric power must incorporate the cost of construction of the turbine and transmission facilities, borrowed funds, return to investors (including the cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment, which may be more than 20 years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially.\nThe presence of wind energy, even when subsidized, can reduce costs for consumers (€5 billion/yr in Germany) by reducing the marginal price and by minimizing the use of expensive peaking power plants.\nThe cost has decreased as wind turbine technology has improved. There are now longer and lighter wind turbine blades, improvements in turbine performance, and increased power generation efficiency. Also, wind project capital expenditure costs and maintenance costs have continued to decline.\nIn 2021, a Lazard study of unsubsidized electricity said that wind power levelized cost of electricity continues to fall but more slowly than before. The study estimated new wind-generated electricity cost from $26 to $50/MWh, compared to new gas power from $45 to $74/MWh. The median cost of fully deprecated existing coal power was $42/MWh, nuclear $29/MWh and gas $24/MWh. The study estimated offshore wind at around $83/MWh. Compound annual growth rate was 4% per year from 2016 to 2021, compared to 10% per year from 2009 to 2021.\n\nThe value of wind power\nWhile the levelised costs of wind power may have reached that of traditional combustion based power technologies, the market value of the generated power is also lower due to the merit order effect, which implies that electricity market prices are lower in hours with substantial generation of variable renewable energy due to the low marginal costs of this technology. The effect has been identified in several European markets. For wind power plants exposed to electricity market pricing in markets with high penetration of variable renewable energy sources, profitability can be challenged.\n\nIncentives and community benefits\nTurbine prices have fallen significantly in recent years due to tougher competitive conditions such as the increased use of energy auctions, and the elimination of subsidies in many markets. As of 2021, subsidies are still often given to offshore wind. However, they are generally no longer necessary for onshore wind in countries with even a very low carbon price such as China, provided there are no competing fossil fuel subsidies.\nSecondary market forces provide incentives for businesses to use wind-generated power, even if there is a premium price for the electricity. For example, socially responsible manufacturers pay utility companies a premium that goes to subsidize and build new wind power infrastructure. Companies use wind-generated power, and in return, they can claim that they are undertaking strong \"green\" efforts. Wind projects provide local taxes, or payments in place of taxes and strengthen the economy of rural communities by providing income to farmers with wind turbines on their land.\nThe wind energy sector can also produce jobs during the construction and operating phase. Jobs include the manufacturing of wind turbines and the construction process, which includes transporting, installing, and then maintaining the turbines. An estimated 1.25 million people were employed in wind power in 2020.\n\nSmall-scale wind power\n\nSmall-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power. Isolated communities, that may otherwise rely on diesel generators, may use wind turbines as an alternative. Individuals may purchase these systems to reduce or eliminate their dependence on grid electric power for economic reasons, or to reduce their carbon footprint. Wind turbines have been used for household electric power generation in conjunction with battery storage over many decades in remote areas.\nExamples of small-scale wind power projects in an urban setting can be found in New York City, where, since 2009, several building projects have capped their roofs with Gorlov-type helical wind turbines. Although the energy they generate is small compared to the buildings' overall consumption, they help to reinforce the building's 'green' credentials in ways that \"showing people your high-tech boiler\" cannot, with some of the projects also receiving the direct support of the New York State Energy Research and Development Authority.\nGrid-connected domestic wind turbines may use grid energy storage, thus replacing purchased electric power with locally produced power when available. The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.\nOff-grid system users can either adapt to intermittent power or use batteries, photovoltaic, or diesel systems to supplement the wind turbine. Equipment such as parking meters, traffic warning signs, street lighting, or wireless Internet gateways may be powered by a small wind turbine, possibly combined with a photovoltaic system, that charges a small battery replacing the need for a connection to the power grid.\nAirborne wind turbines, such as kites, can be used in places at risk of hurricanes, as they can be taken down in advance.\n\nImpact on environment and landscape\n\nThe environmental impact of electricity generation from wind power is minor when compared to that of fossil fuel power. Wind turbines have some of the lowest life-cycle greenhouse-gas emissions of energy sources: far less greenhouse gas is emitted than for the average unit of electricity, so wind power helps limit climate change. Use of engineered wood may allow carbon negative wind power. Wind power consumes no fuel, and emits no local air pollution, unlike fossil fuel power sources.\nOnshore wind farms can have a significant visual impact. Due to a very low surface power density and spacing requirements, wind farms typically need to be spread over more land than other power stations. Their network of turbines, access roads, transmission lines, and substations can result in \"energy sprawl\"; although land between the turbines and roads can still be used for agriculture. Some wind farms are opposed for potentially spoiling protected scenic areas, archaeological landscapes and heritage sites. A report by the Mountaineering Council of Scotland concluded that wind farms harmed tourism in areas known for natural landscapes and panoramic views.\nHabitat loss and fragmentation are the greatest potential impacts on wildlife of onshore wind farms, but the worldwide ecological impact is minimal. Thousands of birds and bats, including rare species, have been killed by wind turbine blades, though wind turbines are responsible for far fewer bird deaths than fossil-fueled power stations when climate change effects are included. The effects of wind turbines on birds can be mitigated with proper wildlife monitoring.\nMany wind turbine blades are made of fiberglass, and have a lifetime of 20 years. Blades are hollow: some blades are crushed to reduce their volume and then landfilled. However, as they can take a lot of weight they can be made into long lasting small bridges for walkers or cyclists. Blade end-of-life is complicated, and blades manufactured in the 2020s are more likely to be designed to be completely recyclable.\nWind turbines also generate noise. At a distance of 300 metres (980 ft), this may be around 45 dB, which is slightly louder than a refrigerator. At 1.5 km (1 mi), they become inaudible. There are anecdotal reports of negative health effects on people who live very close to wind turbines. Peer-reviewed research has generally not supported these claims.\n\nPolitics\n\nCentral government\nAlthough wind turbines with fixed bases are a mature technology and new installations are generally no longer subsidized, floating wind turbines are a relatively new technology so some governments subsidize them, for example to use deeper waters.\nFossil fuel subsidies by some governments are slowing the growth of renewables.\nPermitting of wind farms can take years and some governments are trying to speed up – the wind industry says this will help limit climate change and increase energy security – sometimes groups such as fishers resist this but governments say that rules protecting biodiversity will still be followed.\n\nPublic opinion\n\nSurveys of public attitudes across Europe and in many other countries show strong public support for wind power. Bakker et al. (2012) found in their study that residents who did not want turbines built near them suffered significantly more stress than those who \"benefited economically from wind turbines\".\nAlthough wind power is a popular form of energy generation, onshore or near offshore wind farms are sometimes opposed for their impact on the landscape (especially scenic areas, heritage areas and archaeological landscapes), as well as noise, and impact on tourism.\nIn other cases, there is direct community ownership of wind farms. The hundreds of thousands of people who have become involved in Germany's small and medium-sized wind farms demonstrate such support there.\nA 2010 Harris Poll found strong support for wind power in Germany, other European countries, and the United States.\nPublic support in the United States has decreased from 75% in 2020 to 62% in 2021, with the Democratic Party supporting the use of wind energy twice as much as the Republican Party. President Biden signed an executive order to begin building large scale wind farms.\nIn China, Shen et al. (2019) found that Chinese city-dwellers may be resistant to building wind turbines in urban areas, with a surprisingly high proportion of people citing an unfounded fear of radiation as driving their concerns. Also, the study finds that like their counterparts in OECD countries, urban Chinese respondents are sensitive to direct costs and wildlife externalities. Distributing relevant information about turbines to the public may alleviate resistance.\n\nCommunity\n\nMany wind power companies work with local communities to reduce environmental and other concerns associated with particular wind farms.\nIn other cases there is direct community ownership of wind farm projects. Appropriate government consultation, planning and approval procedures also help to minimize environmental risks.\nSome may still object to wind farms but many say their concerns should be weighed against the need to address the threats posed by air pollution, climate change and the opinions of the broader community.\nIn the US, wind power projects are reported to boost local tax bases, helping to pay for schools, roads, and hospitals, and to revitalize the economies of rural communities by providing steady income to farmers and other landowners.\nIn the UK, both the National Trust and the Campaign to Protect Rural England have expressed concerns about the effects on the rural landscape caused by inappropriately sited wind turbines and wind farms.\n\nSome wind farms have become tourist attractions. The Whitelee Wind Farm Visitor Centre has an exhibition room, a learning hub, a café with a viewing deck and also a shop. It is run by the Glasgow Science Centre.\nIn Denmark, a loss-of-value scheme gives people the right to claim compensation for loss of value of their property if it is caused by proximity to a wind turbine. The loss must be at least 1% of the property's value.\nDespite this general support for the concept of wind power in the public at large, local opposition often exists and has delayed or aborted a number of projects.\nAs",
    "source": "wikipedia:Wind power",
    "domain": "climate"
  },
  {
    "text": "Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Reactors producing controlled fusion power have been operated since 1958 but have yet to generate net power and are not expected to be commercially available in the near future.\nThe first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. Nuclear power plants supplied 2,602 terawatt hours (TWh) of electricity in 2023, equivalent to about 9% of global electricity generation, and were the second largest low-carbon power source after hydroelectricity. As of November 2025, there are 416 civilian fission reactors in the world, with overall capacity of 376 GW, 63 under construction and 87 planned, with a combined capacity of 66 GW and 84 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh per year with an average capacity factor of 92%. The average global capacity factor is 89%. Most new reactors under construction are generation III reactors in Asia.\n\nNuclear power is a safe and sustainable energy source that reduces carbon emissions. Nuclear power generation results in one of the lowest levels of fatalities per unit of energy generated compared to other energy sources. One study estimated that each nuclear plant built could have saved 800,000 life years due to averted air pollution from fossil fueled power plants. Coal, petroleum, natural gas and hydroelectricity have each caused more fatalities per unit of energy due to air pollution and accidents. Nuclear power plants also emit no greenhouse gases and result in less life-cycle carbon emissions than common sources of renewable energy. The radiological hazards associated with nuclear power are the primary motivations of the anti-nuclear movement, which contends that nuclear power poses threats to people and the environment, citing the potential for accidents like the Fukushima nuclear disaster in Japan in 2011, and is too expensive to deploy when compared to alternative sustainable energy sources.\n\nHistory\n\nOrigins\n\nThe process of nuclear fission was discovered in 1938 after over four decades of work on the science of radioactivity and the elaboration of new nuclear physics that described the components of atoms. Soon after the discovery of the fission process, it was realized that neutrons released by a fissioning nucleus could, under the right conditions, induce fissions in nearby nuclei, thus initiating a self-sustaining chain reaction. Once this was experimentally confirmed in 1939, scientists in many countries petitioned their governments for support for nuclear fission research, just on the cusp of World War II, in order to develop a nuclear weapon.\nIn the United States, these research efforts led to the creation of the first human-made nuclear reactor, the Chicago Pile-1 under the Stagg Field stadium at the University of Chicago, which achieved criticality on December 2, 1942. The reactor's development was part of the Manhattan Project, the Allied effort to create atomic bombs during World War II. It led to the building of larger single-purpose production reactors for the production of weapons-grade plutonium for use in the first nuclear weapons. The United States tested the first nuclear weapon in July 1945, the Trinity test, and the atomic bombings of Hiroshima and Nagasaki happened one month later.\n\nDespite the military nature of the first nuclear devices, there was strong optimism in the 1940s and 1950s that nuclear power could provide cheap and endless energy. Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW. In 1953, American President Dwight Eisenhower gave his \"Atoms for Peace\" speech at the United Nations, emphasizing the need to develop \"peaceful\" uses of nuclear power quickly. This was followed by the Atomic Energy Act of 1954 which allowed rapid declassification of U.S. reactor technology and encouraged development by the private sector.\n\nFirst power generation\nThe first organization to develop practical nuclear power was the U.S. Navy, with the S1W reactor for the purpose of propelling submarines and aircraft carriers. The first nuclear-powered submarine, USS Nautilus, was put to sea in January 1954. The S1W reactor was a pressurized water reactor. This design was chosen because it was simpler, more compact, and easier to operate compared to alternative designs, thus more suitable to be used in submarines. This decision would result in the PWR being the reactor of choice also for power generation, thus having a lasting impact on the civilian electricity market in the years to come.\nOn June 27, 1954, the Obninsk Nuclear Power Plant in the USSR became the world's first nuclear power plant to generate electricity for a power grid, producing around 5 megawatts of electric power. The world's first commercial nuclear power station, Calder Hall at Windscale, England was connected to the national power grid on 27 August 1956. In common with a number of other generation I reactors, the plant had the dual purpose of producing electricity and plutonium-239, the latter for the nascent nuclear weapons program in Britain.\n\nExpansion and first opposition\nThe total global installed nuclear capacity initially rose relatively quickly, rising from less than 1 gigawatt (GW) in 1960 to 100 GW in the late 1970s. During the 1970s and 1980s rising economic costs (related to extended construction times largely due to regulatory changes and pressure-group litigation) and falling fossil fuel prices made nuclear power plants then under construction less attractive. In the 1980s in the U.S. and 1990s in Europe electricity liberalization made investment in new nuclear power plants (which have high initial capital costs but low operating costs) less desirable than natural gas plants (which had little political opposition, were faster to build, and had low fuel prices).\nThe 1973 oil crisis had a significant effect on countries, such as France and Japan, which had relied more heavily on oil for electric generation to invest in nuclear power. France would construct 25 nuclear power plants over the next 15 years, and as of 2019, 71% of French electricity was generated by nuclear power, the highest percentage for any nation in the world.\nSome local opposition to nuclear power emerged in the United States in the early 1960s. In the late 1960s, some members of the scientific community began to express pointed concerns. These anti-nuclear concerns related to nuclear accidents, nuclear proliferation, nuclear terrorism and radioactive waste disposal. In the early 1970s, there were large protests about a proposed nuclear power plant in Wyhl, Germany. The project was cancelled in 1975. The anti-nuclear success at Wyhl inspired opposition to nuclear power in other parts of Europe and North America.\nBy the mid-1970s anti-nuclear activism gained a wider appeal and influence, and nuclear power started to become an issue of major public protest. In some countries, the nuclear power debate \"reached an intensity unprecedented in the history of technology controversies\". The increased public hostility to nuclear power led to a longer license procurement process, more regulations and increased requirements for safety equipment, which made new construction much more expensive. In the United States, over 120 reactor proposals were ultimately cancelled and the construction of new reactors ground to a halt. The 1979 accident at Three Mile Island played a major part in the reduction in the number of new plant constructions in many countries.\n\nChernobyl and renaissance\n\nDuring the 1980s one new nuclear reactor started up every 17 days on average. By the end of the decade, global installed nuclear capacity reached 300 GW. Since the late 1980s, new capacity additions slowed significantly, with the installed nuclear capacity reaching 365 GW in 2005.\nThe 1986 Chernobyl disaster in the USSR, involving an RBMK reactor, altered the development of nuclear power and led to a greater focus on meeting international safety and regulatory standards. It is considered the worst nuclear disaster in history both in total casualties, with 56 direct deaths, and financially, with the cleanup and the cost estimated at 18 billion Rbls (US$68 billion in 2019, adjusted for inflation). The international organization to promote safety awareness and the professional development of operators in nuclear facilities, the World Association of Nuclear Operators (WANO), was created as a direct outcome of the 1986 Chernobyl accident. The Chernobyl disaster played a major part in the reduction in the number of new plant constructions in the following years. Influenced by these events, Italy voted against nuclear power in a 1987 referendum, becoming the first major economy to completely phase out nuclear power in 1990.\nIn the early 2000s, nuclear energy was expecting a nuclear renaissance, an increase in the construction of new reactors, due to concerns about carbon dioxide emissions. During this period, newer generation III reactors, such as the EPR began construction.\n\nFukushima accident\nProspects of a nuclear renaissance were delayed by another nuclear accident. The 2011 Fukushima Daiichi nuclear accident was caused by the Tōhoku earthquake and tsunami, one of the largest earthquakes ever recorded. The Fukushima Daiichi Nuclear Power Plant suffered three core meltdowns due to failure of the emergency cooling system for lack of electricity supply. This resulted in the most serious civilian nuclear accident since the 1986 Chernobyl disaster.\nThe accident prompted a re-examination of nuclear safety and nuclear energy policy in many countries. Germany approved plans to close all its reactors by 2022, and many other countries reviewed their nuclear power programs. \nFollowing the disaster, Japan shut down all of its nuclear power reactors, some of them permanently, and in 2015 began a gradual process to restart the remaining 40 reactors, following safety checks and based on revised criteria for operations and public approval.\nIn 2022, the Japanese government, under the leadership of Prime Minister Fumio Kishida, declared that 10 more nuclear power plants were to be reopened since the 2011 disaster. Kishida is also pushing for research and construction of new safer nuclear plants to safeguard Japanese consumers from the fluctuating price of the fossil fuel market and reduce Japan's greenhouse gas emissions. Kishida intends to have Japan become a significant exporter of nuclear energy and technology to developing countries around the world.\n\nCurrent prospects\nBy 2015, the IAEA's outlook for nuclear energy had become more promising, recognizing the importance of low-carbon generation for mitigating climate change. As of 2015, the global trend was for new nuclear power stations coming online to be balanced by the number of old plants being retired. In 2016, the U.S. Energy Information Administration projected for its \"base case\" that world nuclear power generation would increase from 2,344 terawatt hours (TWh) in 2012 to 4,500 TWh in 2040. Most of the predicted increase was expected to be in Asia. As of 2018, there were over 150 nuclear reactors planned including 50 under construction. In January 2019, China had 45 reactors in operation, 13 under construction, and planned to build 43 more, which would make it the world's largest generator of nuclear electricity. As of 2021, 17 reactors were reported to be under construction. Its share of electricity from nuclear power was 5% in 2019. \nIn October 2021, the Japanese cabinet approved the new Plan for Electricity Generation to 2030 prepared by the Agency for Natural Resources and Energy (ANRE) and an advisory committee, following public consultation. The nuclear target for 2030 requires the restart of another ten reactors. Prime Minister Fumio Kishida in July 2022 announced that the country should consider building advanced reactors and extending operating licences beyond 60 years.\nAs of 2022, with world oil and gas prices on the rise, while Germany is restarting its coal plants to deal with loss of Russian gas that it needs to supplement its Energiewende, many other countries have announced ambitious plans to reinvigorate ageing nuclear generating capacity with new investments. French President Emmanuel Macron announced his intention to build six new reactors in coming decades, placing nuclear at the heart of France's drive for carbon neutrality by 2050. Meanwhile, in the United States, the Department of Energy, in collaboration with commercial entities, TerraPower and X-energy, is planning on building two different advanced nuclear reactors by 2027, with further plans for nuclear implementation in its long term green energy and energy security goals.\n\nPower plants\n\nNuclear power plants are thermal power stations that generate electricity by harnessing the thermal energy released from nuclear fission. A fission nuclear power plant is generally composed of: a nuclear reactor, in which the nuclear reactions generating heat take place; a cooling system, which removes the heat from inside the reactor; a steam turbine, which transforms the heat into mechanical energy; an electric generator, which transforms the mechanical energy into electrical energy.\nWhen a neutron hits the nucleus of a uranium-235 or plutonium atom, it can split the nucleus into two smaller nuclei, which is a nuclear fission reaction. The reaction releases energy and neutrons. The released neutrons can hit other uranium or plutonium nuclei, causing new fission reactions, which release more energy and more neutrons. This is called a chain reaction. In most commercial reactors, the reaction rate is contained by control rods that absorb excess neutrons. The controllability of nuclear reactors depends on the fact that a small fraction of neutrons resulting from fission are delayed. The time delay between the fission and the release of the neutrons slows changes in reaction rates and gives time for moving the control rods to adjust the reaction rate.\n\nFuel cycle\n\nThe life cycle of nuclear fuel starts with uranium mining. The uranium ore is then converted into a compact ore concentrate form, known as yellowcake (U3O8), to facilitate transport. Fission reactors generally need uranium-235, a fissile isotope of uranium. The concentration of uranium-235 in natural uranium is low (about 0.7%). Some reactors can use this natural uranium as fuel, depending on their neutron economy. These reactors generally have graphite or heavy water moderators. For light water reactors, the most common type of reactor, this concentration is too low, and it must be increased by a process called uranium enrichment. In civilian light water reactors, uranium is typically enriched to 3.5–5% uranium-235. The uranium is then generally converted into uranium oxide (UO2), a ceramic, that is then compressively sintered into fuel pellets, a stack of which forms fuel rods of the proper composition and geometry for the particular reactor.\nAfter some time in the reactor, the fuel will have reduced fissile material and increased fission products, until its use becomes impractical. At this point, the spent fuel will be moved to a spent fuel pool which provides cooling for the thermal heat and shielding for ionizing radiation. After several months or years, the spent fuel is radioactively and thermally cool enough to be moved to dry storage casks or reprocessed.\n\nUranium resources\n\nUranium is a fairly common element in the Earth's crust: it is approximately as common as tin or germanium, and is about 40 times more common than silver. Uranium is present in trace concentrations in most rocks, dirt, and ocean water, but is generally economically extracted only where it is present in relatively high concentrations. As of 2011 the world's known resources of uranium, economically recoverable at the arbitrary price ceiling of US$130/kg, were enough to last for between 70 and 100 years in current reactors.\nLight water reactors (which account for almost all operational reactors) make relatively inefficient use of nuclear fuel, mostly using only the very rare uranium-235 isotope. \nLimited uranium-235 supply may inhibit substantial expansion with the current nuclear technology. \nNuclear reprocessing can make this waste reusable, and newer reactors also achieve a more efficient use of the available resources than older ones. \nMore advanced nuclear reactor technologies, such as fast reactors, can use much more of the natural uranium, use current nuclear waste as fuel, as well as creating new fuel out of non-fissile material (see breeder reactor). \nWith a pure fast reactor fuel cycle with a burn up of all the uranium and actinides (which presently make up the most hazardous substances in nuclear waste), there is an estimated 160,000 years worth of uranium in total conventional resources and phosphate ore at the price of 60–100 US$/kg. \nThese advanced fuel cycles and nuclear reprocessing are currently not widely used because the price of uranium is very low compared to the cost of nuclear plants, so it's more economically viable to mine new uranium rather than reprocess it. \nNuclear reprocessing also carries higher risk of nuclear proliferation, as it separates material that can be used to manufacture nuclear weapons. \nUnconventional uranium resources also exist. Uranium is naturally present in seawater at a concentration of about 3 micrograms per liter, with 4.4 billion tons of uranium considered present in seawater at any time. In 2014 it was suggested that it would be economically competitive to produce nuclear fuel from seawater if the process was implemented at large scale. Over geological timescales, uranium extracted on an industrial scale from seawater would be replenished by both river erosion of rocks and the natural process of uranium dissolved from the surface area of the ocean floor, both of which maintain the solubility equilibria of seawater concentration at a stable level. Some commentators have argued that this strengthens the case for nuclear power to be considered a renewable energy.\n\nWaste\n\nThe normal operation of nuclear power plants and facilities produce radioactive waste, or nuclear waste. This type of waste is also produced during plant decommissioning. There are two broad categories of nuclear waste: low-level waste and high-level waste. The first has low radioactivity and includes contaminated items such as clothing, which poses limited threat. High-level waste is mainly the spent fuel from nuclear reactors, which is very radioactive and must be cooled and then safely disposed of or reprocessed.\n\nHigh-level waste\n\nThe most important waste stream from nuclear power reactors is spent nuclear fuel, which is considered high-level waste (HLW). For light water reactors (LWRs), spent fuel is typically composed of 95% uranium, 4% fission products, and about 1% transuranic actinides (mostly plutonium, neptunium and americium). The fission products are responsible for the bulk of the short-term radioactivity, whereas the plutonium and other transuranics are responsible for the bulk of the long-term radioactivity.\nHigh-level waste must be stored isolated from the biosphere with sufficient shielding so as to limit radiation exposure. After being removed from the reactors, used fuel bundles are stored for six to ten years in spent fuel pools, which provide cooling and shielding against radiation. After that, the fuel is cool enough that it can be safely transferred to dry cask storage. \nThe radioactivity decreases exponentially with time, such that it will have decreased by 99.5% after 100 years. \nThe more intensely radioactive short-lived fission products (SLFPs) decay into stable elements in approximately 300 years, and after about 100,000 years, the spent fuel becomes less radioactive than natural uranium ore.\nCommonly suggested methods to isolate long-lived fission product (LLFP) waste from the biosphere include separation and transmutation, synroc treatments, or deep geological storage.\nThermal-neutron reactors, which presently constitute the majority of the world fleet, cannot burn up the reactor grade plutonium that is generated during the reactor operation. This limits the life of nuclear fuel to a few years. In some countries, such as the United States, spent fuel is classified in its entirety as a nuclear waste. In other countries, such as France, it is largely reprocessed to produce a partially recycled fuel, known as mixed oxide fuel or MOX. \nFor spent fuel that does not undergo reprocessing, the most concerning isotopes are the medium-lived transuranic elements, which are led by reactor-grade plutonium (with a half-life 24,000 years). \nSome proposed reactor designs, such as the integral fast reactor and molten salt reactors, can use as fuel the plutonium and other actinides in spent fuel from light water reactors, thanks to their fast fission spectrum. This offers a potentially more attractive alternative to deep geological disposal.\nThe thorium fuel cycle results in similar fission products, though creates a much smaller proportion of transuranic elements from neutron capture events within a reactor. Spent thorium fuel, although more difficult to handle than spent uranium fuel, may present somewhat lower proliferation risks.\n\nLow-level waste\n\nThe nuclear industry also produces a large volume of low-level waste, with low radioactivity, in the form of contaminated items like clothing, hand tools, water purifier resins, and (upon decommissioning) the materials of which the reactor itself is built. Low-level waste can be stored on-site until radiation levels are low enough to be disposed of as ordinary waste, or it can be sent to a low-level waste disposal site.\n\nWaste relative to other types\n\nIn countries with nuclear power, radioactive wastes account for less than 1% of total industrial toxic wastes, much of which remains hazardous for long periods. Overall, nuclear power produces far less waste material by volume than fossil-fuel based power plants. Coal-burning plants, in particular, produce large amounts of toxic and mildly radioactive ash resulting from the concentration of naturally occurring radioactive materials in coal. A 2008 report from Oak Ridge National Laboratory concluded that coal power actually results in more radioactivity being released into the environment than nuclear power operation, and that the population effective dose equivalent from radiation from coal plants is 100 times that from the operation of nuclear plants. Although coal ash is much less radioactive than spent nuclear fuel by weight, coal ash is produced in much higher quantities per unit of energy generated. It is also released directly into the environment as fly ash, whereas nuclear plants use shielding to protect the environment from radioactive materials.\nNuclear waste volume is small compared to the energy produced. For example, at Yankee Rowe Nuclear Power Station, which generated 44 billion kilowatt hours of electricity when in service, its complete spent fuel inventory is contained within sixteen casks. It is estimated that to produce a lifetime supply of energy for a person at a western standard of living (approximately 3 GWh) would require on the order of the volume of a soda can of low enriched uranium, resulting in a similar volume of spent fuel generated.\n\nWaste disposal\n\nFollowing interim storage in a spent fuel pool, the bundles of used fuel rod assemblies of a typical nuclear power station are often stored on site in dry cask storage vessels.\nDisposal of nuclear waste is often considered the most politically divisive aspect in the lifecycle of a nuclear power facility. The lack of movement of nuclear waste in the 2 billion year old natural nuclear fission reactors in Oklo, Gabon is cited as \"a source of essential information today.\" Experts suggest that centralized underground repositories which are well-managed, guarded, and monitored, would be a vast improvement. There is an \"international consensus on the advisability of storing nuclear waste in deep geological repositories\". With the advent of new technologies, other methods including horizontal drillhole disposal into geologically inactive areas have been proposed.\n\nThere are no commercial scale purpose built underground high-level waste repositories in operation. However, in Finland the Onkalo spent nuclear fuel repository of the Olkiluoto Nuclear Power Plant was under construction as of 2015.\n\nReprocessing\n\nMost thermal-neutron reactors run on a once-through nuclear fuel cycle, mainly due to the low price of fresh uranium. However, many reactors are also fueled with recycled fissionable materials that remain in spent nuclear fuel. The most common fissionable material that is recycled is the reactor-grade plutonium (RGPu) that is extracted from spent fuel. It is mixed with uranium oxide and fabricated into mixed-oxide or MOX fuel. Because thermal LWRs remain the most common reactor worldwide, this type of recycling is the most common. It is considered to increase the sustainability of the nuclear fuel cycle, reduce the attractiveness of spent fuel to theft, and lower the volume of high level nuclear waste. Spent MOX fuel cannot generally be recycled for use in thermal-neutron reactors. This issue does not affect fast-neutron reactors, which are therefore preferred in order to achieve the full energy potential of the original uranium.\nThe main constituent of spent fuel from LWRs is slightly enriched uranium. This can be recycled into reprocessed uranium (RepU), which can be used in a fast reactor, used directly as fuel in CANDU reactors, or re-enriched for another cycle through an LWR. Re-enriching of reprocessed uranium is common in France and Russia. Reprocessed uranium is also safer in terms of nuclear proliferation potential.\nReprocessing has the potential to recover up to 95% of the uranium and plutonium fuel in spent nuclear fuel, as well as reduce long-term radioactivity within the remaining waste. However, reprocessing has been politically controversial because of the potential for nuclear proliferation and varied perceptions of increasing the vulnerability to nuclear terrorism. Reprocessing also leads to higher fuel cost compared to the once-through fuel cycle. While reprocessing can reduce the volume of high-level waste by 80%, it does not reduce the fission products that are the primary causes of residual heat generation and radioactivity for the first century outside the reactor. Thus, reprocessed waste still requires an almost identical treatment to spent nuclear fuel at least for the first hundred years, after which the radioactivity of reprocessed waste may decline more rapidly. \nReprocessing of civilian fuel from power reactors is currently done in France, the United Kingdom, Russia, Japan, and India. In the United States, spent nuclear fuel is currently not reprocessed. The La Hague reprocessing facility in France has operated commercially since 1976 and is responsible for half the world's reprocessing as of 2010. It produces MOX fuel from spent fuel derived from several countries. More than 32,000 tonnes of spent fuel had been reprocessed as of 2015, with the majority from France, 17% from Germany, and 9% from Japan.\n\nBreeding\n\nBreeding is the process of converting non-fissile material into fissile material that can be used as nuclear fuel. The non-fissile material that can be used for this process is called fertile material, and constitute the vast majority of current nuclear waste. This breeding process occurs naturally in breeder reactors. As opposed to light water thermal-neutron reactors, which use uranium-235 (0.7% of all natural uranium), fast-neutron breeder reactors use uranium-238 (99.3% of all natural uranium) or thorium. A number of fuel cycles and breeder reactor combinations are considered to be sustainable or renewable sources of energy. In 2006 it was estimated that with seawater extraction, there was likely five billion years' worth of uranium resources for use in breeder reactors.\nBreeder technology has been used in several reactors, but as of 2006, the high cost of reprocessing fuel safely requires uranium prices of more than US$200/kg before becoming justified economically. Breeder reactors are however being developed for their potential to burn all of the actinides (the most active and dangerous components) in the present inventory of nuclear waste, while also producing power and creating additional quantities of fuel for more reactors via the breeding process. As of 2017, there are two breeders producing commercial power, BN-600 reactor and the BN-800 reactor, both in Russia. The Phénix breeder reactor in France was powered down in 2009 after 36 years of operation. Both China and India are building breeder reactors. The Indian 500 MWe Prototype Fast Breeder Reactor is in the commissioning phase, with plans to build more.\nAnother alternative to fast-neutron breeders are thermal-neutron breeder reactors that use uranium-233 bred from thorium as fission fuel in the thorium fuel cycle. Thorium is about 3.5 times more common than uranium in the Earth's c",
    "source": "wikipedia:Nuclear power",
    "domain": "climate"
  },
  {
    "text": "An electric vehicle (EV) is a vehicle propelled mostly by electric power. EVs encompass road (cars, buses, trucks and personal transporters), rail (trains, trams and monorails), boats and submersibles, aircraft (fixed-wing and multirotors) and spacecraft.\nEVs originated in the late 19th century. Electricity was among the preferred methods for powering early motor vehicles because it was quieter, provided comfort, and ease of operation. However, its limited range hindered mass adoption throughout the 20th century. Internal combustion engines were the dominant propulsion mechanisms for cars and trucks for about 100 years, although electricity-powered locomotion became commonplace in other vehicle types, such as overhead line-powered mass transit vehicles, as well as special purpose vehicles such as mobility scooters.\nSince the late 20th century, technological advancement in lithium batteries, which offer superior energy density and current output versus lead-acid batteries, has revived public interest as zero-emission vehicle options. Manufacturers mostly switched to hybrids that use internal combustion engines like conventional vehicles, but add electric motors as a supplement, powered by electricity produced internally by motor-generators and recovered from regenerative braking. Plug-in hybrid electric vehicles, which can be recharged from an electric grid and use electric motors as the primary propulsion rather than as a supplement to combustion engines, did not see any mass production until the late 2000s, and battery electric cars did not become practical options for the consumer market until the 2010s. Although spacecraft have been propelled by electricity since the 1960s, non-rocket spacelaunch from Earth remains science fiction.\n\nTechnological progresses in electric vehicle batteries, electric traction motors and automotive electronics (particularly electronic control units) has made electric cars more feasible and, in some cases, more cost efficient than conventional ICE vehicles during the 21st century, with market penetration in some countries like China reaching nearly half of all new vehicles sold. As a means of reducing tailpipe emissions of greenhouse gases and other air pollutants, and to reduce the dependency on fossil fuels, government incentives are also available in many areas to promote the adoption of electric vehicles. As of 2026, the electric vehicle industry in China produces more than the rest of the world combined.\n\nHistory\n\nExperimentation\n\nIn January 1990, General Motors President introduced its EV concept two-seater, the \"Impact\", at the Los Angeles Auto Show. That September, the California Air Resources Board mandated major-automaker sales of EVs, in phases starting in 1998. From 1996 to 1998 GM produced 1117 EV1s, 800 of which were made available through three-year leases.\nChrysler, Ford, GM, Honda, and Toyota also produced limited numbers of EVs for California drivers during this period. In 2003, upon the expiration of GM's EV1 leases, GM discontinued them. The discontinuation has variously been attributed to: the auto industry's successful federal court challenge to California's zero-emissions vehicle mandate, a federal regulation requiring GM to produce and maintain spare parts for the few thousand EV1s and the success of the oil and auto industries' media campaign to reduce public acceptance of EVs.\nA movie made on the subject in 2005–2006 was titled Who Killed the Electric Car? and released theatrically by Sony Pictures Classics in 2006. The film explores the roles of automobile manufacturers, oil industry, the U.S. government, batteries, hydrogen vehicles, and the general public, and each of their roles in limiting the deployment and adoption of this technology.\nFord released a number of their Ford Ecostar delivery vans into the market. Honda, Nissan and Toyota also repossessed and crushed most of their EVs, which, like the GM EV1s, had been available only by closed-end lease. After public protests, Toyota sold 200 of its RAV4 EVs; they later sold at over their original forty-thousand-dollar price. Later, BMW of Canada sold off a number of Mini EVs when their Canadian testing ended.\nThe production of the Citroën Berlingo Electrique stopped in September 2005. Zenn started production in 2006 but ended by 2009.\n\nReintroduction\n\nDuring the late 20th and early 21st century, the environmental impact of the petroleum-based transportation infrastructure, along with the fear of peak oil, led to renewed interest in electric transportation infrastructure. By the 21st century an energy transition to electrify as many things as possible, not just vehicles, rather than burning stuff became to be seen as very important for human health and the environment. EVs differ from fossil fuel-powered vehicles in that the electricity they consume can be generated from a wide range of sources, including fossil fuels, nuclear power, and renewables such as solar power and wind power, or any combination of those. Recent advancements in battery technology and charging infrastructure have addressed many of the earlier barriers to EV adoption, making electric vehicles a more viable option for a wider range of consumers.\nThe carbon footprint and other emissions of electric vehicles vary depending on the fuel and technology used for electricity generation. The electricity may be stored in the vehicle using a battery, flywheel, or SupercapacitorS. Vehicles using internal combustion engines usually only derive their energy from a single or a few sources, usually non-renewable fossil fuels. A key advantage of electric vehicles is regenerative braking, which recovers kinetic energy, typically lost during friction braking as heat, as electricity restored to the on-board battery. Although over 20% of new cars sold in 2024 were electric only 2% of trucks were. China is the world's leading EV producer, accounting for more than 70% of global production and 67% of global sales of electric vehicles in 2024.\n\nElectricity sources\n\nEVs are much more efficient than internal combustion engines and have few direct emissions. At the same time, they do rely on electrical energy that is generally provided by a combination of non-fossil fuel plants and fossil fuel plants.\nThere are many ways to generate electricity, of varying costs, efficiency and ecological desirability. EVs can be made less polluting overall by modifying the source of electricity. In some areas, individuals can ask utilities to provide their electricity from renewable energy. Therefore, it gives the greatest degree of energy resilience.\n\nConnection to generator plants\nDirect connection to electric grids as is common among electric trains, trams, trolleybuses, and trolleytrucks (see also: overhead lines, third rail and conduit current collection)\nOnline electric vehicle collects power from electric power strips buried under the road surface through electromagnetic induction\n\nOnboard generators and hybrid EVs\n\nGenerated on-board using a diesel engine: diesel–electric locomotive and diesel–electric multiple unit (DEMU)\nGenerated on-board using a fuel cell: fuel cell vehicle\nGenerated on-board using nuclear power: nuclear submarines and aircraft carriers\nRenewable sources such as solar power: solar vehicle\nIt is also possible to have hybrid EVs that derive electricity from multiple sources, such as:\n\nOn-board rechargeable electricity storage system (RESS) and a direct continuous connection to land-based generation plants for purposes of on-highway recharging with unrestricted highway range\nOn-board rechargeable electricity storage system and a fueled propulsion power source (internal combustion engine): plug-in hybrid\nFor especially large EVs, such as submarines, the chemical energy of the diesel–electric can be replaced by a nuclear reactor. The nuclear reactor usually provides heat, which drives a steam turbine, which drives a generator, which is then fed to the propulsion. See Nuclear marine propulsion.\nA few experimental vehicles, such as some cars and a handful of aircraft use solar panels for electricity.\n\nOnboard storage\nThese systems are powered from an external generator plant (nearly always when stationary), and then disconnected before motion occurs, and the electricity is stored in the vehicle until needed.\n\nFull Electric Vehicles (FEV). Power storage methods include:\nChemical energy stored on the vehicle in on-board batteries: Battery electric vehicle (BEV) typically with a lithium-ion battery\nKinetic energy storage: flywheels\nStatic energy stored on the vehicle in on-board electric double-layer capacitors\nBatteries, electric double-layer capacitors and flywheel energy storage are forms of rechargeable on-board electricity storage systems. By avoiding an intermediate mechanical step, the energy conversion efficiency can be improved compared to hybrids by avoiding unnecessary energy conversions. Furthermore, electro-chemical batteries conversions are reversible, allowing electrical energy to be stored in chemical form.\n\nComponents\nThe type of battery, the type of traction motor and the motor controller design vary according to the size, power and proposed application, which can be as small as a motorized shopping cart or wheelchair, through pedelecs, electric motorcycles and scooters, neighborhood electric vehicles, industrial fork-lift trucks and including many hybrid vehicles.\n\nBattery\n\nAn electric-vehicle battery (EVB) in addition to the traction battery specialty systems used for industrial (or recreational) vehicles, are batteries used to power the propulsion system of a battery electric vehicle (BEVs). These batteries are usually a secondary (rechargeable) battery, and are typically lithium-ion batteries.\nTraction batteries, specifically designed with a high ampere-hour capacity, are used in forklifts, electric golf carts, riding floor scrubbers, electric motorcycles, electric cars, trucks, vans, and other electric vehicles.\n\nLithium-ion battery\n\nSince their first commercial release in 1991, lithium-ion batteries have become an important technology for achieving low-carbon transportation systems. Most electric vehicles use lithium-ion batteries (Li-Ions or LIBs). Lithium-ion batteries have a higher energy density, longer life span, and higher power density than most other practical batteries. Complicating factors include safety, durability, thermal breakdown, environmental impact, and cost. Li-ion batteries should be used within safe temperature and voltage ranges to operate safely and efficiently.\nIncreasing the battery's lifespan decreases effective costs and environmental impact. One technique is to operate a subset of the battery cells at a time and switching these subsets.\nIn the past, nickel–metal hydride batteries were used in some electric cars, such as those made by General Motors. These battery types are considered outdated due to their tendencies to self-discharge in the heat. Furthermore, a patent for this type of battery was held by Chevron, which created a problem for their widespread development. These factors, coupled with their high cost, has led to lithium-ion batteries leading as the predominant battery for EVs.\nThe prices of lithium-ion batteries have declined dramatically over the past decade, contributing to a reduction in price for electric vehicles, but an increase in the price of critical minerals such as lithium from 2021 to the end of 2022 has put pressure on historical battery price decreases.\n\nElectric motor\n\nThe power of a vehicle's electric motor, as in other machines, is measured in kilowatts (kW). Electric motors can deliver their maximum torque over a wide RPM range. This means that the performance of a vehicle with a 100 kW electric motor exceeds that of a vehicle with a 100 kW internal combustion engine, which can only deliver its maximum torque within a limited range of engine speed.\nEfficiency of charging varies considerably depending on the type of charger, and energy is lost during the process of converting the electrical energy to mechanical energy.\nUsually, direct current (DC) electricity is fed into a DC/AC inverter where it is converted to alternating current (AC) electricity and this AC electricity is connected to a 3-phase AC motor.\nFor electric trains, forklift trucks, and some electric cars, DC motors are often used. In some cases, universal motors are used, and then AC or DC may be employed. In recent production vehicles, various motor types have been implemented; for instance, induction motors within Tesla vehicles and permanent magnet machines in the Nissan Leaf and Chevrolet Bolt.\n\nEnergy and motors\n\nElectric motors are mechanically very simple and often achieve 90% energy conversion efficiency over the full range of speeds and power output and can be precisely controlled.\nMotion is provided by a rotary electric motor. However, it is possible to \"unroll\" the motor to drive directly against a special matched track. These linear motors are used in maglev trains which float above the rails supported by magnetic levitation. This allows for almost no rolling resistance of the vehicle and no mechanical wear and tear of the train or track. In addition to the high-performance control systems needed, switching and curving of the tracks becomes difficult with linear motors, which to date has restricted their operations to high-speed point to point services.\nElectric traction allows the use of regenerative braking, in which the motors are used as brakes and become generators that transform the motion of, usually, a train into electrical power that is then fed back into the lines. This system is particularly advantageous in mountainous operations, as descending vehicles can produce a large portion of the power required for those ascending, and in start-and-stop city use. This regenerative system is only viable if the system is large enough to use the power generated by descending vehicles.\nThey can be finely controlled and provide high torque from stationary-to-moving, unlike internal combustion engines, and do not need multiple gears to match power curves. This removes the need for gearboxes and torque converters.\nEVs provide quiet and smooth operation and consequently have less noise and vibration than internal combustion engines. While this is a desirable attribute, it has also evoked concern that the absence of the usual sounds of an approaching vehicle poses a danger to blind, elderly and very young pedestrians. To mitigate this situation, many countries mandate warning sounds when EVs are moving slowly, up to a speed when normal motion and rotation (road, suspension, electric motor, etc.) noises become audible.\nElectric motors do not require oxygen, unlike internal combustion engines; this is useful for submarines and for space rovers.\n\nTypes\n\nIt is generally possible to equip any kind of vehicle with an electric power-train.\n\nGround vehicles\n\nPure-electric vehicles\n\nA pure-electric vehicle or all-electric vehicle is powered exclusively through electric motors. The electricity may come from a battery (battery electric vehicle), solar panel (solar vehicle) or fuel cell (fuel cell vehicle).\n\nHybrids\n\nThere are different ways that a hybrid electric vehicle can combine the power from an electric motor and the internal combustion engine. The most common type is a parallel hybrid that connects the engine and the electric motor to the wheels through mechanical coupling. In this scenario, the electric motor and the engine can drive the wheels directly. Series hybrids only use the electric motor to drive the wheels and can often be referred to as extended-range electric vehicles (EREVs) or range-extended electric vehicles (REEVs). There are also series–parallel hybrids where the vehicle can be powered by the engine working alone, the electric motor on its own, or by both working together; this is designed so that the engine can run at its optimum range as often as possible.\n\nPlug-ins\n\nA plug-in electric vehicle (PEV) is any motor vehicle that can be recharged from any external source of electricity, such as wall sockets, and the electricity stored in the Rechargeable battery packs drives or contributes to drive the wheels. PEV is a subcategory of electric vehicles that includes battery electric vehicles (BEVs), plug-in hybrid vehicles, (PHEVs), and electric vehicle conversions of hybrid electric vehicles and conventional internal combustion engine vehicles.\n\nRange-extended\n\nA range-extended electric vehicle (REEV) is a vehicle powered by an electric motor and a plug-in battery. An auxiliary combustion engine is used only to supplement battery charging and not as the primary source of power.\n\nOn- and off-road\nOn-road electric vehicles include electric cars, electric trolleybuses, electric buses, battery electric buses, electric trucks, electric bicycles, electric motorcycles and scooters, personal transporters, neighborhood electric vehicles, golf carts, milk floats, and forklifts. Off-road vehicles include electrified all-terrain vehicles and electric tractors.\n\nTrucks\n\nAn electric truck is a battery electric vehicle (BEV) designed to transport cargo, carry specialized payloads, or perform other utilitarian work.\nElectric trucks have serviced niche applications like milk floats, pushback tugs and forklifts for over a hundred years, typically using lead–acid batteries, but the rapid development of lighter and more energy-dense battery chemistries in the twenty-first century has broadened the range of applicability of electric propulsion to trucks in many more roles.\nElectric trucks reduce noise and pollution, relative to internal-combustion trucks. Due to the high efficiency and low component-counts of electric power trains, no fuel burning while idle, and silent and efficient acceleration, the costs of owning and operating electric trucks are dramatically lower than their predecessors.\nLong-distance freight has been the trucking segment least amenable to electrification, since the increased weight of batteries, relative to fuel, detracts from payload capacity, and the alternative, more frequent recharging, detracts from delivery time. By contrast, short-haul urban delivery has been electrified rapidly, since the clean and quiet nature of electric trucks fit well with urban planning and municipal regulation, and the capacities of reasonably sized batteries are well-suited to daily stop-and-go traffic within a metropolitan area.\n\nRailborne\n\nThe fixed nature of a rail line makes it relatively easy to power EVs through permanent overhead lines or electrified third rails, eliminating the need for heavy onboard batteries. Electric locomotives, electric multiple units, electric trams (also called streetcars or trolleys), electric light rail systems, and electric rapid transit are all in common use today, especially in Europe and Asia.\nSince electric trains do not need to carry a heavy internal combustion engine or large batteries, they can have very good power-to-weight ratios. This allows high speed trains such as France's double-deck TGVs to operate at speeds of 320 km/h (200 mph) or higher, and electric locomotives to have a much higher power output than diesel locomotives. In addition, they have higher short-term surge power for fast acceleration, and using regenerative brakes can put braking power back into the electrical grid rather than wasting it.\nMaglev trains are also nearly always EVs.\nThere are also battery electric passenger trains operating on non-electrified rail lines.\n\nHydrogen trains\nParticularly in Europe, fuel-cell electric trains are gaining in popularity to replace diesel–electric locomotive units. In Germany, several Länder have ordered Alstom Coradia iLINT trainsets, in service since 2018, with France also planning to order trainsets. The United Kingdom, the Netherlands, Denmark, Norway, Italy, Canada and Mexico are equally interested. In France, the SNCF plans to replace all its remaining diesel-electric trains with hydrogen trains by 2035. In the United Kingdom, Alstom announced in 2018 their plan to retrofit British Rail Class 321 trainsets with fuel cells.\n\nWatercraft\n\nElectric boats were popular around the turn of the 20th century. Interest in quiet and potentially renewable marine transportation has steadily increased since the late 20th century, as solar cells have given motorboats the infinite range of sailboats. Electric motors can and have also been used in sailboats instead of traditional diesel engines. Electric ferries operate routinely. Submarines use batteries (charged by diesel or gasoline engines at the surface), nuclear power, fuel cells or Stirling engines to run electric motor-driven propellers. Fully electric tugboats are being used in Auckland, New Zealand (June 2022), Vancouver, British Columbia (October 2023), and San Diego, California.\n\nAircraft\n\nSince the beginnings of aviation, electric power for aircraft has received a great deal of experimentation. Currently, flying electric aircraft include piloted and unpiloted aerial vehicles.\n\nSpacecraft\n\nElectric power has a long history of use in spacecraft. The power sources used for spacecraft are batteries, solar panels and nuclear power. Current methods of propelling a spacecraft with electricity include the arcjet rocket, the electrostatic ion thruster, the Hall-effect thruster, and Field Emission Electric Propulsion.\n\nRovers\n\nElectric vehicles are the only option for rovers as there is simply no oxygen gas to drive combustion engines in outer space and Exoplanetary atmospheres. Crewed and uncrewed electric vehicles have been used to explore the Moon and other planets in the Solar System. On the last three missions of the Apollo program in 1971 and 1972, astronauts drove silver-oxide battery-powered Lunar Roving Vehicles distances up to 35.7 kilometers (22.2 mi) on the lunar surface. Solar-powered, remotely controlled uncrewed rovers have also explored the Moon and Mars.\n\nCharging/fueling\n\nStations\n\nBattery swapping\nInstead of recharging EVs from electric sockets, batteries could be mechanically replaced at special stations in a few minutes (battery swapping).\nBatteries with greater energy density such as metal–air fuel cells cannot always be recharged in a purely electric way, so some form of mechanical recharge may be used instead. A zinc–air battery, technically a fuel cell, is difficult to recharge electrically so may be \"refueled\" by periodically replacing the anode or electrolyte instead.\n\nBidirectional charging\nGeneral Motors (GM) is adding a capability called V2H, or bidirectional charging, to allow its new electric vehicles to send power from their batteries to the owner's home. GM will start with 2024 models, including the Silverado and Blazer EVs, and promises to continue the feature through to model year 2026. This could be helpful to the owner during unexpected power grid outages because an electric vehicle is a giant battery on wheels.\n\nConsiderations\n\nEnvironmental impact\n \n\nEVs release no tailpipe air pollutants, and reduce respiratory illnesses such as asthma. By reducing types of air pollution, such as nitrogen dioxide, EVs could also prevent hundreds of thousands of early deaths every year, especially from trucks and traffic in cities. Additionally, EVs have significantly less noise pollution in urban areas, improving the quality of life overall.\nThe carbon emissions from producing and operating an EV are, in the majority of cases less, than those of producing and operating a conventional vehicle. When pursuing a cost-responsive electric charging strategy (instead of an emission-responsive charging strategy), considerably higher emissions might arise as embedded carbon emissions from electricity are dynamic. EVs in urban areas almost always pollute less than internal combustion vehicles.\nHowever, EVs are charged with electricity that may be generated by means that have health and environmental impacts. This is particularly relevant in places that rely on coal-powered electricity grids. It also have negative environmental impacts due to the manufacturing and recycling of batteries. The full environmental impact of electric vehicles includes the life cycle impacts of carbon and sulfur emissions, as well as toxic metals entering the environment.\nDespite that, ICE vehicles use far more raw materials over their lifetime than EVs. One source estimates that over a fifth of the lithium and about 65% of the cobalt needed for electric cars will be from recycled sources by 2035. On the other hand, when counting the large quantities of fossil fuel non-electric cars consume over their lifetime, electric cars can be considered to dramatically reduce raw-material needs.\nOne limitation of the environmental potential of EVs is that simply switching the existing privately owned car fleet from ICEs to EVs will not free up road space for active travel or public transport. Electric micromobility vehicles, such as e-bikes, may contribute to the decarbonisation of transport systems, especially outside of urban areas which are already well-served by public transport.\n\nMining, extraction and production\nInformation regarding the sustainability of the production process of batteries has become a politically charged topic. Business processes of raw material extraction in practice raise issues of transparency and accountability of the management of extractive resources. In the complex supply chain of lithium technology, there are diverse stakeholders representing corporate interests, public interest groups and political elites that are concerned with outcomes from the technology production and use. One possibility to achieve balanced extractive processes would be the establishment of commonly agreed-upon standards on the governance of technology worldwide.\nThe compliance of these standards can be assessed by the Assessment of Sustainability in Supply Chains Frameworks (ASSC). Hereby, the qualitative assessment consists of examining governance and social and environmental commitment. Indicators for the quantitative assessment are management systems and standards, compliance and social and environmental indicators.\nThe initial phase of electric vehicle production incurs an environmental cost, often referred to as a \"carbon debt\", primarily driven by the energy-intensive manufacturing of high-voltage batteries and the extraction of critical raw materials. Rare-earth metals (neodymium, dysprosium) and other mined metals (copper, nickel, iron) are used by EV motors, while lithium, cobalt, manganese are used by the batteries. In 2023 the US State Department said that the supply of lithium would need to increase 42-fold by 2050 globally to support a transition to clean energy. Most of the lithium-ion battery production occurs in China, where the bulk of energy used is supplied by coal-burning power plants.\nThe extraction and processing of these metals contributes to habitat destruction and environmental degradation. For instance, the process of mining minerals such as lithium and cobalt, essential components of current battery chemistries, carries significant localized environmental hazards. Lithium mining, frequently conducted using water-intensive brine extraction, contributes to global carbon emissions, estimated at over 1.3 million tonnes of carbon annually, with every tonne of mined lithium equating to 15 tonnes of CO2 released into the atmosphere. In regions rich in cobalt, such as the Democratic Republic of Congo (DRC), environmental costs are substantial, including deforestation, habitat destruction and water pollution. Scientists have noted high radioactivity levels in some mining regions, and industrial processes, including the pulverization of rock, release dust that causes respiratory health issues for nearby populations. Open-pit nickel mining has led to environmental degradation and pollution in developing countries such as the Philippines and Indonesia. In 2024, nickel mining and processing was one of the main causes of deforestation in Indonesia.\n\nIn 2022, the manufacturing of an EV emitted on average around 50% more CO2 than an equivalent internal combustion engine vehicle, but this difference is more than offset by the much higher emissions from the oil used in driving an internal combustion engine Vehicle over its lifetime compared to those from generating the electricity used for driving the EV.\nIn 2023, Greenpeace issued a video criticizing the view that EVs are \"silver bullet for climate\", arguing that the construction phase has a high environmental impact. For example, the rise in SUV sales by Hyundai almost eliminate the climate benefits of passing to EV in this company, because even electric SUVs have a high carbon footprint as they consume much raw materials and energy during construction. Greenpeace proposes a mobility as a service concept instead, based on biking, public transport and ride sharing.\n\nLife-cycle assessment\nDespite the initial manufacturing footprint, a life-cycle assessment (LCA) approach consistently confirms that electric vehicles yield superior overall lifetime greenhouse gas (GHG) performance compared to equivalent ICE vehicles. The extent of the environmental benefit is intrinsically linked to the carbon intensity of the electricity grid used to power the vehicle. In regions like China, battery electric vehicles currently achieve approximately 40% lower emissions compared to ICE vehicles over their full lifespan. However, in countries with high-intensity grids, such as India, the immediate advantage is more modest, resulting in only about 20% lower emissions (saving less than 10 tonnes of CO2 equivalent). This context is temporary, as significant efforts are underway globally to decarbonize electricity generation; for instance, the emissions intensity of India's grid is projected to fall by 60% by 2035, rapidly increasing the environmental benefit of electrification.\nAn alternative method of sour",
    "source": "wikipedia:Electric vehicle",
    "domain": "climate"
  },
  {
    "text": "Carbon capture and storage (CCS) is a process by which carbon dioxide (CO2) from industrial installations or natural sources is separated before it is released into the atmosphere, then transported to a long-term storage location. The CO2 is captured from a large point source, such as a natural gas processing plant and is typically stored in a deep geological formation. Around 80% of the CO2 captured annually is used for enhanced oil recovery (EOR), a process by which CO2 is injected into partially depleted oil reservoirs in order to extract more oil and then is largely left underground. Since EOR utilizes the CO2 in addition to storing it, CCS is also known as carbon capture, utilization, and storage (CCUS). \nOil and gas companies first used the processes involved in CCS in the mid-20th century. Early CCS technologies were mainly used to purify natural gas and increase oil production. Beginning in the 1980s and accelerating in the 2000s, CCS was discussed as a strategy to reduce greenhouse gas emissions. Around 70% of announced CCS projects have not materialized, with a failure rate above 98% in the electricity sector. As of 2024 CCS was in operation at 44 plants worldwide, collectively capturing about one-thousandth of global carbon dioxide emissions. 90% of CCS operations involve the oil and gas industry. Plants with CCS require more energy to operate, thus they typically burn additional fossil fuels and increase the pollution caused by extracting and transporting fuel.\nCCS could have a critical but limited role in reducing greenhouse gas emissions. However, other emission-reduction options such as solar and wind energy, electrification, and public transit are less expensive than CCS and are much more effective at reducing air pollution. Given its cost and limitations, CCS is envisioned to be most useful in specific niches. These niches include heavy industry and plant retrofits. In the context of deep and sustained cuts in natural gas consumption, CCS can reduce emissions from natural gas processing. In electricity generation and hydrogen production, CCS is envisioned to complement a broader shift to renewable energy. CCS is a component of bioenergy with carbon capture and storage, which can under some conditions remove carbon from the atmosphere. \nThe effectiveness of CCS in reducing carbon emissions depends on the plant's capture efficiency, the additional energy used for CCS itself, leakage, and business and technical issues that can keep facilities from operating as designed. Some large CCS implementations have sequestered far less CO2 than originally expected. Controversy remains over whether using captured CO2 to extract more oil ultimately benefits the climate. Many environmental groups regard CCS as an unproven, expensive technology that perpetuates fossil fuel dependence. They believe other ways to reduce emissions are more effective and that CCS is a distraction.\n\nSome international climate agreements refer to the concept of fossil fuel abatement, which is not defined in these agreements but is generally understood to mean use of CCS. Almost all CCS projects operating today have benefited from government financial support. Countries with programs to support or mandate CCS technologies include the US, Canada, Denmark, China, and the UK.\n\nTerminology\nThe Intergovernmental Panel on Climate Change (IPCC) defines CCS as:\"A process in which a relatively pure stream of carbon dioxide (CO2) from industrial and energy-related sources is separated (captured), conditioned, compressed and transported to a storage location for long-term isolation from the atmosphere.\"The terms carbon capture and storage (CCS) and carbon capture, utilization, and storage (CCUS) are closely related and often used interchangeably. Both terms have been used predominantly to refer to enhanced oil recovery (EOR) a process in which captured CO2 is injected into partially depleted oil reservoirs in order to extract more oil. EOR is both \"utilization\" and \"storage\", as the CO2 left underground is intended to be trapped indefinitely. Prior to 2013, the process was primarily called CCS. In 2013 the term CCUS was introduced to highlight its potential economic benefit, and this term subsequently gained popularity.\nAround 1% of captured CO2 is used as a feedstock for making products such as fertilizer, fuels, and plastics. These uses are forms of carbon capture and utilization. In some cases, the product durably stores the carbon from the CO2 and thus is also considered to be a form of CCS. To qualify as CCS, carbon storage must be long-term, therefore utilization of CO2 to produce fertilizer, fuel, or chemicals is not CCS because these products release CO2 when burned or consumed.\nSome sources use the term CCS, CCU, or CCUS more broadly, encompassing methods such as direct air capture or tree-planting which remove CO2 from the air. In this article, the term CCS is used according to the IPCC's definition, which requires CO2 to be captured from point-sources such as a natural gas processing plant.\n\nHistory and current status\n\nIn the natural gas industry, technology to remove CO2 from raw natural gas was patented in 1930. This processing is essential to make natural gas ready for commercial sale and distribution. Usually after CO2 is removed, it is vented to the atmosphere. In 1972, American oil companies discovered that CO2 could profitably be used for EOR. Subsequently, natural gas companies in Texas began capturing the CO2 produced by their processing plants and selling it to local oil producers for EOR.\nThe use of CCS as a means of reducing human-caused CO2 emissions is more recent. In 1977, the Italian physicist Cesare Marchetti proposed that CCS could be used to reduce emissions from coal power plants and fuel refineries. Small-scale implementations were first demonstrated in the early 1980s and an economic evaluation was published in 1991. The first large-scale CO2 capture and injection project with dedicated CO2 storage and monitoring was commissioned at the Sleipner gas field in Norway in 1996.\nIn 2005, the IPCC released a report highlighting CCS, leading to increased government support for CCS in several countries. Governments spent an estimated US$30 billion on subsidies for CCS and for fossil-fuel-based hydrogen. Globally, 149 projects to store 130 million tonnes of CO2 annually were proposed to be operational by 2020. Of these, around 70% were not implemented. Limited one-off capital grants, the absence of measures to address long-term liability for stored CO2, high operating costs, limited social acceptability and vulnerability of funding programmes to external budget pressures all contributed to project cancellations.\nIn 2020, the International Energy Agency (IEA) stated, \"The story of CCUS has largely been one of unmet expectations: its potential to mitigate climate change has been recognised for decades, but deployment has been slow and so has had only a limited impact on global CO2 emissions.\" \nBy July 2024, commercial-scale CCS was in operation at 44 plants worldwide. Sixteen of these facilities were devoted to separating naturally occurring CO2 from raw natural gas. Seven facilities were for hydrogen, ammonia, or fertilizer production, seven for chemical production, five for electricity and heat, and two for oil refining. CCS was also used in one iron and steel plant. Additionally, three facilities worldwide were devoted to CO2 transport/storage. As of 2024, the oil and gas industry is involved in 90% of CCS capacity in operation around the world. Collectively, the facilities capture about one-thousandth of global greenhouse gas emissions.\nEighteen facilities were in the United States, fourteen in China, five in Canada, and two in Norway. Australia, Brazil, Qatar, Saudi Arabia, and the United Arab Emirates had one project each. As of 2020, North America has more than 8,000 km (5,000 mi) of CO2 pipelines, and there are two CO2 pipeline systems in Europe and two in the Middle East.\n\nProcess overview\nCCS facilities capture carbon dioxide before it enters the atmosphere. Generally, a chemical solvent or a porous solid material is used to separate the CO2 from other components of a plant's exhaust stream. Most commonly, the gas stream passes through an amine solvent, which binds the CO2 molecule. This CO2-rich solvent is heated in a regeneration unit to release the CO2 from the solvent. The CO2 stream then undergoes conditioning to remove impurities and bring the gas to an appropriate temperature for compression. The purified CO2 stream is compressed and transported for storage or end-use and the released solvents are recycled to capture more CO2 from the facility.\nAfter the CO2 has been captured, it is usually compressed into a supercritical fluid and then injected underground. Pipelines are the cheapest way of transporting CO2 in large quantities onshore and, depending on the distance and volumes, offshore. Transport via ship has been researched. CO2 can also be transported by truck or rail, albeit at higher cost per tonne of CO2.\n\nTechnical components\n\nCCS processes involve several different technologies working together. Technological components are used to separate and treat CO2 from a gas mixture, compress and transport the CO2, inject it into the subsurface, and monitor the overall process. \nThere are three ways that CO2 can be separated from a gas mixture: post-combustion capture, pre-combustion capture, and oxy-combustion:\n\nIn post combustion capture, the CO2 is removed after combustion of the fossil fuel.\nThe technology for pre-combustion is widely applied in natural gas processing. In these cases, the fossil fuel is partially oxidized, for instance in a gasifier. The CO from the resulting syngas (CO and H2) reacts with added steam (H2O) and is shifted into CO2 and H2. The resulting CO2 can be captured from a relatively pure exhaust stream. The H2 can be used as fuel. Several advantages and disadvantages apply versus post combustion capture.\nIn oxy-fuel combustion the fuel is burned in pure oxygen instead of air. The gas that is released consists of mostly CO2 and water vapor. After water vapor is condensed through cooling, the result is an almost pure CO2 stream. A disadvantage of this technique is that it requires a relatively large amount of oxygen, which is expensive and energy-intensive to produce.\nAbsorption, or carbon scrubbing with amines is the dominant capture technology. Other technologies proposed for carbon capture are membrane gas separation, chemical looping combustion, calcium looping, and use of metal-organic frameworks and other solid sorbents.\nImpurities in CO2 streams, like sulfur dioxides and water vapor, can have a significant effect on their phase behavior and could cause increased pipeline and well corrosion. In instances where CO2 impurities exist, a process is needed to remove them.\n\nStorage and enhanced oil recovery\n\nStoring CO2 involves the injection of captured CO2 into a deep underground geological reservoir of porous rock overlaid by an impermeable layer of rocks, which seals the reservoir and prevents the upward migration of CO2 and escape into the atmosphere. The gas is usually compressed first into a supercritical fluid. When the compressed CO2 is injected into a reservoir, it flows through it, filling the pore space. The reservoir must be at depths greater than 800 m (2,600 ft) to retain the CO2 in a fluid state.\nAs of 2024, around 80% of the CO2 captured annually is used for enhanced oil recovery (EOR). In EOR, CO2 is injected into partially depleted oil fields to enhance production. The CO2 binds with oil to make it less dense, allowing oil to rise to the surface faster. The addition of CO2 also increases the overall reservoir pressure, thereby improving the mobility of the oil, resulting in a higher flow of oil towards the production wells. Depending on the location, EOR results in around two additional barrels of oil for every tonne of CO2 injected into the ground and using that oil produces approximately one tonne of CO2. Oil extracted through EOR is mixed with CO2, which can then mostly be recaptured and re-injected multiple times. This CO2 recycling process can reduce losses to 1%; however, it is energy-intensive. \nAround 20% of captured CO2 is injected into dedicated geological storage, usually deep saline aquifers. These are layers of porous and permeable rocks saturated with salty water. Worldwide, saline formations have higher potential storage capacity than depleted oil wells. Dedicated geologic storage is generally less expensive than EOR because it does not require a high level of CO2 purity and because suitable sites are more numerous, which means pipelines can be shorter.\nVarious other types of reservoirs for storing captured CO2 were being researched or piloted as of 2021: CO2 could be injected into coal beds for enhanced coal bed methane recovery. Ex-situ mineral carbonation involves reacting CO2 with mine tailings or alkaline industrial waste to form stable minerals such as calcium carbonate. In-situ mineral carbonation involves injecting CO2 and water into underground formations that are rich in highly-reactive rocks such as basalt. There, the CO2 may react with the rock to form stable carbonate minerals relatively quickly. Once this process is complete, the risk of CO2 escape from carbonate minerals is estimated to be close to zero.\nThe global capacity for underground CO2 storage is potentially very large and is unlikely to be a constraint on the development of CCS. Total storage capacity has been estimated at between 8,000 and 55,000 gigatonnes. However, a smaller fraction will most likely prove to be technically or commercially feasible. Global capacity estimates are uncertain, particularly for saline aquifers where more site characterization and exploration is still needed.\n\nLong-term CO2 leakage\n\nIn geologic storage, the CO2 is held within the reservoir through several trapping mechanisms: structural trapping by an impermeable rock layer called a caprock, solubility trapping in pore space water, residual trapping in individual or groups of pores, and mineral trapping by reacting with the reservoir rocks to form carbonate minerals. Mineral trapping progresses over time but is extremely slow. \nAfter injection, supercritical CO2 tends to rise until it is trapped beneath a caprock. Once it encounters a caprock, it spreads laterally until it encounters a gap. If there are fault planes near the injection zone, CO2 could migrate along the fault to the surface, leaking into the atmosphere, which would be potentially dangerous to life in the surrounding area. If the injection of CO2 creates pressures underground that are too high, the formation will fracture, potentially causing an earthquake. While research suggests that earthquakes from injected CO2 would be too small to endanger property, they could be large enough to cause a leak. \nAccording to the IPCC, well-managed storage sites likely retain over 99% of injected CO2 for more than a thousand years, where 'likely' means a 66–90% probability. Estimates of long-term leakage rates rely on complex simulations since field data is limited. If very large amounts of CO2 are sequestered, even a 1% leakage rate over 1000 years could cause significant impact on the climate for future generations.\n\nSocial and environmental impacts\n\nEnergy and water requirements\nFacilities with CCS use more energy than those without CCS. The energy consumed by CCS is called an \"energy penalty\". The energy penalty of CCS varies depending on the source of CO2. If the gas from the source has a very high concentration of CO2, additional energy is needed only to dehydrate, compress, and pump the CO2. If the facility produces gas with a lower concentration of CO2, as is the case for power plants, energy is also required to separate CO2 from other gas components. \nEarly studies indicated that to produce the same amount of electricity, a coal power plant would need to burn 14–40% more coal and a natural gas combined cycle power plant would need to burn 11–22% more gas. When CCS is used in coal power plants, it has been estimated that about 60% of the energy penalty originates from the capture process, 30% comes from compression of the extracted CO2, and the remaining 10% comes from pumps and fans. \nDepending on the technology used, CCS can require large amounts of water. For instance, coal-fired power plants with CCS may need to use 50% more water.\n\nPollution\nSince plants with CCS require more fuel to produce the same amount of electricity or heat, the use of CCS increases the \"upstream\" environmental problems of fossil fuels. Upstream impacts include pollution caused by coal mining, emissions from the fuel used to transport coal and gas, emissions from gas flaring, and fugitive methane emissions. \nSince CCS facilities require more fossil fuel to be burned, CCS can cause a net increase in air pollution from those facilities. This can be mitigated by pollution control equipment, however no equipment can eliminate all pollutants. Since liquid amine solutions are used to capture CO2 in many CCS systems, these types of chemicals can also be released as air pollutants if not adequately controlled. Among the chemicals of concern are volatile nitrosamines and nitramines which are carcinogenic when inhaled or drunk in water. \nStudies that consider both upstream and downstream impacts indicate that adding CCS to power plants increases overall negative impacts on human health. The health impacts of adding CCS in the industrial sector are less well-understood. Health impacts vary significantly depending on the fuel used and the capture technology.\nAfter CO2 injected into underground geologic formations, there is a risk of nearby shallow groundwater becoming contaminated. Contamination can occur either from movement of the CO2 into groundwater or from movement of displaced brine. Careful site selection and long-term monitoring are necessary to mitigate this risk.\n\nSudden CO2 leakage\nCO2 is a colorless and odorless gas that accumulates near the ground because it is heavier than air. In humans, exposure to CO2 at concentrations greater than 5% (50,000 parts per million) causes the development of hypercapnia and respiratory acidosis. Concentrations of more than 10% may cause convulsions, coma, and death. CO2 levels of more than 30% act rapidly leading to loss of consciousness in seconds.\nPipelines and storage sites can be sources of large accidental releases of CO2 that can endanger local communities. A 2005 IPCC report stated that \"existing CO2 pipelines, mostly in areas of low population density, accident numbers reported per kilometre of pipeline are very low and are comparable to those for hydrocarbon pipelines.\" The report also stated that the local health and safety risks of geologic CO2 storage were \"comparable\" to the risks of underground storage of natural gas if good site selection processes, regulatory oversight, monitoring, and incident remediation plans are in place. As of 2020, the ways that pipelines can fail is less well-understood for CO2 pipelines than for natural gas or oil pipelines, and few safety standards exist that are specific to CO2 pipelines.\nWhile infrequent, accidents can be serious. In 2020, a CO2 pipeline ruptured following a mudslide near Satartia, Mississippi, causing people nearby to lose consciousness. About 200 people were evacuated and 45 were hospitalized, and some experienced longer-term effects on their health. High concentrations of CO2 in the air also caused vehicle engines to stop running, hampering the rescue effort.\n\nJobs\n\nRetrofitting facilities with CCS can help to preserve jobs and economic prosperity in regions that rely on emissions-intensive industry, while avoiding the economic and social disruption of early retirements. \n\nEquity\n\nIn the United States, the types of facilities that could be retrofitted with CCS are often located in communities that have already borne the negative environmental and health impacts of living near power or industrial facilities. These facilities are disproportionately located in poor and/or minority communities. While there is evidence that CCS can help reduce non-CO2 pollutants along with capturing CO2, environmental justice groups are often concerned that CCS will be used as a way to prolong a facility's lifetime and continue the local harms it causes. Often, community-based organizations would prefer that a facility be shut down and for investment be focused instead on cleaner production processes, such as renewable electricity.\nConstruction of pipelines often involves setting up work camps in remote areas. In Canada and the United States, oil and gas pipeline construction in remote communities is associated with social harms including sexual violence, and this history has led some Indigenous communities to oppose construction of CO2 pipelines. \n\nCost\nProject cost, low technology readiness levels in capture technologies, and a lack of revenue streams are among the main reasons for CCS projects to stop. A commercial-scale project typically requires an upfront capital investment of up to several billion dollars. \nThe cost of CCS varies greatly by CO2 source. If the facility produces a gas mixture with a high concentration of CO2, as is the case for natural gas processing, it can be captured and compressed for USD 15–25/tonne. Power plants, cement plants, and iron and steel plants produce more dilute gas streams, for which the cost of capture and compression is USD 40–120/tonne CO2. In the United States, the cost of onshore pipeline transport is in the range of USD 2–14/tonne CO2, and more than half of onshore storage capacity is estimated to be available below USD 10/tonne CO2. CCS implementations involve multiple technologies that are highly customized to each site, which limits the industry's ability to reduce costs through learning-by-doing.\n\nRole in climate change mitigation\n\nComparison with other mitigation options\nCompared to other options for reducing emissions, CCS is very expensive. For instance, removing CO2 in fossil fuel power plants increases costs by US$50–$200 per tonne of CO2 removed. There are many ways to reduce emissions that cost less than US$20 per tonne of avoided CO2 emissions. Options that have far more potential to reduce emissions at lower cost than CCS include public transit, electric vehicles, and various energy efficiency measures. Wind and solar power are often the lowest-cost ways to produce electricity, even when compared to power plants that do not use CCS. The dramatic fall in the costs of renewable power and batteries has made it difficult for fossil fuel plants with CCS to be cost-competitive, however the inherent intermittency and geographic dependency of these sources means that a complete phaseout of fossil fired generation may not always be feasible.\n\nPriority uses\n\nIn the literature on climate change mitigation, CCS is described as having a small but critical role in reducing greenhouse gas emissions. The IPCC estimated in 2014 that forgoing CCS altogether would make it 138% more expensive to keep global warming within 2 degrees Celsius. Excessive reliance on CCS as a mitigation tool would also be costly and technically unfeasible. According to the IEA, attempting to abate oil and gas consumption only through CCS and direct air capture would cost USD 3.5 trillion per year, which is about the same as the annual revenue of the entire oil and gas industry. Emissions are relatively difficult or expensive to abate without CCS in the following niches:\n\nHeavy Industry: CCS is one of the few available technologies that can significantly reduce emissions associated with the production of cement, chemicals, and steel. A portion of the CO2 emissions from these processes come from chemical reactions, in addition to emissions from burning fuels for heat. For example, approximately one third of emissions from cement making arise from burning fuels and two thirds arise from the chemical process. The Global Cement and Concrete Association say that CCS could reduce carbon emissions by 36%. Cleaner industrial processes are at varying stages of development and some have been commercialized, but are far from being widely deployed.\nRetrofits: CCS can be retrofitted to existing coal and natural gas power plants and industrial facilities to enable the continued operation of existing plants while reducing their emissions.\nNatural gas processing: CCUS is the only solution to reduce the CO2 emissions from natural gas processing. This does not reduce the emissions released when the gas is burned.\nHydrogen: Nearly all hydrogen today is produced from natural gas or coal. Facilities can incorporate CCS to capture the CO2 released in these processes.\nComplement to renewable electricity: In the IEA's scenario for net zero emissions, 251 GW of electricity worldwide are produced by coal and gas plants equipped with CCS by 2050, while 54,679 GW of electricity are produced by solar PV and wind.Although solar and wind energy are typically cheaper, power plants that burn natural gas, biomass, or coal have the advantage of being able to produce electricity in any season and any time of day, and can be dispatched at times of high demand. A small amount of power plant capacity can help to meet the growing need for system flexibility as the share of wind and solar increases. The potential for a robust power grid using 100% renewable energy has been modelled as a feasible option for many regions, which would make fossil CCS in the electricity sector unnecessary. However, this approach may be more expensive. CO2-Plume Geothermal is a proposed way to combine carbon storage with geothermal energy production.\nBioenergy with carbon capture and storage: Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the CO2 that is produced. Under some conditions, BECCS can remove carbon dioxide from the atmosphere.\nThe IPCC stated in 2022 that \"implementation of CCS currently faces technological, economic, institutional, ecological-environmental and socio-cultural barriers.\" Since CCS can only be used with large, stationary emission sources, it cannot reduce the emissions from burning fossil fuels in vehicles and homes. The IEA describes \"excessive expectations and reliance\" on CCS and direct air capture as a common misconception. To reach targets set in the Paris Agreement, CCS must be accompanied by a steep decline in the production and use of fossil fuels.\n\nEffectiveness in reducing greenhouse gas emissions\n\nWhen CCS is used for electricity generation, most studies assume that 85-90% of the CO2 in the exhaust stream is captured. However, industry representatives say actual capture rates are closer to 75%, and have lobbied for government programs to accept this lower target. The potential for a CCS project to reduce emissions depends on several factors in addition to the capture rate. These factors include the amount of additional energy needed to power CCS processes, the source of the additional energy used, and post-capture leakage. The energy needed for CCS usually comes from fossil fuels whose mining, processing, and transport produce emissions. Some studies indicate that under certain circumstances the overall emissions reduction from CCS can be very low, or that adding CCS can even increase emissions relative to no capture. For instance, one study found that in the Petra Nova CCS retrofit of a coal power plant, the actual rate of emissions reduction was so low that it would average only 10.8% over a 20-year time frame. \nSome CCS implementations have not sequestered carbon at their designed capacity, either for business or technical reasons. For instance, in the Shute Creek Gas Processing Facility, around half of the CO2 that has been captured has been sold for EOR, and the other half vented to the atmosphere because it could not be profitably sold. In one year of operation of the Gorgon gas project in Australia, issues with subsurface water prevented two-thirds of captured CO2 from being injected. A 2022 analysis of 13 major CCS projects found that most had either sequestered far less CO2 than originally expected, or had failed entirely.\n\nEmissions with enhanced oil recovery\nThere is controversy over whether carbon capture followed by enhanced oil recovery is beneficial for the climate. The EOR process is energy-intensive because of the need to separate and re-inject CO2 multiple times to minimize losses. If CO2 losses are kept at 1%, the energy required for EOR operations results in around 0.23 tonnes of CO2 emissions per tonne of CO2 sequestered.\nFurthermore, when the oil that is extracted using EOR is subsequently burned, CO2 is released. If these emissions are included in calculations, carbon capture with EOR is usually found to increase overall emissions compared to not using carbon capture at all. If the emissions from burning extracted oil are excluded from calculations, carbon capture with EOR is found to decrease emissions. In arguments for excluding these emissions, it is assumed that oil produced by EOR displaces conventionally produced oil instead of adding to the global consumption of oil. A 2020 review found that scientific papers were roughly evenly split on the question of whether carbon capture with EOR increased or decreased emissions.\nThe International Energy Agency's model of oil supply and demand indicates that 80% of oil produced in EOR will displace other oil on the market. Using this model, it estimated that for each tonne of CO2 sequestered, burning the oil produced by conventional EOR leads to 0.13 tonnes of CO2 emissions (in addition to the 0.24 tonnes of CO2 emitted during the EOR process itself). \n\nPace of implementation\nAs of 2023 CCS captures around 0.1% of global emissions — around 45 million to",
    "source": "wikipedia:Carbon capture and storage",
    "domain": "climate"
  },
  {
    "text": "Hydrogen is a chemical element; it has the symbol H and atomic number 1. It is the lightest and most abundant chemical element in the universe, constituting about 75% of all normal matter. Under standard conditions, hydrogen is a gas of diatomic molecules with the formula H2, called dihydrogen, or sometimes hydrogen gas, molecular hydrogen, or simply hydrogen. Dihydrogen is colorless, odorless, non-toxic, and highly combustible. Stars, including the Sun, mainly consist of hydrogen in a plasma state, while on Earth, hydrogen is found as the gas H2 (dihydrogen) and in molecules, such as in water and organic compounds. The most common isotope of hydrogen, 1H, consists of one proton, one electron, and no neutrons.\nHydrogen gas was first produced artificially in the 17th century by the reaction of acids with metals. Henry Cavendish, in 1766–1781, identified hydrogen gas as a distinct substance and discovered its property of producing water when burned: this is the origin of hydrogen's name, which means 'water-former' (from Ancient Greek: ὕδωρ, romanized: húdōr, lit. 'water', and γεννάω, gennáō, 'I bring forth'). Understanding the colors of light absorbed and emitted by hydrogen was a crucial part of the development of quantum mechanics.\nHydrogen, typically nonmetallic except under extreme pressure, readily forms covalent bonds with most nonmetals, contributing to the formation of compounds like water and various organic substances. Its role is crucial in acid–base reactions, which mainly involve proton exchange among soluble molecules. In ionic compounds, hydrogen can take the form of either a negatively-charged anion, where it is known as hydride, or as a positively-charged cation, H+, hydron. Although tightly bonded to water molecules, hydrons strongly affect the behavior of aqueous solutions, as reflected in the importance of pH. Hydride, on the other hand, is rarely observed because it tends to deprotonate solvents, yielding H2.\nIn the early universe, neutral hydrogen atoms formed about 370,000 years after the Big Bang as the universe expanded and plasma had cooled enough for electrons to remain bound to protons. After stars began to form, most of the hydrogen in the intergalactic medium was re-ionized.\nNearly all hydrogen production is done by transforming fossil fuels, particularly steam reforming of natural gas. It can also be produced from water or saline by electrolysis, but this process is more expensive. Its main industrial uses include fossil fuel processing and ammonia production for fertilizer. Emerging uses for hydrogen include the use of fuel cells to generate electricity.\n\nProperties\n\nAtomic hydrogen\n\nElectron energy levels\n\nThe ground state energy level of the electron in a hydrogen atom is −13.6 electronvolts (eV), equivalent to an ultraviolet photon of roughly 91 nanometers wavelength. The energy levels of hydrogen are referred to by consecutive quantum numbers, with \n \n \n \n n\n =\n 1\n \n \n {\\displaystyle n=1}\n \n being the ground state. The hydrogen spectral series corresponds to emission of light due to transitions from higher to lower energy levels. Each energy level is further split by spin interactions between the electron and proton into four hyperfine levels.\nHigh-precision values for the hydrogen atom energy levels are required for definitions of physical constants. Quantum calculations have identified nine contributions to the energy levels. The eigenvalue from the Dirac equation is the largest contribution. Other terms include relativistic recoil, the self-energy, and the vacuum polarization terms.\n\nNomenclature\nThe standards organization for chemical names, IUPAC, gives general names when the context assumes natural isotope abundance or ignores the isotope. These general names are hydrogen for the neutral atom, hydron for the cation, H+, hydride for the anion, H-. The name proton is often used for the positively-charged cation but this strictly correct only for the cation of the dominant isotope 1H.\n\nIsotopes\n\nHydrogen has three naturally-occurring isotopes, denoted 1H, 2H and 3H. Other, highly-unstable nuclides (4H to 7H) have been synthesized in laboratories but not observed in nature.\n1H is the most common hydrogen isotope, with an abundance of >99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium. It is the only stable isotope with no neutrons (see diproton for a discussion of why others do not exist).\n2H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in the nucleus. Nearly all deuterium nuclei in the universe are thought to have been produced in Big Bang nucleosynthesis, and have endured since then. Deuterium is not radioactive, and is not a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy. Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion.\n3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through beta decay with a half-life of 12.32 years. It is radioactive enough to be used in luminous paint to enhance the visibility of data displays, such as for painting the hands and dial-markers of watches. The watch glass prevents the small amount of radiation from escaping the case. Small amounts of tritium are produced naturally by cosmic rays striking atmospheric gases; tritium has also been released in nuclear weapons tests. It is used in nuclear fusion, as a tracer in isotope geochemistry, and in specialized self-powered lighting devices. Tritium has also been used in chemical and biological labeling experiments as a radiolabel.\nUnique among the elements, distinct names are assigned to hydrogen's isotopes in common use. During the early study of radioactivity, heavy radioisotopes were given their own names, but these are mostly no longer used. The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, but the symbol P was already used for phosphorus and thus was not available for protium. In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry (IUPAC) allows any of D, T, 2H, and 3H to be used, though 2H and 3H are preferred.\nAntihydrogen (H) is the antimatter counterpart to hydrogen. It consists of an anti­proton with a positron. The exotic atom muonium (symbol Mu), composed of an antimuon and an electron, is the anti­matter analogue of hydrogen; IUPAC nomenclature incorporates such hypothetical compounds as muonium chloride (MuCl) and sodium muonide (NaMu), analogous to hydrogen chloride and sodium hydride respectively.\n\nDihydrogen\nUnder standard conditions, hydrogen is a gas of diatomic molecules with the formula H2, officially called \"dihydrogen\", but also called \"molecular hydrogen\", or simply hydrogen. Dihydrogen is a colorless, odorless, flammable gas.\n\nCombustion\n\nHydrogen gas is highly flammable, reacting with oxygen in air to produce liquid water:\n\nThe amount of heat released per mole of hydrogen is −286 kilojoules (kJ), or 141.865 megajoules (MJ) for a one-kilogram (2.2 lb) mass.\nHydrogen gas forms explosive mixtures with air in concentrations from 4%–74% and with chlorine at 5%–95%. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F). In a high-pressure hydrogen leak, the shock wave from the leak itself can heat air to the autoignition temperature, leading to flaming and possibly explosion.\nHydrogen flames emit faint blue and ultraviolet light. Flame detectors are used to detect hydrogen fires as they are nearly invisible to the naked eye in daylight.\n\nSpin isomers\n\nMolecular H2 exists as two nuclear isomers that differ in the spin states of their nuclei. In the ortho­hydrogen form, the spins of the two nuclei are parallel, forming a spin triplet state having a total molecular spin \n \n \n \n S\n =\n 1\n \n \n {\\displaystyle S=1}\n \n; in the para­hydrogen form the spins are anti­parallel and form a spin singlet state having spin \n \n \n \n S\n =\n 0\n \n \n {\\displaystyle S=0}\n \n. The equilibrium ratio of ortho- to para-hydrogen depends on temperature. At room temperature or warmer, equilibrium hydrogen gas contains about 25% of the para form and 75% of the ortho form. The ortho form is an excited state, having higher energy than the para form by 1.455 kJ/mol, and it converts to the para form over the course of several minutes when cooled to low temperature. The thermal properties of these isomers differ because each has distinct rotational quantum states.\nThe ortho-to-para ratio in H2 is an important consideration in the liquefaction and storage of liquid hydrogen: the conversion from ortho to para is exothermic, and produces sufficient heat to evaporate most of the liquid if the conversion to para­hydrogen does not occur during the cooling process. Catalysts for the ortho-para inter­conversion, such as ferric oxide and activated carbon compounds, are therefore used during hydrogen cooling to avoid this loss of liquid.\n\nPhases\n\nLiquid hydrogen can exist at temperatures below hydrogen's critical point of 33 kelvins (−240.2 °C; −400.3 °F). However, for it to be in a fully liquid state at atmospheric pressure, H2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). Hydrogen was liquefied by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask.\nLiquid hydrogen becomes solid hydrogen at standard pressure below hydrogen's melting point of 14.01 K (−259.14 °C; −434.45 °F). Distinct solid phases exist, known as Phase I through Phase V, each exhibiting a characteristic molecular arrangement. Liquid and solid phases can exist in combination at the triple point; this mixture is known as slush hydrogen.\nMetallic hydrogen, a phase obtained at extremely high pressures (in excess of 400 billion Pa (58,000,000 psi)), is an electrical conductor. It is believed to exist deep within giant planets like Jupiter.\nWhen ionized, hydrogen becomes a plasma. This is the form in which hydrogen exists within stars.\n\nThermal and physical properties\n\nHistory\n\n18th century\n\nIn 1671, Irish scientist Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas.\nBoyle did not note that the gas was flammable, but hydrogen would play a key role in overturning the phlogiston theory of combustion.\nIn 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction \"inflammable air\". He speculated that \"inflammable air\" was in fact identical to the hypothetical substance \"phlogiston\" and further finding in 1781 that the gas produces water when burned. He is usually given credit for the discovery of hydrogen as an element.\n\nIn 1783, Antoine Lavoisier identified the element that came to be known as hydrogen when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned. Lavoisier produced hydrogen for his experiments on mass conservation by treating metallic iron with a stream of water through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactions:\n\nFe + H2O → FeO + H2\n2 Fe + 3 H2O → Fe2O3 + 3 H2\n3 Fe + 4 H2O → Fe3O4 + 4 H2\nMany metals react similarly with water, leading to the production of hydrogen. In some situations, this H2-producing process is problematic, for instance in the case of zirconium cladding on nuclear fuel rods.\n\n19th century\nBy 1806 hydrogen was used to fill balloons.\nFrançois Isaac de Rivaz built the first de Rivaz engine, an internal combustion engine powered by a mixture of hydrogen and oxygen, in 1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819. The Döbereiner's lamp and limelight were invented in 1823. Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask. He produced solid hydrogen the next year.\nOne of the first quantum effects to be explicitly noticed, although not understood at the time, was James Clerk Maxwell's observation that the specific heat capacity of H2 unaccountably departs from that of a diatomic gas below room temperature, and begins to increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H2 because of its low mass. These widely-spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect.\n\n20th century\nThe existence of the hydride anion was suggested by Gilbert N. Lewis in 1916 for group 1 and group 2 salt-like compounds. In 1920, Moers electrolyzed molten lithium hydride (LiH), producing a stoichiometric quantity of hydrogen at the anode.\n\nBecause of its simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structure. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, in which the electron \"orbits\" the proton, like how Earth orbits the Sun. However, the electron and proton are held together by electrostatic attraction, while planets and celestial objects are held by gravity. Due to the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.\nHydrogen's unique position as the only neutral atom for which the Schrödinger equation can be directly solved, has significantly contributed to the understanding of quantum mechanics through the exploration of its energetics. Furthermore, study of the corresponding simplicity of the hydrogen molecule and the corresponding cation, H+2, brought understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.\n\nHydrogen-lifted airship\n\nBecause H2 has only 7% the density of air, it was once widely used as a lifting gas in balloons and airships. The first hydrogen-filled balloon was invented by Jacques Charles in 1783. Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard. German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins, the first of which had its maiden flight in 1900. Regularly-scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships in the form of blimps were used as observation platforms and bombers during World War II, especially on the US Eastern seaboard.\nThe first non-stop transatlantic crossing was made by the British airship R34 in 1919 and regular passenger service resumed in the 1920s. Hydrogen was used in the Hindenburg, which caught fire over New Jersey on 6 May 1937. The hydrogen that filled the airship was ignited, possibly by static electricity, and burst into flames. Following this disaster, commercial hydrogen airship travel ceased. Hydrogen is still used, in preference to non-flammable but more expensive helium, as a lifting gas for weather balloons.\n\nDeuterium and tritium\nDeuterium was discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck. Heavy water, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.\n\nChemistry\n\nReactions of H2\n\nH2 is relatively unreactive. The thermodynamic basis of this low reactivity is the very strong H–H bond, with a bond dissociation energy of 435.7 kJ/mol. It does form coordination complexes called dihydrogen complexes. These species provide insights into the early steps in the interactions of hydrogen with metal catalysts. According to neutron diffraction, the metal and two H atoms form a triangle in these complexes. The H-H bond remains intact but is elongated. They are acidic.\nAlthough exotic on Earth, the H+3 ion is common in the universe. It is a triangular species, like the aforementioned dihydrogen complexes. It is known as protonated molecular hydrogen or the trihydrogen cation.\nHydrogen reacts with chlorine to produce HCl, and with bromine to produce HBr, via a chain reaction. The reaction requires initiation. For example, in the case of Br2, the dibromine molecule is split apart: Br2 + (UV light) → 2Br•. Propagating reactions consume hydrogen molecules and produce HBr, as well as Br and H atoms: \n\nFinally the terminating reaction:\n\nconsumes the remaining atoms.\nThe addition of H2 to unsaturated organic compounds, such as alkenes and alkynes, is called hydrogenation. Even if the reaction is energetically favorable, it does not occur spontaneously even at higher temperatures. In the presence of a catalyst like finely divided platinum or nickel, the reaction proceeds at room temperature.\n\nHydrogen-containing compounds\n\nHydrogen can exist in both +1 and −1 oxidation states, forming compounds through ionic and covalent bonding. The element is part of a wide range of substances, including water, hydrocarbons, and numerous other organic compounds. The H+ ion—commonly referred to as a proton due to its single proton and absence of electrons—is central to acid–base chemistry, although the proton does not move freely. In the Brønsted–Lowry framework, acids are defined by their ability to donate H+ ions to bases.\nHydrogen forms a vast variety of compounds with carbon, known as hydrocarbons, and an even greater diversity with other elements (heteroatoms), giving rise to the broad class of organic compounds often associated with living organisms.\n\nHydrogen compounds with hydrogen in the oxidation state −1 are known as hydrides, which are usually formed between hydrogen and metals. The hydrides can be ionic (aka saline), covalent, or metallic. With heating, H2 reacts efficiently with the alkali and alkaline earth metals to give the ionic hydrides of the formulas MH and MH2, respectively. These salt-like crystalline compounds have high melting points and all react with water to liberate hydrogen. Covalent hydrides include boranes and polymeric aluminium hydride. Transition metals form metal hydrides via continuous dissolution of hydrogen into the metal. A well-known hydride is lithium aluminium hydride: the [AlH4]− anion carries hydridic centers firmly attached to the Al(III). Perhaps the most extensive series of hydrides are the boranes, compounds consisting only of boron and hydrogen.\nHydrides can bond to these electropositive elements not only as a terminal ligand but also as bridging ligands. In diborane (B2H6), four hydrogen atoms are terminal, while two bridge between the two boron atoms.\n\nHydrogen bonding\n\nWhen bonded to a more electronegative element, particularly fluorine, oxygen, or nitrogen, hydrogen can participate in a form of medium-strength noncovalent bonding with another electronegative element with a lone pair like oxygen or nitrogen. This phenomenon, called hydrogen bonding, is critical to the stability of many biological molecules. Hydrogen bonding alters molecule structures, viscosity, solubility, melting and boiling points, and even protein folding dynamics.\n\nProtons and acids\n\nIn water, hydrogen bonding plays an important role in reaction thermodynamics. A hydrogen bond can shift over to proton transfer.\nUnder the Brønsted–Lowry acid–base theory, acids are proton donors, while bases are proton acceptors.\nA bare proton (H+) essentially cannot exist in anything other than a vacuum. Otherwise it attaches to other atoms, ions, or molecules. Even chemical species as inert as methane can be protonated. The term \"proton\" is used loosely and metaphorically to refer to solvated hydrogen cations attached to other solvated chemical species; it is denoted \"H+\" without any implication that any single protons exist freely in solution as a species. To avoid the implication of the naked proton in solution, acidic aqueous solutions are sometimes considered to contain the \"hydronium ion\" ([H3O]+), or still more accurately, [H9O4]+. Other oxonium ions are found when water is in acidic solution with other solvents.\nThe concentration of these solvated protons determines the pH of a solution, a logarithmic scale that reflects its acidity or basicity. Lower pH values indicate higher concentrations of hydronium ions, corresponding to more acidic conditions.\n\nOccurrence\n\nCosmic\n\nHydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass. and >90% by number of atoms. In the early universe, protons formed in the first second after the Big Bang; neutral hydrogen atoms formed about 370,000 years later during the recombination epoch as the universe expanded and plasma had cooled enough for electrons to remain bound to protons.\nIn astrophysics, neutral hydrogen in the interstellar medium is called H I and ionized hydrogen is called H II. Radiation from stars ionizes H I to H II, creating spheres of ionized H II around stars. In the chronology of the universe neutral hydrogen dominated until the birth of stars during the era of reionization, which then produced bubbles of ionized hydrogen that grew and merged over hundreds of millions of years.\nThese are the source of the 21-centimeter hydrogen line, at 1420 MHz, that is detected in order to probe primordial hydrogen. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the universe up to a redshift of z = 4.\nHydrogen is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through the proton-proton reaction in lower-mass stars, and through the CNO cycle of nuclear fusion in stars more massive than the Sun.\nProtonated molecular hydrogen (H+3) is found in the interstellar medium, where it is generated by ionization of molecular hydrogen by cosmic rays. This ion has also been observed in the upper atmosphere of Jupiter. The ion is long-lived in outer space due to the low temperature and density. H+3 is one of the most abundant ions in the universe, and it plays a notable role in the chemistry of the interstellar medium. Neutral triatomic hydrogen H3 can exist only in an excited form and is unstable.\n\nTerrestrial\nHydrogen is the third most abundant element on the Earth's surface, mostly existing within chemical compounds such as hydrocarbons and water. Elemental hydrogen is normally in the form of a gas, H2, at standard conditions. It is present in a very low concentration in Earth's atmosphere (around 0.53 parts per million on a molar basis) because of its light weight, which enables it to escape the atmosphere more rapidly than heavier gases. Despite its low concentration in the atmosphere, terrestrial hydrogen is sufficiently abundant to support the metabolism of several varieties of bacteria.\nLarge underground deposits of hydrogen gas have been discovered in several countries including Mali, France and Australia. As of 2024, it is uncertain how much underground hydrogen can be extracted economically.\n\nProduction and storage\n\nIndustrial routes\nNearly all of the world's current supply of hydrogen gas (H2) is produced from fossil fuels, with less than 1% of hydrogen being produced by low-emissions technologies in 2025. Many methods exist for producing H2, but three dominate commercially: steam reforming often coupled to water-gas shift, partial oxidation of hydrocarbons, and water electrolysis.\n\nSteam reforming\n\nHydrogen is mainly produced by steam methane reforming (SMR), the reaction of water and methane. Thus, at high temperature (1,000–1,400 K [730–1,130 °C; 1,340–2,060 °F]), steam (water vapor) reacts with methane to yield carbon monoxide and H2.\n\nProducing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. The production of natural gas feedstock also produces emissions such as vented and fugitive methane, which further contributes to the overall carbon footprint of hydrogen.\nThis reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa [20 atm; 590 inHg]) because high-pressure H2 is the most marketable product, and pressure swing adsorption (PSA) purification systems work better at higher pressures. The product mixture is known as \"synthesis gas\" because it is often used directly for the production of methanol and many other compounds. Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly-optimized technology is the formation of coke or carbon:\n\nTherefore, steam reforming typically employs an excess of H2O. Additional hydrogen can be recovered from the steam by using carbon monoxide through the water gas shift reaction (WGS). This process requires an iron oxide catalyst:\n\nHydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for ammonia production, hydrogen is generated from natural gas.\n\nPartial oxidation of hydrocarbons\nOther methods for CO and H2 production include partial oxidation of hydrocarbons:\n\nAlthough less important commercially, coal can serve as a prelude to the above shift reaction:\n\nOlefin production units may produce substantial quantities of byproduct hydrogen, particularly from cracking light feedstocks like ethane or propane.\n\nWater electrolysis\n\nElectrolysis of water is a conceptually simple method of producing hydrogen. \n\nCommercial electrolyzers use nickel-based catalysts in strongly alkaline solution. Platinum is a better catalyst but is expensive. The hydrogen created through electrolysis using renewable energy is commonly referred to as \"green hydrogen\".\nElectrolysis of brine to yield chlorine also produces high-purity hydrogen as a co-product, which is used for a variety of transformations such as hydrogenations.\nThe electrolysis process is more expensive than producing hydrogen from methane without carbon capture and storage.\nInnovation in hydrogen electrolyzers could make large-scale production of hydrogen from electricity more cost-competitive.\n\nMethane pyrolysis\nHydrogen can be produced by pyrolysis of natural gas (methane), producing hydrogen gas and solid carbon with the aid of a catalyst and 74 kJ/mol input heat:\n\nThe carbon may be sold as a manufacturing feedstock or fuel, or landfilled. This route could have a lower carbon footprint than existing hydrogen production processes, but mechanisms for removing the carbon and preventing it from reacting with the catalyst remain obstacles for industrial-scale use.\n\nThermochemical\nWater splitting is the process by which water is decomposed into its components. Relevant to the biological scenario is this equation:\n\nThe reaction occurs in the light-dependent reactions in all photosynthetic organisms. A few organisms, including the alga Chlamydomonas reinhardtii and cyanobacteria, have evolved a second step in the dark reactions in which protons and electrons are reduced to form H2 gas by specialized hydrogenases in the chloroplast.\nEfforts have been undertaken to genetically modify cyanobacterial hydrogenases to more efficiently generate H2 gas even in the presence of oxygen. Efforts have also been undertaken with genetically‐modified alga in a bioreactor.\nRelevant to the thermal water-splitting scenario is this simple equation:\n\nOver 200 thermochemical cycles can be used for water splitting. Many of these cycles such as the iron oxide cycle, cerium(IV) oxide–cerium(III) oxide cycle, zinc–zinc oxide cycle, sulfur–iodine cycle, copper–chlorine cycle and hybrid sulfur cycle have been evaluated for their commercial potential to produce hydrogen and oxygen from water and heat without using electricity. A number of labs (including in France, Germany, Greece, Japan, and the United States) are developing thermochemical methods to produce hydrogen from solar energy and water.\n\nNatural routes\n\nBiohydrogen\n\nH2 is produced in organisms by enzymes called hydrogenases. This process allows the host organism to use fermentation as a source of energy. These same enzymes also can oxidize H2, such that the host organisms can subsist by reducing oxidized substrates using electrons extracted from H2.\nHydrogenase enzymes feature iron or iron–nickel centers at their active sites. The natural cycle of hydrogen production and consumption by organisms is called the hydrogen cycle.\nSome bacteria such as Mycobacterium smegmatis can use the small amount of hydrogen in the atmosphere as a source of energy when other sources are lacking. Their hydrogenases feature small channels that exclude oxygen from the active site, permitting the reaction to occur even though the hydrogen concentration is very low and the oxygen concentration is as in normal air.\nConfirming the existence of hydrogenase‐employing microbes in the human gut, H2 occurs in human breath. The concentration in the breath of fasting people at rest is typic",
    "source": "wikipedia:Hydrogen",
    "domain": "climate"
  },
  {
    "text": "Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat, potential and kinetic. Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.\nSome technologies provide short-term energy storage, while others can endure for much longer. Bulk energy storage is currently dominated by hydroelectric dams, both conventional as well as pumped. Grid energy storage is a collection of methods used for energy storage on a large scale within an electrical power grid.\nCommon examples of energy storage are the rechargeable battery, which stores chemical energy readily convertible to electricity to operate a mobile phone; the hydroelectric dam, which stores energy in a reservoir as gravitational potential energy; and ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling. Fossil fuels such as coal and gasoline store ancient energy derived from sunlight by organisms that later died, became buried and over time were then converted into these fuels. Food (which is made by the same process as fossil fuels) is a form of energy stored in chemical form.\n\nHistory\nIn the 20th century grid, electrical power was largely generated by burning fossil fuel. When less power was required, less fuel was burned. Hydropower, a mechanical energy storage method, is the most widely adopted mechanical energy storage, and has been in use for centuries. Large hydropower dams have been energy storage sites for more than one hundred years. Concerns with air pollution, energy imports, and global warming have spawned the growth of renewable energy such as solar and wind power. Wind power is uncontrolled and may be generating at a time when no additional power is needed. Solar power varies with cloud cover and at best is only available during daylight hours, while demand often peaks after sunset (see duck curve). Interest in storing power from these intermittent sources grows as the renewable energy industry begins to generate a larger fraction of overall energy consumption. In 2023 BloombergNEF forecast total energy storage deployments to grow at a compound annual growth rate of 27 percent through 2030.\nOff grid electrical use was a niche market in the 20th century, but in the 21st century, it has expanded. Portable devices are in use all over the world. Solar panels are now common in the rural settings worldwide. Access to electricity is now a question of economics and financial viability, and not solely on technical aspects. Electric vehicles are gradually replacing combustion-engine vehicles. However, powering long-distance transportation without burning fuel remains in development.\n\nMethods\n\nOutline\nThe following list includes a variety of types of energy storage:\n\nMechanical\n\nEnergy can be stored in water pumped to a higher elevation using pumped storage methods or by moving solid matter to higher locations (gravity batteries). Other commercial mechanical methods include compressing air and flywheels that convert electric energy into internal energy or kinetic energy and then back again when electrical demand peaks.\n\nHydroelectricity\n\nHydroelectric dams with reservoirs can be operated to provide electricity at times of peak demand. Water is stored in the reservoir during periods of low demand and released when demand is high. The net effect is similar to pumped storage, but without the pumping loss.\nWhile a hydroelectric dam does not directly store energy from other generating units, it behaves equivalently by lowering output in periods of excess electricity from other sources. In this mode, dams are one of the most efficient forms of energy storage, because only the timing of its generation changes. Hydroelectric turbines have a start-up time on the order of a few minutes.\n\nPumped hydro\n\nWorldwide, pumped-storage hydroelectricity (PSH) is the largest-capacity form of active grid energy storage available, and, as of March 2012, the Electric Power Research Institute (EPRI) reports that PSH accounts for more than 99% of bulk storage capacity worldwide, representing around 127,000 MW. PSH energy efficiency varies in practice between 70% and 80%, with claims of up to 87%.\nAt times of low electrical demand, excess generation capacity is used to pump water from a lower source into a higher reservoir. When demand grows, water is released back into a lower reservoir (or waterway or body of water) through a turbine, generating electricity. Reversible turbine-generator assemblies act as both a pump and turbine (usually a Francis turbine design). Nearly all facilities use the height difference between two water bodies. Pure pumped-storage plants shift the water between reservoirs, while the \"pump-back\" approach is a combination of pumped storage and conventional hydroelectric plants that use natural stream-flow.\n\nCompressed air\n\nCompressed-air energy storage (CAES) uses surplus energy to compress air for subsequent electricity generation. Small-scale systems have long been used in such applications as propulsion of mine locomotives. The compressed air is stored in an underground reservoir, such as a salt dome.\nCompressed-air energy storage (CAES) plants can bridge the gap between production volatility and load. CAES storage addresses the energy needs of consumers by effectively providing readily available energy to meet demand. Renewable energy sources like wind and solar energy vary. So at times when they provide little power, they need to be supplemented with other forms of energy to meet energy demand. Compressed-air energy storage plants can take in the surplus energy output of renewable energy sources during times of energy over-production. This stored energy can be used at a later time when demand for electricity increases or energy resource availability decreases.\nCompression of air creates heat; the air is warmer after compression. Expansion requires heat. If no extra heat is added, the air will be much colder after expansion. If the heat generated during compression can be stored and used during expansion, efficiency improves considerably. A CAES system can deal with the heat in three ways. Air storage can be adiabatic, diabatic, or isothermal. Another approach uses compressed air to power vehicles.\n\nFlywheel\n\nFlywheel energy storage (FES) works by accelerating a rotor (a flywheel) to a very high speed, holding energy as rotational energy. When energy is added the rotational speed of the flywheel increases, and when energy is extracted, the speed declines, due to conservation of energy.\nMost FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are under consideration.\nFES systems have rotors made of high strength carbon-fiber composites, suspended by magnetic bearings and spinning at speeds from 20,000 to over 50,000 revolutions per minute (rpm) in a vacuum enclosure. Such flywheels can reach maximum speed (\"charge\") in a matter of minutes. The flywheel system is connected to a combination electric motor/generator.\nFES systems have relatively long lifetimes (lasting decades with little or no maintenance; full-cycle lifetimes quoted for flywheels range from in excess of 105, up to 107, cycles of use), high specific energy (100–130 W·h/kg, or 360–500 kJ/kg) and power density.\n\nSolid mass gravitational\n\nChanging the altitude of solid masses can store or release energy via an elevating system driven by an electric motor/generator. Studies suggest energy can begin to be released with as little as 1 second warning, making the method a useful supplemental feed into an electricity grid to balance load surges.\nEfficiencies can be as high as 85% recovery of stored energy.\nThis can be achieved by siting the masses inside old vertical mine shafts or in specially constructed towers where the heavy weights are winched up to store energy and allowed a controlled descent to release it. At 2020 a prototype vertical store is being built in Edinburgh, Scotland\nPotential energy storage or gravity energy storage was under active development in 2013 in association with the California Independent System Operator. It examined the movement of earth-filled hopper rail cars driven by electric locomotives from lower to higher elevations.\nOther proposed methods include:\n\nusing rails, cranes, or elevators to move weights up and down\nusing high-altitude solar-powered balloon platforms supporting winches to raise and lower solid masses slung underneath them\nusing winches supported by an ocean barge to take advantage of a 4 km (13,000 ft) elevation difference between the sea surface and the seabed\n\nThermal\n\nThermal energy storage (TES) is the temporary storage or removal of heat.\n\nSensible heat thermal\nSensible heat storage take advantage of sensible heat in a material to store energy.\nSeasonal thermal energy storage (STES) allows heat or cold to be used months after it was collected from waste energy or natural sources. The material can be stored in contained aquifers, clusters of boreholes in geological substrates such as sand or crystalline bedrock, in lined pits filled with gravel and water, or water-filled mines. Seasonal thermal energy storage (STES) projects often have paybacks in four to six years. An example is Drake Landing Solar Community in Canada, for which 97% of the year-round heat is provided by solar-thermal collectors on garage roofs, enabled by a borehole thermal energy store (BTES). In Braedstrup, Denmark, the community's solar district heating system also uses STES, at a temperature of 65 °C (149 °F). A heat pump, which runs only while surplus wind power is available. It is used to raise the temperature to 80 °C (176 °F) for distribution. When wind energy is not available, a gas-fired boiler is used. Twenty percent of Braedstrup's heat is solar.\n\nLatent heat thermal (LHTES)\nLatent heat thermal energy storage systems work by transferring heat to or from a material to change its phase. A phase-change is the melting, solidifying, vaporizing or liquifying. Such a material is called a phase change material (PCM). Materials used in LHTESs often have a high latent heat so that at their specific temperature, the phase change absorbs a large amount of energy, much more than sensible heat.\nA steam accumulator is a type of LHTES where the phase change is between liquid and gas and uses the latent heat of vaporization of water. Ice storage air conditioning systems use off-peak electricity to store cold by freezing water into ice. The stored cold in ice releases during melting process and can be used for cooling at peak hours.\n\nCryogenic thermal energy storage\n\nAir can be liquefied by cooling using electricity and stored as a cryogen with existing technologies. The liquid air can then be expanded through a turbine and the energy recovered as electricity. The system was demonstrated at a pilot plant in the UK in 2012.\nIn 2019, Highview announced plans to build a 50 MW in the North of England and northern Vermont, with the proposed facility able to store five to eight hours of energy, for a 250–400 MWh storage capacity.\n\nCarnot battery\n\nElectrical energy can be stored thermally by resistive heating or heat pumps, and the stored heat can be converted back to electricity via Rankine cycle or Brayton cycle. This technology has been studied to retrofit coal-fired power plants into fossil-fuel free generation systems. Coal-fired boilers are replaced by high-temperature heat storage charged by excess electricity from renewable energy sources. In 2020, German Aerospace Center started to construct the world's first large-scale Carnot battery system, which has 1,000 MWh storage capacity.\n\nElectrochemical\n\nRechargeable battery\n\nA rechargeable battery comprises one or more electrochemical cells. It is known as a 'secondary cell' because its electrochemical reactions are electrically reversible. Rechargeable batteries come in many shapes and sizes, ranging from button cells to megawatt grid systems.\nRechargeable batteries have lower total cost of use and environmental impact than non-rechargeable (disposable) batteries. Some rechargeable battery types are available in the same form factors as disposables. Rechargeable batteries have higher initial cost but can be recharged very cheaply and used many times.\nCommon rechargeable battery chemistries include:\n\nLead–acid battery: Lead acid batteries hold the largest market share of electric storage products. A single cell produces about 2V when charged. In the charged state the metallic lead negative electrode and the lead sulfate positive electrode are immersed in a dilute sulfuric acid (H2SO4) electrolyte. In the discharge process electrons are pushed out of the cell as lead sulfate is formed at the negative electrode while the electrolyte is reduced to water.\nLead–acid battery technology has been developed extensively. Upkeep requires minimal labor and its cost is low. The battery's available energy capacity is subject to a quick discharge resulting in a low life span and low energy density.\nNickel–cadmium battery (NiCd): Uses nickel oxide hydroxide and metallic cadmium as electrodes. Cadmium is a toxic element, and was banned for most uses by the European Union in 2004. Nickel–cadmium batteries have been almost completely replaced by nickel–metal hydride (NiMH) batteries.\nNickel–metal hydride battery (NiMH): First commercial types were available in 1989. These are now a common consumer and industrial type. The battery has a hydrogen-absorbing alloy for the negative electrode instead of cadmium.\nLithium-ion battery: The choice in many consumer electronics and have one of the best energy-to-mass ratios and a very slow self-discharge when not in use.\nLithium-ion polymer battery: These batteries are light in weight and can be made in any shape desired.\nAluminium-sulfur battery with rock salt crystals as electrolyte: aluminium and sulfur are Earth-abundant materials and are much cheaper than traditional lithium.\n\nFlow battery\n\nA flow battery works by passing a solution over a membrane where ions are exchanged to charge or discharge the cell. Cell voltage is chemically determined by the Nernst equation and ranges, in practical applications, from 1.0 V to 2.2 V. Storage capacity depends on the volume of solution. A flow battery is technically akin both to a fuel cell and an electrochemical accumulator cell. Commercial applications are for long half-cycle storage such as backup grid power.\n\nSupercapacitor\n\nSupercapacitors, also called electric double-layer capacitors (EDLC) or ultracapacitors, are a family of electrochemical capacitors that do not have conventional solid dielectrics. Capacitance is determined by two storage principles, double-layer capacitance and pseudocapacitance.\nSupercapacitors bridge the gap between conventional capacitors and rechargeable batteries. They store the most energy per unit volume or mass (energy density) among capacitors. They support up to 10,000 farads/1.2 Volt, up to 10,000 times that of electrolytic capacitors, but deliver or accept less than half as much power per unit time (power density).\nWhile supercapacitors have specific energy and energy densities that are approximately 10% of batteries, their power density is generally 10 to 100 times greater. This results in much shorter charge/discharge cycles. Also, they tolerate many more charge-discharge cycles than batteries.\nSupercapacitors have many applications, including:\n\nLow supply current for memory backup in static random-access memory (SRAM)\nPower for cars, buses, trains, cranes and elevators, including energy recovery from braking, short-term energy storage and burst-mode power delivery\n\nChemical\n\nPower-to-gas\n\nPower-to-gas is the conversion of electricity to a gaseous fuel such as hydrogen or methane. The three commercial methods use electricity to reduce water into hydrogen and oxygen by means of electrolysis.\nIn the first method, hydrogen is injected into the natural gas grid or is used for transportation. The second method is to combine the hydrogen with carbon dioxide to produce methane using a methanation reaction such as the Sabatier reaction, or biological methanation, resulting in an extra energy conversion loss of 8%. The methane may then be fed into the natural gas grid. The third method uses the output gas of a wood gas generator or a biogas plant, after the biogas upgrader is mixed with the hydrogen from the electrolyzer, to upgrade the quality of the biogas.\n\nHydrogen\n\nThe element hydrogen can be a form of stored energy. Hydrogen can produce electricity via a hydrogen fuel cell.\nAt penetrations below 20% of the grid demand, renewables do not severely change the economics; but beyond about 20% of the total demand, external storage becomes important. If these sources are used to make ionic hydrogen, they can be freely expanded. A 5-year community-based pilot program using wind turbines and hydrogen generators began in 2007 in the remote community of Ramea, Newfoundland and Labrador. A similar project began in 2004 on Utsira, a small Norwegian island.\nEnergy losses involved in the hydrogen storage cycle come from the electrolysis of water, liquification or compression of the hydrogen and conversion to electricity.\nHydrogen can also be produced from aluminum and water by stripping aluminum's naturally occurring aluminum oxide barrier and introducing it to water. This method is beneficial because recycled aluminum cans can be used to generate hydrogen; however, systems to harness this option have not been commercially developed and are much more complex than electrolysis systems. Common methods to strip the oxide layer include caustic catalysts such as sodium hydroxide and alloys with gallium, mercury and other metals.\nUnderground hydrogen storage is the practice of hydrogen storage in caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in caverns by Imperial Chemical Industries for many years without any difficulties. The European Hyunder project indicated in 2013 that storage of wind and solar energy using underground hydrogen would require 85 caverns.\nPowerpaste is a magnesium and hydrogen -based fluid gel that releases hydrogen when reacting with water. It was invented, patented and is being developed by the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) of the Fraunhofer-Gesellschaft. Powerpaste is made by combining magnesium powder with hydrogen to form magnesium hydride in a process conducted at 350 °C and five to six times atmospheric pressure. An ester and a metal salt are then added to make the finished product. Fraunhofer states that they are building a production plant slated to start production in 2021, which will produce 4 tons of Powerpaste annually. Fraunhofer has patented their invention in the United States and EU. Fraunhofer claims that Powerpaste is able to store hydrogen energy at 10 times the energy density of a lithium battery of a similar dimension and is safe and convenient for automotive situations.\n\nMethane\n\nMethane is the simplest hydrocarbon with the molecular formula CH4. Methane is more easily stored and transported than hydrogen. Storage and combustion infrastructure (pipelines, gasometers, power plants) are mature.\nSynthetic natural gas (syngas or SNG) can be created in a multi-step process, starting with hydrogen and oxygen. Hydrogen is then reacted with carbon dioxide in a Sabatier process, producing methane and water. Methane can be stored and later used to produce electricity. The resulting water is recycled, reducing the need for water. In the electrolysis stage, oxygen is stored for methane combustion in a pure oxygen environment at an adjacent power plant, eliminating nitrogen oxides.\nMethane combustion produces carbon dioxide (CO2) and water. The carbon dioxide can be recycled to boost the Sabatier process and water can be recycled for further electrolysis. Methane production, storage and combustion recycles the reaction products.\nThe CO2 has economic value as a component of an energy storage vector, not a cost as in carbon capture and storage.\n\nPower-to-liquid\nPower-to-liquid is similar to power to gas except that the hydrogen is converted into liquids such as methanol or ammonia. These are easier to handle than gases, and require fewer safety precautions than hydrogen. They can be used for transportation, including aircraft, but also for industrial purposes or in the power sector.\n\nBiofuels\n\nVarious biofuels such as biodiesel, vegetable oil, alcohol fuels, or biomass can replace fossil fuels. Various chemical processes can convert the carbon and hydrogen in coal, natural gas, plant and animal biomass and organic wastes into short hydrocarbons suitable as replacements for existing hydrocarbon fuels. Examples are Fischer–Tropsch diesel, methanol, dimethyl ether and syngas. This diesel source was used extensively in World War II in Germany, which faced limited access to crude oil supplies. South Africa produces most of the country's diesel from coal for similar reasons. A long term oil price above US$35/bbl may make such large scale synthetic liquid fuels economical.\n\nPower-to-Solid\nSimilar to power-to-liquid and power-to-gas concepts, energy may be stored in solid materials, for example in metals such as iron, aluminium, and non-metallic materials such as sulfur. Energy in the form of electricity or solar heat is stored chemically and can be released on-demand. Historically, solid energy carriers have been long used in fireworks and rockets.\n\nAluminum\nAluminum has been proposed as an energy store by a number of researchers. Its electrochemical equivalent (8.04 Ah/cm3) is nearly four times greater than that of lithium (2.06 Ah/cm3). Energy can be extracted from aluminum by reacting it with water to generate hydrogen. However, it must first be stripped of its natural oxide layer, a process which requires pulverization, chemical reactions with caustic substances, or alloys. The byproduct of the reaction to create hydrogen is aluminum oxide, which can be recycled into aluminum with the Hall–Héroult process, making the reaction theoretically renewable. If the Hall-Héroult Process is run using solar or wind power, aluminum could be used to store the energy produced at higher efficiency than direct solar electrolysis.\n\nBoron, silicon, and zinc\nBoron, silicon, and zinc have been proposed as energy storage solutions.\n\nOther chemical\nThe organic compound norbornadiene converts to quadricyclane upon exposure to light, storing solar energy as the energy of chemical bonds. A working system has been developed in Sweden as a molecular solar thermal system.\n\nElectrical methods\n\nCapacitor\n\nA capacitor (originally known as a 'condenser') is a passive two-terminal electrical component used to store energy electrostatically. Practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system. Capacitors are commonly used in electronic devices to maintain power supply while batteries change. (This prevents loss of information in devices with volatile memory.) Conventional capacitors provide less than 360 joules per kilogram, while a conventional alkaline battery has a density of 590 kJ/kg.\nCapacitors store energy in an electrostatic field between their plates. Given a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate and negative charge (-Q) to collect on the other plate. If a battery is attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or alternating voltage is applied across the leads of the capacitor, a displacement current can flow. Besides capacitor plates, charge can also be stored in a dielectric layer.\nCapacitance is greater given a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates emits a small amount of leakage current and has an electric field strength limit, known as the breakdown voltage. However, the effect of recovery of a dielectric after a high-voltage breakdown holds promise for a new generation of self-healing capacitors. The conductors and leads introduce undesired inductance and resistance.\nResearch is assessing the quantum effects of nanoscale capacitors for digital quantum batteries.\n\nSuperconducting magnetics\n\nSuperconducting magnetic energy storage (SMES) systems store energy in a magnetic field created by the flow of direct current in a superconducting coil that has been cooled to a temperature below its superconducting critical temperature. A typical SMES system includes a superconducting coil, power conditioning system and refrigerator. Once the superconducting coil is charged, the current does not decay and the magnetic energy can be stored indefinitely.\nThe stored energy can be released to the network by discharging the coil. The associated inverter/rectifier accounts for about 2–3% energy loss in each direction. SMES loses the least amount of electricity in the energy storage process compared to other methods of storing energy. SMES systems offer round-trip efficiency greater than 95%.\nDue to the energy requirements of refrigeration and the cost of superconducting wire, SMES is used for short duration storage such as improving power quality. It also has applications in grid balancing.\n\nApplications\n\nMills\n\nThe classic application before the Industrial Revolution was the control of waterways to drive water mills for processing grain or powering machinery. Complex systems of reservoirs and dams were constructed to store and release water (along with the potential energy it contained) when required.\n\nHomes\n\nHome energy storage is expected to become increasingly common given the growing importance of distributed generation of renewable energies (especially photovoltaics) and the important share of energy consumption in buildings. To exceed a self-sufficiency of 40% in a household equipped with photovoltaics, energy storage is needed. Multiple manufacturers produce rechargeable battery systems for storing energy, generally to hold surplus energy from home solar or wind generation. Today, for home energy storage, Li-ion batteries are preferable to lead-acid ones given their similar cost but much better performance.\nTesla Motors produces two models of the Tesla Powerwall. One is a 10 kWh weekly cycle version for backup applications and the other is a 7 kWh version for daily cycle applications. In 2016, a limited version of the Tesla Powerpack 2 cost $398(US)/kWh to store electricity worth 12.5 cents/kWh (US average grid price) making a positive return on investment doubtful unless electricity prices are higher than 30 cents/kWh.\nRoseWater Energy produces two models of the \"Energy & Storage System\", the HUB 120 and SB20. Both versions provide 28.8 kWh of output, enabling it to run larger houses or light commercial premises, and protecting custom installations. The system provides five key elements into one system, including providing a clean 60 Hz Sine wave, zero transfer time, industrial-grade surge protection, renewable energy grid sell-back (optional), and battery backup.\nEnphase Energy announced an integrated system that allows home users to store, monitor and manage electricity. The system stores 1.2 kWh of energy and 275W/500W power output.\nStoring wind or solar energy using thermal energy storage though less flexible, is considerably cheaper than batteries. A simple 52-gallon electric water heater can store roughly 12 kWh of energy for supplementing hot water or space heating.\nFor purely financial purposes in areas where net metering is available, home generated electricity may be sold to the grid through a grid-tie inverter without the use of batteries for storage.\n\nGrid electricity and power stations\n\nRenewable energy\n\nThe largest source and the greatest store of renewable energy is provided by hydroelectric dams. A large reservoir behind a dam can store enough water to average the annual flow of a river between dry and wet seasons, and a very large reservoir can store enough water to average the flow of a river between dry and wet years. While a hydroelectric dam does not directly store energy from intermittent sources, it does balance the grid by lowering its output and retaining its water when power is generated by solar or wind. If wind or solar generation exceeds the region's hydroelectric capacity, then some additional source of energy is needed.\nMany renewable energy sources (notably solar and wind) produce variable power. Storage systems can level out the imbalances between supply and demand that this causes. Electricity must be used as it is generated or converted immediately into storable forms.\nThe main method of electrical grid storage is pumped-storage hydroelectricity. Areas of the world such as Norway, Wales, Japan and the US have used elevated geographic features for reservoirs, using electrically powered pumps to fill them. When needed, the water passes through generators and converts the gravitational potential of the falling water into electricity. Pumped storage in Norway, which gets almost all its electricity from hydro, has",
    "source": "wikipedia:Energy storage",
    "domain": "climate"
  },
  {
    "text": "A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geological formations. Reservoirs of such compound mixtures, such as coal, petroleum and natural gas, can be extracted and burnt as fuel for human consumption to provide energy for direct use (such as for cooking, heating or lighting), to power heat engines (such as steam or internal combustion engines) that can propel vehicles, or to generate electricity via steam turbine generators. Some fossil fuels are further refined into derivatives such as kerosene, gasoline and diesel, or converted into petrochemicals such as polyolefins (plastics), aromatics and synthetic resins.\nThe origin of fossil fuels is the anaerobic decomposition of buried dead organisms. The conversion from these organic materials to high-carbon fossil fuels is typically the result of a geological process of millions of years. Due to the length of time it takes for them to form, fossil fuels are considered non-renewable resources.\nIn 2023, 77% of primary energy consumption in the world and over 60% of its electricity supply were from fossil fuels. The large-scale burning of fossil fuels causes serious environmental damage. Over 70% of the greenhouse gas emissions due to human activity in 2022 was carbon dioxide (CO2) released from burning fossil fuels. Natural carbon cycle processes on Earth, mostly absorption by the ocean, can remove only a small part of this, and terrestrial vegetation loss due to deforestation, land degradation and desertification further compounds this deficiency. Therefore, there is a net increase of many billion tonnes of atmospheric CO2 per year. Although methane leaks are significant, the burning of fossil fuels is the main source of greenhouse gas emissions causing global warming and ocean acidification. Additionally, most air pollution deaths are due to fossil fuel particulates and noxious gases, and it is estimated that this costs over 3% of the global gross domestic product and that fossil fuel phase-out will save millions of lives each year.\nRecognition of the climate crisis, pollution and other negative effects caused by fossil fuels has led to a widespread policy transition and activist movement focused on ending their use in favor of renewable and sustainable energy. Because the fossil-fuel industry is so heavily integrated in the global economy and heavily subsidized, this transition is expected to have significant economic consequences. Many stakeholders argue that this change needs to be a just transition and create policy that addresses the societal burdens created by the stranded assets of the fossil fuel industry. International policy, in the form of United Nations' sustainable development goals for affordable and clean energy and climate action, as well as the Paris Climate Agreement, is designed to facilitate this transition at a global level. In 2021, the International Energy Agency concluded that no new fossil fuel extraction projects could be opened if the global economy and society wants to avoid the worst effects of climate change and meet international goals for climate change mitigation.\n\nOrigin\n\nThe theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in Earth's crust over millions of years was first introduced by Andreas Libavius \"in his 1597 Alchemia [Alchymia]\" and later by Mikhail Lomonosov \"as early as 1757 and certainly by 1763\". The first recorded use of the term \"fossil fuel\" occurs in the work of the German chemist Caspar Neumann, in English translation in 1759. The Oxford English Dictionary notes that, in the phrase \"fossil fuel\", the adjective \"fossil\" means \"[o]btained by digging; found buried in the earth\", which dates to at least 1652, before the English noun \"fossil\" came to refer primarily to long-dead organisms in the early 18th century.\nAquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago began forming petroleum and natural gas as a result of anaerobic decomposition. Over geological time this organic matter, mixed with mud, became buried under further heavy layers of inorganic sediment. The resulting high temperature and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen, which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. Despite these heat-driven transformations, the energy released in combustion is still photosynthetic in origin.\nTerrestrial plants tend to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas. Although fossil fuels are continually formed by natural processes, they are classified as non-renewable resources because they take millions of years to form and known viable reserves are being depleted much faster than new ones are generated.\n\nImportance\n\nFossil fuels have been important to human development because they can be readily burned in the open atmosphere to produce heat. The use of peat as a domestic fuel predates recorded history. Coal was burned in some early furnaces for the smelting of metal ore, while semi-solid hydrocarbons from oil seeps were also burned in ancient times, they were mostly used for waterproofing and embalming.\nCommercial exploitation of petroleum began in the 19th century.\nNatural gas, once flared-off as an unneeded byproduct of petroleum production, is now considered a very valuable resource. Natural gas deposits are also the main source of helium.\nHeavy crude oil, which is much more viscous than conventional crude oil, and oil sands, where bitumen is found mixed with sand and clay, began to become more important as sources of fossil fuel in the early 2000s. Oil shale and similar materials are sedimentary rocks containing kerogen, a complex mixture of high-molecular weight organic compounds, which yield synthetic crude oil when heated (pyrolyzed). With additional processing, they can be employed instead of other established fossil fuels. During the 2010s and 2020s there was disinvestment from exploitation of such resources due to their high carbon cost relative to more easily-processed reserves.\nPrior to the latter half of the 18th century, windmills and watermills provided the energy needed for work such as milling flour, sawing wood or pumping water, while burning wood or peat provided domestic heat. The wide-scale use of fossil fuels, coal at first and petroleum later, in steam engines enabled the Industrial Revolution. At the same time, gas lights using natural gas or coal gas were coming into wide use. The invention of the internal combustion engine and its use in automobiles and trucks greatly increased the demand for gasoline and diesel oil, both made from fossil fuels. Other forms of transportation, railways and aircraft, also require fossil fuels. The other major use for fossil fuels is in generating electricity and as feedstock for the petrochemical industry. Tar, a leftover of petroleum extraction, is used in the construction of roads.\nThe energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon-fueled irrigation. The development of synthetic nitrogen fertilizer has significantly supported global population growth; it has been estimated that almost half of the Earth's population are currently fed as a result of synthetic nitrogen fertilizer use. According to head of a fertilizers commodity price agency, \"50% of the world's food relies on fertilisers.\"\n\nEnvironmental effects\n\nThe burning of fossil fuels has a number of negative externalities – harmful environmental consequences where the effects extend beyond the people using the fuel. These effects vary between different fuels. All fossil fuels release CO2 when they burn, thus accelerating climate change. Burning coal, and to a lesser extent oil and its derivatives, contributes to atmospheric particulate matter, smog and acid rain.\nAir pollution from fossil fuels in 2018 has been estimated to cost US$2.9 trillion, or 3.3% of the global gross domestic product (GDP).\n\nClimate change is largely driven by the release of greenhouse gases like CO2, and the burning of fossil fuels is the main source of these emissions. In most parts of the world climate change is negatively impacting ecosystems. This includes contributing to the extinction of species and reducing people's ability to produce food, thus adding to the problem of world hunger. Continued rises in global temperatures will lead to further adverse effects on both ecosystems and people; the World Health Organization has said that climate change is the greatest threat to human health in the 21st century.\nCombustion of fossil fuels generates sulfuric and nitric acids, which fall to Earth as acid rain, impacting both natural areas and the built environment. Monuments and sculptures made from marble and limestone are particularly vulnerable, as the acids dissolve calcium carbonate.\nFossil fuels also contain radioactive materials, mainly uranium and thorium, which are released into the atmosphere. In 2000, about 12,000 tonnes of thorium and 5,000 tonnes of uranium were released worldwide from burning coal. It is estimated that during 1982, US coal burning released 155 times as much radioactivity into the atmosphere as the Three Mile Island accident.\nBurning coal also generates large amounts of bottom ash and fly ash. These materials are used in a wide variety of applications (see Fly ash reuse), utilizing, for example, about 40% of the United States production.\nIn addition to the effects that result from burning, the harvesting, processing, and distribution of fossil fuels also have environmental effects. Coal mining methods, particularly mountaintop removal and strip mining, have negative environmental impacts, and offshore oil drilling poses a hazard to aquatic organisms. Fossil fuel wells can contribute to methane release via fugitive gas emissions. Oil refineries also have negative environmental impacts, including air and water pollution. Coal is sometimes transported by diesel-powered locomotives, while crude oil is typically transported by tanker ships, requiring the combustion of additional fossil fuels.\n\nA variety of mitigating efforts have arisen to counter the negative effects of fossil fuels. This includes a movement to use alternative energy sources, such as renewable energy. Environmental regulation uses a variety of approaches to limit these emissions; for example, rules against releasing waste products like fly ash into the atmosphere.\nIn December 2020, the United Nations released a report saying that despite the need to reduce greenhouse emissions, various governments are \"doubling down\" on fossil fuels, in some cases diverting over 50% of their COVID-19 recovery stimulus funding to fossil fuel production rather than to alternative energy. The UN secretary general António Guterres declared that \"Humanity is waging war on nature. This is suicidal. Nature always strikes back – and it is already doing so with growing force and fury.\" He also claimed there is still cause for hope, anticipating the US plan to join other large emitters like China and the EU in adopting targets to reach net zero emissions by 2050.\n\nInflation effects\nFossilflation is a term that describes the impact of fossil fuels on inflation.\nAccording to Vox in August 2022, \"Economists have pointed to energy prices as the main reason for high inflation\", noting that \"energy prices indirectly affect virtually every part of the economy\". Sectors that raise prices significantly as a result of higher fossil fuel prices include transportation, food, and shipping.\n\nHistory\nMark Zandi of Moody's says that fossil fuel prices have driven every big episode of inflation since WWII.\nThe economic impact of the Russian Invasion of Ukraine in 2022 was a major recent example of fossil fuels causing inflation. Some economists, including Isabel Schnabel, believe that dependence on fossil fuels is the main driver of the 2021–2022 inflation spike.\n\nEfforts to combat fossilflation\nGernot Wagner argues that commodities are undesirable energy sources because they are susceptible to volatile price swings that technologies like renewable energy are not. He also argues that technologies improve and get relatively cheaper over time. Coming out of the COVID-19 pandemic, some argued for the possibility of a base effect phenomenon due to cheaper than normal prices, such as for oil, at the onset of the pandemic, followed by above-average prices which exacerbated the perceived inflation.\n\nInflation Reduction Act\nWhile not expected to provide much short-term relief, the Inflation Reduction Act seeks to make the United States less dependent on fossil fuels and their ability to cause inflation in the economy. Moody's estimates that by 2030, the bill could reduce the typical American household's spending on energy by more than $300 each year, in 2022 dollars.\n\nIllness and deaths\n\nEnvironmental pollution from fossil fuels impacts humans because particulates and other air pollution from fossil fuel combustion may cause illness and death when inhaled. These health effects include premature death, acute respiratory illness, aggravated asthma, chronic bronchitis and decreased lung function. The poor, undernourished, very young and very old, and people with preexisting respiratory disease and other ill health are more at risk. Global air pollution deaths due to fossil fuels have been estimated at over 8 million people (2018, nearly 1 in 5 deaths worldwide) at 10.2 million (2019), and 5.13 million excess deaths from ambient air pollution from fossil fuel use (2023).\nWhile all energy sources inherently have adverse effects, the data show that fossil fuels cause the highest levels of greenhouse gas emissions and are the most dangerous for human health. In contrast, modern renewable energy sources appear to be safer for human health and cleaner. The death rates from accidents and air pollution in the EU are as follows per terawatt-hour (TWh):\n\n As the data shows, coal, oil, natural gas, and biomass cause higher death rates and higher levels of greenhouse gas emissions than hydropower, nuclear energy, wind, and solar power. Scientists propose that 1.8 million lives have been saved by replacing fossil fuel sources with nuclear power.\n\nPhase-out\n\nJust transition\n\nDivestment\n\nIndustrial sector\n\nIn 2019, Saudi Aramco was listed and it reached a US$2 trillion valuation on its second day of trading, after the world's largest initial public offering.\n\nSubsidies\n\nLobbying activities\n\nSee also\n\nNotes\n\nReferences\n\nFurther reading\nBarrett, Ross; Worden, Daniel (eds.), Oil Culture. Minneapolis, MN: University of Minnesota Press, 2014.\nBob Johnson, Carbon Nation: Fossil Fuels in the Making of American Culture. Lawrence, KS: University Press of Kansas, 2014.\nShaye Wolf et al.: Scientists' warning on fossil fuels, in: Oxford Open Climate Change, Volume 5, Issue 1, 2025, doi:10.1093/oxfclm/kgaf011\n\nExternal links\n\nGlobal Fossil Infrastructure Tracker Archived 10 December 2019 at the Wayback Machine\nCentre for Research on Energy and Clean Air",
    "source": "wikipedia:Fossil fuel",
    "domain": "climate"
  },
  {
    "text": "Coal is a combustible black or brownish-black sedimentary rock, formed as layers called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. It is a fossil fuel, formed when plants decay into peat which is converted into coal by the heat and pressure of deep burial over millions of years. Vast deposits formed from wetlands called coal forests that covered much of the tropics during the late Carboniferous and early Permian.\nCoal is used primarily as a fuel. While coal has been known and used for thousands of years, its usage was limited until the Industrial Revolution. With the invention of the steam engine, coal consumption increased. In 2020, coal supplied about a quarter of the world's primary energy and over a third of its electricity. Some iron and steel-making and other industrial processes burn coal.\nThe extraction and burning of coal damages the environment and human health, causing premature death and illness, and is the largest source of carbon dioxide contributing to climate change. Over fifteen billion tonnes of carbon dioxide were emitted by burning coal in 2024, which was more than a quarter of total global greenhouse gas emissions.As part of worldwide energy transition, many countries have reduced or eliminated their use of coal power. The United Nations Secretary General asked governments to stop building new coal plants by 2020.\nA record amount of coal was burnt in 2024, but consumption is expected to peak before 2030. To meet the Paris Agreement target of keeping global warming below 2 °C (3.6 °F) coal use needs to halve from 2020 to 2030, and \"phasing down\" coal was agreed upon in the Glasgow Climate Pact.\nThe largest consumer and importer of coal is China, which mines almost half the world's coal, followed by India with about a tenth. Indonesia and Australia export the most, followed by Russia.\n\nEtymology\nThe word originally took the form col in Old English, from reconstructed Proto-Germanic *kula(n), from Proto-Indo-European root *g(e)u-lo- \"live coal\". Germanic cognates include the Old Frisian kole, Middle Dutch cole, Dutch kool, Old High German chol, German Kohle and Old Norse kol. Irish gual is also a cognate via the Indo-European root.\n\nFormation of coal\n\nThe conversion of dead vegetation into coal is called coalification. At various times in the geologic past, the Earth had dense forests in low-lying areas. In these wetlands, the process of coalification began when dead plant matter was protected from oxidation, usually by mud or acidic water, and was converted into peat. The resulting peat bogs, which trapped immense amounts of carbon, were eventually deeply buried by sediments. Then, over millions of years, the heat and pressure of deep burial caused the loss of water, methane and carbon dioxide and increased the proportion of carbon. The grade of coal produced depended on the maximum pressure and temperature reached, with lignite (also called \"brown coal\") produced under relatively mild conditions, and sub-bituminous coal, bituminous coal, or anthracite coal (also called \"hard coal\" or \"black coal\") produced in turn with increasing temperature and pressure.\nOf the factors involved in coalification, temperature is much more important than either pressure or time of burial. Subbituminous coal can form at temperatures as low as 35 to 80 °C (95 to 176 °F) while anthracite requires a temperature of at least 180 to 245 °C (356 to 473 °F).\nAlthough coal is known from most geologic periods, 90% of all coal beds were deposited in the Carboniferous and Permian periods. Paradoxically, this was during the Late Paleozoic icehouse, a time of global glaciation. However, the drop in global sea level accompanying the glaciation exposed continental shelves that had previously been submerged, and to these were added wide river deltas produced by increased erosion due to the drop in base level. These widespread areas of wetlands provided ideal conditions for coal formation. The rapid formation of coal ended with the coal gap in the Permian–Triassic extinction event, where coal is rare.\nFavorable geography alone does not explain the extensive Carboniferous coal beds. Other factors contributing to rapid coal deposition were high oxygen levels, above 30%, that promoted intense wildfires and formation of charcoal that was all but indigestible by decomposing organisms; high carbon dioxide levels that promoted plant growth; and the nature of Carboniferous forests, which included lycophyte trees whose determinate growth meant that carbon was not tied up in heartwood of living trees for long periods.\nOne theory suggested that about 360 million years ago, some plants evolved the ability to produce lignin, a complex polymer that made their cellulose stems much harder and more woody. The ability to produce lignin led to the evolution of the first trees. But bacteria and fungi did not immediately evolve the ability to decompose lignin, so the wood did not fully decay but became buried under sediment, eventually turning into coal. About 300 million years ago, mushrooms and other fungi developed this ability, ending the main coal-formation period of earth's history. Although some authors pointed at some evidence of lignin degradation during the Carboniferous, and suggested that climatic and tectonic factors were a more plausible explanation, reconstruction of ancestral enzymes by phylogenetic analysis corroborated a hypothesis that lignin degrading enzymes appeared in fungi approximately 200 MYa.\nOne likely tectonic factor was the Central Pangean Mountains, an enormous range running along the equator that reached its greatest elevation near this time. Climate modeling suggests that the Central Pangean Mountains contributed to the deposition of vast quantities of coal in the late Carboniferous. The mountains created an area of year-round heavy precipitation, with no dry season typical of a monsoon climate. This is necessary for the preservation of peat in coal swamps.\nCoal is known from Precambrian strata, which predate land plants. This coal is presumed to have originated from residues of algae.\nSometimes coal seams (also known as coal beds) are interbedded with other sediments in a cyclothem. Cyclothems are thought to have their origin in glacial cycles that produced fluctuations in sea level, which alternately exposed and then flooded large areas of continental shelf.\n\nChemistry of coalification\nThe woody tissue of plants is composed mainly of cellulose, hemicellulose, and lignin. Modern peat is mostly lignin, with a content of cellulose and hemicellulose ranging from 5% to 40%. Various other organic compounds, such as waxes and nitrogen- and sulfur-containing compounds, are also present. Lignin has a weight composition of about 54% carbon, 6% hydrogen, and 30% oxygen, while cellulose has a weight composition of about 44% carbon, 6% hydrogen, and 49% oxygen. Bituminous coal has a composition of about 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis. The low oxygen content of coal shows that coalification removed most of the oxygen and much of the hydrogen a process called carbonization.\nCarbonization proceeds primarily by dehydration, decarboxylation, and demethanation. Dehydration removes water molecules from the maturing coal via reactions such as\n\n2 R–OH → R–O–R + H2O\nDecarboxylation removes carbon dioxide from the maturing coal:\n\nRCOOH → RH + CO2\nwhile demethanation proceeds by reaction such as\n\n2 R-CH3 → R-CH2-R + CH4\nR-CH2-CH2-CH2-R → R-CH=CH-R + CH4\nIn these formulas, R represents the remainder of a cellulose or lignin molecule to which the reacting groups are attached.\nDehydration and decarboxylation take place early in coalification, while demethanation begins only after the coal has already reached bituminous rank. The effect of decarboxylation is to reduce the percentage of oxygen, while demethanation reduces the percentage of hydrogen. Dehydration does both, and (together with demethanation) reduces the saturation of the carbon backbone (increasing the number of double bonds between carbon).\nAs carbonization proceeds, aliphatic compounds convert to aromatic compounds. Similarly, aromatic rings fuse into polyaromatic compounds (linked rings of carbon atoms). The structure increasingly resembles graphene, the structural element of graphite.\nChemical changes are accompanied by physical changes, such as decrease in average pore size.\n\nMacerals\nMacerals are coalified plant parts that retain the morphology and some properties of the original plant. In many coals, individual macerals can be identified visually. Some macerals include:\n\nvitrinite, derived from woody parts\nlipinite, derived from spores and algae\ninertite, derived from woody parts that had been burnt in prehistoric times\nhuminite, a precursor to vitrinite.\nIn coalification huminite is replaced by vitreous (shiny) vitrinite. Maturation of bituminous coal is characterized by bitumenization, in which part of the coal is converted to bitumen, a hydrocarbon-rich gel. Maturation to anthracite is characterized by debitumenization (from demethanation) and the increasing tendency of the anthracite to break with a conchoidal fracture, similar to the way thick glass breaks.\n\nTypes\n\nAs geological processes apply pressure to dead biotic material over time, under suitable conditions, its metamorphic grade or rank increases successively into:\n\nPeat, a precursor of coal\nLignite, or brown coal, the lowest rank of coal, most harmful to health when burned, used almost exclusively as fuel for electric power generation\nSub-bituminous coal, whose properties range between those of lignite and those of bituminous coal, is used primarily as fuel for steam-electric power generation.\nBituminous coal, a dense sedimentary rock, usually black, but sometimes dark brown, often with well-defined bands of bright and dull material. It is used primarily as fuel in steam-electric power generation and to make coke. Known as steam coal in the UK, and historically used to raise steam in steam locomotives and ships\nAnthracite coal, the highest rank of coal, is a harder, glossy black coal used primarily for residential and commercial space heating.\nGraphite, a difficult to ignite coal that is used mostly in pencils, or in powdered form for lubrication.\nCannel coal (sometimes called \"candle coal\"), a variety of fine-grained, high-rank coal with significant hydrogen content, that consists primarily of liptinite. It is related to boghead coal.\nThere are several international standards for coal. The classification of coal is generally based on the content of volatiles. However the most important distinction is between thermal coal (also known as steam coal), which is burnt to generate electricity via steam; and metallurgical coal (also known as coking coal), which is burnt at high temperature to make steel.\nHilt's law is a geological observation that (within a small area) the deeper the coal is found, the higher its rank (or grade). It applies if the thermal gradient is entirely vertical; however, metamorphism may cause lateral changes of rank, irrespective of depth. For example, some of the coal seams of the Madrid, New Mexico coal field were partially converted to anthracite by contact metamorphism from an igneous sill while the remainder of the seams remained as bituminous coal.\n\nHistory\n\nThe oldest intentional use of black coal was documented in Ostrava, Petřkovice, in a settlement from the older Stone Age on the top of Landek Hill. According to radiocarbon dating, the site falls within the period 25,000–23,000 years BC.\n\nIn China, the earliest recognized use is from the Shenyang where by 4000 BC Neolithic inhabitants had begun carving ornaments from black lignite. Coal from the Fushun mine in northeastern China was used to smelt copper as early as 1000 BC. Marco Polo, the Italian who traveled to China in the 13th century, described coal as \"black stones ... which burn like logs\", and said coal was so plentiful, people could take three hot baths a week. In Europe, the earliest reference to the use of coal as fuel is from the geological treatise On Stones(c. 371–287 BC):\nOutcrop coal was used in Britain during the Bronze Age (3000–2000 BC), where it formed part of funeral pyres. In Roman Britain, \"the Romans were exploiting coals in all the major coalfields in England and Wales by the end of the second century AD\". Coal from the Midlands was transported via the Car Dyke for use in drying grain. Coal cinders have been found in the hearths of villas and Roman forts, particularly in Northumberland, dated to around AD 400. In the west of England, contemporary writers described the wonder of a permanent brazier of coal on the altar of Minerva at Aquae Sulis (modern day Bath), although in fact easily accessible surface coal from what became the Somerset coalfield was in common use in quite lowly dwellings locally. Evidence of coal's use for iron-working in the city during the Roman period has been found. In Eschweiler, Rhineland, deposits of bituminous coal were used by the Romans for the smelting of iron ore.\n\nNo evidence exists of coal being of great importance in Britain before about AD 1000, the High Middle Ages. Coal came to be referred to as \"seacoal\" in the 13th century; the wharf where the material arrived in London was known as Seacoal Lane, so identified in a charter of King Henry III granted in 1253. Initially, the name was given because much coal was found on the shore, having fallen from the exposed coal seams on cliffs above or washed out of underwater coal outcrops. In 1257–1259, coal from Newcastle upon Tyne was shipped to London for the smiths and lime-burners building Westminster Abbey. Coal continues to arrive on beaches around the world from both natural erosion of exposed coal seams and windswept spills from cargo ships. Many homes in such areas gather this coal as a significant, and sometimes primary, source of home heating fuel.\nThese easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground extraction by shaft mining or adits was developed. The alternative name was \"pitcoal\", because it came from mines.\n\nCooking and home heating with coal (in addition to firewood or instead of it) has been done in various times and places throughout human history, especially in times and places where ground-surface coal was available and firewood was scarce, but a widespread reliance on coal for home hearths probably never existed until such a switch in fuels happened in London in the late sixteenth and early seventeenth centuries. Historian Ruth Goodman has traced the socioeconomic effects of that switch and its later spread throughout Britain and suggested that its importance in shaping the industrial adoption of coal has been previously underappreciated.\nThe development of the Industrial Revolution led to the large-scale use of coal, as the steam engine took over from the water wheel. In 1700, five-sixths of the world's coal was mined in Britain. Britain would have run out of suitable sites for watermills by the 1830s if coal had not been available as a source of energy. In 1947 there were some 750,000 miners in Britain, but the last deep coal mine in the UK closed in 2015.\nA grade between bituminous coal and anthracite was once known as \"steam coal\" as it was widely used as a fuel for steam locomotives. In this specialized use, it is sometimes known as \"sea coal\" in the United States. Small \"steam coal\", also called dry small steam nuts (DSSN), was used as a fuel for domestic water heating.\nCoal played an important role in industry in the 19th and 20th century. The predecessor of the European Union, the European Coal and Steel Community, was based on the trading of this commodity.\n\nComposition\n\nCoal is a mixture of diverse organic compounds and polymers. Several kinds exist, with variable dark colors and composition. Young coals (brown coal, lignite) are not completely black. The two main black coals are bituminous, which is more abundant, and anthracite. The type of coal with the highest percentage of carbon in its chemical composition is anthracite, followed by bituminous, then lignite, and finally brown coal. The fuel value of coal varies in the same order. Some anthracite deposits contain pure carbon in the form of graphite.\nFor bituminous coal, the elemental composition on a dry, ash-free basis is 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur by weight. This composition partly reflects the composition of the precursor plants. The second main fraction of coal is ash, an undesirable, noncombustable mixture of inorganic minerals. The composition of ash is often discussed in terms of oxides obtained after combustion in air:\n\nOf particular interest is the sulfur content of coal, which can vary from less than 1% to as much as 4%. Most of the sulfur and most of the nitrogen is incorporated into the organic fraction in the form of organosulfur compounds and organonitrogen compounds. This sulfur and nitrogen are strongly bound within the hydrocarbon matrix. These elements are released as SO2 and NOx upon combustion. They cannot be removed, economically at least, otherwise. Some coals contain inorganic sulfur, mainly in the form of iron pyrite (FeS2). Being a dense mineral, iron pyrite can be removed from coal by mechanical means, e.g. by froth flotation. Some sulfate occurs in coal, especially weathered samples. It is not volatilized and can be removed by washing.\nMinor components include:\n\nAs minerals, Hg, As, and Se are not problematic for the environment, especially since they are only trace components. They become mobile (volatile or water-soluble), however, when these minerals are combusted.\n\nUses\nMost coal is used as fuel. 27.6% of world energy was supplied by coal in 2017 and Asia used almost three-quarters of it. Other large-scale applications also exist. The energy density of coal is roughly 24 megajoules per kilogram (approximately 6.7 kilowatt-hours per kg). For a coal power plant with a 40% efficiency, it takes an estimated 325 kg (717 lb) of coal to power a 100 W lightbulb for one year.\n\nElectricity generation\n\nIn 2022, 68% of global coal use was used for electricity generation. \nThe International Energy Agency (IEA) has estimated global coal demand to be 5,946 Megatonnes in 2024, and 5,964 Mt in 2025.\nCoal burnt in coal power stations to generate electricity is called thermal coal. It is usually pulverized and then burned in a furnace with a boiler. \nThe furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and produce electricity. The thermodynamic efficiency of this process varies between about 25% and 50% depending on the pre-combustion treatment, turbine technology (e.g. supercritical steam generator) and the age of the plant. \nA few integrated gasification combined cycle (IGCC) power plants have been built, which burn coal more efficiently. Instead of pulverizing the coal and burning it directly as fuel in the steam-generating boiler, the coal is gasified to create syngas, which is burned in a gas turbine to produce electricity (just like natural gas is burned in a turbine). Hot exhaust gases from the turbine are used to raise steam in a heat recovery steam generator which powers a supplemental steam turbine. The overall plant efficiency when used to provide combined heat and power can reach as much as 94%. IGCC power plants emit less local pollution than conventional pulverized coal-fueled plants. Other ways to use coal are as coal-water slurry fuel (CWS), which was developed in the Soviet Union, or in an MHD topping cycle. However these are not widely used due to lack of profit.\nIn 2017 38% of the world's electricity came from coal, the same percentage as 30 years previously. In 2018 global installed capacity was 2 TW (of which 1 TW was in China) which was 30% of total electricity generation capacity. \nThe most dependent major country was South Africa, with over 80% of its electricity generated by coal; but in 2020 China alone generated more than half of the world's coal-generated electricity. Efforts around the world to reduce the use of coal have led many regions to switch to natural gas and renewable energy. In 2018 coal-fired power station capacity factor averaged 51%, that is they operated for about half their available operating hours.\n\nCoke\n\nCoke is a solid carbonaceous residue that is used in manufacturing steel and other iron-containing products. Coke is made when metallurgical coal (also known as coking coal) is baked in an oven without oxygen at temperatures as high as 1,000 °C, driving off the volatile constituents and fusing together the fixed carbon and residual ash. Metallurgical coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. The carbon monoxide produced by its combustion reduces hematite (an iron oxide) to iron.\n\n2 Fe2O3 + 6 CO → 4 Fe + 6 CO2\nPig iron, which is too rich in dissolved carbon, is also produced.\nThe coke must be strong enough to resist the weight of overburden in the blast furnace, which is why coking coal is so important in making steel using the conventional route. Coke from coal is grey, hard, and porous and has a heating value of 29.6 MJ/kg. Some coke-making processes produce byproducts, including coal tar, ammonia, light oils, and coal gas.\nPetroleum coke (petcoke) is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.\n\nProduction of chemicals\n\nChemicals have been produced from coal since the 1940s. \nCoal can be used as a feedstock in the production of a wide range of chemical fertilizers and other chemical products. The main route to these products was coal gasification to produce syngas. Primary chemicals that are produced directly from the syngas include methanol, hydrogen, and carbon monoxide, which are the chemical building blocks from which a whole spectrum of derivative chemicals are manufactured, including olefins, acetic acid, formaldehyde, ammonia, urea, and others. The versatility of syngas as a precursor to primary chemicals and high-value derivative products provides the option of using coal to produce a wide range of commodities. In the 21st century, the use of coalbed methane has become more important.\nBecause the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived from natural gas and petroleum, the chemical industry tends to use whatever feedstocks are most cost-effective. Therefore, interest in using coal tended to increase for higher oil and natural gas prices and during periods of high global economic growth that might have strained oil and gas production.\nCoal to chemical processes require substantial quantities of water. Much coal to chemical production is in China where coal dependent provinces such as Shanxi are struggling to control its pollution.\n\nLiquefaction\n\nCoal can be converted directly into synthetic fuels equivalent to gasoline or diesel by hydrogenation or carbonization. Coal liquefaction emits more carbon dioxide than liquid fuel production from crude oil. Mixing in biomass and using carbon capture and storage (CCS) would emit slightly less than the oil process but at a high cost. State owned China Energy Investment runs a coal liquefaction plant and plans to build 2 more.\nCoal liquefaction may also refer to the cargo hazard when shipping coal.\n\nGasification\n\nCoal gasification, as part of an integrated gasification combined cycle (IGCC) coal-fired power station, is used to produce syngas, a mixture of carbon monoxide (CO) and hydrogen (H2) gas to fire gas turbines to produce electricity. Syngas can also be converted into transportation fuels, such as gasoline and diesel, through the Fischer–Tropsch process; alternatively, syngas can be converted into methanol, which can be blended into fuel directly or converted to gasoline via the methanol to gasoline process. Gasification combined with Fischer–Tropsch technology was used by the Sasol chemical company of South Africa to make chemicals and motor vehicle fuels from coal.\nDuring gasification, the coal is mixed with oxygen and steam while also being heated and pressurized. During the reaction, oxygen and water molecules oxidize the coal into carbon monoxide (CO), while also releasing hydrogen gas (H2). This used to be done in underground coal mines, and also to make town gas, which was piped to customers to burn for illumination, heating, and cooking.\n\n3C (as Coal) + O2 + H2O → H2 + 3CO\nIf the refiner wants to produce gasoline, the syngas is routed into a Fischer–Tropsch reaction. This is known as indirect coal liquefaction. If hydrogen is the desired end-product, however, the syngas is fed into the water gas shift reaction, where more hydrogen is liberated:\n\nCO + H2O → CO2 + H2\n\nCoal industry\n\nMining\n\nAbout 8,000 Mt of coal are produced annually, about 90% of which is hard coal and 10% lignite. As of 2018 just over half is from underground mines. The coal mining industry employs almost 2.7 million workers. More accidents occur during underground mining than surface mining. Not all countries publish mining accident statistics so worldwide figures are uncertain, but it is thought that most deaths occur in coal mining accidents in China: in 2017 there were 375 coal mining related deaths in China. Most coal mined is thermal coal (also called steam coal as it is used to make steam to generate electricity) but metallurgical coal (also called \"metcoal\" or \"coking coal\" as it is used to make coke to make iron) accounts for 10% to 15% of global coal use.\n\nAs a traded commodity\n\nChina mines almost half the world's coal, followed by India with about a tenth. At 471 Mt and a 34% share of global exports, Indonesia was the largest exporter by volume in 2022, followed by Australia with 344 Mt and Russia with 224 Mt. Other major exporters of coal are the United States, South Africa, Colombia, and Canada. In 2022, China, India, and Japan were the biggest importers of coal, importing 301, 228, and 184 Mt respectively. Russia is increasingly orienting its coal exports from Europe to Asia as Europe transitions to renewable energy and subjects Russia to sanctions over its invasion of Ukraine.\nThe price of metallurgical coal is volatile and much higher than the price of thermal coal because metallurgical coal must be lower in sulfur and requires more cleaning. Coal futures contracts provide coal producers and the electric power industry an important tool for hedging and risk management.\nIn some countries, new onshore wind or solar generation already costs less than coal power from existing plants.\nHowever, for China this is forecast for the early 2020s and for southeast Asia not until the late 2020s. In India, building new plants is uneconomic and, despite being subsidized, existing plants are losing market share to renewables.\nIn many countries in the Global North, there is a move away from the use of coal and former mine sites are being used as a tourist attraction.\n\nMarket trends\n\nIn 2022, China used 4520 Mt of coal, comprising more than half of global coal consumption. India, the European Union, and the United States, were the next largest consumers of coal, using 1162, 461, and 455 Mt respectively. Over the past decade, China has almost always accounted for the lion's share of the global growth in coal demand. Therefore, international market trends depend on Chinese energy policy. \nAlthough the government effort to reduce air pollution in China means that the global long-term trend is to burn less coal, the short and medium term trends may differ, in part due to Chinese financing of new coal-fired power plants in other countries.\nPreliminary analysis by International Energy Agency (IEA) indicates that global coal exports reached an all-time high in 2023. Through to 2026, the IEA expects global coal trade to decline by about 12%, driven by growing domestic production in coal-intensive economies such as China and India and coal phase-out plans elsewhere, such as in Europe. While thermal coal exports are expected to decline by about 16% by 2026, exports of metallurgical coal are expected to slightly increase by almost 2%. \n\nDamage to human health\n\nThe use of coal as fuel causes health problems and deaths. The mining and processing of coal causes air and water pollution. Coal-powered plants emit nitrogen oxides, sulfur dioxide, particulate pollution, and heavy metals, which adversely affect human health. Coalbed methane extraction is important to avoid mining accidents.\nThe deadly London smog was caused primarily by the heavy use of coal. Globally coal is estimated to cause 800,000 premature deaths every year, mostly in India and China.\nBurning coal is a major contributor to sulfur dioxide emissions, which creates PM2.5 particulates, the most dangerous form of air pollution.\nCoal smokestack emissions cause asthma, strokes, reduced intelligence, artery blockages, heart attacks, congestive heart failure, cardiac arrhythmias, mercury poisoning, arterial occlusion, and lung cancer.\nAnnual health costs in Europe from use of coal to generate electricity are estimated at up to €43 billion.\nIn China, early deaths due to air pollution coal plants have been estimated at 200 per GW-year, however they may be higher around power plants where scrubbers are not used or lower if they are far from cities. Improvements to China's air quality and human health would grow with more stringent climate policies, mainly because the country's energy is so heavily reliant on coal. And there would be a net economic benefit.\nA 2017 study in the Economic Journal found that for Britain during the period 1851–1860, \"a one standard deviation increase in coal use raised",
    "source": "wikipedia:Coal",
    "domain": "climate"
  },
  {
    "text": "Natural gas (also gas, methane gas or fossil gas) is a fossil fuel, naturally occurring in geological formations. Typically, the gas is a mix of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium. Methane is a colorless and odorless gas, and, after carbon dioxide, is the second-greatest greenhouse gas that contributes to global climate change. Because natural gas is odorless, a commercial odorizer, such as methanethiol, that smells of hydrogen sulfide (rotten eggs) is added to the gas for the ready detection of gas leaks.\nNatural gas is a fossil fuel that is formed when layers of organic matter (primarily marine microorganisms) are thermally decomposed under oxygen-free conditions, subjected to intense heat and pressure underground over millions of years. The energy that the decayed organisms originally obtained from the sun via photosynthesis is stored as chemical energy within the molecules of methane and other hydrocarbons. Most natural gas is collected from underground geological formations, often alongside other fossil fuels like coal and oil (petroleum). Natural gas is often a byproduct of petroleum production, where it can either be vented without burning, flared (burned off) or collected. \nThe extraction and consumption of natural gas is a major industry. According to a 2025 IEA report, demand has increased in recent years. When burned for heat or electricity, natural gas emits fewer toxic air pollutants, less carbon dioxide, and almost no particulate matter compared to other fossil fuels. However, the natural gas industry is one of the largest drivers of climate change: gas venting and unintended fugitive emissions throughout the supply chain can result in natural gas having a similar or greater carbon footprint to other fossil fuels overall. Much of this is driven by methane's greater effect on radiative forcing. Globally, new installed natural gas infrastructure is one of the largest sources of increased greenhouse gas emissions for energy production. To meet climate goals, 2023 IPCC Sixth Assessment report concluded that new fossil gas infrastructure only make sense under very specific conditions with carbon capture and fugitive gas prevention technologies, otherwise it risks emissions overshoot or becoming stranded assets.\n\nBefore natural gas can be burned as a fuel or used in manufacturing processes, it almost always has to be processed to remove impurities such as water. The byproducts of this processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons. Hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen must also be removed. While natural gas is frequently transported in a gaseous state in gas pipelines, inter-country transportation and long-term storage of natural gas was not widely available until the widespread adoption of liquefied natural gas.\nNatural gas is measured in standard cubic meters or standard cubic feet. The density compared to air ranges from 0.58 (16.8 g/mole, 0.71 kg per standard cubic meter) to as high as 0.79 (22.9 g/mole, 0.97 kg per scm), but generally less than 0.64 (18.5 g/mole, 0.78 kg per scm). For comparison, pure methane (16.0425 g/mole) has a density 0.5539 times that of air (0.678 kg per standard cubic meter).\n\nName\nIn the early 1800s, natural gas became known as \"natural\" to distinguish it from the dominant gas fuel at the time, coal gas. Unlike coal gas, which is manufactured by heating coal, natural gas can be extracted from the ground in its native gaseous form. When the use of natural gas overtook the use of coal gas in English-speaking countries in the 20th century, it was increasingly referred to as simply \"gas.\" However, it is not to be confused with gasoline, which is also shortened in colloquial usage to \"gas\", especially in North America.\nIn order to highlight its role in exacerbating the climate crisis, however, many organizations have criticized the continued use of the word \"natural\" in referring to the gas. These advocates prefer the term \"fossil gas\" or \"methane gas\" as better conveying to the public its climate threat. A 2020 study of Americans' perceptions of the fuel found that, across political identifications, the term \"methane gas\" led to better estimates of its harms and risks.\n\nHistory\n\nNatural gas can come out of the ground and cause a long-burning fire. In ancient Greece, the gas flames at Mount Chimaera contributed to the legend of the fire-breathing creature Chimera. In ancient China, gas resulting from the drilling for brines was first used by about 400 BC. The Chinese transported gas seeping from the ground in crude pipelines of bamboo to where it was used to boil salt water to extract the salt in the Ziliujing District of Sichuan.\nNatural gas was not widely used before the development of long distance pipelines in the early 20th century. Before that, most use was near to the source of the well, and the predominant gas for fuel and lighting during the industrial revolution was manufactured coal gas.\nThe history of natural gas in the United States begins with localized use. In the seventeenth century, French missionaries witnessed the American Indians setting fire to natural gas seeps around Lake Erie, and scattered observations of these seeps were made by European-descended settlers throughout the eastern seaboard through the 1700s. In 1821, William Hart dug the first commercial natural gas well in the United States at Fredonia, New York, United States, which led in 1858 to the formation of the Fredonia Gas Light Company. Further such ventures followed near wells in other states, until technological innovations allowed the growth of major long distance pipelines from the 1920s onwards.\nBy 2010, 66,000 km3 (16,000 mi3) (or 8%) had been used out of the total 850,000 km3 (200,000 mi3) of estimated remaining recoverable reserves of natural gas.\n\nSources\n\nNatural gas\n\nIn the 19th century, natural gas was primarily obtained as a by-product of producing oil. The small, light gas carbon chains came out of solution as the extracted fluids underwent pressure reduction from the reservoir to the surface, similar to uncapping a soft drink bottle where the carbon dioxide effervesces. The gas was often viewed as a by-product, a hazard, and a disposal problem in active oil fields. The large volumes produced could not be used until relatively expensive pipeline and storage facilities were constructed to deliver the gas to consumer markets.\nUntil the early part of the 20th century, most natural gas associated with oil was either simply released or burned off at oil fields. Gas venting and production flaring are still practiced in modern times, but efforts are ongoing around the world to retire them, and to replace them with other commercially viable and useful alternatives.\nIn addition to transporting gas via pipelines for use in power generation, other end uses for natural gas include export as liquefied natural gas (LNG) or conversion of natural gas into other liquid products via gas to liquids (GTL) technologies. GTL technologies can convert natural gas into liquids products such as gasoline, diesel or jet fuel. A variety of GTL technologies have been developed, including Fischer–Tropsch (F–T), methanol to gasoline (MTG) and syngas to gasoline plus (STG+). F–T produces a synthetic crude that can be further refined into finished products, while MTG can produce synthetic gasoline from natural gas. STG+ can produce drop-in gasoline, diesel, jet fuel and aromatic chemicals directly from natural gas via a single-loop process. In 2011, Royal Dutch Shell's 140,000 barrels (22,000 m3) per day F–T plant went into operation in Qatar.\nNatural gas can be \"associated\" (found in oil fields), or \"non-associated\" (isolated in natural gas fields), and is also found in coal beds (as coalbed methane). It sometimes contains a significant amount of ethane, propane, butane, and pentane—heavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons such as carbon dioxide, nitrogen, helium (rarely), and hydrogen sulfide must also be removed before the natural gas can be transported.\nNatural gas extracted from oil wells is called casinghead gas (whether or not truly produced up the annulus and through a casinghead outlet) or associated gas. The natural gas industry is extracting an increasing quantity of gas from challenging, unconventional resource types: sour gas, tight gas, shale gas, and coalbed methane.\nThere is some disagreement on which country has the largest proven gas reserves. Sources that consider that Russia has by far the largest proven reserves include the US Central Intelligence Agency (47,600 km3) and Energy Information Administration (47,800 km3), as well as the Organization of Petroleum Exporting Countries (48,700 km3). Contrarily, BP credits Russia with only 32,900 km3, which would place it in second, slightly behind Iran (33,100 to 33,800 km3, depending on the source).\n\nIt is estimated that there are about 900,000 km3 of \"unconventional\" gas such as shale gas, of which 180,000 km3 may be recoverable. In turn, many studies from MIT, Black & Veatch and the US Department of Energy predict that natural gas will account for a larger portion of electricity generation and heat in the future.\nThe world's largest gas field is the offshore South Pars/North Dome Gas-Condensate field, shared between Iran and Qatar. It is estimated to have 51,000 cubic kilometers (12,000 mi3) of natural gas and 50 billion barrels (7.9 billion cubic meters) of natural gas condensates.\nBecause natural gas is not a pure product, as the reservoir pressure drops when non-associated gas is extracted from a field under supercritical (pressure/temperature) conditions, the higher molecular weight components may partially condense upon isothermic depressurizing—an effect called retrograde condensation. The liquid thus formed may get trapped as the pores of the gas reservoir get depleted. One method to deal with this problem is to re-inject dried gas free of condensate to maintain the underground pressure and to allow re-evaporation and extraction of condensates. More frequently, the liquid condenses at the surface, and one of the tasks of the gas plant is to collect this condensate. The resulting liquid is called natural gas liquid (NGL) and has commercial value.\n\nShale gas\n\nShale gas is natural gas produced from shale. Because shale's matrix permeability is too low to allow gas to flow in economical quantities, shale gas wells depend on fractures to allow the gas to flow. Early shale gas wells depended on natural fractures through which gas flowed; almost all shale gas wells today require fractures artificially created by hydraulic fracturing. Since 2000, shale gas has become a major source of natural gas in the United States and Canada. Because of increased shale gas production the United States was in 2014 the number one natural gas producer in the world. The production of shale gas in the United States has been described as a \"shale gas revolution\" and as \"one of the landmark events in the 21st century.\"\nFollowing the increased production in the United States, shale gas exploration is beginning in countries such as Poland, China, and South Africa. Chinese geologists have identified the Sichuan Basin as a promising target for shale gas drilling, because of the similarity of shales to those that have proven productive in the United States. Production from the Wei-201 well is between 10,000 and 20,000 m3 per day. In late 2020, China National Petroleum Corporation claimed daily production of 20 million cubic meters of gas from its Changning-Weiyuan demonstration zone.\n\nCoal gas\n\nCoal gas or Town gas is a flammable gaseous fuel made by the destructive distillation of coal. It contains a variety of calorific gases including hydrogen, carbon monoxide, methane, and other volatile hydrocarbons, together with small quantities of non-calorific gases such as carbon dioxide and nitrogen, and was used in a similar way to natural gas. This is a historical technology and is not usually economically competitive with other sources of fuel gas today.\nMost town \"gashouses\" located in the eastern US in the late 19th and early 20th centuries were simple by-product coke ovens that heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected and distributed through networks of pipes to residences and other buildings where it was used for cooking and lighting. (Gas heating did not come into widespread use until the last half of the 20th century.) The coal tar (or asphalt) that collected in the bottoms of the gashouse ovens was often used for roofing and other waterproofing purposes, and when mixed with sand and gravel was used for paving streets.\n\nSynthetic natural gas\nSynthetic natural gas (SNG), is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels or using electricity with power-to-gas system. Gasification process is used to generate SNG. When the gasification is conducted with hydrogen in place of oxygen/air, it is called hydrogasification.\n\nRenewable natural gas\nRenewable natural gas (RNG), also known as biomethane, is a renewable fuel made from biogas that has been upgraded to a quality similar to fossil gas and has a methane concentration of 90% or greater.\n\nCrystallized natural gas – clathrates\nHuge quantities of natural gas (primarily methane) exist in the form of clathrates under sediment on offshore continental shelves and on land in arctic regions that experience permafrost, such as those in Siberia. Hydrates require a combination of high pressure and low temperature to form.\nIn 2013, Japan Oil, Gas and Metals National Corporation (JOGMEC) announced that they had recovered commercially relevant quantities of natural gas from methane hydrate.\n\nProcessing\n\nThe image below is a schematic block flow diagram of a typical natural gas processing plant. It shows the various unit processes used to convert raw natural gas into sales gas pipelined to the end user markets.\nThe block flow diagram also shows how processing of the raw natural gas yields byproduct sulfur, byproduct ethane, and natural gas liquids (NGL) propane, butanes and natural gasoline (denoted as pentanes +).\n\nDemand\n\nAs of mid-2020, natural gas production in the US had peaked three times, with current levels exceeding both previous peaks. It reached 24.1 trillion cubic feet per year in 1973, followed by a decline, and reached 24.5 trillion cubic feet in 2001. After a brief drop, withdrawals increased nearly every year since 2006 (owing to the shale gas boom), with 2017 production at 33.4 trillion cubic feet and 2019 production at 40.7 trillion cubic feet. After the third peak in December 2019, extraction continued to fall from March onward due to decreased demand caused by the COVID-19 pandemic in the US.\nThe 2021 global energy crisis was driven by a global surge in demand as the world quit the economic recession caused by COVID-19, particularly due to strong energy demand in Asia.\n\nStorage and transport\n\nBecause of its low density, it is not easy to store natural gas or to transport it by vehicle. Natural gas pipelines are impractical across oceans, since the gas needs to be cooled down and compressed, as the friction in the pipeline causes the gas to heat up. Many existing pipelines in the US are close to reaching their capacity, prompting some politicians representing northern states to speak of potential shortages. The large trade cost implies that natural gas markets are globally much less integrated, causing significant price differences across countries. In Western Europe, the gas pipeline network is already dense. New pipelines are planned or under construction between Western Europe and the Near East or Northern Africa.\nWhenever gas is bought or sold at custody transfer points, rules and agreements are made regarding the gas quality. These may include the maximum allowable concentration of CO2, H2S and H2O. Usually sales quality gas that has been treated to remove contamination is traded on a \"dry gas\" basis and is required to be commercially free from objectionable odours, materials, and dust or other solid or liquid matter, waxes, gums and gum forming constituents, which might damage or adversely affect operation of equipment downstream of the custody transfer point.\nBased on their geographic origin, H-gas (high-calorific gas) and L-gas (low-calorific gas) are to be distinguished. Both types require separate transport, leading to two separate pipeline networks, e.g. in parts of Germany (with a strengthened focus and transition towards H-gas, as the L-gas reservoirs in Germany and the Netherlands are declining).\n\nLiquified natural gas\n\nCompressed Natural gas\nCNG is transported at high pressure, typically above 200 bars (20,000 kPa; 2,900 psi). Compressors and decompression equipment are less capital intensive and may be economical in smaller unit sizes than liquefaction/regasification plants. Natural gas trucks and carriers may transport natural gas directly to end-users, or to distribution points such as pipelines.\n\nFlaring\n\nIn the past, the natural gas which was recovered in the course of recovering petroleum could not be profitably sold, and was simply burned at the oil field in a process known as flaring. Flaring is now illegal in many countries. Additionally, higher demand in the last 20–30 years has made production of gas associated with oil economically viable. As a further option, the gas is now sometimes re-injected into the formation for enhanced oil recovery by pressure maintenance as well as miscible or immiscible flooding. Conservation, re-injection, or flaring of natural gas associated with oil is primarily dependent on proximity to markets (pipelines), and regulatory restrictions.\nNatural gas can be indirectly exported through the absorption in other physical output. The expansion of shale gas production in the US has caused prices to drop relative to other countries. This has caused a boom in energy intensive manufacturing sector exports, whereby the average dollar unit of US manufacturing exports has almost tripled its energy content between 1996 and 2012.\nA \"master gas system\" was invented in Saudi Arabia in the late 1970s, ending any necessity for flaring. Satellite and nearby infra-red camera observations, however, shows that flaring and venting are still happening in some countries.\nSimilarly, some landfills that also discharge methane gases have been set up to capture the methane and generate electricity.\n\nSalt domes and underground storage\nNatural gas is often stored underground [references about geological storage needed]inside depleted gas reservoirs from previous gas wells, salt domes, or in tanks as liquefied natural gas. The gas is injected in a time of low demand and extracted when demand picks up. Storage nearby end users helps to meet volatile demands, but such storage may not always be practicable.\n\nFloating liquefied natural gas\nFloating liquefied natural gas (FLNG) is an innovative technology designed to enable the development of offshore gas resources that would otherwise remain untapped due to environmental or economic factors which currently make them impractical to develop via a land-based LNG operation. FLNG technology also provides a number of environmental and economic advantages:\n\nEnvironmental – Because all processing is done at the gas field, there is no requirement for long pipelines to shore, compression units to pump the gas to shore, dredging and jetty construction, and onshore construction of an LNG processing plant, which significantly reduces the environmental footprint. Avoiding construction also helps preserve marine and coastal environments. In addition, environmental disturbance will be minimised during decommissioning because the facility can easily be disconnected and removed before being refurbished and re-deployed elsewhere.\nEconomic – Where pumping gas to shore can be prohibitively expensive, FLNG makes development economically viable. As a result, it will open up new business opportunities for countries to develop offshore gas fields that would otherwise remain stranded, such as those offshore East Africa.\nMany gas and oil companies are considering the economic and environmental benefits of floating liquefied natural gas (FLNG). There are currently projects underway to construct five FLNG facilities. Petronas is close to completion on their FLNG-1 at Daewoo Shipbuilding and Marine Engineering and are underway on their FLNG-2 project at Samsung Heavy Industries. Shell Prelude is due to start production 2017. The Browse LNG project will commence FEED in 2019.\n\nUses\nNatural gas is primarily used in the northern hemisphere. North America and Europe are major consumers.\nOften well head gases require removal of various hydrocarbon molecules contained within the gas. Some of these gases include heptane, pentane, propane and other hydrocarbons with molecular weights above methane (CH4). The natural gas transmission lines extend to the natural gas processing plant or unit which removes the higher-molecular weight hydrocarbons to produce natural gas with energy content between 35–39 megajoules per cubic metre (950–1,050 British thermal units per cubic foot). The processed natural gas may then be used for residential, commercial and industrial uses.\n\nMid-stream natural gas\nNatural gas flowing in the distribution lines is called mid-stream natural gas and is often used to power engines which rotate compressors. These compressors are required in the transmission line to pressurize and repressurize the mid-stream natural gas as the gas travels. Typically, natural gas powered engines require 35–39 MJ/m3 (950–1,050 BTU/ft3) natural gas to operate at the rotational name plate specifications. Several methods are used to remove these higher molecular weighted gases for use by the natural gas engine. A few technologies are as follows:\n\nJoule–Thomson skid\nCryogenic or chiller system\nChemical enzymology system\n\nPower generation\n\nDomestic use\n\nIn the US, over one-third of households (>40 million homes) cook with gas. Natural gas dispensed in a residential setting can generate temperatures in excess of 1,100 °C (2,000 °F) making it a powerful domestic cooking and heating fuel. Stanford scientists estimated that gas stoves emit 0.8–1.3% of the gas they use as unburned methane and that total U.S. stove emissions are 28.1 gigagrams of methane. In much of the developed world it is supplied through pipes to homes, where it is used for many purposes including ranges and ovens, heating/cooling, outdoor and portable grills, and central heating. Heaters in homes and other buildings may include boilers, furnaces, and water heaters. Both North America and Europe are major consumers of natural gas.\nDomestic appliances, furnaces, and boilers use low pressure, usually with a standard pressure around 1.7 kilopascals (0.25 psi) over atmospheric pressure. The pressures in the supply lines vary, either the standard utilization pressure (UP) mentioned above or elevated pressure (EP), which may be anywhere from 7 to 800 kilopascals (1 to 120 psi) over atmospheric pressure. Systems using EP have a regulator at the service entrance to step down to UP.\nNatural gas piping systems inside buildings are often designed with pressures of 14 to 34 kilopascals (2 to 5 psi), and have downstream pressure regulators to reduce pressure as needed. In the United States the maximum allowable operating pressure for natural gas piping systems within a building is based on NFPA 54: National Fuel Gas Code, except when approved by the Public Safety Authority or when insurance companies have more stringent requirements.\nGenerally, natural gas system pressures are not allowed to exceed 5 psi (34 kPa) unless all of the following conditions are met:\n\nThe AHJ will allow a higher pressure.\nThe distribution pipe is welded. (Note: 2. Some jurisdictions may also require that welded joints be radiographed to verify continuity).\nThe pipes are closed for protection and placed in a ventilated area that does not allow gas accumulation.\nThe pipe is installed in the areas used for industrial processes, research, storage or mechanical equipment rooms.\nGenerally, a maximum liquefied petroleum gas pressure of 20 psi (140 kPa) is allowed, provided the building is constructed in accordance with NFPA 58: Liquefied Petroleum Gas Code, Chapter 7.\nA seismic earthquake valve operating at a pressure of 55 psig (3.7 bar) can stop the flow of natural gas into the site wide natural gas distribution piping network (that runs (outdoors underground, above building roofs, and or within the upper supports of a canopy roof). Seismic earthquake valves are designed for use at a maximum of 60 psig.\nIn Australia, natural gas is transported from gas processing facilities to regulator stations via transmission pipelines. Gas is then regulated down to distributed pressures and the gas is distributed around a gas network via gas mains. Small branches from the network, called services, connect individual domestic dwellings, or multi-dwelling buildings to the network. The networks typically range in pressures from 7 kPa (low pressure) to 515 kPa (high pressure). Gas is then regulated down to 1.1 kPa or 2.75 kPa, before being metered and passed to the consumer for domestic use. Natural gas mains are made from a variety of materials: historically cast iron, though more modern mains are made from steel or polyethylene.\nIn some states in the USA, natural gas can be supplied by independent natural gas wholesalers/suppliers using existing pipeline owners' infrastructure through Natural Gas Choice programs.\nLPG (liquefied petroleum gas) typically fuels outdoor and portable grills. Although, compressed natural gas (CNG) is sparsely available for similar applications in the US in rural areas underserved by the existing pipeline system and distribution network of the less expensive and more abundant LPG (liquefied petroleum gas).\n\nTransportation\n\nCNG is a cleaner and also cheaper alternative to other automobile fuels such as gasoline (petrol). By the end of 2014, there were over 20 million natural gas vehicles worldwide, led by Iran (3.5 million), China (3.3 million), Pakistan (2.8 million), Argentina (2.5 million), India (1.8 million), and Brazil (1.8 million). The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines. Gasoline/petrol vehicles converted to run on natural gas suffer because of the low compression ratio of their engines, resulting in a cropping of delivered power while running on natural gas (10–15%). CNG-specific engines, however, use a higher compression ratio due to this fuel's higher octane number of 120–130.\nBesides use in road vehicles, CNG can also be used in aircraft. Compressed natural gas has been used in some aircraft like the Aviat Aircraft Husky 200 CNG and the Chromarat VX-1 KittyHawk\nLNG is also being used in aircraft. Russian aircraft manufacturer Tupolev for instance is running a development program to produce LNG- and hydrogen-powered aircraft. The program has been running since the mid-1970s, and seeks to develop LNG and hydrogen variants of the Tu-204 and Tu-334 passenger aircraft, and also the Tu-330 cargo aircraft. Depending on the current market price for jet fuel and LNG, the consumption cost advantage for LNG-powered aircraft is approximately 18.96%, along with a 53.72% reduction to carbon monoxide, hydrocarbon and nitrogen oxide emissions.\nThe advantages of liquid methane as a jet engine fuel are that it has more specific energy than the standard kerosene mixes do and that its low temperature can help cool the air which the engine compresses for greater volumetric efficiency, in effect replacing an intercooler. Alternatively, it can be used to lower the temperature of the exhaust.\n\nFertilizers\n\nNatural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production. The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.\n\nHydrogen\n\nNatural gas can be used to produce hydrogen, with one common method being the hydrogen reformer. Hydrogen has many applications: it is a primary feedstock for the chemical industry, a hydrogenating agent, an important commodity for oil refineries, and the fuel source in hydrogen vehicles.\n\nAnimal and fish feed\nProtein rich animal and fish feed is produced by feeding natural gas to Methylococcus capsulatus bacteria on commercial scale.\n\nOlefins(alkenes)\nNatural gas components(alkanes) can be converted into olefins(alkenes) or other chemical synthesis. Ethane by oxidative dehydrogenation converts to ethylene, which can be further converted to ethylene oxide, ethylene glycol, acetaldehyde or other olefins. Propane by oxidative hydrogenation converts to propylene or can be oxidized to acrylic acid and acrylonitrile.\n\nOther\nNatural gas is also used in the manufacture of fabrics, glass, steel, plastics, paint, synthetic oil, and other products.\nFuel for industrial heating and desiccation processes.\nRaw material for large-scale fuel production using gas-to-liquid (GTL) process (e.g. to produce sulphur-and aromatic-free diesel with low-emission combustion).\n\nHealth effects\nCooking with natural gas contributes to poor indoor air quality and can lead to severe respiratory diseases such as asthma.\n\nEnvironmental effects\n\nGreenhouse effect and natural gas release\n\nNatural ga",
    "source": "wikipedia:Natural gas",
    "domain": "climate"
  },
  {
    "text": "Oil is a liquid with varying degrees of viscosity depending on temperature. Oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated lipids that are liquid at room temperature.\nThe general definition of oil includes classes of chemical compounds that may be otherwise unrelated in structure, properties, and uses. Oils may be animal, vegetable, or petrochemical in origin, and may be volatile or non-volatile. They are used for food (e.g., olive oil), fuel (e.g., heating oil), medical purposes (e.g., mineral oil), lubrication (e.g. motor oil), and the manufacture of many types of paints, plastics, and other materials. Specially prepared oils are used in some religious ceremonies and rituals as purifying agents.\n\nEtymology\n First usage in a form resembling the modern is in Anglo-Norman before (a)1300 in Land of Cokaygne in Middle English from Old French oile as a consequence of influence of Edward the Confessor (1042–1066) and after the killing of King Harold on 14 October 1066\n after the 1066 invasion from Normandy, the earliest extant source a translation from Latin during the 12th or 13th century (Marbode Lapidaire) from Classical Latin oleum, (the earliest extant source being: Plautus, Poenulus)\n which in turn comes from the Greek ἔλαιον (elaion), \"olive oil, oil\" and that from ἐλαία (elaia), \"olive tree\", \"olive fruit\". \"Olive oil\" in Mycenaean Greek (transliteration) is e-rai-wo.\n\nTypes\n\nOrganic oils\nOrganic oils are produced in remarkable diversity by plants, animals, and other organisms through natural metabolic processes. Lipid is the scientific term for the fatty acids, steroids and similar chemicals often found in the oils produced by living things, while oil refers to an overall mixture of chemicals. Organic oils may also contain chemicals other than lipids, including proteins, waxes (class of compounds with oil-like properties that are solid at common temperatures) and alkaloids.\nLipids can be classified by the way that they are made by an organism, their chemical structure and their limited solubility in water compared to oils. They have a high carbon and hydrogen content and are considerably lacking in oxygen compared to other organic compounds and minerals; they tend to be relatively nonpolar molecules, but may include both polar and nonpolar regions as in the case of phospholipids and steroids.\n\nMineral oils\n\nCrude oil, or petroleum, and its refined components, collectively termed petrochemicals, are crucial resources in the modern economy. Crude oil originates from ancient fossilized organic materials, such as zooplankton and algae, which geochemical processes convert into oil. The name \"mineral oil\" is a misnomer, in that minerals are not the source of the oil—ancient plants and animals are. Mineral oil is organic. However, it is classified as \"mineral oil\" instead of as \"organic oil\" because its organic origin is remote (and was unknown at the time of its discovery), and because it is obtained in the vicinity of rocks, underground traps, and sands. Mineral oil also refers to several specific distillates of crude oil.\n\nApplications\n\nCooking\n\nEdible vegetable and animal oils, as well as fats, are used for various purposes in cooking and food preparation. In particular, many foods are fried in oil much hotter than boiling water. Oils are also used for flavoring and for modifying the texture of foods (e.g. stir fry). Cooking oils are derived either from animal fat, as butter, lard and other types, or plant oils from olive, maize, sunflower and many other species.\n\nCosmetics\nOils are applied to hair to give it a lustrous look, to prevent tangles and roughness and to stabilize the hair to promote growth. See hair conditioner.\n\nReligion\nOil has been used throughout history as a religious medium. It is often considered a spiritually purifying agent and is used for anointing purposes. As a particular example, holy anointing oil has been an important ritual liquid for Judaism and Christianity.\n\nHealth\nOils have been consumed since ancient times. Oils are rich in fats and may contain beneficial health properties. A good example is olive oil. Olive oil contains a high amount of fat, which is why it was also historically used for lighting in ancient Greece and Rome. So people would use it to bulk out food so they would have more energy to burn through the day. Olive oil was also used as a cleanser, as it helped retain moisture in the skin while drawing grime to the surface. It served as a primitive form of soap. It was applied on the skin then scrubbed off with a wooden stick pulling off the excess grime and creating a layer where new grime could form but be easily washed off in the water as oil is hydrophobic. Fish oils hold the omega-3 fatty acid. This fatty acid helps with inflammation and reduces fat in the bloodstream. \n\nPainting\n \nColor pigments are easily suspended in oil, making it suitable as a supporting medium for paints. The oldest known extant oil paintings date from 650 AD.\n\nHeat transfer\n\nOils are used as coolants in oil cooling, for instance in electric transformers. Heat transfer oils are used both as coolants (see oil cooling), for heating (e.g. in oil heaters) and in other applications of heat transfer.\n\nLubrication\n\nGiven that they are non-polar, oils do not easily adhere to other substances. This makes them useful as lubricants for various engineering purposes. Mineral oils are more commonly used as machine lubricants than biological oils are. Whale oil is preferred for lubricating clocks, because it does not evaporate, leaving dust, although its use was banned in the US in 1980.\nIt is a long-running myth that spermaceti from whales has still been used in NASA projects such as the Hubble Space Telescope and the Voyager probe because of its extremely low freezing temperature. Spermaceti is not actually an oil, but a mixture mostly of wax esters, and there is no evidence that NASA has used whale oil.\n\nFuel\n\nSome oils burn in liquid or aerosol form, generating light, and heat which can be used directly or converted into other forms of energy such as electricity or mechanical work. In order to obtain many fuel oils, crude oil is pumped from the ground and is shipped via oil tanker or a pipeline to an oil refinery. There, it is converted from crude oil to diesel fuel (petrodiesel), ethane (and other short-chain alkanes), fuel oils (heaviest of commercial fuels, used in ships/furnaces), gasoline (petrol), jet fuel, kerosene, benzene (historically), and liquefied petroleum gas. A 42-US-gallon (35 imp gal; 160 L) barrel of crude oil produces approximately 10 US gallons (8.3 imp gal; 38 L) of diesel, 4 US gallons (3.3 imp gal; 15 L) of jet fuel, 19 US gallons (16 imp gal; 72 L) of gasoline, 7 US gallons (5.8 imp gal; 26 L) of other products, 3 US gallons (2.5 imp gal; 11 L) split between heavy fuel oil and liquified petroleum gases, and 2 US gallons (1.7 imp gal; 7.6 L) of heating oil. The total production of a barrel of crude into various products results in an increase to 45 US gallons (37 imp gal; 170 L).\nIn the 18th and 19th centuries, whale oil was commonly used for lamps, which was replaced with natural gas and then electricity.\n\nChemical feedstock\n\nCrude oil can be refined into a wide variety of component hydrocarbons using fractional distillation. Petrochemicals are the refined components of crude oil and the chemical products made from them. They are used as detergents, fertilizers, medicines, paints, plastics, synthetic fibers, and synthetic rubber.\nOrganic oils are another important chemical feedstock, especially in green chemistry.\n\nSee also\nEmulsifier, a chemical which allows oil and water to mix\n\nNotes\n\nReferences\n\nExternal links\n\n Media related to Oil at Wikimedia Commons\n\nPetroleum Online e-Learning resource from IHRDC",
    "source": "wikipedia:Oil",
    "domain": "climate"
  },
  {
    "text": "Biodiversity is the variability of life on Earth. It can be measured on various levels, for example, genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth—it is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.\nSince life began on Earth, six major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic aeon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion. In this period, the majority of multicellular phyla first appeared. The next 400 million years included repeated, massive biodiversity losses. Those events have been classified as mass extinction events. In the Carboniferous, rainforest collapse may have led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years.\nHuman activities have led to an ongoing biodiversity loss and an accompanying loss of genetic diversity. This process is often referred to as Holocene extinction, or the sixth mass extinction. For example, it was estimated in 2007 that up to 30% of all species will be extinct by 2050. Destroying habitats for farming is a key reason why biodiversity is decreasing today. Climate change also plays a role. This can be seen for example in the effects of climate change on biomes. This anthropogenic extinction may have started toward the end of the Pleistocene, as some studies suggest that the megafaunal extinction event that took place around the end of the last ice age partly resulted from overhunting. \n\nDefinitions\n\nBiologists most often define biodiversity as the \"totality of genes, species and ecosystems of a region\". An advantage of this definition is that it presents a unified view of the traditional types of biological variety previously identified:\n\ntaxonomic diversity (usually measured at the species diversity level)\necological diversity (often viewed from the perspective of ecosystem diversity)\nmorphological diversity (which stems from genetic diversity and molecular diversity)\nfunctional diversity (which is a measure of the number of functionally disparate species within a population (e.g. different feeding mechanisms, different motility, predator vs prey, etc.))\nBiodiversity is most commonly used to replace the more clearly-defined and long-established terms, species diversity and species richness. However, there is no concrete definition for biodiversity, as its definition continues to be reimagined and redefined. To give a couple of examples, the Food and Agriculture Organization of the United Nations (FAO) defined biodiversity in 2019 as \"the variability that exists among living organisms (both within and between species) and the ecosystems of which they are part.\" The World Health Organization updated its website's definition of biodiversity to be the \"variability among living organisms from all sources.\" Both these definitions, although broad, give a current understanding of what is meant by the term biodiversity.\n\nNumber of species\n\nAccording to estimates by Mora et al. (2011), there are approximately 8.7 million terrestrial species and 2.2 million oceanic species. The authors note that these estimates are strongest for eukaryotic organisms and likely represent the lower bound of prokaryotic diversity. Other estimates include:\n\n220,000 vascular plants, estimated using the species-area relation method\n0.7–1 million marine species\n10–30 million insects; (of some 0.9 million we know today)\n5–10 million bacteria;\n1.5-3 million fungi, estimates based on data from the tropics, long-term non-tropical sites and molecular studies that have revealed cryptic speciation. Some 0.075 million species of fungi had been documented by 2001;\n1 million mites\nThe number of microbial species is not reliably known, but the Global Ocean Sampling Expedition dramatically increased the estimates of genetic diversity by identifying an enormous number of new genes from near-surface plankton samples at various marine locations, initially over the 2004–2006 period. The findings may eventually cause a significant change in the way science defines species and other taxonomic categories.\nSince the rate of extinction has increased, many extant species may become extinct before they are described. Not surprisingly, in the Animalia the most studied groups are birds and mammals, whereas fishes and arthropods are the least studied animal groups.\n\nCurrent biodiversity loss\n\nDuring the last century, decreases in biodiversity have been increasingly observed. It was estimated in 2007 that up to 30% of all species will be extinct by 2050. Of these, about one eighth of known plant species are threatened with extinction. Estimates reach as high as 140,000 species per year (based on Species-area theory). This figure indicates unsustainable ecological practices, because few species emerge each year. The rate of species loss is greater now than at any time in human history, with extinctions occurring at rates hundreds of times higher than background extinction rates. and expected to still grow in the upcoming years. As of 2012, some studies suggest that 25% of all mammal species could be extinct in 20 years.\nIn absolute terms, the planet has lost 58% of its biodiversity since 1970 according to a 2016 study by the World Wildlife Fund. The Living Planet Report 2014 claims that \"the number of mammals, birds, reptiles, amphibians, and fish across the globe is, on average, about half the size it was 40 years ago\". Of that number, 39% accounts for the terrestrial wildlife gone, 39% for the marine wildlife gone and 76% for the freshwater wildlife gone. Biodiversity took the biggest hit in Latin America, plummeting 83 percent. High-income countries showed a 10% increase in biodiversity, which was canceled out by a loss in low-income countries. This is despite the fact that high-income countries use five times the ecological resources of low-income countries, which was explained as a result of a process whereby wealthy nations are outsourcing resource depletion to poorer nations, which are suffering the greatest ecosystem losses.\nA 2017 study published in PLOS One found that the biomass of insect life in Germany had declined by three-quarters in the last 25 years. Dave Goulson of Sussex University stated that their study suggested that humans \"appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon. If we lose the insects then everything is going to collapse.\"\nIn 2020 the World Wildlife Fund published a report saying that \"biodiversity is being destroyed at a rate unprecedented in human history\". The report claims that 68% of the population of the examined species were destroyed in the years 1970 – 2016.\nOf 70,000 monitored species, around 48% are experiencing population declines from human activity (in 2023), whereas only 3% have increasing populations.\n\nRates of decline in biodiversity in the current sixth mass extinction match or exceed rates of loss in the five previous mass extinction events in the fossil record. Biodiversity loss is in fact \"one of the most critical manifestations of the Anthropocene\" (since around the 1950s); the continued decline of biodiversity constitutes \"an unprecedented threat\" to the continued existence of human civilization. The reduction is caused primarily by human impacts, particularly habitat destruction.\nSince the Stone Age, species loss has accelerated above the average basal rate, driven by human activity. Estimates of species losses are at a rate 100–10,000 times as fast as is typical in the fossil record.\nLoss of biodiversity results in the loss of natural capital that supplies ecosystem goods and services. Species today are being wiped out at a rate 100 to 1,000 times higher than baseline, and the rate of extinctions is increasing. This process destroys the resilience and adaptability of life on Earth.\nIn 2006, many species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized. About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction—a total of 16,119. As of late 2022 9251 species were considered part of the IUCN's critically endangered.\nNumerous scientists and the IPBES Global Assessment Report on Biodiversity and Ecosystem Services assert that human population growth and overconsumption are the primary factors in this decline. However, other scientists have criticized this finding and say that loss of habitat caused by \"the growth of commodities for export\" is the main driver. A 2025 study found that human activities are responsible for biodiversity loss across all species and ecosystems.\nClimate change is an important driver of global biodiversity loss because of its impacts on ecosystems. At the same time, biodiversity and climate are closely interconnected, as biodiversity influences the mitigation and adaptation potential of ecosystems. For more information on these interactions, see the 'Regulating services' section below. Other studies, however, have pointed out that habitat destruction for the expansion of agriculture and the overexploitation of wildlife are the more significant drivers of contemporary biodiversity loss, not climate change. \n\nDistribution\n\nBiodiversity is not evenly distributed, rather it varies greatly across the globe as well as within regions and seasons. Among other factors, the diversity of all living things (biota) depends on temperature, precipitation, altitude, soils, geography and the interactions between other species. The study of the spatial distribution of organisms, species and ecosystems, is the science of biogeography.\nDiversity consistently measures higher in the tropics and in other localized regions such as the Cape Floristic Region and lower in polar regions generally. Rain forests that have had wet climates for a long time, such as Yasuní National Park in Ecuador, have particularly high biodiversity.\nThere is local biodiversity, which directly impacts daily life, affecting the availability of fresh water, food choices, and fuel sources for humans. Regional biodiversity includes habitats and ecosystems that synergizes and either overlaps or differs on a regional scale. National biodiversity within a country determines the ability for a country to thrive according to its habitats and ecosystems on a national scale. Also, within a country, endangered species are initially supported on a national level then internationally. Ecotourism may be utilized to support the economy and encourages tourists to continue to visit and support species and ecosystems they visit, while they enjoy the available amenities provided. International biodiversity impacts global livelihood, food systems, and health. Problematic pollution, over consumption, and climate change can devastate international biodiversity. Nature-based solutions are a critical tool for a global resolution. Many species are in danger of becoming extinct and need world leaders to be proactive with the Kunming-Montreal Global Biodiversity Framework.\nTerrestrial biodiversity is thought to be up to 25 times greater than ocean biodiversity. Forests harbour most of Earth's terrestrial biodiversity. The conservation of the world's biodiversity is thus utterly dependent on the way in which we interact with and use the world's forests. A new method used in 2011, put the total number of species on Earth at 8.7 million, of which 2.1 million were estimated to live in the ocean. However, this estimate seems to under-represent the diversity of microorganisms. Forests provide habitats for 80 percent of amphibian species, 75 percent of bird species and 68 percent of mammal species. About 60 percent of all vascular plants are found in tropical forests. Mangroves provide breeding grounds and nurseries for numerous species of fish and shellfish and help trap sediments that might otherwise adversely affect seagrass beds and coral reefs, which are habitats for many more marine species. Forests span around 4 billion acres (nearly a third of the Earth's land mass) and are home to approximately 80% of the world's biodiversity. About 1 billion hectares are covered by primary forests. Over 700 million hectares of the world's woods are officially protected.\nThe biodiversity of forests varies considerably according to factors such as forest type, geography, climate and soils – in addition to human use. Most forest habitats in temperate regions support relatively few animal and plant species and species that tend to have large geographical distributions, while the montane forests of Africa, South America and Southeast Asia and lowland forests of Australia, coastal Brazil, the Caribbean islands, Central America and insular Southeast Asia have many species with small geographical distributions. Areas with dense human populations and intense agricultural land use, such as Europe, parts of Bangladesh, China, India and North America, are less intact in terms of their biodiversity. Northern Africa, southern Australia, coastal Brazil, Madagascar and South Africa, are also identified as areas with striking losses in biodiversity intactness. European forests in EU and non-EU nations comprise more than 30% of Europe's land mass (around 227 million hectares), representing an almost 10% growth since 1990.\n\nLatitudinal gradients\n\nGenerally, there is an increase in biodiversity from the poles to the tropics. Thus localities at lower latitudes have more species than localities at higher latitudes. This is often referred to as the latitudinal gradient in species diversity. Several ecological factors may contribute to the gradient, but the ultimate factor behind many of them is the greater mean temperature at the equator compared to that at the poles.\nEven though terrestrial biodiversity declines from the equator to the poles, some studies claim that this characteristic is unverified in aquatic ecosystems, especially in marine ecosystems. The latitudinal distribution of parasites does not appear to follow this rule. Also, in terrestrial ecosystems the soil bacterial diversity has been shown to be highest in temperate climatic zones, and has been attributed to carbon inputs and habitat connectivity.\nIn 2016, an alternative hypothesis (\"the fractal biodiversity\") was proposed to explain the biodiversity latitudinal gradient. In this study, the species pool size and the fractal nature of ecosystems were combined to clarify some general patterns of this gradient. This hypothesis considers temperature, moisture, and net primary production (NPP) as the main variables of an ecosystem niche and as the axis of the ecological hypervolume. In this way, it is possible to build fractal hyper volumes, whose fractal dimension rises to three moving towards the equator.\n\nBiodiversity Hotspots\nA biodiversity hotspot is a region with a high level of endemic species that have experienced great habitat loss. The term hotspot was introduced in 1988 by Norman Myers. While hotspots are spread all over the world, the majority are forest areas and most are located in the tropics.\nBrazil's Atlantic Forest is considered one such hotspot, containing roughly 20,000 plant species, 1,350 vertebrates and millions of insects, about half of which occur nowhere else. The island of Madagascar and India are also particularly notable. Colombia is characterized by high biodiversity, with the highest rate of species by area unit worldwide and it has the largest number of endemics (species that are not found naturally anywhere else) of any country. About 10% of the species of the Earth can be found in Colombia, including over 1,900 species of bird, more than in Europe and North America combined, Colombia has 10% of the world's mammals species, 14% of the amphibian species and 18% of the bird species of the world. Madagascar dry deciduous forests and lowland rainforests possess a high ratio of endemism. Since the island separated from mainland Africa 66 million years ago, many species and ecosystems have evolved independently. Indonesia's 17,000 islands cover 735,355 square miles (1,904,560 km2) and contain 10% of the world's flowering plants, 12% of mammals and 17% of reptiles, amphibians and birds—along with nearly 240 million people. Many regions of high biodiversity and/or endemism arise from specialized habitats which require unusual adaptations, for example, alpine environments in high mountains, or Northern European peat bogs.\nAccurately measuring differences in biodiversity can be difficult. Selection bias amongst researchers may contribute to biased empirical research for modern estimates of biodiversity. In 1768, Rev. Gilbert White succinctly observed of his Selborne, Hampshire \"all nature is so full, that that district produces the most variety which is the most examined.\"\n\nEvolution over geologic timeframes\n\nBiodiversity is the result of 3.5 billion years of evolution. The origin of life has not been established by science, however, some evidence suggests that life may already have been well-established only a few hundred million years after the formation of the Earth. Until approximately 2.5 billion years ago, all life consisted of microorganisms – archaea, bacteria, and single-celled protozoans and protists.\n\nBiodiversity grew fast during the Phanerozoic (the last 540 million years), especially during the so-called Cambrian explosion—a period during which nearly every phylum of multicellular organisms first appeared. However, recent studies suggest that this diversification had started earlier, at least in the Ediacaran, and that it continued in the Ordovician. Over the next 400 million years or so, invertebrate diversity showed little overall trend and vertebrate diversity shows an overall exponential trend. This dramatic rise in diversity was marked by periodic, massive losses of diversity classified as mass extinction events. A significant loss occurred in anamniotic limbed vertebrates when rainforests collapsed in the Carboniferous, but amniotes seem to have been little affected by this event; their diversification slowed down later, around the Asselian/Sakmarian boundary, in the early Cisuralian (Early Permian), about 293 Ma ago. The worst was the Permian-Triassic extinction event, 251 million years ago. Vertebrates took 30 million years to recover from this event.\nThe most recent major mass extinction event, the Cretaceous–Paleogene extinction event, occurred 66 million years ago. This period has attracted more attention than others because it resulted in the extinction of the non-avian dinosaurs, which were represented by many lineages at the end of the Maastrichtian, just before that extinction event. However, many other taxa were affected by this crisis, which affected even marine taxa, such as ammonites, which also became extinct around that time.\nThe biodiversity of the past is called Paleobiodiversity. The fossil record suggests that the last few million years featured the greatest biodiversity in history. However, not all scientists support this view, since there is uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of recent geologic sections. Some scientists believe that corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago, whereas others consider the fossil record reasonably reflective of the diversification of life. Estimates of the present global macroscopic species diversity vary from 2 million to 100 million, with a best estimate of somewhere near 9 million, the vast majority arthropods. Diversity appears to increase continually in the absence of natural selection.\n\nDiversification\nThe existence of a global carrying capacity, limiting the amount of life that can live at once, is debated, as is the question of whether such a limit would also cap the number of species. While records of life in the sea show a logistic pattern of growth, life on land (insects, plants and tetrapods) shows an exponential rise in diversity. As one author states, \"Tetrapods have not yet invaded 64 percent of potentially habitable modes and it could be that without human influence the ecological and taxonomic diversity of tetrapods would continue to increase exponentially until most or all of the available eco-space is filled.\"\nIt also appears that the diversity continues to increase over time, especially after mass extinctions.\nOn the other hand, changes through the Phanerozoic correlate much better with the hyperbolic model (widely used in population biology, demography and macrosociology, as well as fossil biodiversity) than with exponential and logistic models. The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a negative feedback arising from resource limitation. Hyperbolic model implies a second-order positive feedback. Differences in the strength of the second-order feedback due to different intensities of interspecific competition might explain the faster rediversification of ammonoids in comparison to bivalves after the end-Permian extinction. The hyperbolic pattern of the world population growth arises from a second-order positive feedback between the population size and the rate of technological growth. The hyperbolic character of biodiversity growth can be similarly accounted for by a feedback between diversity and community structure complexity. The similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics.\nMost biologists agree however that the period since human emergence is part of a new mass extinction, named the Holocene extinction event, caused primarily by the impact humans are having on the environment. It has been argued that the present rate of extinction is sufficient to eliminate most species on the planet Earth within 100 years.\nNew species are regularly discovered (on average between 5–10,000 new species each year, most of them insects) and many, though discovered, are not yet classified (estimates are that nearly 90% of all arthropods are not yet classified). Most of the terrestrial diversity is found in tropical forests and in general, the land has more species than the ocean; some 8.7 million species may exist on Earth, of which some 2.1 million live in the ocean.\n\nSpecies diversity in geologic time frames\n\nIt is estimated that 5 to 50 billion species have existed on the planet. Assuming that there may be a maximum of about 50 million species currently alive, it stands to reason that greater than 99% of the planet's species went extinct prior to the evolution of humans. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86% have not yet been described. However, a May 2016 scientific report estimates that 1 trillion species are currently on Earth, with only one-thousandth of one percent described. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as four trillion tons of carbon. In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth.\nThe age of Earth is about 4.54 billion years. The earliest undisputed evidence of life dates at least from 3.7 billion years ago, during the Eoarchean era after a geological crust started to solidify following the earlier molten Hadean eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland. More recently, in 2015, \"remains of biotic life\" were found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, \"If life arose relatively quickly on Earth...then it could be common in the universe.\"\n\nRole and benefits of biodiversity\n\nEcosystem services\n\nThere have been many claims about biodiversity's effect on the ecosystem services, especially provisioning and regulating services. Some of those claims have been validated, some are incorrect and some lack enough evidence to draw definitive conclusions.\nEcosystem services have been grouped in three types:\n\nProvisioning services which involve the production of renewable resources (e.g.: food, wood, fresh water)\nRegulating services which are those that lessen environmental change (e.g.: climate regulation, pest/disease control)\nCultural services represent human value and enjoyment (e.g.: landscape aesthetics, cultural heritage, outdoor recreation and spiritual significance)\nExperiments with controlled environments have shown that humans cannot easily build ecosystems to support human needs; for example insect pollination cannot be mimicked, though there have been attempts to create artificial pollinators using unmanned aerial vehicles. The economic activity of pollination alone represented between $2.1–14.6 billion in 2003. Other sources have reported somewhat conflicting results and in 1997 Robert Costanza and his colleagues reported the estimated global value of ecosystem services (not captured in traditional markets) at an average of $33 trillion annually.\n\nProvisioning services\nWith regards to provisioning services, greater species diversity has the following benefits:\n\nGreater species diversity of plants increases fodder yield (synthesis of 271 experimental studies).\nGreater species diversity of plants (i.e. diversity within a single species) increases overall crop yield (synthesis of 575 experimental studies). Although another review of 100 experimental studies reported mixed evidence.\nGreater species diversity of trees increases overall wood production (synthesis of 53 experimental studies). However, there is not enough data to draw a conclusion about the effect of tree trait diversity on wood production.\n\nRegulating services\nBiodiversity plays a role in multiple ecological regulating services that strengthen the stability, functioning and adaptability of ecosystems. For example, plant species richness can increase functional diversity in many ecosystems. Different plant organisms living together can perform complementary roles such as nutrient cycling and water regulation, which can contribute to the stabilisation of ecosystem processes under climate stress, a mechanism known as niche complementarity. This could include enhanced transpiration and soil moisture regulation, as more efficient water use can be promoted by the variety of different leaf traits and root depths, which in turn can reduce drought stress and mitigate heat impact.\nClimate change is also associated with higher pathogen pressure on terrestrial and marine ecosystems. In many ecosystems higher biodiversity could contribute to greater resilience to pests and diseases, as diversity in host traits and interactions can interrupt disease spread and reduce the severity of the outbreak. In coastal ecosystems genetic diversity within a species can further enhance its adaptive capacity by providing a range of traits that support populations to persist under changing temperature and precipitation regimes. Furthermore, in terrestrial ecosystems higher biodiversity can promote mutualistic interactions (like pollination or mycorrhizal networks), which can enhance nutrient uptake and support overall productivity and resilience.\nA long-term grassland experiment in Germany found that species-rich plant communities can also enhance resistance in both dry and wet climatic conditions and maintain productivity during periods of climatic stress, although species richness reduced resilience under dry extremes and had no effect under wet extremes.\nFurther studies have shown that greater species diversity:\n\nof fish increases the stability of fisheries yield (synthesis of 8 observational studies)\nof plants increases carbon sequestration, but note that this finding only relates to actual uptake of carbon dioxide and not long-term storage; synthesis of 479 experimental studies)\nof plants increases soil nutrient remineralization (synthesis of 103 experimental studies), increases soil organic matter (synthesis of 85 experimental studies) and decreases disease prevalence on plants (synthesis of 107 experimental studies)\nof natural pest enemies decreases herbivorous pest populations, according to data from two separate reviews; including a synthesis of 266 experimental and observational studies; Synthesis of 18 observational studies. Although another review of 38 experimental studies found mixed support for this claim, suggesting that in cases where mutual intraguild predation occurs, a single predatory species is often more effective\n\nAgriculture\n\nAgricultural diversity can be divided into two categories: intraspecific diversity, which includes the genetic variation within a single species, like the potato (Solanum tuberosum) that is composed of many different forms and types (e.g. in the U.S. they might compare russet potatoes with new potatoes or purple potatoes, all different, but all part o",
    "source": "wikipedia:Biodiversity",
    "domain": "climate"
  },
  {
    "text": "Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. About 31% of Earth's land surface is covered by forests at present. This is one-third less than the forest cover before the expansion of agriculture, with half of that loss occurring in the last century. On average 2,400 trees are cut down each minute. Estimates vary widely as to the extent of deforestation in the tropics. In 2019, nearly a third of the overall tree cover loss, or 3.8 million hectares, occurred within humid tropical primary forests. These are areas of mature rainforest that are especially important for biodiversity and carbon storage.\nBy far, the direct cause of most deforestation is agriculture. More than 80% of deforestation was attributed to agriculture in 2012. Forests are being converted to plantations for coffee, palm oil, rubber and various other popular products. Livestock grazing also drives deforestation. Further drivers are the wood industry (logging), urbanization and mining. The effects of climate change are another cause via the increased risk of wildfires (see deforestation and climate change).\nDeforestation results in habitat destruction which in turn leads to biodiversity loss. Deforestation also leads to extinction of animals and plants, changes to the local climate, and displacement of indigenous people who live in forests. Deforested regions often also suffer from other environmental problems such as desertification and soil erosion.\nAnother problem is that deforestation reduces the uptake of carbon dioxide (carbon sequestration) from the atmosphere. This reduces the potential of forests to assist with climate change mitigation. The role of forests in capturing and storing carbon and mitigating climate change is also important for the agricultural sector. The reason for this linkage is that the effects of climate change on agriculture pose new risks to global food systems.\nSince 1990, it is estimated that some 420 million hectares of forest have been lost through conversion to other land uses, although the rate of deforestation has decreased over the past three decades. Between 2015 and 2020, the rate of deforestation was estimated at 10 million hectares per year, down from 16 million hectares per year in the 1990s. The area of primary forest worldwide has decreased by over 80 million hectares since 1990. More than 100 million hectares of forests are adversely affected by forest fires, pests, diseases, invasive species, drought and adverse weather events.\n\nDefinition\n\nDeforestation is defined as the conversion of forest to other land uses (regardless of whether it is human-induced).\nDeforestation and forest area net change are not the same: the latter is the sum of all forest losses (deforestation) and all forest gains (forest expansion) in a given period. Net change, therefore, can be positive or negative, depending on whether gains exceed losses, or vice versa.\n\nCurrent status by continent, region, country\n\nThe FAO estimates that the global forest carbon stock has decreased 0.9%, and tree cover 4.2% between 1990 and 2020.\n\nAs of 2019 there is still disagreement about whether the global forest is shrinking or not: \"While above-ground biomass carbon stocks are estimated to be declining in the tropics, they are increasing globally due to increasing stocks in temperate and boreal forest.\nDeforestation in many countries—both naturally occurring and human-induced—is an ongoing issue. Between 2000 and 2012, 2.3 million square kilometres (890,000 square miles) of forests around the world were cut down. Deforestation and forest degradation continue to take place at alarming rates, which contributes significantly to the ongoing loss of biodiversity.\n\nDeforestation is more extreme in tropical and subtropical forests in emerging economies. More than half of all plant and land animal species in the world live in tropical forests. As a result of deforestation, only 6.2 million square kilometres (2.4 million square miles) remain of the original 16 million square kilometres (6 million square miles) of tropical rainforest that formerly covered the Earth. More than 3.6 million hectares of virgin tropical forest was lost in 2018.\nThe global annual net loss of trees is estimated to be approximately 10 billion. According to the Global Forest Resources Assessment 2020 the global average annual deforested land in the 2015–2020 demi-decade was 10 million hectares and the average annual forest area net loss in the 2000–2010 decade was 4.7 million hectares. The world has lost 178 million ha of forest since 1990, which is an area about the size of Libya.\nAn analysis of global deforestation patterns in 2021 showed that patterns of trade, production, and consumption drive deforestation rates in complex ways. While the location of deforestation can be mapped, it does not always match where the commodity is consumed. For example, consumption patterns in G7 countries are estimated to cause an average loss of 3.9 trees per person per year. In other words, deforestation can be directly related to imports—for example, coffee.\nIn 2023, the Global Forest Watch reported a 9% decline in tropical primary forest loss compared to the previous year, with significant regional reductions in Brazil and Colombia overshadowed by increases elsewhere, leading to a 3.2% rise in global deforestation. Massive wildfires in Canada, exacerbated by climate change, contributed to a 24% increase in global tree cover loss, highlighting the ongoing threats to forests essential for carbon storage and biodiversity. Despite some progress, the overall trends in forest destruction and climate impacts remain off track.\nThe IPCC Sixth Assessment Report stated in 2022: \"Over 420 million ha of forest were lost to deforestation from 1990 to 2020; more than 90% of that loss took place in tropical areas (high confidence), threatening biodiversity, environmental services, livelihoods of forest communities and resilience to climate shocks (high confidence).\"\nSee also:\n\nDeforestation by continent\nAll pages with titles containing deforestation in\nAll pages with titles containing deforestation of\nAll pages with titles containing land clearing in\n\nRates of deforestation\n\nGlobal deforestation sharply accelerated around 1852. As of 1947, the planet had 15 to 16 million km2 (5.8 to 6.2 million mi2) of mature tropical forests, but by 2015, it was estimated that about half of these had been destroyed. Total land coverage by tropical rainforests decreased from 14% to 6%. Much of this loss happened between 1960 and 1990, when 20% of all tropical rainforests were destroyed. At this rate, extinction of such forests is projected to occur by the mid-21st century.\nIn the early 2000s, some scientists predicted that unless significant measures (such as seeking out and protecting old growth forests that have not been disturbed) are taken on a worldwide basis, by 2030 there will only be 10% remaining, with another 10% in a degraded condition. 80% will have been lost, and with them hundreds of thousands of irreplaceable species.\nEstimates vary widely as to the extent of deforestation in the tropics. In 2019, the world lost nearly 12 million hectares of tree cover. Nearly a third of that loss, 3.8 million hectares, occurred within humid tropical primary forests, areas of mature rainforest that are especially important for biodiversity and carbon storage. This is equivalent to losing an area of primary forest the size of a football pitch every six seconds.\n\nRates of change\n\nA 2002 analysis of satellite imagery suggested that the rate of deforestation in the humid tropics (approximately 5.8 million hectares per year) was roughly 23% lower than the most commonly quoted rates. A 2005 report by the United Nations Food and Agriculture Organization (FAO) estimated that although the Earth's total forest area continued to decrease at about 13 million hectares per year, the global rate of deforestation had been slowing. On the other hand, a 2005 analysis of satellite images reveals that deforestation of the Amazon rainforest is twice as fast as scientists previously estimated.\nFrom 2010 to 2015, worldwide forest area decreased by 3.3 million ha per year, according to FAO. During this five-year period, the biggest forest area loss occurred in the tropics, particularly in South America and Africa. Per capita forest area decline was also greatest in the tropics and subtropics but is occurring in every climatic domain (except in the temperate) as populations increase.\nAn estimated 420 million ha of forest has been lost worldwide through deforestation since 1990, but the rate of forest loss has declined substantially. In the most recent five-year period (2015–2020), the annual rate of deforestation was estimated at 10 million ha, down from 12 million ha in 2010–2015.\n\nAfrica had the largest annual rate of net forest loss in 2010–2020, at 3.9 million ha, followed by South America, at 2.6 million ha. The rate of net forest loss has increased in Africa in each of the three decades since 1990. It has declined substantially in South America, however, to about half the rate in 2010–2020 compared with 2000–2010. Asia had the highest net gain of forest area in 2010–2020, followed by Oceania and Europe. Nevertheless, both Europe and Asia recorded substantially lower rates of net gain in 2010–2020 than in 2000–2010. Oceania experienced net losses of forest area in the decades 1990–2000 and 2000–2010.\nSome claim that rainforests are being destroyed at an ever-quickening pace. The London-based Rainforest Foundation notes that \"the UN figure is based on a definition of forest as being an area with as little as 10% actual tree cover, which would therefore include areas that are actually savanna-like ecosystems and badly damaged forests\". Other critics of the FAO data point out that they do not distinguish between forest types, and that they are based largely on reporting from forestry departments of individual countries, which do not take into account unofficial activities like illegal logging. Despite these uncertainties, there is agreement that destruction of rainforests remains a significant environmental problem.\nThe rate of net forest loss declined from 7.8 million ha per year in the decade 1990–2000 to 5.2 million ha per year in 2000–2010 and 4.7 million ha per year in 2010–2020. The rate of decline of net forest loss slowed in the most recent decade due to a reduction in the rate of forest expansion.\n\nReforestation and afforestation\n\nIn many parts of the world, especially in East Asian countries, reforestation and afforestation are increasing the area of forested lands. The amount of forest has increased in 22 of the world's 50 most forested nations. Asia as a whole gained 1 million hectares of forest between 2000 and 2005. Tropical forest in El Salvador expanded more than 20% between 1992 and 2001. Based on these trends, one study projects that global forestation will increase by 10%—an area the size of India—by 2050. 36% of globally planted forest area is in East Asia – around 950,000 square kilometers. From those 87% are in China.\n\nStatus by region\n\nRates of deforestation vary around the world. Up to 90% of West Africa's coastal rainforests have disappeared since 1900. Madagascar has lost 90% of its eastern rainforests. In South Asia, about 88% of the rainforests have been lost.\nMexico, India, the Philippines, Indonesia, Thailand, Burma, Malaysia, Bangladesh, China, Sri Lanka, Laos, Nigeria, the Democratic Republic of the Congo, Liberia, Guinea, Ghana and the Ivory Coast, have lost large areas of their rainforest.\n\nMuch of what remains of the world's rainforests is in the Amazon basin, where the Amazon rainforest covers approximately 4 million square kilometres. Some 80% of the deforestation of the Amazon can be attributed to cattle ranching, as Brazil is the largest exporter of beef in the world. The Amazon region has become one of the largest cattle ranching territories in the world. The regions with the highest tropical deforestation rate between 2000 and 2005 were Central America—which lost 1.3% of its forests each year—and tropical Asia. In Central America, two-thirds of lowland tropical forests have been turned into pasture since 1950 and 40% of all the rainforests have been lost in the last 40 years. Brazil has lost 90–95% of its Mata Atlântica forest. Deforestation in Brazil increased by 88% for the month of June 2019, as compared with the previous year. However, Brazil still destroyed 1.3 million hectares in 2019. Brazil is one of several countries that have declared their deforestation a national emergency. \nParaguay was losing its natural semi-humid forests in the country's western regions at a rate of 15,000 hectares at a randomly studied 2-month period in 2010. In 2009, Paraguay's parliament refused to pass a law that would have stopped cutting of natural forests altogether.\nAs of 2007, less than 50% of Haiti's forests remained.\nFrom 2015 to 2019, the rate of deforestation in the Democratic Republic of the Congo doubled. In 2021, deforestation of the Congolese rainforest increased by 5%.\nThe World Wildlife Fund's ecoregion project catalogues habitat types throughout the world, including habitat loss such as deforestation, showing for example that even in the rich forests of parts of Canada such as the Mid-Continental Canadian forests of the prairie provinces half of the forest cover has been lost or altered.\nIn 2011, Conservation International listed the top 10 most endangered forests, characterized by having all lost 90% or more of their original habitat, and each harboring at least 1500 endemic plant species (species found nowhere else in the world).\nAs of 2015, it is estimated that 70% of the world's forests are within one kilometer of a forest edge, where they are most prone to human interference and destruction.\n\nBy country\nDeforestation in particular countries:\n\nCauses\n\nAgricultural expansion continues to be the main driver of deforestation and forest fragmentation and the associated loss of forest biodiversity. Large-scale commercial agriculture (primarily cattle ranching and cultivation of soya bean and oil palm) accounted for 40 percent of tropical deforestation between 2000 and 2010, and local subsistence agriculture for another 33 percent. Trees are cut down for use as building material, timber or sold as fuel (sometimes in the form of charcoal or timber), while cleared land is used as pasture for livestock and agricultural crops.\nThe vast majority of agricultural activity resulting in deforestation is subsidized by government tax revenue. Disregard of ascribed value, lax forest management, and deficient environmental laws are some of the factors that lead to large-scale deforestation.\nThe types of drivers vary greatly depending on the region in which they take place. The regions with the greatest amount of deforestation for livestock and row crop agriculture are Central and South America, while commodity crop deforestation was found mainly in Southeast Asia. The region with the greatest forest loss due to shifting agriculture was sub-Saharan Africa.\n\nAgriculture\n\nThe overwhelming direct cause of deforestation is agriculture. Subsistence farming is responsible for 48% of deforestation; commercial agriculture is responsible for 32%; logging is responsible for 14%, and fuel wood removals make up 5%.\nMore than 80% of deforestation was attributed to agriculture in 2018. Forests are being converted to plantations for coffee, tea, palm oil, rice, rubber, and various other popular products. The rising demand for certain products and global trade arrangements causes forest conversions, which ultimately leads to soil erosion. The top soil oftentimes erodes after forests are cleared which leads to sediment increase in rivers and streams.\n\nMost deforestation also occurs in tropical regions. The estimated amount of total land mass used by agriculture is around 38%.\nSince 1960, roughly 15% of the Amazon has been removed with the intention of replacing the land with agricultural practices. It is no coincidence that Brazil has recently become the world's largest beef exporter at the same time that the Amazon rainforest is being clear cut.\nAnother prevalent method of agricultural deforestation is slash-and-burn agriculture, which was primarily used by subsistence farmers in tropical regions but has now become increasingly less sustainable. The method does not leave land for continuous agricultural production but instead cuts and burns small plots of forest land which are then converted into agricultural zones. The farmers then exploit the nutrients in the ashes of the burned plants. As well as, intentionally set fires can possibly lead to devastating measures when unintentionally spreading fire to more land, which can result in the destruction of the protective canopy.\nThe repeated cycle of low yields and shortened fallow periods eventually results in less vegetation being able to grow on once burned lands and a decrease in average soil biomass. In small local plots sustainability is not an issue because of longer fallow periods and lesser overall deforestation. The relatively small size of the plots allowed for no net input of CO2 to be released.\n\nLivestock ranching\nConsumption and production of beef is the primary driver of deforestation in the Amazon, with around 80% of all converted land being used to rear cattle. 91% of Amazon land deforested since 1970 has been converted to cattle ranching.\nLivestock ranching requires large portions of land to raise herds of animals and livestock crops for consumer needs. According to the World Wildlife Fund, \"Extensive cattle ranching is the number one culprit of deforestation in virtually every Amazon country, and it accounts for 80% of current deforestation.\"\nThe cattle industry is responsible for a significant amount of methane emissions since 60% of all mammals on earth are livestock cows. Replacing forest land with pastures creates a loss of forest stock, which leads to the implication of increased greenhouse gas emissions by burning agriculture methodologies and land-use change.\n\nJunk Mail\n\nOver 100 million trees per year are cut down for the purpose of junk mail. A major reason for the United States allowing this deforestation practice is to fund the United States Postal Service.\n\nWood industry\n\nA large contributing factor to deforestation is the lumber industry. A total of almost 4 million hectares (9.9 million acres) of timber, or about 1.3% of all forest land, is harvested each year. In addition, the increasing demand for low-cost timber products only supports the lumber company to continue logging.\nExperts do not agree on whether industrial logging is an important contributor to global deforestation. Some argue that poor people are more likely to clear forest because they have no alternatives, others that the poor lack the ability to pay for the materials and labour needed to clear forest.\n\nEconomic development\nOther causes of contemporary deforestation may include corruption of government institutions, the inequitable distribution of wealth and power, population growth and overpopulation, and urbanization. The impact of population growth on deforestation has been contested. One study found that population increases due to high fertility rates were a primary driver of tropical deforestation in only 8% of cases. In 2000 the United Nations Food and Agriculture Organization (FAO) found that \"the role of population dynamics in a local setting may vary from decisive to negligible\", and that deforestation can result from \"a combination of population pressure and stagnating economic, social and technological conditions\".\nGlobalization is often viewed as another root cause of deforestation, though there are cases in which the impacts of globalization (new flows of labor, capital, commodities, and ideas) have promoted localized forest recovery.\n\nThe degradation of forest ecosystems has also been traced to economic incentives that make forest conversion appear more profitable than forest conservation. Many important forest functions have no markets, and hence, no economic value that is readily apparent to the forests' owners or the communities that rely on forests for their well-being.\nSome commentators have noted a shift in the drivers of deforestation over the past 30 years. Whereas deforestation was primarily driven by subsistence activities and government-sponsored development projects like transmigration in countries like Indonesia and colonization in Latin America, India, Java, and so on, during the late 19th century and the first half of the 20th century, by the 1990s the majority of deforestation was caused by industrial factors, including extractive industries, large-scale cattle ranching, and extensive agriculture. Since 2001, commodity-driven deforestation, which is more likely to be permanent, has accounted for about a quarter of all forest disturbance, and this loss has been concentrated in South America and Southeast Asia.\nAs the human population grows, new homes, communities, and expansions of cities will occur, leading to an increase in roads to connect these communities. Rural roads promote economic development but also facilitate deforestation. About 90% of the deforestation has occurred within 100 km of roads in most parts of the Amazon.\n\nMining\nThe importance of mining as a cause of deforestation increased quickly in the beginning the 21st century, among other because of increased demand for minerals. The direct impact of mining is relatively small, but the indirect impacts are much more significant. More than a third of the earth's forests are possibly impacted, at some level and in the years 2001–2021, \"755,861 km2... ...had been deforested by causes indirectly related to mining activities alongside other deforestation drivers (based on data from WWF)\"\nIn the year 2023, mining, including for the elements needed for the energy transition strongly contributed to deforestation. Mining is a particular threat to biodiversity: \"in 2019, 79 percent of global metal ore extraction originated from five of the six most species-rich biomes\".\n\nClimate change\n\nAnother cause of deforestation is due to the effects of climate change: More wildfires, insect outbreaks, invasive species, and more frequent extreme weather events (such as storms) are factors that increase deforestation.\nA study suggests that \"tropical, arid and temperate forests are experiencing a significant decline in resilience, probably related to increased water limitations and climate variability\" which may shift ecosystems towards critical transitions and ecosystem collapses. By contrast, \"boreal forests show divergent local patterns with an average increasing trend in resilience, probably benefiting from warming and CO2 fertilization, which may outweigh the adverse effects of climate change\". It has been proposed that a loss of resilience in forests \"can be detected from the increased temporal autocorrelation (TAC) in the state of the system, reflecting a decline in recovery rates due to the critical slowing down (CSD) of system processes that occur at thresholds\".\n23% of tree cover losses result from wildfires and climate change increase their frequency and power. The rising temperatures cause massive wildfires especially in the Boreal forests. One possible effect is the change of the forest composition. Deforestation can also cause forests to become more fire prone through mechanisms such as logging.\n\nMilitary causes\n\nOperations in war can also cause deforestation. For example, in the 1945 Battle of Okinawa, bombardment and other combat operations reduced a lush tropical landscape into \"a vast field of mud, lead, decay and maggots\".\nDeforestation can also result from the intentional tactics of military forces. Clearing forests became an element in the Russian Empire's successful conquest of the Caucasus in the mid-19th century.\nThe British (during the Malayan Emergency) and the United States (in the Korean War and in the Vietnam War) used defoliants (like Agent Orange or others). The destruction of forests in Vietnam War is one of the most commonly used examples of ecocide, including by Swedish Prime Minister Olof Palme, lawyers, historians and other academics.\n\nImpacts\n\nOn atmosphere and climate\n\nDeforestation is a major contributor to climate change. It is often cited as one of the major causes of the enhanced greenhouse effect. Recent calculations suggest that CO2 emissions from deforestation and forest degradation (excluding peatland emissions) contribute about 12% of total anthropogenic CO2 emissions, with a range from 6% to 17%. A 2022 study shows annual carbon emissions from tropical deforestation have doubled during the last two decades and continue to increase: by 0.97 ± 0.16 PgC (petagrams of carbon, i.e. billions of tons) per year in 2001–2005 to 1.99 ± 0.13 PgC per year in 2015–2019.\nAccording to a review, north of 50°N, large scale deforestation leads to an overall net global cooling; but deforestation in the tropics leads to substantial warming: not just due to CO2 impacts, but also due to other biophysical mechanisms (making carbon-centric metrics inadequate). Moreover, it suggests that standing tropical forests help cool the average global temperature by more than 1 °C. According to a later study, deforestation in northern latitudes can also increase warming, while the conclusion about cooling from deforestation in these areas made by previous studies results from the failure of models to properly capture the effects of evapotranspiration.\nThe incineration and burning of forest plants to clear land releases large amounts of CO2, which contributes to global warming. Scientists also state that tropical deforestation releases 1.5 billion tons of carbon each year into the atmosphere.\n\nCarbon sink or source\n\nA study suggests logged and structurally degraded tropical forests are carbon sources for at least a decade – even when recovering – due to larger carbon losses from soil organic matter and deadwood, indicating that the tropical forest carbon sink (at least in South Asia) \"may be much smaller than previously estimated\", contradicting that \"recovering logged and degraded tropical forests are net carbon sinks\".\n\nOn the environment\nAccording to a 2020 study, if deforestation continues at current rates it can trigger a total or almost total extinction of humanity in the next 20 to 40 years. They conclude that \"from a statistical point of view... the probability that our civilisation survives itself is less than 10% in the most optimistic scenario.\" To avoid this collapse, humanity should pass from a civilization dominated by the economy to \"cultural society\" that \"privileges the interest of the ecosystem above the individual interest of its components, but eventually in accordance with the overall communal interest.\"\n\nChanges to the water cycle\nThe water cycle is also affected by deforestation. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the trees no longer transpire this water, resulting in a much drier climate. Deforestation reduces the content of water in the soil and groundwater as well as atmospheric moisture. The dry soil leads to lower water intake for the trees to extract. Deforestation reduces soil cohesion, so that erosion, flooding and landslides ensue.\nShrinking forest cover lessens the landscape's capacity to intercept, retain and transpire precipitation. Instead of trapping precipitation, which then percolates to groundwater systems, deforested areas become sources of surface water runoff, which moves much faster than subsurface flows. Forests return most of the water that falls as precipitation to the atmosphere by transpiration. In contrast, when an area is deforested, almost all precipitation is lost as run-off. That quicker transport of surface water can translate into flash flooding and more localized floods than would occur with the forest cover. Deforestation also contributes to decreased evapotranspiration, which lessens atmospheric moisture which in some cases affects precipitation levels downwind from the deforested area, as water is not recycled to downwind forests, but is lost in runoff and returns directly to the oceans. According to one study, in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s.\n\nTrees, and plants in general, affect the water cycle significantly:\n\ntheir canopies intercept a proportion of precipitation, which is then evaporated back to the atmosphere (canopy interception);\ntheir litter, stems and trunks slow down surface runoff;\ntheir roots create macropores – large conduits – in the soil that increase infiltration of water;\nthey contribute to terrestrial evaporation and reduce soil moisture via transpiration;\ntheir litter and other organic residue change soil properties that affect the capacity of soil to store water.\ntheir leaves control the humidity of the atmosphere by transpiring. 99% of the water absorbed by the roots moves up to the leaves and is transpired.\nAs a result, the presence or absence of trees can change the quantity of water on the surface, in the soil or groundwater, or in the atmosphere. This in turn changes erosion rates and the availability of water for either ecosystem functions or human services. Deforestation on lowland plains moves cloud formation and rainfall to higher elevations.\nThe forest may have little impact on flooding in the case of large rainfall events, which overwhelm the storage capacity of forest soil if the soils are at or close to saturation.\nTropical rainforests produce about 30% of Earth's fresh ",
    "source": "wikipedia:Deforestation",
    "domain": "climate"
  },
  {
    "text": "Desertification is a type of gradual land degradation of fertile land into arid desert due to a combination of natural processes and human activities.\nThe immediate cause of desertification is the loss of most vegetation. This is driven by a number of factors, alone or in combination, such as drought, climatic shifts, tillage for agriculture, overgrazing and deforestation for fuel or construction materials. Though vegetation plays a major role in determining the biological composition of the soil, studies have shown that, in many environments, the rate of erosion and runoff decreases exponentially with increased vegetation cover. Unprotected, dry soil surfaces blow away with the wind or are washed away by flash floods, leaving infertile lower soil layers that bake in the sun and become an unproductive hardpan.\nAt least 90% of the inhabitants of drylands live in developing countries, where they also suffer from poor economic and social conditions. This situation is exacerbated by land degradation because of the reduction in productivity, the precariousness of living conditions and the difficulty of access to resources and opportunities.\nGeographic areas most affected are located in Africa (Sahel region), Asia (Gobi Desert and Mongolia) and parts of South America. Drylands occupy approximately 40–41% of Earth's land area and are home to more than 2 billion people. Effects of desertification include sand and dust storms, food insecurity, and poverty.\nMethods of mitigating or reversing desertification include improving soil quality, greening deserts, managing grazing, and tree-planting (reforestation and afforestation).\nThroughout geological history, the development of deserts has occurred naturally over long intervals of time. The modern study of desertification emerged from the study of the 1980s drought in the Sahel.\n\nDefinitions\nDesertification is a gradual process of increased soil aridity. Desertification has been defined in the text of the United Nations Convention to Combat Desertification (UNCCD) as \"land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors, including climatic variations and human activities.\"\nDefinition of Desert – That area of the earth where the sum of rain and snowfall is much less than other areas, where the annual average rainfall is less than 25CM. Definition by UNO (1995) – Land degradation in barren, humid and sub-humid areas due to climate change and human activities is called desertification.\nAs of 2005, considerable controversy existed over the proper definition of the term desertification with more than 100 formal definitions in existence. The most widely accepted of these was that of the Princeton University Dictionary which defined it as \"the process of fertile land transforming into desert typically as a result of deforestation, drought or improper/inappropriate agriculture\". This definition clearly demonstrated the interconnectedness of desertification and human activities, in particular land use and land management practices. It also highlighted the economic, social and environmental implications of desertification. However, this original understanding that desertification involved the physical expansion of deserts has been rejected as the concept has further evolved since then.\nThere exists also controversy around the sub-grouping of types of desertification, including, for example, the validity and usefulness of such terms as \"man-made desert\" and \"non-pattern desert\".\n\nCauses\n\nImmediate causes\nThe immediate cause of desertification is the loss of most vegetation. This is driven by a number of factors, alone or in combination, such as drought, climatic shifts, tillage for agriculture, overgrazing and deforestation for fuel or construction materials. Though vegetation plays a major role in determining the biological composition of the soil, studies have shown that, in many environments, the rate of erosion and runoff decreases exponentially with increased vegetation cover. Unprotected, dry soil surfaces blow away with the wind or are washed away by flash floods, leaving infertile lower soil layers that bake in the sun and become an unproductive hardpan.\n\nInfluence of human activities\nEarly studies argued one of the most common causes of desertification was overgrazing, over consumption of vegetation by cattle or other livestock. However, the role of local overexploitation in driving desertification in the recent past is controversial. Drought in the Sahel region is now thought to be principally the result of seasonal variability in rainfall caused by large-scale sea surface temperature variations, largely driven by natural variability and anthropogenic emissions of aerosols (reflective sulphate particles) and greenhouse gases. As a result, changing ocean temperature and reductions in sulfate emissions have caused a re-greening of the region. This has led some scholars to argue that agriculture-induced vegetation loss is a minor factor in desertification.\nHuman population dynamics have a considerable impact on overgrazing, over-farming and deforestation, as previously acceptable techniques have become unsustainable.\nThere are multiple reasons farmers use intensive farming as opposed to extensive farming but the main reason is to maximize yields. By increasing productivity, they require a lot more fertilizer, pesticides, and labor to upkeep machinery. This continuous use of the land rapidly depletes the nutrients of the soil causing desertification to spread.\n\nNatural variations\nScientists agree that the existence of a desert in the place where the Sahara desert is now located is due to natural variations in solar insolation due to orbital precession of the Earth. Such variations influence the strength of the West African Monsoon, inducing feedback in vegetation and dust emission that amplify the cycle of wet and dry Sahara climate. There is also a suggestion the transition of the Sahara from savanna to desert during the mid-Holocene was partially due to overgrazing by the cattle of the local population.\nScientists have further studied critical regions, confirming that human activities and soil health join meteorological factors as main contributors towards desertification. In the Mu Us Desert, soil health makes up 37% of desertification events while meteorological and human activities work to counteract this phenomenon by 46% and 17%, respectively. Inner Mongolia desertification is characterized by 24% meteorological contributions and 34.7% soil benefits throughout this environment. Shaanxi is a counterexample in which meteorological factors work against desertification and soil exacerbates it, demonstrating the various influences of natural factors throughout regions.\n\nClimate change\n\nResearch into desertification is complex, and there is no single metric which can define all aspects. However, more intense climate change is still expected to increase the current extent of drylands on the Earth's continents: from 38% in late 20th century to 50% or 56% by the end of the century, under the \"moderate\" and high-warming Representative Concentration Pathways 4.5 and 8.5. Most of the expansion will be seen over regions such as \"southwest North America, the northern fringe of Africa, southern Africa, and Australia\".\nDrylands cover 41% of the earth's land surface and include 45% of the world's agricultural land. These regions are among the most vulnerable ecosystems to anthropogenic climate and land use change and are under threat of desertification. An observation-based attribution study of desertification was carried out in 2020 which accounted for climate change, climate variability, CO2 fertilization as well as both the gradual and rapid ecosystem changes caused by land use. The study found that, between 1982 and 2015, 6% of the world's drylands underwent desertification driven by unsustainable land use practices compounded by anthropogenic climate change. Despite an average global greening, anthropogenic climate change has degraded 12.6% (5.43 million km2) of drylands, contributing to desertification and affecting 213 million people, 93% of who live in developing economies.\n\nEffects\n\nSand and dust storms\n\nThere has been a 25% increase in global annual dust emissions between the late nineteenth century to present day. The increase of desertification has also increased the amount of loose sand and dust that the wind can pick up ultimately resulting in a storm. For example, dust storms in the Middle East \"are becoming more frequent and intense in recent years\" because \"long-term reductions in rainfall [cause] lower soil moisture and vegetative cover\".\nDust storms can contribute to certain respiratory disorders such as pneumonia, skin irritations, asthma and many more. They can pollute open water, reduce the effectiveness of clean energy efforts, and halt most forms of transportation.\nDust and sand storms can have a negative effect on the climate which can make desertification worse. Dust particles in the air scatter incoming radiation from the sun (Hassan, 2012). The dust can provide momentary coverage for the ground temperature but the atmospheric temperature will increase. This can disform and shorten the lifetime of clouds which can result in less rainfall.\n\nFood insecurity\nGlobal food security is being threatened by desertification. The more that population grows, the more food that has to be grown. The agricultural business is being displaced from one country to another. For example, Europe on average imports over 50% of its food. Meanwhile, 44% of agricultural land is located in dry lands and it supplies 60% of the world's food production. Desertification is decreasing the amount of sustainable land for agricultural uses but demands are continuously growing. In the near future, the demands will overcome the supply. The violent herder–farmer conflicts in Nigeria, Sudan, Mali and other countries in the Sahel region have been exacerbated by climate change, land degradation and population growth.\n\nIncreasing poverty\n\nAt least 90% of the inhabitants of drylands live in developing countries, where they also suffer from poor economic and social conditions. This situation is exacerbated by land degradation because of the reduction in productivity, the precariousness of living conditions and the difficulty of access to resources and opportunities.\nMany underdeveloped countries are affected by overgrazing, land exhaustion and overdrafting of groundwater due to pressures to exploit marginal drylands for farming. Decision-makers are understandably averse to invest in arid zones with low potential. This absence of investment contributes to the marginalization of these zones. When unfavorable agri-climatic conditions are combined with an absence of infrastructure and access to markets, as well as poorly adapted production techniques and an underfed and undereducated population, most such zones are excluded from development.\nDesertification often causes rural lands to become unable to support the same sized populations that previously lived there. This results in mass migrations out of rural areas and into urban areas particularly in Africa creating unemployment and slums. The number of these environmental refugees grows every year, with projections for sub-Saharan Africa showing a probable increase from 14 million in 2010 to nearly 200 million by 2050. This presents a future crisis for the region, as neighboring nations do not always have the ability to support large populations of refugees.\nIn Mongolia, the land is 90% fragile dry land, which causes many herders to migrate to the city for work. With very limited resources, the herders that stay on the dry land graze very carefully in order to preserve the land.\nAgriculture is a main source of income for many desert communities. The increase in desertification in these regions has degraded the land to such an extent where people can no longer productively farm and make a profit. This has negatively impacted the economy and increased poverty rates.\nThere is, however, increased global advocacy e.g. the UN SDG 15 to combat desertification and restore affected lands.\n\nGeographic areas affected\nDrylands occupy approximately 40–41% of Earth's land area and are home to more than 2 billion people. It has been estimated that some 10–20% of drylands are already degraded, the total area affected by desertification being between 6 and 12 million square kilometers, that about 1–6% of the inhabitants of drylands live in desertified areas, and that a billion people are under threat from further desertification.\n\nSahel\n\nThe impact of climate change and human activities on desertification are exemplified in the Sahel region of Africa. The region is characterized by a dry hot climate, high temperatures and low rainfall (100–600 mm per year). So, droughts are the rule in the Sahel region. The Sahel has lost approximately 650,000 km2 of its productive agricultural land over the past 50 years; the propagation of desertification in this area is considerable.\n\nThe climate of the Sahara has undergone enormous variations over the last few hundred thousand years, oscillating between wet (grassland) and dry (desert) every 20,000 years (a phenomenon believed to be caused by long-term changes in the North African climate cycle that alters the path of the North African Monsoon, caused by an approximately 40,000-year cycle in which the axial tilt of the earth changes between 22° and 24.5°). Some statistics have shown that, since 1900, the Sahara has expanded by 250 km to the south over a stretch of land from west to east 6,000 km long.\nLake Chad, located in the Sahel region, has undergone desiccation due to water withdrawal for irrigation and decrease in rainfall. The lake has shrunk by over 90% since 1987, displacing millions of inhabitants. Recent efforts have managed to make some progress toward its restoration, but it is still considered to be at risk of disappearing entirely.\nTo limit desertification, the Great Green Wall (Africa) initiative was started in 2007 involving the planting of vegetation along a stretch of 7,775 km, 15 km wide, involving 22 countries to 2030. The purpose of this mammoth planting initiative is to enhance retention of water in the ground following the seasonal rainfall, thus promoting land rehabilitation and future agriculture. Senegal has already contributed to the project by planting 50,000 acres of trees. It is said to have improved land quality and caused an increase in economic opportunity in the region.\n\nGobi Desert and Mongolia\n\nAnother major area that is being impacted by desertification is the Gobi Desert located in Northern China and Southern Mongolia. The Gobi Desert is the fastest expanding desert on Earth, as it transforms over 3,600 square kilometres (1,400 square miles) of grassland into wasteland annually. Although the Gobi Desert itself is still a distance away from Beijing, reports from field studies state there are large sand dunes forming only 70 km (43.5 mi) outside the city.\nIn Mongolia, around 90% of grassland is considered vulnerable to desertification by the UN. An estimated 13% of desertification in Mongolia is caused by natural factors; the rest is due to human influence particularly overgrazing and increased erosion of soils in cultivated areas. During the period 1940 to 2015, the mean air temperature increased by 2.24 °C. The warmest ten-year period was during the latest decade to 2021. Precipitation has decreased by 7% over this period resulting in increased arid conditions throughout Mongolia. The Gobi desert continues to expand northward, with over 70% of Mongolia's land degraded through overgrazing, deforestation, and climate change. In addition, the Mongolia government has listed forest fires, blights, unsustainable forestry and mining activities as leading causes of desertification in the country. The transition from sheep to goat farming in order to meet export demands for cashmere wool has caused degradation of grazing lands. Compared to sheep, goats do more damage to grazing lands by eating roots and flowers.\nTo mitigate the financial impact of desertification in Inner Mongolia, Bai Jingying teaches women how to do traditional embroidery, which they then sell to provide additional income.\n\nSouth America\nSouth America is another area vulnerable by desertification, as 25% of the land is classified as drylands and over 68% of the land area has undergone soil erosion as a result of deforestation and overgrazing. 27 to 43% of the land areas in Bolivia, Chile, Ecuador and Peru are at risk due to desertification. In Argentina, Mexico and Paraguay, greater than half the land area is degraded by desertification and cannot be used for agriculture. In Central America, drought has caused increased unemployment and decreased food security - also causing migration of people. Similar impacts have been seen in rural parts of Mexico where about 1,000 km2 of land have been lost yearly due to desertification. In Argentina, desertification has the potential to disrupt the nation's food supply.\n\nReversing desertification\n\nTechniques and countermeasures exist for mitigating or reversing desertification. For some of these measures, there are numerous barriers to their implementation. Yet for others, the solution simply requires the exercise of human reason.\nOne proposed barrier is that the costs of adopting sustainable agricultural practices sometimes exceed the benefits for individual farmers, even while they are socially and environmentally beneficial. Another issue is a lack of political will, and lack of funding to support land reclamation and anti-desertification programs.\nDesertification is recognized as a major threat to biodiversity. Some countries have developed biodiversity action plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.\n\nImproving soil quality\n\nTechniques focus on two aspects: provisioning of water, and fixation and hyper-fertilizing soil. Fixating the soil is often done through the use of shelter belts, woodlots and windbreaks. Windbreaks are made from trees and bushes and are used to reduce soil erosion and evapotranspiration.\nSome soils (for example, clay), due to lack of water can become consolidated rather than porous (as in the case of sandy soils). Some techniques as zaï or tillage are then used to still allow the planting of crops.\nAnother technique that is useful is contour trenching. This involves the digging of 150 m long, 1 m deep trenches in the soil. The trenches are made parallel to the height lines of the landscape, preventing the water from flowing within the trenches and causing erosion. Stone walls are placed around the trenches to prevent the trenches from closing up again. This method was invented by Peter Westerveld.\nEnriching of the soil and restoration of its fertility is often achieved by plants. Of these, leguminous plants which extract nitrogen from the air and fix it in the soil, succulents (such as Opuntia), and food crops/trees as grains, barley, beans and dates are the most important. Sand fences can also be used to control drifting of soil and sand erosion.\nAnother way to restore soil fertility is through the use of nitrogen-rich fertilizer. Due to the higher cost of this fertilizer, many smallholder farmers are reluctant to use it, especially in areas where subsistence farming is common. Several nations, including India, Zambia, and Malawi have responded to this by implementing subsidies to help encourage adoption of this technique.\nSome research centres (such as Bel-Air Research Center IRD/ISRA/UCAD) are also experimenting with the inoculation of tree species with mycorrhiza in arid zones. The mycorrhiza are basically fungi attaching themselves to the roots of the plants. They hereby create a symbiotic relation with the trees, increasing the surface area of the tree's roots greatly (allowing the tree to gather much more nutrient from the soil).\nThe bioengineering of soil microbes, particularly photosynthesizers, has also been suggested and theoretically modeled as a method to protect drylands. The aim would be to enhance the existing cooperative loops between soil microbes and vegetation.\n\nDesert greening\n\nAs there are many different types of deserts, there are also different types of desert reclamation methodologies. An example for this is the salt flats in the Rub' al Khali desert in Saudi Arabia. These salt flats are one of the most promising desert areas for seawater agriculture and could be revitalized without the use of freshwater or much energy.\nFarmer-managed natural regeneration (FMNR) is another technique that has produced successful results for desert reclamation. Since 1980, this method to reforest degraded landscape has been applied with some success in Niger. This simple and low-cost method has enabled farmers to regenerate some 30,000 square kilometers in Niger. The process involves enabling native sprouting tree growth through selective pruning of shrub shoots. The residue from pruned trees can be used to provide mulching for fields thus increasing soil water retention and reducing evaporation. Additionally, properly spaced and pruned trees can increase crop yields. The Humbo Assisted Regeneration Project which uses FMNR techniques in Ethiopia has received money from The World Bank's BioCarbon Fund, which supports projects that sequester or conserve carbon in forests or agricultural ecosystems.\nThe Food and Agriculture Organization of the United Nations launched the FAO Drylands Restoration Initiative in 2012 to draw together knowledge and experience on dryland restoration. In 2015, FAO published global guidelines for the restoration of degraded forests and landscapes in drylands, in collaboration with the Turkish Ministry of Forestry and Water Affairs and the Turkish Cooperation and Coordination Agency.\nThe \"Green Wall of China\" is a high-profile example of one method that has been finding success in this battle with desertification. This wall is a much larger-scale version of what American farmers did in the 1930s to stop the great Midwest dust bowl. This plan was proposed in the late 1970s, and has become a major ecological engineering project that is not predicted to end until the year 2055. According to Chinese reports, there have been nearly 66 billion trees planted in China's great green wall. The green wall of China has decreased desert land in China by an annual average of 1,980 square km. The frequency of sandstorms nationwide have fallen 20% due to the green wall. Due to the success that China has been finding in stopping the spread of desertification, plans are currently being made in Africa to start a \"wall\" along the borders of the Sahara desert as well to be financed by the United Nations Global Environment Facility trust.\n\nIn 2007 the African Union started the Great Green Wall of Africa project in order to combat desertification in 20 countries. The wall is 8,000 km wide, stretching across the entire width of the continent and has 8 billion dollars in support of the project. The project has restored 36 million hectares of land, and by 2030 the initiative plans to restore a total of 100 million hectares. The Great Green Wall has created many job opportunities for the participating countries, with over 20,000 jobs created in Nigeria alone.\n\nBetter managed grazing\nRestored grasslands store CO2 from the atmosphere as organic plant material. Grazing livestock, usually not left to wander, consume the grass and minimize its growth. A method proposed to restore grasslands uses fences with many small paddocks, moving herds from one paddock to another after a day or two in order to mimic natural grazers and allowing the grass to grow optimally. Proponents of managed grazing methods claim that increasing this method could increase carbon content of the soils in the world's 3.5 billion hectares of agricultural grassland and offset nearly 12 years of CO2 emissions. However, many researchers have contested such claims and stated that it does not reverse desertification nor offset its emissions.\n\nAgrivoltaics\nResearchers in northern China have suggested that strategically placed agrivoltaic systems can support desert ecosystem function, even in low-precipitation areas. A 2025 peer reviewed study published in Scientific Reports reported that microbial count, soil quality and nutrient content had improved \"most prominently\" under integrated agrivoltaic systems, when compared with non-solar plantings and solar-only installations in the Kubuqui desert, which receives only around 12 inches (~300 mm) of annual rainfall. The researchers attributed these differences to shading from the panels, which reduced soil temperature and limited evaporation, to the panels' windbreaker effects, which prevented sand from burying vegetation, and to the interaction with planted vegetation, which together created a more favourable microclimate than the comparison systems. A 2 GW agrivoltaic project in Inner Mongolia is planned to apply these principles at scale, aiming to combat desertification by restoring vegetation, stabilizing sand dunes, and reducing dust storm intensity and wind speeds.\n\nHistory\n\nThe world's most noted deserts have been formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independently of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara, the largest hot desert.\nHistorical evidence shows that the serious and extensive land deterioration occurring several centuries ago in arid regions had three centers: the Mediterranean, the Mesopotamian Valley, and the Loess Plateau of China, where population was dense.\nThe earliest known discussion of the topic arose soon after the French colonization of West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore the prehistoric expansion of the Sahara Desert. The modern study of desertification emerged from the study of the 1980s drought in the Sahel.\n\nSee also\nAridification\nOasification\nDeforestation and climate change\nSoil retrogression and degradation\nWater scarcity\nWorld Day to Combat Desertification and Drought\nStraw checkerboard\n\nReferences\n\nSources\n This article incorporates public domain material from Desertification. United States Geological Survey. Retrieved 4 May 2021.\n\nExternal links\n\nOfficial website of the Secretariat of the United Nations Convention to Combat Desertification (UNCCD)\nProcedural history and related documents on the UNCCD, from the United Nations Audiovisual Library of International Law\nOfficial website of Action Against Desertification, a United Nations Food and Agriculture Organization initiative of the African, Caribbean and Pacific Group of States\nGlobal Deserts Outlook (2006), thematic assessment report in the Global Environment Outlook (GEO) series of the United Nations Environment Program (UNEP).",
    "source": "wikipedia:Desertification",
    "domain": "climate"
  },
  {
    "text": "Food security is the state of having reliable access to a sufficient quantity of affordable, healthy food. The availability of food for people of any class, gender, status, ethnicity, or religion is another element of food protection. Similarly, household food security is considered to exist when all the members of a family have consistent access to enough food for an active, healthy life. Food-secure individuals do not live in hunger or fear of starvation. Food security includes resilience to future disruptions of food supply. Such a disruption could occur due to various risk factors such as droughts and floods, shipping disruptions, fuel shortages, economic instability, and wars. Food insecurity is the opposite of food security: a state where there is only limited or uncertain availability of suitable food.\nThe concept of food security has evolved over time. The four pillars of food security include availability, access, utilization, and stability. In addition, there are two more dimensions that are important: agency and sustainability. These six dimensions of food security are reinforced in conceptual and legal understandings of the right to food. The World Food Summit in 1996 declared that \"food should not be used as an instrument for political and economic pressure.\"\nThere are many causes of food insecurity. The most important ones are high food prices and disruptions in global food supplies for example due to war. There is also climate change, water scarcity, land degradation, agricultural diseases, pandemics and disease outbreaks that can all lead to food insecurity. Additionally, food insecurity affects individuals with low socioeconomic status, affects the health of a population on an individual level, and causes divisions in interpersonal relationships. Food insecurity due to unemployment causes a higher rate of poverty.\nThe effects of food insecurity can include hunger and even famines. Chronic food insecurity translates into a high degree of vulnerability to hunger and famine. Chronic hunger and malnutrition in childhood can lead to stunted growth of children. Once stunting has occurred, improved nutritional intake after the age of about two years is unable to reverse the damage. Severe malnutrition in early childhood often leads to defects in cognitive development.\nAbout 2.3 billion people in the world are estimated to have been moderately or severely food insecure in 2024. The global prevalence of moderate or severe food insecurity has declined gradually since 2021, reaching 28.0% in 2024. Food insecurity is on the rise in Africa and falling in Latin America and the Caribbean; it has been decreasing gradually in Asia for several consecutive years, while in Oceania and in Northern America and Europe, new estimates point to a slight decline from 2023 to 2024 following a several-year rise. Globally and in almost every region, food insecurity is more prevalent in rural areas than in urban areas and affects more women than men.\n\nDefinition\n\nFood security, as defined by the World Food Summit in 1996, is \"when all people, at all times, have physical and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life\".\nFood insecurity, on the other hand, as defined by the United States Department of Agriculture (USDA), is a situation of \"limited or uncertain availability of nutritionally adequate and safe foods or limited or uncertain ability to acquire acceptable foods in socially acceptable ways.\"\nAt the 1974 World Food Conference, the term food security was defined with an emphasis on supply; it was defined as the \"availability at all times of adequate, nourishing, diverse, balanced and moderate world food supplies of basic foodstuffs to sustain a steady expansion of food consumption and to offset the fluctuations in production and prices.\" Later definitions added demand and access issues to the definition. The first World Food Summit, held in 1996, stated that food security \"exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.\"\nChronic (or permanent) food insecurity is defined as the long-term, persistent lack of adequate food. In this case, households are constantly at risk of being unable to acquire food to meet the needs of all members. Chronic and transitory food insecurity are linked since the recurrence of transitory food security can make households more vulnerable to chronic food insecurity.\nAs of 2015, the concept of food security has mostly focused on food calories rather than the quality and nutrition of food. The concept of nutrition security or nutritional security evolved as a broader concept. In 1995, it was defined as \"adequate nutritional status in terms of protein, energy, vitamins, and minerals for all household members at all times.\"\nIt is also related to the concepts of nutrition education and nutritional deficiency.\n\nMeasurement\n\nFood security can be measured by the number of calories to digest per person per day, available on a household budget. In general, the objective of food security indicators and measurements is to capture some or all of the main components of food security in terms of food availability, accessibility, and utilization/adequacy. While availability (production and supply) and utilization/adequacy (nutritional status/ anthropometric measurement) are easier to estimate and therefore more popular, accessibility (the ability to acquire a sufficient quantity and quality of food) remains largely elusive. The factors influencing household food accessibility are often context-specific.\nFAO has developed the Food Insecurity Experience Scale (FIES) as a universally applicable experience-based food security measurement scale derived from the scale used in the United States. Thanks to the establishment of a global reference scale and the procedure needed to calibrate measures obtained in different countries, it is possible to use the FIES to produce cross-country comparable estimates of the prevalence of food insecurity in the population. Since 2015, the FIES has been adopted as the basis to compile one of the indicators included in the Sustainable Development Goals (SDG) monitoring framework.\n\nThe Food and Agriculture Organization of the United Nations (FAO), the World Food Programme (WFP), the International Fund for Agricultural Development (IFAD), the World Health Organization (WHO), and the United Nations Children's Fund (UNICEF) collaborate every year to produce The State of Food Security and Nutrition in the World, or SOFI report (known as The State of Food Insecurity in the World until 2015).\nThe SOFI report measures chronic hunger (or undernourishment) using two main indicators, the Number of undernourished (NoU) and the Prevalence of undernourishment (PoU). Beginning in the early 2010s, FAO incorporated more complex metrics into its calculations, including estimates of food losses in retail distribution for each country and the volatility in agri-food systems. Since 2014, it has also reported the prevalence of moderate or severe food insecurity based on the FIES.\nThe report plays a critical role in tracking global progress toward Sustainable Development Goal 2 (Zero Hunger), identifying emerging crises, and shaping international policy responses by providing reliable, comparable data across regions and over time.\nSeveral measurements have been developed to capture the access component of food security, with some notable examples developed by the USAID-funded Food and Nutrition Technical Assistance (FANTA) project. These include:\n\nHousehold Food Insecurity Access Scale – measures the degree of food insecurity (inaccessibility) in the household in the previous month on a discrete ordinal scale.\nHousehold Dietary Diversity Scale – measures the number of different food groups consumed over a specific reference period (24hrs/48hrs/7days).\nHousehold Hunger Scale – measures the experience of household food deprivation based on a set of predictable reactions, captured through a survey and summarized in a scale.\nCoping Strategies Index (CSI) – assesses household behaviors and rates them based on a set of varied established behaviors on how households cope with food shortages. The methodology for this research is based on collecting data on a single question: \"What do you do when you do not have enough food, and do not have enough money to buy food?\"\n\nPrevalence\n\nClose to 12 percent of the global population was severely food insecure in 2020, representing 928 million people -148 million more than in 2019. In 2023 prevalence of moderate or severe food insecurity in Africa (58.0%) is nearly double the global average. A variety of reasons lie behind the increase in hunger over the past few years. Slowdowns and downturns since the 2008–9 financial crisis have conspired to degrade social conditions, making undernourishment more prevalent. Structural imbalances and a lack of inclusive policies have combined with extreme weather events, altered environmental conditions, and the spread of pests and diseases, such as the COVID-19 pandemic, triggering stubborn cycles of poverty and hunger. In 2019, the high cost of healthy diets together with persistently high levels of income inequality put healthy diets out of reach for around 3 billion people, especially the poor, in every region of the world. In 2023 28.9 percent of the global population – 2.33 billion people – were moderately or severely food insecure, meaning they did not have regular access to adequate food. These estimates include 10.7 percent of the population – or more than 864 million people – who were severely food insecure, meaning they had run out of food at times during the year and, at worst, gone an entire day or more without eating.\nInequality in the distributions of assets, resources and income, compounded by the absence or scarcity of welfare provisions in the poorest of countries, is further undermining access to food. Nearly a tenth of the world population still lives on US$1.90 or less a day, with sub-Saharan Africa and southern Asia the regions most affected.\nHigh import and export dependence ratios are meanwhile making many countries more vulnerable to external shocks. In many low-income economies, debt has swollen to levels far exceeding GDP, eroding growth prospects.\nFinally, there are increasing risks to institutional stability, persistent violence, and large-scale population relocation as a consequence of the conflicts. With the majority of them being hosted in developing nations, the number of displaced individuals between 2010 and 2018 increased by 70% between 2010 and 2018 to reach 70.8 million.\nRecent editions of the SOFI report (The State of Food Security and Nutrition in the World) present evidence that the decades-long decline in hunger in the world, as measured by the number of undernourished (NoU), has ended. In the 2020 report, FAO used newly accessible data from China to revise the global NoU downwards to nearly 690 million, or 8.9 percent of the world population – but having recalculated the historic hunger series accordingly, it confirmed that the number of hungry people in the world, albeit lower than previously thought, had been slowly increasing since 2014. On broader measures, the SOFI report found that far more people suffered some form of food insecurity, with 3 billion or more unable to afford even the cheapest healthy diet. Nearly 2.37 billion people did not have access to adequate food in 2020 – an increase of 320 million people compared to 2019.\nFAO's 2021 edition of The State of Food and Agriculture (SOFA) further estimates that an additional 1 billion people (mostly in lower- and upper-middle-income countries) are at risk of not affording a healthy diet if a shock were to reduce their income by a third.\nThe 2021 edition of the SOFI report estimated the hunger excess linked to the COVID-19 pandemic at 30 million people by the end of the decade – FAO had earlier warned that even without the pandemic, the world was off track to achieve Zero Hunger or Goal 2 of the Sustainable Development Goals – it further found that already in the first year of the pandemic, the prevalence of undernourishment (PoU) had increased 1.5 percentage points, reaching a level of around 9.9 percent. This is the mid-point of an estimate of 720 to 811 million people facing hunger in 2020 – as many as 161 million more than in 2019. The number had jumped by some 446 million in Africa, 57 million in Asia, and about 14 million in Latin America and the Caribbean.\nAt the global level, the prevalence of food insecurity at a moderate or severe level, and severe level only, is higher among women than men, magnified in rural areas.\nIn 2023, the Global Report on Food Crises revealed that acute hunger affected approximately 282 million people across 59 countries, an increase of 24 million from the previous year. This rise in food insecurity was primarily driven by conflicts, economic shocks, and extreme weather. Regions like the Gaza Strip and South Sudan were among the hardest hit, highlighting the urgent need for targeted interventions to address and mitigate global hunger effectively.\nAbout 2.3 billion people in the world are estimated to have been moderately or severely food insecure in 2024. The global prevalence of moderate or severe food insecurity has declined gradually since 2021, reaching 28.0% in 2024. Food insecurity is on the rise in Africa and falling in Latin America and the Caribbean; it has been decreasing gradually in Asia for several consecutive years, while in Oceania and in Northern America and Europe, new estimates point to a slight decline from 2023 to 2024 following a several-year rise. Globally and in almost every region, food insecurity is more prevalent in rural areas than in urban areas and affects more women than men.\n\nVulnerable groups most affected\n\nChildren\nFood insecurity in children can lead to developmental impairments and long term consequences such as weakened physical, intellectual and emotional development.\nBy way of comparison, in one of the largest food producing countries in the world, the United States, approximately one out of six people are \"food insecure,\" including 17 million children, according to the U.S. Department of Agriculture in 2009. A 2012 study in the Journal of Applied Research on Children found that rates of food security varied significantly by race, class and education. In both kindergarten and third grade, 8% of the children were classified as food insecure, but only 5% of white children were food insecure, while 12% and 15% of black and Hispanic children were food insecure, respectively. In third grade, 13% of black and 11% of Hispanic children were food insecure compared to 5% of white children.\nHouseholds with children are also more susceptible to being food insecure. In 2016, 16.5% of families with children under the age of 18 did not have food security. According to a report from American Journal of Nursing, there are times where parents will reduce their own food intake in order to let their children be more food secure. However, this does not always protect the children, leaving many children of larger families to be vulnerable to food insecurity. A U.S. Department of Agriculture report in 2016 showed that half of the children in food insecure households were also food insecure themselves. Furthermore, 5% of children in food insecure households had very low food security.\n\nWomen\n\nGender inequality both leads to and is a result of food insecurity. According to estimates, girls and women make up 60% of the world's chronically hungry and little progress has been made in ensuring the equal right to food for women enshrined in the Convention on the Elimination of All Forms of Discrimination against Women.\nAt the global level, the gender gap in the prevalence of moderate or severe food insecurity grew even larger in the year of COVID-19 pandemic. The 2021 SOFI report finds that in 2019 an estimated 29.9 percent of women aged between 15 and 49 years around the world were affected by anemia.\nThe gap in food insecurity between men and women widened from 1.7 percentage points in 2019 to 4.3 percentage points in 2021.\nWomen play key roles in maintaining all four pillars of food security: as food producers and agricultural entrepreneurs; as decision-makers for the food and nutritional security of their households and communities and as \"managers\" of the stability of food supplies in times of economic hardship.\nThe gender gap in accessing food increased from 2018 to 2019, particularly at moderate or severe levels. In 2024 food insecurity still more prevalent among adult women than men in every region of the world. The gender gap widened considerably at the global level in the wake of the pandemic, most notably in 2021; it then grew smaller for two consecutive years followed by a widening of the gap at the global level between 2023 and 2024.\n\nRacial and ethnic groups\nAccording to a 2024 USDA study, between 2016 and 2021, the prevalence of food insecurity in the United States exhibited significant variation across different racial and ethnic groups. All households had a prevalence of food insecurity of 11.1%. Households led by individuals identifying as American Indian and Alaska Native experienced a food insecurity rate of 23.3%, while those identifying as Multiracial, American Indian-White reported a rate of 21.7%. Black households faced a 21.0% rate. Multiracial households of all other combinations reported 18.4%, and Multiracial, Black-White households had an 18.0% rate. Hispanic households experienced a 16.9% rate, and Native Hawaiian and Pacific Islander households reported 15.6%.\nThese rates were all significantly higher than the national average for all households. In contrast, households headed by White individuals had a food insecurity rate of 8.0%, and those headed by Asian individuals reported a rate of 5.4%, both significantly lower than the national average.\nThe pattern was similar for very low food security, a more severe form of food insecurity. Multiracial, American Indian-White households experienced the highest rate at 11.3%, while Asian households had the lowest at 1.6%. These disparities highlight the persistent differences in food security status across and within various racial and ethnic groups in the United States.\n\nHistory\n\nFamines have been frequent in world history. Some have killed millions and substantially diminished the population of a large area. The most common causes have been drought and war, but the greatest famines in history were caused by economic policy. One economic policy example of famine was the Holodomor (Great Famine) induced by the Soviet Union's communist economic policy resulting in 7–10 million deaths.\nIn the late 20th century the Nobel Prize-winning economist Amartya Sen observed that \"there is no such thing as an apolitical food problem.\" While drought and other naturally occurring events may trigger famine conditions, it is government action or inaction that determines its severity, and often even whether or not a famine will occur. The 20th century has examples of governments, such as Collectivization in the Soviet Union or the Great Leap Forward in the People's Republic of China undermining the food security of their nations. Mass starvation is frequently a weapon of war, as in the blockade of Germany in World War I and World War II, the Battle of the Atlantic, and the blockade of Japan during World War I and World War II and in the Hunger Plan enacted by Nazi Germany.\n\nPillars of food security\n\nThe WHO states that three pillars that determine food security: food availability, food access, and food use and misuse. The FAO added a fourth pillar: the stability of the first three dimensions of food security over time. In 2009, the World Summit on Food Security stated that the \"four pillars of food security are availability, access, utilization, and stability.\"\nTwo additional pillars of food security were recommended in 2020 by the High-Level Panel of Experts for the Committee on World Food Security: agency and sustainability.\n\nAvailability\nFood availability relates to the supply of food through production, distribution, and exchange. Food production is determined by a variety of factors including land ownership and use; soil management; crop selection, breeding, and management; livestock breeding and management; and harvesting. Crop production can be affected by changes in rainfall and temperatures. The use of land, water, and energy to grow food often compete with other uses, which can affect food production. Land used for agriculture can be used for urbanization or lost to desertification, salinization or soil erosion due to unsustainable agricultural practices. Crop production is not required for a country to achieve food security. Nations do not have to have the natural resources required to produce crops to achieve food security, as seen in the examples of Japan and Singapore.\nBecause food consumers outnumber producers in every country, food must be distributed to different regions or nations.\nFood distribution involves the storage, processing, transport, packaging, and marketing of food. Food-chain infrastructure and storage technologies on farms can also affect the amount of food wasted in the distribution process. Poor transport infrastructure can increase the price of supplying water and fertilizer as well as the price of moving food to national and global markets. Around the world, few individuals or households are continuously self-reliant on food. This creates the need for a bartering, exchange, or cash economy to acquire food. The exchange of food requires efficient trading systems and market institutions, which can affect food security. Per capita world food supplies are more than adequate to provide food security to all, and thus food accessibility is a greater barrier to achieving food security.\n\nAccess\n\nFood access refers to the affordability and allocation of food, as well as the preferences of individuals and households. The UN Committee on Economic, Social and Cultural Rights noted that the causes of hunger and malnutrition are often not a scarcity of food but an inability to access available food, usually due to poverty. Poverty can limit access to food, and can also increase how vulnerable an individual or household is to food price spikes. Access depends on whether the household has enough income to purchase food at prevailing prices or has sufficient land and other resources to grow its food. Households with enough resources can overcome unstable harvests and local food shortages and maintain their access to food.\n\nThere are two distinct types of access to food: direct access, in which a household produces food using human and material resources, and economic access, in which a household purchases food produced elsewhere. Location can affect access to food and which type of access a family will rely on. The assets of a household, including income, land, products of labor, inheritances, and gifts can determine a household's access to food. However, the ability to access sufficient food may not lead to the purchase of food over other materials and services. Demographics and education levels of members of the household as well as the gender of the household head determine the preferences of the household, which influences the type of food that is purchased. A household's access to adequate nutritious food may not assure adequate food intake for all household members, as intrahousehold food allocation may not sufficiently meet the requirements of each member of the household. The USDA adds that access to food must be available in socially acceptable ways, without, for example, resorting to emergency food supplies, scavenging, stealing, or other coping strategies.\nThe monetary value of global food exports multiplied by 4.4 in nominal terms between 2000 and 2021, from US$380 billion in 2000 to US$1.66 trillion in 2021.\n\nUtilization\nThe next pillar of food security is food utilization, which refers to the metabolism of food by individuals. Once the food is obtained by a household, a variety of factors affect the quantity and quality of food that reaches members of the household. To achieve food security, the food ingested must be safe and must be enough to meet the physiological requirements of each individual. Food safety affects food utilization, and can be affected by the preparation, processing, and cooking of food in the community and household.\nNutritional values of the household determine food choice, and whether food meets cultural preferences is important to utilization in terms of psychological and social well-being. Access to healthcare is another determinant of food utilization since the health of individuals controls how the food is metabolized. For example, intestinal parasites can take nutrients from the body and decrease food utilization. Sanitation can also decrease the occurrence and spread of diseases that can affect food utilization. Education about nutrition and food preparation can affect food utilization and improve this pillar of food security.\n\nStability\nFood stability refers to the ability to obtain food over time. Food insecurity can be transitory, seasonal, or chronic. In transitory food insecurity, food may be unavailable during certain periods of time. At the food production level, natural disasters and drought result in crop failure and decreased food availability. Civil conflicts can also decrease access to food. Instability in markets resulting in food-price spikes can cause transitory food insecurity. Other factors that can temporarily cause food insecurity are loss of employment or productivity, which can be caused by illness. Seasonal food insecurity can result from the regular pattern of growing seasons in food production.\n\nAgency\nAgency refers to the capacity of individuals or groups to make their own decisions about what foods they eat, what foods they produce, how that food is produced, processed, and distributed within food systems, and their ability to engage in processes that shape food system policies and governance. This term shares similar values to those of another important concept, Food sovereignty.\n\nSustainability\nSustainability refers to the long-term ability of food systems to provide food security and nutrition in a way that does not compromise the economic, social, and environmental bases that generate food security and nutrition for future generations.\n\nCauses of food insecurity\n\nHigh food prices\n\nPandemics and disease outbreaks\n\nThe World Food Programme has stated that pandemics such as the COVID-19 pandemic risk undermining the efforts of humanitarian and food security organizations to maintain food security. The International Food Policy Research Institute expressed concerns that the increased connections between markets and the complexity of food and economic systems could cause disruptions to food systems during the COVID-19 pandemic, specifically affecting the poor.\nThe Ebola outbreak in 2014 led to increases in the prices of staple foods in West Africa. Stringent lockdowns, travel restrictions, and disruptions to labor forces resulted in bottlenecks affecting the production and distribution of goods. Notably, the food supply chain experienced significant disruptions as the pandemic strained logistics, labor availability, and demand patterns. While progress in combating COVID-19 has provided some relief, the pandemic's lasting effects persist, including shifts in consumer behavior and the ongoing necessity for health and safety measures.\n\nFossil fuel dependence\n\nBetween 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%. The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon-fueled irrigation.\nNatural gas is a major feedstock for the production of ammonia, via the Haber process, for use in fertilizer production. The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on Earth are currently fed as a result of synthetic nitrogen fertilizer use.\n\nAgricultural diseases\nDiseases affecting livestock or crops can have devastating effects on food availability especially if there are no contingency plans in place.\nFor example, Ug99, a lineage of wheat stem rust, which can cause up to 100% crop losses, is present in wheat fields in several countries in Africa and the Middle East and is predicted to spread rapidly through these regions and possibly further afield, potentially causing a wheat production disaster that would affect food security worldwide. As of 2025, the Avian Flu has plagued the U.S. poultry industry, resulting in rapidly increasing egg prices for consumers and farmers unable to keep up with demand. U.S. Department of Agriculture (USDA), looks for solutions to combat increasing prices and the spread of pathogenic avian influenza (HPAI). Proposed solutions include, increasing investments in biosecurity to stop the spread of HPAI, extending relief to poultry farmers impacted, and removing unnecessary regulatory burdens to expand the commercial market for eggs.\n\nDisruption in global food supplies due to war\nThe Russian invasion of Ukraine has disrupted global food supplies. The conflict has severely impacted food supply chains with noteworthy effects on production, sourcing, manufacturing, processing, logistics, and significant shifts in demand among nations reliant on imports from Ukraine. The European Union's imposition of sanctions on Russia has added complexity to trade relati",
    "source": "wikipedia:Food security",
    "domain": "climate"
  },
  {
    "text": "Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. These resources can be either freshwater from natural sources, or water produced artificially from other sources, such as from reclaimed water (wastewater) or desalinated water (seawater). 97% of the water on Earth is salt water and only three percent is fresh water; slightly over two-thirds of this is frozen in glaciers and polar ice caps. The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air. Natural sources of fresh water include frozen water, groundwater, surface water, and under river flow. People use water resources for agricultural, household, and industrial activities.\nWater resources are under threat from multiple issues. There is water scarcity, water pollution, water conflict and climate change. Fresh water is in principle a renewable resource. However, the world's supply of groundwater is steadily decreasing. Groundwater depletion (or overdrafting) is occurring for example in Asia, South America and North America. \n\nNatural sources of fresh water\nNatural sources of fresh water include surface water, under river flow, groundwater and frozen water.\n\nSurface water\n\nSurface water is water in a river, lake or fresh water wetland. Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans, evaporation, evapotranspiration and groundwater recharge. The only natural input to any surface water system is precipitation within its watershed. The total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial reservoirs, the permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water loss.\nHumans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing the stream flow.\nNatural surface water can be augmented by importing surface water from another watershed through a canal or pipeline.\nBrazil is estimated to have the largest supply of fresh water in the world, followed by Russia and Canada.\n\nWater from glaciers\nGlacier runoff is considered to be surface water. The Himalayas, which are often called \"The Roof of the World\", contain some of the most extensive and rough high altitude areas on Earth as well as the greatest area of glaciers and permafrost outside of the poles. Ten of Asia's largest rivers flow from there, and more than a billion people's livelihoods depend on them. To complicate matters, temperatures there are rising more rapidly than the global average. In Nepal, the temperature has risen by 0.6 degrees Celsius over the last decade, whereas globally, the Earth has warmed approximately 0.7 degrees Celsius over the last hundred years.\n\nGroundwater\n\nUnder river flow\nThroughout the course of a river, the total volume of water transported downstream will often be a combination of the visible free water flow together with a substantial contribution flowing through rocks and sediments that underlie the river and its floodplain called the hyporheic zone. For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. The hyporheic zone often forms a dynamic interface between surface water and groundwater from aquifers, exchanging flow between rivers and aquifers that may be fully charged or depleted. This is especially significant in karst areas where pot-holes and underground rivers are common.\n\nArtificial sources of usable water\nThere are several artificial sources of fresh water. One is treated wastewater (reclaimed water). Another is atmospheric water generators. Desalinated seawater is another important source. It is important to consider the economic and environmental side effects of these technologies.\n\nWastewater reuse\n \n\nDesalinated water\n\nResearch into other options\n\nResearchers proposed air capture over oceans which would \"significantly increasing freshwater through the capture of humid air over oceans\" to address present and, especially, future water scarcity/insecurity.\nA 2021 study proposed hypothetical portable solar-powered atmospheric water harvesting devices. However, such off-the-grid generation may sometimes \"undermine efforts to develop permanent piped infrastructure\" among other problems.\n\nWater uses\nThe total quantity of water available at any given time is an important consideration. Some human water users have an intermittent need for water. For example, many farms require large quantities of water in the spring, and no water at all in the winter. Other users have a continuous need for water, such as a power plant that requires water for cooling. Over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed.\n\nAgriculture and other irrigation\n\nIndustries\nIt is estimated that 22% of worldwide water is used in industry. Major industrial users include hydroelectric dams, thermoelectric power plants, which use water for cooling, ore and oil refineries, which use water in chemical processes, and manufacturing plants, which use water as a solvent. Water withdrawal can be very high for certain industries, but consumption is generally much lower than that of agriculture.\nWater is used in renewable power generation. Hydroelectric power derives energy from the force of water flowing downhill, driving a turbine connected to a generator. This hydroelectricity is a low-cost, non-polluting, renewable energy source. Significantly, hydroelectric power can also be used for load following unlike most renewable energy sources which are intermittent. Ultimately, the energy in a hydroelectric power plant is supplied by the sun. Heat from the sun evaporates water, which condenses as rain in higher altitudes and flows downhill. Pumped-storage hydroelectric plants also exist, which use grid electricity to pump water uphill when demand is low, and use the stored water to produce electricity when demand is high.\nThermoelectric power plants using cooling towers have high consumption, nearly equal to their withdrawal, as most of the withdrawn water is evaporated as part of the cooling process. The withdrawal, however, is lower than in once-through cooling systems.\nWater is also used in many large scale industrial processes, such as thermoelectric power production, oil refining, fertilizer production and other chemical plant use, and natural gas extraction from shale rock. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes and increased water temperature (thermal pollution).\n\nDrinking water and domestic use (households)\n\nIt is estimated that 8% of worldwide water use is for domestic purposes. These include drinking water, bathing, cooking, toilet flushing, cleaning, laundry and gardening. Basic domestic water requirements have been estimated by Peter Gleick at around 50 liters per person per day, excluding water for gardens.\nDrinking water is water that is of sufficiently high quality so that it can be consumed or used without risk of immediate or long term harm. Such water is commonly called potable water. In most developed countries, the water supplied to domestic, commerce and industry is all of drinking water standard even though only a very small proportion is actually consumed or used in food preparation.\n844 million people still lacked even a basic drinking water service in 2017. Of those, 159 million people worldwide drink water directly from surface water sources, such as lakes and streams. One in eight people in the world do not have access to safe water. Unsafe drinking water leads to 1.2 million deaths per year according to the World Bank.\n\nChallenges and threats\n\nWater scarcity\n\nWater pollution\n\nWater conflict\n \n\nClimate change\n\nGroundwater overdrafting\nThe world's supply of groundwater is steadily decreasing. Groundwater depletion (or overdrafting) is occurring for example in Asia, South America and North America. It is still unclear how much natural renewal balances this usage, and whether ecosystems are threatened.\n\nWater resource management\n\nWater resource management is the activity of planning, developing, distributing and managing the optimum use of water resources. It is an aspect of water cycle management. The field of water resources management will have to continue to adapt to the current and future issues facing the allocation of water. With the growing uncertainties of global climate change and the long-term impacts of past management actions, this decision-making will be even more difficult. It is likely that ongoing climate change will lead to situations that have not been encountered. As a result, alternative management strategies, including participatory approaches and adaptive capacity are increasingly being used to strengthen water decision-making.\nIdeally, water resource management planning has regard to all the competing demands for water and seeks to allocate water on an equitable basis to satisfy all uses and demands. As with other resource management, this is rarely possible in practice so decision-makers must prioritise issues of sustainability, equity and factor optimisation (in that order!) to achieve acceptable outcomes. One of the biggest concerns for water-based resources in the future is the sustainability of the current and future water resource allocation.\nSustainable Development Goal 6 has a target related to water resources management: \"Target 6.5: By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.\"\n\nSustainable water management\nAt present, only about 0.08 percent of all the world's fresh water is accessible. And there is ever-increasing demand for drinking, manufacturing, leisure and agriculture. Due to the small percentage of water available, optimizing the fresh water we have left from natural resources has been a growing challenge around the world.\nMuch effort in water resource management is directed at optimizing the use of water and in minimizing the environmental impact of water use on the natural environment. The observation of water as an integral part of the ecosystem is based on integrated water resources management, based on the 1992 Dublin Principles (see below).\nSustainable water management requires a holistic approach based on the principles of Integrated Water Resource Management, originally articulated in 1992 at the Dublin (January) and Rio (July) conferences. The four Dublin Principles, promulgated in the Dublin Statement are:\n\nFresh water is a finite and vulnerable resource, essential to sustain life, development and the environment;\nWater development and management should be based on a participatory approach, involving users, planners and policy-makers at all levels;\nWomen play a central part in the provision, management and safeguarding of water;\nWater has an economic value in all its competing uses and should be recognized as an economic good.\nImplementation of these principles has guided reform of national water management law around the world since 1992.\nFurther challenges to sustainable and equitable water resources management include the fact that many water bodies are shared across boundaries which may be international (see water conflict) or intra-national (see Murray-Darling basin).\n\nIntegrated water resources management\n\nIntegrated water resources management (IWRM) has been defined by the Global Water Partnership (GWP) as \"a process which promotes the coordinated development and management of water, land and related resources, in order to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems\".\nSome scholars say that IWRM is complementary to water security because water security is a goal or destination, whilst IWRM is the process necessary to achieve that goal.\nIWRM is a paradigm that emerged at international conferences in the late 1900s and early 2000s, although participatory water management institutions have existed for centuries. Discussions on a holistic way of managing water resources began already in the 1950s leading up to the 1977 United Nations Water Conference. The development of IWRM was particularly recommended in the final statement of the ministers at the International Conference on Water and the Environment in 1992, known as the Dublin Statement. This concept aims to promote changes in practices which are considered fundamental to improved water resource management. IWRM was a topic of the second World Water Forum, which was attended by a more varied group of stakeholders than the preceding conferences and contributed to the creation of the GWP.\nIn the International Water Association definition, IWRM rests upon three principles that together act as the overall framework:\n\nSocial equity: ensuring equal access for all users (particularly marginalized and poorer user groups) to an adequate quantity and quality of water necessary to sustain human well-being.\nEconomic efficiency: bringing the greatest benefit to the greatest number of users possible with the available financial and water resources.\nEcological sustainability: requiring that aquatic ecosystems are acknowledged as users and that adequate allocation is made to sustain their natural functioning.\nIn 2002, the development of IWRM was discussed at the World Summit on Sustainable Development held in Johannesburg, which aimed to encourage the implementation of IWRM at a global level. The third World Water Forum recommended IWRM and discussed information sharing, stakeholder participation, and gender and class dynamics.\nOperationally, IWRM approaches involve applying knowledge from various disciplines as well as the insights from diverse stakeholders to devise and implement efficient, equitable and sustainable solutions to water and development problems. As such, IWRM is a comprehensive, participatory planning and implementation tool for managing and developing water resources in a way that balances social and economic needs, and that ensures the protection of ecosystems for future generations. In addition, in light of contributing the achievement of Sustainable Development goals (SDGs), IWRM has been evolving into more sustainable approach as it considers the Nexus approach, which is a cross-sectoral water resource management. The Nexus approach is based on the recognition that \"water, energy and food are closely linked through global and local water, carbon and energy cycles or chains.\"\nAn IWRM approach aims at avoiding a fragmented approach of water resources management by considering the following aspects: Enabling environment, roles of Institutions, management Instruments. Some of the cross-cutting conditions that are also important to consider when implementing IWRM are: Political will and commitment, capacity development, adequate investment, financial stability and sustainable cost recovery, monitoring and evaluation. There is not one correct administrative model. The art of IWRM lies in selecting, adjusting and applying the right mix of these tools for a given situation. IWRM practices depend on context; at the operational level, the challenge is to translate the agreed principles into concrete action.\n\nManaging water in urban settings\n\nBy country\nWater resource management and governance is handled differently by different countries. For example, in the United States, the United States Geological Survey (USGS) and its partners monitor water resources, conduct research and inform the public about groundwater quality. Water resources in specific countries are described below:\n\nSee also\n\nList of sovereign states by freshwater withdrawal\nList of countries by total renewable water resources\nSocio-hydrology – Interdisciplinary field studying the dynamic interactions between water and people\nVirtual water – Concept on hidden water in traded commodities\nWater resources law – Law and regulations that relate to water resources\nWater rights – Right of a user to use water from a water sourcePages displaying short descriptions of redirect targets\nWater storage – Storage of water by various means\n\nReferences\n\nExternal links\nRenewable water resources in the world by country\nPortal to international hydrology and water resources\nSustainable Sanitation and Water Management Toolbox",
    "source": "wikipedia:Water resources",
    "domain": "climate"
  },
  {
    "text": "A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.\nCoral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny, and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian.\nSometimes called rainforests of the sea, shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France. Yet, they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas.\nShallow tropical coral reefs have declined by 50% since 1950, partly because they are sensitive to water conditions. They are under threat from excess nutrients (nitrogen and phosphorus), rising ocean heat content and acidification, overfishing (e.g., from blast fishing, cyanide fishing, spearfishing on scuba), sunscreen use, and harmful land-use practices, including runoff and seeps (e.g., from injection wells and cesspools).\nCoral reefs deliver ecosystem services for tourism, fisheries, and shoreline protection. The annual global economic value of coral reefs has been estimated at anywhere from US$30–375 billion (1997 and 2003 estimates) to US$2.7 trillion (a 2020 estimate) to US$9.9 trillion (a 2014 estimate).\n\nFormation\n\nMost coral reefs were formed after the Last Glacial Period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upward, keeping pace with rising sea levels. Reefs that rose too slowly could become drowned, without sufficient light. Coral reefs are also found in the deep sea away from continental shelves, around oceanic islands and atolls. The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor.\nIn The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle. He theorized that uplift and subsidence of Earth's oceanic crust beneath the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the island and ocean floor subside. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef.\n\nDarwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the underlying earth allows, corals grow along the coast to form fringing reefs, which can eventually become barrier reefs.\n\nWhere the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upward on a base of older, dead coral, forming a barrier reef that encloses a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level, a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms. Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure.\nThe two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, and the history of the change in sea level relative to that substrate.\nThe approximately 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was then 120 m (390 ft) lower than in the 21st century. As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to 60 m (200 ft) lower than at present, and many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years. The age of living reef structure is estimated to be between 6,000 and 8,000 years. Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, 300–1,000 m (980–3,280 ft) from shore, stretching for 2,000 km (1,200 mi).\nHealthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.\n\nMaterial\nAs the name implies, coral reefs are made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However, shell fragments and the remains of coralline algae such as the green-segmented genus Halimeda can add to the reef's ability to withstand damage from storms and other threats. Such mixtures are visible in structures such as Eniwetok Atoll.\n\nIn the geologic past\n\nThe times of maximum reef development were in the Middle Cambrian (513–501 Ma), Devonian (416–359 Ma) and Carboniferous (359–299 Ma), owing to extinct order Rugosa corals, and Late Cretaceous (100–66 Ma) and Neogene (23 Ma–present), owing to order Scleractinia corals.\nNot all reefs in the past were formed by corals: those in the Early Cambrian (542–513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100–66 Ma), when reefs formed by a group of bivalves called rudists existed; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.\nMeasurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as Porites, can indicate changes in sea surface temperature and sea surface salinity conditions during the growth of the coral. Climate scientists often use this technique to infer a region's paleoclimate.\n\nTypes\nSince Darwin's identification of the three classical reef formations – the fringing reef around a volcanic island becoming a barrier reef and then an atoll – scientists have identified further reef types. While some sources find only three, Thomas lists \"Four major forms of large-scale coral reefs\" – the fringing reef, barrier reef, atoll and table reef based on Stoddart, D.R. (1969). Spalding et al. list four main reef types that can be clearly illustrated – the fringing reef, barrier reef, atoll, and \"bank or platform reef\"—and notes that many other structures exist which do not conform easily to strict definitions, including the \"patch reef\".\n\nFringing reef\n\nA fringing reef, also called a shore reef, is directly attached to a shore, or borders it with an intervening narrow, shallow channel or lagoon. It is the most common reef type. Fringing reefs follow coastlines and can extend for many kilometres. They are usually less than 100 metres wide, but some are hundreds of metres wide. Fringing reefs are initially formed on the shore at the low water level and expand seawards as they grow in size. The final width depends on where the seabed begins to drop steeply. The surface of the fringe reef generally remains at the same height: just below the waterline. In older fringing reefs, with outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a lagoon. Fringing reef lagoons can become over 100 metres wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the Red Sea are \"some of the best developed in the world\" and occur along all its shores except off sandy bays.\n\nBarrier reef\n\nBarrier reefs are separated from a mainland or island shore by a deep channel or lagoon. They resemble the later stages of a fringing reef with its lagoon, but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 30 to 70 metres deep. Above all, the offshore outer reef edge formed in open water rather than next to a shoreline. Like an atoll, it is thought that these reefs are formed either as the seabed lowered or the sea level rose. Formation takes considerably longer than for a fringing reef; thus, barrier reefs are much rarer.\nThe best known and largest example of a barrier reef is the Australian Great Barrier Reef. Other major examples are the Mesoamerican Barrier Reef System and the New Caledonian Barrier Reef. Barrier reefs are also found on the coasts of Providencia, Mayotte, the Gambier Islands, on the southeast coast of Kalimantan, on parts of the coast of Sulawesi, southeastern New Guinea and the south coast of the Louisiade Archipelago.\n\nPlatform reef\n\nPlatform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals. Platform reefs are found in the southern Great Barrier Reef, the Swain and Capricorn Group on the continental shelf, about 100–200 km from the coast. Some platform reefs of the northern Mascarenes are several thousand kilometres from the mainland. Unlike fringing and barrier reefs, which extend only seaward, platform reefs grow in all directions. They are variable in size, ranging from a few hundred metres to many kilometres across. Their usual shape is oval to elongated. Parts of these reefs can reach the surface, forming sandbanks and small islands around which fringing reefs may form. A lagoon may form in the middle of a platform reef.\nPlatform reefs are typically situated within atolls, where they adopt the name \"patch reefs\" and often span a diameter of just a few dozen meters. When platform reefs develop along elongated structures, such as old, weathered barrier reefs, they tend to form a linear arrangement. This is the case, for example, on the east coast of the Red Sea near Jeddah. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll. These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow.\n\nAtoll\n\nAtolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level. Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which encloses a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands, and Micronesia.\nAtolls are found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles, and around Cocos Island. The entire Maldives consists of 26 atolls.\n\nOther reef types or variants\n\nApron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore. The initial stage of a fringing reef.\nBank reef – isolated, flat-topped reef larger than a patch reef and usually on mid-shelf regions and linear or semi-circular in shape; a type of platform reef.\nPatch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass. It can be considered as a type of platform reef or as features of fringing reefs, atolls, and barrier reefs. The patches may be surrounded by a ring of reduced seagrass cover referred to as a grazing halo.\nRibbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon and also called a shelf-edge reef or sill reef.\nDrying reef – a part of a reef which is above water at low tide but submerged at high tide\nHabili – reef specific to the Red Sea; does not reach near enough to the surface to cause visible surf; may be a hazard to ships (from the Arabic for \"unborn\")\nMicroatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels\nCays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, creating an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land\nSeamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded, and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes\n\nZones\n\nCoral reef ecosystems contain distinct zones that host different kinds of habitats. Usually, three major zones are recognized: the fore reef, the reef crest, and the back reef (also called the reef lagoon).\nThe three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for the exchange of seawater, sediment, nutrients, and marine life.\nMost coral reefs exist in waters less than 50 m deep. Some inhabit tropical continental shelves where cool, nutrient-rich upwelling does not occur, such as the Great Barrier Reef. Others are found in the deep ocean surrounding islands or as atolls, such as in the Maldives. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea.\nAlternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.\n\nThe reef surface is the shallowest part of the reef. It is subject to surge and tides. When waves pass over shallow areas, they shoal, as shown in the adjacent diagram. This means the water is often agitated. These are the precise conditions under which corals flourish. The light is sufficient for photosynthesis by the symbiotic zooxanthellae, and agitated water brings plankton to feed the coral.\nThe off-reef floor is the shallow sea floor surrounding a reef. This zone occurs next to reefs on continental shelves. Reefs around tropical islands and atolls drop abruptly to great depths and do not have such a floor. Usually sandy, the floor often supports seagrass meadows, which are important foraging areas for reef fish.\nThe reef drop-off is, for its first 50 m, habitat for reef fish who find shelter on the cliff face and plankton in the water nearby. The drop-off zone primarily occurs around oceanic islands and atolls.\nThe reef face is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and calcareous algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms. A common feature of this forereef zone is spur and groove formations that serve to transport sediment downslope.\nThe reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as a protective area, or it may lie between the reef and the shore, and in this case, it is a flat, rocky area. Fish tend to prefer it when it is present.\nThe reef lagoon is an entirely enclosed region, which creates an area less affected by wave action and often contains small reef patches.\nHowever, the topography of coral reefs is constantly changing. Each reef is made up of irregular patches of algae, sessile invertebrates, and bare rock and sand. The size, shape, and relative abundance of these patches change from year to year in response to the various factors that favor one type of patch over another. Growing coral, for example, produces constant change in the fine structure of reefs. On a larger scale, tropical storms may knock out large sections of reef and cause boulders in sandy areas to move.\n\nLocations\n\nCoral reefs are estimated to cover 284,300 km2 (109,800 sq mi), just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific, including Australia, accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.\nAlthough corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F). When the net production by reef-building corals no longer keeps pace with relative sea level, and the reef structure permanently drowns, a Darwin Point is reached. One such point exists at the northwestern end of the Hawaiian Archipelago; see Evolution of Hawaiian volcanoes#Coral atoll stage.\nHowever, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (100 °F) in summer. 37 species of scleractinian corals inhabit such an environment around Larak Island.\nDeep-water coral inhabits greater depths and colder temperatures at much higher latitudes, as far north as Norway. Although deep water corals can form reefs, little is known about them.\nThe northernmost coral reef on Earth is located near Eilat, Israel. Coral reefs are rare along the west coasts of the Americas and Africa, due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (the Humboldt, Benguela, and Canary Currents, respectively). Corals are seldom found along the coastline of South Asia—from the eastern tip of India (Chennai) to the Bangladesh and Myanmar borders—as well as along the coasts of northeastern South America and Bangladesh, due to the freshwater release from the Amazon and Ganges Rivers respectively.\nSignificant coral reefs include:\n\nThe Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia\nThe Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras\nThe New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)\nThe Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau\nThe Red Sea—includes 6,000-year-old fringing reefs located along a 2,000 km (1,240 mi) coastline\nThe Florida Reef Tract—largest continental US reef and the third-largest coral barrier reef, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico\nBlake Plateau has the world's largest known deep-water coral reef, comprising a 6.4 million-acre reef that stretches from Miami to Charleston, S. C. Its discovery was announced in January 2024.\nPulley Ridge—deepest photosynthetic coral reef, Florida\nNumerous reefs around the Maldives\nThe Philippines coral reef area, the second-largest in Southeast Asia, is estimated at 26,000 square kilometres. They are populated by over 900 reef fish species and 400 scleractinian coral species, 12 of which are endemic.\nThe Raja Ampat Islands in Indonesia's Southwest Papua province offer the highest known marine diversity.\nBermuda is known for its northernmost coral reef system, located at 32.4°N 64.8°W / 32.4; -64.8. The presence of coral reefs at this high latitude is due to the proximity of the Gulf Stream. Bermuda coral species represent a subset of those found in the greater Caribbean.\nThe world's northernmost individual coral reef is located in the Finlayson Channel, in the inside passage of British Columbia, Canada.\nThe world's southernmost coral reef is at Lord Howe Island, in the Pacific Ocean off the east coast of Australia.\n\nCoral\n\nWhen alive, corals are colonies of small animals embedded in calcium carbonate shells. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes. Polyps are usually tiny, but they can range in size from a pinhead to 12 inches (30 cm) across.\nReef-building or hermatypic corals live only in the photic zone (above 70 m), the depth to which sufficient sunlight penetrates the water.\n\nZooxanthellae\n\nCoral polyps do not photosynthesize, but have a symbiotic relationship with microscopic algae (dinoflagellates) of the genus Symbiodinium, commonly referred to as zooxanthellae. These organisms live within the polyps' tissues and provide organic nutrients that nourish the polyp in the form of glucose, glycerol, and amino acids. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts. In return, as an example of mutualism, the corals shelter the zooxanthellae, averaging one million for every cubic centimetre of coral, and provide a constant supply of the carbon dioxide they need for photosynthesis.\n\nThe varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance and give brown corals their colors. Other pigments, such as reds, blues, and greens, are produced by colored proteins in coral animals. Coral that loses a significant fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are pigmented with their own proteins) and is said to be bleached, a condition which, unless corrected, can kill the coral.\nThere are eight clades of Symbiodinium phylotypes. Most research has been conducted on clades A–D. Each clade contributes both benefits and less compatible attributes to the survival of its coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage to compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow waters. It can produce mycosporine-like amino acids that are UV-resistant, using a derivative of glycerin to absorb UV radiation, thereby allowing them to better adapt to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.\nClades B and C are found more frequently in deeper water, which may explain their higher vulnerability to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth are analogous to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, these phylotypes are more prone to coral bleaching than the shallow clade A.\nClade D has been observed to be high temperature-tolerant, and has a higher rate of survival than clades B and C during modern bleaching events.\n\nSkeleton\n\nReefs grow as polyps and other organisms deposit calcium carbonate, the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards. Waves, grazing fish (such as parrotfish), sea urchins, sponges and other forces and organisms act as bioeroders, breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons.\nTypical shapes for coral species are named by their resemblance to terrestrial objects such as wrinkled brains, cabbages, table tops, antlers, wire strands, and pillars. These shapes can depend on the life history of the coral, like light exposure and wave action, and events such as breakages.\n\nReproduction\n\nCorals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesenteries, membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few species change sex as they grow.\nInternally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during synchronized spawning. Polyps across a reef simultaneously release eggs and sperm into the water en masse. Spawn disperse over a large area. The timing of spawning depends on the time of year, water temperature, and tidal and lunar cycles. Spawning is most successful when there is little variation between high and low tide. The less water movement, the better the chance for fertilization. The release of eggs or planula usually occurs at night and is sometimes in phase with the lunar cycle (three to six days after a full moon).\n\nThe period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. During this process, the larvae may use several cues to find a suitable settlement site. At long distances sounds from existing reefs are likely important, while at short distances chemical compounds become important. The larvae are vulnerable to predation and environmental conditions. The lucky few planulae that successfully attach to the substrate then compete for food and space.\n\nGallery of reef-building corals\n\nOther reef builders\nCorals are the most prodigious reef-builders. However, many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner as corals. These include coralline algae, some sponges and bivalves. Reefs are always built by the combined efforts of these different phyla, with other organisms leading reef-building in other geological periods.\n\nCoralline algae\n\nCoralline algae are essential contributors to reef structure. Although their mineral deposition rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the most significant forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface. Furthermore, in locations unfavorable to the growth of corals, coralline algae can be the primary builders of an algal reef.\n\nSponges\n\nSponge reefs are reefs produced by sea sponges. Hexactinellid sponges are known to form reefs off the coast of British Columbia, southeast Alaska, and Washington state. Reefs discovered in Hecate Strait, British Columbia, have grown to up to 7 kilometres long and 20 metres high. Hexactinellid sponge reefs were first identified in the Middle Triassic (245–208 million years ago). The sponges reached their full extent in the late Jurassic (201–145 million years ago) when a discontinuous reef system 7,000 km long stretched across the northern Tethys and North Atlantic basins, but have since declined and were thought to be extinct until existing reefs were discovered in 1987–1988.\nArchaeocyatha, an extinct clade of sponges, were the planet's first reef-building animals and are an index fossil for the Lower Cambrian worldwide. Similarly, Stromatoporoidea was another extinct clade of reef-building sponges. Unlike corals, stromatoporoids usually settled on soft substrates, so their 'reefs' occupied only a single level rather than a multi-tiered vertical framework of built-up skeletons.\n\nBivalves\n\nOyster reefs are dense aggregations of oysters living in colonial communities. Other regionally specific names for these structures in",
    "source": "wikipedia:Coral reef",
    "domain": "climate"
  },
  {
    "text": "An ecosystem (or ecological system) is a system formed by organisms in interaction with their environment. The biotic and abiotic components are linked together through nutrient cycles and energy flows.\nEcosystems are controlled by external and internal factors. External factors—including climate—control the ecosystem's structure, but are not influenced by it. By contrast, internal factors control and are controlled by ecosystem processes; these include decomposition, the types of species present, root competition, shading, disturbance, and succession. While external factors generally determine which resource inputs an ecosystem has, their availability within the ecosystem is controlled by internal factors. Ecosystems are dynamic, subject to periodic disturbances and always in the process of recovering from past disturbances. The tendency of an ecosystem to remain close to its equilibrium state, is termed its resistance. Its capacity to absorb disturbance and reorganize, while undergoing change so as to retain essentially the same function, structure, identity, is termed its ecological resilience. \nEcosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Biomes are general classes or categories of ecosystems. However, there is no clear distinction between biomes and ecosystems. Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy. Biotic factors are living things, such as plants, while abiotic factors are non-living components, such as soil. Plants allow energy to enter the system through photosynthesis, building up plant tissue. Animals play an important role in the movement of matter and energy through the system, by feeding on plants and one another. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.\nEcosystems provide a variety of goods and services upon which people depend, and may be part of. Ecosystem goods include the \"tangible, material products\" of ecosystem processes such as water, food, fuel, construction material, and medicinal plants. Ecosystem services, on the other hand, are generally \"improvements in the condition or location of things of value\". These include maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination, and opportunities for research. Many ecosystems become degraded through human impacts, such as soil loss, air and water pollution, habitat fragmentation, water diversion, fire suppression, and introduced species and invasive species. These threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of abiotic conditions of the ecosystem. Once the original ecosystem has lost its defining features, it is considered \"collapsed\". Ecosystem restoration can contribute to achieving the Sustainable Development Goals.\n\nDefinition\nAn ecosystem (or ecological system) consists of all the organisms and the abiotic pools (or physical environment) with which they interact. The biotic and abiotic components are linked together through nutrient cycles and energy flows.\n\"Ecosystem processes\" are the transfers of energy and materials from one pool to another. Ecosystem processes are known to \"take place at a wide range of scales\". Therefore, the correct scale of study depends on the question asked.\n\nOrigin and development of the term\nThe term \"ecosystem\" was first used in 1935 in a publication by British ecologist Arthur Tansley. The term was coined by Arthur Roy Clapham, who came up with the word at Tansley's request. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment. He later refined the term, describing it as \"The whole system, ... including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment\". Tansley regarded ecosystems not simply as natural units, but as \"mental isolates\". Tansley later defined the spatial extent of ecosystems using the term \"ecotope\".\nG. Evelyn Hutchinson, a limnologist who was a contemporary of Tansley's, combined Charles Elton's ideas about trophic ecology with those of Russian geochemist Vladimir Vernadsky. As a result, he suggested that mineral nutrient availability in a lake limited algal production. This would, in turn, limit the abundance of animals that feed on algae. Raymond Lindeman took these ideas further to suggest that the flow of energy through a lake was the primary driver of the ecosystem. Hutchinson's students, brothers Howard T. Odum and Eugene P. Odum, further developed a \"systems approach\" to the study of ecosystems. This allowed them to study the flow of energy and material through ecological systems.\n\nProcesses\n\nExternal and internal factors\nEcosystems are controlled by both external and internal factors. External factors, also called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem. On broad geographic scales, climate is the factor that \"most strongly determines ecosystem processes and structure\". Climate determines the biome in which the ecosystem is embedded. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of energy available to the ecosystem.\nParent material determines the nature of the soil in an ecosystem, and influences the supply of mineral nutrients. Topography also controls ecosystem processes by affecting things like microclimate, soil development and the movement of water through a system. For example, ecosystems can be quite different if situated in a small depression on the landscape, versus one present on an adjacent steep hillside.\nOther external factors that play an important role in ecosystem functioning include time and potential biota, the organisms that are present in a region and could potentially occupy a particular site. Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present. The introduction of non-native species can cause substantial shifts in ecosystem function.\nUnlike external factors, internal factors in ecosystems not only control ecosystem processes but are also controlled by them. While the resource inputs are generally controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Other factors like disturbance, succession or the types of species present are also internal factors.\n\nPrimary production\n\nPrimary production is the production of organic matter from inorganic carbon sources. This mainly occurs through photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass, soil carbon and fossil fuels. It also drives the carbon cycle, which influences global climate via the greenhouse effect.\nThrough the process of photosynthesis, plants capture energy from light and use it to combine carbon dioxide and water to produce carbohydrates and oxygen. The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP). About half of the gross GPP is respired by plants in order to provide the energy that supports their growth and maintenance. The remainder, that portion of GPP that is not used up by respiration, is known as the net primary production (NPP). Total photosynthesis is limited by a range of environmental factors. These include the amount of light available, the amount of leaf area a plant has to capture light (shading by other plants is a major limitation of photosynthesis), the rate at which carbon dioxide can be supplied to the chloroplasts to support photosynthesis, the availability of water, and the availability of suitable temperatures for carrying out photosynthesis.\n\nEnergy flow\n\nEnergy and carbon enter ecosystems through photosynthesis, are incorporated into living tissue, transferred to other organisms that feed on the living and dead plant matter, and eventually released through respiration. The carbon and energy incorporated into plant tissues (net primary production) is either consumed by animals while the plant is alive, or it remains uneaten when the plant tissue dies and becomes detritus. In terrestrial ecosystems, the vast majority of the net primary production ends up being broken down by decomposers. The remainder is consumed by animals while still alive and enters the plant-based trophic system. After plants and animals die, the organic matter contained in them enters the detritus-based trophic system.\nEcosystem respiration is the sum of respiration by all living organisms (plants, animals, and decomposers) in the ecosystem. Net ecosystem production is the difference between gross primary production (GPP) and ecosystem respiration. In the absence of disturbance, net ecosystem production is equivalent to the net carbon accumulation in the ecosystem.\nEnergy can also be released from an ecosystem through disturbances such as wildfire or transferred to other ecosystems (e.g., from a forest to a stream to a lake) by erosion.\nIn aquatic systems, the proportion of plant biomass that gets consumed by herbivores is much higher than in terrestrial systems. In trophic systems, photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers or secondary producers—herbivores. Organisms which feed on microbes (bacteria and fungi) are termed microbivores. Animals that feed on primary consumers—carnivores—are secondary consumers. Each of these constitutes a trophic level.\nThe sequence of consumption—from plant to herbivore, to carnivore—forms a food chain. Real systems are much more complex than this—organisms will generally feed on more than one form of food, and may feed at more than one trophic level. Carnivores may capture some prey that is part of a plant-based trophic system and others that are part of a detritus-based trophic system (a bird that feeds both on herbivorous grasshoppers and earthworms, which consume detritus). Real systems, with all these complexities, form food webs rather than food chains which present a number of common, non random properties in the topology of their network.\n\nDecomposition\n\nThe carbon and nutrients in dead organic matter are broken down by a group of processes known as decomposition. This releases nutrients that can then be re-used for plant and microbial production and returns carbon dioxide to the atmosphere (or water) where it can be used for photosynthesis. In the absence of decomposition, the dead organic matter would accumulate in an ecosystem, and nutrients and atmospheric carbon dioxide would be depleted.\nDecomposition processes can be separated into three categories—leaching, fragmentation and chemical alteration of dead material. As water moves through dead organic matter, it dissolves and carries with it the water-soluble components. These are then taken up by organisms in the soil, react with mineral soil, or are transported beyond the confines of the ecosystem (and are considered lost to it). Newly shed leaves and newly dead animals have high concentrations of water-soluble components and include sugars, amino acids and mineral nutrients. Leaching is more important in wet environments and less important in dry ones.\nFragmentation processes break organic material into smaller pieces, exposing new surfaces for colonization by microbes. Freshly shed leaf litter may be inaccessible due to an outer layer of cuticle or bark, and cell contents are protected by a cell wall. Newly dead animals may be covered by an exoskeleton. Fragmentation processes, which break through these protective layers, accelerate the rate of microbial decomposition. Animals fragment detritus as they hunt for food, as does passage through the gut. Freeze-thaw cycles and cycles of wetting and drying also fragment dead material.\nThe chemical alteration of the dead organic matter is primarily achieved through bacterial and fungal action. Fungal hyphae produce enzymes that can break through the tough outer structures surrounding dead plant material. They also produce enzymes that break down lignin, which allows them access to both cell contents and the nitrogen in the lignin. Fungi can transfer carbon and nitrogen through their hyphal networks and thus, unlike bacteria, are not dependent solely on locally available resources.\n\nDecomposition rates\nDecomposition rates vary among ecosystems. The rate of decomposition is governed by three sets of factors—the physical environment (temperature, moisture, and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself. Temperature controls the rate of microbial respiration; the higher the temperature, the faster the microbial decomposition occurs. Temperature also affects soil moisture, which affects decomposition. Freeze-thaw cycles also affect decomposition—freezing temperatures kill soil microorganisms, which allows leaching to play a more important role in moving nutrients around. This can be especially important as the soil thaws in the spring, creating a pulse of nutrients that become available.\nDecomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in wet, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true in wetlands), which slows microbial growth. In dry soils, decomposition slows as well, but bacteria continue to grow (albeit at a slower rate) even after soils become too dry to support plant growth.\n\nDynamics and resilience\n\nEcosystems are dynamic entities. They are subject to periodic disturbances and are always in the process of recovering from past disturbances. When a perturbation occurs, an ecosystem responds by moving away from its initial state. The tendency of an ecosystem to remain close to its equilibrium state, despite that disturbance, is termed its resistance. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its ecological resilience. Resilience thinking also includes humanity as an integral part of the biosphere where we are dependent on ecosystem services for our survival and must build and maintain their natural capacities to withstand shocks and disturbances. Time plays a central role over a wide range, for example, in the slow development of soil from bare rock and the faster recovery of a community from disturbance.\nDisturbance also plays an important role in ecological processes. F. Stuart Chapin and coauthors define disturbance as \"a relatively discrete event in time that removes plant biomass\". This can range from herbivore outbreaks, treefalls, fires, hurricanes, floods, glacial advances, to volcanic eruptions. Such disturbances can cause large changes in plant, animal and microbe populations, as well as soil organic matter content. Disturbance is followed by succession, a \"directional change in ecosystem structure and functioning resulting from biotically driven changes in resource supply.\"\nThe frequency and severity of disturbance determine the way it affects ecosystem function. A major disturbance like a volcanic eruption or glacial advance and retreat leave behind soils that lack plants, animals or organic matter. Ecosystems that experience such disturbances undergo primary succession. A less severe disturbance like forest fires, hurricanes or cultivation result in secondary succession and a faster recovery. More severe and more frequent disturbance result in longer recovery times.\nFrom one year to another, ecosystems experience variation in their biotic and abiotic environments. A drought, a colder than usual winter, and a pest outbreak all are short-term variability in environmental conditions. Animal populations vary from year to year, building up during resource-rich periods and crashing as they overshoot their food supply. Longer-term changes also shape ecosystem processes. For example, the forests of eastern North America still show legacies of cultivation which ceased in 1850 when large areas were reverted to forests. Another example is the methane production in eastern Siberian lakes that is controlled by organic matter which accumulated during the Pleistocene.\n\nNutrient cycling\n\nEcosystems continually exchange energy and carbon with the wider environment. Mineral nutrients, on the other hand, are mostly cycled back and forth between plants, animals, microbes and the soil. Most nitrogen enters ecosystems through biological nitrogen fixation, is deposited through precipitation, dust, gases or is applied as fertilizer. Most terrestrial ecosystems are nitrogen-limited in the short term making nitrogen cycling an important control on ecosystem production. Over the long term, phosphorus availability can also be critical.\nMacronutrients which are required by all plants in large quantities include the primary nutrients (which are most limiting as they are used in largest amounts): Nitrogen, phosphorus, potassium. Secondary major nutrients (less often limiting) include: Calcium, magnesium, sulfur. Micronutrients required by all plants in small quantities include boron, chloride, copper, iron, manganese, molybdenum, zinc. Finally, there are also beneficial nutrients which may be required by certain plants or by plants under specific environmental conditions: aluminum, cobalt, iodine, nickel, selenium, silicon, sodium, vanadium.\nUntil modern times, nitrogen fixation was the major source of nitrogen for ecosystems. Nitrogen-fixing bacteria either live symbiotically with plants or live freely in the soil. The energetic cost is high for plants that support nitrogen-fixing symbionts—as much as 25% of gross primary production when measured in controlled conditions. Many members of the legume plant family support nitrogen-fixing symbionts. Some cyanobacteria are also capable of nitrogen fixation. These are phototrophs, which carry out photosynthesis. Like other nitrogen-fixing bacteria, they can either be free-living or have symbiotic relationships with plants. Other sources of nitrogen include acid deposition produced through the combustion of fossil fuels, ammonia gas which evaporates from agricultural fields which have had fertilizers applied to them, and dust. Anthropogenic nitrogen inputs account for about 80% of all nitrogen fluxes in ecosystems.\nWhen plant tissues are shed or are eaten, the nitrogen in those tissues becomes available to animals and microbes. Microbial decomposition releases nitrogen compounds from dead organic matter in the soil, where plants, fungi, and bacteria compete for it. Some soil bacteria use organic nitrogen-containing compounds as a source of carbon, and release ammonium ions into the soil. This process is known as nitrogen mineralization. Others convert ammonium to nitrite and nitrate ions, a process known as nitrification. Nitric oxide and nitrous oxide are also produced during nitrification. Under nitrogen-rich and oxygen-poor conditions, nitrates and nitrites are converted to nitrogen gas, a process known as denitrification.\nMycorrhizal fungi which are symbiotic with plant roots, use carbohydrates supplied by the plants and in return transfer phosphorus and nitrogen compounds back to the plant roots. This is an important pathway of organic nitrogen transfer from dead organic matter to plants. This mechanism may contribute to more than 70 Tg of annually assimilated plant nitrogen, thereby playing a critical role in global nutrient cycling and ecosystem function.\nPhosphorus enters ecosystems through weathering. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics). Calcium and sulfur are also produced by weathering, but acid deposition is an important source of sulfur in many ecosystems. Although magnesium and manganese are produced by weathering, exchanges between soil organic matter and living cells account for a significant portion of ecosystem fluxes. Potassium is primarily cycled between living cells and soil organic matter.\n\nFunction and biodiversity\n\nBiodiversity plays an important role in ecosystem functioning. Ecosystem processes are driven by the species in an ecosystem, the nature of the individual species, and the relative abundance of organisms among these species. Ecosystem processes are the net effect of the actions of individual organisms as they interact with their environment. Ecological theory suggests that in order to coexist, species must have some level of limiting similarity—they must be different from one another in some fundamental way, otherwise, one species would competitively exclude the other. Despite this, the cumulative effect of additional species in an ecosystem is not linear: additional species may enhance nitrogen retention, for example. However, beyond some level of species richness, additional species may have little additive effect unless they differ substantially from species already present. This is the case for example for exotic species.\nThe addition (or loss) of species that are ecologically similar to those already present in an ecosystem tends to only have a small effect on ecosystem function. Ecologically distinct species, on the other hand, have a much larger effect. Similarly, dominant species have a large effect on ecosystem function, while rare species tend to have a small effect. Keystone species tend to have an effect on ecosystem function that is disproportionate to their abundance in an ecosystem.\nAn ecosystem engineer is any organism that creates, significantly modifies, maintains or destroys a habitat.\n\nStudy approaches\n\nEcosystem ecology\n\nEcosystem ecology is the \"study of the interactions between organisms and their environment as an integrated system\". The size of ecosystems can range up to ten orders of magnitude, from the surface layers of rocks to the surface of the planet.\nThe Hubbard Brook Ecosystem Study started in 1963 to study the White Mountains in New Hampshire. It was the first successful attempt to study an entire watershed as an ecosystem. The study used stream chemistry as a means of monitoring ecosystem properties, and developed a detailed biogeochemical model of the ecosystem. Long-term research at the site led to the discovery of acid rain in North America in 1972. Researchers documented the depletion of soil cations (especially calcium) over the next several decades.\nEcosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Studies can be carried out at a variety of scales, ranging from whole-ecosystem studies to studying microcosms or mesocosms (simplified representations of ecosystems). American ecologist Stephen R. Carpenter has argued that microcosm experiments can be \"irrelevant and diversionary\" if they are not carried out in conjunction with field studies done at the ecosystem scale. In such cases, microcosm experiments may fail to accurately predict ecosystem-level dynamics.\n\nClassifications\n\nBiomes are general classes or categories of ecosystems. However, there is no clear distinction between biomes and ecosystems. Biomes are always defined at a very general level. Ecosystems can be described at levels that range from very general (in which case the names are sometimes the same as those of biomes) to very specific, such as \"wet coastal needle-leafed forests\".\nBiomes vary due to global variations in climate. Biomes are often defined by their structure: at a general level, for example, tropical forests, temperate grasslands, and arctic tundra. There can be any degree of subcategories among ecosystem types that comprise a biome, e.g., needle-leafed boreal forests or wet tropical forests. Although ecosystems are most commonly categorized by their structure and geography, there are also other ways to categorize and classify ecosystems such as by their level of human impact (see anthropogenic biome), or by their integration with social processes or technological processes or their novelty (e.g. novel ecosystem). Each of these taxonomies of ecosystems tends to emphasize different structural or functional properties. None of these is the \"best\" classification.\nEcosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy. Different approaches to ecological classifications have been developed in terrestrial, freshwater and marine disciplines, and a function-based typology has been proposed to leverage the strengths of these different approaches into a unified system.\n\nHuman interactions with ecosystems\nHuman activities are important in almost all ecosystems. Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.\n\nEcosystem goods and services\n\nEcosystems provide a variety of goods and services upon which people depend. Ecosystem goods include the \"tangible, material products\" of ecosystem processes such as water, food, fuel, construction material, and medicinal plants. They also include less tangible items like tourism and recreation, and genes from wild plants and animals that can be used to improve domestic species.\nEcosystem services, on the other hand, are generally \"improvements in the condition or location of things of value\". These include things like the maintenance of hydrological cycles, cleaning air and water, the maintenance of oxygen in the atmosphere, crop pollination and even things like beauty, inspiration and opportunities for research. While material from the ecosystem had traditionally been recognized as being the basis for things of economic value, ecosystem services tend to be taken for granted.\nThe Millennium Ecosystem Assessment is an international synthesis by over 1000 of the world's leading biological scientists that analyzes the state of the Earth's ecosystems and provides summaries and guidelines for decision-makers. The report identified four major categories of ecosystem services: provisioning, regulating, cultural and supporting services. It concludes that human activity is having a significant and escalating impact on the biodiversity of the world ecosystems, reducing both their resilience and biocapacity. The report refers to natural systems as humanity's \"life-support system\", providing essential ecosystem services. The assessment measures 24 ecosystem services and concludes that only four have shown improvement over the last 50 years, 15 are in serious decline, and five are in a precarious condition.\nThe Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) is an intergovernmental organization established to improve the interface between science and policy on issues of biodiversity and ecosystem services. It is intended to serve a similar role to the Intergovernmental Panel on Climate Change. \nEcosystem services are limited and also threatened by human activities. To help inform decision-makers, many ecosystem services are being assigned economic values, often based on the cost of replacement with anthropogenic alternatives. The ongoing challenge of prescribing economic value to nature, for example through biodiversity banking, is prompting transdisciplinary shifts in how we recognize and manage the environment, social responsibility, business opportunities, and our future as a species.\n\nDegradation and decline\n\nAs human population and per capita consumption grow, so do the resource demands imposed on ecosystems and the effects of the human ecological footprint. Natural resources are vulnerable and limited. The environmental impacts of anthropogenic actions are becoming more apparent. Problems for all ecosystems include: environmental pollution, climate change and biodiversity loss. For terrestrial ecosystems further threats include air pollution, soil degradation, and deforestation. For aquatic ecosystems threats also include unsustainable exploitation of marine resources (for example overfishing), marine pollution, microplastics pollution, the effects of climate change on oceans (e.g. warming and acidification), and building on coastal areas.\nMany ecosystems become degraded through human impacts, such as soil loss, air and water pollution, habitat fragmentation, water diversion, fire suppression, and introduced species and invasive species.\nThese threats can lead to abrupt transformation of the ecosystem or to gradual disruption of biotic processes and degradation of abiotic conditions of the ecosystem. Once the original ecosystem has lost its defining fea",
    "source": "wikipedia:Ecosystem",
    "domain": "climate"
  },
  {
    "text": "In physical geography, a tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. There are three regions and associated types of tundra: Arctic, Alpine, and Antarctic.\nTundra vegetation is composed of dwarf shrubs, sedges, grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline. The tundra soil is rich in nitrogen and phosphorus. The soil also contains large amounts of biomass and decomposed biomass that has been stored as methane and carbon dioxide in the permafrost, making the tundra soil a carbon sink. As global warming heats the ecosystem and causes soil thawing, the permafrost carbon cycle accelerates and releases much of these soil-contained greenhouse gases into the atmosphere, creating a feedback cycle that contributes to climate change.\n\nEtymology\nThe word comes from the Russian \"ту́ндра\" (tundra). The first use of tundra in English was in 1824, spelled \"toundra\", possibly indicating borrowing from French. The origin of the Russian word is uncertain: it may be a borrowing of the word \"тундар\" (tundar) the Sámi language family word for \"fell\", \"elevated wasteland\" or \"marshy plain\", from the 16th century.\nSome sources attribute the origin to Finnish.\n\nArctic\n\nArctic tundra occurs in the far Northern Hemisphere (Arctic), north of the taiga belt. The word \"tundra\" usually refers only to the areas where the subsoil is permafrost, or permanently frozen soil. (It may also refer to the treeless plain in general so that northern Sápmi would be included.) Permafrost tundra includes vast areas of northern Russia and Canada. The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area (and the Sámi in Sápmi).\n\nArctic tundra contains areas of stark landscape and is frozen for much of the year. The soil there is frozen from 25 to 90 cm (10 to 35 in) down, making it impossible for trees to grow there. Instead, bare and sometimes rocky land can only support certain kinds of Arctic vegetation, low-growing plants such as moss, heath (Ericaceae varieties such as crowberry and black bearberry), and lichen.\nThere are two main seasons, winter and summer, in the polar tundra areas. During the winter it is very cold, dark, and windy with the average temperature around −28 °C (−18 °F), sometimes dipping as low as −50 °C (−58 °F). However, extreme cold temperatures on the tundra generally do not drop as low as those experienced in taiga areas further south (for example, Russia's, Canada's, and Alaska's lowest temperatures were recorded in locations south of the tree line). During the summer, temperatures rise somewhat, and the top layer of seasonally-frozen soil melts, leaving the ground very soggy. The tundra is covered in marshes, lakes, bogs, and streams during the warm months. Generally daytime temperatures during the summer rise to about 12 °C (54 °F) but can often drop to 3 °C (37 °F) or even below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national biodiversity action plan.\n\nArctic tundra tends to be windy, with winds often blowing upwards of 50–100 km/h (31–62 mph). It is also a polar desert, with only about 150–250 mm (6–10 in) of precipitation falling per year (the summer is typically the season of maximum precipitation). Although precipitation is light, evaporation is also relatively minimal. During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, so the water forms the lakes and marshes found during the summer months. There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals (FRIs) that typically vary from 150 to 200 years, with dryer lowland areas burning more frequently than wetter highland areas.\n\nThe biodiversity of tundras is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. There are also a few fish species. There are few species with large populations. Notable plants in the Arctic tundra include blueberry (Vaccinium uliginosum), crowberry (Empetrum nigrum), reindeer lichen (Cladonia rangiferina), lingonberry (Vaccinium vitis-idaea), and Labrador tea (Rhododendron groenlandicum). Notable animals include reindeer (caribou), musk ox, Arctic hare, Arctic fox, snowy owl, ptarmigan, northern red-backed voles, lemmings, the mosquito, and even polar bears near the ocean. The tundra is largely devoid of poikilotherms such as frogs or lizards.\nDue to the harsh climate of Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such as petroleum, natural gas, and uranium. In recent times this has begun to change in Alaska, Russia, and some other parts of the world: for example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas. \n\nRelationship to climate change\n\nA severe threat to tundra is climate change, which causes permafrost to thaw. The thawing of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there. It also represents a significant risk to infrastructure built on top of permafrost, such as roads and pipelines. \nIn locations where dead vegetation and peat have accumulated, there is a risk of wildfire, such as the 1,039 km2 (401 sq mi) of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska. Such events may both result from and contribute to global warming.\nCarbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a positive climate change feedback. The warming also intensifies the Arctic water cycle, and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.\nThe IPCC Sixth Assessment Report estimates that carbon dioxide and methane released from permafrost could amount to the equivalent of 14–175 billion tonnes (1.4×1010–1.72×1011 long tons; 1.5×1010–1.93×1011 short tons) carbon dioxide per 1 °C (1.8 °F) of warming. For comparison, by 2019, annual anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes (3.9×1010 long tons; 4.4×1010 short tons). A 2018 perspectives article discussing tipping points in the climate system activated around 2 °C (3.6 °F) of global warming suggested that at this threshold, permafrost thaw would add a further 0.09 °C (0.16 °F) to global temperatures by 2100, with a range of 0.04–0.16 °C (0.07–0.29 °F)\n\nAntarctic\n\nAntarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, and most of the continent is covered by ice fields or cold deserts. However, some portions of the continent, particularly the Antarctic Peninsula, have areas of rocky soil that support plant life. The flora presently consists of around 300–400 species of lichens, 100 mosses, 25 liverworts, and around 700 terrestrial and aquatic algae species, which live on the areas of exposed rock and soil around the shore of the continent. Antarctica's two flowering plant species, the Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula.\nIn contrast with the Arctic tundra, the Antarctic tundra lacks a large mammal fauna, mostly due to its physical isolation from the other continents. Sea mammals and seabirds, including seals and penguins, inhabit areas near the shore, and some small mammals, like rabbits and cats, have been introduced by humans to some of the subantarctic islands. The Antipodes Subantarctic Islands tundra, an ecoregion that includes the Bounty Islands, Auckland Islands, Antipodes Islands, the Campbell Islands, and Macquarie Island. Species endemic to this ecoregion include the windswept helmet-orchid (Corybas dienemus) and the grooved helmet-orchid (Corybas sulcatus), the only subantarctic orchids; the royal penguin; and the Antipodean albatross.\nThere is some ambiguity on whether Magellanic moorland, on the west coast of Patagonia, should be considered tundra or not. Edmundo Pisano, a Chilean Phytogeographer, called it tundra (Spanish: tundra Magallánica) since he considered the low temperatures key to restrict plant growth. More recent approaches have since recognized it as a temperate grassland, restricting southern tundra to coastal Antarctica and its islands.\nThe flora and fauna of Antarctica and the Antarctic Islands (south of 60° south latitude) are protected by the Antarctic Treaty System.\n\nAlpine\n\nAlpine tundra does not contain trees because the climate and soils at high altitude block tree growth. The cold climate of the alpine tundra is caused by the low air temperatures, and is similar to polar climate. Alpine tundra is generally better drained than arctic soils. Alpine tundra transitions to subalpine forests below the tree line; stunted forests occurring within the forest-tundra ecotone are known as Krummholz. Alpine tundra can be affected by woody plant encroachment.\nAlpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by plants that grow close to the ground, including perennial grasses, sedges, forbs, cushion plants, mosses, and lichens. The flora is adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, and a short growing season.\n\nClimatic classification\n\nTundra climates ordinarily fit the Köppen climate classification ET, signifying a local climate in which at least one month has an average temperature high enough to melt snow (0 °C (32 °F)), but no month with an average temperature in excess of 10 °C (50 °F). The cold limit generally meets the EF climates of permanent ice and snows; the warm-summer limit generally corresponds with the poleward or altitudinal limit of trees, where they grade into the subarctic climates designated Dfd, Dwd and Dsd (extreme winters as in parts of Siberia), Dfc typical in Alaska, Canada, mountain areas of Scandinavia, European Russia, and Western Siberia (cold winters with months of freezing).\nDespite the potential diversity of climates in the ET category involving precipitation, extreme temperatures, and relative wet and dry seasons, this category is rarely subdivided. Rainfall and snowfall are generally slight due to the low vapor pressure of water in the chilly atmosphere, but as a rule potential evapotranspiration is extremely low, allowing soggy terrain of swamps and bogs even in places that get precipitation typical of deserts of lower and middle latitudes. The amount of native tundra biomass depends more on the local temperature than the amount of precipitation.\n\nSee also\nAlas\nFellfield\nList of tundra ecoregions from the World Wide Fund for Nature\nMammoth steppe\nPark Tundra\nTundra of North America\nInternational Tundra Experiment\n\nReferences\n\nFurther reading\n\nExternal links\nWWF Tundra Ecoregions Archived 23 February 2010 at the Wayback Machine\nThe Arctic biome at Classroom of the Future\nArctic Feedbacks to Global Warming: Tundra Degradation in the Russian Arctic\nBritish Antarctica Survey\nAntarctica: West of the Transantarctic Mountains\nWorld Map of Tundra",
    "source": "wikipedia:Tundra",
    "domain": "climate"
  },
  {
    "text": "The Amazon rainforest, also called the Amazon jungle or Amazonia, is a moist broadleaf tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. This basin encompasses 7 million km2 (2.7 million sq mi), of which 6 million km2 (2.3 million sq mi) are covered by the rainforest. This region includes territory belonging to nine nations and 3,344 indigenous territories.\nThe majority of the forest, 60%, is in Brazil, followed by Peru with 13%, Colombia with 10%, and with minor amounts in Bolivia, Ecuador, French Guiana, Guyana, Suriname, and Venezuela. Four nations have \"Amazonas\" as the name of one of their first-level administrative regions, and France uses the name \"Guiana Amazonian Park\" for French Guiana's protected rainforest area. The Amazon represents over half of the total area of remaining rainforests on Earth, and comprises the largest and most biodiverse tract of tropical rainforest in the world, with an estimated 390 billion individual trees in about 16,000 species.\nMore than 30 million people of 350 different ethnic groups live in the Amazon, which are subdivided into 9 different national political systems and 3,344 formally acknowledged indigenous territories. Indigenous peoples make up 9% of the total population, and 60 groups remain largely isolated.\nLarge scale deforestation is occurring in the forest, creating different harmful effects. Economic losses due to deforestation in Brazil could be approximately 7 times higher in comparison to the cost of all commodities produced through deforestation. In 2023, the World Bank published a report proposing a non-deforestation based economic program in the region. Deforestation hurts agriculture so severely that it can lead to \"agro-suicide.\"\n\nEtymology\nThe name Amazon is said to arise from a war Francisco de Orellana fought with the Tapuyas and other tribes. The women of the tribe fought alongside the men, as was their custom. Orellana derived the name Amazonas from the Amazons of Greek mythology, described by Herodotus and Diodorus.\n\nHistory\n\nBased on archaeological evidence from an excavation at Caverna da Pedra Pintada, human inhabitants first settled in the Amazon region at least 11,200 years ago. Subsequent development led to late-prehistoric settlements along the periphery of the forest by AD 1250, which induced alterations in the forest cover.\nFor a long time, it was thought that the Amazon rainforest was never more than sparsely populated, as it was impossible to sustain a large population through agriculture given the poor soil. Archeologist Betty Meggers was a prominent proponent of this idea, as described in her book Amazonia: Man and Culture in a Counterfeit Paradise. She claimed that a population density of 0.2 inhabitants per square kilometre (0.52/sq mi) is the maximum that can be sustained in the rainforest through hunting, with agriculture needed to host a larger population. However, recent anthropological findings have suggested that the region was actually densely populated. The Upano Valley sites in present-day eastern Ecuador predate all known complex Amazonian societies.\nSome 5 million people may have lived in the Amazon region in AD 1500, divided between dense coastal settlements, such as that at Marajó, and inland dwellers. Based on projections of food production, one estimate suggests over 8 million people living in the Amazon in 1492. By 1900, the native indigenous population had fallen to 1 million and by the early 1980s it was less than 200,000.\nThe first European to travel the length of the Amazon River was Francisco de Orellana in 1542. The BBC's Unnatural Histories presents evidence that Orellana, rather than exaggerating his claims as previously thought, was correct in his observations that a complex civilization was flourishing along the Amazon in the 1540s. The Pre-Columbian agriculture in the Amazon Basin was sufficiently advanced to support prosperous and populous societies. It is believed that civilization was later devastated by the spread of diseases from Europe, such as smallpox. This civilization was investigated by the British explorer Percy Fawcett in the early twentieth century. The results of his expeditions were inconclusive, and he disappeared mysteriously on his last trip. His name for this lost civilization was the City of Z.\nSince the 1970s, numerous geoglyphs have been discovered on deforested land dating between AD 1–1250, furthering claims about Pre-Columbian civilizations. Ondemar Dias is accredited with first discovering the geoglyphs in 1977, and Alceu Ranzi is credited with furthering their discovery after flying over Acre. The BBC's Unnatural Histories presented evidence that the Amazon rainforest, rather than being a pristine wilderness, has been shaped by man for at least 11,000 years through practices such as forest gardening and terra preta. Terra preta is found over large areas in the Amazon forest; and is now widely accepted as a product of indigenous soil management. The development of this fertile soil allowed agriculture and silviculture in the previously hostile environment; meaning that large portions of the Amazon rainforest are probably the result of centuries of human management, rather than naturally occurring as has previously been supposed. In the region of the Xingu tribe, remains of some of these large settlements in the middle of the Amazon forest were found in 2003 by Michael Heckenberger and colleagues of the University of Florida. Among those were evidence of roads, bridges and large plazas.\nIn the Amazonas, there has been fighting and wars between the neighboring tribes of the Jivaro. Several tribes of the Jivaroan group, including the Shuar, practised headhunting for trophies and headshrinking. The accounts of missionaries to the area in the borderlands between Brazil and Venezuela have recounted constant infighting in the Yanomami tribes. More than a third of the Yanomamo males, on average, died from warfare.\nThe Munduruku were a warlike tribe that expanded along the Tapajós river and its tributaries and were feared by neighboring tribes. In the early 19th century, the Munduruku were pacified and subjugated by the Brazilians. It is documented that large war parties of the Bororo, Kayapo, Munduruku, Guaraní, and Tupi people carried out long-distance raids. Most Bororo groups were continually at war with their neighbors. In contrast, the Xingu have been described by ethnographers as a \"peaceful\" society, resorting to violence only in defense against their warlike neighbors. In the early 20th century, thirty indigenous tribes in the Amazon basin were listed as \"peaceful\" and eighty-three were specifically described as \"warlike\".\nDuring the Amazon rubber boom it is estimated that diseases brought by immigrants, such as typhus and malaria, killed 40,000 native Amazonians.\nIn the 1950s, Brazilian explorer and defender of indigenous people, Cândido Rondon, supported the Villas-Bôas brothers' campaign, which faced strong opposition from the government and the ranchers of Mato Grosso and led to the establishment of the first Brazilian National Park for indigenous people along the Xingu River in 1961.\nIn 1961, British explorer Richard Mason was killed by an uncontacted Amazon tribe known as the Panará.\nThe Matsés made their first permanent contact with the outside world in 1969. Before that date, they were effectively at-war with the Peruvian government.\n\nGeography\n\nLocation\nNine countries share the Amazon basin—most of the rainforest, 58.4%, is contained within the borders of Brazil. The other eight countries are Peru with 12.8%, Bolivia with 7.7%, Colombia with 7.1%, Venezuela with 6.1%, Guyana with 3.1%, Suriname with 2.5%, French Guiana with 1.4% and Ecuador with 1%.\n\nNatural\n\nThe rainforest likely formed during the Eocene era (from 56 million years to 33.9 million years ago). It appeared following a global reduction of tropical temperatures when the Atlantic Ocean had widened sufficiently to provide a warm, moist climate to the Amazon basin. The rainforest has been in existence for at least 55 million years, and most of the region remained free of savanna-type biomes at least until the current ice age when the climate was drier and savanna more widespread.\nFollowing the Cretaceous–Paleogene extinction event, the extinction of the dinosaurs and the wetter climate may have allowed the tropical rainforest to spread out across the continent. From 66 to 34 Mya, the rainforest extended as far south as 45°. Climate fluctuations during the last 34 million years have allowed savanna regions to expand into the tropics. During the Oligocene, for example, the rainforest spanned a relatively narrow band. It expanded again during the Middle Miocene, then retracted to a mostly inland formation at the last glacial maximum. However, the rainforest still managed to thrive during these glacial periods, allowing for the survival and evolution of a broad diversity of species.\n\nDuring the mid-Eocene, it is believed that the drainage basin of the Amazon was split along the middle of the continent by the Purus Arch. Water on the eastern side flowed toward the Atlantic, while to the west water flowed toward the Pacific across the Amazonas Basin. As the Andes Mountains rose, however, a large basin was created that enclosed a lake; now known as the Solimões Basin. Within the last 5–10 million years, this accumulating water broke through the Purus Arch, joining the easterly flow toward the Atlantic.\n\nThere is evidence that there have been significant changes in the Amazon rainforest vegetation over the last 21,000 years through the last glacial maximum (LGM) and subsequent deglaciation. Analyses of sediment deposits from Amazon basin paleolakes and the Amazon Fan indicate that rainfall in the basin during the LGM was lower than for the present, and this was almost certainly associated with reduced moist tropical vegetation cover in the basin. In present day, the Amazon receives approximately 9 feet of rainfall annually. There is a debate, however, over how extensive this reduction was. Some scientists argue that the rainforest was reduced to small, isolated refugia separated by open forest and grassland; other scientists argue that the rainforest remained largely intact but extended less far to the north, south, and east than is seen today. This debate has proved difficult to resolve because the practical limitations of working in the rainforest mean that data sampling is biased away from the center of the Amazon basin, and both explanations are reasonably well supported by the available data.\n\nSahara Desert dust windblown to the Amazon\nMore than 56% of the dust fertilizing the Amazon rainforest comes from the Bodélé depression in Northern Chad in the Sahara desert. The dust contains phosphorus, important for plant growth. The yearly Sahara dust replaces the equivalent amount of phosphorus washed away yearly in Amazon soil from rains and floods.\nNASA's CALIPSO satellite has measured the amount of dust transported by wind from the Sahara to the Amazon: an average of 182 million tons of dust are windblown out of the Sahara each year (some dust falls into the Atlantic), 15% of which of falls over the Amazon basin (22 million tons of it consisting of phosphorus).\nCALIPSO uses a laser range finder to scan the Earth's atmosphere for the vertical distribution of dust and other aerosols. and regularly tracks the Sahara-Amazon dust plume. CALIPSO has measured variations in the dust amounts transported – an 86 percent drop between the highest amount of dust transported in 2007 and the lowest in 2011. This is possibly caused by rainfall variations in the Sahel, a strip of semi-arid land on the southern border of the Sahara.\nAmazon phosphorus also comes as smoke due to biomass burning in Africa.\n\nBiodiversity\n\nWet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than the wet forests in Africa and Asia. As the largest tract of tropical rainforest in the Americas, the Amazonian rainforests have unparalleled biodiversity. One in ten known species in the world lives in the Amazon rainforest. This constitutes the largest collection of living plants and animal species in the world.\nThe region is home to about 2.5 million insect species, tens of thousands of plants, and some 2,000 birds and mammals. To date, at least 40,000 plant species, 2,200 fishes, 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically classified in the region. One in five of all bird species are found in the Amazon rainforest, and one in five of the fish species live in Amazonian rivers and streams. Scientists have described between 96,660 and 128,843 invertebrate species in Brazil alone.\nThe biodiversity of plant species is the highest on Earth with one 2001 study finding a quarter square kilometer (62 acres) of Ecuadorian rainforest supports more than 1,100 tree species. A study in 1999 found one square kilometer (247 acres) of Amazon rainforest can contain about 90,790 tonnes of living plants. The average plant biomass is estimated at 356 ± 47 tonnes per hectare. To date, an estimated 438,000 species of plants of economic and social interest have been registered in the region with many more remaining to be discovered or catalogued. The total number of tree species in the region is estimated at 16,000.\nThe green leaf area of plants and trees in the rainforest varies by about 25% as a result of seasonal changes. Leaves expand during the dry season when sunlight is at a maximum, then undergo abscission in the cloudy wet season. These changes provide a balance of carbon between photosynthesis and respiration.\nEach hectare of the Amazon rainforest contains around 1 billion invertebrates. The number of species per hectare in the Amazon rainforest is presented in the following table:\n\nThe rainforest contains several species that can pose a hazard. Among the largest predatory creatures are the black caiman, jaguar, cougar, and anaconda. In the river, electric eels can produce an electric shock that can stun or kill, while piranha are known to bite and injure humans. Various species of poison dart frogs secrete lipophilic alkaloid toxins through their flesh. There are also numerous parasites and disease vectors. Vampire bats dwell in the rainforest and can spread the rabies virus. Malaria, yellow fever and dengue fever can also be contracted in the Amazon region.\nThe biodiversity in the Amazon is becoming increasingly threatened, primarily by habitat loss from deforestation as well as increased frequency of fires. Over 90% of Amazonian plant and vertebrate species (13,000–14,000 in total) may have been impacted to some degree by fires.\n\nThreats\n\nDeforestation\n\nDeforestation is the conversion of forested areas to non-forested areas. The main sources of deforestation in the Amazon are human settlement and the development of the land. In 2022, about 20% of the Amazon rainforest has already been deforested and a further 6% was \"highly degraded\". Research suggests that upon reaching about 20–25% (hence 0–5% more), the tipping point to flip it into a non-forest ecosystem – degraded savannah – (in eastern, southern and central Amazonia) will be reached. This process of savanisation would take decades to take full effect.\nPrior to the early 1960s, access to the forest's interior was highly restricted, and the forest remained basically intact. Farms established during the 1960s were based on crop cultivation and the slash and burn method. However, the colonists were unable to manage their fields and the crops because of the loss of soil fertility and weed invasion. The soils in the Amazon are productive for just a short period of time, so farmers are constantly moving to new areas and clearing more land. These farming practices led to deforestation and caused extensive environmental damage. Deforestation is considerable, and areas cleared of forest are visible to the naked eye from outer space.\nIn the 1970s, construction began on the Trans-Amazonian highway. This highway represented a major threat to the Amazon rainforest. The highway still has not been completed, limiting the environmental damage.\nBetween 1991 and 2000, the total area of forest lost in the Amazon rose from 415,000 to 587,000 km2 (160,000 to 227,000 sq mi), with most of the lost forest becoming pasture for cattle. Seventy percent of formerly forested land in the Amazon, and 91% of land deforested since 1970, have been used for livestock pasture. Currently, Brazil is the largest global producer of soybeans. New research however, conducted by Leydimere Oliveira et al., has shown that the more rainforest is logged in the Amazon, the less precipitation reaches the area and so the lower the yield per hectare becomes. So despite the popular perception, there has been no economical advantage for Brazil from logging rainforest zones and converting these to pastoral fields.\n\nThe needs of soy farmers have been used to justify many of the controversial transportation projects that are currently developing in the Amazon. The first two highways successfully opened up the rainforest and led to increased settlement and deforestation. The mean annual deforestation rate from 2000 to 2005 (22,392 km2 or 8,646 sq mi per year) was 18% higher than in the previous five years (19,018 km2 or 7,343 sq mi per year). Although deforestation declined significantly in the Brazilian Amazon between 2004 and 2014, there has been an increase to the present day.\n\nBrazil's President, Jair Bolsonaro, has supported the relaxation of regulations placed on agricultural land. He has used his time in office to allow for more deforestation and more exploitation of the Amazon's rich natural resources. Deforestation reached a 15 year high in 2021.\nSince the discovery of fossil fuel reservoirs in the Amazon rainforest, oil drilling activity has steadily increased, peaking in the Western Amazon in the 1970s and ushering another drilling boom in the 2000s. Oil companies have to set up their operations by opening new roads through the forests, which often contributes to deforestation in the region. 9.4% of the territory of the Amazon is affected by oil fields.\nMining is also a major driver of deforestation. 17% of the area of the Amazon Rainforest is affected by mining.\nThe transition to solar and wind energy, digitalization, raised the demand for cassiterite (the main ore of tin used also for financing gold mining), manganese and copper, which attracrted many illegal miners to the Amazon. This led to deforestation, different environmental and social problems. Hydropower also creates significant problems in the Amazon. Such activities are defined by the World Rainforest Movement as \"Green extractivism\".\nThe European Union–Mercosur free trade agreement, which would form one of the world's largest free trade areas, has been denounced by environmental activists and indigenous rights campaigners. The fear is that the deal could lead to more deforestation of the Amazon rainforest as it expands market access to Brazilian beef.\nAccording to a November 2021 report by Brazil's INPE, based on satellite data, deforestation has increased by 22% over 2020 and is at its highest level since 2006.\n\n2019 fires\n\nThere were 72,843 fires in Brazil in 2019, with more than half within the Amazon region. In August 2019 there were a record number of fires. Deforestation in the Brazilian Amazon rose more than 88% in June 2019 compared with the same month in 2018.\nThe increased area of fire-impacted forest coincided with a relaxation of environmental regulations from the Brazilian government. Notably, before those regulations were put in place in 2008 the fire-impacted area was also larger compared to the regulation period of 2009–2018. As these fire continue to move closer to the heart of the Amazon basin, their impact on biodiversity will only increase in scale, as the cumulative fire-impacted area is correlated with the number of species impacted.\n\nImpact of early 21st-century Amazon droughts\nIn 2005, parts of the Amazon basin experienced the worst drought in one hundred years, and there were indications that 2006 may have been a second successive year of drought. A 2006 article in the UK newspaper The Independent reported the Woods Hole Research Center results, showing that the forest in its present form could survive only three years of drought. Scientists at the Brazilian National Institute of Amazonian Research argued in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a \"tipping point\" where it would irreversibly start to die. It concluded that the forest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate. A study published in Nature Communications in October 2020 found that about 40% of the Amazon rainforest is at risk of becoming a savanna-like ecosystem due to reduced rainfall. A study published in Nature climate change provided direct empirical evidence that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale. Research from 2025 using hundreds of climate-model simulations says even passing 1.5C of global warming temporarily would trigger a significant risk of Amazon forest dieback.\n\nAccording to the World Wide Fund for Nature, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.In 2010, the Amazon rainforest experienced another severe drought, in some ways more extreme than the 2005 drought. The affected region was approximately 3,000,000 km2 (1,160,000 sq mi) of rainforest, compared with 1,900,000 km2 (734,000 sq mi) in 2005. The 2010 drought had three epicenters where vegetation died off, whereas in 2005, the drought was focused on the southwestern part. The findings were published in the journal Science. In a typical year, the Amazon absorbs 1.5 gigatons of carbon dioxide; during 2005 instead 5 gigatons were released and in 2010 8 gigatons were released. Additional severe droughts occurred in 2010, 2015, and 2016.\nIn 2019 Brazil's protections of the Amazon rainforest were slashed, resulting in a severe loss of trees. According to Brazil's National Institute for Space Research (INPE), deforestation in the Brazilian Amazon rose more than 50% in the first three months of 2020 compared to the same three-month period in 2019.\nIn 2020, a 17 percent rise was noted in the Amazon wildfires, marking the worst start to the fire season in a decade. The first 10 days of August 2020 witnessed 10,136 fires. An analysis of the government figures reflected 81 per cent increase in fires in federal reserves, in comparison with the same period in 2019. However, President Jair Bolsonaro turned down the existence of fires, calling it a \"lie\", despite the data produced by his own government. Satellites in September recorded 32,017 hotspots in the world's largest rainforest, a 61% rise from the same month in 2019. In addition, October saw a huge surge in the number of hotspots in the forest (more than 17,000 fires are burning in the Amazon's rainforest) – with more than double the amount detected in the same month last year.\n\nClimate change\nEnvironmentalists are concerned about loss of biodiversity that will result from destruction of the forest, and also about the release of the carbon contained within the vegetation, which could accelerate global warming. Amazonian evergreen forests account for about 10% of the world's terrestrial primary productivity and 10% of the carbon stores in ecosystems – of the order of 1.1 × 1011 metric tonnes of carbon. Amazonian forests are estimated to have accumulated 0.62 ± 0.37 tons of carbon per hectare per year between 1975 and 1996. In 2021 it was reported that the Amazon emitted more greenhouse gases than it absorbed for the first time. Though often referenced as producing more than a quarter of the Earth's oxygen, this often stated, but misused statistic actually refers to oxygen turnover. The net contribution of the ecosystem is approximately zero.\nDeforestation in the Amazon rainforest region has a negative impact on local climate. It was one of the main causes of the severe drought of 2014–2015 in Brazil. This is because the moisture from the forests is important to the rainfall in Brazil, Paraguay and Argentina. Half of the rainfall in the Amazon area is produced by the forests.\nA 2009 study found that a 4 °C rise (above pre-industrial levels) in global temperatures by 2100 would kill 85% of the Amazon rainforest while a temperature rise of 3 °C would kill some 75% of the Amazon.\nResults of a 2021 scientific synthesis indicate that, in terms of global warming, the Amazon basin with the Amazon rainforest is currently emitting more greenhouse gases than it absorbs overall. Climate change impacts and human activities in the area – mainly wildfires, current land-use and deforestation – are causing a release of forcing agents that likely result in a net warming effect.\n\nOne computer model of future climate change caused by greenhouse gas emissions shows that the Amazon rainforest could become unsustainable under conditions of severely reduced rainfall and increased temperatures, leading to an almost complete loss of rainforest cover in the basin by 2100., and severe economic, natural capital and ecosystem services impacts of not averting the tipping point. However, simulations of Amazon basin climate change across many different models are not consistent in their estimation of any rainfall response, ranging from weak increases to strong decreases. The result indicates that the rainforest could be threatened through the 21st century by climate change in addition to deforestation.\n\nConservation\n\nIn 1989, environmentalist C.M. Peters and two colleagues stated there is economic as well as biological incentive to protecting the rainforest. One hectare in the Peruvian Amazon has been calculated to have a value of $6820 if intact forest is sustainably harvested for fruits, latex, and timber; $1000 if clear-cut for commercial timber (not sustainably harvested); or $148 if used as cattle pasture.\n\n \nAs indigenous territories continue to be destroyed by deforestation and ecocide (such as in the Peruvian Amazon), indigenous peoples' rainforest communities continue to disappear, while others, like the Urarina continue to struggle to fight for their cultural survival and the fate of their forested territories. Meanwhile, the relationship between non-human primates in the subsistence and symbolism of indigenous lowland South American peoples has gained increased attention, as have ethno-biology and community-based conservation efforts.\nA 2020 study in the Brazilian Amazon shows that protection of freshwater biodiversity can be increased by up to 600% through integrated freshwater-terrestrial planning \n.\nFrom 2002 to 2006, the conserved land in the Amazon rainforest almost tripled and deforestation rates dropped up to 60%. About 1,000,000 km2 (250,000,000 acres) have been put onto some sort of conservation, which adds up to a current amount of 1,730,000 km2 (430,000,000 acres).\nIn April 2019, the Ecuadorian court stopped oil exploration activities in 180,000 hectares (440,000 acres) of the Amazon rainforest. In July 2019, the Ecuadorian court forbade the government to sell territory with forests to oil companies.\nIn September 2019, the US and Brazil agreed to promote private-sector development in the Amazon. They also pledged a $100m biodiversity conservation fund for the Amazon led by the private sector. Brazil's foreign minister stated that opening the rainforest to economic development was the only way to protect it.\n\nIn 2022 the supreme court of Ecuador decided that \"\"under no circumstances can a project be carried out that generates excessive sacrifices to the collective rights of communities and nature.\" It also required the government to respect the opinion of Indigenous peoples of the Americas about different industrial projects on their land. Advocates of the decision argue that it will have consequences far beyond Ecuador. In general, ecosystems are in better shape when indigenous peoples own or manage the land.Due to the conservation policies of Luiz Inácio Lula da Silva in the first 10 months of 2023 deforestation in the Brazilian Amazon decreased by around 50% compared to the same period in 2022. This was despite a severe drought, one of the worst on record, that exacerbated the situation. Climate change, El Nino, deforestation increases the likelihood of drought condition in the Amazon.\nAccording to Amazon Conservation's MAAP forest monitoring program, the deforestation rate in the Amazon from the January 1 to November 8, 2023, decreased by 56% in comparison to the same period in 2022. The main cause is the decline in deforestation rate in Brazil, due to the government's policies, while Columbia, Peru and Bolivia also reduced deforestation.\nIn January 2024 published data showed a 50% decline in deforestation rate in the Amazon rainforest and 43% rise in vegetation loss in the neighbor Cerrado during the year of 2023 in comparison to 2022. Both biomes together lose 12,980 km², 18% less than in 2022.\nConservation International Brazil is an implementing partner in large-scale conservation programmes in the Brazilian Amazon, including the Global Environment Facility (GEF)-financed Amazon Sustainable Landscapes Project and restoration actions funded through the Amazon Fund initiative Restaura Amazônia in Pará and Maranhão.\n\nRemote sensing\n\nThe use of remotely sensed data is dramatically improving conservationists' knowledge of the Amazon basin. Given the",
    "source": "wikipedia:Amazon rainforest",
    "domain": "climate"
  }
]