Hockey stick graph

Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records . These reconstructions have consistently shown a slow long term cooling trend changing into relatively rapid warming in the 20th century , with the instrumental temperature record by 2000 exceeding earlier temperatures .   The term `` hockey stick graph '' was coined by the climatologist Jerry Mahlman , to describe the pattern shown by the ( MBH99 ) reconstruction , envisaging a graph that is relatively flat with a downward trend to 1900 as forming an ice hockey stick 's `` shaft '' followed by a sharp , steady increase corresponding to the `` blade '' portion . The reconstructions have featured in Intergovernmental Panel on Climate Change ( IPCC ) reports as evidence of global warming . Arguments over the reconstructions have been taken up by fossil fuel industry funded lobbying groups attempting to cast doubt on climate science .   Paleoclimatology dates back to the 19th century , and the concept of examining varves in lake beds and tree rings to track local climatic changes was suggested in the 1930s . In the 1960s , Hubert Lamb generalised from historical documents and temperature records of central England to propose a Medieval Warm Period from around 900 to 1300 , followed by Little Ice Age . This was the basis of a `` schematic diagram '' featured in the IPCC First Assessment Report of 1990 beside cautions that the medieval warming might not have been global . The use of indicators to get quantitative estimates of the temperature record of past centuries was developed , and by the late 1990s a number of competing teams of climatologists found indications that recent warming was exceptional . introduced the `` Composite Plus Scaling '' ( CPS ) method used by most later large scale reconstructions . Their study was featured in the IPCC Second Assessment Report of 1995 .   In 1998 Michael E. Mann , Raymond S. Bradley and Malcolm K. Hughes developed new statistical techniques to produce ( MBH98 ) , the first eigenvector-based climate field reconstruction ( CFR ) . This showed global patterns of annual surface temperature , and included a graph of average hemispheric temperatures back to 1400 with shading emphasising that uncertainties ( to two standard error limits ) were much greater in earlier centuries . independently produced a CPS reconstruction extending back for a thousand years , and ( MBH99 ) used the MBH98 methodology to extend their study back to 1000 .   A version of the MBH99 graph was featured prominently in the 2001 IPCC Third Assessment Report ( TAR ) , which also drew on Jones et al. 1998 and three other reconstructions to support the conclusion that , in the Northern Hemisphere , the 1990s was likely to have been the warmest decade and 1998 the warmest year during the past 1,000 years . The graph became a focus of dispute for those opposed to the strengthening scientific consensus that late 20th century warmth was exceptional . In 2003 , as lobbying over the 1997 Kyoto Protocol intensified , a paper claiming greater medieval warmth was quickly dismissed by scientists in the Soon and Baliunas controversy . Later in 2003 , Stephen McIntyre and Ross McKitrick published disputing the data used in MBH98 paper . In 2004 Hans von Storch published criticism of the statistical techniques as tending to underplay variations in earlier parts of the graph , though this was disputed and he later accepted that the effect was very small . In 2005 McIntyre and McKitrick published criticisms of the principal components analysis methodology as used in MBH98 and MBH99 . Their analysis was subsequently disputed by published papers including and which pointed to errors in the McIntyre and McKitrick methodology . Political disputes led to the formation of a panel of scientists convened by the National Research Council , their North Report in 2006 supported Mann 's findings with some qualifications , including agreeing that there were some statistical failings but these had little effect on the result .   More than two dozen reconstructions , using various statistical methods and combinations of proxy records , support the broad consensus shown in the original 1998 hockey-stick graph , with variations in how flat the pre-20th century `` shaft '' appears . The 2007 IPCC Fourth Assessment Report cited 14 reconstructions , 10 of which covered 1,000 years or longer , to support its strengthened conclusion that it was likely that Northern Hemisphere temperatures during the 20th century were the highest in at least the past 1,300 years . Further reconstructions , including Mann et al. 2008 and , have supported these general conclusions .


Holarctic

The Holarctic is the name for the biogeographic realm that encompasses the majority of habitats found throughout the northern continents of the world , combining Wallace 's Palearctic zoogeographical region , consisting of North Africa and all of Eurasia ( with the exception of the southern Arabian Peninsula , Southeast Asia , and the Indian subcontinent ) , and the Nearctic zoogeographical region , consisting of North America , north of Mexico . These regions are further subdivided into a variety of ecoregions . Many ecosystems , and the animal and plant communities that depend on them , are found across multiple continents in large portions of this realm . The continuity of these ecosystems results from the shared glacial history of the realm . The floristic Boreal Kingdom corresponds to the Holarctic realm .


Holocene

The Holocene ( -LSB- pronˈhɒləˌsiːn , _ ˈhoʊ - -RSB- ) is the geological epoch that began after the Pleistocene at approximately 11,700 years before present . The term `` Recent '' ( usually capitalised ) has often been used as an exact synonym of `` Holocene '' , although this usage is discouraged in 21st-century science . The Holocene is part of the Quaternary period . Its name comes from the Ancient Greek words ὅλος ( holos , whole or entire ) and καινός ( kainos , new ) , meaning `` entirely recent '' . It has been identified with the current warm period , known as MIS 1 , and can be considered an interglacial in the current ice age based on that evidence .   The Holocene also encompasses the growth and impacts of the human species worldwide , including all its written history , development of major civilizations , and overall significant transition toward urban living in the present . Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species , including approximately synchronous lithospheric evidence , or more recently atmospheric evidence of human impacts . Given these , a new term , Anthropocene , is specifically proposed and used informally only for the very latest part of modern history involving significant human impact .


Holocene extinction

The Holocene extinction , otherwise referred to as the Sixth extinction or Anthropocene extinction , is the ongoing extinction event of species during the present Holocene epoch , mainly due to human activity . The large number of extinctions spans numerous families of plants and animals , including mammals , birds , amphibians , reptiles and arthropods . With widespread degradation of highly biodiverse habitats such as coral reefs and rainforest , as well as other areas , the vast majority of these extinctions is thought to be undocumented . According to the species-area theory , and based on upper-bound estimating , the present rate of extinction may be up to 140,000 species per year , making it the greatest loss of biodiversity since the Cretaceous -- Paleogene extinction event .   The Holocene extinction includes the disappearance of large land animals known as megafauna , starting at the end of the last Ice Age . Megafauna outside of the African continent , which did not evolve alongside humans , proved highly sensitive to the introduction of new predation , and many died out shortly after early humans began spreading and hunting across the Earth ( additionally , many African species have also gone extinct in the Holocene ) . These extinctions , occurring near the Pleistocene -- Holocene boundary , are sometimes referred to as the Quaternary extinction event .   The arrival of humans on different continents coincides with megafaunal extinction . The most popular theory is that human overhunting of species added to existing stress conditions . Although there is debate regarding how much human predation affected their decline , certain population declines have been directly correlated with human activity , such as the extinction events of New Zealand and Hawaii . Aside from humans , climate change may have been a driving factor in the megafaunal extinctions , especially at the end of the Quaternary .   The ecology of humanity has been noted as being that of an unprecedented `` global superpredator '' that regularly preys on the adults of other apex predators and has worldwide effects on food webs . Extinctions of species have occurred on every land mass and ocean , with many famous examples within Africa , Asia , Europe , Australia , North and South America , and on smaller islands . Overall , the Holocene extinction can be characterized by the human impact on the environment . The Holocene extinction continues into the 21st century , with meat consumption , overfishing , ocean acidification and the amphibian crisis being a few broader examples of an almost universal , cosmopolitan decline in biodiversity . A ballooning human population along with profligate consumption are considered to be the primary drivers of this rapid decline .


Holocene glacial retreat

Holocene glacial retreat had a profound effect on landscapes in many areas that were covered by ice at the Last Glacial Maximum .


Homeland security

Homeland security is an American umbrella term for `` the national effort to ensure a homeland that is safe , secure , and resilient against terrorism and other hazards where American interests , aspirations , and ways of life can thrive to the national effort to prevent terrorist attacks within the United States , reduce the vulnerability of the U.S. to terrorism , and minimize the damage from attacks that do occur . ''   Homeland security is not constrained to terrorist incidents . Terrorism is one of many threats that endanger society . Within the U.S. , an all-hazards approach exists regarding homeland security endeavors . In this sense , homeland security encompasses both natural disasters and man-made events . Thus , the domain of homeland security must accommodate a plethora of situations and scenarios , ranging from natural disasters ( e.g. , Hurricane Katrina ) to acts of terrorism ( e.g. , Boston Marathon bombing ) .   The term came about following enactment of the Homeland Security Act of 2002 and reorganization of many U.S. government civil agencies effective March 1 , 2003 , to form the United States Department of Homeland Security after the September 11 attacks , and may be used to refer to the actions of that department , the United States Senate Committee on Homeland Security and Governmental Affairs , or the United States House of Representatives Committee on Homeland Security .   Homeland defense ( HD ) is the military protection of U.S. territory , sovereignty , domestic population , and critical infrastructure against external threats and aggression .


Homelessness

Homelessness is the condition of people without a permanent dwelling , such as a house or apartment . People who are homeless are most often unable to acquire and maintain regular , safe , secure and adequate housing . The legal definition of homeless varies from country to country , or among different jurisdictions in the same country or region . The term homeless may also include people whose primary night-time residence is in a homeless shelter , a domestic violence shelter , long-term residence in a motel , a vehicle , squatting , cardboard boxes , a tent city , tarpaulins , shanty town structures made of discarded building materials or other ad hoc housing situations . According to the UK homelessness charity Crisis , a home is not just a physical space : it also provides roots , identity , security , a sense of belonging and a place of emotional wellbeing . American government homeless enumeration studies also include people who sleep in a public or private place not designed for use as a regular sleeping accommodation for human beings . There are a number of organizations who provide help for the homeless .   In 2005 , an estimated 100 million ( 1 in 65 ) people worldwide were homeless and as many as 1 billion people live as squatters , refugees or in temporary shelter , all lacking adequate housing . In Western countries , the large majority of homeless are men ( 75 -- 80 % ) , with single males particularly overrepresented .   Most countries provide a variety of services to assist homeless people . These services often provide food , shelter ( beds ) and clothing and may be organized and run by community organizations ( often with the help of volunteers ) or by government departments or agencies . These programs may be supported by the government , charities , churches and individual donors . Many cities also have street newspapers , which are publications designed to provide employment opportunity to homeless people . While some homeless have jobs , some must seek other methods to make a living . Begging or panhandling is one option , but is becoming increasingly illegal in many cities . People who are homeless may have additional conditions , such as physical or mental health issues or substance addiction ; these issues make resolving homelessness a challenging policy issue .


Hong Kong

Hong Kong , officially the Hong Kong Special Administrative Region of the People 's Republic of China , is an autonomous territory on the Pearl River Delta of China . Macau lies across the delta to the west , and the province of Guangdong borders the territory to the north . With a total land area of 1,106 km2 and a population of over 7.3 million of various nationalities , it ranks as the world 's fourth most densely populated sovereign state or territory .   After the First Opium War ( 1839 -- 42 ) , Hong Kong became a British colony with the perpetual cession of Hong Kong Island , followed by the Kowloon Peninsula in 1860 and a 99-year lease of the New Territories from 1898 . Hong Kong was later occupied by Japan during World War II until British control resumed in 1945 . In the early 1980s , negotiations between the United Kingdom and China resulted in the 1984 Sino-British Joint Declaration , which paved way for the transfer of sovereignty of Hong Kong in 1997 , when it became a special administrative region ( SAR ) of the Peoples Republic of China with a high degree of autonomy .   Under the principle of `` one country , two systems '' , Hong Kong maintains a separate political and economic system from China . Except in military defence and foreign affairs , Hong Kong maintains its independent executive , legislative and judiciary powers . In addition , Hong Kong develops relations directly with foreign states and international organisations in a broad range of `` appropriate fields '' .   Hong Kong is one of the world 's most significant financial centres , with the highest Financial Development Index score and consistently ranks as the world 's most competitive and freest economic entity . As the world 's 8th largest trading entity , its legal tender , the Hong Kong dollar , is the world 's 13th most traded currency . It 's also a member of the World Trade Organization ( WTO ) and the Asia-Pacific Economic Cooperation ( APEC ) . Hong Kong 's tertiary sector dominated economy is characterised by simple taxation with a competitive level of corporate tax and supported by its independent judiciary system . However , while Hong Kong has one of the highest per capita incomes in the world , it suffers from severe income inequality .   Hong Kong is renowned for its deep natural harbour , which enables ready access by international cargo ships , and its impressive skyline , with a very high density of skyscrapers ; the territory boasts the second largest number of high rises of any city in the world . It has a very high Human Development Index ranking and the world 's longest life expectancy . Over 90 % of the population makes use of well-developed public transportation . Seasonal air pollution with origins from neighbouring industrial areas of Mainland China , which adopts loose emissions standards , has resulted in a high level of atmospheric particulates .


Houston

Houston ( -LSB- ˈhjuːstən -RSB- ) is the most populous city in the state of Texas and the fourth-most populous city in the United States . With a census-estimated 2014 population of 2.239 million within an area of 667 sqmi , it is also the largest city in the southern United States and the seat of Harris County . Located in Southeast Texas near the Gulf of Mexico , it is the principal city of the Greater Houston metro area , which is the fifth-most populated MSA in the United States .   Houston was founded on August 28 , 1836 , near the banks of Buffalo Bayou ( now known as Allen 's Landing ) and incorporated as a city on June 5 , 1837 . The city was named after former General Sam Houston , who was president of the Republic of Texas and had commanded and won at the Battle of San Jacinto 25 mi east of where the city was established . The burgeoning port and railroad industry , combined with oil discovery in 1901 , has induced continual surges in the city 's population . In the mid-20th century , Houston became the home of the Texas Medical Center -- the world 's largest concentration of healthcare and research institutions -- and NASA 's Johnson Space Center , where the Mission Control Center is located .   Houston 's economy has a broad industrial base in energy , manufacturing , aeronautics , and transportation . Leading in health care sectors and building oilfield equipment , outside of New York City , Houston has more Fortune 500 headquarters than any other U.S. municipality within its city limits . The Port of Houston ranks first in the United States in international waterborne tonnage handled and second in total cargo tonnage handled . Nicknamed the `` Space City '' , Houston is a global city , with strengths in business , international trade , entertainment , culture , media , fashion , science , sports , technology , education , medicine , and research . The city has a population from various ethnic and religious backgrounds and a large and growing international community . Houston is the most diverse city in Texas and has been described as the most racially and ethnically diverse major metropolis in the U.S. . It is home to many cultural institutions and exhibits , which attract more than 7 million visitors a year to the Museum District . Houston has an active visual and performing arts scene in the Theater District and offers year-round resident companies in all major performing arts .


Huaynaputina

Huaynaputina ( -LSB- wainapuˈtina -RSB- , Pronounced : -LSB- waɪnəpʊˈtiːnə -RSB- ; from young volcano , meaning `` Young Volcano '' ) is a stratovolcano in a volcanic upland in southern Peru . The volcano does not have an identifiable mountain profile , but instead is a large volcanic crater . It has produced high-potassium andesite and dacite . On 19 February 1600 , it exploded catastrophically ( Volcanic Explosivity Index -LSB- VEI -RSB- 6 ) , in the largest volcanic explosion in South America in historic times . The eruption continued with a series of events into March . An account of the event was included in Fray Antonio Vázquez de Espinosa 's Compendio y Descripción de las Indias , which was translated into English as Compendium and description of the West Indies in 1942 .


Hubble Space Telescope

The Hubble Space Telescope ( HST ) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation . Although not the first space telescope , Hubble is one of the largest and most versatile , and is well known as both a vital research tool and a public relations boon for astronomy . The HST is named after the astronomer Edwin Hubble , and is one of NASA 's Great Observatories , along with the Compton Gamma Ray Observatory , the Chandra X-ray Observatory , and the Spitzer Space Telescope .   With a 2.4 m mirror , Hubble 's four main instruments observe in the near ultraviolet , visible , and near infrared spectra . Hubble 's orbit outside the distortion of Earth 's atmosphere allows it to take extremely high-resolution images , with substantially lower background light than ground-based telescopes . Hubble has recorded some of the most detailed visible light images ever , allowing a deep view into space and time . Many Hubble observations have led to breakthroughs in astrophysics , such as accurately determining the rate of expansion of the universe .   The HST was built by the United States space agency NASA , with contributions from the European Space Agency . The Space Telescope Science Institute ( STScI ) selects Hubble 's targets and processes the resulting data , while the Goddard Space Flight Center controls the spacecraft .   Space telescopes were proposed as early as 1923 . Hubble was funded in the 1970s , with a proposed launch in 1983 , but the project was beset by technical delays , budget problems , and the Challenger disaster ( 1986 ) . When finally launched in 1990 , Hubble 's main mirror was found to have been ground incorrectly , compromising the telescope 's capabilities . The optics were corrected to their intended quality by a servicing mission in 1993 .   Hubble is the only telescope designed to be serviced in space by astronauts . After launch by in 1990 , five subsequent Space Shuttle missions repaired , upgraded , and replaced systems on the telescope , including all five of the main instruments . The fifth mission was canceled on safety grounds following the Columbia disaster ( 2003 ) . However , after spirited public discussion , NASA administrator Mike Griffin approved the fifth servicing mission , completed in 2009 . The telescope is operating , and could last until 2030 -- 2040 . Its scientific successor , the James Webb Space Telescope ( JWST ) , is scheduled for launch in 2018 .


Human

Modern humans ( Homo sapiens , primarily ssp . Homo sapiens sapiens ) are the only extant members of Hominina tribe ( or human tribe ) , a branch of the tribe Hominini belonging to the family of great apes . They are characterized by erect posture and bipedal locomotion ; high manual dexterity and heavy tool use compared to other animals ; and a general trend toward larger , more complex brains and societies .   Early hominins -- particularly the australopithecines , whose brains and anatomy are in many ways more similar to ancestral non-human apes -- are less often referred to as `` human '' than hominins of the genus Homo . Several of these hominins used fire , occupied much of Eurasia , and gave rise to anatomically modern Homo sapiens in Africa about 200,000 years ago . They began to exhibit evidence of behavioral modernity around 50,000 years ago . In several waves of migration , anatomically modern humans ventured out of Africa and populated most of the world .   The spread of humans and their large and increasing population has had a profound impact on large areas of the environment and millions of native species worldwide . Advantages that explain this evolutionary success include a relatively larger brain with a particularly well-developed neocortex , prefrontal cortex and temporal lobes , which enable high levels of abstract reasoning , language , problem solving , sociality , and culture through social learning . Humans use tools to a much higher degree than any other animal , are the only extant species known to build fires and cook their food , and are the only extant species to clothe themselves and create and use numerous other technologies and arts .   Humans are uniquely adept at utilizing systems of symbolic communication ( such as language and art ) for self-expression and the exchange of ideas , and for organizing themselves into purposeful groups . Humans create complex social structures composed of many cooperating and competing groups , from families and kinship networks to political states . Social interactions between humans have established an extremely wide variety of values , social norms , and rituals , which together form the basis of human society . Curiosity and the human desire to understand and influence the environment and to explain and manipulate phenomena ( or events ) has provided the foundation for developing science , philosophy , mythology , religion , anthropology , and numerous other fields of knowledge .   Though most of human existence has been sustained by hunting and gathering in band societies , increasing numbers of human societies began to practice sedentary agriculture approximately some 10,000 years ago , domesticating plants and animals , thus allowing for the growth of civilization . These human societies subsequently expanded in size , establishing various forms of government , religion , and culture around the world , unifying people within regions to form states and empires . The rapid advancement of scientific and medical understanding in the 19th and 20th centuries led to the development of fuel-driven technologies and increased lifespans , causing the human population to rise exponentially . Today the global human population is estimated by the United Nations to be near billion .


Human extinction

In futures studies , human extinction is the hypothetical end of the human species . This may be caused by natural causes or it may be anthropogenic , i.e. the result of human action .   The likelihood of human extinction in the near future by wholly natural scenarios , such as a meteorite impact or large-scale volcanism , is generally considered to be extremely low .   For anthropogenic extinction , many possible scenarios have been proposed : Human global nuclear annihilation , biological warfare or the release of a pandemic-causing agent , dysgenics , overpopulation , ecological collapse , and global warming ; in addition , emerging technologies could bring about new extinction scenarios , such as advanced artificial intelligence , biotechnology or self-replicating nanobots . The probability of anthropogenic human extinction within the next hundred years is the topic of an active debate .   Human extinction needs to be differentiated from the extinction of all life on Earth ( see also future of Earth ) and from the extinction of major components of human culture ( e.g. , through a global catastrophe leaving only small , scattered human populations , which might evolve in isolation ) .


Human impact on marine life

Human activities affect marine life and marine habitats through overfishing, habitat loss, the introduction of invasive species, ocean pollution, ocean acidification and ocean warming. These impact marine ecosystems and food webs and may result in consequences as yet unrecognised for the biodiversity and continuation of marine life forms.According to the IPCC (2019), since 1950 "many marine species across various groups have undergone shifts in geographical range and seasonal activities in response to ocean warming, sea ice change and biogeochemical changes, such as oxygen loss, to their habitats."It has been estimated only 13% of the ocean area remains as wilderness, mostly in open ocean areas rather than along the coast.


Human impact on the environment

Human impact on the environment or anthropogenic impact on the environment includes impacts on biophysical environments , biodiversity , and other resources . The term anthropogenic designates an effect or object resulting from human activity . The term was first used in the technical sense by Russian geologist Alexey Pavlov , and was first used in English by British ecologist Arthur Tansley in reference to human influences on climax plant communities . The atmospheric scientist Paul Crutzen introduced the term `` Anthropocene '' in the mid-1970s . The term is sometimes used in the context of pollution emissions that are produced as a result of human activities but applies broadly to all major human impacts on the environment .


Human nutrition

Human nutrition refers to the provision of essential nutrients necessary to support human life and health . Generally , people can survive up to 40 days without food , a period largely depending on the amount of water consumed , stored body fat , muscle mass and genetic factors .   Poor nutrition is a chronic problem often linked to poverty , poor nutrition understanding and practices , and deficient sanitation and food security . Malnutrition and its consequences are immense contributors to deaths and disabilities worldwide . Promoting good nutrition helps children grow , promotes human development and eradication of poverty .


Human overpopulation

Human overpopulation occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group . Overpopulation can further be viewed , in a long term perspective , as existing when a population can not be maintained given the rapid depletion of non-renewable resources or given the degradation of the capacity of the environment to give support to the population .   The term human overpopulation refers to the relationship between the entire human population and its environment : the Earth , or to smaller geographical areas such as countries . Overpopulation can result from an increase in births , a decline in mortality rates , an increase in immigration , or an unsustainable biome and depletion of resources . It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life ( e.g. a desert ) . Advocates of population moderation cite issues like quality of life , carrying capacity , and risk of starvation as a basis to argue against continuing high human population growth and for population decline . Scientists suggest that the human impact on the environment as a result of overpopulation , profligate consumption and proliferation of technology has pushed the planet into a new geological epoch known as the Anthropocene .


Human population planning

Human population planning is the practice of intentionally managing the rate of growth of a human population . Historically human population planning has been implemented with the goal of increasing the rate of human population growth . However , in the period from the 1950s to the 1980s , concerns about global population growth and its effects on poverty , environmental degradation and political stability led to efforts to reduce human population growth rates . More recently , some countries , such as Iran and Spain , have begun efforts to increase their birth rates once again .   While population planning can involve measures that improve people 's lives by giving them greater control of their reproduction , a few programs , most notably the Chinese government 's `` one-child policy '' , have resorted to coercive measures .


Humboldt Current

The Humboldt Current System ( HCS ) , also called the Peru Current , is a major Eastern Boundary Upwelling Ecosystem that flows north along the western coast of South America . It is an eastern boundary current flowing in the direction of the equator , and extend 500-1 ,000 kilometers offshore . The Humboldt Current is named after the Prussian naturalist Alexander von Humboldt . In 1846 , von Humboldt reported measurements of the cold-water current in his book Cosmos .   The current extends from the southern Chile ( ~ 45 'S ) to northern Peru ( ~ 4 'S ) where cold , upwelled waters intersect warm tropical waters to form the Equatorial Front . Sea surface temperatures off the coast of Peru , around 5 'S , reach temperatures as low as 16 ' C . This is highly uncharacteristic of tropical waters , as most other regions have temperatures measuring above 25 ' C. Upwelling brings nutrients to the surface , which support phytoplankton and ultimately increase biological productivity .   Upwelling within the current is not uniform across the entire system . Three notable upwelling subsystems are produced by this current : i ) seasonal upwelling in Chile , ii ) upwelling `` shadow '' that is less productive , but still large in northern Chile and Southern Peru , and iii ) year-round upwelling in Peru .   The Humboldt Current is considered a Class I , highly productive ( > 300 gC/m2-yr ) , ecosystem . It is the most productive eastern boundary current system . It accounts for roughly 18-20 % of the total worldwide marine fish catch . The species are mostly pelagic : sardines , anchovies and jack mackerel . The system 's high productivity supports other important fishery resources as well as marine mammals ( eared seals and cetaceans ) and seabirds . The cold , nutrient-rich water brought to the surface by upwelling drives the system 's extraordinary productivity.Periodically , the upwelling that drives the system 's productivity is disrupted by the El Niño-Southern Oscillation ( ENSO ) event . When this occurs , fish abundance and distribution are significantly affected , often leading to stock crashes and cascading social and economic impacts . These events have led to sequential changes , where sardines and anchovies have replaced each other periodically as the dominant species in the ecosystem . These species changes can have negative consequences for the fishing industry and the economies of the countries that fish the system .   The Humboldt has a considerable cooling influence on the climate of Chile , Peru and Ecuador . It is also largely responsible for the aridity of Atacama Desert in northern Chile and coastal areas of Peru and also of the aridity of southern Ecuador . Marine air is cooled by the current and thus is not conducive to generating precipitation ( although clouds and fog are produced ) .


Humid subtropical climate

A humid subtropical climate is a zone of climate characterised by hot and humid summers where tropical air masses dominate , and mild winters . These climates normally lie on the southeast side of all continents , generally between latitudes 25 ° and 40 ° and are adjacent to tropical climates to the south . While many subtropical climates tend to be located at coastal or near coastal locations . in some cases they extend inland , most notably in southern China and the southern United States .   Under the Köppen climate classification , Cfa and Cwa climates are described as mild temperate climates . This climate features mean temperatures in the coldest month between 0 ° C and 18 ° C and mean temperatures in the warmest month 22 ° C or higher . The Trewartha system was a 1966 update of the Köppen climate classification , and sought to redefine middle latitude climates into smaller zones ( the original Köppen system grouped all middle latitude climates into a single zone ) . Under the Trewartha climate classification , climates are termed humid subtropical when they have monthly mean air temperatures higher than 10 ° C ( 50 ° F ) for eight or more months a year and at least one month with mean temperature below 18 ° C ( 64.4 ° F ) . Normally , humid subtropical climates occupy the southernmost portions of the temperate zone from 23.5 to 35.0 north and south latitude .   Rainfall often shows a summer peak , especially where monsoons are well developed , as in Southeast Asia and Florida ( USA ) . Other areas have a more uniform or varying rainfall cycles . Most summer rainfall occurs during thunderstorms that build up due to the intense surface heating and strong subtropical sun angle . Weak tropical lows that move in from adjacent warm tropical oceans , as well as infrequent tropical storms often contribute to high sun ( summer ) seasonal rainfall peaks . Winter rainfall is often associated with large storms in the westerlies that have fronts that reach down into subtropical latitudes . However , many subtropical climates such as southeast Asia or Florida have very dry winters , with frequent brush fires and water shortages .


Humidity

Humidity is the amount of water vapor present in the air . Water vapor is the gaseous state of water and is invisible to the human eye . Humidity indicates the likelihood of precipitation , dew , or fog . Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin . This effect is calculated in a heat index table or humidex . The amount of water vapor that is needed to achieve saturation increases as the temperature increases . As the temperature of a parcel of water becomes lower it will eventually reach the point of saturation without adding or losing water mass . The differences in the amount of water vapor in a parcel of air can be quite large . For example , a parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 ° C , but only 8 grams of water per cubic meter of air at 8 ° C.   There are three main measurements of humidity : absolute , relative and specific . Absolute humidity is the water content of air expressed in gram per cubic meter . Relative humidity , expressed as a percent , measures the current absolute humidity relative to the maximum ( highest point ) for that temperature . Specific humidity is the ratio of the mass of water vapor to the total mass of the moist air parcel .


Hurricane Agnes

Hurricane Agnes was , at the time , the costliest hurricane to hit the United States in recorded history . The second tropical cyclone and first named storm of the 1972 Atlantic hurricane season , Agnes developed on June 14 from the interaction of a polar front and an upper trough over the Yucatán Peninsula . Initially forming as a tropical depression , the storm headed slowly eastward and emerged into the western Caribbean Sea on June 15 . Once in the Caribbean , the depression began to strengthen , and by the following day , it became Tropical Storm Agnes . Thereafter , Agnes slowly curved northward and passed just west of Cuba on June 17 . Early on June 18 , the storm intensified enough to be upgraded to Hurricane Agnes . Heading northward , the hurricane eventually made landfall near Panama City , Florida late on June 19 . After moving inland , Agnes rapidly weakened and was only a tropical depression when it entered Georgia . The weakening trend halted as the storm crossed over Georgia and into South Carolina . While over eastern North Carolina , Agnes re-strengthened into a tropical storm on June 21 , as a result of baroclinic activity . Early the following day , the storm emerged into the Atlantic Ocean before re-curving northwestward and making landfall near New York City as a strong tropical storm . Agnes quickly became an extratropical cyclone on June 23 , and tracked to the northwest of Great Britain before becoming absorbed by another cyclone on July 6 .   Though it moved slowly across the Yucatán Peninsula , damage in Mexico is unknown . Although the storm bypassed the tip of Cuba , heavy rainfall occurred , killing seven people . In Florida , Agnes caused a significant tornado outbreak , with at least 26 confirmed twisters , two of which were spawned in Georgia . The tornadoes and two initially unconfirmed tornadoes in Florida alone resulted in over $ 4.5 million ( 1972 USD ) in damage and six fatalities . At least 2,082 structures in Florida suffered either major damage or were destroyed . About 1,355 other dwellings experienced minor losses . Though Agnes made landfall as a hurricane , no hurricane-force winds were reported . Along the coast abnormally high tides resulted in extensive damage , especially between Apalachicola and Cedar Key . Light to moderate rainfall was reported in Florida , though no significant flooding occurred . In Georgia , damage was limited to two tornadoes , which caused approximately $ 275,000 in losses . Minimal effects were also recorded in Alabama , Connecticut , Delaware , Rhode Island , South Carolina , and Tennessee ; though one fatality was reported in Delaware . The most significant effects , by far , occurred in Pennsylvania , mostly due to intense flooding . The hurricane severely flooded the Susquehanna River and the Lackawanna River causing major damage to the Scranton/Wilkes-Barre metropolitan area . In both Pennsylvania and New Jersey combined , about 43,594 structures were either destroyed or significantly damaged . In Canada , a mobile home was toppled , killing two people . Overall , Agnes caused 128 fatalities and nearly $ 3 billion in damage , though more recently , it is estimated that there were $ 2.1 billion in losses associated with the storm . Due to the significant effects , the name Agnes was retired in the spring of 1973 .


Hurricane Andrew

Hurricane Andrew was , at the time of its occurrence in August 1992 , the most destructive hurricane in United States history . It caused major damage in the Bahamas and Louisiana , but the greatest impact was in South Florida , where it made landfall at Category 5 hurricane intensity on the Saffir -- Simpson hurricane scale , with wind speeds up to 165 mph ( 270 km/h ) . Passing directly through the town of Homestead , Florida , a city south of Miami , Andrew obliterated entire blocks of homes , in many cases leaving only the concrete foundations . Over 25,500 houses were destroyed in Miami-Dade County alone , and nearly 100,000 more were severely damaged . A total of 65 people were killed and damage across the affected regions exceeded $ 26.5 billion ( 1992 USD ) .   Andrew originated from a tropical wave on August 16 over the central Atlantic , becoming the fourth tropical cyclone and the first hurricane of the season . Initially , strong wind shear prevented much intensification , but after turning westward , Andrew entered a stage of rapid intensification , peaking as a powerful Category 5 hurricane near the Bahamas on August 23 . Though it briefly weakened to Category 4 strength while traversing the island nation , Andrew regained its Category 5 status before making two separate landfalls in South Florida -- the first on Elliott Key and the second in Homestead . A barometric pressure of 922 mbar ( 27.23 inHg ) in the latter made Andrew the fourth most intense hurricane to strike the United States . Several hours later , the hurricane emerged over the Gulf of Mexico at Category 4 strength , with the Gulf Coast of the United States in its projected path . After weakening slightly , Andrew moved ashore near Morgan City , Louisiana , as low-end Category 3 storm . The effects of land caused the small hurricane to rapidly lose its intensity , and it diminished to a depression by August 27 while crossing Mississippi . The next day , Andrew merged with a frontal system over the southern Appalachian Mountains .   In the Bahamas , Andrew brought storm surge , hurricane-force winds , and tornadoes , causing widespread structural damage , especially on Cat Cays . About 800 houses were destroyed in the archipelago , and there was substantial damage to the transport , water , sanitation , agriculture , and fishing sectors . Overall , Andrew left four dead and $ 250 million in damage throughout the Bahamas . In parts of southern Florida , Andrew produced severe winds ; a wind gust of 177 mph ( 282 km/h ) was observed at a house in Perrine . These winds wreaked catastrophic damage in Florida -- Miami-Dade County cities of Florida City , Homestead , and Cutler Ridge receiving the brunt of the storm . A total of 63,000 homes were destroyed and more than 101,000 others were damaged throughout Florida , leaving roughly 175,000 people homeless . As many as 1.4 million people lost power at the height of the storm . In the Everglades , 70,000 acres ( 280 km2 ) of trees were downed . Rainfall in Florida was substantial , peaking at 13.98 in ( 355 mm ) in western Miami-Dade County . Altogether , Andrew killed 44 and left a record $ 25 billion in damage in the state .   Before moving ashore , Andrew caused extensive damage to oil platforms in the Gulf of Mexico , leading to $ 500 million in losses for oil companies . It produced hurricane-force winds along its path through Louisiana , leaving about 152,000 without electricity . Over 80 % of trees in the Atchafalaya River Basin were downed , and the agriculture there was devastated . Throughout the basin and Bayou Lafourche , 187 million freshwater fish were killed in the hurricane . An F3 tornado in St. John the Baptist Parish wrecked 163 structures . With 23,000 houses damaged , 985 others destroyed , and 1,951 mobile homes demolished , property losses in Louisiana exceeded $ 1.5 billion . The hurricane caused the deaths of 17 people in the state , six of whom drowned offshore . Andrew spawned at least 28 tornadoes along the Gulf Coast , especially in Alabama , Georgia , and Mississippi . Throughout its path , Andrew left 65 dead and $ 26.5 billion in damage ; it is currently the fifth costliest hurricane in Atlantic hurricane history , behind only hurricanes Katrina , Sandy , Ike , and Wilma , and the fourth costliest hurricane in the United States , behind Katrina , Sandy , and Ike .


Hurricane Donna

Hurricane Donna was the strongest hurricane of the 1960 Atlantic hurricane season , and caused severe damage to the Lesser Antilles , the Greater Antilles , and the East Coast of the United States , especially Florida , in August -- September . The fifth tropical cyclone , third hurricane , and first major hurricane of the season , Donna developed south of Cape Verde on August 29 , spawned by a tropical wave to which 63 deaths from a plane crash in Senegal were attributed . The depression strengthened into Tropical Storm Donna by the following day . Donna moved west-northwestward at roughly 20 mph and by September 1 , it reached hurricane status . Donna deepened significantly and reached its peak intensity early on September 4 , with maximum sustained winds of 145 mph ( 230 km/h ) . Thereafter , it weakened slightly as it brushed the Lesser Antilles later that day . On Sint Maarten , the storm left a quarter of the island homeless and killed seven people . An additional five deaths were reported in Anguilla and there were seven other fatalities throughout the Virgin Islands . In Puerto Rico , severe flash flooding led to 107 fatalities , 85 of them in Humacao alone . Donna further weakened to a Category 3 hurricane late on September 5 , but eventually became a Category 4 hurricane again . While passing through The Bahamas , several small island communities in the central regions of the country were leveled , but no damage total or fatalities were reported .   Early on September 10 , Donna made landfall near Marathon , Florida with winds of 130 mph ( 215 km/h ) , hours before another landfall south of Naples at the same intensity . Florida bore the brunt of Hurricane Donna . In the Florida Keys , coastal flooding severely damaged 75 % of buildings , destroyed several subdivisions in Marathon . On the mainland , 5,200 houses were impacted , which does not include the 75 % of homes damaged at Fort Myers Beach ; 50 % of buildings were also destroyed in the city of Everglades . Crop losses were also extensive . A total of 50 % of grapefruit crop was lost , 10 % of the orange and tangerine crop was lost , and the avocado crop was almost destroyed . In the state of Florida alone , there were 13 deaths and $ 300 million in losses . Donna weakened over Florida and was a Category 2 hurricane when it re-emerged into the Atlantic from North Florida . By early on September 12 , the storm made landfall near Topsail Beach , North Carolina as a strong Category 2 hurricane . Donna brought tornadoes and wind gusts up to 100 mph ( 155 km/h ) , damaging or destroying several buildings in Eastern North Carolina , while crops were impacted as far as 50 mi inland . Additionally , storm surge caused significant beach erosion and structural damage at Wilmington and Nags Head . Eight people were killed and there were over 100 injuries . Later on September 12 , Donna reemerged into the Atlantic Ocean and continued to move northeastward . The storm struck Long Island , New York late on September 12 and rapidly weakened inland . On the following day , Donna became extratropical over Maine .


Hurricane Floyd

Hurricane Floyd was a very powerful Cape Verde-type hurricane which struck the east coast of the United States . It was the sixth named storm , fourth hurricane , and third major hurricane in the 1999 Atlantic hurricane season . Floyd triggered the third largest evacuation in US history ( behind Hurricane Gustav and Hurricane Rita ) when 2.6 million coastal residents of five states were ordered from their homes as it approached . The Cape Verde-type hurricane formed off the coast of Africa and lasted from September 7 to September 19 , peaking in strength as a very strong Category 4 hurricane -- just 2 mph short of the highest possible rating on the Saffir -- Simpson Hurricane Scale . It was among the largest Atlantic hurricanes of its strength ever recorded .   Floyd was once forecast to strike Florida , but turned away . Instead , Floyd struck The Bahamas at peak strength , causing heavy damage . It then paralleled the East Coast of the United States , causing massive evacuations and costly preparations from Florida through the Mid-Atlantic states . The storm weakened significantly , however , before striking the Cape Fear region , North Carolina as a very strong Category 2 hurricane , and caused further damage as it traveled up the Mid-Atlantic region and into New England .   The hurricane produced torrential rainfall in Eastern North Carolina , adding more rain to an area hit by Hurricane Dennis just weeks earlier . The rains caused widespread flooding over a period of several weeks ; nearly every river basin in the eastern part of the state exceeded 500-year flood levels . In total , Floyd was responsible for 57 fatalities and $ 6.9 billion ( 1999 USD ; $ USD ) in damage . Due to the destruction , the World Meteorological Organization retired the name Floyd .


Hurricane Gustav

Hurricane Gustav ( -LSB- ˈɡʊstɑːv -RSB- ) was the second most destructive hurricane of the 2008 Atlantic hurricane season . The seventh tropical cyclone , third hurricane , and second major hurricane of the season , Gustav caused serious damage and casualties in Haiti , the Dominican Republic , Jamaica , the Cayman Islands , Cuba and the United States . Gustav caused at least $ 6.6 billion ( 2008 USD ) in damages .   It formed on the morning of August 25 , 2008 , about 260 mi southeast of Port-au-Prince , Haiti , and rapidly strengthened into a tropical storm that afternoon and into a hurricane early on August 26 . Later that day it made landfall near the Haitian town of Jacmel . It inundated Jamaica and ravaged Western Cuba and then steadily moved across the Gulf of Mexico .   Once into the Gulf , Gustav gradually weakened because of increased wind shear and dry air . It weakened to a Category 2 hurricane late on August 31 , and remained at that intensity until landfall on the morning of September 1 near Cocodrie , Louisiana . Weakening continued , and Gustav weakened to a tropical storm that evening and to a tropical depression the next day as it meandered around the south-central US . The weak system became extratropical on September 4 and was absorbed by another low on September 5 .   In total , an estimated 153 deaths had been attributed to Gustav in the U.S. and Caribbean . Damage in the U.S. totaled to $ 4.3 billion ( 2008 USD ) with additional damage of $ 2.1 billion in Cuba and $ 210 million in damage in Jamaica .


Hurricane Harvey

The name Harvey has been used for five tropical cyclones in the Atlantic Ocean .  Hurricane Harvey ( 1981 ) - threatened Bermuda but turned away before striking , no damage .  Hurricane Harvey ( 1993 ) - short-lived storm that threatened no land .  Tropical Storm Harvey ( 1999 ) - struck Florida , causing $ 15 million in damage .  Tropical Storm Harvey ( 2005 ) - earliest eighth-storm formation in the Atlantic Ocean since record-keeping began , breaking the old record set in 1936 by 12 days . Threatened Bermuda .  Tropical Storm Harvey ( 2011 ) - record eighth-storm failing to reach hurricane strength , in a single season , since reliable records began . Strong tropical storm that affected parts of Central America .   Category : Atlantic hurricane disambiguation pages


Hurricane Irma

Hurricane Irma was an extremely powerful Cape Verde hurricane that caused widespread destruction across its path in September 2017. Irma was the first Category 5 hurricane to strike the Leeward Islands on record, followed by Maria two weeks later. At the time, it was considered as the most powerful hurricane on record in the open Atlantic region, outside of the Caribbean Sea and Gulf of Mexico until it was surpassed by Hurricane Dorian two years later. It was also the third strongest Atlantic hurricane at landfall ever recorded, just behind the 1935 Labor Day Hurricane and Hurricane Dorian. The ninth named storm, fourth hurricane, second major hurricane, and first Category 5 hurricane of the 2017 season, Irma caused widespread and catastrophic damage throughout its long lifetime, particularly in the northeastern Caribbean and the Florida Keys. It was also the most intense hurricane to strike the continental United States since Katrina in 2005, the first major hurricane to make landfall in Florida since Wilma in the same year, and the first Category 4 hurricane to strike the state since Charley in 2004. The word Irmageddon was coined soon after the hurricane to describe the damage caused by the hurricane.


Hurricane Katrina

Hurricane Katrina was the costliest natural disaster and one of the five deadliest hurricanes in the history of the United States . The storm is currently ranked as the third most intense United States landfalling tropical cyclone , behind only the 1935 Labor Day hurricane and Hurricane Camille in 1969 . Overall , at least 1,245 people died in the hurricane and subsequent floods , making it the deadliest United States hurricane since the 1928 Okeechobee hurricane . Total property damage was estimated at $ 108 billion ( 2005 USD ) , roughly four times the damage wrought by Hurricane Andrew in 1992 in the United States .   The eleventh named storm and fifth hurricane of the 2005 Atlantic hurricane season , Katrina originated over the Bahamas on August 23 from the interaction between a tropical wave and the remnants of Tropical Depression Ten . Early the following day , the new depression intensified into Tropical Storm Katrina . The cyclone headed generally westward toward Florida and strengthened into a hurricane only two hours before making landfall at Hallandale Beach and Aventura on August 25 . After very briefly weakening to a tropical storm , Katrina emerged into the Gulf of Mexico on August 26 and began to rapidly deepen . The storm strengthened to a Category 5 hurricane over the warm waters of the Gulf of Mexico , but weakened before making its second landfall as a Category 3 hurricane on August 29 in southeast Louisiana .   The storm caused severe destruction along the Gulf coast from central Florida to Texas , much of it due to the storm surge and levee failure . Severe property damage occurred in coastal areas , such as Mississippi beachfront towns ; over 90 percent of these were flooded . Boats and casino barges rammed buildings , pushing cars and houses inland ; water reached 6 - from the beach .   Over fifty breaches in New Orleans 's hurricane surge protection were the cause of the majority of the death and destruction during Katrina on August 29 , 2005 . Eventually 80 % of the city and large tracts of neighboring parishes became flooded , and the floodwaters lingered for weeks . According to a modeling exercise conducted by the U.S. Army Corps of Engineers ( USACE ) , two-thirds of the deaths in Greater New Orleans were due to levee and floodwall failure . All of the major studies concluded that the USACE , the designers and builders of the levee system as mandated by the Flood Control Act of 1965 , is responsible . This is mainly due to a decision to use shorter steel sheet pilings in an effort to save money . In January 2008 , Judge Stanwood Duval , U.S. District Court , ruled that despite the Corps ' role in the flooding , the agency could not be held financially liable because of sovereign immunity in the Flood Control Act of 1928 . Exactly ten years after Katrina , J. David Rogers , lead author of a new report in the official journal of the World Water Council concluded that the flooding during Katrina `` could have been prevented had the corps retained an external review board to double-check its flood-wall designs . ''   There was also an investigation of the responses from federal , state and local governments , resulting in the resignation of Federal Emergency Management Agency ( FEMA ) director Michael D. Brown , and of New Orleans Police Department ( NOPD ) Superintendent Eddie Compass . Many other government officials were criticized for their responses , especially New Orleans Mayor Ray Nagin , Louisiana Governor Kathleen Blanco , and President George W. Bush . Several agencies including the United States Coast Guard ( USCG ) , National Hurricane Center ( NHC ) , and National Weather Service ( NWS ) were commended for their actions . They provided accurate hurricane weather tracking forecasts with sufficient lead time .


Hurricane Sandy

Hurricane Sandy ( unofficially referred to as `` Superstorm Sandy '' ) was the deadliest and most destructive hurricane of the 2012 Atlantic hurricane season , and the second-costliest hurricane in United States history . Classified as the eighteenth named storm , tenth hurricane and second major hurricane of the year , Sandy was a Category 3 storm at its peak intensity when it made landfall in Cuba . While it was a Category 2 storm off the coast of the Northeastern United States , the storm became the largest Atlantic hurricane on record ( as measured by diameter , with winds spanning 1100 mi ) . Estimates as of 2015 assessed damage to have been about $ 75 billion ( 2012 USD ) , a total surpassed only by Hurricane Katrina . At least 233 people were killed along the path of the storm in eight countries .   Sandy developed from a tropical wave in the western Caribbean Sea on October 22 , quickly strengthened , and was upgraded to Tropical Storm Sandy six hours later . Sandy moved slowly northward toward the Greater Antilles and gradually intensified . On October 24 , Sandy became a hurricane , made landfall near Kingston , Jamaica , re-emerged a few hours later into the Caribbean Sea and strengthened into a Category 2 hurricane . On October 25 , Sandy hit Cuba as a Category 3 hurricane , then weakened to a Category 1 hurricane . Early on October 26 , Sandy moved through the Bahamas . On October 27 , Sandy briefly weakened to a tropical storm and then restrengthened to a Category 1 hurricane . Early on October 29 , Sandy curved west-northwest ( the `` left turn '' or `` left hook '' ) and then moved ashore near Brigantine , New Jersey , just to the northeast of Atlantic City , as a post-tropical cyclone with hurricane-force winds .   In Jamaica , winds left 70 % of residents without electricity , blew roofs off buildings , killed one , and caused about $ 100 million ( 2012 USD ) in damage . Sandy 's outer bands brought flooding to Haiti , killing at least 54 , causing food shortages , and leaving about 200,000 homeless ; the hurricane also caused two deaths in the Dominican Republic . In Puerto Rico , one man was swept away by a swollen river . In Cuba , there was extensive coastal flooding and wind damage inland , destroying some 15,000 homes , killing 11 , and causing $ 2 billion ( 2012 USD ) in damage . Sandy caused two deaths and damage estimated at $ 700 million ( 2012 USD ) in The Bahamas .   In the United States , Hurricane Sandy affected 24 states , including the entire eastern seaboard from Florida to Maine and west across the Appalachian Mountains to Michigan and Wisconsin , with particularly severe damage in New Jersey and New York . Its storm surge hit New York City on October 29 , flooding streets , tunnels and subway lines and cutting power in and around the city . Damage in the United States amounted to $ 71.4 billion ( 2013 USD ) . In Canada , two were killed in Ontario and an estimated $ 100 million ( 2012 CAD ) in damage was caused throughout Ontario and Quebec .


Hydrocarbon

In organic chemistry , a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon , and thus are group 14 hydrides . Hydrocarbons from which one hydrogen atom has been removed are functional groups , called hydrocarbyls .  Aromatic hydrocarbons ( arenes ) , alkanes , alkenes , cycloalkanes and alkyne-based compounds are different types of hydrocarbons .   The majority of hydrocarbons found on Earth naturally occur in crude oil , where decomposed organic matter provides an abundance of carbon and hydrogen which , when bonded , can catenate to form seemingly limitless chains .


Hydrofluorocarbon

Hydrofluorocarbons ( HFCs ) , organic compounds that contain fluorine and hydrogen atoms , are the most common type of organofluorine compounds . They are commonly used in air conditioning and as refrigerants in place of the older chlorofluorocarbons such as R-12 and hydrochlorofluorocarbons such as R-21 . They do not harm the ozone layer as much as the compounds they replace ; however , they do contribute to global warming . Their atmospheric concentrations and contribution to anthropogenic greenhouse gas emissions are rapidly increasing , causing international concern about their radiative forcing .   Fluorocarbons with few C -- F bonds behave similarly to the parent hydrocarbons , but their reactivity can be altered significantly . For example , both uracil and 5-fluorouracil are colourless , high-melting crystalline solids , but the latter is a potent anti-cancer drug . The use of the C-F bond in pharmaceuticals is predicated on this altered reactivity . Several drugs and agrochemicals contain only one fluorine center or one trifluoromethyl group .   Unlike other greenhouse gases in the Paris Agreement , hydrofluorocarbons have other international negotiations .   In September 2016 , the so-called New York Declaration urged a global reduction in the use of HFCs . On 15 October 2016 , due to these chemicals ' contribution to climate change , negotiators from 197 nations meeting at the summit of the United Nations Environment Programme in Kigali , Rwanda reached a legally-binding accord to phase out hydrofluorocarbons ( HFCs ) in an amendment to the Montreal Protocol .


Hydrology

Hydrology is the scientific study of the movement , distribution , and quality of water on Earth and other planets , including the water cycle , water resources and environmental watershed sustainability . A practitioner of hydrology is a hydrologist , working within the fields of earth or environmental science , physical geography , geology or civil and environmental engineering . Using various analytical methods and scientific techniques , they collect and analyze data to help solve water related problems such as environmental preservation , natural disasters , and water management .   Hydrology subdivides into surface water hydrology , groundwater hydrology ( hydrogeology ) , and marine hydrology . Domains of hydrology include hydrometeorology , surface hydrology , hydrogeology , drainage-basin management and water quality , where water plays the central role .   Oceanography and meteorology are not included because water is only one of many important aspects within those fields .   Hydrological research can inform environmental engineering , policy and planning .   The term hydrology comes from Greek : ὕδωρ , hýdōr , `` water '' ; and λόγος , lógos , `` study '' .


Hydroponics

Hydroponics is a subset of hydroculture , the method of growing plants without soil , using mineral nutrient solutions in a water solvent . Terrestrial plants may be grown with only their roots exposed to the mineral solution , or the roots may be supported by an inert medium , such as perlite or gravel . The nutrients in hydroponics can be from fish waste , duck manure , or chemical fertilizer .


Hypertension

Hypertension ( HTN or HT ) , also known as high blood pressure ( HBP ) , is a long term medical condition in which the blood pressure in the arteries is persistently elevated . High blood pressure usually does not cause symptoms . Long term high blood pressure , however , is a major risk factor for coronary artery disease , stroke , heart failure , peripheral vascular disease , vision loss , and chronic kidney disease .   High blood pressure is classified as either primary ( essential ) high blood pressure or secondary high blood pressure . About 90 -- 95 % of cases are primary , defined as high blood pressure due to nonspecific lifestyle and genetic factors . Lifestyle factors that increase the risk include excess salt , excess body weight , smoking , and alcohol . The remaining 5 -- 10 % of cases are categorized as secondary high blood pressure , defined as high blood pressure due to an identifiable cause , such as chronic kidney disease , narrowing of the kidney arteries , an endocrine disorder , or the use of birth control pills .   Blood pressure is expressed by two measurements , the systolic and diastolic pressures , which are the maximum and minimum pressures , respectively . Normal blood pressure at rest is within the range of 100 -- 140 millimeters mercury ( mmHg ) systolic and 60 -- 90 mmHg diastolic . High blood pressure is present if the resting blood pressure is persistently at or above 140/90 mmHg for most adults . Different numbers apply to children . Ambulatory blood pressure monitoring over a 24-hour period appears more accurate than office best blood pressure measurement .   Lifestyle changes and medications can lower blood pressure and decrease the risk of health complications . Lifestyle changes include weight loss , decreased salt intake , physical exercise , and a healthy diet . If lifestyle changes are not sufficient then blood pressure medications are used . Up to three medications can control blood pressure in 90 % of people . The treatment of moderately high arterial blood pressure ( defined as > 160/100 mmHg ) with medications is associated with an improved life expectancy . The effect of treatment of blood pressure between 140/90 mmHg and 160/100 mmHg is less clear , with some reviews finding benefit and others finding a lack of evidence for benefit . High blood pressure affects between 16 and 37 % of the population globally . In 2010 hypertension was believed to have been a factor in 18 % of all deaths ( 9.4 million globally ) .


Hyperthermia

Hyperthermia is elevated body temperature due to failed thermoregulation that occurs when a body produces or absorbs more heat than it dissipates . Extreme temperature elevation then becomes a medical emergency requiring immediate treatment to prevent disability or death .   The most common causes include heat stroke and adverse reactions to drugs . The former is an acute temperature elevation caused by exposure to excessive heat , or combination of heat and humidity , that overwhelms the heat-regulating mechanisms . The latter is a relatively rare side effect of many drugs , particularly those that affect the central nervous system . Malignant hyperthermia is a rare complication of some types of general anesthesia .   Hyperthermia differs from fever in that the body 's temperature set point remains unchanged . The opposite is hypothermia , which occurs when the temperature drops below that required to maintain normal metabolism . The term is from Greek ὑπέρ , hyper , meaning `` above '' or `` over '' , and θέρμος , thermos , meaning `` heat '' .


Hypothermia

Hypothermia is reduced body temperature that happens when a body dissipates more heat than it absorbs . In humans , it is defined as a body core temperature below 35.0 C. Symptoms depend on the temperature . In mild hypothermia there is shivering and mental confusion . In moderate hypothermia shivering stops and confusion increases . In severe hypothermia there may be paradoxical undressing , in which a person removes his or her clothing , as well as an increased risk of the heart stopping .   Hypothermia has two main types of causes . It classically occurs from exposure to extreme cold . It may also occur from any condition that decreases heat production or increases heat loss . Commonly this includes alcohol intoxication but may also include low blood sugar , anorexia , and advanced age , among others . Body temperature is usually maintained near a constant level of 36.5 -- through thermoregulation . Efforts to increase body temperature involve shivering , increased voluntary activity , and putting on warmer clothing . Hypothermia may be diagnosed based on either a person 's symptoms in the presence of risk factors or by measuring a person 's core temperature .   The treatment of mild hypothermia involves warm drinks , warm clothing and physical activity . In those with moderate hypothermia heating blankets and warmed intravenous fluids are recommended . People with moderate or severe hypothermia should be moved gently . In severe hypothermia extracorporeal membrane oxygenation ( ECMO ) or cardiopulmonary bypass may be useful . In those without a pulse cardiopulmonary resuscitation ( CPR ) is indicated along with the above measures . Rewarming is typically continued until a person 's temperature is greater than 32 C . If there is no improvement at this point or the blood potassium level is greater than 12 mmol/liter at any time resuscitation may be discontinued .   Hypothermia is the cause of at least 1500 deaths a year in the United States . It is more common in older people and males . One of the lowest documented body temperatures from which someone with accidental hypothermia has survived is 13.0 C in a near-drowning of a 7-year-old girl in Sweden . Survival after more than six hours of CPR has been described . In those in whom ECMO or bypass is used survival is around 50 % . Deaths due to hypothermia have played an important role in many wars . The term is from Greek ὑπο , ypo , meaning `` under '' , and θερμία , thermía , meaning `` heat '' . The opposite of hypothermia is hyperthermia , an increased body temperature due to failed thermoregulation .


Hysterectomy

Hysterectomy ( from Greek ὑστέρα , hystera , `` uterus '' + ἐκτομή , ektomḗ , `` a cutting out of '' ) is the surgical removal of the uterus . It may also involve removal of the cervix , ovaries , fallopian tubes and other surrounding structures .   Usually performed by a gynecologist , hysterectomy may be total ( removing the body , fundus , and cervix of the uterus ; often called `` complete '' ) or partial ( removal of the uterine body while leaving the cervix intact ; also called `` supracervical '' ) . It is the most commonly performed gynecological surgical procedure . In 2003 , over 600,000 hysterectomies were performed in the United States alone , of which over 90 % were performed for benign conditions . Such rates being highest in the industrialized world has led to the major controversy that hysterectomies are being largely performed for unwarranted and unnecessary reasons .   Removal of the uterus renders the patient unable to bear children ( as does removal of ovaries and fallopian tubes ) and has surgical risks as well as long-term effects , so the surgery is normally recommended when other treatment options are not available or have failed . It is expected that the frequency of hysterectomies for non-malignant indications will fall as there are good alternatives in many cases .   Oophorectomy ( removal of ovaries ) is frequently done together with hysterectomy to decrease the risk of ovarian cancer . However , recent studies have shown that prophylactic oophorectomy without an urgent medical indication decreases a woman 's long-term survival rates substantially and has other serious adverse effects . This effect is not limited to pre-menopausal women ; even women who have already entered menopause were shown to have experienced a decrease in long-term survivability post-oophorectomy .


IPCC Fifth Assessment Report

The Fifth Assessment Report ( AR5 ) of the United Nations Intergovernmental Panel on Climate Change ( IPCC ) is the fifth in a series of such reports . The IPCC was established in 1988 by the World Meteorological Organization ( WMO ) and the United Nations Environment Programme ( UNEP ) to assess scientific , technical and socio-economic information concerning climate change , its potential effects and options for adaptation and mitigation .   The Fifth Assessment Report was finalized in 2014 . As had been the case in the past , the outline of the AR5 was developed through a scoping process which involved climate change experts from all relevant disciplines and users of IPCC reports ; in particular representatives from governments . Governments and organizations involved in the Fourth Report were asked to submit comments and observations in writing with the submissions analysed by the panel . The report was delivered in stages , starting with Working Group I 's report on the physical science basis , based on 9,200 peer-reviewed studies . The summaries for policy makers were released on 27 September 2013 for the first report , on 31 March 2014 for the second report entitled `` Impacts , Adaptation , and Vulnerability '' , and on 14 April 2014 for the third report entitled `` Mitigation of Climate Change '' . The Synthesis Report was released on 2 November 2014 , in time to pave the way for negotiations on reducing carbon emissions at the UN Climate Change Conference in Paris during late 2015 .


IPCC First Assessment Report

The First Assessment Report ( FAR ) of the Intergovernmental Panel on Climate Change ( IPCC ) was completed in 1990 . It served as the basis of the United Nations Framework Convention on Climate Change ( UNFCCC ) .   The report was issued in three main sections , corresponding to the three Working Groups of scientists that the IPCC had established .   Working Group I : Scientific Assessment of Climate Change , edited by J.T. Houghton , G.J. Jenkins and J.J. Ephraums  Working Group II : Impacts Assessment of Climate Change , edited by W.J. McG . Tegart , G.W. Sheldon and D.C. Griffiths  Working Group III : The IPCC Response Strategies   Each section included a summary for policymakers . This format was followed in subsequent Assessment Reports .   The executive summary of the policymakers ' summary of the WG I report includes :   We are certain of the following : there is a natural greenhouse effect ... ; emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases : CO2 , methane , CFCs and nitrous oxide . These increases will enhance the greenhouse effect , resulting on average in an additional warming of the Earth 's surface . The main greenhouse gas , water vapour , will increase in response to global warming and further enhance it .  We calculate with confidence that : ... CO2 has been responsible for over half the enhanced greenhouse effect ; long-lived gases would require immediate reductions in emissions from human activities of over 60 % to stabilise their concentrations at today 's levels ...  Based on current models , we predict : under -LSB- BAU -RSB- increase of global mean temperature during the -LSB- 21st -RSB- century of about 0.3 oC per decade ( with an uncertainty range of 0.2 to 0.5 oC per decade ) ; this is greater than that seen over the past 10,000 years ; under other ... scenarios which assume progressively increasing levels of controls , rates of increase in global mean temperature of about 0.2 oC -LSB- to -RSB- about 0.1 oC per decade .  There are many uncertainties in our predictions particularly with regard to the timing , magnitude and regional patterns of climate change , due to our incomplete understanding of : sources and sinks of GHGs ; clouds ; oceans ; polar ice sheets .  Our judgement is that : global mean surface air temperature has increased by 0.3 to 0.6 oC over the last 100 years ... ; The size of this warming is broadly consistent with predictions of climate models , but it is also of the same magnitude as natural climate variability . Thus the observed increase could be largely due to this natural variability ; alternatively this variability and other human factors could have offset a still larger human-induced greenhouse warming . The unequivocal detection of the enhanced greenhouse effect is not likely for a decade or more .  under the IPCC business as usual emissions scenario , an average rate of global mean sea level rise of about 6 cm per decade over the next century ( with an uncertainty range of 3 -- 10 cm per decade ) , mainly due to thermal expansion of the oceans and the melting of some land ice . The predicted rise is about 20 cm ... by 2030 , and 65 cm by the end of the next century .


IPCC Fourth Assessment Report

Climate Change 2007 , the Fourth Assessment Report ( AR4 ) of the United Nations Intergovernmental Panel on Climate Change ( IPCC ) , is the fourth in a series of reports intended to assess scientific , technical and socio-economic information concerning climate change , its potential effects , and options for adaptation and mitigation . The report is the largest and most detailed summary of the climate change situation ever undertaken , produced by thousands of authors , editors , and reviewers from dozens of countries , citing over 6,000 peer-reviewed scientific studies .   It supersedes the Third Assessment Report ( 2001 ) , and is superseded by the Fifth Assessment Report .   The headline findings of the report were : `` warming of the climate system is unequivocal '' , and `` most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations . ''


IPCC Second Assessment Report

The Second Assessment Report ( SAR ) of the Intergovernmental Panel on Climate Change ( IPCC ) , published in 1996 , is an assessment of the then available scientific and socio-economic information on climate change . It was superseded by the Third Assessment Report ( TAR ) in 2001 .


IPCC Third Assessment Report

The IPCC Third Assessment Report , Climate Change 2001 , is an assessment of available scientific and socio-economic information on climate change by the IPCC . The IPCC was established in 1988 by the United Nations Environment Programme ( UNEP ) and the UN 's World Meteorological Organization ( WMO ) '' ... to assess scientific , technical and socio-economic information relevant for the understanding of climate change , its potential impacts and options for adaptation and mitigation . '' -LSB- IPCC website -RSB- The Third Assessment Report ( TAR ) is the third of a series of assessments ; it has been superseded by the IPCC Fourth Assessment Report ( AR4 ) , released in 2007 .   Statements of the IPCC or information from the TAR are often used as a reference showing a scientific consensus on the subject of global warming , although a small minority of scientists take issue with the UN assessments ( see also Global warming controversy and Politics of global warming ) .


Ice age

An ice age is a period of long-term reduction in the temperature of Earth 's surface and atmosphere , resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers . Within a long-term ice age , individual pulses of cold climate are termed `` glacial periods '' ( or alternatively `` glacials '' or `` glaciations '' or colloquially as `` ice age '' ) , and intermittent warm periods are called `` interglacials '' . In the terminology of glaciology , ice age implies the presence of extensive ice sheets in both northern and southern hemispheres . By this definition , we are in an interglacial period -- the Holocene -- of the ice age . The ice age began 2.6 million years ago at the start of the Pleistocene epoch , because the Greenland , Arctic , and Antarctic ice sheets still exist .


Ice core

An ice core is a core sample that is typically removed from an ice sheet , most commonly from the polar ice caps of Antarctica , Greenland or from high mountain glaciers elsewhere . As the ice forms from the incremental buildup of annual layers of snow , lower layers are older than upper , and an ice core contains ice formed over a range of years . The properties of the ice and the recrystallized inclusions within the ice can then be used to reconstruct a climatic record over the age range of the core , normally through isotopic analysis . This enables the reconstruction of local temperature records and the history of atmospheric composition .   Ice cores contain an abundance of information about climate . Inclusions in the snow of each year remain in the ice , such as wind-blown dust , ash , pollen , bubbles of atmospheric gas and radioactive substances . The variety of climatic proxies is greater than in any other natural recorder of climate , such as tree rings or sediment layers . These include ( proxies for ) temperature , ocean volume , precipitation , chemistry and gas composition of the lower atmosphere , volcanic eruptions , solar variability , sea-surface productivity , desert extent and forest fires .   The length of the record depends on the depth of the ice core and varies from a few years up to 800 kyr ( 800,000 years ) for the EPICA core . The time resolution ( i.e. the shortest time period which can be accurately distinguished ) depends on the amount of annual snowfall , and reduces with depth as the ice compacts under the weight of layers accumulating on top of it . Upper layers of ice in a core correspond to a single year or sometimes a single season . Deeper into the ice the layers thin and annual layers become indistinguishable .   An ice core from the right site can be used to reconstruct an uninterrupted and detailed climate record extending over hundreds of thousands of years , providing information on a wide variety of aspects of climate at each point in time . It is the simultaneity of these properties recorded in the ice that makes ice cores such a powerful tool in paleoclimate research .


Ice sheet

An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50000 km2 , thus also known as continental glacier . The only current ice sheets are in Antarctica and Greenland ; during the last glacial period at Last Glacial Maximum ( LGM ) the Laurentide ice sheet covered much of North America , the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America .   Ice sheets are bigger than ice shelves or alpine glaciers . Masses of ice covering less than 50,000 km2 are termed an ice cap . An ice cap will typically feed a series of glaciers around its periphery .   Although the surface is cold , the base of an ice sheet is generally warmer due to geothermal heat . In places , melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly . This process produces fast-flowing channels in the ice sheet -- these are ice streams .   The present-day polar ice sheets are relatively young in geological terms . The Antarctic Ice Sheet first formed as a small ice cap ( maybe several ) in the early Oligocene , but retreating and advancing many times until the Pliocene , when it came to occupy almost all of Antarctica . The Greenland ice sheet did not develop at all until the late Pliocene , but apparently developed very rapidly with the first continental glaciation . This had the unusual effect of allowing fossils of plants that once grew on present-day Greenland to be much better preserved than with the slowly forming Antarctic ice sheet .


Ice shelf

An ice shelf is a thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface . Ice shelves are only found in Antarctica , Greenland , Canada and the Russian Arctic . The boundary between the floating ice shelf and the grounded ( resting on bedrock ) ice that feeds it is called the grounding line . The thickness of ice shelves ranges from about 100 to 1000 meters .   In contrast , sea ice is formed on water , is much thinner ( typically less than 3m ) , and forms throughout the Arctic Ocean . It also is found in the Southern Ocean around the continent of Antarctica .   Ice shelves are principally driven by gravity-driven pressure from the grounded ice . That flow continually moves ice from the grounding line to the seaward front of the shelf . The primary mechanism of mass loss from ice shelves was thought to have been iceberg calving , in which a chunk of ice breaks off from the seaward front of the shelf . A study by NASA and university researchers - published in the June 14 , 2013 issue of Science - found however that ocean waters melting the undersides of Antarctic ice shelves are responsible for most of the continent 's ice shelf mass loss .   Typically , a shelf front will extend forward for years or decades between major calving events . Snow accumulation on the upper surface and melting from the lower surface are also important to the mass balance of an ice shelf . Ice may also accrete onto the underside of the shelf .   The density contrast between glacial ice , which is denser than normal ice , and liquid water means that only about 1/9 of the floating ice is above the ocean surface . The world 's largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica .   The term captured ice shelf has been used for the ice over a subglacial lake , such as Lake Vostok .


Iceberg

An iceberg or ice mountain is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open water . It may subsequently become frozen into pack ice ( one form of sea ice ) . As it drifts into shallower waters , it may come into contact with the seabed , a process referred to as seabed gouging by ice . Almost 91 % of an iceberg is below the surface of the water .


Illinois

Illinois ( -LSB- ɪlᵻˈnɔɪ -RSB- ) is a state in the Midwestern region of the United States , achieving statehood in 1818 . It is the 6th-most populous state and 25th-largest state in terms of land area , and is noted as a microcosm of the entire country . The word `` Illinois '' comes from a French rendering of a native Algonquin word . With Chicago in the northeast , small industrial cities and great agricultural productivity in central and northern Illinois , and natural resources like coal , timber , and petroleum in the south , Illinois has a diverse economic base and is a major transportation hub . The Port of Chicago connects the state to other global ports from the Great Lakes , via the Saint Lawrence Seaway , to the Atlantic Ocean , as well as the Great Lakes to the Mississippi River , via the Illinois Waterway . For decades , O'Hare International Airport has been ranked as one of the world 's busiest airports . Illinois has long had a reputation as a bellwether both in social and cultural terms and politics .   Although today the state 's largest population center is around Chicago in the northern part of the state , the state 's European population grew first in the west , with French Canadian colonists who settled along the Mississippi River in the 17th and 18th century , and gave the area the name , `` Pays des Illinois '' or Illinois Country a region that was known as part of New France . After the American Revolutionary War established the United States , American settlers began arriving crossing the Appalachians barrier range in the 1810s via the gaps of the Allegheny to boat building centers in Pittsburgh , from Cumberland , Maryland via the Cumberland Narrows pass to outfit in Brownsville , Pennsylvania , from North Carolina and Virginia via the Cumberland Gap to Kentucky and Tennessee , all on the Ohio River .   With the War of 1812 , the growth of Illinois slowed as both Native Americans and Canadian forces often raided the American Frontier . After the war 's end , the federal government re-established forts such as Fort Dearborn ( in 1816 -- now the site is within Chicago ) and army patrols west of the Mississippi diminished the threat from Amerindian raids , so settlers were able to move into all of Illinois from the eastern and southern emigrant trails .   Mineral finds and timber stands also had spurred immigration -- by the 1810s , the Eastern U.S. had exhausted most timber stands close to the established cities creating a hard felt first energy crisis by the late-1790s , and after 1818 , the industrial revolution was being fueled by new canals such as the Lehigh Canal feeding the furnaces of the rapidly industrializing east coast . Also in 1818 , Illinois achieved statehood and its growth , as yet untroubled by the speed of as yet unrefined railway technology , would be fueled by the new religion of industrialized forward thinking .   After construction of the Erie Canal with increasing traffic and trade through the Great Lakes , Chicago was founded in the 1830s on the banks of the Chicago River , at one of the few natural harbors on southern Lake Michigan . John Deere 's invention of the self-scouring steel plow turned Illinois ' rich prairie into some of the world 's most productive and valuable farmlands , attracting new immigrant farmers from Germany and Sweden . Railroads arose and matured in the 1840s , and soon carried immigrants to new homes in Illinois , as well as being a resource to ship their commodity crops out to markets . Railroads freed most of the land of Illinois and other mid-western states from the tyranny of water transport ; no longer was a location near a river or canal a need to ship bulk goods .   By 1900 , the growth of industrial jobs in the northern cities and coal mining in the central and southern areas attracted a new group of immigrants , from Eastern and Southern Europe . Illinois was an important manufacturing center during both world wars . The Great Migration from the South established a large community of African Americans in Chicago , who created the city 's famous jazz and blues cultures .   Three U.S. presidents have been elected while living in Illinois : Abraham Lincoln , Ulysses S. Grant , and most recently Barack Obama . Additionally , Ronald Reagan , whose political career was based in California , was the only U.S. president born and raised in Illinois . Today , Illinois honors Lincoln with its official state nickname `` The Land of Lincoln , '' which has been displayed on its license plates since 1954 . The Abraham Lincoln Presidential Library and Museum is located in the state capital of Springfield , and the Barack Obama Presidential Center will be completed in Chicago by 2020 .


Imagism

Imagism was a movement in early 20th-century Anglo-American poetry that favored precision of imagery and clear , sharp language .   Imagism has been described as the most influential movement in English poetry since the activity of the Pre-Raphaelites . As a poetic style it gave Modernism its start in the early 20th century , and is considered to be the first organized Modernist literary movement in the English language . Imagism is sometimes viewed as ' a succession of creative moments ' rather than any continuous or sustained period of development . René Taupin remarked that ` It is more accurate to consider Imagism not as a doctrine , nor even as a poetic school , but as the association of a few poets who were for a certain time in agreement on a small number of important principles ' .   The Imagists rejected the sentiment and discursiveness typical of much Romantic and Victorian poetry , in contrast to their contemporaries , the Georgian poets , who were generally content to work within that tradition . In contrast , Imagism called for a return to what were seen as more Classical values , such as directness of presentation and economy of language , as well as a willingness to experiment with non-traditional verse forms . Imagists use free verse .   Imagist publications appearing between 1914 and 1917 featured works by many of the most prominent modernist figures , both in poetry and in other fields . The Imagist group was centered in London , with members from Great Britain , Ireland and the United States . Somewhat unusually for the time , a number of women writers were major Imagist figures .   A characteristic feature of Imagism is its attempt to isolate a single image to reveal its essence . This feature mirrors contemporary developments in avant-garde art , especially Cubism . Although Imagism isolates objects through the use of what Ezra Pound called `` luminous details '' , Pound 's Ideogrammic Method of juxtaposing concrete instances to express an abstraction is similar to Cubism 's manner of synthesizing multiple perspectives into a single image .


Incineration

Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials . Incineration and other high-temperature waste treatment systems are described as `` thermal treatment '' . Incineration of waste materials converts the waste into ash , flue gas and heat . The ash is mostly formed by the inorganic constituents of the waste , and may take the form of solid lumps or particulates carried by the flue gas . The flue gases must be cleaned of gaseous and particulate pollutants before they are dispersed into the atmosphere . In some cases , the heat generated by incineration can be used to generate electric power .   Incineration with energy recovery is one of several waste-to-energy ( WtE ) technologies such as gasification , pyrolysis and anaerobic digestion . While incineration and gasification technologies are similar in principle , the energy product from incineration is high-temperature heat whereas combustible gas is often the main energy product from gasification . Incineration and gasification may also be implemented without energy and materials recovery .   In several countries , there are still concerns from experts and local communities about the environmental effect of incinerators ( see arguments against incineration ) .   In some countries , incinerators built just a few decades ago often did not include a materials separation to remove hazardous , bulky or recyclable materials before combustion . These facilities tended to risk the health of the plant workers and the local environment due to inadequate levels of gas cleaning and combustion process control . Most of these facilities did not generate electricity .   Incinerators reduce the solid mass of the original waste by 80 -- 85 % and the volume ( already compressed somewhat in garbage trucks ) by 95 -- 96 % , depending on composition and degree of recovery of materials such as metals from the ash for recycling . This means that while incineration does not completely replace landfilling , it significantly reduces the necessary volume for disposal . Garbage trucks often reduce the volume of waste in a built-in compressor before delivery to the incinerator . Alternatively , at landfills , the volume of the uncompressed garbage can be reduced by approximately 70 % by using a stationary steel compressor , albeit with a significant energy cost . In many countries , simpler waste compaction is a common practice for compaction at landfills .   Incineration has particularly strong benefits for the treatment of certain waste types in niche areas such as clinical wastes and certain hazardous wastes where pathogens and toxins can be destroyed by high temperatures . Examples include chemical multi-product plants with diverse toxic or very toxic wastewater streams , which can not be routed to a conventional wastewater treatment plant .   Waste combustion is particularly popular in countries such as Japan where land is a scarce resource . Denmark and Sweden have been leaders in using the energy generated from incineration for more than a century , in localised combined heat and power facilities supporting district heating schemes . In 2005 , waste incineration produced 4.8 % of the electricity consumption and 13.7 % of the total domestic heat consumption in Denmark . A number of other European countries rely heavily on incineration for handling municipal waste , in particular Luxembourg , the Netherlands , Germany , and France .


Indian Ocean

The Indian Ocean is the third largest of the world 's oceanic divisions , covering 70,560,000 km2 ( approximately 20 % of the water on the Earth 's surface ) . It is bounded by Asia on the north , on the west by Africa , on the east by Australia , and on the south by the Southern Ocean or , depending on definition , by Antarctica . It is named after India . The Indian Ocean is known as Ratnākara , `` the mine of gems '' in ancient Sanskrit literature , and as Hind Mahāsāgar , in Hindi .


Indo-Aryan migration

The Indo-Aryan migrations were the migrations into the Indian subcontinent of Indo-Aryan peoples, an ethnolinguistic group that spoke Indo-Aryan languages, the predominant languages of today's North India, Pakistan, Nepal, Bangladesh, Sri Lanka and the Maldives. Indo-Aryan population movements into the region and Anatolia (ancient Mitanni) from Central Asia are considered to have started after 2000 BCE, as a slow diffusion after the Late Harappan period, which led to a language shift in the northern Indian subcontinent. The Iranian languages were brought into the Iranian plateau by the Iranians, who were closely related to the Indo-Aryans.