Developing country

A developing country , also called a less developed country or an underdeveloped country , is a nation or a sovereign state with a less developed industrial base and a low Human Development Index ( HDI ) relative to other countries . There are no universally agreed-upon criteria for what makes a country developing versus developed and which countries fit these two categories , although there are general reference points such as a nation 's GDP per capita compared with other nations . Also , the general term less-developed country should not be confused with the specific least developed country . The term `` developing '' describes a currently observed situation and not a dynamic or expected direction of progress . Since the late 1990s developing countries tended to demonstrate higher growth rates than the developed ones .   There is criticism for using the term developing country . The term implies inferiority of a developing country or undeveloped country compared with a developed country , which many countries dislike . It assumes a desire to develop along the traditional Western model of economic development which a few countries , such as Cuba and Bhutan , choose not to follow . An alternative measurement that has been suggested is that of gross national happiness . Countries on the boundary between developed and developing are often categorized under the term newly industrialized countries .   According to authors such as Walt Whitman Rostow , developing countries are in transition from traditional lifestyles towards the modern lifestyle which began in the Industrial Revolution in the 18th and 19th centuries .   In the 2016 edition of its World Development Indicators , the World Bank made a decision to no longer distinguish between `` developed '' and `` developing '' countries in the presentation of its data . Nobody has ever agreed on a definition for these terms in the first place .


Development communication

See also Communication for social change   Development communication refers to the use of communication to facilitate social development . Development communication engages stakeholders and policy makers , establishes conducive environments , assesses risks and opportunities and promotes information exchanges to bring about positive social change via sustainable development . Development communication techniques include information dissemination and education , behavior change , social marketing , social mobilization , media advocacy , communication for social change and community participation .   Development communication has been labeled the `` Fifth Theory of the Press , '' with `` social transformation and development , '' and `` the fulfillment of basic needs '' as its primary purposes . Jamias articulated the philosophy of development communication which is anchored on three main ideas , namely : purposive , value-laden and pragmatic . Nora C. Quebral expanded the definition , calling it `` the art and science of human communication applied to the speedy transformation of a country and the mass of its people from poverty to a dynamic state of economic growth that makes possible greater social equality and the larger fulfilment of the human potential . '' Melcote and Steeves saw it as `` emancipation communication '' , aimed at combating injustice and oppression . The term `` development communication '' is sometimes used to refer to a type of marketing and public opinion research , but that is not the topic of this article .


Devonian

The Devonian is a geologic period and system of the Paleozoic , spanning 60 million years from the end of the Silurian , million years ago ( Mya ) , to the beginning of the Carboniferous , Mya . It is named after Devon , England , where rocks from this period were first studied .  The first significant adaptive radiation of life on dry land occurred during the Devonian . Free-sporing vascular plants began to spread across dry land , forming extensive forests which covered the continents . By the middle of the Devonian , several groups of plants had evolved leaves and true roots , and by the end of the period the first seed-bearing plants appeared . Various terrestrial arthropods also became well-established . Fish reached substantial diversity during this time , leading the Devonian to often be dubbed the `` Age of Fish '' . The first ray-finned and lobe-finned bony fish appeared , while the placodermi began dominating almost every known aquatic environment .   The ancestors of all four-limbed vertebrates ( tetrapods ) began adapting to walking on land , as their strong pectoral and pelvic fins gradually evolved into legs . In the oceans , primitive sharks became more numerous than in the Silurian and Late Ordovician . The first ammonites , species of molluscs , appeared . Trilobites , the mollusk-like brachiopods and the great coral reefs , were still common . The Late Devonian extinction which started about 375 million years ago severely affected marine life , killing off all placodermi , and all trilobites , save for a few species of the order Proetida .   The palaeogeography was dominated by the supercontinent of Gondwana to the south , the continent of Siberia to the north , and the early formation of the small continent of Euramerica in between .


Dew point

Dew point is the temperature to which air must be cooled to become saturated with water vapor . When further cooled , the airborne water vapor will condense to form liquid dew . When air with a high dew point contacts surfaces at colder temperatures , then liquid dew will form on the surfaces as condensation . Dew point is sometimes called frost point when the temperature is below freezing . The measurement of dew point is related to humidity . A higher dew point means there will be more moisture in the air .


Dielectric heating

Dielectric heating , also known as electronic heating , RF ( radio frequency ) heating , and high-frequency heating , is the process in which a high-frequency alternating electric field , or radio wave or microwave electromagnetic radiation heats a dielectric material . At higher frequencies , this heating is caused by molecular dipole rotation within the dielectric .   RF dielectric heating at intermediate frequencies , due to its greater penetration over microwave heating , shows greater promise than microwave systems as a method of very rapidly heating and uniformly preparing certain food items , and also killing parasites and pests in certain harvested crops .


Diesel exhaust

Diesel exhaust is the gaseous exhaust produced by a diesel type of internal combustion engine , plus any contained particulates . Its composition may vary with the fuel type or rate of consumption , or speed of engine operation ( e.g. , idling or at speed or under load ) , and whether the engine is in an on-road vehicle , farm vehicle , locomotive , marine vessel , or stationary generator or other application .   Diesel exhaust is a Group 1 carcinogen , which causes lung cancer and has a positive association with bladder cancer . It contains several substances that are also listed individually as human carcinogens by the IARC .   Methods exist to reduce nitrogen oxides ( NOx ) and particulate matter ( PM ) in the exhaust .


Diesel particulate filter

A diesel particulate filter ( or DPF ) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine .


Digital radio

Digital radio is the use of digital technology to transmit and/or receive across the radio spectrum . They may refer to digital transmission by radio waves , including digital broadcasting , and especially to Digital audio radio services .   The term is also applied to radio equipment using digital electronics to process analog radio signals .


Dimensional analysis

In engineering and science , dimensional analysis is the analysis of the relationships between different physical quantities by identifying their fundamental dimensions ( such as length , mass , time , and electric charge ) and units of measure ( such as miles vs. kilometers , or pounds vs. kilograms vs. grams ) and tracking these dimensions as calculations or comparisons are performed . Converting from one dimensional unit to another is often somewhat complex . Dimensional analysis , or more specifically the factor-label method , also known as the unit-factor method , is a widely used technique for such conversions using the rules of algebra .   The concept of physical dimension was introduced by Joseph Fourier in 1822 . Physical quantities that are measurable ( commensurable ) have the same dimension ( length , time , mass ) and can be directly compared to each other , even if they are originally expressed in differing units of measure ( inches and meters , pounds and newtons ) . If physical quantities have different dimensions ( length verses mass ) , they can not be compared by similar units ( are incommensurable ) and can not be compared in quantity . Hence , it is meaningless to ask whether a kilogram is greater than , equal to , or less than an hour .   Any physically meaningful equation ( and likewise any inequality and inequation ) will have the same dimensions on their left and right sides , a property known as `` dimensional homogeneity '' . Checking for dimensional homogeneity is a common application of dimensional analysis . Dimensional analysis is also routinely used as a check of the plausibility of derived equations and computations . It is generally used to categorize types of physical quantities and units based on their relationship to or dependence on other units .


Disaster risk reduction

Disaster risk reduction ( DRR ) is a systematic approach to identifying , assessing and reducing the risks of disaster . It aims to reduce socio-economic vulnerabilities to disaster as well as dealing with the environmental and other hazards that trigger them . Here it has been strongly influenced by the mass of research on vulnerability that has appeared in print since the mid-1970s . It is the responsibility of development and relief agencies alike . It should be an integral part of the way such organizations do their work , not an add-on or one-off action . DRR is very wide-ranging : Its scope is much broader and deeper than conventional emergency management . There is potential for DRR initiatives in just about every sector of development and humanitarian work .   The most commonly cited definition of DRR is one used by UN agencies such as UNISDR , also known as the UN Office for Disaster Risk Reduction , and UNDP : `` The conceptual framework of elements considered with the possibilities to minimize vulnerabilities and disaster risks throughout a society , to avoid ( prevention ) or to limit ( mitigation and preparedness ) the adverse impacts of hazards , within the broad context of sustainable development . ''


Divergence problem

The divergence problem is an anomaly from the field of dendroclimatology , the study of past climate through observations of old trees , primarily the properties of their annual growth rings . It is the disagreement between the temperatures measured by the thermometers ( instrumental temperatures ) and the temperatures reconstructed from the latewood densities or , in some cases , widths of tree rings in the far northern forests .   While the thermometer records indicate a substantial late 20th century warming trend , many tree rings from such sites do not display a corresponding change in their maximum latewood density . In some studies this issue has also been found with tree ring width . A temperature trend extracted from tree rings alone would not show any substantial warming since the 1950s . The temperature graphs calculated in these two ways thus `` diverge '' from one another , which is the origin of the term .


Diversity of fish

Fish are very diverse animals and can be categorised in many ways . This article is an overview of some of ways in which fish are categorised . Although most fish species have probably been discovered and described , about 250 new ones are still discovered every year . According to FishBase , 33,100 species of fish had been described by April 2015 . That is more than the combined total of all other vertebrate species : mammals , amphibians , reptiles and birds .   Fish species diversity is roughly divided equally between marine ( oceanic ) and freshwater ecosystems . Coral reefs in the Indo-Pacific constitute the centre of diversity for marine fishes , whereas continental freshwater fishes are most diverse in large river basins of tropical rainforests , especially the Amazon , Congo , and Mekong basins . More than 5,600 fish species inhabit Neotropical freshwaters alone , such that Neotropical fishes represent about 10 % of all vertebrate species on the Earth . Exceptionally rich sites in the Amazon basin , such as Cantão State Park , can contain more freshwater fish species than occur in all of Europe .


Doctor of Philosophy

A Doctor of Philosophy ( PhD , Ph.D. , or DPhil ; Latin Philosophiae Doctor ) is a type of doctoral degree awarded by universities in many countries . Ph.D. s are awarded for a wide range of programs in the sciences ( e.g. , biology , chemistry , physics , mathematics , etc. ) , engineering , and humanities ( e.g. , history , geography , literature , musicology , etc. ) , among others . The Ph.D. is a terminal degree in many fields . The completion of a Ph.D. is often a requirement for employment as a university professor , researcher , or scientist in many fields . A clear distinction is made between an `` earned doctorate '' , which is awarded for completion of a course of study and a thesis or dissertation , and an `` honorary doctorate '' , a title granted by a university to a successful or notable person who has not completed doctoral academic work or completed a dissertation at the university . Individuals with an earned doctorate can use the title of `` Doctor '' with their name and use the post-nominal letters `` Ph.D. '' , `` PhD '' or `` DPhil '' .   The requirements to earn a Ph.D. degree vary considerably according to the country , institution , and time period , from entry-level research degrees to higher doctorates . A person who attains a doctorate of philosophy is automatically awarded the academic title of doctor . During the studies that lead to the degree , the student is called doctoral student or Ph.D. student , but also doctoral candidate or Ph.D. candidate once the student has completed all of the coursework and comprehensive examinations and is working on their thesis/dissertation ( all but dissertation ) . A student attaining this level may be granted a Candidate of Philosophy degree at some institutions .   A Ph.D. candidate must submit a project , thesis or dissertation often consisting of a body of original academic research , which is in principle worthy of publication in a peer-reviewed journal . In many countries , a candidate must defend this work before a panel of expert examiners appointed by the university . Universities award other types of doctorates besides the Ph.D. , such as the Doctor of Musical Arts ( D.M.A. ) , a degree for music performers and the Doctor of Education ( Ed.D. ) , a degree for professional educators . In 2016 , ELIA ( European League of the Institutes of the Arts ) launched The ` Florence Principles ' on the Doctorate in the Arts . The Florence Principles relating to the Salzburg Principles and the Salzburg Recommendations of EUA ( European University Association ) name seven points of attention to specify the Doctorate / Ph.D. in the Arts compared to a scientific doctorate / Ph.D. . The Florence Principles have been endorsed are supported also by AEC , CILECT , CUMULUS and SAR .   In the context of academic degrees , the term `` philosophy '' does not refer solely to the field or academic discipline of philosophy , but is used in a broader sense in accordance with its original Greek meaning , which is `` love of wisdom '' . In most of Europe , all fields ( history , philosophy , social sciences , mathematics , and natural philosophy/natural sciences ) other than theology , law , and medicine ( the so-called professional , vocational , or technical curriculum ) were traditionally known as philosophy , and in Germany and elsewhere in Europe the basic faculty of liberal arts was known as the `` faculty of philosophy '' .


Don't ask, don't tell

`` Do n't ask , do n't tell '' ( DADT ) was the official United States policy on military service by gays , bisexuals , and lesbians , instituted by the Clinton Administration on February 28 , 1994 , when Department of Defense Directive 1304.26 issued on December 21 , 1993 , took effect , lasting until September 20 , 2011 . The policy prohibited military personnel from discriminating against or harassing closeted homosexual or bisexual service members or applicants , while barring openly gay , lesbian , or bisexual persons from military service . This relaxation of legal restrictions on service by gays and lesbians in the armed forces was mandated by United States federal law , which was signed November 30 , 1993 . The policy prohibited people who `` demonstrate a propensity or intent to engage in homosexual acts '' from serving in the armed forces of the United States , because their presence `` would create an unacceptable risk to the high standards of morale , good order and discipline , and unit cohesion that are the essence of military capability '' .   The act prohibited any homosexual or bisexual person from disclosing his or her sexual orientation or from speaking about any homosexual relationships , including marriages or other familial attributes , while serving in the United States armed forces . The act specified that service members who disclose that they are homosexual or engage in homosexual conduct should be separated ( discharged ) except when a service member 's conduct was `` for the purpose of avoiding or terminating military service '' or when it `` would not be in the best interest of the armed forces '' . Since DADT ended in 2011 , persons who are openly homosexual and bisexual have been able to serve .   The `` do n't ask '' part of the DADT policy specified that superiors should not initiate investigation of a service member 's orientation without witnessing disallowed behaviors , though credible evidence of homosexual behavior could be used to initiate an investigation . Unauthorized investigations and harassment of suspected servicemen and women led to an expansion of the policy to `` do n't ask , do n't tell , do n't pursue , do n't harass '' .   Legislation to repeal DADT was enacted in December 2010 , specifying that the policy would remain in place until the President , the Secretary of Defense , and the Chairman of the Joint Chiefs of Staff certified that repeal would not harm military readiness , followed by a 60-day waiting period . A July 6 , 2011 , ruling from a federal appeals court barred further enforcement of the U.S. military 's ban on openly gay service members . President Barack Obama , Secretary of Defense Leon Panetta , and Chairman of the Joint Chiefs of Staff Admiral Mike Mullen sent that certification to Congress on July 22 , 2011 , which set the end of DADT to September 20 , 2011 .


Donald Trump

Donald John Trump ( born June 14 , 1946 ) is the 45th and current President of the United States . Before entering politics , he was a businessman and television personality .   Trump was born and raised in Queens , New York City , and earned an economics degree from the Wharton School . He then took charge of The Trump Organization , the real estate and construction firm founded by his paternal grandmother , which he ran for 45 years until 2016 . During his real estate career , Trump built , renovated , and managed numerous office towers , hotels , casinos , and golf courses . Besides real estate , he started several side ventures and has licensed the use of his name for the branding of various products and properties , including Trump Entertainment Resorts , Trump Steaks , and Trump Vodka . He was the founder of Trump University . He owned the Miss USA and Miss Universe pageants from 1996 to 2015 , and he produced and hosted The Apprentice , a reality television series on NBC , from 2004 to 2015 . His net worth was estimated to be $ 3.5 billion , making him the 544th richest person in the world .   Trump first publicly expressed interest in running for political office in 1987 . He won two Reform Party presidential primaries in 2000 , but withdrew his candidacy early on . In June 2015 , he launched his campaign for the 2016 presidential election and quickly emerged as the front-runner among seventeen candidates in the Republican primaries . His remaining opponents all suspended their campaigns by the end of May 2016 , and in July he was formally nominated at the Republican National Convention along with Indiana governor Mike Pence as his running mate . Many of his campaign statements were controversial or false , generating much free media coverage .   Trump won the general election on November 8 , 2016 , in a surprise victory against Democratic opponent Hillary Clinton and commenced his presidency on January 20 , 2017 . He became the oldest and wealthiest person ever to assume the presidency , the first without prior military or government service , and the fifth to have won the election while losing the popular vote . His political positions have been described by scholars and commentators as populist , protectionist , and nationalist .


Donald Trump 2016 presidential campaign

The 2016 presidential campaign of Donald Trump was formally launched on June 16, 2015, at Trump Tower in New York City. Trump was the Republican nominee for President of the United States in the 2016 election, having won the most state primaries, caucuses, and delegates at the 2016 Republican National Convention. He chose Mike Pence, the sitting Governor of Indiana, as his vice presidential running mate. On November 8, 2016, Trump and Pence were elected president and vice president of the United States. Trump's populist positions in opposition to illegal immigration and various trade agreements, such as the Trans-Pacific Partnership, earned him support especially among voters who were male, white, blue-collar, working class, and those without college degrees.Many of Trump's remarks were controversial and helped his campaign garner extensive coverage by the mainstream media, trending topics, and social media. Trump's campaign rallies attracted large crowds as well as public controversy. Some of the events were marked by incidents of violence between Trump supporters and protesters, mistreatment of some journalists, and disruption by a large group of protesters who effectively shut down a major rally in Chicago. Trump himself was accused of inciting violence at his rallies.Trump's disdain for political correctness was a staple theme of his campaign and proved popular among his supporters. Many, including some mainstream commentators and some prominent Republicans, viewed him as appealing to racism, a charge that Trump has repeatedly denied. Trump's most polarizing and widely reported proposals were about issues of immigration and border security, especially his proposed deportation of all illegal immigrants, the proposed construction of a substantial wall on the Mexico–United States border at Mexican expense, his characterizations of many illegal Mexican immigrants as "criminals, drug dealers, rapists, etc", and a temporary ban on foreign Muslims entering the U.S. (which he later modified to apply to people originating from countries which he described as having a history of terrorism against the United States or its allies).Opposition to Trump grew during his campaign among both Republicans (who viewed Trump as irrevocably damaging to the party and its chances of winning elections during and after 2016, leading to the coalescence of the Stop Trump movement) and Democrats (who decried Trump's anti-immigrant and anti-Muslim policies, his behavior toward critics, his treatment of the media, and his support from the ethno-nationalist alt-right). Although some prominent Republican leaders declined to endorse Trump after he won the Republican nomination, many Republican congress-members showed support for Trump and his policy positions despite major personal or political conflicts with him. Some such supporters of Trump's campaign were accused, by both conservatives and liberals, of prioritizing party loyalty and avoiding alienation of Trump supporters to ensure re-election, thereby refraining from condemning Trump's actions.On January 6, 2017, the United States government's intelligence agencies concluded that the Russian government interfered in the 2016 United States elections against the campaign of Hillary Clinton and in support of Trump. As president, Trump has repeatedly rejected the conclusions of the U.S. intelligence agencies.


Drought

A drought is a period of below-average precipitation in a given region , resulting in prolonged shortages in its water supply , whether atmospheric , surface water or ground water . A drought can last for months or years , or may be declared after as few as 15 days . It can have a substantial impact on the ecosystem and agriculture of the affected region and harm to the local economy . Annual dry seasons in the tropics significantly increase the chances of a drought developing and subsequent bush fires . Periods of heat can significantly worsen drought conditions by hastening evaporation of water vapour .   Many plant species , such as those in the family Cactaceae ( or cacti ) , have drought tolerance adaptations like reduced leaf area and waxy cuticles to enhance their ability to tolerate drought . Some others survive dry periods as buried seeds . Semi-permanent drought produces arid biomes such as deserts and grasslands . Prolonged droughts have caused mass migrations and humanitarian crises . Most arid ecosystems have inherently low productivity . The most prolonged drought ever in the world in recorded history occurred in the Atacama Desert in Chile ( 400 Years ) .


Drought in the United Kingdom

Droughts are a relatively common feature of the weather in the United Kingdom , with one around every 5 -- 10 years on average . These droughts are usually during the summer , when a blocking high causes hot , dry weather for an extended period . However droughts can vary in their characteristics . All types of drought cause issues across all sectors , with impacts extending to the ecosystem , agriculture and the economy of the whole country in severe cases of drought . The south east of the country usually suffers most , as it has the highest population ( and therefore demand ) and the lowest average precipitation per year , which is even lower in a drought . Even in these areas in severe droughts , the definition , impacts , effects and management are all minimal in comparison to drought prone areas such as Australia and parts of the United States . In recent years however , the summers of 2007 , 2008 , 2009 and August 2010 were wetter than normal , 2007 being wettest on record .


Droughts in the United States

Drought in the United States is similar to that of other portions of the globe . Below normal precipitation leads to drought , which is caused by an above average persistence of high pressure over the drought area . Changes in the track of extratropical cyclones , which can occur during climate cycles such as the El Niño-Southern Oscillation , or ENSO , as well as the North Atlantic Oscillation , Pacific Decadal Oscillation , and Atlantic multidecadal oscillation , modulates which areas would be more prone to drought and when drought develops . Increased drought frequency is expected to be one of the effects of global warming . In dry areas , removing grass cover and going with a more natural vegetation for the area can reduce the impact of drought , since a significant amount of fresh water is used to keep lawns green . Droughts are periodic , alternating with floods over a series of years .   The worst droughts in the history of the United States occurred during the 1930s and 1950s , periods of time known as ` Dust Bowl ' years in which droughts lead to significant economic damages and social changes . In particular , relief and health agencies became overburdened and many local community banks had to close .


Drowning

Drowning is defined as respiratory impairment from being in or under a liquid . It is further classified by outcome into : death , ongoing health problems , and no ongoing health problems . Drowning itself is quick and silent , although it may be preceded by distress which is more visible .   Generally , in the early stages of drowning , very little water enters the lungs : a small amount of water entering the trachea causes a muscular spasm that seals the airway and prevents the passage of both air and water until unconsciousness occurs . This means a person drowning is unable to shout or call for help , or seek attention , as they can not obtain enough air . The instinctive drowning response is the final set of autonomic reactions in the 20 -- 60 seconds before sinking underwater , and to the untrained eye can look similar to calm safe behavior . Lifeguards and other persons trained in rescue learn to recognize drowning people by watching for these movements . If the process is not interrupted , loss of consciousness due to hypoxia is followed rapidly by cardiac arrest . At this stage , the process is still usually reversible by prompt and effective rescue and first aid . Survival rates depend strongly on the duration of immersion .   In 2013 , there were about 1.7 million cases of drowning . Unintentional drowning is the third leading cause of unintentional injury resulting in death worldwide . In 2013 , it was estimated to have resulted in 368,000 deaths , down from 545,000 deaths in 1990 . Of these deaths , 82,000 occurred in children less than five years old . It accounts for 7 % of all injury related deaths ( excluding those due to natural disasters ) , with 91 % of these deaths occurring in low-income and middle-income countries . Drowning occurs more frequently in males and the young . The rate of drowning in populations around the world varies widely according to their access to water , the climate and the national swimming culture .  Most drownings are preventable .


Durban

Durban ( eThekwini , from itheku meaning `` bay/lagoon '' ) is the largest city in the South African province of KwaZulu-Natal . Durban 's metropolitan municipality ranks third among the most populous urban areas in South Africa after Johannesburg and Cape Town . It is also the second most important manufacturing hub in South Africa after Johannesburg . It forms part of the eThekwini Metropolitan Municipality . Durban is famous for being the busiest port in South Africa . It is also seen as one of the major centres of tourism because of the city 's warm subtropical climate and extensive beaches . The municipality , which includes neighbouring towns , has a population of almost 3.5 million , making the combined municipality one of the biggest cities on the Indian Ocean coast of the African continent . It is the largest city in KwaZulu-Natal which is the 2nd most populous province in South Africa . It has the highest number of dollar millionaires added per year of any South African city with the number rising 200 per cent between 2000 and 2014 . In May 2015 , Durban was officially recognised as one of the New7Wonders Cities together with Vigan , Doha , La Paz , Havana , Beirut , and Kuala Lumpur .


Dwarf forest

Dwarf forest , elfin forest , or pygmy forest is a rare ecosystem featuring miniature trees , inhabited by small species of fauna such as rodents and lizards . They are usually located at high elevations , under conditions of sufficient air humidity but poor soil . There are two main dwarf forest ecosystem types , involving different species and environmental characteristics : coastal temperate and montane tropical regions . Temperate coastal dwarf forest is common for parts of Southern California . Montane tropical forests are found across tropical highlands of Central America , northern South America and Southeast Asia . There are also other isolated examples of dwarf forests scattered across the world .


Dysentery

Dysentery is a type of gastroenteritis that results in diarrhea with blood . Other symptoms may include fever , abdominal pain , and a feeling of incomplete defecation .   It is caused by several types of infections such as bacteria , viruses , parasitic worms , or protozoa . The mechanism is an inflammatory disorder of the intestine , especially of the colon .


Early 2014 North American cold wave

The 2014 North American cold wave was an extreme weather event that extended through the late winter months of the 2013 -- 2014 winter season , and was also part of an unusually cold winter affecting parts of Canada and parts of the north-central and upper eastern United States . The event occurred in early 2014 and was caused by a southward shift of the North Polar Vortex . Record-low temperatures also extended well into March .   On January 2 , an Arctic cold front initially associated with a nor'easter tracked across Canada and the United States , resulting in heavy snowfall . Temperatures fell to unprecedented levels , and low temperature records were broken across the United States . Business , school , and road closures were common , as well as mass flight cancellations . Altogether , more than 200 million people were affected , in an area ranging from the Rocky Mountains to the Atlantic Ocean and extending south to include roughly 187 million residents of the Continental United States .


Earth

Earth ( from Eorðe -LSB- Γαῖα , Gaia -RSB- Terra ) , otherwise known as the World or the Globe , is the third planet from the Sun and the only object in the Universe known to harbor life . It is the densest planet in the Solar System and the largest of the four terrestrial planets .   According to radiometric dating and other sources of evidence , Earth formed about 4.54 billion years ago . Earth 's gravity interacts with other objects in space , especially the Sun and the Moon , Earth 's only natural satellite . During one orbit around the Sun , Earth rotates about its axis over 365 times ; thus , an Earth year is about 365.26 days long . Earth 's axis of rotation is tilted , producing seasonal variations on the planet 's surface . The gravitational interaction between the Earth and Moon causes ocean tides , stabilizes the Earth 's orientation on its axis , and gradually slows its rotation .   Earth 's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years . About 71 % of Earth 's surface is covered with water , mostly by its oceans . The remaining 29 % is land consisting of continents and islands that together have many lakes , rivers and other sources of water that contribute to the hydrosphere . The majority of Earth 's polar regions are covered in ice , including the Antarctic ice sheet and the sea ice of the Arctic ice pack . Earth 's interior remains active with a solid iron inner core , a liquid outer core that generates the Earth 's magnetic field , and a convecting mantle that drives plate tectonics .   Within the first billion years of Earth 's history , life appeared in the oceans and began to affect the Earth 's atmosphere and surface , leading to the proliferation of aerobic and anaerobic organisms . Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago . Since then , the combination of Earth 's distance from the Sun , physical properties , and geological history have allowed life to evolve and thrive . In the history of the Earth , biodiversity has gone through long periods of expansion , occasionally punctuated by mass extinction events . Over 99 % of all species that ever lived on Earth are extinct . Estimates of the number of species on Earth today vary widely ; most species have not been described . Over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival . Humans have developed diverse societies and cultures ; politically , the world has about 200 sovereign states .


Earth's energy budget

Earth 's energy budget accounts for the energy Earth receives from the Sun . Much of this energy is lost when the earth re-radiates it back into outer space , and the rest of the energy is distributed throughout the five components of Earth 's climate system . This system is made up of earth 's water , ice , atmosphere , rocky crust , and all living things .   Quantifying changes in these amounts is required to accurately model the Earth 's climate .   Received radiation is unevenly distributed over the planet , because the Sun heats equatorial regions more than polar regions . Energy is absorbed by the atmosphere , hydrosphere , and lithosphere , and , in a process informally described as Earth 's heat engine , the solar heating is redistributed through evaporation of surface water , convection , rainfall , winds , and ocean circulation . When the incoming solar energy is balanced by an equal flow of heat to space , the Earth is said to be in radiative equilibrium and under that condition , global temperatures will be stable .   Disturbances of Earth 's radiative equilibrium , such as an increase of greenhouse gases , will change global temperatures in response . However , Earth 's energy balance and heat fluxes depend on many factors , such as atmospheric composition ( mainly aerosols and greenhouse gases ) , the albedo ( reflectivity ) of surface properties , cloud cover and vegetation and land use patterns . Changes in surface temperature due to Earth 's energy budget do not occur instantaneously , due to the inertia of the oceans and the cryosphere . The net heat flux is buffered primarily by becoming part of the ocean 's heat content , until a new equilibrium state is established between radiative forcings and the climate response .


Earth Summit 2002

The World Summit on Sustainable Development , WSSD or ONG Earth Summit 2002 took place in Johannesburg , South Africa , from 26 August to 4 September 2002 . It was convened to discuss sustainable development by the United Nations . WSSD gathered a number of leaders from business and non-governmental organizations , 10 years after the first Earth Summit in Rio de Janeiro . ( It was therefore also informally nicknamed `` Rio +10 '' . )


Earth in science fiction

An overwhelming majority of fiction is set on or features the Earth . However , authors of speculative fiction novels and writers and directors of science fiction film deal with Earth quite differently from authors of conventional fiction . Unbound from the same ties that bind authors of traditional fiction to the Earth , they can either completely ignore the Earth or use it as but one of many settings in a more complicated universe , exploring a number of common themes through examining outsiders perceptions of and interactions with Earth .


Earth in the Balance

Earth in the Balance : Ecology and the Human Spirit ( ISBN 0-452-26935-0 , paperback ISBN 1-85383-743-1 ) is a 1992 book written by Al Gore , published in June 1992 , shortly before he was elected Vice President in the 1992 presidential election . Known by the short title Earth in the Balance , the book explains the world 's ecological predicament and describes a range of policies to deal with the most pressing problems . It includes a proposed `` Global Marshall Plan '' to address current ecological issues .   Written while his son was recovering from a serious accident , Earth in the Balance became the first book written by a sitting U.S. Senator to make the New York Times bestseller list since John F. Kennedy 's Profiles in Courage .   In 1993 , Earth in the Balance was released in paperback and audiobook format on audio cassette tape .   It received the Robert F. Kennedy Center for Justice and Human Rights 1993 Book award given annually to a book that `` most faithfully and forcefully reflects Robert Kennedy 's purposes - his concern for the poor and the powerless , his struggle for honest and even-handed justice , his conviction that a decent society must assure all young people a fair chance , and his faith that a free democracy can act to remedy disparities of power and opportunity . ''   The book was followed by An Inconvenient Truth , a book that was the companion for a movie  narrated by Al Gore , shown at the 2006 Sundance Film Festival and released on 24 May 2006 .   In the Futurama episode `` Crimes of the Hot , '' Al Gore himself references the book and its `` far more popular '' fictional future sequel , Harry Potter and the Balance of Earth .


Earth shelter

An earth shelter is a structure (usually a house) with earth (soil) against the walls, on the roof, or that is entirely buried underground. Earth acts as thermal mass, making it easier to maintain a steady indoor air temperature and therefore reduces energy costs for heating or cooling. Earth sheltering became relatively popular after the mid 1970s, especially among environmentalists. However, the practice has been around for nearly as long as humans have been constructing their own shelters.


East Antarctic Ice Sheet

The East Antarctic Ice Sheet ( EAIS ) is one of two large ice sheets in Antarctica , and the largest on the entire planet . The EAIS lies between 45 ° west and 168 ° east longitudinally .   The EAIS is considerably larger in area and mass than the West Antarctic Ice Sheet ( WAIS ) . It is separated from the WAIS by the Transantarctic Mountains . The EAIS rests upon a large land mass , contrary to that of the WAIS , which rests mainly on bedrock below sea level . The EAIS is also home to the thickest ice on the frozen white continent , at 15,700 ft ( 4,800 m ) . More well known , however , is that the EAIS is home to the geographic South Pole as well as of the Amundsen-Scott South Pole Station .


East Antarctica

East Antarctica , also called Greater Antarctica , constitutes the majority ( two-thirds ) of the Antarctic continent , lying on the Indian Ocean side of the continent , separated from West Antarctica by the Transantarctic Mountains . It lies almost entirely within the Eastern Hemisphere and its name has been accepted for more than a century . It is generally higher than West Antarctica and includes the Gamburtsev Mountain Range in the centre .   Apart from small areas of the coast , East Antarctica is permanently covered by ice . The only terrestrial plant life is lichens , mosses and algae clinging to rocks , and there are a limited range of invertebrates including nematodes , springtails , mites and midges . The coasts are the breeding ground for various seabirds and penguins , and the leopard seal , Weddell seal , elephant seal , crabeater seal and Ross seal breed on the surrounding pack ice in summer .


East Coast of the United States

The East Coast of the United States is the coastline along which the Eastern United States meets the North Atlantic Ocean . This area is also known as the Eastern Seaboard , the Atlantic Coast , and the Atlantic Seaboard . The coastal states that have shoreline on the Atlantic Ocean are , from north to south , Maine , New Hampshire , Massachusetts , Rhode Island , Connecticut , Pennsylvania , New York , New Jersey , Delaware , Maryland , Virginia , North Carolina , South Carolina , Georgia , and Florida .


Eastern Time Zone

The Eastern Time Zone ( ET ) is a time zone encompassing 17 U.S. states in the eastern part of the contiguous United States , parts of eastern Canada , the state of Quintana Roo in Mexico , Panama in Central America , and the Caribbean Islands .   Places that use Eastern Standard Time ( EST ) when observing standard time ( autumn/winter ) are 5 hours behind Coordinated Universal Time ( UTC − 05:00 ) .   Eastern Daylight Time ( EDT ) , when observing daylight saving time DST ( spring/summer ) is 4 hours behind Coordinated Universal Time ( UTC − 04:00 ) .   In the northern parts of the time zone , on the second Sunday in March , at 2:00 a.m. EST , clocks are advanced to 3:00 a.m. EDT leaving a one-hour `` gap '' . On the first Sunday in November , at 2:00 a.m. EDT , clocks are moved back to 1:00 a.m. EST , thus `` duplicating '' one hour . Southern parts of the zone ( Panama and the Caribbean ) do not observe daylight saving time .


Ecology

Ecology ( from οἶκος , `` house '' , or `` environment '' ; - λογία , `` study of '' ) is the scientific analysis and study of interactions among organisms and their environment . It is an interdisciplinary field that includes biology , geography , and Earth science . Ecology includes the study of interactions that organisms have with each other , other organisms , and with abiotic components of their environment . Topics of interest to ecologists include the diversity , distribution , amount ( biomass ) , and number ( population ) of particular organisms , as well as cooperation and competition between organisms , both within and among ecosystems . Ecosystems are composed of dynamically interacting parts including organisms , the communities they make up , and the non-living components of their environment . Ecosystem processes , such as primary production , pedogenesis , nutrient cycling , and various niche construction activities , regulate the flux of energy and matter through an environment . These processes are sustained by organisms with specific life history traits , and the variety of organisms is called biodiversity . Biodiversity , which refers to the varieties of species , genes , and ecosystems , enhances certain ecosystem services .   Ecology is not synonymous with environment , environmentalism , natural history , or environmental science . It is closely related to evolutionary biology , genetics , and ethology . An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function . Ecologists seek to explain :   Life processes , interactions , and adaptations  The movement of materials and energy through living communities  The successional development of ecosystems  The abundance and distribution of organisms and biodiversity in the context of the environment .   There are many practical applications of ecology in conservation biology , wetland management , natural resource management ( agroecology , agriculture , forestry , agroforestry , fisheries ) , city planning ( urban ecology ) , community health , economics , basic and applied science , and human social interaction ( human ecology ) . For example , the Circles of Sustainability approach treats ecology as more than the environment ` out there ' . It is not treated as separate from humans . Organisms ( including humans ) and resources compose ecosystems which , in turn , maintain biophysical feedback mechanisms that moderate processes acting on living ( biotic ) and non-living ( abiotic ) components of the planet . Ecosystems sustain life-supporting functions and produce natural capital like biomass production ( food , fuel , fiber , and medicine ) , the regulation of climate , global biogeochemical cycles , water filtration , soil formation , erosion control , flood protection , and many other natural features of scientific , historical , economic , or intrinsic value .   The word `` ecology '' ( '' Ökologie '' ) was coined in 1866 by the German scientist Ernst Haeckel ( 1834 -- 1919 ) . Ecological thought is derivative of established currents in philosophy , particularly from ethics and politics . Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history . Modern ecology became a much more rigorous science in the late 19th century . Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory .


Econometrics

Econometrics is the application of statistical methods to economic data and is described as the branch of economics that aims to give empirical content to economic relations . More precisely , it is `` the quantitative analysis of actual economic phenomena based on the concurrent development of theory and observation , related by appropriate methods of inference . '' An introductory economics textbook describes econometrics as allowing economists `` to sift through mountains of data to extract simple relationships . '' The first known use of the term `` econometrics '' ( in cognate form ) was by Polish economist Paweł Ciompa in 1910 . Ragnar Frisch is credited with coining the term in the sense in which it is used today .   The basic tool for econometrics is the multiple linear regression model . Econometric theory uses statistical theory and mathematical statistics to evaluate and develop econometric methods . Econometricians try to find estimators that have desirable statistical properties including unbiasedness , efficiency , and consistency . Applied econometrics uses theoretical econometrics and real-world data for assessing economic theories , developing econometric models , analyzing economic history , and forecasting .


Economic growth

Economic growth is the increase in the inflation-adjusted market value of the goods and services produced by an economy over time . It is conventionally measured as the percent rate of increase in real gross domestic product , or real GDP , usually in per capita terms .   Growth is usually calculated in real terms -- i.e. , inflation-adjusted terms -- to eliminate the distorting effect of inflation on the price of goods produced . Measurement of economic growth uses national income accounting . Since economic growth is measured as the annual percent change of gross domestic product ( GDP ) , it has all the advantages and drawbacks of that measure .   The `` rate of economic growth '' refers to the geometric annual rate of growth in GDP between the first and the last year over a period of time . Implicitly , this growth rate is the trend in the average level of GDP over the period , which implicitly ignores the fluctuations in the GDP around this trend .   An increase in economic growth caused by more efficient use of inputs ( such as labor productivity , physical capital , energy or materials ) is referred to as intensive growth . GDP growth caused only by increases in the amount of inputs available for use ( increased population , new territory ) is called extensive growth .


Economic impacts of climate change

This article describes the economic impacts of climate change . Given the inherent nature of economic forecasting , which involves significant degrees of uncertainty , estimates of the results of global warming over the 21st century have varied widely . Many analyses , such as that of the Stern Review presented to the British Government , have predicted reductions by several percent of world gross domestic product due to climate related costs such as dealing with increased extreme weather events and stresses to low-lying areas due to sea level rises . Other studies by independent economists looking at the effects of climate change have found more ambiguous results around the range of net-neutral changes when all aspects of the issue are evaluated , though the issue remains intensely debated .


Economics

Economics ( UK English : -LSB- iːkəˈnɒmɪks -RSB- , -LSB- ɛkəˈnɒmɪks -RSB- US English : -LSB- ɛkəˈnɑːmɪks -RSB- , -LSB- ikəˈnɑːmɪks -RSB- ) is `` a social science concerned chiefly with description and analysis of the production , distribution , and consumption of goods and services '' .   Economics focuses on the behaviour and interactions of economic agents and how economies work . Consistent with this focus , textbooks often distinguish between microeconomics and macroeconomics . Microeconomics examines the behaviour of basic elements in the economy , including individual agents and markets , their interactions , and the outcomes of interactions . Individual agents may include , for example , households , firms , buyers , and sellers . Macroeconomics analyzes the entire economy ( meaning aggregated production , consumption , savings , and investment ) and issues affecting it , including unemployment of resources ( labour , capital , and land ) , inflation , economic growth , and the public policies that address these issues ( monetary , fiscal , and other policies ) .   Other broad distinctions within economics include those between positive economics , describing `` what is '' , and normative economics , advocating `` what ought to be '' ; between economic theory and applied economics ; between rational and behavioural economics ; and between mainstream economics and heterodox economics .   Economic analysis can be applied throughout society , in business , finance , health care , and government . Economic analyses is sometimes also applied to such diverse subjects as crime , education , the family , law , politics , religion , social institutions , war , science , and the environment .


Economics of global warming

The economics of global warming concerns the economic aspects of global warming ; this can inform policies that governments might consider in response . A number of factors make this a difficult problem from both economic and political perspectives : it is a long-term , intergenerational problem ; benefits and costs are distributed unequally both within and across countries ; and scientific and public opinions may diverge .   One of the most important greenhouse gases is carbon dioxide . Around 20 % of carbon dioxide which is emitted due to human activities can remain in the atmosphere for many thousands of years . The long time scales and uncertainty associated with global warming have led analysts to develop `` scenarios '' of future environmental , social and economic changes . These scenarios can help governments understand the potential consequences of their decisions .   The impacts of climate change include the loss of biodiversity , sea level rise , increased frequency and severity of some extreme weather events , and acidification of the oceans . Economists have attempted to quantify these impacts in monetary terms , but these assessments can be controversial .   The two main policy responses to global warming are to reduce greenhouse gas emissions ( climate change mitigation ) and to adapt to the impacts of global warming ( e.g. , by building levees in response to sea level rise ) . Another policy response which has recently received greater attention is geoengineering of the climate system ( e.g. injecting aerosols into the atmosphere to reflect sunlight away from the Earth 's surface ) .   One of the responses to the uncertainties of global warming is to adopt a strategy of sequential decision making . This strategy recognizes that decisions on global warming need to be made with incomplete information , and that decisions in the near term will have potentially long-term impacts . Governments might choose to use risk management as part of their policy response to global warming . For instance , a risk-based approach can be applied to climate impacts which are difficult to quantify in economic terms , e.g. , the impacts of global warming on indigenous peoples .   Analysts have assessed global warming in relation to sustainable development . Sustainable development considers how future generations might be affected by the actions of the current generation . In some areas , policies designed to address global warming may contribute positively towards other development objectives . In other areas , the cost of global warming policies may divert resources away from other socially and environmentally beneficial investments ( the opportunity costs of climate change policy ) .


Economy of Venezuela

The economy of Venezuela is largely based on the petroleum sector and manufacturing . Revenue from petroleum exports accounts for more than 50 % of the country 's GDP and roughly 95 % of total exports . Venezuela is the sixth largest member of OPEC by oil production . From the 1950s to the early 1980s the Venezuelan economy experienced a steady growth that attracted many immigrants , with the nation enjoying the highest standard of living in Latin America . During the collapse of oil prices in the 1980s the economy contracted , the monetary sign commenced a progressive devaluation , and inflation skyrocketed to reach peaks of 84 % in 1989 and 99 % in 1996 , three years prior to Hugo Chávez taking office .   Venezuela manufactures and exports heavy industry products such as steel , aluminium and cement , with production concentrated around Ciudad Guayana , near the Guri Dam , one of the largest in the world and the provider of about three-quarters of Venezuela 's electricity . Other notable manufacturing includes electronics and automobiles , as well as beverages , and foodstuffs . Agriculture in Venezuela accounts for approximately 3 % of GDP , 10 % of the labor force , and at least one-fourth of Venezuela 's land area . Venezuela exports rice , corn , fish , tropical fruit , coffee , pork , and beef . The country is not self-sufficient in most areas of agriculture .   In spite of strained relations between the two countries , the United States has been Venezuela 's most important trading partner . U.S. exports to Venezuela have included machinery , agricultural products , medical instruments , and cars . Venezuela is one of the top four suppliers of foreign oil to the United States . About 500 U.S. companies are represented in Venezuela . According to Central Bank of Venezuela , the government received from 1998 to 2008 around 325 billion USD through oil production and export in general , and according to the International Energy Agency , to August 2015 has production of 2.4 million barrels per day , 500,000 of which go to the United States of America .   Since Hugo Chávez 's `` socialist revolution '' half-dismantled its PDVSA oil giant corporation in 2002 by firing most of its 20,000-strong dissident professional human capital , and imposed stringent currency controls in 2003 in an attempt to prevent capital flight , there has been a steady decline in oil production and exports and a series of stern currency devaluations , disrupting the economy . Further yet , price controls , expropriation of numerous farmlands and various industries , among other disputable government policies including a near-total freeze on any access to foreign currency at reasonable `` official '' exchange rates , have resulted in severe shortages in Venezuela and steep price rises of all common goods , including food , water , household products , spare parts , tools and medical supplies ; forcing many manufacturers to either cut production or close down , with many ultimately abandoning the country , as has been the case with several technological firms and most automobile makers . In 2015 , Venezuela had over 100 % inflation -- the highest in the world and the highest in the country 's history at that time . The rate increased to nearly 500 % by the end of 2016 with Venezuela spiraling into hyperinflation while the population poverty rate was between 76 % to 80 % according to independent sources .


Economy of the United Kingdom

The United Kingdom is the fifth-largest national economy in the world measured by nominal gross domestic product ( GDP ) , ninth-largest in the world measured by purchasing power parity ( PPP ) , and nineteenth-largest in the world measured by GDP per capita , comprising 4 % of world GDP . It is the second-largest economy in the European Union by both metrics . In 2016 , the UK was 19/28 for GDP growth in Europe , with the third lowest unemployment rate .   In 2016 , the UK was the tenth-largest goods exporter in the world and the fifth-largest goods importer . In 2015 , the UK had the fourth-largest inward foreign direct investment , and in 2013 the UK had the second-largest outward foreign direct investment . It is one of the most globalised economies , and is composed of ( in descending order of size ) the economies of England , Scotland , Wales and Northern Ireland .   The service sector dominates the UK economy , contributing around 78 % of GDP ; the financial services industry is particularly important , and London is the world 's largest international financial centre . Britain 's aerospace industry is the second - or third-largest national aerospace industry depending on the method of measurement . Its pharmaceutical industry plays an important role in the economy and the UK has the third-highest share of global pharmaceutical research and development . Of the world 's 500 largest companies , 26 are headquartered in the UK . The British economy is boosted by North Sea oil and gas production ; its reserves were estimated at 2.9 billion barrels in 2015 , although it has been a net importer of oil since 2005 . There are significant regional variations in prosperity , with South East England and North East Scotland being the richest areas per capita . The size of London 's economy makes it the largest city by GDP in Europe .   In the 18th century the UK was the first country to industrialise , and during the 19th century it had a dominant role in the global economy , accounting for 9.1 % of the world 's GDP in 1870 . From the late 19th century the Second Industrial Revolution was also taking place rapidly in the United States and the German Empire ; this presented an increasing economic challenge for the UK . The costs of fighting World War I and World War II further weakened the UK 's relative position . In the 21st century , however , it remains a great power and has an influential role in the world economy .   Government involvement in the British economy is primarily exercised by Her Majesty 's Treasury , headed by the Chancellor of the Exchequer , and the Department for Business , Energy and Industrial Strategy . Since 1979 management of the economy has followed a broadly laissez-faire approach . The Bank of England is the UK 's central bank and its Monetary Policy Committee is responsible for setting interest rates , quantitative easing , and forward guidance .   The currency of the UK is the pound sterling , which is the world 's third-largest reserve currency after the United States dollar and the euro , and is also one of the ten most-valued currencies in the world .   The UK is a member of the Commonwealth of Nations , the European Union ( although negotiations to leave the EU are currently taking place ) , the G7 , the G8 , the G20 , the International Monetary Fund , the Organisation for Economic Co-operation and Development , the Organisation for Security and Co-operation in Europe , the World Bank , the World Trade Organisation , Asian Infrastructure Investment Bank and the United Nations .


Economy of the United States

The United States is the world 's largest national economy in nominal terms and second largest according to purchasing power parity ( PPP ) , representing 22 % of nominal global GDP and 17 % of gross world product ( GWP ) . The United States ' GDP was estimated to be $ 18.56 trillion in 2016 . The U.S. dollar is the currency most used in international transactions and is the world 's foremost reserve currency , backed by its science and technology , its military , the full faith of the US government to reimburse its debts , its central role in a range of international institutions since World War II and the petrodollar system . Several countries use it as their official currency , and in many others it is the de facto currency . The United States has a mixed economy and has maintained a stable overall GDP growth rate , a moderate unemployment rate , and high levels of research and capital investment . Its seven largest trading partners are Canada , China , Mexico , Japan , Germany , South Korea , and the United Kingdom .   The US has abundant natural resources , a well-developed infrastructure , and high productivity . It has the world 's ninth-highest per capita GDP ( nominal ) and tenth-highest per capita GDP ( PPP ) as of 2013 . Americans have the highest average household and employee income among OECD nations , and in 2010 had the fourth highest median household income , down from second highest in 2007 . It has been the world 's largest national economy ( not including colonial empires ) since at least the 1890s .   The U.S. is the world 's third largest producer of oil and natural gas . It is one of the largest trading nations in the world as well as the world 's second largest manufacturer , representing a fifth of the global manufacturing output . The US not only has the largest internal market for goods , but also dominates the trade in services . US total trade amounted to $ 4.93 T in 2012 . Of the world 's 500 largest companies , 128 are headquartered in the US .   The United States has one of the world 's largest and most influential financial markets . The New York Stock Exchange is by far the world 's largest stock exchange by market capitalization . Foreign investments made in the US total almost $ 2.4 trillion , while American investments in foreign countries total over $ 3.3 trillion . The economy of the U.S. leads in international ranking on venture capital and Global Research and Development funding . Consumer spending comprises 71 % of the US economy in 2013 . The United States has the largest consumer market in the world , with a household final consumption expenditure five times larger than Japan 's . The labor market has attracted immigrants from all over the world and its net migration rate is among the highest in the world . The U.S. is one of the top-performing economies in studies such as the Ease of Doing Business Index , the Global Competitiveness Report , and others .   The US economy went through an economic downturn following the financial crisis of 2007 -- 08 , with output as late as 2013 still below potential according to the Congressional Budget Office . The economy , however , began to recover in the second half of 2009 , and as of 2016 , unemployment had declined from a high of 10 % to 4.7 % .   In December 2014 , public debt was slightly more than 100 % of GDP . Domestic financial assets totaled $ 131 trillion and domestic financial liabilities totaled $ 106 trillion .


Ecosystem ecology

Ecosystem ecology is the integrated study of living ( biotic ) and non-living ( abiotic ) components of ecosystems and their interactions within an ecosystem framework . This science examines how ecosystems work and relates this to their components such as chemicals , bedrock , soil , plants , and animals .   Ecosystem ecology examines physical and biological structures and examines how these ecosystem characteristics interact with each other . Ultimately , this helps us understand how to maintain high quality water and economically viable commodity production . A major focus of ecosystem ecology is on functional processes , ecological mechanisms that maintain the structure and services produced by ecosystems . These include primary productivity ( production of biomass ) , decomposition , and trophic interactions .   Studies of ecosystem function have greatly improved human understanding of sustainable production of forage , fiber , fuel , and provision of water . Functional processes are mediated by regional-to-local level climate , disturbance , and management . Thus ecosystem ecology provides a powerful framework for identifying ecological mechanisms that interact with global environmental problems , especially global warming and degradation of surface water .   This example demonstrates several important aspects of ecosystems :  Ecosystem boundaries are often nebulous and may fluctuate in time  Organisms within ecosystems are dependent on ecosystem level biological and physical processes  Adjacent ecosystems closely interact and often are interdependent for maintenance of community structure and functional processes that maintain productivity and biodiversity   These characteristics also introduce practical problems into natural resource management . Who will manage which ecosystem ? Will timber cutting in the forest degrade recreational fishing in the stream ? These questions are difficult for land managers to address while the boundary between ecosystems remains unclear ; even though decisions in one ecosystem will affect the other . We need better understanding of the interactions and interdependencies of these ecosystems and the processes that maintain them before we can begin to address these questions .   Ecosystem ecology is an inherently interdisciplinary field of study . An individual ecosystem is composed of populations of organisms , interacting within communities , and contributing to the cycling of nutrients and the flow of energy . The ecosystem is the principal unit of study in ecosystem ecology .   Population , community , and physiological ecology provide many of the underlying biological mechanisms influencing ecosystems and the processes they maintain . Flowing of energy and cycling of matter at the ecosystem level are often examined in ecosystem ecology , but , as a whole , this science is defined more by subject matter than by scale . Ecosystem ecology approaches organisms and abiotic pools of energy and nutrients as an integrated system which distinguishes it from associated sciences such as biogeochemistry .   Biogeochemistry and hydrology focus on several fundamental ecosystem processes such as biologically mediated chemical cycling of nutrients and physical-biological cycling of water . Ecosystem ecology forms the mechanistic basis for regional or global processes encompassed by landscape-to-regional hydrology , global biogeochemistry , and earth system science .


Eemian

The Eemian ( also called the last interglacial , Sangamonian , Ipswichian , Mikulin , Kaydaky , Valdivia or Riss-Würm ) was the interglacial period which began about 130,000 years ago and ended about 115,000 years ago . It corresponds to Marine Isotope Stage 5e . Although sometimes referred to as the `` last interglacial '' ( in the `` most recent previous '' sense of `` last '' ) , it was the second-to-latest interglacial period of the current Ice Age , the most recent being the Holocene which extends to the present day ( having followed the last glacial period ) . The prevailing Eemian climate is believed to have been warmer than that of the Holocene .   The Eemian is known as the Ipswichian in the UK , the Mikulin interglacial in Russia , the Valdivia interglacial in Chile and the Riss-Würm interglacial in the Alps . Depending on how a specific publication defines the Sangamonian Stage of North America , the Eemian is equivalent to either all or part of it .


Effective temperature

The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation . Effective temperature is often used as an estimate of a body 's surface temperature when the body 's emissivity curve ( as a function of wavelength ) is not known .   When the star 's or planet 's net emissivity in the relevant wavelength band is less than unity ( less than that of a black body ) , the actual temperature of the body will be higher than the effective temperature . The net emissivity may be low due to surface or atmospheric properties , including greenhouse effect .


Effects of Hurricane Katrina in New Orleans

As the center of Hurricane Katrina passed southeast of New Orleans on August 29 , 2005 , winds downtown were in the Category 1 range with frequent intense gusts and tidal surge . Hurricane-force winds were experienced throughout the city , although the most severe portion of Katrina missed the city , hitting nearby St. Bernard and Plaquemines parishes . Hurricane Katrina made its final landfall in eastern St. Tammany Parish . The western eye wall passed directly over St. Tammany Parish , Louisiana as a Category 3 hurricane at about 9:45 am CST , August 29 , 2005 . The communities of Slidell , Avery Estates , Lakeshore Estates , Oak Harbor , Eden Isles and Northshore Beach were inundated by the storm surge that extended over six miles inland . The storm surge affected all 57 miles of St. Tammany Parish 's coastline , including Lacombe , Mandeville and Madisonville . The storm surge in the area of the Rigolets Pass was estimated to be 16 feet , not including wave action , declining to 7 ft at Madisonville . The surge had a second peak in eastern St. Tammany as the westerly winds from the southern eye wall pushed the surge to the east , backing up at the bottleneck of the Rigolets Pass .   In the City of New Orleans , the storm surge caused approximately 23 breaches in drainage canal and navigational canal levees and floodwalls . The failures of structures are considered by experts to be the worst engineering disaster in the history of the United States . By August 31 , 2005 , 80 % of New Orleans was flooded , with some parts under 15 ft of water . The famous French Quarter and Garden District escaped flooding because those areas are above sea level . Responsibility for the performance of the city 's levees belongs to the United States Army Corps of Engineers . The major breaches included the 17th Street Canal levee , the Industrial Canal levee , and the London Avenue Canal floodwall . These breaches caused the majority of the flooding , according to a June 2007 report by the American Society of Civil Engineers . The flood disaster halted oil production and refining which increased oil prices worldwide .   Between 80 and 90 percent of the residents of New Orleans were evacuated before the hurricane struck , testifying to some of the success of the evacuation measures . Despite this , many remained in the city , mainly those who did not have access to personal vehicles or who were isolated from the dissemination of news from the local governments . The Louisiana Superdome was used to house and support some of those who were unable to evacuate . Television shots frequently focused on the Superdome as a symbol of the flooding occurring in New Orleans .   The disaster had major implications for a large segment of the population , economy , and politics of the entire United States . It has prompted a Congressional review of the Army Corps of Engineers and the failure of portions of the federally built flood protection system which experts agree should have protected the city 's inhabitants from Katrina 's surge . Katrina has also stimulated significant research in the academic community into urban planning , real estate finance , and economic issues in the wake of a natural disaster .


Effects of climate change on plant biodiversity

Environmental conditions play a key role in defining the function and distribution of plants , in combination with other factors . Changes in long term environmental conditions that can be collectively coined climate change are known to have had enormous impacts on current plant diversity patterns ; further impacts are expected in the future . It is predicted that climate change will remain one of the major drivers of biodiversity patterns in the future .


Effects of climate change on terrestrial animals

Climate change has had a significant direct effect on terrestrial animals , by being a major driver of the processes of speciation and extinction . The best known example of this is the Carboniferous Rainforest Collapse which occurred 350 million years ago . This event decimated amphibian populations and spurred on the evolution of reptiles .   Climate change is a natural event that has occurred throughout history . However , with the recent increased emission of CO2 in the Earth 's atmosphere , abrupt climate change has occurred . It has been hypothesized that anthropogenic greenhouse gas forcing has significantly influenced global climate since about 8000 before present ( Van Hoof 2006 ) .   Animals have had specific responses to climate change . Species respond to climate changes by migration , adaptation , or if neither of those occur , death . These migrations can sometimes follow an animal 's preferred temperature , elevation , soil , etc. , as said terrain moves due to climate change . Adaptation can be either genetic or phenological , and death can occur in a local population only ( extirpation ) or as an entire species , otherwise known as extinction .   Climate changes is projected to affect individual organisms , populations , species distributions and ecosystem composition and function both directly ( ex . Increased temperatures and changes in precipitation ) and indirectly ( through climate changing the intensity and frequency of disturbances such as wildfires and severe storms ) ( IPCC 2002 ) .   Every organism has a unique set of preferences or requirements , a niche and biodiversity has been tied to the diversity of animals ' niches . These can include or be affected by temperature , aridity , resource availability , habitat requirements , enemies , soil characteristics , competitors , and pollinators . Since the factors that compose a niche can be so complex and interconnected , the niches of many animals are bound to be affected by climate change ( Parmesan Yohe 2003 ) .   One study done by Camille Parmesan and Gary Yohe from University of Texas , Austin shows the global fingerprint of climate change on natural systems . The results of their global analysis of 334 species were recorded to demonstrate the correlation of patterns consistent with global climate change of the 20th century . Using the IPCC 's ( Intergovernmental Panel on Climate Change ) ` levels of confidence ' , this study proved significant nonrandom behavioral changes due to global climate change with very high confidence ( > 95 ) . Furthermore , an accuracy of 74-91 % change in species has displayed predicted change for species in response to climate change .


Effects of global warming

The effects of global warming are the environmental and social changes caused ( directly or indirectly ) by human emissions of greenhouse gases . There is a scientific consensus that climate change is occurring , and that human activities are the primary driver . Many impacts of climate change have already been observed , including glacier retreat , changes in the timing of seasonal events ( e.g. , earlier flowering of plants ) , and changes in agricultural productivity .   Future effects of climate change will vary depending on climate change policies and social development . The two main policies to address climate change are reducing human greenhouse gas emissions ( climate change mitigation ) and adapting to the impacts of climate change . Geoengineering is another policy option .   Near-term climate change policies could significantly affect long-term climate change impacts . Stringent mitigation policies might be able to limit global warming ( in 2100 ) to around 2 ° C or below , relative to pre-industrial levels . Without mitigation , increased energy demand and extensive use of fossil fuels might lead to global warming of around 4 ° C. Higher magnitudes of global warming would be more difficult to adapt to , and would increase the risk of negative impacts .


Effects of global warming on human health

The effects of global warming include effects on human health . The observed and projected increased frequency and severity of climate related impacts will further exacerbate the effects on human health . This article describes some of those effects on individuals and populations .


Effects of global warming on humans

Climate change has brought about possibly permanent alterations to Earth 's geological , biological and ecological systems . These changes have led to the emergence of large-scale environmental hazards to human health , such as extreme weather , ozone depletion , increased danger of wildland fires , loss of biodiversity , stresses to food-producing systems and the global spread of infectious diseases . The World Health Organization ( WHO ) estimates that 160,000 deaths , since 1950 , are directly attributable to climate change . Many believe this to be a conservative estimate .   To date , a neglected aspect of the climate change debate , much less research has been conducted on the impacts of climate change on health , food supply , economic growth , migration , security , societal change , and public goods , such as drinking water , than on the geophysical changes related to global warming . Human impacts can be both negative and positive . Climatic changes in Siberia , for instance , are expected to improve food production and local economic activity , at least in the short to medium term . Numerous studies suggest , however , that the current and future impacts of climate change on human society are and will continue to be overwhelmingly negative .   The majority of the adverse effects of climate change are experienced by poor and low-income communities around the world , who have much higher levels of vulnerability to environmental determinants of health , wealth and other factors , and much lower levels of capacity available for coping with environmental change . A report on the global human impact of climate change published by the Global Humanitarian Forum in 2009 , estimated more than 300,000 deaths and about $ 125 billion in economic losses each year , and indicating that most climate change induced mortality is due to worsening floods and droughts in developing countries .


Effects of global warming on oceans

Global warming can affect sea levels , coastlines , ocean acidification , ocean currents , seawater , sea surface temperatures , tides , the sea floor , weather , and trigger several changes in ocean bio-geochemistry ; all of these affect the functioning of a society .


Efficient energy use

Efficient energy use , sometimes simply called energy efficiency , is the goal to reduce the amount of energy required to provide products and services . For example , insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature . Installing fluorescent lights , LED lights or natural skylights reduces the amount of energy required to attain the same level of illumination compared with using traditional incandescent light bulbs . Improvements in energy efficiency are generally achieved by adopting a more efficient technology or production process or by application of commonly accepted methods to reduce energy losses .   There are many motivations to improve energy efficiency . Reducing energy use reduces energy costs and may result in a financial cost saving to consumers if the energy savings offset any additional costs of implementing an energy efficient technology . Reducing energy use is also seen as a solution to the problem of reducing greenhouse gas emissions . According to the International Energy Agency , improved energy efficiency in buildings , industrial processes and transportation could reduce the world 's energy needs in 2050 by one third , and help control global emissions of greenhouse gases .   Energy efficiency and renewable energy are said to be the twin pillars of sustainable energy policy and are high priorities in the sustainable energy hierarchy . In many countries energy efficiency is also seen to have a national security benefit because it can be used to reduce the level of energy imports from foreign countries and may slow down the rate at which domestic energy resources are depleted .


Effigy Mounds National Monument

Effigy Mounds National Monument preserves more than 200 prehistoric mounds built by Native Americans . Numerous effigy mounds are shaped like animals , including bears and birds . These were built mostly in the first millennium , by peoples of the Woodland Culture . As of 2017 , they have been featured on the US quarter .   The monument is located primarily in Allamakee County , with a small part in Clayton County , Iowa , in the midwestern United States . The park 's visitor center is located in Harpers Ferry , Iowa , just north of Marquette .


El Niño

El Niño -LSB- ɛl_ˈniːnjoʊ -RSB- ( -LSB- el ˈniɲo -RSB- ) is the warm phase of the El Niño Southern Oscillation ( commonly called ENSO ) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific ( between approximately the International Date Line and 120 ° W ) , including off the Pacific coast of South America . El Niño Southern Oscillation refers to the cycle of warm and cold temperatures , as measured by sea surface temperature , SST , of the tropical central and eastern Pacific Ocean . El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific . The cool phase of ENSO is called `` La Niña '' with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific . The ENSO cycle , both El Niño and La Niña , cause global changes of both temperatures and rainfall .   Developing countries that are dependent upon agriculture and fishing , particularly those bordering the Pacific Ocean , are usually most affected . In American Spanish , the capitalized term `` El Niño '' refers to `` the little boy '' , so named because the pool of warm water in the Pacific near South America is often at its warmest around Christmas . The original name , `` El Niño de Navidad '' , traces its origin centuries back to Peruvian fisherman , who named the weather phenomenon in reference to the newborn Christ . `` La Niña '' , chosen as the ` opposite ' of El Niño , literally translates to `` the little girl '' .


El Niño–Southern Oscillation

El Niño -- Southern Oscillation ( ENSO ) is an irregularly periodical variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean , affecting much of the tropics and subtropics . The warming phase is known as El Niño and the cooling phase as La Niña . Southern Oscillation is the accompanying atmospheric component , coupled with the sea temperature change : El Niño is accompanied with high , and La Niña with low air surface pressure in the tropical western Pacific . The two periods last several months each ( typically occur every few years ) and their effects vary in intensity .   The two phases relate to the Walker circulation , discovered by Gilbert Walker during the early twentieth century . The Walker circulation is caused by the pressure gradient force that results from a high pressure system over the eastern Pacific Ocean , and a low pressure system over Indonesia . When the Walker circulation weakens or reverses , an El Niño results , causing the ocean surface to be warmer than average , as upwelling of cold water occurs less or not at all . An especially strong Walker circulation causes a La Niña , resulting in cooler ocean temperatures due to increased upwelling .   Mechanisms that cause the oscillation remain under study . The extremes of this climate pattern 's oscillations cause extreme weather ( such as floods and droughts ) in many regions of the world . Developing countries dependent upon agriculture and fishing , particularly those bordering the Pacific Ocean , are the most affected .


El Salvador

El Salvador ( -LSB- ɛl_ˈsælvədɔr -RSB- -LSB- el salβaˈðor -RSB- ) , officially the Republic of El Salvador ( -LSB- República de El Salvador , links = no -RSB- , literally `` Republic of The Savior '' ) , is the smallest and the most densely populated country in Central America . El Salvador 's capital and largest city is San Salvador . , the country had a population of approximately 6.38 million , consisting largely of Mestizos of European and Indigenous American descent .   El Salvador was for centuries inhabited by several Mesoamerican nations , especially the Cuzcatlecs , as well as the Lenca and Maya . In the early 16th century , the Spanish Empire conquered the territory , incorporating it into the Viceroyalty of New Spain ruled from Mexico City . In 1821 , the country achieved independence from Spain as part of the First Mexican Empire , only to further secede as part of the Federal Republic of Central America in 1823 . Upon the republic 's dissolution in 1841 , El Salvador became sovereign until forming a short-lived union with Honduras and Nicaragua called the Greater Republic of Central America , which lasted from 1895 to 1898 .   From the late 19th to the mid-20th century , El Salvador endured chronic political and economic instability characterized by coups , revolts , and a succession of authoritarian rulers . Persistent socioeconomic inequality and civil unrest culminated in the devastating Salvadoran Civil War ( 1979 -- 1992 ) , which was fought between the military-led government and a coalition of left-wing guerrilla groups . The conflict ended with a negotiated settlement that established a multiparty constitutional republic , which remains in place to this day .   El Salvador 's economy was historically dominated by agriculture , beginning with the indigo plant ( añil '' in Spanish ) , the most important crop during the colonial period , and followed thereafter by coffee , which by the early 20th century accounted for 90 percent of export earnings . El Salvador has since reduced its dependence on coffee and embarked on diversifying the economy by opening up trade and financial links and expanding the manufacturing sector . The colón , the official currency of El Salvador since 1892 , was replaced by the U.S. dollar in 2001 .   , El Salvador ranks 12th among Latin American countries in terms of the Human Development Index and fourth in Central America ( behind Panama , Costa Rica , and Belize ) due in part to ongoing rapid industrialisation . However , the country continues to struggle with high rates of poverty , inequality , and crime .


Electric vehicle

An electric vehicle , also called an electric drive vehicle , uses one or more electric motors or traction motors for propulsion . An electric vehicle may be powered through a collector system by electricity from off-vehicle sources , or may be self-contained with a battery , solar panels or a generator to convert fuel to electricity . EVs include road and rail vehicles , surface and underwater vessels , electric aircraft and electric spacecraft .   EVs first came into existence in the mid-19th century , when electricity was among the preferred methods for motor vehicle propulsion , providing a level of comfort and ease of operation that could not be achieved by the gasoline cars of the time . The internal combustion engine has been the dominant propulsion method for motor vehicles for almost 100 years , but electric power has remained commonplace in other vehicle types , such as trains and smaller vehicles of all types .   In the 21st century , EVs saw a resurgence due to technological developments and an increased focus on renewable energy . Government incentives to increase adoptions were introduced , including in the United States and the European Union .


Electrical grid

An electrical grid is an interconnected network for delivering electricity from producers to consumers . It consists of generating stations that produce electrical power , high voltage transmission lines that carry power from distant sources to demand centers , and distribution lines that connect individual customers .   Power stations may be located near a fuel source , at a dam site , or to take advantage of renewable energy sources , and are often located away from heavily populated areas . They are usually quite large to take advantage of the economies of scale . The electric power which is generated is stepped up to a higher voltage at which it connects to the electric power transmission network .   The bulk power transmission network will move the power long distances , sometimes across international boundaries , until it reaches its wholesale customer ( usually the company that owns the local electric power distribution network ) .   On arrival at a substation , the power will be stepped down from a transmission level voltage to a distribution level voltage . As it exits the substation , it enters the distribution wiring . Finally , upon arrival at the service location , the power is stepped down again from the distribution voltage to the required service voltage ( s ) .   Electrical grids vary in size from covering a single building through national grids which cover whole countries , to transnational grids which can cross continents .


Electricity generation

Electricity generation is the process of generating electric power from sources of primary energy . For electric utilities , it is the first process in the delivery of electricity to consumers . The other processes as transmission , distribution , energy storage and recovery using pumped-storage methods are normally carried out by the electric power industry . Electricity is most often generated at a power station by electromechanical generators , primarily driven by heat engines fuelled by combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind . Other energy sources include solar photovoltaics and geothermal power .


Electricity sector in Argentina

The electricity sector in Argentina constitutes the third largest power market in Latin America . It relies mostly on thermal generation ( 60 % of installed capacity ) and hydropower generation ( 36 % ) . The country still has a large untapped hydroelectric potential . The prevailing natural gas-fired thermal generation is at risk due to the uncertainty about future gas supply .   Faced with rising electricity demand ( over 6 % annually ) and declining reserve margins , the government of Argentina is in the process of commissioning large projects , both in the generation and transmission sectors . To keep up with rising demand , it is estimated that about 1,000 MW of new generation capacity are needed each year . An important number of these projects are being financed by the government through trust funds , while independent private initiative is still limited as it has not fully recovered yet from the effects of the Argentine economic crisis .   The electricity sector was unbundled in generation , transmission and distribution by the reforms carried out in the early 1990s . Generation occurs in a competitive and mostly liberalized market in which 75 % of the generation capacity is owned by private utilities . In contrast , the transmission and distribution sectors are highly regulated and much less competitive than generation .


Electromagnetic radiation

In physics , electromagnetic radiation ( EM radiation or EMR ) refers to the waves ( or their quanta , photons ) of the electromagnetic field , propagating ( radiating ) through space carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , ( visible ) light , ultraviolet , X - , and gamma radiation .   Classically , electromagnetic radiation consists of electromagnetic waves , which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum . The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation , forming a transverse wave . The wavefront of electromagnetic waves emitted from a point source ( such as a lightbulb ) is a sphere . The position of an electromagnetic wave within the electromagnetic spectrum could be characterized by either its frequency of oscillation or its wavelength . The electromagnetic spectrum includes , in order of increasing frequency and decreasing wavelength : radio waves , microwaves , infrared radiation , visible light , ultraviolet radiation , X-rays and gamma rays .   Electromagnetic waves are produced whenever charged particles are accelerated , and these waves can subsequently interact with other charged particles . EM waves carry energy , momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact . Quanta of EM waves are called photons , whose rest mass is zero , but whose energy , or equivalent total ( relativistic ) mass , is not zero so they are still affected by gravity . Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ( `` radiate '' ) without the continuing influence of the moving charges that produced them , because they have achieved sufficient distance from those charges . Thus , EMR is sometimes referred to as the far field . In this language , the near field refers to EM fields near the charges and current that directly produced them , specifically , electromagnetic induction and electrostatic induction phenomena .   In the quantum theory of electromagnetism , EMR consists of photons , the elementary particles responsible for all electromagnetic interactions . Quantum effects provide additional sources of EMR , such as the transition of electrons to lower energy levels in an atom and black-body radiation . The energy of an individual photon is quantized and is greater for photons of higher frequency . This relationship is given by Planck 's equation E = hν , where E is the energy per photon , ν is the frequency of the photon , and h is Planck 's constant . A single gamma ray photon , for example , might carry ~ 100,000 times the energy of a single photon of visible light .   The effects of EMR upon chemical compounds and biological organisms depend both upon the radiation 's power and its frequency . EMR of visible or lower frequencies ( i.e. , visible light , infrared , microwaves , and radio waves ) is called non-ionizing radiation , because its photons do not individually have enough energy to ionize atoms or molecules . The effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons . In contrast , high ultraviolet , X-rays and gamma rays are called ionizing radiation since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds . These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating , and can be a health hazard .