Climate is the statistics of weather over long periods of time.[1][2] It is measured by assessing the patterns of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate differs from weather, in that weather only describes the short-term conditions of these variables in a given region.

A region's climate is generated by the climate system, which has five components: atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere.[3]

The climate of a location is affected by its latitude, terrain, and altitude, as well as nearby water bodies and their currents. Climates can be classified according to the average and the typical ranges of different variables, most commonly temperature and precipitation. The most commonly used classification scheme was the Köppen climate classification. The Thornthwaite system,[4] in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and is used in studying biological diversity and how climate change affects it. The Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.

Paleoclimatology is the study of ancient climates. Since direct observations of climate are not available before the 19th century, paleoclimates are inferred from proxy variables that include non-biotic evidence such as sediments found in lake beds and ice cores, and biotic evidence such as tree rings and coral. Climate models are mathematical models of past, present and future climates. Climate change may occur over long and short timescales from a variety of factors; recent warming is discussed in global warming. Global warming results in redistributions. For example, "a 3°C change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km in latitude (in the temperate zone) or 500 m in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones".[5][6]


WorldMap cold hot
Generalistic map of global temperature in simple warm and cold differential.
WorldMap cold warm hot
Same but in threefold levels of temperature differential.

Climate (from Ancient Greek klima, meaning inclination) is commonly defined as the weather averaged over a long period.[7] The standard averaging period is 30 years,[8] but other periods may be used depending on the purpose. Climate also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. The Intergovernmental Panel on Climate Change (IPCC) 2001 glossary definition is as follows:

Climate in a narrow sense is usually defined as the "average weather," or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.[9]

The World Meteorological Organization (WMO) describes climate "normals" as "reference points used by climatologists to compare current climatological trends to that of the past or what is considered 'normal'. A Normal is defined as the arithmetic average of a climate element (e.g. temperature) over a 30-year period. A 30 year period is used, as it is long enough to filter out any interannual variation or anomalies, but also short enough to be able to show longer climatic trends."[10] The WMO originated from the International Meteorological Organization which set up a technical commission for climatology in 1929. At its 1934 Wiesbaden meeting the technical commission designated the thirty-year period from 1901 to 1930 as the reference time frame for climatological standard normals. In 1982 the WMO agreed to update climate normals, and these were subsequently completed on the basis of climate data from 1 January 1961 to 31 December 1990.[11]

The difference between climate and weather is usefully summarized by the popular phrase "Climate is what you expect, weather is what you get."[12] Over historical time spans there are a number of nearly constant variables that determine climate, including latitude, altitude, proportion of land to water, and proximity to oceans and mountains. These change only over periods of millions of years due to processes such as plate tectonics. Other climate determinants are more dynamic: the thermohaline circulation of the ocean leads to a 5 °C (9 °F) warming of the northern Atlantic Ocean compared to other ocean basins.[13] Other ocean currents redistribute heat between land and water on a more regional scale. The density and type of vegetation coverage affects solar heat absorption,[14] water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming or global cooling. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least insofar as the determinants of historical climate change are concerned.[15]

Climate classification

World koppen
Worldwide Köppen climate classifications

There are several ways to classify climates into similar regimes. Originally, climes were defined in Ancient Greece to describe the weather depending upon a location's latitude. Modern climate classification methods can be broadly divided into genetic methods, which focus on the causes of climate, and empiric methods, which focus on the effects of climate. Examples of genetic classification include methods based on the relative frequency of different air mass types or locations within synoptic weather disturbances. Examples of empiric classifications include climate zones defined by plant hardiness,[16] evapotranspiration,[17] or more generally the Köppen climate classification which was originally designed to identify the climates associated with certain biomes. A common shortcoming of these classification schemes is that they produce distinct boundaries between the zones they define, rather than the gradual transition of climate properties more common in nature.

Bergeron and Spatial Synoptic

The simplest classification is that involving air masses. The Bergeron classification is the most widely accepted form of air mass classification.[18] Air mass classification involves three letters. The first letter describes its moisture properties, with c used for continental air masses (dry) and m for maritime air masses (moist). The second letter describes the thermal characteristic of its source region: T for tropical, P for polar, A for Arctic or Antarctic, M for monsoon, E for equatorial, and S for superior air (dry air formed by significant downward motion in the atmosphere). The third letter is used to designate the stability of the atmosphere. If the air mass is colder than the ground below it, it is labeled k. If the air mass is warmer than the ground below it, it is labeled w.[19] While air mass identification was originally used in weather forecasting during the 1950s, climatologists began to establish synoptic climatologies based on this idea in 1973.[20]

Based upon the Bergeron classification scheme is the Spatial Synoptic Classification system (SSC). There are six categories within the SSC scheme: Dry Polar (similar to continental polar), Dry Moderate (similar to maritime superior), Dry Tropical (similar to continental tropical), Moist Polar (similar to maritime polar), Moist Moderate (a hybrid between maritime polar and maritime tropical), and Moist Tropical (similar to maritime tropical, maritime monsoon, or maritime equatorial).[21]


Monthly average surface temperatures from 1961–1990. This is an example of how climate varies with location and season
BlueMarble monthlies animation
Monthly global images from NASA Earth Observatory (interactive SVG)

The Köppen classification depends on average monthly values of temperature and precipitation. The most commonly used form of the Köppen classification has five primary types labeled A through E. These primary types are A) tropical, B) dry, C) mild mid-latitude, D) cold mid-latitude, and E) polar. The five primary classifications can be further divided into secondary classifications such as rainforest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic climate, Mediterranean climate, desert, steppe, subarctic climate, tundra, and polar ice cap.

Rainforests are characterized by high rainfall, with definitions setting minimum normal annual rainfall between 1,750 millimetres (69 in) and 2,000 millimetres (79 in). Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year.[22]

A monsoon is a seasonal prevailing wind which lasts for several months, ushering in a region's rainy season.[23] Regions within North America, South America, Sub-Saharan Africa, Australia and East Asia are monsoon regimes.[24]

Globalcldfr amo 200207-201504 lrg
The world's cloudy and sunny spots. NASA Earth Observatory map using data collected between July 2002 and April 2015.[25]

A tropical savanna is a grassland biome located in semiarid to semi-humid climate regions of subtropical and tropical latitudes, with average temperatures remain at or above 18 °C (64 °F) year round and rainfall between 750 millimetres (30 in) and 1,270 millimetres (50 in) a year. They are widespread on Africa, and are found in India, the northern parts of South America, Malaysia, and Australia.[26]

5 11 15 Brian AquabyMonth
Cloud cover by month for 2014. NASA Earth Observatory[27][28]

The humid subtropical climate zone where winter rainfall (and sometimes snowfall) is associated with large storms that the westerlies steer from west to east. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones.[29] Humid subtropical climates lie on the east side of continents, roughly between latitudes 20° and 40° degrees away from the equator.[30]

A humid continental climate is marked by variable weather patterns and a large seasonal temperature variance. Places with more than three months of average daily temperatures above 10 °C (50 °F) and a coldest month temperature below −3 °C (27 °F) and which do not meet the criteria for an arid or semiarid climate, are classified as continental.[31]

An oceanic climate is typically found along the west coasts at the middle latitudes of all the world's continents, and in southeastern Australia, and is accompanied by plentiful precipitation year-round.[32]

The Mediterranean climate regime resembles the climate of the lands in the Mediterranean Basin, parts of western North America, parts of Western and South Australia, in southwestern South Africa and in parts of central Chile. The climate is characterized by hot, dry summers and cool, wet winters.[33]

A steppe is a dry grassland with an annual temperature range in the summer of up to 40 °C (104 °F) and during the winter down to −40 °C (−40 °F).[34]

A subarctic climate has little precipitation,[35] and monthly temperatures which are above 10 °C (50 °F) for one to three months of the year, with permafrost in large parts of the area due to the cold winters. Winters within subarctic climates usually include up to six months of temperatures averaging below 0 °C (32 °F).[36]

Map of arctic tundra

Tundra occurs in the far Northern Hemisphere, north of the taiga belt, including vast areas of northern Russia and Canada.[37]

A polar ice cap, or polar ice sheet, is a high-latitude region of a planet or moon that is covered in ice. Ice caps form because high-latitude regions receive less energy as solar radiation from the sun than equatorial regions, resulting in lower surface temperatures.[38]

A desert is a landscape form or region that receives very little precipitation. Deserts usually have a large diurnal and seasonal temperature range, with high or low, depending on location daytime temperatures (in summer up to 45 °C or 113 °F), and low nighttime temperatures (in winter down to 0 °C or 32 °F) due to extremely low humidity. Many deserts are formed by rain shadows, as mountains block the path of moisture and precipitation to the desert.[39]


Precipitation by month

Devised by the American climatologist and geographer C. W. Thornthwaite, this climate classification method monitors the soil water budget using evapotranspiration.[40] It monitors the portion of total precipitation used to nourish vegetation over a certain area.[41] It uses indices such as a humidity index and an aridity index to determine an area's moisture regime based upon its average temperature, average rainfall, and average vegetation type.[42] The lower the value of the index in any given area, the drier the area is.

The moisture classification includes climatic classes with descriptors such as hyperhumid, humid, subhumid, subarid, semi-arid (values of −20 to −40), and arid (values below −40).[43] Humid regions experience more precipitation than evaporation each year, while arid regions experience greater evaporation than precipitation on an annual basis. A total of 33 percent of the Earth's landmass is considered either arid or semi-arid, including southwest North America, southwest South America, most of northern and a small part of southern Africa, southwest and portions of eastern Asia, as well as much of Australia.[44] Studies suggest that precipitation effectiveness (PE) within the Thornthwaite moisture index is overestimated in the summer and underestimated in the winter.[45] This index can be effectively used to determine the number of herbivore and mammal species numbers within a given area.[46] The index is also used in studies of climate change.[45]

Thermal classifications within the Thornthwaite scheme include microthermal, mesothermal, and megathermal regimes. A microthermal climate is one of low annual mean temperatures, generally between 0 °C (32 °F) and 14 °C (57 °F) which experiences short summers and has a potential evaporation between 14 centimetres (5.5 in) and 43 centimetres (17 in).[47] A mesothermal climate lacks persistent heat or persistent cold, with potential evaporation between 57 centimetres (22 in) and 114 centimetres (45 in).[48] A megathermal climate is one with persistent high temperatures and abundant rainfall, with potential annual evaporation in excess of 114 centimetres (45 in).[49]



Global Temperature Anomaly
Global mean surface temperature change since 1880. Source: NASA GISS

Details of the modern climate record are known through the taking of measurements from such weather instruments as thermometers, barometers, and anemometers during the past few centuries. The instruments used to study weather over the modern time scale, their known error, their immediate environment, and their exposure have changed over the years, which must be considered when studying the climate of centuries past.[50]


Paleoclimatology is the study of past climate over a great period of the Earth's history. It uses evidence from ice sheets, tree rings, sediments, coral, and rocks to determine the past state of the climate. It demonstrates periods of stability and periods of change and can indicate whether changes follow patterns such as regular cycles.[51]

Climate change

Vostok Petit data
Variations in CO2, temperature and dust from the Vostok ice core over the past 450,000 years

Climate change is the variation in global or regional climates over time. It reflects changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities.[52][53]

2015 – Warmest Global Year on Record (since 1880) – Colors indicate temperature anomalies (NASA/NOAA; 20 January 2016).[54]

In recent usage, especially in the context of environmental policy, the term "climate change" often refers only to changes in modern climate, including the rise in average surface temperature known as global warming. In some cases, the term is also used with a presumption of human causation, as in the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations.[55]

Earth has undergone periodic climate shifts in the past, including four major ice ages. These consisting of glacial periods where conditions are colder than normal, separated by interglacial periods. The accumulation of snow and ice during a glacial period increases the surface albedo, reflecting more of the Sun's energy into space and maintaining a lower atmospheric temperature. Increases in greenhouse gases, such as by volcanic activity, can increase the global temperature and produce an interglacial period. Suggested causes of ice age periods include the positions of the continents, variations in the Earth's orbit, changes in the solar output, and volcanism.[56]

Climate models

Climate models use quantitative methods to simulate the interactions of the atmosphere,[57] oceans, land surface and ice. They are used for a variety of purposes; from the study of the dynamics of the weather and climate system, to projections of future climate. All climate models balance, or very nearly balance, incoming energy as short wave (including visible) electromagnetic radiation to the earth with outgoing energy as long wave (infrared) electromagnetic radiation from the earth. Any imbalance results in a change in the average temperature of the earth.

The most talked-about applications of these models in recent years have been their use to infer the consequences of increasing greenhouse gases in the atmosphere, primarily carbon dioxide (see greenhouse gas). These models predict an upward trend in the global mean surface temperature, with the most rapid increase in temperature being projected for the higher latitudes of the Northern Hemisphere.

Models can range from relatively simple to quite complex:

  • Simple radiant heat transfer model that treats the earth as a single point and averages outgoing energy
  • this can be expanded vertically (radiative-convective models), or horizontally
  • finally, (coupled) atmosphere–ocean–sea ice global climate models discretise and solve the full equations for mass and energy transfer and radiant exchange.[58]

Climate forecasting is used by some scientists to predict climate change. In 1997 the prediction division of the International Research Institute for Climate and Society at Columbia University began generating seasonal climate forecasts on a real-time basis. To produce these forecasts an extensive suite of forecasting tools was developed, including a multimodel ensemble approach that required thorough validation of each model's accuracy level in simulating interannual climate variability.[59]

See also


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Further reading

External links

Climate change

Climate change occurs when changes in Earth's climate system result in new weather patterns that last for at least a few decades, and maybe for millions of years. The climate system is comprised of five interacting parts, the atmosphere (air), hydrosphere (water), cryosphere (ice and permafrost), biosphere (living things), and lithosphere (earth's crust and upper mantle). The climate system receives nearly all of its energy from the sun, with a relatively tiny amount from earth's interior. The climate system also gives off energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.

As this energy moves through Earth's climate system, it creates Earth's weather and long-term averages of weather are called "climate". Changes in the long term average are called "climate change". Such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter Earth's energy budget. Examples include cyclical ocean patterns such as the well-known El Nino Southern Oscillation and less familiar Pacific decadal oscillation and Atlantic multidecadal oscillation. Climate change can also result from "external forcing", when events outside of the climate system's five parts nonetheless produce changes within the system. Examples include changes in solar output and volcanism.

Human activities can also change earth's climate, and are presently driving climate change through global warming. There is no general agreement in scientific, media or policy documents as to the precise term to be used to refer to anthropogenic forced change; either "global warming" or "climate change" may be used.The field of climatology incorporates many disparate fields of research. For ancient periods of climate change, researchers rely on evidence preserved in climate proxies, such as ice cores, ancient tree rings, geologic records of changes in sea level, and glacial geology. Physical evidence of current climate change covers many independent lines of evidence, a few of which are temperature records, the disappearance of ice, and extreme weather events.

Climate change denial

Climate change denial, or global warming denial, is part of the global warming controversy. It involves denial, dismissal, or unwarranted doubt that contradicts the scientific opinion on climate change, including the extent to which it is caused by humans, its impacts on nature and human society, or the potential of adaptation to global warming by human actions. Some deniers endorse the term, while others prefer the term climate change skepticism. Several scientists have noted that "skepticism" is an inaccurate description for those who deny anthropogenic global warming. In effect, the two terms form a continuous, overlapping range of views, and generally have the same characteristics: both reject, to a greater or lesser extent, the scientific consensus on climate change. Climate change denial can also be implicit, when individuals or social groups accept the science but fail to come to terms with it or to translate their acceptance into action. Several social science studies have analyzed these positions as forms of denialism and pseudoscience.The campaign to undermine public trust in climate science has been described as a "denial machine" organized by industrial, political and ideological interests, and supported by conservative media and skeptical bloggers to manufacture uncertainty about global warming. In the public debate, phrases such as climate skepticism have frequently been used with the same meaning as climate denialism. The labels are contested: those actively challenging climate science commonly describe themselves as "skeptics", but many do not comply with common standards of scientific skepticism and, regardless of evidence, persistently deny the validity of human caused global warming.Although scientific opinion on climate change is that human activity is extremely likely to be the primary driver of climate change, the politics of global warming have been affected by climate change denial, hindering efforts to prevent climate change and adapt to the warming climate. Those promoting denial commonly use rhetorical tactics to give the appearance of a scientific controversy where there is none.Of the world's countries, the climate change denial industry is most powerful in the United States. From 2015 to 2017 (after having already served from 2003 to 2007), the United States Senate Committee on Environment and Public Works was chaired by oil lobbyist and climate change denier Jim Inhofe, who had previously called climate change "the greatest hoax ever perpetrated against the American people" and claimed to have debunked the alleged hoax in February 2015 when he brought a snowball with him in the Senate chamber and tossed it across the floor. He was succeeded in 2017 by John Barrasso, who similarly said: "The climate is constantly changing. The role human activity plays is not known." Organised campaigning to undermine public trust in climate science is associated with conservative economic policies and backed by industrial interests opposed to the regulation of CO2 emissions. Climate change denial has been associated with the fossil fuels lobby, the Koch brothers, industry advocates and conservative think tanks, often in the United States. More than 90% of papers sceptical on climate change originate from right-wing think tanks.

The total annual income of these climate change counter-movement-organizations is roughly $900 million. Between 2002 and 2010, nearly $120 million (£77 million) was anonymously donated via the Donors Trust and Donors Capital Fund to more than 100 organisations seeking to undermine the public perception of the science on climate change. In 2013 the Center for Media and Democracy reported that the State Policy Network (SPN), an umbrella group of 64 U.S. think tanks, had been lobbying on behalf of major corporations and conservative donors to oppose climate change regulation.Since the late 1970s, oil companies have published research broadly in line with the standard views on global warming. Despite this, oil companies organized a climate change denial campaign to disseminate public disinformation for several decades, a strategy that has been compared to the organized denial of the hazards of tobacco smoking by the tobacco industry.

Desert climate

The desert climate (in the Köppen climate classification BWh and BWk), is a climate in which there is an excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in desert climates hold little moisture and evaporate the little rainfall they receive. Covering 14.2% of earth's land area, hot deserts may be the most common type of climate on earth.Although no part of Earth is known for certain to be absolutely rainless, in the Atacama Desert in northern Chile, the average annual rainfall over a period of 17 years was only 5 mm (0.2 in.). Some locations in the Sahara Desert such as Kufra, Libya record only .86 mm (0.03 inches) of rainfall annually. The official weather station in Death Valley, United States reports only 60 mm (2.3 inches) annually, and in one period between 1931 and 1934 (40 months) only 16 mm (0.64 inches) of rainfall was measured.

There are two variations of a desert climate: a hot desert climate (BWh), and a cold desert climate (BWk). To delineate "hot desert climates" from "cold desert climates", there are three widely used isotherms: either a mean annual temperature of 18 °C (which is the most accurate and most commonly used), or a mean temperature of 0 °C or −3 °C in the coldest month, so that a location with a "BW" type climate with the appropriate temperature above whichever isotherm is being used is classified as "hot arid" (BWh), and a location with the appropriate temperature below the given isotherm is classified as "cold arid".

Most desert and arid climates receive between 25 and 200 mm (1 to 8 inches) of rainfall annually. In the Köppen classification system, a climate will be classed as arid if its mean annual precipitation in millimeters is less than ten times its defined precipitation threshold, and it will be classed as a desert if its mean annual precipitation is less than five times this threshold. The precipitation threshold is twice its mean annual temperature in degrees Celsius, plus a constant to represent the distribution of its rainfall throughout the year. This constant is 280 for regions that receive 70% or more of their rainfall during the six winter months. The constant is 0 for regions that receive 70% or more of their rainfall during the six summer months. And it is 140 for any climates falling between these two extremes.

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.

Anthropogenic forcing has likely contributed to some of the observed changes, including sea level rise, changes in climate extremes, declines in Arctic sea ice extent and glacier retreat.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.This article doesn't cover ocean acidification, which is directly caused by atmospheric carbon dioxide, not global warming.

Global warming

Global warming is a long-term rise in the average temperature of the Earth's climate system, an aspect of climate change shown by temperature measurements and by multiple effects of the warming. Though earlier geological periods also experienced episodes of warming, the term commonly refers to the observed and continuing increase in average air and ocean temperatures since 1900 caused mainly by emissions of greenhouse gasses in the modern industrial economy. In the modern context the terms global warming and climate change are commonly used interchangeably, but climate change includes both global warming and its effects, such as changes to precipitation and impacts that differ by region. Many of the observed warming changes since the 1950s are unprecedented in the instrumental temperature record, and in historical and paleoclimate proxy records of climate change over thousands to millions of years.In 2013, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded, "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) to 2.6 to 4.8 °C (4.7 to 8.6 °F) depending on the rate of greenhouse gas emissions and on climate feedback effects. These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing.Future climate change effects are expected to include rising sea levels, ocean acidification, regional changes in precipitation, and expansion of deserts in the subtropics. Surface temperature increases are greatest in the Arctic, with the continuing retreat of glaciers, permafrost, and sea ice. Predicted regional precipitation effects include more frequent extreme weather events such as heat waves, droughts, wildfires, heavy rainfall with floods, and heavy snowfall. Effects directly significant to humans are predicted to include the threat to food security from decreasing crop yields, and the abandonment of populated areas due to rising sea levels. Environmental impacts appear likely to include the extinction or relocation of ecosystems as they adapt to climate change, with coral reefs, mountain ecosystems, and Arctic ecosystems most immediately threatened. Because the climate system has a large "inertia" and greenhouse gases will remain in the atmosphere for a long time, climatic changes and their effects will continue to become more pronounced for many centuries even if further increases to greenhouse gases stop.Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, and possible future climate engineering. Almost all countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC), whose ultimate objective is to prevent dangerous anthropogenic climate change. Parties to the UNFCCC have agreed that deep cuts in emissions are required and that global warming should be limited to well below 2.0 °C (3.6 °F) compared to pre-industrial levels, with efforts made to limit warming to 1.5 °C (2.7 °F). Some scientists call into question climate adaptation feasibility, with higher emissions scenarios, or the two degree temperature target.Public reactions to global warming and concern about its effects are also increasing. A 2015 global survey showed that a median of 54% of respondents consider it "a very serious problem", with significant regional differences: Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) are among the least concerned.

Green New Deal

The Green New Deal (GND) is a proposed stimulus program that aims to address climate change and economic inequality. The name refers to the New Deal, a set of social and economic reforms and public works projects undertaken by President Franklin D. Roosevelt in response to the Great Depression. The Green New Deal combines Roosevelt's economic approach with modern ideas such as renewable energy and resource efficiency.In the 116th Congress, it is a pair of resolutions, H. Res. 109 and S. Res. 59, sponsored by Rep. Alexandria Ocasio-Cortez (D-NY) and Sen. Ed Markey (D-MA). On March 25, 2019, Markey's resolution failed to advance in the U.S. Senate in a margin of 0-57, with most Senate Democrats voting "present" in protest to the vote.

Greenhouse effect

The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere.If a planet's atmosphere contains radiatively active gases (i.e., greenhouse gases) they will radiate energy in all directions. Part of this radiation is directed towards the surface, warming it.

The intensity of the downward radiation – that is, the strength of the greenhouse effect – will depend on the atmosphere's temperature and on the amount of greenhouse gases that the atmosphere contains.

Earth’s natural greenhouse effect is critical to supporting life. Human activities, mainly the burning of fossil fuels and clearing of forests, have strengthened the greenhouse effect and caused global warming.The term "greenhouse effect" is a misnomer that arose from a faulty analogy with the effect of sunlight passing through glass and warming a greenhouse. The way a greenhouse retains heat is fundamentally different, as a greenhouse works mostly by reducing airflow so that warm air is kept inside.

Greenhouse gas

A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

Human activities since the beginning of the Industrial Revolution (around 1750) have produced a 45% increase in the atmospheric concentration of carbon dioxide (CO2), from 280 ppm in 1750 to 406 ppm in early 2017. This increase has occurred despite the uptake of more than half of the emissions by various natural "sinks" involved in the carbon cycle. The vast majority of anthropogenic carbon dioxide emissions (i.e., emissions produced by human activities) come from combustion of fossil fuels, principally coal, oil, and natural gas, with additional contributions coming from deforestation, changes in land use, soil erosion and agriculture (including livestock).Should greenhouse gas emissions continue at their rate in 2017, Earth's surface temperature could exceed historical values as early as 2047, with potentially harmful effects on ecosystems, biodiversity and human livelihoods. At current emission rates temperatures could increase by 2 °C, which the United Nations' IPCC designated as the upper limit to avoid "dangerous" levels, by 2036.

Humid continental climate

A humid continental climate (Köppen prefix D and a third letter of a or b) is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold in the northern areas) winters. Precipitation is usually distributed throughout the year. The definition of this climate regarding temperature is as follows: the mean temperature of the coldest month must be below −3 °C (26.6 °F) (or 0 °C (32.0 °F)) and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F). In addition, the location in question must not be semi-arid or arid. The Dfb, Dwb and Dsb subtypes are also known as hemiboreal.

Humid continental climates are generally found roughly between latitudes 40° N and 60° N, within the central and northeastern portions of North America, Europe, and Asia. They are much less commonly found in the Southern Hemisphere due to the larger ocean area at that latitude and the consequent greater maritime moderation. In the Northern Hemisphere some of the humid continental climates, typically in Scandinavia, Nova Scotia, and Newfoundland are heavily maritime-influenced, with relatively cool summers and winters being just below the freezing mark. More extreme humid continental climates found in northeast China, southern Siberia, the Canadian Prairies, and the Great Lakes region of the American Midwest and Central Canada combine hotter summer maxima and colder winters than the marine-based variety.

Humid subtropical climate

A humid subtropical climate is a zone of climate characterized by hot and humid summers, and mild winters. These climates normally lie on the southeast side of all continents, generally between latitudes 25° and 40° and are located poleward from adjacent tropical climates. While many subtropical climates tend to be located at or near coastal locations, in some cases they extend inland, most notably in China and the United States, where they exhibit more pronounced seasonal variations and sharper contrasts between summer and winter, as part of a gradient between the more tropical climates of the southern coasts of these countries and the more continental climates of China and the United States’ northern and central regions (localities around the Ohio and Yangtze rivers exhibiting continental influence from the north, compared to climates around the Gulf of Mexico and the South China Sea, which exhibit tropical influence due to their southern coastal positions).

Under the Köppen climate classification, Cfa and Cwa climates are either described as humid subtropical climates or mild temperate climates. This climate features mean temperatures in the coldest month between 0 °C (32 °F) or −3 °C (27 °F) and 18 °C (64 °F) and mean temperatures in the warmest month 22 °C (72 °F) or higher. However, while some climatologists have opted to describe this climate type as a "humid subtropical climate", Köppen himself never used this term. The humid subtropical climate classification was officially created under the Trewartha Climate classification.

The Trewartha system was a 1966 update of the Köppen climate classification, and sought to redefine middle latitude climates into smaller zones (the original Köppen system grouped all middle latitude climates into a single zone). Under the Trewartha climate classification, climates are termed humid subtropical when they have monthly mean air temperatures higher than 10 °C (50 °F) for eight or more months a year and at least one month with mean temperature below 18 °C (64.4 °F). Under the Trewartha system, humid subtropical climates typically occupy the southernmost portions of the temperate zone from 23.5 to 35.0 north and south latitude.Rainfall often shows a summer peak, especially where monsoons are well developed, as in Southeast Asia and South Asia. Other areas have a more uniform or varying rainfall cycles, but consistently lack any predictably dry summer months. Most summer rainfall occurs during thunderstorms that build up due to the intense surface heating and strong subtropical sun angle. Weak tropical lows that move in from adjacent warm tropical oceans, as well as infrequent tropical storms often contribute to summer seasonal rainfall peaks. Winter rainfall is often associated with large storms in the westerlies that have fronts that reach down into subtropical latitudes. However, many subtropical climates such as southeast Asia or Florida have very dry winters, with frequent brush fires and water shortages.

Intergovernmental Panel on Climate Change

The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations, dedicated to providing the world with an objective, scientific view of climate change, its natural, political and economic impacts and risks, and possible response options.It was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), and later endorsed by the United Nations General Assembly. Membership is open to all members of the WMO and UN.

The IPCC produces reports that contribute to the work of the United Nations Framework Convention on Climate Change (UNFCCC), the main international treaty on climate change. The objective of the UNFCCC is to "stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic (human-induced) interference with the climate system". The IPCC's Fifth Assessment Report was a critical scientific input into the UNFCCC's Paris Agreement in 2015.IPCC reports cover the "scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation." The IPCC does not carry out original research, nor does it monitor climate or related phenomena itself. Rather, it assesses published literature including peer-reviewed and non-peer-reviewed sources. However, the IPCC can be said to stimulate research in climate science. Chapters of IPCC reports often close with sections on limitations and knowledge or research gaps, and the announcement of an IPCC special report can catalyse research activity in that area.

Thousands of scientists and other experts contribute on a voluntary basis to writing and reviewing reports, which are then reviewed by governments. IPCC reports contain a "Summary for Policymakers", which is subject to line-by-line approval by delegates from all participating governments. Typically, this involves the governments of more than 120 countries.The IPCC provides an internationally accepted authority on climate change, producing reports which have the agreement of leading climate scientists and the consensus of participating governments. The 2007 Nobel Peace Prize was shared, in equal parts, between the IPCC and Al Gore.Following the election of a new Bureau in 2015, the IPCC embarked on its sixth assessment cycle. Besides the Sixth Assessment Report, to be completed in 2022, the IPCC released the Special Report on Global Warming of 1.5 °C in October 2018, will release an update to its 2006 Guidelines for National Greenhouse Gas Inventories—the 2019 Refinement—in May 2019, and will deliver two further special reports in 2019: the Special Report on the Ocean and Cryosphere in a Changing Climate, and Climate Change and Land. This makes the sixth assessment cycle the most ambitious in the IPCC's 30-year history. The IPCC also decided to prepare a special report on cities and climate change in the seventh assessment cycle, and held a conference in March 2018 to stimulate research in this area.

Kyoto Protocol

The Kyoto Protocol is an international treaty which extends the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits state parties to reduce greenhouse gas emissions, based on the scientific consensus that (part one) global warming is occurring and (part two) it is extremely likely that human-made CO2 emissions have predominantly caused it. The Kyoto Protocol was adopted in Kyoto, Japan on 11 December 1997 and entered into force on 16 February 2005. There are currently 192 parties (Canada withdrew from the protocol, effective December 2012) to the Protocol.

The Kyoto Protocol implemented the objective of the UNFCCC to reduce the onset of global warming by reducing greenhouse gas concentrations in the atmosphere to "a level that would prevent dangerous anthropogenic interference with the climate system" (Article 2). The Kyoto Protocol applies to the six greenhouse gases listed in Annex A: Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), and Sulphur hexafluoride (SF6).The Protocol is based on the principle of common but differentiated responsibilities: it acknowledges that individual countries have different capabilities in combating climate change, owing to economic development, and therefore puts the obligation to reduce current emissions on developed countries on the basis that they are historically responsible for the current levels of greenhouse gases in the atmosphere.

The Protocol's first commitment period started in 2008 and ended in 2012. A second commitment period was agreed in 2012, known as the Doha Amendment to the Kyoto Protocol, in which 37 countries have binding targets: Australia, the European Union (and its 28 member states), Belarus, Iceland, Kazakhstan, Liechtenstein, Norway, Switzerland, and Ukraine. Belarus, Kazakhstan, and Ukraine have stated that they may withdraw from the Kyoto Protocol or not put into legal force the Amendment with second round targets. Japan, New Zealand, and Russia have participated in Kyoto's first-round but have not taken on new targets in the second commitment period. Other developed countries without second-round targets are Canada (which withdrew from the Kyoto Protocol in 2012) and the United States (which has not ratified). As of January 2019, 124 states have accepted the Doha Amendment, while entry into force requires the acceptances of 144 states. Of the 37 countries with binding commitments, 7 have ratified.

Negotiations were held in the framework of the yearly UNFCCC Climate Change Conferences on measures to be taken after the second commitment period ends in 2020. This resulted in the 2015 adoption of the Paris Agreement, which is a separate instrument under the UNFCCC rather than an amendment of the Kyoto Protocol.

Köppen climate classification

The Köppen climate classification is one of the most widely used climate classification systems. It was first published by the Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notably in 1918 and 1936. Later, the climatologist Rudolf Geiger (1954, 1961) introduced some changes to the classification system, which is thus sometimes called the Köppen–Geiger climate classification system.The Köppen climate classification divides climates into five main climate groups, with each group being divided based on seasonal precipitation and temperature patterns. The five main groups are A (tropical), B (dry), C (temperate), D (continental), and E (polar). Each group and subgroup is represented by a letter. All climates are assigned a main group (the first letter). All climates except for those in the E group are assigned a seasonal precipitation subgroup (the second letter). For example, Af indicates a tropical rainforest climate. The system assigns a temperature subgroup for all groups other than those in the A group, indicated by the third letter for climates in B, C, and D, and the second letter for climates in E. For example, Cfb indicates an oceanic climate with warm summers as indicated by the ending b. Climates are classified based on specific criteria unique to each climate type.Köppen designed the system based on his experience as a botanist, so the main climate groups are based on the different variety of vegetation that grows in climates belonging to each group. In addition to identifying climates, the system can be used to analyze ecosystem conditions and identify the main types of vegetation within climates. Due to its link with the plant life of a region, the system is useful in predicting future changes in plant life within a region.The Köppen climate classification system has been further modified, within the Trewartha climate classification system in the middle 1960s (revised in 1980). The Trewartha system sought to create a more refined middle latitude climate zone, which was one of the criticisms of the Köppen system (the C climate group was too broad).

Mediterranean climate

A Mediterranean climate or dry summer climate is characterized by rainy winters and dry summers, with less than 40 mm of precipitation for at least three summer months. While the climate receives its name from the Mediterranean Basin, these are generally located on the western coasts of continents, between roughly 30 and 45 degrees north and south of the equator, typically between oceanic climates towards the poles (where they tend to be wetter and cooler), and semi-arid and arid climates towards the equator (where they tend to be drier and hotter).

In essence, and due to the seasonal shift of the subtropical high-pressure belts with the apparent movement of the Sun, a Mediterranean climate is an intermediate type between these other climates, with winters warmer and drier (and sunnier) than oceanic climates and summers imitating sunny weather in semi-arid and arid climates.

The resulting vegetation of Mediterranean climates are the garrigue or maquis in the Mediterranean Basin, the chaparral in California, the fynbos in South Africa, the mallee in Australia, and the matorral in Chile. Areas with this climate are where the so-called "Mediterranean trinity" of agricultural products have traditionally developed: wheat, vine and olive.

Most large, historic cities of the Mediterranean basin also lie within Mediterranean climatic zones, including Algiers, Athens, Beirut, İzmir, Jerusalem, Marseille, Naples, Rome, Tunis, and Valencia. Examples of major cities with Mediterranean climates that lie outside of the historic Mediterranean basin include major examples as Adelaide, Cape Town, Casablanca, Dushanbe, Los Angeles, Lisbon, Perth, San Francisco, Santiago and Victoria.

Oceanic climate

An oceanic climate, also known as a marine climate or maritime climate, is the Köppen classification of climate typical of west coasts in higher middle latitudes of continents, and generally features mild summers (relative to their latitude) and mild winters, with a relatively narrow annual temperature range and few extremes of temperature, with the exception for transitional areas to continental, subarctic and highland climates. Oceanic climates are defined as having a monthly mean temperature below 22 °C (72 °F) in the warmest month, and above 0 °C (32 °F) (or −3 °C (27 °F)) in the coldest month.

It typically lacks a dry season, as precipitation is more evenly dispersed throughout the year. It is the predominant climate type across much of Western Europe including the United Kingdom, the Pacific Northwest region of the United States and Canada, portions of central Mexico, southwestern South America, southeastern Australia including Tasmania, and New Zealand, as well as isolated locations elsewhere. Oceanic climates are generally characterised by a narrower annual range of temperatures than in other places at a comparable latitude, and generally do not have the extremely dry summers of Mediterranean climates or the hot summers of humid subtropical. Oceanic climates are most dominant in Europe, where they spread much farther inland than in other continents.Oceanic climates can have considerable storm activity as they are located in the belt of the stormy westerlies. Many oceanic climates have frequent cloudy or overcast conditions due to the near constant storms and lows tracking over or near them. The annual range of temperatures is smaller than typical climates at these latitudes due to the constant stable marine air masses that pass through oceanic climates, which lack both very warm and very cool fronts.

Paris Agreement

The Paris Agreement (French: Accord de Paris) is an agreement within the United Nations Framework Convention on Climate Change (UNFCCC), dealing with greenhouse-gas-emissions mitigation, adaptation, and finance, signed in 2016. The agreement's language was negotiated by representatives of 196 state parties at the 21st Conference of the Parties of the UNFCCC in Le Bourget, near Paris, France, and adopted by consensus on 12 December 2015. As of March 2019, 195 UNFCCC members have signed the agreement, and 185 have become party to it. The Paris Agreement's long-term goal is to keep the increase in global average temperature to well below 2 °C above pre-industrial levels; and to limit the increase to 1.5 °C, since this would substantially reduce the risks and effects of climate change.

Under the Paris Agreement, each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming. No mechanism forces a country to set a specific target by a specific date, but each target should go beyond previously set targets. In June 2017, U.S. President Donald Trump announced his intention to withdraw his country from the agreement. Under the agreement, the earliest effective date of withdrawal for the U.S. is November 2020, shortly before the end of President Trump's current term. In practice, changes in United States policy that are contrary to the Paris Agreement have already been put in place.In July 2017 French Environment Minister Nicolas Hulot announced a plan to ban all petrol and diesel vehicles in France by 2040 as part of the Paris Agreement. Hulot also stated that France would no longer use coal to produce electricity after 2022 and that up to €4 billion will be invested in boosting energy efficiency. To reach the agreement's emission targets, Norway will ban the sale of petrol- and diesel-powered cars by 2025; the Netherlands will do the same by 2030. Electric trains running on the Dutch national rail network are already entirely powered by wind energy. The House of Representatives of the Netherlands passed a bill in June 2018 mandating that by 2050 the Netherlands will cut its 1990 greenhouse-gas emissions level by 95%—exceeding the Paris Agreement goals.

Semi-arid climate

A semi-arid climate or steppe climate is the climate of a region that receives precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different biomes.

Temperate climate

In geography, the temperate or tepid climates of Earth occur in the middle latitudes, which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout the year and more distinct seasonal changes compared to tropical climates, where such variations are often small. They typically feature four distinct seasons, Summer the warmest, Autumn the transitioning season to Winter, the colder season, and Spring the transitioning season from winter back into summer. On the northern hemisphere the year starts with winter, transitions in the first halfyear through spring into summer which is in mid-year, then at the second halfyear through autumn into winter at year-end. On the southern hemisphere seasons are swapped with summer in between years and winter in mid-year.

The temperate zones (latitudes from 23.5° to the polar circles at about 66.5°, north and south) are where the widest seasonal changes occur, with most climates found in it having some influence from both the tropics and the poles. The subtropics (latitudes from about 23.5° to 35°, north and south) have temperate climates that have the least seasonal change and the warmest in winter, while at the other end, Boreal climates located from 55 to 65 north latitude have the most seasonal changes and long and severe winters.

In temperate climates, not only due latitudinal positions influence temperature changes, but sea currents, prevailing wind direction, continentality (how large a landmass is), and altitude also shape temperate climates.

The Köppen climate classification defines a climate as "temperate" when the mean temperature is above −3 °C (26.6 °F) but below 18 °C (64.4 °F) in the coldest month. However, in more recent climate classifications climatologists use the 0 °C (32.0 °F) line .


In physical geography, tundra () is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра (tûndra) from the Kildin Sami word тӯндар (tūndâr) meaning "uplands", "treeless mountain tract". Tundra vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.

There are three regions and associated types of tundra: Arctic tundra, alpine tundra, and Antarctic tundra.

Climate oscillations
Meteorological data and variables
Climate types under the Köppen climate classification
Class A
Class B
Class C
Class D
Class E
Elements of nature
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Climate of the World

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