Global warming

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Global mean surface-temperature change from 1880 to 2017, relative to the 1951–1980 mean. The 1951–1980 mean is 14.19 °C (57.54 °F).[1] The black line is the global annual mean, and the red line is the five-year local regression line. The blue uncertainty bars show a 95% confidence interval.
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Future CO2 projections, including all forcing agents' atmospheric CO2-equivalent concentrations (in parts-per-million-by-volume (ppmv)) according to four RCPs (Representative Concentration Pathways).

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.[2][3] The term commonly refers to the mainly human-caused observed warming since pre-industrial times and its projected continuation,[4] though there were also much earlier periods of global warming.[5] In the modern context the terms are commonly used interchangeably,[6] but global warming more specifically relates to worldwide surface temperature increases; while climate change is any regional or global statistically identifiable persistent change in the state of climate which lasts for decades or longer, including warming or cooling.[7][8] 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.[2]

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."[9] The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. In view of the dominant role of human activity in causing it, the phenomenon is sometimes called "anthropogenic global warming" or "anthropogenic climate change". 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.[10] These findings have been recognized by the national science academies of the major industrialized nations[11][a] and are not disputed by any scientific body of national or international standing.[13][14]

Future climate change and associated impacts will differ from region to region.[15][16] Ongoing and anticipated effects include rising sea levels, changing precipitation, and expansion of deserts in the subtropics.[17] Future warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing retreat of glaciers, permafrost, and sea ice. Other likely changes include more frequent extreme weather events such as heat waves, droughts, wildfires, heavy rainfall with floods, and heavy snowfall;[18] ocean acidification; and massive extinctions of species due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels.[19][20] Because the climate system has a large "inertia" and greenhouse gases will remain in the atmosphere for a long time, many of these effects will persist for not only decades or centuries, but tens of thousands of years.[21]

Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),[22] whose ultimate objective is to prevent dangerous anthropogenic climate change.[23] Parties to the UNFCCC have agreed that deep cuts in emissions are required[24] and that global warming should be limited to well below 2.0 °C (3.6 °F) compared to pre-industrial levels,[b] with efforts made to limit warming to 1.5 °C (2.7 °F).[26] Some scientists call into question climate adaptation feasibility, with higher emissions scenarios,[27] or the two degree temperature target.[28]

Public reactions to global warming and concern about its effects are also increasing. A global 2015 Pew Research Center report showed that a median of 54% of all respondents asked consider it "a very serious problem". Significant regional differences exist, with Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) among the least concerned.[29]

Observed temperature changes

Annual (thin lines) and five-year lowess smooth (thick lines) for the temperature anomalies averaged over the Earth's land area (red line) and sea surface temperature anomalies (blue line) averaged over the part of the ocean that is free of ice at all times (open ocean).
Two millennia of mean surface temperatures according to different reconstructions from climate proxies, each smoothed on a decadal scale, with the instrumental temperature record overlaid in black.

Multiple independently produced datasets confirm that from 1880 to 2012 the global average (land and ocean) surface temperature increased by 0.85 [0.65 to 1.06] °C.[30] From 1906 to 2005, Earth's average surface temperature rose by 0.74±0.18 °C. The rate of warming almost doubled in the last half of that period (0.13±0.03 °C per decade, against 0.07±0.02 °C per decade).[31] Although the popular press often reports the increase of the average near-surface atmospheric temperature as the measure of global warming, most of the additional energy stored in the climate system since 1970 has accumulated in the oceans. The rest has melted ice and warmed the continents and the atmosphere.[32][c]

Since 1979, the average temperature of the lower troposphere has increased between 0.12 and 0.135 °C (0.216 and 0.243 °F) per decade, satellite temperature measurements confirm.[33][34] Climate proxies show the temperature to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.[35]

The warming evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups.[36] Examples include sea level rise,[37] widespread melting of snow and land ice,[38] increased heat content of the oceans,[36] increased humidity,[36] and the earlier timing of spring events,[39] e.g., the flowering of plants.[40] The probability that these changes could have occurred by chance is virtually zero.[36]

Regional trends and short-term fluctuations

Difference between average temperature in 2000–2009 compared to the 1951-1980 period, showing strong arctic amplification.

Global warming refers to global averages. It is not uniform around the world: effects can vary by region.[41] Since 1979, global average land temperatures have increased about twice as fast as global average ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[42] Ocean temperatures increase more slowly than land temperatures because of the larger heat capacity of the oceans and because oceans lose more heat by evaporation.[43] Since the beginning of industrialisation in the 18th century, the temperature difference between the hemispheres has increased due to melting of sea ice and snow in the North, and because there is more land in the Northern Hemisphere.[44] In the past 100 years, average Arctic temperatures have increased at almost twice the rate of the rest of the world.[45] This has been referred to as Arctic amplification.

Although more greenhouse gases are emitted in the Northern than in the Southern Hemisphere, this does not contribute to the difference in warming because the major greenhouse gases persist long enough to diffuse within and between the two hemispheres.[46]

There are different ways in which a climate can be forced to change, but because the climate system has large thermal inertia, it can take centuries – or even longer – for the climate to fully adjust. One climate commitment study concluded that if greenhouse gases were stabilized at year 2000 levels, surface temperatures would still increase by about 0.5 °C,[47] and another found that if they were stabilized at 2005 levels, surface warming could exceed a whole degree Celsius. Some of this surface warming would be driven by past natural forcings which have not yet reached equilibrium in the climate system. One study using a highly simplified climate model indicates these past natural forcings may account for as much as 64% of the committed 2050 surface warming, and their influence will fade with time compared to the human contribution.[48]

Global temperature is subject to short-term fluctuations that overlay long-term trends, and can temporarily mask or magnify them.[49][50] The relative stability in surface temperature from 2002 to 2009, which has since been dubbed the global warming hiatus by the media and some scientists,[51] may be an example of such an episode.[52][53] 2015 updates to account for differing methods of ocean surface temperature measurements show a positive trend over the recent decade.[54][55]

Warmest years vs. overall trend

Sixteen of the seventeen warmest years on record have occurred since 2000.[56] While record-breaking years attract considerable public interest, individual years are less significant than the overall trend. Some climatologists have criticized the attention that the popular press gives to "warmest year" statistics. In particular, ocean oscillations such as the El Niño–Southern Oscillation (ENSO) can cause temperatures of a given year to be abnormally warm or cold for reasons unrelated to the overall trend of climate change. Gavin Schmidt stated: "the long-term trends or the expected sequence of records are far more important than whether any single year is a record or not."[57]

Other Languages
Afrikaans: Aardverwarming
Alemannisch: Globale Erwärmung
azərbaycanca: Qlobal istiləşmə
башҡортса: Глобаль йылыныу
беларуская (тарашкевіца)‎: Глябальнае пацяпленьне
Boarisch: Eadaweamung
Fiji Hindi: Global warming
한국어: 지구 온난화
Bahasa Indonesia: Pemanasan global
interlingua: Calefaction global
íslenska: Heimshlýnun
Basa Jawa: Pamanasan global
Kreyòl ayisyen: Rechofman atmosferik
Lëtzebuergesch: Global Erwiermung
Lingua Franca Nova: Caldi global
മലയാളം: ആഗോളതാപനം
Bahasa Melayu: Pemanasan global
日本語: 地球温暖化
Nordfriisk: Globaal apwarmin
norsk nynorsk: Global oppvarming
Oromoo: Ho'a Adunya
ਪੰਜਾਬੀ: ਆਲਮੀ ਤਪਸ਼
português: Aquecimento global
Simple English: Global warming
slovenščina: Globalno segrevanje
srpskohrvatski / српскохрватски: Globalno zatopljenje
Basa Sunda: Jagat nyongkab
татарча/tatarça: Глобаль җылыну
vepsän kel’: Globaline lämšund
Tiếng Việt: Ấm lên toàn cầu
文言: 天地日暖
吴语: 全球暖化
粵語: 全球變暖
中文: 全球变暖