Global warming

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Global mean surface-temperature change from 1880 to 2018, 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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Average global temperatures from 2014 to 2018 compared to a baseline average from 1951 to 1980, according to NASA's Goddard Institute for Space Studies.

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 global warming and climate change are commonly used interchangeably,[6] but climate change includes both global warming and its effects, such as changes to precipitation and impacts that differ by region.[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. 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.[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 effects are expected to include rising sea levels, ocean acidification, regional changes in precipitation, and expansion of deserts in the subtropics.[15][16][17] 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.[18] 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.[19][20] Environmental impacts appear likely to include the extinction or relocation of ecosystems as they adapt to climate change, with coral reefs,[21] mountain ecosystems, and Arctic ecosystems most immediately threatened.[22] 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.[23]

Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),[24] whose ultimate objective is to prevent dangerous anthropogenic climate change.[25] Parties to the UNFCCC have agreed that deep cuts in emissions are required[26] 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).[28] Some scientists call into question climate adaptation feasibility, with higher emissions scenarios,[29] or the two degree temperature target.[30]

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.[31]

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.
The geologic temperature record for the last 65 million years, showing potential global temperature steady states that greenhouse gases could trigger through feedback tipping points. [32]

Multiple independently produced datasets confirm that between 1880 and 2012, the global average (land and ocean) surface temperature increased by 0.85 [0.65 to 1.06] °C.[33] Since 1979 the rate of warming has approximately doubled (0.13±0.03 °C per decade, against 0.07±0.02 °C per decade).[34][35] 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.[36]

Although the increase of the average near-surface atmospheric temperature is commonly used to track global warming, over 90% of the additional energy stored in the climate system over the last 50 years has accumulated in the oceans.[37] The rest has melted ice and warmed the continents and the atmosphere.[38][c]

The warming evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups.[39] Examples include sea level rise,[40] widespread melting of snow and land ice,[41] increased heat content of the oceans,[39] increased humidity,[39] and the earlier timing of spring events,[42] e.g., the flowering of plants.[43]

Regional trends

Global warming refers to global averages, with the amount of warming varying by region. Since 1979, global average land temperatures have increased about twice as fast as global average ocean temperatures.[44] This is due to the larger heat capacity of the oceans and because oceans lose more heat by evaporation.[45] Where greenhouse gas emissions occur does not impact the location of warming because the major greenhouse gases persist long enough to diffuse across the planet, although localized black carbon deposits on snow and ice do contribute to Arctic warming.[46]

The Northern Hemisphere and North Pole have heated much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, its arrangement around the Arctic Ocean has resulted in the maximum surface area flipping from reflective snow and ice cover to ocean and land surfaces that absorb more sunlight.[47] Arctic temperatures have increased and are predicted to continue to increase during this century at over twice the rate of the rest of the world.[48] As the temperature difference between the Arctic and the equator decreases, ocean currents like the gulf stream that are driven by that temperature difference are weakening.[49] Studies have also linked the rapidly warming Arctic to extreme weather in mid-latitudes as the jet stream becomes more erratic.[50]

The rate of ice loss from glaciers and ice sheets in the Antarctic is a key area of uncertainty since Antarctica contains 90% of potential sea level rise.[51] Polar amplification and increased ocean warmth are undermining and threatening to unplug Antarctic glacier outlets, potentially resulting in more rapid sea level rise.[52] To date, increased snowfall in Antarctica has offset a third of ice loss from West Antarctica, with East Antarctica ice sheets recently beginning to shed mass as well.[53][54][55]

Short-term fluctuations vs. overall trend

Because the climate system has large thermal inertia, it can take centuries for the climate to fully adjust. While record-breaking years attract considerable public interest, individual years are less significant than the overall trend. Global surface temperature is subject to short-term fluctuations that overlay long-term trends, and can temporarily mask or magnify them.[56][57]

An example of such an episode is the slower rate of surface temperature increase from 1998 to 2012, which was dubbed the global warming hiatus by the media and some scientists.[58][59][60] Throughout this period ocean heat storage continued to progress steadily upwards, and in subsequent years surface temperatures have spiked upwards. Climate models account for the global warming hiatus by incorporating heating and cooling from El Niño / La Nina events, sunspot cycles, and volcanic eruptions that reach the stratosphere.[61]

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