Global warming
This page is about the current warming of the Earth's climate system. " Climate change" can also refer to climate trends at any point in Earth's history. For other uses see Global warming (disambiguation)
Global mean surface-temperature change from 1880 to 2016, relative to the 1951–1980 mean. The black line is the global annual mean and the red line is the five-year lowest smooth. The blue uncertainty bars show a 95% confidence interval.
Global warming and climate change are terms for the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. [1] [2]Multiple lines of scientific evidence show that the climate system is warming. [3] [4] [5]Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid 19th century, and in paleoclimate proxy records over a thousand years. [6]
In 2014, the Intergovernmental Panel on Climate Change(IPCC) Fifth Assessment Report
concluded that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." [7]The largest human influence has been emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Climate model projections summarised 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) for their lowest emissions scenario and 2.6 to 4.8 °C (4.7 to 8.6 °F) for the highest emissions scenario. [8]These findings have been recognized by the national science academies of the major industrialized nations [9] [a]and are not disputed by any scientific body of national or international standing. [11]
Future climate change and associated impacts will differ from region to region around the globe. [12] [13]Anticipated effects include
warming global temperature, rising sea levels, changing precipitation, and expansion of desertsin the subtopics. [14]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 including heat waves, droughts, heavy rainfall with floods and heavy snowfall; [15] ocean acidification; and species extinctions 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 raising sea levels. [16] [17]Because the climate system has a large " inertia" and greenhouse gases will stay in the atmosphere for a long time, many of these effects will not only exist for decades or centuries, but will persist for tens of thousands of years. [18]
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), [19]whose ultimate objective is to prevent dangerous anthropogenic climate change. [20]Parties to the UNFCCC have agreed that deep cuts in emissions are required [21]and that global warming should be limited to well below 2.0 °C (3.6 °F) relative to pre-industrial levels, [b]with efforts made to limit warming to 1.5 °C (2.7 °F). [23]
Public reactions to global warming and concern about its effects are also increasing. A global 2015 Pew Research Center report showed a median of 54% consider it "a very serious problem". There are significant regional
differences, with Americans and Chinese(whose economies are responsible for the greatest annual CO 2 emissions) among the least concerned. [24]
Contents[ hide]
1 Observed temperature changes
1.1 Trends
1.2 Warmest years
2 Initial causes of temperature changes (external forcings)
2.1 Greenhouse gases
2.2 Aerosols and soot
2.3 Solar activity
2.4 Variations in Earth's orbit
3 Feedback
4 Climate models
5 Observed and expected environmental effects
5.1 Extreme weather
5.2 Sea level rise
5.3 Ecological systems
5.4 Long-term effects
5.5 Large-scale and abrupt impacts
6 Observed and expected effects on social systems
6.1 Habitat inundation
6.2 Economy
6.3 Infrastructure
7 Possible responses to global warming
7.1 Mitigation
7.2 Adaptation
7.3 Climate engineering
8 Discourse about global warming
8.1 Political discussion
8.2 Scientific discussion
8.3 Discussion by the public and in popular media
8.3.1 Surveys of public opinion
9 Etymology
10 See also
11 Notes
12 Citations
13 References
14 Further reading
15 External links
15.1 Research
15.2 Educational
Observed temperature changes
Main article: Instrumental temperature record
World map showing surface temperature trends (°C per decade) between 1950 and 2014. [25]
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.
NOAA graph of global annual temperature anomalies 1950–2012, showing the El Niño Southern Oscillation
The global average (land and ocean) surface temperature shows a warming of 0.85 [0.65 to
1.06] °C in the period 1880 to 2012, based on multiple independently produced datasets. [26] Earth's average surface temperature rose by0.74±0.18 °Cover the period 1906–2005. The rate of warming almost doubled for the last half of that period (0.13±0.03 °C per decade, versus0.07±0.02 °C per decade). [27]Although the increase of near-surface atmospheric temperature is the measure of global warming often reported in the popular press, most of the additional energy stored in the climate system since 1970 has gone into the oceans. The rest has melted ice and warmed the continents and atmosphere. [28] [c]
The average temperature of the lower troposphere has increased between 0.12 and 0.135 °C (0.216 and 0.243 °F) per decade since 1979, according to satellite temperature measurements. [29] [30] 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. [31]
The warming that is evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups. [32]Examples include sea level rise, [33]widespread melting of snow and land ice, [34]increased heat content of the oceans, [32]increased humidity, [32]and the earlier timing of spring events, [35]e.g., the flowering of plants. [36]The probability that these changes could have occurred by chance is virtually zero. [32]
Trends
Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25
°C per decadeagainst0.13 °C per decade). [37]Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. [38]Since the beginning of industrialisation the temperature difference between the hemispheres has increases due to melting of sea ice and snow in the North. [39]Average arctic temperatures have been increasing at almost twice the rate of the rest of the world in the past 100 years; however arctic temperatures are also highly variable. [40]Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres. [41]
The thermal inertia of the oceans and slow
responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. One climate commitment study concludes that if greenhouse gases were stabilized at year 2000 levels, surface temperatures would still increase by about one-half degree Celsius, [42]and another found that if they were stabilized at 2005 levels surface warming could exceed a whole degree Celsius. Some of this surface warming will be driven by past natural forcings which are still seeking 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. [43]
Global temperature is subject to short-term fluctuations that overlay long-term trends and
can temporarily mask them. The relative stability in surface temperature from 2002 to 2009, which has been dubbed the global warming hiatus by the media and some scientists, [44]is consistent with such an episode. [45] [46]2015 updates to account for differing methods of measuring ocean surface temperature measurements show a positive trend over the recent decade. [47] [48]
Global mean surface-temperature change from 1880 to 2016, relative to the 1951–1980 mean. The black line is the global annual mean and the red line is the five-year lowest smooth. The blue uncertainty bars show a 95% confidence interval.
Global warming and climate change are terms for the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. [1] [2]Multiple lines of scientific evidence show that the climate system is warming. [3] [4] [5]Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid 19th century, and in paleoclimate proxy records over a thousand years. [6]
In 2014, the Intergovernmental Panel on Climate Change(IPCC) Fifth Assessment Report
concluded that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." [7]The largest human influence has been emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Climate model projections summarised 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) for their lowest emissions scenario and 2.6 to 4.8 °C (4.7 to 8.6 °F) for the highest emissions scenario. [8]These findings have been recognized by the national science academies of the major industrialized nations [9] [a]and are not disputed by any scientific body of national or international standing. [11]
Future climate change and associated impacts will differ from region to region around the globe. [12] [13]Anticipated effects include
warming global temperature, rising sea levels, changing precipitation, and expansion of desertsin the subtopics. [14]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 including heat waves, droughts, heavy rainfall with floods and heavy snowfall; [15] ocean acidification; and species extinctions 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 raising sea levels. [16] [17]Because the climate system has a large " inertia" and greenhouse gases will stay in the atmosphere for a long time, many of these effects will not only exist for decades or centuries, but will persist for tens of thousands of years. [18]
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), [19]whose ultimate objective is to prevent dangerous anthropogenic climate change. [20]Parties to the UNFCCC have agreed that deep cuts in emissions are required [21]and that global warming should be limited to well below 2.0 °C (3.6 °F) relative to pre-industrial levels, [b]with efforts made to limit warming to 1.5 °C (2.7 °F). [23]
Public reactions to global warming and concern about its effects are also increasing. A global 2015 Pew Research Center report showed a median of 54% consider it "a very serious problem". There are significant regional
differences, with Americans and Chinese(whose economies are responsible for the greatest annual CO 2 emissions) among the least concerned. [24]
Contents[ hide]
1 Observed temperature changes
1.1 Trends
1.2 Warmest years
2 Initial causes of temperature changes (external forcings)
2.1 Greenhouse gases
2.2 Aerosols and soot
2.3 Solar activity
2.4 Variations in Earth's orbit
3 Feedback
4 Climate models
5 Observed and expected environmental effects
5.1 Extreme weather
5.2 Sea level rise
5.3 Ecological systems
5.4 Long-term effects
5.5 Large-scale and abrupt impacts
6 Observed and expected effects on social systems
6.1 Habitat inundation
6.2 Economy
6.3 Infrastructure
7 Possible responses to global warming
7.1 Mitigation
7.2 Adaptation
7.3 Climate engineering
8 Discourse about global warming
8.1 Political discussion
8.2 Scientific discussion
8.3 Discussion by the public and in popular media
8.3.1 Surveys of public opinion
9 Etymology
10 See also
11 Notes
12 Citations
13 References
14 Further reading
15 External links
15.1 Research
15.2 Educational
Observed temperature changes
Main article: Instrumental temperature record
World map showing surface temperature trends (°C per decade) between 1950 and 2014. [25]
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.
NOAA graph of global annual temperature anomalies 1950–2012, showing the El Niño Southern Oscillation
The global average (land and ocean) surface temperature shows a warming of 0.85 [0.65 to
1.06] °C in the period 1880 to 2012, based on multiple independently produced datasets. [26] Earth's average surface temperature rose by0.74±0.18 °Cover the period 1906–2005. The rate of warming almost doubled for the last half of that period (0.13±0.03 °C per decade, versus0.07±0.02 °C per decade). [27]Although the increase of near-surface atmospheric temperature is the measure of global warming often reported in the popular press, most of the additional energy stored in the climate system since 1970 has gone into the oceans. The rest has melted ice and warmed the continents and atmosphere. [28] [c]
The average temperature of the lower troposphere has increased between 0.12 and 0.135 °C (0.216 and 0.243 °F) per decade since 1979, according to satellite temperature measurements. [29] [30] 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. [31]
The warming that is evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups. [32]Examples include sea level rise, [33]widespread melting of snow and land ice, [34]increased heat content of the oceans, [32]increased humidity, [32]and the earlier timing of spring events, [35]e.g., the flowering of plants. [36]The probability that these changes could have occurred by chance is virtually zero. [32]
Trends
Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25
°C per decadeagainst0.13 °C per decade). [37]Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. [38]Since the beginning of industrialisation the temperature difference between the hemispheres has increases due to melting of sea ice and snow in the North. [39]Average arctic temperatures have been increasing at almost twice the rate of the rest of the world in the past 100 years; however arctic temperatures are also highly variable. [40]Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres. [41]
The thermal inertia of the oceans and slow
responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. One climate commitment study concludes that if greenhouse gases were stabilized at year 2000 levels, surface temperatures would still increase by about one-half degree Celsius, [42]and another found that if they were stabilized at 2005 levels surface warming could exceed a whole degree Celsius. Some of this surface warming will be driven by past natural forcings which are still seeking 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. [43]
Global temperature is subject to short-term fluctuations that overlay long-term trends and
can temporarily mask them. The relative stability in surface temperature from 2002 to 2009, which has been dubbed the global warming hiatus by the media and some scientists, [44]is consistent with such an episode. [45] [46]2015 updates to account for differing methods of measuring ocean surface temperature measurements show a positive trend over the recent decade. [47] [48]
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