Global Warming

Global warming
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For past climate change, see paleoclimatology and geologic temperature record.

Global mean surface temperature difference relative to the 1961–1990 average

Comparison of ground based (blue) and satellite based (red: UAH; green: RSS) records of temperature variations since 1979. Trends plotted since January1982.

Mean surface temperature change for the period 1999 to 2008 relative to the average temperatures from 1940 to 1980.
Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the start and the end of the 20thcentury.[1][A] The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the middle of the 20th century was caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation.[1] The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanismproduced most of the warming from pre-industrial times to 1950 and had a small cooling effect afterward.[2][3] These basic conclusions have been endorsed by more than 40 scientific societies and academies of science,[B] including all of the national academies of science of the major industrialized countries.[4]
Climate model projections summarized in the latest IPCC report indicate that the globalsurface temperature is likely to rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century.[1] The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. Some other uncertainties include how warming and related changes will vary from region to region aroundthe globe. Most studies focus on the period up to the year 2100. However, warming is expected to continue beyond 2100 even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere.[5][6]
An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably includingexpansion of subtropical deserts.[7] Warming will be strongest in the Arctic and will be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects include increases in the intensity of extreme weather events, species extinctions, and changes in agricultural yields.
Political and public debate continues regarding global warming, and what actions (if any) to take inresponse. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.
Contents[hide] * 1 Temperature changes * 2 External forcing of climate * 2.1Greenhouse gases * 2.2 Aerosols and soot * 2.3 Solar variation * 3 Feedback * 4 Climate models * 5 Attributed and expected effects * 5.1 Environmental * 5.2 Economic * 6 Responses to global warming * 6.1 Mitigation * 6.2 Adaptation * 6.3 Geoengineering * 7 Debate and skepticism * 8 See also * 9 Notes * 10 References * 11 Further reading * 12External links |
Temperature changes
Main article: Temperature record

Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.
The most commonly discussed measure of global warming is the trend in globally averaged temperature near the Earth's surface. Expressed as...