global warming

Global warming is the increase in the average temperature of the Earth's near-surface air and the oceans since the mid-twentieth century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C(1.33 ± 0.32 °F) during the last century. The Intergovernmental Panel on Climate Change(IPCC) concludes that anthropogenic greenhouse gases are responsible for most of the observed temperature increase since the middle of the twentieth century, and that natural phenomena such as solar variation and volcanoes probably had a small warming effect from pre-indutrial times to 1950 and a small cooling effect afterward. These basic conclusions have been endorsed by more than 40 scientific society and academies of science, including all of the national academies of science of the major industrialized countries.

Climate model projections summarized in the latest IPCC report indicate that global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. The uncertainty in this estimate arises from the use of models with differing climate sentivity, and the use of differing estimates of future greenhouse gas emissions. Some other uncertaities include how warming and related changes will vary from region to region around the globe. Most studies focus on the period up to 2100. However, warming is expected to continue beyond 2100, even if emissions stop, because of the large heat capacity of the ocean and the long lifetime ofcarbon dioxide in the atmosphere.

Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, likely including expansion of subtropical deserts . The continuing retreat of glaciers,permafrost and sea ice is expected, with the Artic region being particularly affected. Other likely effects include shrinkage of the Amazon Rainforest and Boreal forests, increases in the intensity of extreme weather events, species extinctions and changes in agricultural yields .

Political and public debate continues regarding the appropriate response to global warming. 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 govermentshave signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.

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