Global warming


Global warming is the rise in the average temperature of Earth's atmosphere and oceans since the late 19th century and its projected continuation. Since the early 20th century, Earth's mean surfacetemperature has increased by about 0.8 °C (1.4 °F), with about two-thirds of the increase occurring since 1980.Warming of the climate system is unequivocal, and scientists are more than 90% certainthat it is primarily caused by increasing concentrations of greenhouse gases produced by human activities such as the burning of fossil fuels and deforestation.These findings are recognized by thenational science academies of all major industrialized nations.
Climate model projections were summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change(IPCC). They indicated that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2 to 5.2 °F) for their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5°F) for their highest.The ranges of these estimates arise from the use of models with differing sensitivity to greenhouse gas concentrations.
According to AR4, warming and related changes will varyfrom region to region around the globe. The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well a probable expansionof subtropical deserts.Warming is expected to be strongest in the Arctic and would be associated with the continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warminginclude a more frequent occurrence of extreme-weather events including heat waves, droughts and heavy rainfall, ocean acidification and species extinctions due to shifting temperature regimes. Effectssignificant to humans include the threat to food security from decreasing crop yields and the loss of habitat from inundation
Proposed policy responses to global warming include mitigation by...