Climate change is the increase in the average measured temperature of the Earth's near-surface air and oceans since the mid-20th century, and its projected continuation3.
Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) of the United Nations Environmental Programme (UNEP) concludes that most of the increase since the mid-twentieth century is "very likely" due to the increase in greenhouse gas concentrations, primarily CO2 from the use of fossil fuels. These basic conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with these findings, the overwhelming majority of scientists working on climate change agree with the IPCC's main conclusions3.
Climate model projections summarized by the IPCC indicate that average 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. This range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to year 2100, warming and sea level rise are expected to continue for more than a thousand years even if greenhouse gas levels are stabilized3.
Increasing global temperature is expected to cause sea levels to rise, an increase in the intensity of extreme weather events, and significant changes to the amount and pattern of precipitation, likely including an expanse of the subtropical desert regions. Other expected effects of climate change include changes in agricultural yields, modifications of trade routes, glacier retreat, mass species extinctions and increases in the ranges of disease vectors3.
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