Impacts of Global Warming
If the climate changes in response to an enhanced greenhouse effect as current computer models have projected, global average surface temperature could be anywhere from 1.4 to 5.8°C (with a best estimate of 3°C) higher by the end of the 21st century. To put this temperature change into context, the increase in global average surface temperature which brought the Earth out of the last major ice age 14,000 years ago was of the order of 4 to 5°C. This climate change took thousands of years. Man-made global warming, in contrast, may occur at rate that is unprecedented on Earth.
Such a rapid change in climate will probably be too great to allow many ecosystems to suitably adapt, and the rate of species extinction will most likely increase. In addition to impacts on wildlife and species biodiversity, human agriculture, forestry, drylands, water resources and health will all be affected. Such impacts will be related to changes in precipitation (rainfall and snowfall), sea level, and the frequency and intensity of extreme weather events, resulting from global warming. It is expected that the societies currently experiencing existing social, economic and climatic stresses will be both worst affected and least able to adapt. These will include many in the developing world, low-lying islands and coastal regions, and the urban poor.