The Big Picture 

:Projections of future climate change

The IPCC also developed several scenarios of climate change that might result over the 21st
century if no action is taken to reduce GHG emissions. Scenarios were developed for future
emissions of CO2 and other GHGs, as well as sulfate aerosols (which reflect sunlight and
therefore tend to cool the climate), and were used to drive computer models of the Earth's
climate system. Models project increases in global average temperature by the year 2100 of
13.5 C relative to today, with a "best guess" estimate of about 2 C, under such "business
as usual" conditions. It might be thought that a world in which the average temperature is a
few degrees warmer would not differ greatly from the world in which we now live. However,
average surface temperature is an index of the overall state of the Earths climate, and a
change of a few degrees is a major global event. For example, during the last ice age, global
average temperature was probably just 5 C lower than it is today, but this difference was
enough to cause ice sheets to cover vast areas of Europe and North America that are
currently ice free. The high end of the range of IPCC projections, especially beyond 2100,
approaches a warming of a magnitude similar to that of the glacial cooling.

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*Global Change                    Online Journal on climate Change and Ozone Depletion

*N.Y.Times Global Warming Archive

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