Projected Changes in Global Temperature

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21. Using the IS92 emission scenarios, projected global mean temperature changes relative to 1990 were calculated up to 2100. Climate models calculate that the global mean surface temperature could rise by about 1 to 4.5 centigrade by 2100. The topmost curve is for IS92e, assuming constant aerosol concentrations beyond 1990 and high climate sensitivity of 4.5 °C. The lowest curve is for IS92c and assumes constant aerosol concentrations beyond 1990 and a low climate sensitivity of 1.5 °C. The two middle curves show the results for IS92a with "best estimate" of climate sensitivity of 2.5 °C: the upper curve assumes a constant aerosol concentration beyond 1990, and the lower one includes changes in aerosol concentration beyond 1990. (It is assumed that the Greenhouse effect is reduced with increased aerosols.)

Note: In IPCC reports, climate sensitivity usually refers to the long- term or equilibrium, change in global mean surface temperature following a doubling of CO2-equivalent atmospheric concentrations. More generally, it refers to the equilibrium change in surface air temperature following a unit change in radiative forcing (°C/Wm-2)

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