Figure 6. Projections of changes in global average temperature (1990-2100) based on results from an upwelling- diffusion model calibrated to global circulation model results and corresponding to IPCC concentration scenario IS95a. Note that this scenario accounts for projected changes in the concentrations CO2, CH4, N2O, chlorofluorocarbons, and sulfate aerosols. Projections are for different equilibrium sensitivities of the climate to a doubling of the concentration: (a) 1.5 ° , (b) 2.5° , and (c) 4.5°C. Also shown are observed annual mean surface temperature anomalies for the period 1854-1990 [Source: T. Wigley, UCAR].