Figure 10.20. (a) 21st-century atmospheric CO2 concentration as simulated by the 11 C4MIP models for the SRES A2 emission scenario (red) compared with the standard atmospheric CO2 concentration used as a forcing for many IPCC AR4 climate models (black). The standard CO2 concentration values were calculated by the BERN-CC model and are identical to those used in the TAR. For some IPCC-AR4 models, different carbon cycle models were used to convert carbon emissions to atmospheric concentrations. (b) Globally averaged surface temperature change (relative to 2000) simulated by the C4MIP models forced by CO2 emissions (red) compared to global warming simulated by the IPCC AR4 models forced by CO2 concentration (black). The C4MIP global temperature change has been corrected to account for the non-CO2 radiative forcing used by the standard IPCC AR4 climate models.