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.