Structural similarities and differences in climate responses to CO2 increase between two perturbed physics ensembles
Equilibrium climate sensitivity (ECS) of two perturbed physics ensembles generated by structurally different general circulation models (GCMs) are investigated. The GCMs used for the analysis are MIROC3.2 and HadSM3. The difference in ECS between the two ensemble means and variance within the ensembles is mainly driven by variations in the shortwave (SW) cloud feedback. We develop a method to quantify contributions of clouds with different cloud top pressure to the SW cloud feedback by using the model output. We find that contributions from the low level cloud play an important role in determining the difference in the SW cloud feedback between the two ensemble means, as well as their variance. We also find a strong anti-correlation between the SW feedback by the low level cloud and the present-day cloud albedo in one of the two ensembles, HadSM3. The relationship between the strength of climate feedback and the present-day climate states demonstrated in the present study could lead to an observational constraint on ECS.
J. Climate, 23 , 1392-1410