Long-term cloud change imprinted in seasonal cloud variation: More evidence of high climate sensitivity

Abstract

The large spread of model equilibrium climate sensitivity (ECS) is mainly caused by the differences in the simulated marine boundary layer cloud (MBLC) radiative feedback. We examine the variations of MBLC fraction in response to the changes of sea surface temperature (SST) at seasonal and centennial time scales for 27 climate models that participated in the Coupled Model Intercomparison Project phase 3 and phase 5. We find that the intermodel spread in the seasonal variation of MBLC fraction with SST is strongly correlated with the intermodel spread in the centennial MBLC fraction change per degree of SST warming and that both are well correlated with ECS. Seven models that are consistent with the observed seasonal variation of MBLC fraction with SST at a rate -1.28 ± 0.56%/K all have ECS higher than the multimodel mean of 3.3 K yielding an ensemble-mean ECS of 3.9 K and a standard deviation of 0.45 K. Key Points Boundary cloud variations at seasonal and centennial scales are correlated Boundary cloud seasonal response is correlated with sensitivity Observations suggest a higher climate sensitivity than multimodel mean