Wednesday, October 14, 2015

Higher sensitivity still quite possible

Most of the talk over the last couple of years has been about observational studies indicating that climate sensitivity to CO2 was perhaps on the lower side, rather than the high side.  Yet I see that in a paper that has just come out, some NASA based researchers give reason to think the high side is more likely:   
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 timescales for 27 climate models that participated in the Coupled Model Intercomparison Project Phase 3 and Phase 5. We find that the inter-model spread in the seasonal variation of MBLC fraction with SST is strongly correlated with the inter-model 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 multi-model mean of 3.3 K yielding an ensemble-mean ECS of 3.9 K and a standard deviation of 0.45 K.
That seems important...

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