Abstract

We compare the radiative feedbacks resulting from a uniform warming and cooling of sea surface temperatures by 4 K in an ensemble of global climate models. The global-mean net feedback is less stabilising in response to warming in all nine models. This is primarily due to a stronger tropical water vapour feedback, with a smaller contribution from the shortwave cloud feedback. The zonal-mean feedbacks are similarly robust across the ensemble. In the extra-tropics, more positive shortwave cloud feedback under warming is associated with further poleward migration of the mean Southern Hemisphere jet latitude in some models. However, additional experiments with an aquaplanet version of the HadGEM3 model suggest that the asymmetry of the jet shift is not driving that in the cloud feedbacks at these latitudes. In the tropics, stronger water vapour feedback under warming is offset by a weaker shortwave cloud feedback. The result is that the ensemble spread in the differences between the global feedbacks under warming and cooling is mainly determined by their differences in the tropics. The spatial distribution of the feedbacks largely reflects the zonal mean behaviour, although there is considerable intermodel variation in the regional cloud feedbacks, particularly in the tropical shortwave cloud feedback. Comparison with CO2- and solar-forced coupled experiments suggests that the global-mean longwave cloud feedback is nearly invariant to warming and cooling, regardless of the nature of the forcing. The shortwave cloud feedback is generally more positive under warming in the coupled models, consistent with the uniform SST perturbation experiments.