Sensitivity of Simulated Global Climate to Perturbations in Low Cloud Microphysical Properties. Part II: Spatially Localized Perturbations

Abstract

Abstract The sensitivity of the global climate to spatially localized (20°–70°N) perturbations in the microphysical properties of low clouds is investigated using a general circulation model coupled to a mixed layer ocean with fixed cloud distributions. By comparing with earlier experiments involving globally uniform perturbations, insights are obtained into the climate responses to spatially inhomogeneous radiative forcings, such as that due to the contrast in the effective drop radius of land and ocean clouds and the anthropogenic sulfate aerosol-induced alteration of cloud albedo. The main findings of this study are as follows: 1) The model's climate sensitivity (ratio of global-mean surface temperature response to the global-mean radiative forcing) is virtually independent of the distribution and magnitude of forcing. 2) Although the total feedback is very similar in the different experiments, the strengths of the individual feedback mechanisms (water vapor, albedo, lapse rate) are dissimilar. 3) For ...