The Dependence of Climate Sensitivity on the Meridional Distribution of Radiative Forcing

This study investigates how climate sensitivity depends upon the spatial pattern of radiative forcing. Sensitivity experiments using a coupled ocean-atmosphere model were conducted by adding anomalous incoming solar radiation over the entire globe, Northern Hemisphere mid-latitudes, Southern Ocean, and tropics. The varied forcing patterns led to highly divergent climate sensitivities. Specifically, the climate is nearly twice as sensitive to Southern Ocean forcing as tropical forcing. Strong coupling between the surface and free troposphere in the tropics increases the inversion strength, leading to smaller cloud feedback in the tropical forcing experiments. In contrast, the extratropics exhibit weaker coupling, a decrease or near-zero change in the inversion strength, and strong positive cloud feedback. These results contrast with the conventional SST-pattern effect in which tropical surface temperature changes regulate climate sensitivity. They also have important implications for other potentially asymmetric forcings, such as those from geoengineering, volcanic eruptions, and paleoclimatic changes. The way surface temperature responds to radiative forcing depends on where such forcing is applied. Numerical model integrations show that the global mean surface temperature change is doubled when the forcing is imposed over the Southern Ocean compared to when the forcing is applied in the tropics. Changes in the vertical temperature profiles and clouds contribute to the dependence of surface temperature change on the forcing geographic locations. The solar forcing pattern effect is investigated in a coupled ocean-atmosphere modelClimate sensitivity is doubled from tropical forcing to Southern Ocean forcingThe radiative forcing pattern effect involves changes in lapse rate feedback, cloud feedback, and tropospheric stability