Dependence of Climate Feedbacks on the Latitudinal Distribution of Radiative Forcing .

The climate response to radiative forcing depends on several radiative feedback processes, which amplify or dampen the initial change caused by the radiative forcing. These radiative feedback processes in response to any radiative forcing vary with spatial patterns of the surface temperature change. Several past studies have shown that the climate is more sensitive to a radiative forcing that is focused in polar regions than a tropically concentrated radiative forcing. In the present study, we investigate the sensitivity of the climate response to the latitudinal distribution of solar radiative forcing using NCAR CAM4 coupled to a slab ocean model. We apply the forcing to Arctic (60°N- 90°N), Tropical (20°S- 20°N), and Antarctic (90°S- 60°S) latitude bands by increasing the solar insolation by different amounts such that the global mean radiative forcing is nearly the same in all three experiments and find that the climate sensitivity parameter is largest in the Antarctic simulation (1.25 K/Wm-2), followed by the Arctic (0.97 K/Wm-2) and Tropical simulations (0.48 K/Wm-2). We further estimate the individual feedbacks using radiative kernels. The albedo feedback is largest in the Arctic experiment (0.5 Wm-2K-1) and has smaller magnitudes in the Tropical (0.23 Wm-2K-1) and Antarctic (0.22 Wm-2K-1) cases. The water vapor feedback has values of 0.92 and 1.01 Wm-2K-1 in the Arctic and Antarctic simulation and is largest in the Tropical (1.85 Wm-2K-1) simulation. The lapse rate feedback is positive and largest in the Arctic simulation (0.37 Wm-2K-1), followed by the Antarctic simulation (-0.01 Wm-2K-1), and has a large negative value in the Tropical simulation (-0.94 Wm-2K-1). Cloud feedbacks are estimated as 0.16 Wm-2K-1 for the Arctic, -0.41 in the Tropical, and 0.38 in the Antarctic simulations. The Planck feedback differs the least among these three experiments (-2.77, -3.05, -2.81 Wm-2K-1 for the Arctic, Tropical, and Antarctic simulation, respectively). This study contributes to an improved mechanistic understanding of physical processes associated with the sensitivity of the climate response to the latitudinal distribution of radiative forcing. Our study also has implications for solar geoengineering approaches that involve latitudinal variation in imposed solar forcing.