Climate response to interhemispheric differences in radiative forcing governed by shortwave cloud feedbacks

Abstract

Understanding the climate response to interhemispheric differences in imposed radiative forcing is crucial for solar radiative modification (SRM) investigations. While previous studies have shown that climate sensitivity to solar insolation changes imposed in the Northern (NH) versus the Southern Hemisphere (SH) is different, the underlying mechanisms remain unclear. In this study, we investigate the climate response to three different radiative forcing scenarios: globally uniform radiative forcing, radiative forcing imposed only in the NH, and radiative forcing confined only to the SH. We find that the climate sensitivity is larger when forcing is imposed only in the SH. To explain the mechanisms for this, we estimate climate feedbacks using the radiative kernel approach. We find that albedo and Planck feedbacks are insensitive to hemisphere of forcing, and the larger climate sensitivity to the southern hemispheric radiative forcing is primarily due to differences in shortwave cloud feedbacks. Additionally, we examine impacts of interhemispheric differences in radiative forcing on tropical circulation, planetary albedo, and land/sea warming contrast. Our results clearly demonstrate how the intertropical convergence zone moves into the hemisphere where the radiative forcing is larger without maintaining a symmetric planetary albedo. Overall, our study provides insights into climate system responses to interhemispheric differences in radiative forcing caused by forcing agents such as aerosols from volcanic eruptions and human activities, and land cover changes, in addition to solar geoengineering.