Contrasting impacts of Asian sulfate aerosols on regional summer extreme precipitation under different climate backgrounds

Asian sulfate aerosols substantially affect regional summer precipitation, yet whether and how their effects vary with the background climate state remains unclear. This study investigates these impacts under pre-industrial and pre-industrial +1 K climates, using the reduced-complexity climate model Fast Ocean Rapid Troposphere Experiment version 2 with the Systematic Regional Aerosol Perturbations simulations. Results show that increased Asian sulfate aerosols reduce the summer mean and extreme precipitation over East and South Asia in both climates, with stronger suppression over northern India in the +1 K climate. The atmospheric energy budget analysis reveals that this is primarily due to enhanced dynamic effects in the warmer climate. When aerosols are added to the pre-industrial climate, the increased horizontal dry static energy (DSE) gradient partially offsets the aerosol-induced dynamic suppression over northern India. Under the +1 K climate, higher atmospheric static stability weakens the local meridional circulation induced by aerosol forcing, thereby reducing the meridional temperature gradient and diminishing the offsetting effect, making the dynamic suppression more dominant. Further analysis indicates that this difference in precipitation responses results from the nonlinear interaction between the aerosol-radiation and aerosol-cloud interactions under the +1 K climate, whereas the two effects combine approximately linearly under the pre-industrial climate. This study suggests that the reduction in precipitation, including extremes, over northern India caused by Asian sulfate aerosols is amplified under a warmer climate background. This implies that future aerosol emissions reductions may unmask or amplify extreme precipitation increases in this region.