Higher Sensitivity of Northern Hemisphere Monsoon to Anthropogenic Aerosol Than Greenhouse Gases

Abstract

Because increased greenhouse gas emissions considerably warm and moisten the Earth's atmosphere, one may expect an increase in monsoon precipitation during the historical period. However, we find the observed Northern Hemisphere land summer monsoon (NHLM) precipitation has significantly decreased since 1901. Simulations from Coupled Model Intercomparison Project Phase 6 (CMIP6) well reproduce global warming and the drying of NHLM since the industrial revolution when forced by observed external forcings. Result from single forcing experiment shows that the anthropogenic aerosol (AA) dominates the Northern Hemisphere (NH) monsoon precipitation drying, while the greenhouse gases (GHG) largely control surface warming. Thus, the NH monsoon precipitation responds to AA more sensitively than the GHG. The AA can more effectively modulate downward solar radiation reaching the surface, decreasing evaporation and weakening monsoon circulations by reducing the interhemispheric temperature difference and land-ocean thermal contrast, albeit with the same efficiency of the thermodynamic effect in the two forcings. Our result indicates the future intensive reduction of aerosol emission may rapidly recover the NH monsoon precipitation.