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

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. Plain Language Summary Increased anthropogenic emissions from human activities significantly warm the Earth system. In common sense, it would increase monsoon precipitation. However, observed Northern Hemisphere (NH) monsoon precipitation shows a significant decline since the beginning of the 20th century. The current state‐of‐the‐art models reproduce the global warming and weakened NH monsoon under anthropogenic aerosol (AA) and greenhouse gases (GHG) forcing. We find that AA dominates the monsoon precipitation change but only has a minor role in the Earth's surface temperature. In contrast, the GHG controls the Earth's surface warming but has a minor role in changing monsoon precipitation. It suggests that the aerosols are more effective in changing NH monsoon precipitation than GHG. Our result indicates the future intensive reduction of aerosol emission may rapidly increase the NH monsoon precipitation under global warming. Key Points Northern Hemisphere land monsoon precipitation has significantly decreased over the past 120 years Anthropogenic aerosol has a more significant contribution to precipitation reduction than greenhouse gases Surface radiation and monsoon circulation dominate the aerosol's high efficiency in reducing monsoon pr