Future intensification of Northern Hemisphere Monsoons due to Declining Remote Aerosols

Anthropogenic aerosol emissions have significantly shaped historical monsoon precipitation, yet uncertainties persist in the projected response to future emissions. This study employs models contributing at least ten ensemble members to the Detection and Attribution Model Intercomparison Project—MIROC6 and CanESM5—to examine the mid-century response of the Northern Hemisphere (NH) summer monsoons to changes in aerosol burdens. We focus on a scenario characterized by an increase in aerosol burdens over South Asia, but strong reductions over the NH extra-tropical continents (i.e., over United States, Europe, and East Asia), since this is consistent with observed trends. These anomalous reductions induce an inter-hemispheric energy imbalance, prompting a large-scale response in the atmospheric meridional overturning circulation. The upper-tropospheric levels of the overturning circulation enhance heat transport towards the Southern Hemisphere, while the lower levels bring enhanced moisture convergence into the NH, leading to more rainfall across NH monsoon regions. Our findings highlight that global aerosol pollution control measures may have wide-ranging impacts well beyond the aerosol source regions. For South Asia, these findings suggest that widespread remote aerosol reductions could offset the precipitation suppression from rising local aerosols.