Declining Aerosols and Recovering Monsoon

Abstract

South Asian summer monsoon went through a period of drastic decline since the 1950s for nearly 5 decades. It was attributed to the net cooling effect of increasing anthropogenic aerosol concentrations that happened around the same time. Recent decades have seen a slight recovery of monsoon rainfall. Through this project, we have made a detailed note of how this trend carries forward into the near future and what factors will play a role by analysing data of the SSP245 experiments from the CMIP6 archive. Our investigations reveal that the rainfall will continue to increase but at a slow rate till the 2040s and then a steep recovery thereafter. Aerosols and GHGs through their opposite effects of cooling and warming respectively involve in a tug of war for the control over monsoon rainfall. Till the 2040s aerosols will be able to slow down rainfall recovery but after that GHGs take over with their ability to maintain a significant land-sea thermal contrast crucial to bring monsoon winds towards South Asia. The enhanced moisture availability will also play its part in the recovery. Further analysis on ENSO statistics from multiple simulations clearly implies that ENSO will take a backseat in the tug of war in controlling the monsoon precipitation once anthropogenic influences become significant.