Can the weakening of Indian Monsoon be attributed to anthropogenic aerosols?

Abstract

Abstract Literature found that the increasing concentration of Anthropogenic Aerosol (AA) is the key reason behind the weakening trend of Indian Summer Monsoon Rainfall (ISMR), based on the Coupled Model Intercomparison Project Phase5 (CMIP5) simulations with AA-only forcing. Here, we re-examine and find that AA-only simulations show country-wide drying, in contrast to the observed east-west asymmetry in the recent ISMR trend. For further evaluation, we decompose the changes in moisture convergence during summer monsoon into dynamic and thermodynamic components. We find that multi-run ensemble averages for individual CMIP5 models do not capture the observed dominance of the changes in dynamic component over the thermodynamic one. An optimal fingerprinting technique for detection and attribution also fail to attribute the changes in ISMR to AA, either because of large internal variability and/or intermodel spread. This implies the need for more careful assessment of AA-only simulations for the ISMR before attributing the changes to AA.