Studies into the impact of anthropogenic aerosols on regional summer monsoon rainfall have focused on a black carbon-induced enhancement and a sulfate-induced suppression. The latter encompasses significant Asian and non-Asian sources, but their relative roles in forcing historical global and regional monsoon trends are largely unexplored. Using targeted 20th century coupled climate simulations, designed to isolate the impact from anthropogenic aerosols, we show that Asian aerosols induce a weak suppression of global summer monsoon, confined to the East Asian region. The addition of non-Asian aerosols generates an enhancement and broadening of cooler temperatures over Europe and Asia relative to the ambient oceans, supporting stronger northerly flows that further suppress Asian monsoon rainfall. Furthermore, atmospheric convection is directed away from the Asian monsoon regions, resulting in an equatorward shift in rainfall. Our results highlight the importance of the non-Asian aerosols in exacerbating the impact of Asian aerosols on global monsoon rainfall, particularly across Asia.
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