Uncertainty in aerosol radiative forcing impacts the simulated global
monsoon in the 20th century
Abstract
Anthropogenic aerosols are dominant drivers of historical monsoon
rainfall change. However, large uncertainties in the radiative forcing
associated with anthropogenic aerosol emissions, and the dynamical
response to this forcing, lead to uncertainty in the simulated monsoon
response. We use historical simulations in which aerosol emissions are
scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to
aerosol forcing uncertainty (−0.3 W m to −1.6 W m). Hemispheric
asymmetry in emissions generates a strong relationship between scaling
factor and both hemispheric temperature contrast and meridional location
of tropical rainfall. Increasing the scaling from 0.2 to 1.5 reduces the
global monsoon area by 3% and the global monsoon intensity by 2% over
1950–2014, and changes the dominant influence on the 1950–1980 monsoon
rainfall trend from greenhouse gas to aerosol. Regionally, aerosol
scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.