Decadal variation of East Asian radiative forcing due to anthropogenic aerosols during 1850-2100, and the role of atmospheric moisture

An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is used in an atmospheric general circulation model to investigate anthropogenic aerosol radiative forcing (RF) with a focus on East Asia. Compared to the pre-industrial era, the calculated strongest global mean direct RF (DRF) of -0.30 W m(-2) at the all-sky top of the atmosphere (TOA) occurs in the 1980s and an indirect cloud albedo forcing (CAF) of -0.67 W m(-2) in the 2000s; a maximum atmospheric DRF of 0.48 W m(-2), mainly by black carbon absorption, is found in the 2010s. Much larger aerosol DRF and CAF values are distributed over East Asia until the 2010s, and the negative surface and positive atmospheric DRF in Eastern China is even projected to maintain a magnitude of 5.0 W m(-2) until the 2030s. Increasing East Asian aerosol loading has shifted the anthropogenic aerosol RF centers to lower latitudes in the Northern Hemisphere since the 1980s, and this trend is more severe under future mid-and high-range emission scenarios. Further results indicate that larger DRF values over East Asia can be partly attributed to climato-logical summer atmospheric moisture that is higher relative to Norther American and European regions, which enhances the aerosol hygroscopic effect, then strengthens aerosol optical depth and DRF at clear-sky TOA and surface, and even influences their long-term changes. The observational comparisons reveal that present day simulated surface concentrations of key anthropogenic aerosol species and resulting optical depth are highly underestimated in Eastern China. Further research on simulated meteorology and aerosol features is therefore recommended to reduce the uncertainties in estimating aerosol RF over East Asia.