Comprehensive estimate of the anthropogenic aerosol radiative effects
using an atmospheric model with reduced aerosol forcing complexity
Abstract
The simplified anthropogenic aerosol optical properties and an
associated Twomey effect provided by CMIP6 (i.e., MACv2-SP) were used in
the Grid-point Atmospheric Model of IAP LASG (GAMIL). With the benefit
of MACv2-SP, instantaneous radiative forcing (RF) from aerosol-radiation
interactions (RFari) and aerosol-cloud interactions (RFaci) can be
calculated by double radiation calls in one present-day (PD) simulation.
The RFaci determined by this straightforward method is the exact Twomey
effect, which previously was impossible to separate from its subsequent
rapid adjustments using the default GAMIL model with physically based
aerosol-cloud interactions. The RFaci is very robust, with a global
average of −0.10 W m. The RFari can be calculated by different methods.
The all-sky RFari with and without natural aerosol influence (i.e.,
different methods) is estimated at −0.21 and −0.33 W m, respectively.
This suggests that the natural aerosol burden might substantially impact
the estimate of RFari. Furthermore, the RFari determined by the
difference between two simulations is more sensitive to model internal
year-to-year variability compared with the RFari determined from one PD
simulation. The RFaci efficiency usually enhances with increasing cloud
cover, whereas the RFari efficiency becomes weaker under cloudy
conditions. As a result, the seasonal variability of the global average
RFaci is stronger than that of RFari. From 1975 to 2000, both RFari and
RFaci show a clear response to the spatial changes in anthropogenic
aerosols, and the global average RF (RFari + RFaci) is enhanced by
~6%, even with a slight decrease in the global average
anthropogenic aerosols.