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.