The ultimate purpose of this study is to estimate anthropogenic aerosol effects on the planetary energy balance based on hypothetical anthropogenic aerosol forcings given by Coupled Model Intercomparison Project Phase 6(CMIP6).In order to achieve the confidence of these estimates,we also analyzed how natural variability contributes to uncertainty in these estimates.The climate model used in this study is NESM,which is an Earth system model developed by Nanjing University of Information Science and Technology(NUIST).The anthropogenic aerosol forcing officially recommended by CMIP6 is a hypothetical dataset derived from the second version of the Max Planck Institute Aerosol Climatology(MACv2-SP).MACv2-SP is implemented into the NESM model to represent anthropogenic aerosol optical properties and an associated Twomey effect.The NESM model results show that the global annual mean anthropogenic aerosol optical depth (AOD) in the visible band and the normalized change in cloud droplet number(dNovrN) calculated from MACv2-SP are 0.025 and 1.075,respectively.The anthropogenic aerosol forcings used in this study are similar to those in the paper which introduces MACv2-SP.This indicates that the MACv2-SP is used correctly in the NESM model.In the present study,the fixed-SST method is used to diagnose the aerosol effective radiative forcing (ERF).We set up two experiments:Base and Both.The Base experiment turns off MACv2-SP,while the anthropogenic aerosol optical properties and Twomey effect described by MACv2-SP are used in the Both experiment.The Base and Both experiments results show that anthropogenic aerosol ERF is estimated at -0.45 W·m^-2.The contribution to this ERF from direct radiative effect is -0.34 W·m^-2,which is significantly greater than its corresponding standard deviation (0.01 W·m^-2).The contribution to this ERF from aerosol-induced changes in clouds (i.e.semi-direct effect and Twomey effect) is -0.10 W·m^-2,which is only one third of its corresponding standard deviation (0.30 W·m^-2).These indicate that climate model is capable of achieving high confidence in estimating direct radiative effect,yet only very low confidence in estimating aerosol effects on cloud radiative forcing.The Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5),using expert judgment,assessed the ERF to be -0.9 W·m^-2,with a 5 to 95% uncertainty range of -1.9 to -0.1 W·m^-2 (moderate confidence).Compared with IPCC AR5,the ERF described in this study is in the uncertainty range,although it is weak (less negative).The second phase of the Aerosol Comparisons between Observations and Models (AeroCom II) model results provide a direct radiative effect estimate of -0.35 W·m^-2,with a model range of about -0.60 to -0.13 W·m^-2.The direct radiative effect estimate from our model results is similar to that of AeroCom II.This also suggests that the aerosol effects on cloud radiative forcing are the main sources of the difference in ERF between this study and IPCC AR5.CMIP6 only considers the Twomey effect,ahilw other aerosol indirect effects are not included.This may be the reason for which the aerosol effects on cloud radiative forcing in this study are weaker than those of IPCC AR5.