A multi-mode, two-moment aerosol model has been incorporated in the NCAR CAM3.0 to study the impact of anthropogenic aerosols on the global climate system. Seven aerosol modes, namely three sulfate, one external black carbon, one primary organic carbon, one sulfate/black carbon mixed mode and one sulfate/organic carbon mixed mode, are included in the model. Each aerosol mode predicts both number and mass concentration and thus aerosol size distribution which is critical to aerosol microphysics and optical property. When aerosols are assumed to be internally mixed, their chemical and optical properties are different than when they are externally mixed. Model results suggest that the major portions of black carbon and sulfate masses exist as mixed aerosols while two thirds of organic carbon mass is also in mixed form. In this study, multiple 60-year long simulations are carried out to examine the impact of the carbonaceous and sulfate aerosols in the climate system. Strong positive atmospheric forcing and negative surface forcing by the mixed aerosols affect the atmospheric thermal structure and consequently alter values of important parameters including cloud cover, height of planetary boundary layer, surface heat fluxes, and precipitation.