1Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
3Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA, USA
4Atmospheric and Environmental Research (AER), Lexington, MA, USA
5Department of Earth System Science, University of California, Irvine, CA, USA
Abstract. The direct radiative effect (DRE) of aerosols, which is the instantaneous radiative impact of all atmospheric particles on the Earth's energy balance, is often confused with the direct radiative forcing (DRF), which is the change in DRE from pre-industrial to present-day (not including climate feedbacks). We use here a coupled global chemical transport model (GEOS-Chem) and radiative transfer model (RRTMG) to contrast these concepts. We estimate a global mean all-sky aerosol DRF of −0.36 Wm−2 and a DRE of −1.83 Wm−2 for 2010. Therefore, natural sources of aerosol (here including fire) affect the global energy balance over four times more than do present-day anthropogenic aerosols. If global anthropogenic emissions of aerosols and their precursors continue to decline as projected in recent scenarios due to effective pollution emission controls, the DRF will shrink (−0.22 Wm−2 for 2100), while the climate feedbacks on aerosols under rising global temperatures will likely amplify. Secondary metrics, like DRE, that quantify temporal changes in both natural and anthropogenic aerosol burdens are therefore needed to quantify the total effect of aerosols on climate.