Natural aerosol direct and indirect radiative effects

[1] Natural aerosol plays a significant role in the Earth’s system due to its ability to alter the radiative balance of the Earth. Here we use a global aerosol microphysics model together with a radiative transfer model to estimate radiative effects for five natural aerosol sources in the present-day atmosphere: dimethyl sulfide (DMS), sea-salt, volcanoes, monoterpenes, and wildfires. We calculate large annual global mean aerosol direct and cloud albedo effects especially for DMS-derived sulfate (–0.23 Wm and –0.76 Wm, respectively), volcanic sulfate (–0.21 Wm and –0.61 Wm) and sea-salt (–0.44 Wm and –0.04 Wm). The cloud albedo effect responds nonlinearly to changes in emission source strengths. The natural sources have both markedly different radiative efficiencies and indirect/direct radiative effect ratios. Aerosol sources that contribute a large number of small particles (DMS-derived and volcanic sulfate) are highly effective at influencing cloud albedo per unit of aerosol mass burden. Citation: Rap, A., C. E. Scott, D. V. Spracklen, N. Bellouin, P. M. Forster, K. S. Carslaw, A. Schmidt, and G. Mann (2013), Natural aerosol direct and indirect radiative effects, Geophys. Res. Lett., 40, 3297–3301, doi:10.1002/grl.50441.