POLDER satellite retrievals of aerosol properties over oceans are used to estimate a global-mean clear-sky aerosol shortwave flux perturbation of order -5 to -6 Wm-2. Uncertainties due to aerosol absorption and POLDER cloud screening algorithm are quantified. In order to bound the radiative forcing by anthropogenic aerosols, we attempt to remove the contribution of background aerosols from these estimates and present all-sky aerosol radiative effects for three regions and two methods. The results are sensitive to the thresholds used to define the background conditions. ¿ 2000 American Geophysical Union