© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics Total aerosol effect: radiative forcing or radiative flux perturbation?

Abstract. Uncertainties in aerosol radiative forcings, es-pecially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation in-troduces feedbacks which can affect the rate of precipita-tion formation. In former assessments of aerosol radia-tive forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forc-ing agents (aerosols and greenhouse gases) the radiative forc-ings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturba-tions (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to com-pare the effects of particular forcing agents in different mod-els.