ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-3235-2010 Total aerosol effect: radiative forcing or radiative flux perturbation? Lohmann U. 1 Rotstayn L. 2 Storelvmo T. 1 Jones A. 3 Menon S. 4 Quaas J. 5 Ekman A. M. L. 6 Koch D. 7 Ruedy R. 7 Institute of Atmospheric and Climate Science, ETH Zurich, Switzerland Centre for Australian Weather and Climate Research, CSIRO, Aspendale, Victoria, Australia Met Office Hadley Centre, Exeter, UK Lawrence Berkeley National Laboratory, Berkeley, USA Max Planck Institute for Meteorology, Hamburg, Germany Stockholm University, Stockholm, Sweden NASA GISS, New York, NY, USA 06 04 2010 10 7 3235 3246 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/3235/2010/acp-10-3235-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/3235/2010/acp-10-3235-2010.pdf

Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation formation. In former assessments of aerosol radiative 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 forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (<i>RFP</i>), that takes these fast feedbacks and interactions into account. Based on our results, we recommend <i>RFP</i> as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

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