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Extreme wet and dry conditions affected differently by greenhouse gases and aerosols

Jana Sillmann, Camilla Weum Stjern, Gunnar Myhre, Bjørn Hallvard Samset, Øivind Hodnebrog, Timothy Andrews, Oliviér Boucher, Gregory Faluvegi, Piers Forster, Matthew R. Kasoar, Viatcheslav V. Kharin, Alf Kirkevåg, Jean-Francois Lamarque, Dirk Jan Leo Oliviè, Thomas B. Richardson, Drew Shindell, Toshihiko Takemura, Apostolos Voulgarakis, Francis W. Zwiers

Global warming due to greenhouse gases and atmospheric aerosols alter precipitation rates, but the influence on extreme precipitation by aerosols relative to greenhouse gases is still not well known. Here we use the simulations from the Precipitation Driver and Response Model Intercomparison Project that enable us to compare changes in mean and extreme precipitation due to greenhouse gases with those due to black carbon and sulfate aerosols, using indicators for dry extremes as well as for moderate and very extreme precipitation. Generally, we find that the more extreme a precipitation event is, the more pronounced is its response relative to global mean surface temperature change, both for aerosol and greenhouse gas changes. Black carbon (BC) stands out with distinct behavior and large differences between individual models. Dry days become more frequent with BC-induced warming compared to greenhouse gases, but so does the intensity and frequency of extreme precipitation. An increase in sulfate aerosols cools the surface and thereby the atmosphere, and thus induces a reduction in precipitation with a stronger effect on extreme than on mean precipitation. A better understanding and representation of these processes in models will provide knowledge for developing strategies for both climate change and air pollution mitigation.

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