Future impact of anthropogenic sulfate aerosol on North Atlantic climate |
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Authors: | Irene Fischer-Bruns Dorothea F Banse Johann Feichter |
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Institution: | (1) Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany;(2) International Max Planck Research School on Earth System Modelling, Bundesstrasse 53, 20146 Hamburg, Germany |
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Abstract: | We examine the simulated future change of the North Atlantic winter climate influenced by anthropogenic greenhouses gases
and sulfate aerosol. Two simulations performed with the climate model ECHAM4/OPYC3 are investigated: a simulation forced by
greenhouse gases and a simulation forced by greenhouse gases and sulfate aerosol. Only the direct aerosol effect on the clear-sky
radiative fluxes is considered. The sulfate aerosol has a significant impact on temperature, radiative quantities, precipitation
and atmospheric dynamics. Generally, we find a similar, but weaker future climate response if sulfate aerosol is considered
additionally. Due to the induced negative top-of-the-atmosphere radiative forcing, the future warming is attenuated. We find
no significant future trends in North Atlantic Oscillation (NAO) index in both simulations. However, the aerosol seems to
have a balancing effect on the occurence of extreme NAO events. The simulated correlation patterns of the NAO index with temperature
and precipitation, respectively, agree well with observations up to the present. The extent of the regions influenced by the
NAO tends to be reduced under strong greenhouse gas forcing. If sulfate is included and the warming is smaller, this tendency
is reversed. Also, the future decrease in baroclinicity is smaller due to the aerosols’ cooling effect and the poleward shift
in track density is partly offset. Our findings imply that in simulations where aerosol cooling is neglected, the magnitude
of the future warming over the North Atlantic region is overestimated, and correlation patterns differ from those based on
the future simulation including aerosols. |
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Keywords: | Sulfate aerosol Direct aerosol effect Climate change North Atlantic cyclones NAO |
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