Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-1152
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
10 Jan 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Cloud albedo changes in response to anthropogenic sulfate and non-sulfate aerosol forcings in CMIP5 models
Lena Frey, Frida A.-M. Bender, and Gunilla Svensson Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
Abstract. The effects of different aerosol types on cloud albedo are analyzed using the linear relation between total albedo and cloud fraction found on monthly mean scale in regions of subtropical marine stratocumulus clouds, and the influence of Aerosol Optical Depth (AOD) on this relation. Model experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to separately study the responses to increases in sulfate, non-sulfate and all anthropogenic aerosols. A cloud brightening on month-to month scale due to variability in the background aerosol is found to dominate even in the cases where anthropogenic aerosols are added. The aerosol composition is found to be of importance for this cloud brightening, that is thereby region dependent. There is indication that absorbing aerosols to some extent counteract the cloud brightening, but scene darkening with increasing aerosol burden is generally not supported, even in regions where absorbing aerosols dominate. Regional, monthly mean cloud albedo is found to increase with the addition of anthropogenic aerosols, and more so with sulfate than non-sulfate. The changes in AOD due to anthropogenic aerosols are typically small compared to the AOD variability within a given aerosol forcing scenario, and the magnitude of the change in cloud albedo due to anthropogenic aerosols is small and not directly related to the strength of the month-to-month cloud brightening due to aerosols. The diversity in changes in cloud albedo in this set of models is rather related to the different changes in cloud water content between the experiments.

Citation: Frey, L., Bender, F. A.-M., and Svensson, G.: Cloud albedo changes in response to anthropogenic sulfate and non-sulfate aerosol forcings in CMIP5 models, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1152, in review, 2017.
Lena Frey et al.
Lena Frey et al.
Lena Frey et al.

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Short summary
In this study the cloud albedo effect in climate models is investigated, separating the influence of anthropogenic sulfate and non-sulfate aerosols. Cloud albedo changes induced by added anthropogenic aerosols are found to be determined by changes in the cloud water content rather than model sensitivity to monthly aerosol variations. The results also indicate that the background aerosol is the main driver for a cloud brightening effect on the month-to-month scale.
In this study the cloud albedo effect in climate models is investigated, separating the...
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