Atmos. Chem. Phys. Discuss., 10, 19195-19217, 2010
www.atmos-chem-phys-discuss.net/10/19195/2010/
doi:10.5194/acpd-10-19195-2010
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under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Impact of parametric uncertainties on the present-day climate and on the anthropogenic aerosol effect
U. Lohmann and S. Ferrachat
Institute of Atmospheric and Climate Science, ETH Zurich, Switzerland

Abstract. Clouds constitute a large uncertainty in global climate modeling and climate change projections as many clouds are smaller than the size of a model grid box. Some processes, such as the rates of rain and snow formation that have a large impact on climate, cannot be observed. These processes are thus used as tuning parameters in order to achieve radiation balance. Here we systematically investigate the impact of various tunable parameters within the convective and stratiform cloud schemes and of the ice cloud optical properties on the present-day climate in terms of clouds, radiation and precipitation. The total anthropogenic aerosol effect between pre-industrial and present-day times amounts to −1.00 W m−2 obtained as an average over all simulations as compared to −1.02 W m−2 from those simulations where the global annual mean top-of-the atmosphere radiation balance is within ±1 W m−2. The parametric uncertainty when taking all simulations into account has an uncertainty range of 25% between the minimum and maximum value. It is reduced to 11% when only the simulations with a balanced top-of-the atmosphere radiation are considered.

Citation: Lohmann, U. and Ferrachat, S.: Impact of parametric uncertainties on the present-day climate and on the anthropogenic aerosol effect, Atmos. Chem. Phys. Discuss., 10, 19195-19217, doi:10.5194/acpd-10-19195-2010, 2010.
 
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