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Stronger constraints on the anthropogenic indirect aerosol effect
1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada. Ulrike.Lohmann@Dal.Ca
Science (New York, N.Y.)
|November 2, 2002
Summary
Climate models require a modeling component to deduce indirect aerosol effects on clouds. This study validates a climate model using satellite data, finding it agrees better with observations when indirect aerosol effects are included, though it overestimates their impact.
Area of Science:
- Climate science
- Atmospheric science
- Earth system science
Background:
- Anthropogenic aerosols significantly influence Earth's energy balance by modifying cloud properties.
- Indirect aerosol effects, such as changes in cloud albedo and lifetime, are crucial but challenging to quantify using observations alone.
- Climate models are essential tools for understanding and quantifying these aerosol-cloud interactions.
Purpose of the Study:
- To validate a climate model's representation of indirect aerosol effects using satellite observations.
- To assess the model's agreement with observed cloud properties when indirect aerosol effects are included versus excluded.
- To refine the estimation of the global mean total anthropogenic aerosol effect.
Main Methods:
- Utilized satellite observations (POLDER) to validate a climate model.
- Compared model simulations with and without indirect aerosol effects against observational data.
- Quantified the difference in cloud susceptibility to aerosols between the model and observations.
Main Results:
- The climate model shows improved agreement with satellite observations when indirect aerosol effects are incorporated.
- Simulated clouds exhibit higher susceptibility to aerosols than observed clouds, leading to an overestimation of the indirect aerosol effect.
- Adjusting for the difference in susceptibility reduced the estimated global mean total anthropogenic aerosol effect from -1.4 W/m² to -0.85 W/m².
Conclusions:
- Indirect aerosol effects are vital for accurate climate modeling, necessitating their inclusion.
- Model parameterizations of aerosol-cloud interactions require refinement to match observational constraints.
- The net anthropogenic aerosol forcing is likely smaller than previously estimated by models without observational adjustments.
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