A New Method To Improve the Evaluation of Clouds in Climate Models


How do clouds change with climate change? This is one of the great unsolved problems of climate change whose solution is critical because cloud changes may counter or enhance temperature changes. Climate models struggle to accurately represent clouds, because the equations used cannot completely describe clouds. Satellite observations of clouds have provided important tests for models, but models and satellites “view” clouds differently since satellites only get time-limited snapshots of clouds. Scientists at Lawrence Livermore National Laboratory, in collaboration with scientists worldwide, have created a diagnostic tool known as the Cloud Feedback Model Intercomparison Project Observation Simulator Package (COSP) that enables scientists to compare satellite and climate model views of clouds. COSP converts model clouds into pseudo-satellite observations with an approach that mimics the satellite view of an atmospheric column with model-specified physical properties. COSP is now used worldwide by most of the major models for climate and weather prediction, and it will play an important role in the model evaluation being reviewed in the next report of the Intergovernmental Panel on Climate Change. This study already reveals information on cloud representation in climate models: for example, an under-representation in all models of mid-level and cumulus clouds, and better performance by a detailed regional model compared to global models. In sum, COSP facilitates a more rapid improvement of climate models, and it will ultimately reduce uncertainty in climate predictions.

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Bodas-Salcedo, A., et al. 2011. “COSP: Satellite Simulation Software for Model Assessment,” Bulletin of the American Meteorological Society 92(68), 1023-1043. DOI:10.1175/2011BAMS2856.1.