Climate Data

COSP: Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package

Cloud processes and feedbacks are recognized as the largest uncertainty in climate model projections of climate change. Progress in understanding the roles of clouds in climate change has in part been hampered by the lack of a consistent definition of clouds and cloud types in models and observations. It has been difficult to compare model output to observations, or even to compare model simulations to each other. The World Climate Research Program's (WCRP) Working Group on Coupled Modeling (WGCM) has recommended that climate models participating in CMIP5 use COSP. COSP includes simulators that are compatible with the ISCCP, PARASOL, CALIPSO, CALIOP, MISR, MODIS, and CloudSat observational products.

Key Strengths:

  • Facilitates "apples-to-apples" comparison of observed cloud data and model-simulated clouds
  • Can be adapted to many types of numerical models

Key Limitations:

  • Enabling the COSP package can substantially increase the run time of an experiment
  • Some cloud definition issues still not resolved; for example simulators do not capture differences in optically thin clouds between MODIS and ISCCP due to the latter's inclusion of partly cloudy pixels

Expert User Guidance

The following was contributed by Jennifer Kay (NCAR), May, 2012:

#Cloud processes and feedbacks remain the largest uncertainty in climate model projections. As a result, the Cloud Feedback Model Intercomparison Project (CFMIP), an international effort to understand cloud feedbacks and evaluate climate models with observations, was initiated (Bony et al. 2011). As a part of CFMIP, scientists and software engineers have integrated the CFMIP Observation Simulator Package (COSP, Bodas-Salcedo et al. 2012) into the atmospheric components of global climate models around the world. Many climate modeling centers are now producing diagnostics to contribute to CFMIP. For example, COSP now runs inline within Community Atmosphere Model (CAM), the atmospheric component of NCAR's Community Earth System Model (CESM) (Kay et al. 2012). COSP calculates model cloud diagnostics that can be directly compared with satellite observations from ISCCP, CloudSat, CALIOP, MISR, and MODIS. More information on COSP, including observations for comparison with COSP-simulated fields is available at

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Input Data

model output

Earth system components and main variables

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Key Figures

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Cite this page

Kay, Jennifer & National Center for Atmospheric Research Staff (Eds). Last modified 07 Oct 2013. "The Climate Data Guide: COSP: Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package." Retrieved from

Acknowledgement of any material taken from this page is appreciated. On behalf of experts who have contributed data, advice, and/or figures, please cite their work as well.