The Community Climate System Model (CCSM) is a national, community-wide project that is based at the National Center for Atmospheric Research (NCAR). The primary support is provided by the National Science Foundation and the Department of Energy, with additional support from the National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration. The first version of the model was released in 1996, and the June 1998 Journal of Climate was a special issue devoted to results from that version of the model. The third version of the CCSM and its documentation were released in June 2004 and are available for download from the Web site http://www.ccsm.ucar.edu/models/ccsm3.0/. Since then, the CCSM3 has been applied to a variety of scientific studies, and many further experiments have been run in support of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). The output from the IPCC runs is widely available to the climate science community at the Web sites https://www.earthsystemgrid.org or http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php.
This special issue is devoted to results from the CCSM3: there is an introductory paper, and then 25 more papers documenting many aspects of the atmosphere, ocean, land, and sea ice components, and the fully coupled model. The fully coupled model can be run at three different resolutions: a low resolution intended for paleoclimate studies, a standard resolution, and a high resolution, which was used for the IPCC runs. Four of the papers compare simulations and the climate sensitivity across the three CCSM3 resolutions. These 25 papers are authored by members of seven of the CCSM Working Groups: Atmosphere Model, Ocean, Land Model, Polar Climate, Climate Variability, Climate Change, and Paleoclimate. Papers by members of the Biogeochemistry Working Group have recently been published in the August 2005 Proceedings of the National Academy of Sciences, and in the Journal of Climate, 2006. The fall 2005 issue of The International Journal of High Performance Computing Applications was a special issue on climate modeling, and several papers were authored by members of the Software Engineering Working Group. These working groups are the foundation of the CCSM project, and their meetings are open to anyone from the scientific community who wishes to attend. The CCSM project is managed by the Science Steering Committee, and most of the credit for organizing this special issue must go to Bill Collins of NCAR. He was chairman of the SSC from July 2003 through June 2005, and during this period the CCSM3 was defined, released, the IPCC and other scientific experiments run, and the papers for this Journal of Climate special issue organized.