The Community Climate System Model (CCSM)4 is a comprehensive system for studying the past, present, and future of the Earth. In contrast to traditional weather-forecast models that focus only on the atmosphere, the CCSM includes components that simulate the evolution and interactions among the atmosphere, ocean, land surface, and sea ice. The principal objectives of the CCSM program are to develop a comprehensive numerical model with which to study the Earth’s present climate, to investigate seasonal and inter-annual variability in the climate, to explore the history of the Earth’s climate, and to simulate the future of the environment for policy formation.
CCSM has been designed with input from a broad community of climate scientists, computer scientists, and software engineers. This community also shares the scientific code and results produced by the model. In fact, CCSM is the only climate model that is developed as open source code and is distributed via the web to the world-wide climate community. CCSM is funded with support from the National Science Foundation (NSF), DOE, the National Space and Aeronautics Administration (NASA), and the National Oceanographic and Atmospheric Administration (NOAA). The CCSM community includes some 900 members located at universities and laboratories throughout the world.
In order to support a broad community, CCSM must operate both as a research and an operational climate model, and therefore must be easily portable to a wide range of computational platforms. CCSM or its components can be run “out of the box” on a variety of Linux clusters, Apple servers, SGI Origin and Altix systems, and IBM and Intel clusters. It has also been enabled on NEC and Cray vector supercomputers, IBM Power-series clusters, and Cray clusters of scalar processors. The developers are now exploring modifications to CCSM to ensure efficient execution on other massively parallel architectures. The CCSM team has developed a comprehensive suite of tests to ensure that the model algorithms work reliably and transparently across such a heterogeneous computing environment.
CCSM is designed to be flexible and extensible, an important characteristic since it will serve as a basis for the development of a more complete Earth System model over the next several years. This Earth System model will simulate the chemical, biogeochemical, and physical state of the climate system. The CCSM development effort is managed by a Scientific Steering Committee with membership from the broad academic research community, as well as from NCAR.
The CCSM results for the IPCC provide a sobering look into the future of the planet and are being documented in more than 200 peer reviewed scientific publications. Figure 5 shows projections of the time evolution of summer Arctic ice area for several IPCC greenhouse gas forcing scenarios. Note that summer ice is projected to disappear from the Arctic toward the latter part of this century under the IPCC “A2” scenario for socio-economic development.
