The community Earth system model: progress and future plans

An imperative for NCAR is to develop and continuously improve a comprehensive Earth modeling system that is at the forefront of international efforts to understand and predict the behavior of Earth's climate. For many years the Community Climate System Model (CCSM) has met this challenge. Its output, for instance, has been used in hundreds of peer-reviewed studies to better understand the processes and mechanisms responsible for climate variability and climate change. In addition, simulations performed with CCSM have made a significant contribution to both national and international assessments of climate, including those of the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Global Change Research Program (USGCRP). Version 4 of CCSM was released to the community in April 2010, and it features many notable improvements over previous versions of the model. Moreover, an extremely ambitious set of simulations currently being performed with CCSM4.0 will make a significant contribution to the upcoming Fifth Assessment Report (AR5) of IPCC. Yet, in order to address an even wider range of pressing scientific questions, additional capabilities have been added to CCSM4. These include, for instance, an interactive carbon cycle in the land component and an ecosystem-biogeochemical module in the ocean component. There is also an updated atmospheric chemistry component, a global dynamic vegetation component, and land use changes due to human activity in the land component. A new version of the atmospheric component model will allow scientists to study both the direct and indirect effects of aerosols. The model can be run using the Whole Atmosphere Community Climate Model (WACCM), in order to better understand the role of the upper atmosphere in climate variability and change. There is also an early version of a land-ice component that can be used to simulate changes to the Greenland ice sheet and its role in future climate change. Since the most widely used description of a model with these capabilities is an “Earth System Model”, the project and supported model is called the “Community Earth System Model”, or CESM. The release of Version 1 of CESM occurred in June 2010, and a large number of simulations with it will also be assessed in AR5, including fully coupled carbon cycle experiments. These aspects will be summarized, including how the community can become involved in CESM. In addition, some results from early CCSM4 and CESM1 simulations will be highlighted.