II.A. Community Earth System Model (CESM) Intrastructure
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. The Community Earth System Model (CESM) and its predecessor, the Community Climate System Model (CCSM), have met this challenge for many years. The simulation output from these modeling systems, 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 CESM and CCSM have made significant contributions 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). A trademark of the CESM project is that it is community collaboration. It is unique in the climate modeling sphere because of its commitment to make the model readily available to, and usable by, the climate research community. Community members are actively engaged in the ongoing process of model development and overall governance of the project.
The development of the model is a continuous process. Significant progress was made with the last major release of the CESM1.0 model in June, 2010. This model version represented many new capabilities allowing for a wider range of pressing scientific questions to be addressed. In particular, the model incorporates an interactive carbon cycle in the land component and an ecosystem-biogeochemical module in the ocean component allowing for the investigation of carbon cycle-climate feedbacks. It also has 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 now allows scientists to study both the direct and indirect effects of aerosols. The model can be run using the Whole Atmosphere Community Climate Model (WACCM) to better understand the role of the upper atmosphere in climate variability and change. There is also the incorporation of the Community Ice Sheet Model (CISM) that has been used to simulate changes in the Greenland ice sheet and its role in future climate change. These new model capabilities have enabled investigations into carbon cycle-climate feedbacks, changing ice sheet conditions, and the role of changes in the stratosphere on coupled climate processes. For example, 20th and 21st century simulations which incorporate an active Greenland ice sheet component have been used to assess the surface mass budget for Greenland and how it is projected to change in the next century (Figure 1). Additionally, data assimilation using the Data Assimilation Research Testbed (DART) is now possible within the atmosphere and ocean model components allowing for the simulation of initialized forecasts. The model release of CESM1.0 provided support for multiple configurations of the model. Simulations with these various configurations have been completed in the last several years and are now available for community analysis. Numerous aspects of these simulations have been investigated in multiple papers that are included or under review for a special issue of the Journal of Climate.
The model developments available through CESM1.0 represent a significant advancement in community modeling capability. Development efforts are continuing within this model version. In particular, CESM1.0.4 was released in February 2012. This included expanded portability of the model to enable wide community use of the modeling system. It also included new support for the Thermosphere/Ionosphere extension of the WACCM model (termed WACCMX). In addition, a release of the CESM1.1 model version is planned for November 2012. This release will have significant infrastructure improvements to the model, which will benefit the broad model development community. These include new mapping capability to enable new model grids, a new river runoff component to allow for the incorporation of different river runoff schemes, and new scripting functionality.
CMIP-5 and IPCC
Simulations with CESM1.0 have been used to conduct an extremely ambitious set of simulations in support of the upcoming Fifth Assessment Report (AR5) of IPCC. The simulations are part of the CMIP-5 experimental design, which is a set of coordinated climate model experiments on two time scales: (1) near-term, initialized decadal prediction simulations; and (2) long-term simulations. The long-term simulations include experiments from 1850 through the end of the current century and beyond and paleoclimate simulations for a number of different time periods. The CESM project has completed a large number of these simulations including experiments with a number of different CESM configurations. These configurations include simulations with an active prognostic carbon cycle, experiments with active atmospheric chemistry, simulations with an active Greenland ice sheet component, and simulations with several different atmospheric components. Additionally, a number of “single forcing” simulations have been performed for use in climate attribution studies. The simulation output has been made freely available through the Earth System Grid so it can be fully utilized by the community for scientific investigations. The availability of CESM1.0 simulations with multiple configurations of the atmospheric model is enabling estimates of the indirect aerosol effect on climate, the determination of the role of upper-atmospheric processes in climate, and the analysis of transient chemistry-climate simulations. Configurations with an active carbon cycle are allowing for the investigation of carbon cycle-climate feedbacks, while simulations with an active Greenland ice sheet are allowing for the investigation of changing ice sheet conditions. These simulations will contribute significantly to the scientific assessment being compiled for the IPCC-AR5.
Educating the next generation of scientists in the use and development of Earth System Models is a priority for the CESM project. The third annual CESM tutorial occurred in August 2012 and, based on participant feedback, was extremely successful. The tutorial included 76 full participants and 15 auditors from over 35 U.S. and Canadian (UCAR member) universities, eight foreign universities and organizations, NASA facilities and four DOE National Laboratories. The participants primarily included graduate students and early career scientists. Web-based tutorial materials have been made freely available and are considerably extending the reach of the in-person tutorials. As of August 31, 2012, over 900 people from about 40 countries, with a majority from US universities, had registered to access and use the 2010 and 2011 online tutorial materials.