CESM

CESM
Name	CESM
Developer	National Center for Atmospheric Research; University Corporation for Atmospheric Research
First release	1990s
Latest release	Community Earth System Model versions (e.g., CESM2)
Programming language	Fortran; C; Python (programming language)
License	Open-source; community-developed

CESM The Community Earth System Model is a coupled Earth system model used for simulating climate and biogeochemical processes. It supports experiments relevant to the Intergovernmental Panel on Climate Change assessments, the United States Department of Energy, and academic research at institutions such as NASA, NOAA, and Princeton University. CESM integrates atmosphere, ocean, land, and ice components to study past, present, and future climate states and to inform assessments like the IPCC Fifth Assessment Report and IPCC Sixth Assessment Report.

Overview

CESM is designed as a modular coupled model that links independently developed component models to represent interactions among the Atmosphere, Ocean, Cryosphere, Biosphere, and Anthroposphere in a single framework. It is widely used in multi-model intercomparison projects such as the Coupled Model Intercomparison Project and supports scenario experiments framed by Representative Concentration Pathways and Shared Socioeconomic Pathways. Major contributing organizations include the National Science Foundation, Department of Energy (United States), and the National Oceanic and Atmospheric Administration. The model supports studies ranging from decadal prediction and paleo-reconstructions tied to events like the Younger Dryas to projections of future change pertinent to the Paris Agreement.

Model Components

CESM couples several primary component models, each with specialized physics and parameterizations: the atmospheric component (e.g., Community Atmosphere Model), the ocean component (e.g., Parallel Ocean Program), the sea-ice component (e.g., Community Ice CodE), the land component (e.g., Community Land Model), and the land-ice or glacier modules. Biogeochemical cycles are represented through modules like the Biogeochemistry Model and marine ecosystem components applied in studies involving El Niño–Southern Oscillation and Atlantic Meridional Overturning Circulation. The coupling infrastructure is provided by frameworks such as Model Coupling Toolkit or bespoke couplers that manage fields, fluxes, and timestep synchronization. Process representations draw on parameter sets and schemes developed in collaboration with groups at Stanford University, University of California, Davis, and Lamont–Doherty Earth Observatory.

Development and Version History

CESM development builds on predecessors like the Community Climate System Model and earlier Earth system frameworks. Major milestone releases (for example, CESM1, CESM2) introduced updated dynamical cores, chemistry modules, and data assimilation interfaces that reflect advances from projects at NCAR and partner labs such as Los Alamos National Laboratory and Oak Ridge National Laboratory. Release notes and version histories document additions such as interactive atmospheric chemistry influenced by efforts at Harvard University and improved sea-ice rheology informed by research at University of Washington. Collaborative governance includes steering committees with representatives from European Centre for Medium-Range Weather Forecasts partners and U.S. federal laboratories.

Applications and Use Cases

CESM underpins a broad set of applications: attribution studies of extreme events tied to episodes like the 2010 Russian heat wave, future climate projection ensembles used in IPCC reports, and process studies of feedbacks such as permafrost carbon release relevant to Arctic Council interests. It is used for regional downscaling linked to North American Regional Climate Change Assessment Program efforts and for paleo simulations coordinated with sites like Vostok Station and Greenland Summit Camp. Policy-relevant applications include assessments for agencies such as Environmental Protection Agency (United States) and planning activities by regional bodies like the European Union climate services. Researchers employ CESM in coupled model intercomparison projects to test hypotheses about modes of variability including the Madden–Julian Oscillation and North Atlantic Oscillation.

Evaluation and Validation

Validation of CESM involves comparisons to observational datasets and reanalysis products maintained by organizations such as NOAA National Centers for Environmental Information, European Centre for Medium-Range Weather Forecasts reanalyses, and satellite missions like TOPEX/Poseidon, MODIS, and GRACE. Model evaluation activities include metrics from initiatives like the Climate Model Intercomparison Project diagnostics package and benchmarking against paleoclimate proxies archived through programs affiliated with the Paleoclimate Modelling Intercomparison Project. Skill assessments examine representation of phenomena including monsoon systems studied in Indian Institute of Tropical Meteorology collaborations and tropical cyclones catalogued by the International Best Track Archive for Climate Stewardship.

Computational Implementation and Data Management

CESM is implemented in high-performance computing environments at centers such as National Energy Research Scientific Computing Center, Oak Ridge Leadership Computing Facility, and university clusters. The codebase is written primarily in Fortran (programming language) with interfaces and workflow tools using Python (programming language) and shell utilities. Ensemble experiments produce large volumes of output archived in community repositories and data portals coordinated with World Data Center networks and the Earth System Grid Federation. Data management practices follow metadata conventions like Climate and Forecast (CF) metadata convention standards and utilize file formats such as NetCDF. Workflow and provenance are tracked through tools inspired by projects at Lawrence Berkeley National Laboratory and Argonne National Laboratory.

Category:Climate models