CESM2

CESM2
Name	CESM2
Developer	National Center for Atmospheric Research; University Corporation for Atmospheric Research
Initial release	2020
Latest release	2020
Programming language	Fortran; C; Python (programming language)
License	Open-source (community model)
Website	National Center for Atmospheric Research

CESM2

CESM2 is the second major release of the Community Earth System Model family produced by the National Center for Atmospheric Research in collaboration with University Corporation for Atmospheric Research, designed for coupled climate simulation across atmosphere, ocean, land, and ice components. It provides enhanced representations of radiative transfer, biogeochemistry, cryosphere dynamics, and atmospheric chemistry for studies ranging from decadal prediction to paleoclimate and Earth system projections used by agencies like the Intergovernmental Panel on Climate Change and the United States Global Change Research Program. CESM2 integrates contributions from centers such as NOAA, NASA, LAMONT-DOHERTY EARTH OBSERVATORY, and universities including Princeton University, Massachusetts Institute of Technology, and University of Colorado Boulder.

Overview

CESM2 is a coupled Earth system model linking atmosphere, ocean, land, sea ice, and biogeochemical modules to simulate physical and chemical interactions relevant to climate and environmental change. The project builds on heritage from predecessors developed at institutions like Geophysical Fluid Dynamics Laboratory, Scripps Institution of Oceanography, and Hadley Centre to address questions posed by bodies such as the World Meteorological Organization and the National Academies of Sciences, Engineering, and Medicine. CESM2 outputs are used in assessments by the Intergovernmental Panel on Climate Change and in operational and research centers including European Centre for Medium-Range Weather Forecasts and Met Office.

Model Components

Atmosphere component improvements derive from modules used at NOAA and NASA with updated dynamics, parameterizations, and the Community Atmosphere Model core. The ocean component uses schemes comparable to those from Scripps Institution of Oceanography and Woods Hole Oceanographic Institution to represent circulation and mixing. The land model incorporates vegetation and carbon cycle processes informed by research at Oregon State University and Yale University. The sea ice component integrates thermodynamics and dynamics influenced by studies at University of Alaska Fairbanks and University of Washington. Chemistry and aerosols leverage research from Harvard University and California Institute of Technology. Couplers and infrastructure draw on software engineering practices used at Argonne National Laboratory and Lawrence Livermore National Laboratory.

Development and Versions

CESM2 was developed through multi-institutional collaboration coordinated by National Center for Atmospheric Research with community input from groups such as PAGES, AGU, and American Meteorological Society. Major version milestones reflect integration of new parameterizations championed by teams at Princeton University, Columbia University, and University of California, Berkeley. Coupled experiments and tuning involved datasets and initiatives like Argo (oceanography), GRACE (satellite), and MODIS products from NASA. Model intercomparisons include participation in projects led by World Climate Research Programme and the Coupled Model Intercomparison Project.

Scientific Applications and Findings

CESM2 has been applied to studies of historical forcing attribution used by Intergovernmental Panel on Climate Change chapters, to quantify regional impacts examined in assessments by Union of Concerned Scientists, and to analyze carbon cycle feedbacks relevant to Paris Agreement goals. It has supported research on Arctic amplification investigated by groups at University of Cambridge and Alfred Wegener Institute, and tropical dynamics studied by teams at Columbia University and University of Hawaiʻi at Mānoa. Applications include paleoclimate simulations informed by Paleoclimate Modelling Intercomparison Project and projections used in national studies by U.S. Department of Energy and European Commission programs.

Performance and Evaluation

Model evaluation employs observational benchmarks from NOAA National Centers for Environmental Information, NASA Goddard Institute for Space Studies, and reanalysis products such as ERA5 produced by European Centre for Medium-Range Weather Forecasts. Performance metrics compare climate sensitivity, aerosol forcing, and ocean heat uptake with estimates from IPCC assessments and analyses by National Oceanic and Atmospheric Administration. Computational performance has been profiled on systems at Oak Ridge National Laboratory, NERSC, and National Energy Research Scientific Computing Center with scaling studies referencing architectures from vendors like Cray and IBM.

Usage and Accessibility

CESM2 source code and documentation are distributed through repositories and portals hosted by National Center for Atmospheric Research and collaborative platforms used by institutions including GitHub mirrors and the Community Earth System Model (CESM) website. Training and tutorials are provided at workshops organized by NCAR Advanced Study Program, ARGONNE Training Center, and sessions at meetings like American Geophysical Union and European Geosciences Union. Data outputs are archived and shared via data centers such as Earth System Grid Federation and repositories used by Pangeo and Zenodo participants.

Limitations and Future Directions

Known limitations reflect biases documented by evaluation teams at Princeton University and University of Exeter, including regional precipitation and cloud representation issues noted in comparisons with CloudSat and CALIPSO observations. Future development priorities include coupling improvements emphasized by World Climate Research Programme, enhanced resolution leveraging DOE Exascale Computing Project resources, and integration of new process models contributed by groups at Max Planck Institute for Meteorology, Laboratoire des Sciences du Climat et de l'Environnement, and RIKEN. Community plans involve coordination with initiatives like Coupled Model Intercomparison Project Phase 7 and collaborations with stakeholders including European Commission research programs and national laboratories.

Category:Earth system models