The Community Earth System Model (CESM) is a coupled climate model for simulating Earth’s climate system, also the first completely open-source Earth System Model. The code and its documentation are available on the CESM website: http://www.cesm.ucar.edu/models/cesm1.0/. The CESM is composed of an Atmosphere General Circulation Model (CAM), an Ocean General Circulation Model (POP), a land model (CLM), a sea-ice model (CICE) and a dynamical ice sheets model (CISM), which is developed jointly by NCAR and LANL (POP, CICE, CISM) and is maintained by NCAR. Composed of these five separate models plus one central coupler component, CESM allows researchers to conduct fundamental research into the Earth’s past, present, and future climate states.
The CESM system can be configured a number of different ways from both a science and technical perspective. CESM supports several different resolutions and component configurations. In addition, each model component has input options to configure specific model physics and parameterizations. CESM can be run on a number of different hardware platforms and has a relatively flexible design with respect to processor layout of components.
The CESM has been successfully tested for paleoclimate simulations. Simulating past climates implicates various changes in the Earth’s topography. Fifty million years ago (Myrs), the continental distribution highly differed from present-day one and the modern configuration emerged about 10 Myrs ago. “Near past climate” refers more or less to the last 10 Myrs, during which, only sea-level and surface elevation changed as a result of the alternation of glacial/interglacial cycles (Figure 2). On the contrary “Deep past climate” refers to periods older than 10 Myrs, more specifically when the continental distribution was totally different than the modern one. Although climate components of CESM are not flexible to simulate near or deep past climates requiring different topographies and or bathymetry relative to present-day, associated procedure has been tested successfully by NCAR Paleo Working Group for various time periods (Last Glaciation and deglaciation, Pliocene, Miocene, Permian, Cretaceous etc…).
CESM Software/Operating System Prerequisites
The following are the external system and software requirements for installing and running CESM.
• UNIX style operating system such as CNL, AIX and Linux
• csh, sh, and perl scripting languages
• subversion client version 1.4.2 or greater
• Fortran (2003 recommended, 90 required) and C compilers. pgi, intel, and xlf are recommended compilers.
•MPI (although CESM does not absolutely require it for running on one processor)
•NetCDF 4.2.0 or newer.
•ESMF 5.2.0 or newer (optional).
•pnetcdf 1.2.0 is required and 1.3.1 is recommended
•Trilinos may be required for certain configurations
• LAPACKm or a vendor supplied equivalent may also be required for some configurations.
• CMake 2.8.6 or newer is required for configurations that include CISM.
CCSM3 (Previous version of CESM)
The CCSM consists of four dynamical geophysical models linked by a central coupler. Each model contains “active”, “data”, or “dead” component versions allowing for a variety of “plug and play” combinations. The active dynamical models consume substantial amounts of memory and CPU time and produce large volumes of output data. The data-cycling models (data models), on the other hand, are small, simple models which simply read existing datasets that were previously written by the dynamical models and pass the resulting data to the coupler. These data-cycling components are very inexpensive to run and produce no output data. All model components are written primarily in FORTRAN 90.
The dynamical atmosphere model is the Community Atmosphere Model (CAM), a global atmospheric general circulation model developed from the NCAR CCM3. The primary horizontal resolution is 128 longitudinal by 64 latitudinal points (T42) with 26 vertical levels. The hybrid vertical coordinate merges a terrain-following sigma coordinate at the bottom surface with a pressure-level coordinate at the top of the model. The central source for information on CAM is the CAM web page (http://www.ccsm.ucar.edu/models/atm-cam). Here you can find model up- dates, bug reports, the latest documentation, and much, much more.
Over the last fifteen years, the NCAR Climate and Global Dynamics (CGD) Division has provided a comprehensive, three-dimensional global atmospheric model to university and NCAR scientists for use in the analysis and understanding of global climate. Because of its widespread use, the model was designated a community tool and given the name Community Climate Model (CCM). The original versions of the NCAR Community Climate Model, CCM0A [Washington, 1982] and CCM0B [Williamson, 1983], were based on the Australian spectral model [Bourke et al., 1977; McAvaney et al., 1978] and an adiabatic, inviscid version of the ECMWF spectral model [Baede et al., 1979]. The second generation community model, CCM1, was introduced in July of 1987. The third generation of the Community Climate Model (CCM2) was released in October of 1992. The standard CCM2 model configuration was significantly different from its predecessor in almost every way, starting with resolution where the CCM2 employed a horizontal T42 spectral resolution (approximately 2.8 x 2.8 degree transform grid), with 18 vertical levels and a rigid lid at 2.917 mb.
The CCM3 was the fourth generation in the series of NCAR’s Community Climate Model. The CCM3 incorporated version 1 of the Land Surface Model (LSM) developed by Bonan  which provided for the comprehensive treatment of land surface processes. The CCM3 can run with a simple slab ocean-thermodynamic sea ice model.
The CAM 3.0 is the fifth generation of the NCAR atmospheric GCM. The name of the model series has been changed from Community Climate Model to Community Atmosphere Model to reflect the role of CAM 3.0 in the fully coupled climate system.
Component Resolutions of CCSM3
The following component resolutions are supported in CCSM3.0:
• atmosphere, land
T85 – gaussian grid, 256 longitudes, 128 latitudes [cam, clm]
T42 – gaussian grid, 128 longitudes, 64 latitudes [cam, clm, datm, dlnd]
T31 – gaussian grid, 96 longitudes, 48 latitudes [cam, clm, datm, dlnd]
2×2.5 – type C grid, 144 longitudes, 91 latitudes [cam-FV dycore, clm]
T62 – gaussian grid, 192 longitudes, 94 latitudes [latm, dlnd]
• ocean, ice
gx1v3 – 320 longitudes, 384 latitudes
gx3v5 – 100 longitudes, 116 latitudes
Comprehensive diagnostic packages exist for each model component. Not all are publicly available. CCSM3 diagnostic packages are designed to do bulk file processing (e.g. concatenate files and average using the NCO), conduct the necessary data processing, and output NCL graphics in a web format. Atmosphere diagnostic package download location:
For Further Information
• CCSM web pages
• CCSM Bulletin Board – http://bb.cgd.ucar.edu
While coupled atmosphere-ocean general circulation models (GCMs) are frequently used to understand both past, present and future climates and climate variability, the computational expense associated with these models often precludes their use for undertaking extensive parameter sensitivity studies. Simple and intermediate complexity climate models are designed with a particular class of scientific questions in mind. The University of Victoria (UVic) Earth System Climate Model (UViC_ESCM, http://climate.uvic.ca/model/) is a medium complexity model that makes use of a simplified atmosphere to speed up model integrations, which can compute several hundred years of model time per day.
The UVic Earth System Climate Model consists of a three-dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea-ice model, an energy-moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land-ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used.
The model uses prescribed present-day winds in its climatology, although a dynamical wind feedback is included which exploits a latitudinally-varying empirical relationship between atmospheric surface temperature and density. The ocean component of the coupled model is based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model 2.2, with a global resolution of 3.6° (zonal) by 1.8° (meridional) and 19 vertical levels.