Release Series Information

View notable improvements and release series information for versions of The Community Climate System Model (CCSM).


CCSM4.0 is a subset of CESM1.0. All CCSM4.0 compsets and resolutions are also found in the currently supported release of CESM1.0.


CCSM4 contains totally new infrastructure capabilities that permit new flexibility and extensibility to address the challenges involved in earth system modeling. An integral part of CCSM4 is the implementation of a coupling architecture that takes a completely new approach with respect to the high-level design of the system. The CCSM4 coupling infrastructure now provides the ability to use a single code base in a start-to-end development cycle; from model parameterization development that might only require a single processor, to performing ultra high resolution simulations on HPC platforms using tens-of-thousands of cores. The CCSM4 coupling architecture also provides "plug and play" capability of data and active components and includes a user-friendly scripting system and informative timing utilities. Together, these tools enable a user to create a wide variety of "out-of-the-box" experiments for different model configurations and resolutions and also to determine the optimal load balance for those experiments to ensure maximal throughput and efficiency. CCSM4 is also targeting much higher resolutions than any previous CCSM coupled model and efforts have been made to reduce the memory footprint and to improve scaling in all components.


CAM contains notable improvements to the deep convection, arctic cloud fraction, radiation interface and computational scalability. The calculation of Convective Available Potential Energy (CAPE) has been reformulated in the deep convection to include more realistic dilution effects through an explicit representation of entrainment. Sub-grid scale momentum transports have also been added to the deep convection parametrization. A freeze-drying process contributes to a greater consistency between polar cloud fraction and water condensate properties. The finite volume dynamical core has been made the default and has improved accuracy for transport processes. The option of the HOMME spectral element dynamical core on a cubed sphere grid vastly increases the computational scalability of CAM. A new radiation constituent interface expands flexibility in the specification of properties for individual gas and aerosol species and their radiative interaction. The TROP-MOZART chemistry and aerosol package is now available and is used to generate evolving aerosol burden changes from the most recent emission inventories. Additional physical process improvements from CAM development will be available in CAM5.


CLM has been modified substantially and includes several new capabilities, input datasets, and parameterization updates. The model is extended with a carbon-nitrogen (CN) cycle model that is prognostic in carbon and nitrogen as well as vegetation phenology. A transient landcover change capability, including wood harvest, is introduced and the dynamic vegetation model is merged with CN (CNDV). An urban model (CLMU) is added and the BVOC model is replaced with the MEGAN model. The hydrology scheme is updated with a TOPMODEL-based runoff model, a simple groundwater model, a new frozen soil scheme, a new soil evaporation parameterization, and a corrected numerical solution of the Richards equation. The snow model incorporates SNICAR - which includes aerosol deposition, grain-size dependent snow ageing, and vertically resolved snowpack heating - as well as new snow cover fraction and snow burial fraction parameterizations. CLM4 also includes a new canopy integration scheme, new canopy interception scaling, and a representation of organic soil thermal and hydraulic properties. The ground column is extended to ~50-m depth by adding 5 bedrock layers (15 total layers). New surface datasets based on MODIS products have been derived, providing a basis for the transient land cover datasets. To improve global energy conservation, runoff is split into separate liquid and ice water streams that are passed separately to the ocean model.


The CCSM sea ice component is now CICE, the Los Alamos Sea Ice Model, sometimes referred to as the Community Ice CodE. The main areas of enhancement fall into two categories: physics and computation. The scientific enhancements include new tracers, a new shortwave radiative transfer scheme, a melt pond scheme, and aerosol deposition, all applied to the snow and sea ice. The new computational enhancements include: more flexible computational decomposition strategies, high resolution support, parallel input / output, and OpenMP threading capability.


The ocean model has been updated to the Parallel Ocean Program version 2 (POP2) of the Los Alamos National Laboratory. Many physical and software developments have been incorporated. The physical improvements include a near-surface eddy flux parameterization; an abyssal tidally driven mixing parameterization; an overflow parameterization to represent the Denmark Strait, Faroe Bank Channel, Weddell Sea, and Ross Sea overflows; a submesoscale mixing scheme; vertically-varying thickness and isopycnal diffusivity coefficients; modified anisotropic horizontal viscosity coefficients with much lower magnitudes than in CCSM3; and modified K-Profile Parameterization that uses horizontally-varying background vertical diffusivity and viscosity coefficients. The software developments include capability for multiple time-averaged history files and space-filling curves. The number of vertical levels has been increased from 40 levels in CCSM3 to 60 levels in CCSM4. POP2 includes passive tracer infrastructures and ecosystem codes.

Data Models

The CCSM4 data models have been completely rewritten. They are now parallelized and share significant amounts of source code. The new data models have created a natural hierarchy in the system and methods for reading and interpolating data have been established that can easily be reused.


Numerous multi-century control runs have been conducted at low, medium, and high resolutions and are available to the general public for examination and analysis.

  • New treatments of cloud and ice-phase processes;
  • Improved representation of the interactions among water vapor, solar radiation, and terrestrial thermal radiation;
  • New treatment of the effects of aerosols, including prognostic sulfate, on the reflection and absorption of solar radiation; and
  • New dynamical frameworks suitable for modeling atmospheric chemistry.
  • Improved performance and scalability on parallel supercomputers;
  • Faster multi-way communication among the component models; and
  • New communications infrastructure.
  • New methods to enable simulation of the terrestrial carbon cycle;
  • New methods to enable simulation of dynamic vegetation; and
  • Improvements in land-surface physics to reduce temperature biases; and
  • New load balancing implementation results in substantial performance improvement.
  • Improvements to the representation of the ocean mixed layer;
  • Inclusion of solar heating by chlorophyll; and
  • New infrastructure for studying vertical mixing in the ocean.
  • New advanced sea ice rheology;
  • Explicit ice-thickness distribution physics;
  • Explicit treatment of brine pockets; and
  • Improved scheme for horizontal advection of sea ice.
Complete System
  • New portability for vector and Linux supercomputers;
  • New, easy-to-use methods to run IPCC climate-change experiments;
  • Flexibility to simulate climate over a wide range of spatial resolutions with greater fidelity; and
  • New built-in test facilities suitable for validating installation and verifying some types of model changes.

Provides an incremental improvement over CCSM2.0. A number of minor problems were fixed, forcing datasets were updated, and a lower-resolution paleo version (T31/gx3v4) of the model was included.

Grids and Model Resolutions

New Coarse-Resolution "Paleo" Resolution Supported in CCSM2.0.1

The CCSM2.0 release officially supported only one resolution, referred to as "T42_gx1v3," which was used in the CCSM2.0 Control Run. The CCSM2.0.1 release supports a second, coarser resolution, "T31_gx3v4," which has been validated in a paleo control run. A sample setup for the paleo run can be found in the CCSM2.0.1 release, in the scripts/test.a2 directory.

Obsolete Grid Eliminated from CCSM2.0.1

All references to the older, unsupported coarse resolution, T31_gx3, which was never scientifically validated, have been eliminated from CCSM2.0.1

Description of Supported Grid Resolutions

Please refer to the CCSM2.0.1 FAQ page for a discussion on the specifics of the various model grids and resolutions.

Data Models

Data-Model Input Datasets Updated

The input datasets for the data models were, in many cases, either outdated, incomplete, or both. The following datasets have been updated in the CCSM2.0.1 data models:

  • datm -- The forcing datasets have been updated. Two 10-year "F" (active atmosphere, active land, thermodynamic ice, and data ocean model) cases were run for 10 years, one at the "T42_gx1v3" resolution and one at the new "T31_gx3v4" resolution. The last five years of atmosphere-model output are now available for use by the datm model. The datm.setup.csh script has been modified to cycle through only one of these years, but all five are available from NCAR's Mass Storage System (MSS).
  • dlnd -- The forcing datasets have been updated. The last five years of the 10-year "F" runs described above are now available for use by the dlnd model. The dlnd.setup.csh script has been modified to cycle through only one of these years, but all five are available from NCAR's Mass Storage System (MSS).
  • dice -- The ice-fraction dataset has been updated to use the datasets based upon those created by Jim Hurrell. The ice-fraction data are combined with corresponding sea-surface temperature data into a single file. The data are on a regular, 1-degree latitude/longitude grid. The dice.setup.csh script has been modified to reference this dataset.
  • docn -- The sea-surface temperatures from the combined sea-surface temperature/ice-fraction dataset described above is used by the data ocean model. The docn.setup.csh script has been modified to reference this dataset.
Bug Fixes

Model Bugs Detected and Corrected

Active Atmosphere Model (CAM)

  • CAM has an array-allocation problem that does not affect any CCSM2.0 coupled run configurations. It has been fixed in the stand-alone model and in CCSM2.0.1. (reported May 17, 2002)
  • CAM has an array-allocation problem in ccsm_msg.F90. It has been fixed in CCSM2.0.1. (reported May 22, 2002)

Active Ocean Model (POP)

  • There is a bug in hmix_gm.F in CCSM2.0 POP, which results in not insignificant, but small changes in the results. In tests, the average boundary layer depth changes by 2 - 2.5m in the convection regions in the GIN and Weddell Seas. The average heat flux into the ocean after 30 years is reduced by 0.09 W/m**2. Changes in the barotropic streamfunction are < 1Sv everywhere, and there are very small changes in the meridional overturning and poleward heat flux.

    A patch which corrects this error is available on the CCSM2.0.1 download site (patch1). The correction to hmix_gm.F is implemented by default in the test.a2 T31/gx3v4 case, but the patch has not been applied generally because it changes the answers of the control case. Users who are not trying to re-create the control case should apply the patch before running.
  • There is a bounds overflow in a physics routine in the CCSM2.0, but only in an option that is not turned on by default. Thus, the overflow did not affect the CCSM2.0 control run. The error occurs when kappa_choice = 'variable' is chosen in the namelist input. The error has been fixed in CCSM2.0.1.

Correction in Reading Restart Files

The CCSM2.0 version will not read b20.007 control run restart files. This has been fixed in CCSM2.0.1.


All components have been upgraded. Target architectures were IBM SP, SGI Origin 2000, and Compaq/alpha. A multi-century control run was presented at the annual CCSM Workshop in June, 2002.


This version introduces further improvements to the code, build procedures, and run scripts. This code distribution will run on Cray machines and SGI Origin 2000 machines.

CSM 1.4, released July 11, 2000, is the fourth major release of the CSM, a comprehensive coupled model of the Earth's climate system. Both active and data models are available. Standard resolutions are T31 & T42 for the atmosphere and land components, and a nominal 3x3 and 2x2 degree resolution for the sea-ice and ocean components. Other resolutions are also possible.

This model and the resulting science are documented in a special issue of the Journal of Climate, June 1998.


This version introduces a choice of two atm/lnd resolutions, T31 and T42, and two ocn/ice resolutions, 3x3 and 2x2 degree. Also, the atm and lnd models are now separate components. This code distribution runs on NCAR Cray machines.


This was the first public release of the CCSM software. This code and corresponding control runs were presented at the firest CSM Workshop in May 1996.