About the WCRP CMIP3 Multi-Model Dataset Archive at PCMDI


In response to a proposed activity of the World Climate Research Programme’s (WCRP’s) Working Group on Coupled Modelling (WGCM), PCMDI volunteered to collect model output contributed by leading modeling centers around the world. Climate model output from simulations of the past, present and future climate was collected by PCMDI mostly during the years 2005 and 2006, and this archived data constitutes phase 3 of the Coupled Model Intercomparison Project (CMIP3). In part, the WGCM organized this activity to enable those outside the major modeling centers to perform research of relevance to climate scientists preparing the Fourth Asssessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The IPCC was established by the World Meteorological Organization and the United Nations Environmental Program to assess scientific information on climate change. The IPCC publishes reports that summarize the state of the science.

This unprecedented collection of recent model output is officially known as the “WCRP CMIP3 multi-model dataset.” It is meant to serve IPCC’s Working Group 1, which focuses on the physical climate system – atmosphere, land surface, ocean and sea ice – and the choice of variables archived at the PCMDI reflects this focus. A more comprehensive set of output for a given model may be available from the modeling center that produced it.

With the consent of participating climate modelling groups, the WGCM has declared the CMIP3 multi-model dataset open and free for non-commercial purposes. After registering and agreeing to the “terms of use,” anyone can now obtain model output via the ESG data portal, ftp, or the OPeNDAP server.

As of January 2007, over 35 terabytes of data were in the archive and over 337 terabytes of data had been downloaded among the more than 1200 registered users. Over 250 journal articles, based at least in part on the dataset, have been published or have been accepted for peer-reviewed publication. Latest statistics can be found at: 1) usage, 2) download rate, 3) CMIP3 subprojects, and 4) publications

Information for analysts

Terms of use agreement

Proper citation and acknowledgement

How to access CMIP3 archive and getting started

Output availability at a glance

Check errata page frequently

List of simulation specifications

Precise definitions of variables

Official model names

Model documentation (including simulation forcing information)

Which control simulation (and time period) should each perturbation run be compared to?

IPCC AR4 historical details

Information for modeling groups contributing model output to the CMIP3 archive:

  1. Please fill out a brief questionnaire, indicating your intention to contribute model output to the IPCC archive.
  2. Follow the established procedure for preparing and transferring model output to the IPCC archive, as summarized in:
  3. Additional important requests and information

Overview presentations concerning the WCRP CMIP3 multi-model dataset archived at PCMDI:

To IPCC WG1 AR4 First Lead Authors Meeting (Trieste, Italy, 26-29 September 2004)

To Workshop on Analyses of Climate Model Simulations for the IPCC AR4 (Honolulu, Hawaii, 1-4 March 2005)

Climate Forcing

In order to perform the experiments called for in support of the IPCC’s Fourth Assessment Report, models require certain so-called “forcing” datasets. The forcing is mainly given in terms of atmospheric concentrations of greenhouse gases, ozone and aerosols. Although the atmospheric concentrations are based on emissions scenarios developed by IPCC, concentrations do not uniquely follow from emissions. Different concentrations can be derived from the same emissions scenarios, depending on the model used to derive them.

One set of concentrations that may be used to drive climate simulations can be obtained from Dr. Curt Covey. Use of this dataset is not mandatory.