These data represent monthly averaged values of selected variables for the Data Distribution Centre (DDC) of the Intergovernmental Panel on Climate Change (IPCC). (see also http://www.ipcc-data.org/) The model output prepared for IPCC Fourth Assessment climate of the 20th Century experiment (20C3M). These datasets are available in netCDF and GRIB format. ##This simulation was initiated from year 360 of CCSM3 model run b30.020 and executed on hardware bluesky.ucar.edu. For this experiment there are 9 ensemble runs available. Model output data for CMIP3 in higher temporal resolutions and further variables are available in ESGF at https://esgf-node.llnl.gov/search/cmip3/.