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 run was initiated after 300-year spin-up of the coupled model from an arbitrary chosen initial condition (a snapshot result of a previous version of the model). The preceding spinup was forced by fixed external conditions for the year 1850, including solar and volcanic forcings, GHGs concentration, various aerosols emissions and land use, while all those conditions were changed according to historical data during the 20C in the course of this run. For this experiment there are 3 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/.