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 https://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. Experiment was initiated from year 111 of the control simulation CT1 (nominal year 1970), when equilibrium was reached (corresponds to nominal year 1860 of 20C3M XX1). Forcing agents included: CO2,CH4,N2O,O3,CFC11(including other CFCs and HFCs),CFC12; sulfate (Boucher),BC,sea salt,desert dust aerosols. For this experiment there is only one run 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/.