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). _ Spinup: 6y coupled spinup with ocean restart files from end of year 199 from a preindustrial control run performed at the FUB; the latter sim. initialized with Levitus 94 (oce). Anthropogenic (GHGs, sulfate aerosol direct and first indirect effects) and natural forcing (solar irradiance and volcanc activity implemented through varying solar constant) are used for the 20C3M simulations. _ For this experiment there are 5 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/.