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 Pre-industrial control experiment (picntrl). _ These datasets are available in netCDF and GRIB format. _ Spinup: Same as 20C3M (realisation 1). GHGs fixed at 1860 values (CO2 = 286.20 ppm, CH4 = 805.60 ppb, N2O = 76.69 ppb, equi. CFC11 = 12.48 ppb), sulfate aerosol emissions fixed at 1860 values , solar constant of 1365 W/m^2. _ 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/.