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. The dataset names are composed of - centre/model acronym (e.g. MPEH5: Max-Planck-Institute/Echam5) - scenario acronym (e.g. 20C3M: 20C3M) - run number (e.g. 1: run 1) - format identifier (e.g. N: netCDF, G: GRIB) - variable acronym [with level value] (e.g. hur850: relative humidity, 850 hPa) --> example: MPEH5_20C3M_1_G_hur850 For this experiment there are 4 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/.