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 1%/year CO2 increase experiment (to quadrupling). 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. 1PTO4X: 1PCTTO4X) - 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_1PTO4X_1_G_hur850 For this experiment there are 3 ensemble runs available. 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 only the CO2 concentration was changed from those conditions in the course of this run. Model output data for CMIP3 in higher temporal resolutions and further variables are available in ESGF at https://esgf-node.llnl.gov/search/cmip3/.