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 1%year CO2 increase experiment (to doubling). These datasets are available in netCDF and GRIB format. The initial condition is identical to the beginning of PDcntrl experiment. The CO2 concentration starts increasing (from 348 ppmv) with 1%/year (compound) rate and reaches doubled (696 ppmv) at 70th year, and is fixed doubled after that. The other forcing is same as in the PDcntrl experiment (CH4 = 1650 ppmv, N2O = 306 ppbv, solar constant = 1367 W/m2). 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/.