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). These datasets are available in netCDF and GRIB format. This integration started at the same point as the preindustrial control run, and spans the period 1850 to 2000. GHG concentrations are prescribed following observations and match the IPCC SRES concentrations at year 1990. The direct aerosol forcing is incorporated via a change in surface albedo which is proportional to the prescribed, time-evolving column burden of sulphate aerosols obtained from O. Boucher, Laboratoire d`Optique Atmospherique, France. For this experiment there are 9 ensemble runs available. For model output data in higher temporal resulution and more variables visit the web page https://esg.llnl.gov:8443/home/publicHomePage.do.