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 SRES B1 experiment. These datasets are available in netCDF and GRIB format. For this experiment there is only one run available. Includes indirect and direct sulphate aerosol effects from 2000. The N2O concentrations were calculated using a fixed lifetime. CH4 and H(C)FCs (HCFC22 HFC125 HFC134A) were calculated using the 2D atmospheric chemistry model and no climate change. Other H(C)FCs have forcings of O(0.01-0.1) W m-2 but we did not include them in other SRES scenarios either. CFCs (CFC11 CFC12 CFC113) were assumed to be the same as in SRES A2 because they are controlled by the Montreal Protocol so should be identical in all scenarios. Tropospheric ozone was calculated using STOCHEM with surface emissions of NOx etc from the SRES web site converted to 5x5 degrees and no climate change. Fields were calculated in single-year runs (with 3-month spinup) for 1990 2030 2060 2099. Stratospheric ozone was calculated using the same Cl and Br concentrations as in other SRES scenarios. For model output data in higher temporal resulution and more variables visit the web page https://esg.llnl.gov:8443/home/publicHomePage.do.