Various input data were used by the 20th Century Reanalysis project team including surface pressure observations from the International Surface Pressure Databank version 2. The original observations from the International Surface Pressure Databank version 2 used in the project are archived with associated original metadata and model quality control information. These are the only records which have the original station metadata and source information and model quality control information on the same record. The 20th Century Reanalysis dataset provides 6 hourly analyses on a Global 2.0 degree latitude x 2.0 degree longitude global grid from 1871 to present produced from a series of 56-member ensemble runs. For each output time step ensemble means and associated spreads have been calculated and form a continuous dataset over the entire timespan of the dataset. The data contain fields at the surface and on pressure levels from 1000 hPa to 10 hPa and are also available as part of the copy held by the British Atmospheric Data Centre.

The dataset authors request that the following acknowledgment be included in all papers using the dataset:

'Support for the Twentieth Century Reanalysis Project dataset is provided by the U.S. Department of Energy, Office of Science Innovative and Novel Computational Impact on Theory and Experiment (DOE INCITE - http://www.doeleadershipcomputing.org/incite-program/ ) program, and Office of Biological and Environmental Research (BER - http://science.energy.gov/ber/ ), and by the National Oceanic and Atmospheric Administration Climate Program Office (http://www.climate.noaa.gov/).'