Public access to this dataset will be closed on June 1st, 2023. For more information and possible alternatives, please consult the dedicated page on Decommissioning of ECMWF Public Datasets service.
The ECMWF's first atmospheric reanalysis of the 20th Century is known as ERA-20C and it provides a long, gridded dataset of many climate variables, spanning 1900-2010. Observations assimilated include surface pressures from the International Surface Pressure Databank v3.2.6 and ICOADS v 2.5.1, and surface winds over the oceans from ICOADSv2.5.1. Upper-air and satellite data are omitted.
For details of ERA-20C are available at https://www.ecmwf.int/en/forecasts/datasets/search?search_api_fulltext=era-20c
ECMWF also released an "AMIP style" (Atmospheric Model Intercomparison Project) version of the 20th Century reanalysis, known as ERA-20CM, which includes no data assimilation. It's an ensemble of ten atmospheric model integrations for the years 1899–2010.
For more information on ERA-20CM please see Hersbach et al. (2015)
ERA-20C and ERA-20CM are forced with the same time-varying SSTs, sea ice concentrations from HadISST22.214.171.124, and radiative forcings from CMIP5.
For a comparison of ECMWF's ERA-20C with NOAA's 20CR see https://climatedataguide.ucar.edu/climate-data/era-20c-ecmwfs-atmospheric-reanalysis-20th-century-and-comparisons-noaas-20cr