Monitoring climate change requires timely access to observations and reanalyses.
An important requirement for reanalysis is that it uses a single model version and data assimilation method, in order to produce a consistent data set for the full reanalysis period. If, in addition, the reanalysis can be continued close to real time, then it can be used to monitor changes in the climate and its variability on long time scales.
ERA5, produced by C3S at ECMWF, is the current atmospheric reanalysis and is based on a 2016 version of the Integrated Forecasting System (IFS). ERA5 is available for dates from 1979 (eventually, it will be available for dates from 1950) and is being extended forward in near real time.
ERA-Interim is ECMWF's previous atmospheric reanalysis, based on a 2006 version of the IFS. ERA-Interim data are available for dates from 1979 until 31st August 2019 and are no longer updated.