European Reananlysis of the Global Climate System

European Reanalysis of Global Climate Observations (ERA-CLIM)

Main Challenge

To integrate the instrumental record of the previous century into coherent global data sets suitable for climate services.


ERA-CLIM will prepare accurate and detailed estimates of the global evolution of the climate system during the previous century, based on reanalyses of in-situ and satellite observations. The project involves recovery, digitisation, and quality control of large numbers of earObserving_system.pngly 20th-century meteorological data, many from remote and sparsely observed regions of the globe. ERA-CLIM will work with satellite agencies and climate centres to obtain recently reprocessed and recalibrated earth observations from satellites, including many data sets that have not previously been used for climate reanalysis. A sequence of ERA-CLIM test reanalyses will be produced, to provide a coherent view of the evolution in time of the global atmosphere, extending from the surface to the upper stratosphere, together with the underlying ocean- and land-surface conditions.

All ERA-CLIM reanalysis data, and all observations used to produce them, will be made available via the internet.


In-situ observations from around the world made with various instruments at meteorological land stations, on ships, buoys, or aircraft, will be combined together with earth observations from satellites using reanalysis techniques. Reanalysis applies state-of-the-art modelling and data assimilation tools to estimate the past evolution of the climate system. Reanalysis products are global gridded data sets comprising a large number of physical and dynamical parameters, which together provide a comprehensive view of the climate system at any point in space and time. The most advanced reanalysis systems and the computational infrastructure required to implement them have been developed during the last few decades at major numerical weather prediction centres, such as the European Centre for Medium-Range Weather Forecasts. From the early 1980s ECMWF has had a leading role in the development of successive generations of increasingly accurate global reanalysis products, most recently ERA-40 (spanning the years 1957-2002) and ERA-Interim (from 1979 onward).

The ERA-CLIM project will produce approximately 1 petabyte of high-quality global data sets suitable for studying atmospheric, oceanic, and terrestrial processes, for assessing climate variability and change, and for supporting the development of improved climate prediction models. ERA-CLIM data products will provide essential resources for the newly emerging European climate services, with global information for planners and decision makers in areas such as agriculture, energy, health, security, and welfare. In addition, a fundamental contribution to climate science will be made by substantially improving the early 20th century instrumental record, and by providing open access to many newly uncovered observations from remote regions of the globe.