We are developing a coupled atmosphere-ocean data assimilation system to produce consistent climate reanalyses of the coupled Earth system. 

ECMWF is leading two successive international research projects funded by the European Commission (ERA-CLIM and ERA-CLIM2). The main goal of these projects is to develop suitable input observations and improved data assimilation methods for climate reanalysis. A technical framework for coupled data assimilation, based on the IFS atmospheric forecast model coupled with the NEMO ocean model, has been developed in the ESA-funded CERA project. Production of a first coupled atmosphere-ocean reanalysis of the 20th century is planned for 2015.