ECMWF is a participant in the COCO project funded by the European Union.
The project aims to use measurements from the latest (and future) satellite
missions to monitor carbon dioxide levels in the atmosphere.
ECMWF's contribution to the project is the estimation of atmospheric
CO2 by assimilating radiances from the Atmospheric Infrared Sounder (AIRS)
in the 4D-Var system. Currently, a simple tropospheric mean value is estimated
at the AIRS observation locations without CO2 being part of the forecast
model. The tropopause level is dynamically estimated from the forecast
model temperature profile. These individual estimates are then gridded
and averaged in time to provide global tropospheric CO2 fields. Main focus
is on the tropics, because the CO2 information content of the observations
reduces drastically at higher latitudes. Examples of monthly mean fields
using clear field-of-views (fovs) only are given below for July and December.