. Models of atmospheric transport can be used to interpret spatiotemporal differences in the observed concentrations of CO 2 in terms of its surface exchange fluxes. Inversion of the atmospheric transport is the systematic search for both a flux field that yields an optimal match between modeled and observed concentrations and, equally importantly, the uncertainties in this inferred flux field. The present inversion study combines observations of the CO 2 concentration at the global station network of the NOAA/CMDL in the 1980s with a representation of the atmospheric transport model TM2 by its Jacobian matrix, which has been previously computed by the adjoint model of TM2. This Jacobian matrix maps monthly fluxes on the approximately 8 o latitude by 10 o longitude horizontal model grid onto the resulting changes in the monthly CO 2 concentration at every station. Since the number of observational sites is much smaller than the number of grid cells, the inverse problem ...