ABSTRACTA two-dimensional atmospheric transport model with transport fields derived from a GCM is used to perform the inverse calculation of determining surface CO2 sources from surface concentration data. The concentration data are filtered spatially and temporally with a minimum period of 6 months and a maximum spatial wave number of 5 in order to suppress the unbounded error amplification that occurs in such inverse problems. The distribution of sources and sinks is consistent with recent results concerning oceanic uptake of CO2. The results also show an additional northern hemisphere sink that is interpreted as additional biotic growth and a seasonal tropical source that may represent seasonal burning of cleared biomass.