Roughly half of all anthropogenic CO2 emissions have been taken up by the oceans and terrestrial biosphere, however, the spatial structure of this uptake is highly uncertain. Even with the recent introduction of space-borne CO2 observation systems, natural sources and sinks of CO2 remain highly uncertain of sub-continental scales. In this talk, I will review the instruments used to measure total column CO2 and discuss the challenges in providing a global observations of CO2. I will also introduce a method to examine the sensitivity of these observations to surface fluxes that can be used to assess the efficacy of the global atmospheric CO2 monitoring network.