Spaceborne remote sensing of greenhouse gas concentrations

Despite their primary contribution to climate change, there are still large uncertainties on the sources and sinks of the main greenhouse gases: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). A better knowledge of these sources is necessary to understand the processes that control them and therefore to predict their variations. Indeed, large feedbacks between climate change and greenhouse gas fluxes are expected during the 21st century. Sources and sinks of these gases generate spatial and temporal gradients that can be measured either in situ or from space. One can then estimate the surface fluxes, either positive or negative, from concentration measurements through a so-called atmospheric inversion. Surface measurements are currently used to estimate the fluxes at continental scales. The high density of spaceborne observations allows potentially a much higher resolution. Several remote sensing techniques can be used to measure atmospheric concentration of greenhouse gases. These techniques have motivated the development of spaceborne instruments, some of them already in space and others under development. However, the accuracy of the current estimates is still not sufficient to improve our knowledge on the greenhouse gases sources and sinks. Rapid improvements are expected during the forthcoming years with a strong implication of the scientific community and the launch of dedicated instruments, optimized for the measurement of CO2 and CH4 concentrations.