Space- and ground-based CO2 measurements: A review

The climate warming is mainly due to the increase in concentrations of anthropogenic greenhouse gases, of which CO₂ is the most important one responsible for radiative forcing of the climate. In order to reduce the great estimation uncertainty of atmospheric CO₂ concentrations, several CO₂-related satellites have been successfully launched and many future greenhouse gas monitoring missions are planned. In this paper, we review the development of CO₂ retrieval algorithms, spatial interpolation methods and ground observations. The main findings include: 1) current CO₂ retrieval algorithms only partially account for atmospheric scattering effects; 2) the accurate estimation of the vertical profile of greenhouse gas concentrations is a long-term challenge for remote sensing techniques; 3) ground-based observations are too sparse to accurately infer CO₂ concentrations on regional scales; and 4) accuracy is the primary challenge of satellite estimation of CO₂ concentrations. These findings, taken as a whole, point to the need to develop a high accuracy method for simulation of carbon sources and sinks on the basis of the fundamental theorem of Earth’s surface modelling, which is able to efficiently fuse space- and ground-based measurements on the one hand and work with atmospheric transport models on the other hand.