Observing the global distribution of atmospheric CH4 from space

Atmospheric methane (CH4) plays a significant role in global warming despite being present in the atmosphere in smaller quantities than carbon dioxide (CO2) and has a radiative forcing efficiency or ‘global warming potential’ of 21 times greater than that of CO2. The annual global source strength of CH4 is fairly well constrained to 550 (±50) Tg from the study of tropospheric OH which is the dominant sink for atmospheric CH4. However there is a distinct lack of knowledge surrounding the temporal and spatial variability of individual methane sources and sinks, leaving a number of scientific questions unanswered. For example, it is unclear why the atmospheric growth rate of CH4 has recently begun to rise again, following a 20 year decline, despite no obvious change in global emissions. It is clear that an accurate and comprehensive dataset of CH4 retrievals is required in order to properly quantify CH4 sources and sinks and hence allow problems such as this to be better understood.