Methane in the Climate System: Monitoring Emissions from Satellites
The climate forcing from methane emissions since pre-industrial times has been 60% of that from CO2, meaning that methane has made a large contribution to observed warming over the past century. However, the climate impact of methane emissions is very different than that of CO2 emissions in terms of time scales, and this must be recognized when setting climate policy targets: use of a single climate metric to compare the effects of methane and CO2 emissions is not appropriate. An additional complication is that methane is emitted by a variety of sources, and there is large uncertainty in the contribution of different source regions and sectors to the overall methane budget. The recent decadal uptick in methane has generated much interest and is still unexplained, but it represents only a few percent of the methane budget; it should not be surprising that its attribution is difficult considering the uncertainty in the baseline budget. Satellites offer considerable potential for global monitoring of methane emissions, quantifying the contributions from different sources, detecting temporal variability, and attributing long-term trends. Atmospheric methane has been measured continuously from space since 2003, and new instruments are planned for launch in the near future that will greatly expand the capabilities of space-based observations. I will discuss the value of these observations to better quantify and monitor methane emissions, from the global scale down to the scale of point sources.