Using Satellite Observations of Atmospheric Methane to Quantify the Methane Budget and Its Trends from the Global Scale down to Point Sources (Invited Presentation)

Atmospheric methane originates from a number of sources that are difficult to quantify in bottom-up emission inventories. Satellite observations of atmospheric methane in the shortwave infrared (SWIR) provide top-down information that can be used through inverse modeling to improve our understanding of emissions. We use GOSAT satellite observations for 2010-2017 to improve global estimates of methane sources, OH concentrations (the main methane sink), and their trends over the period. The inversion uses an improved representation of wetland emissions that allows optimization of their seasonality and interannual variability. It also uses a new bottom-up inventory for methane emissions from oil, gas, and coal that is anchored to national emission reports to the United Nations. Results show that the 2010-2017 trend in atmospheric methane is driven by a combination of increases in emissions from wetlands, tropical livestock, and Chinese coal, and also by a decrease in the OH concentration. Complementary observations of methane in the thermal infrared (TIR) from AIRS and CrIS would improve our ability to monitor trends in OH. Preliminary observations from the TROPOMI satellite instrument launched in October 2017 offer major promise for improved mapping of methane emissions. A challenge when developing a strategy for methane emission controls is that anthropogenic emissions originate from a very large number of relatively small point sources that are temporally variable with a skewed distribution. Observation of methane plumes at the scale of individual facilities has been demonstrated from space by the GHGSat instrument (50x50 m² pixel resolution) and has revealed anomalously large emissions from Turkmenistan oil fields. The GHGSat observations are also proving effective for continuous monitoring of point sources and we will show an example for coal mine vents. The new generation of imaging spectrometers designed to observe land surfaces (PRISMA, EnMAP, EMIT) includes SWIR channels with sufficient spectral resolution that these instruments should enable global mapping of large methane point sources and provide an important addition to the methane observing system.