John Worden (JPL) - Quantifying The Global Methane Budget and Its Uncertainties Using Satellite and Ground Measurements

October 9, 2019 3:30pm
MS 7124



Methane is the second most important anthropogenic greenhouse gas. Fossil and agricultural emissions have increased atmospheric methane from ~750 ppb in pre-industrial times to about ~1900 ppb today, contributing to about a third of the warming since then. Atmospheric methane concentrations stopped increasing in the late 20th century but then the growth rate begin to increase in 2006. Attributing this growth rate to specific sources remains challenging because substantial uncertainties remain in the global methane budget. The primary sources of ambiguity in global CH4 source and sink estimates – and the attribution of the growth rate to underlying source and sink processes – include the confounding roles of transport and chemistry errors, prior budget assumptions, and uncertainties in sector-specific isotopic CH4 fractions. Here, we produce a first continental-scale and sector-specific estimate of the global CH4 budget and its uncertainties constrained simultaneously by satellite based atmospheric CH4 and CO inversion results, surface-based measurement of the total and isotopic CH4 budgets and new state-of-the art wetland and fossil fuel emissions.  While the current observing system of surface measurements and satellite observations of total column methane from the JAXA GOSAT satellite, and constraints on fire emissions from MODIS And MOPITT, can reduce uncertainty on tropical fluxes as well as the total anthropogenic and wetland emissions, we cannot yet identify with 95% confidence which sector has contributed to rising atmospheric methane concentrations since 2009. The launch of TROPOMI, with its orders of magnitude more sampling than GOSAT, as well as use of AIRS methane measurements, offers the potential to dramatically reduce and better characterize uncertainties in the global methane budget.