Reply on RC1

Abstract

We interpret space-borne observations from the TROPOspheric Monitoring Instrument (TROPOMI) in a multi-inversion framework to characterize the 2018–2019 global methane budget. Evaluation of the inverse solutions indicates that methane sources and sinks cannot be separately resolved by methane observations alone—even with the dense TROPOMI sampling coverage. Employing remote carbon monoxide (CO) and hydroxyl radical (OH) observations as additional constraints, we infer from TROPOMI a global methane source of 587 Tg/y and sink of 571 Tg/y for our analysis period. We apply a new downscaling method to map these emissions to 0.1°×0.1° resolution, using the results to uncover key gaps in the prior methane budget. The TROPOMI data point to an underestimate of tropical wetland emissions (+13 %; 20 Tg/y), with adjustments following regional hydrology. Some simple wetland parameterizations represent these patterns as accurately as more sophisticated process-based models. Fossil fuel emissions are strongly underestimated over the Middle East (+5 Tg/y), where they have been increasing rapidly over the past decade, and over Venezuela. The TROPOMI observations reveal many fossil fuel emission hotspots missing from the prior inventory, including over Mexico, Oman, Yemen, Turkmenistan, Iran, Iraq, Libya, and Algeria. Agricultural methane sources are underestimated in India, Brazil, the California Central Valley, and Asia. More than 45 % of the global upward anthropogenic source adjustment occurs over India and southeast Asia during the summer monsoon (+8.5 Tg in Jul–Oct), likely due to rainfall-enhanced emissions from rice, manure, and landfills/sewers, which increase during this season along with the natural wetland source.