A high-resolution satellite-based map of global methane emissions reveals missing wetland, fossil fuel, and monsoon sources

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 simultaneous source + sink optimization

using methane observations alone remains an ill-posed problem – even with

the dense TROPOMI sampling coverage. Employing remote carbon monoxide (CO)

and hydroxyl radical (OH) observations with independent methane measurements

to distinguish between candidate solutions, we infer from TROPOMI a global

methane source of 587 (586–589) Tg yr−1 and sink of 571 Tg yr−1 for our analysis

period. We apply a new downscaling method to map the derived monthly

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 (a posteriori increase

of +13 % [6 %–25 %] or 20 [7–25] Tg yr−1), with adjustments following

regional hydrology. Some simple wetland parameterizations represent these

patterns as accurately as more sophisticated process-based models. Emissions

from fossil fuel activities are strongly underestimated over the Middle East

(+5 [2–6] Tg yr−1 a posteriori increase) and over Venezuela. The TROPOMI

observations also 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. Overall,

anthropogenic sources worldwide are increased by +19 [11–31] Tg yr−1 over

the prior estimate. More than 45 % of this adjustment occurs over India

and Southeast Asia during the summer monsoon (+8.5 [3.1–10.7] Tg in

July–October), likely due to rainfall-enhanced emissions from rice, manure, and

landfills/sewers, which increase during this season along with the natural

wetland source.