Attribution of Excess Methane Emissions Over Marine Environments of the Mediterranean and Arabian Peninsula

Abstract

To accurately assess the current atmospheric methane budget and its future trends, it is essential to apportion and quantify the anthropogenic methane emissions to specific sources. This poses a significant challenge in the under-sampled Middle East, where estimates predominantly depend on remote sensing observations and bottom-up reporting of national emissions. Here, we present in situ shipborne observations of greenhouse gases (GHGs) and non-methane hydrocarbons (NMHCs) collected along a >10,000-km route from Vigo, Spain, to Abu Dhabi, UAE. By comparing our observations with Lagrangian dispersion model simulations, coupled with two methane emission inventories, we identify periods of considerable mismatch and apportion the responsible sources. Employing interspecies relationships with NMHCs has enabled the characterization of methane emissions from oil and gas (O&G) operations, urban centers, Red Sea deep water, enteric fermentation, and agriculture across diverse atmospheric environments. Our analysis reveals that the Suez area is a regional emission hotspot, where simulations consistently underestimate the methane emission sources. Importantly, the Middle Eastern O&G sector has been identified as an additional source of considerable uncertainty. Here, methane emissions were alternately underestimated and overestimated by the two inventories, exposing significant gaps in our understanding of fuel exploitation-related emissions in the Middle East. This underscores the need for further targeted field campaigns and long-term observations to improve the accuracy of emission data in the inventories.