Hydroxyl Interannual Variability Impacts Estimation of Regional Methane Emissions

Abstract Methane is a major greenhouse gas in the Earth's atmosphere, but understanding of its sources and removal budget remains incomplete. Using MIROC4‐ACTM inverse model simulations, we examine the impact of hydroxyl (OH) variation on global and regional CH 4 budgets from 2001 to 2019. Our results show CH 4 emissions inferred from climatological (OH CLM ) and interannually varying (OH IAV ) OH fields align well for global emission (∼564 Tg‐CH 4 yr −1 ) but show clear regional differences. East Asia experiences the strongest OH‐related enhancement (∼+10 Tg‐CH 4 yr −1 , or ∼20% higher compared with the OH CLM scenario), with notable effects in Boreal North America (+16.2%), Europe (−16.4%), North Africa (−8.6%), and Central Africa (−11.8%). The OH IAV influence is strongest from 2001 to 2012, with a cumulative CH 4 emission difference of −72.0 ± 2.0 Tg‐CH 4 between OH CLM and OH IAV inversions. This study reiterates the need for improved estimation OH IAV using models and proxy observations.