A Review of the Fate of Atmospheric Methane: Interactions with Oxidants and Climate Impacts

Atmospheric methane (CH4) growth reflects both emissions and chemical removal, but their contributions remain difficult to separate because the dominant sink, reaction with hydroxyl radicals (OH), is incompletely constrained. This review links methane sources and attribution with OH variability, methane lifetime, atmospheric oxidation capacity (AOC), and climate. Tropospheric OH accounts for roughly 90% of methane removal. Methane oxidation consumes OH, contributing to a nonlinear feedback that extends its perturbation lifetime. Fire co-emissions, low-NOx biogenic chemistry, reactive halogens, and climate variability add further spatial and temporal variability. Comparisons of methyl chloroform and hydrofluorocarbon inversions with chemistry models show that inferred OH trends and spatial patterns depend on tracer emissions, transport, and chemical mechanisms. The Amazon and boreal–Arctic regions show contrasting examples of coupled source and oxidant variability. The 2020–2023 methane surge further illustrates the difficulty of distinguishing enhanced wetland emissions from changes in OH-mediated removal. Future methane concentrations and the benefits of mitigation will depend on coordinated changes in methane and reactive precursor emissions. Better constraints on AOC, particularly OH variability and methane–oxidant feedbacks, would improve methane attribution and future projections.