Why methane surged in the atmosphere during the early 2020s

The atmospheric methane (CH₄) growth rate surged after 2019, peaking at 16.2 parts per billion per year (ppb year^-1) in 2020 before declining to 8.6 ppb year^-1 in 2023. Using multiple atmospheric inversions constrained by observation- and model-based prescribed hydroxyl radical (OH) fields and CH₄ atmospheric data, we show that a drop of OH radicals in 2020-2021, followed by recovery in 2022-2023, accounted for 83% of year-on-year variations in the CH₄ growth rate, the rest being explained by wetland and inland water emissions, which increased between 2019 and 2020-2022 [+8.6 ± 2.6 teragrams of CH₄ per year (TgCH₄ year^-1)] and then decreased between 2022 and 2023 (-9.9 ± 3.3 TgCH₄ year^-1). Most emission changes from 2019 to 2023 occurred in northern tropical wetlands in Africa and Asia, whereas South American wetlands emissions declined and Arctic emissions increased after 2019.