Philippe Ciais: Why methane spiked in the atmosphere since 2020, and is it calming down

Abstract

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. In the presentation, I will present the first preliminary results for the update of our low-latency CH₄ budget until 2025.

Bio

Philippe Ciais is a senior researcher working at Laboratoire des Sciences du Climat et de l’Environnement in France near Paris. He is an expert of the global carbon cycle and greenhouse gases emissions monitoring. He is the author of many peer-reviewed publications including many in high-impact journals, recently ranked as best environmental scientist in the world. Philippe Ciais is an elected member of the French National Academy of Sciences and an elected foreign member of the Chinese Academy of Science.