Wetland emission and atmospheric sink changes explain methane growth in 2020

Shushi Peng (), Xin Lin (), Rona L. Thompson, Yi Xi, Gang Liu, Didier Hauglustaine, Xin Lan, Benjamin Poulter, Michel Ramonet, Marielle Saunois, Yi Yin, Zhen Zhang, Bo Zheng and Philippe Ciais
Additional contact information
Shushi Peng: Peking University
Xin Lin: Université Paris-Saclay
Rona L. Thompson: Norwegian Institute for Air Research (NILU)
Yi Xi: Peking University
Gang Liu: Peking University
Didier Hauglustaine: Université Paris-Saclay
Xin Lan: Cooperative Institute for Research in Environmental Sciences of University of Colorado
Benjamin Poulter: NASA Goddard Space Flight Center
Michel Ramonet: Université Paris-Saclay
Marielle Saunois: Université Paris-Saclay
Yi Yin: California Institute of Technology
Zhen Zhang: University of Maryland
Bo Zheng: Tsinghua University
Philippe Ciais: Université Paris-Saclay

Nature, 2022, vol. 612, issue 7940, 477-482

Abstract: Abstract Atmospheric methane growth reached an exceptionally high rate of 15.1 ± 0.4 parts per billion per year in 2020 despite a probable decrease in anthropogenic methane emissions during COVID-19 lockdowns1. Here we quantify changes in methane sources and in its atmospheric sink in 2020 compared with 2019. We find that, globally, total anthropogenic emissions decreased by 1.2 ± 0.1 teragrams of methane per year (Tg CH4 yr−1), fire emissions decreased by 6.5 ± 0.1 Tg CH4 yr−1 and wetland emissions increased by 6.0 ± 2.3 Tg CH4 yr−1. Tropospheric OH concentration decreased by 1.6 ± 0.2 per cent relative to 2019, mainly as a result of lower anthropogenic nitrogen oxide (NOx) emissions and associated lower free tropospheric ozone during pandemic lockdowns2. From atmospheric inversions, we also infer that global net emissions increased by 6.9 ± 2.1 Tg CH4 yr−1 in 2020 relative to 2019, and global methane removal from reaction with OH decreased by 7.5 ± 0.8 Tg CH4 yr−1. Therefore, we attribute the methane growth rate anomaly in 2020 relative to 2019 to lower OH sink (53 ± 10 per cent) and higher natural emissions (47 ± 16 per cent), mostly from wetlands. In line with previous findings3,4, our results imply that wetland methane emissions are sensitive to a warmer and wetter climate and could act as a positive feedback mechanism in the future. Our study also suggests that nitrogen oxide emission trends need to be taken into account when implementing the global anthropogenic methane emissions reduction pledge5.

Date: 2022
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DOI: 10.1038/s41586-022-05447-w

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