Preprints
https://doi.org/10.5194/acp-2022-425
https://doi.org/10.5194/acp-2022-425
 
17 Jun 2022
17 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Methane emissions responsible for record-breaking atmospheric methane growth rates in 2020 and 2021

Liang Feng1, Paul I. Palmer1,2, Robert J. Parker3,4, Mark F. Lunt2, and Hartmut Boesch3,4 Liang Feng et al.
  • 1National Centre for Earth Observation, University of Edinburgh, Edinburgh, UK
  • 2School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 3National Centre for Earth Observation, Space Park Leicester, University of Leicester, UK
  • 4Earth Observation Science, School of Physics and Astronomy, University of Leicester, UK

Abstract. The global atmospheric methane growth rates reported by NOAA for 2020 and 2021 are the largest since systematic measurements began in 1983. To explore the underlying reasons for these anomalous growth rates we use newly available methane data from the Japanese Greenhouse gases Observing SATellite (GOSAT) to estimate methane surface emissions. Relative to baseline values in 2019 we see the largest annual increases in methane emissions during 2020 over Eastern Africa (13 Tg), tropical Asia (4 Tg), tropical South America (3 Tg), and temperate Eurasia (3 Tg), and the largest reductions over China (-6 Tg) and India (-2 Tg). We find comparable emission changes in 2021, relative to 2019, except for tropical and temperate South America where emissions increased to 9 Tg and 5 Tg, respectively, and tropical Asian emissions increased to 8 Tg. The elevated contributions we saw in 2020 over the western half of Africa (-5 Tg) and Europe (-3 Tg) are substantially reduced in 2021, compared to our 2019 baseline. We find statistically significant positive correlations between anomalies of tropical methane emissions and groundwater, consistent with recent studies that have highlighted a growing role for microbial sources over the tropics. Emission reductions over India and China are expected in 2020 due to the Covid-19 shutdown but continued in 2021, which we do not currently understand. Based on a sensitivity study for which we assume a conservative 5 % decrease in hydroxyl concentrations in 2020, due to reduced pollutant emissions during the Covid-19 shutdown, we find that the global increase in our a posteriori emissions in 2020 is ~22 % lower than our control calculation. We conclude therefore that most of the observed increase in atmospheric methane during 2020 and 2021 is due to increased emissions.

Liang Feng et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Reviewer comment on Feng et al', Anonymous Referee #1, 18 Jun 2022
    • AC1: 'Reply on RC1', Paul Palmer, 24 Jun 2022
      • RC2: 'Reply on AC1', Anonymous Referee #1, 24 Jun 2022
        • AC2: 'Reply on RC2', Paul Palmer, 24 Jun 2022
  • CC1: 'Comment on acp-2022-425', Janne Hakkarainen, 01 Jul 2022
  • RC3: 'Comment on acp-2022-425', Anonymous Referee #2, 06 Aug 2022

Liang Feng et al.

Liang Feng et al.

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Short summary
Our understanding of recent changes in atmospheric methane has defied explanation. The atmospheric growth of methane has since 2007 accelerated to record-breaking values in 2020 and 2021. We use satellite observations of methane to show that 1) increasing emissions over the tropics are mostly responsible for these recent atmospheric changes, and 2) changes in the OH sink during the 2020 Covid-19 shutdown can explain up to 20 % of changes in atmospheric methane for that year.
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