Preprints
https://doi.org/10.5194/acp-2021-1056
https://doi.org/10.5194/acp-2021-1056

  04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal ACP.

Quantification of methane emissions from hotspots and during COVID-19 using a global atmospheric inversion

Joe McNorton1, Nicolas Bousserez1, Anna Agustí-Panareda1, Gianpaolo Balsamo1, Richard Engelen1, Vincent Huijnen2, Antje Inness1, Zak Kipling1, Mark Parrington1, and Roberto Ribas1 Joe McNorton et al.
  • 1European Centre for Medium-Range Weather Forecasts, Reading, RG2 9AX, UK
  • 2Royal Netherlands Meteorological Institute (KNMI), De Bilt, NL-3731, Netherlands

Abstract. Concentrations of atmospheric methane (CH4), the second most important greenhouse gas, continue to grow. In recent years this growth rate has increased further (2020: +14.7 ppb), the cause of which remains largely unknown. Here, we demonstrate a high-resolution (~80 km), short-window (24-hour) 4D-Var global inversion system based on the ECMWF Integrated Forecasting System (IFS) and newly available satellite observations. The largest national disagreement found between prior (63.1 Tg yr−1) and posterior (59.8 Tg yr−1) CH4 emissions is from China, mainly attributed to the energy sector. Emissions estimated form our global system agree well with previous basin-wide regional studies and point source specific studies. Emission events (leaks/blowouts) >10 t hr−1 were detected, but without accurate prior uncertainty information, were not well quantified. Our results suggest that global anthropogenic CH4 emissions for 2020 were 5.7 Tg yr−1 (+1.6 %) higher than for 2019, mainly attributed to the energy and agricultural sectors. Regionally, the largest 2020 increases were seen from China (+2.6 Tg yr−1, 4.3 %), with smaller increases from India (+0.8 Tg yr−1, 2.2 %) and Indonesia (+0.3 Tg yr−1, 2.6 %). Results show the rise in emissions, and subsequent atmospheric growth, would have occurred with or without the COVID-19 slowdown. During the onset of the global slowdown (March–April, 2020) energy sector CH4 emissions from China increased; however, during later months (May–June, 2020) emissions decreased below expected pre-slowdown levels. The accumulated impact of the slowdown on CH4 emissions from March–June 2020 is found to be small. Changes in atmospheric chemistry, not investigated here, may have contributed to the observed growth in 2020. Future work aims to develop the global IFS inversion system and to extend the 4D-Var window-length using a hybrid ensemble-variational method.

Joe McNorton et al.

Status: open (until 16 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Joe McNorton et al.

Joe McNorton et al.

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Short summary
Concentrations of atmospheric methane continue to grow and in recent years at an increasing rate, the reason for which is unknown. Using newly available satellite observations and a state-of-the-art weather prediction model we perform global estimates of emissions from hotspots at high-resolution. Results show the system can accurately report on biases in inventory reporting and is used to conclude the COVID-19 slowdown had very little impact on global methane emissions.
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