Pandemic Methane Surge Linked to Wetland Flooding, Study Finds

A new study has found that the surge in atmospheric methane during the COVID-19 pandemic was mainly caused by flooding in wetlands. This increase in methane levels underscores the influence of natural ecosystems on greenhouse gas emissions. Researchers emphasize the importance of understanding how climate change affects methane sources, particularly in wetlands, to better address global warming and its impacts on the environment.

A recent analysis of satellite data reveals that the unprecedented rise in atmospheric methane emissions from 2020 to 2022 was largely attributed to increased flooding and water retention in wetlands, along with a minor reduction in atmospheric hydroxide (OH). These findings have significant implications for strategies aimed at reducing atmospheric methane and its effects on climate change.

Zhen Qu, assistant professor of marine, earth, and atmospheric sciences at North Carolina State University and the lead author of the study, noted, "Between 2010 and 2019, we observed consistent increases in atmospheric methane concentrations, but the spikes during 2020 to 2022, coinciding with the COVID-19 lockdowns, were considerably more pronounced." He stated, "Global methane emissions rose from approximately 499 teragrams (Tg) to 550 Tg during 2010 to 2019, then surged to between 570 and 590 Tg from 2020 to 2022."

Atmospheric methane emissions are measured in teragrams, with one teragram equivalent to about 1.1 million U.S. tons.

One prominent theory regarding the abrupt rise in atmospheric methane is that the reduction in human-made air pollution from vehicles and industries during the pandemic in 2020 and 2021 played a significant role. This pollution normally contributes hydroxyl radicals (OH) to the lower atmosphere, which interact with gases like methane to facilitate their breakdown.

Qu explained, "The prevailing hypothesis suggested that the pandemic led to a reduction in OH levels, resulting in less OH available in the atmosphere to react with and decompose methane."

To investigate this theory, Qu and a team of researchers from the U.S., U.K., and Germany examined global satellite emissions data and atmospheric simulations for both methane and OH from 2010 to 2019 and compared it with the data from 2020 to 2022 to identify the source of the methane surge.

The researchers utilized data from satellite measurements of atmospheric composition and chemical transport models to create a model that helped quantify both the amounts and sources of methane and OH during the two periods.

They discovered that the majority of the methane surge from 2020 to 2022 was linked to inundation events—primarily flooding—in equatorial Asia and Africa, which contributed 43% and 30% of the additional atmospheric methane, respectively. Although OH levels did decline during this time, this reduction accounted for only 28% of the surge.

Qu remarked, "The increased precipitation in these wetland and rice-growing areas is likely related to the La Niña conditions observed from 2020 to early 2023. Microbes in wetlands generate methane as they metabolize and decompose organic matter anaerobically, or without oxygen. Greater water retention in wetlands leads to heightened anaerobic microbial activity and subsequently more methane released into the atmosphere."

The researchers believe that enhancing our understanding of wetland emissions is crucial for developing effective mitigation strategies.

Qu emphasized, "Our findings highlight the wet tropics as a key driver of increased methane concentrations since 2010. Improved observations of wetland methane emissions and their response to precipitation changes are essential for comprehending how precipitation patterns impact tropical wetland ecosystems."

The study is published in the Proceedings of the National Academy of Sciences and received partial support from NASA’s Early Career Investigator Program under grant 80NSSC24K1049. Qu is the corresponding author and initiated the research while serving as a postdoctoral researcher at Harvard University. Other contributors include Daniel Jacob from Harvard, Anthony Bloom and John Worden from the California Institute of Technology's Jet Propulsion Laboratory, Robert Parker from the University of Leicester, U.K., and Hartmut Boesch from the University of Bremen, Germany.

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Source: sciencedaily‍