A recent examination of satellite data has revealed that the significant rise in atmospheric methane emissions between 2020 and 2022 was primarily due to increased flooding and water retention in wetlands, paired with a minor reduction in atmospheric hydroxide (OH). These findings could impact efforts aimed at reducing atmospheric methane and addressing its effects on climate change.
A recent examination of satellite data has revealed that the significant rise in atmospheric methane emissions between 2020 and 2022 was primarily due to increased flooding and water retention in wetlands, paired with a minor reduction in atmospheric hydroxide (OH). These findings could impact efforts aimed at reducing atmospheric methane and addressing its effects on climate change.
“Between 2010 and 2019, we observed consistent rises in atmospheric methane levels, with minor accelerations, but the increases observed from 2020 to 2022, coinciding with the COVID-19 lockdowns, were much more pronounced,” explains Zhen Qu, assistant professor of marine, earth, and atmospheric sciences at North Carolina State University and principal investigator of the study. “Global methane emissions grew from approximately 499 teragrams (Tg) to 550 Tg from 2010 to 2019, then surged to between 570 and 590 Tg in the period from 2020 to 2022.”
Atmospheric methane emissions are quantified in teragrams, where one teragram is roughly equivalent to 1.1 million U.S. tons.
One key hypothesis regarding the abrupt rise in atmospheric methane suggested that reduced human-caused air pollution from vehicles and industrial activities during the 2020 and 2021 pandemic lockdowns played a role. Such air pollution typically adds hydroxyl radicals (OH) to the lower atmosphere. These OH radicals interact with other gases like methane to facilitate their breakdown.
“The prevailing belief was that the pandemic led to a reduction in OH concentration, which means there was less OH in the atmosphere to interact with and decompose methane,” Qu remarks.
To assess this theory, Qu and a team of scientists from the U.S., U.K., and Germany analyzed global satellite emissions data alongside atmospheric simulations for both methane and OH during the 2010 to 2019 timeframe and compared them to similar data from 2020 to 2022 to trace the source of the increase.
Utilizing information derived from satellite observations of atmospheric makeup and chemical transport models, the researchers developed a model to determine both the quantities and origins of methane and OH for both time spans.
The results indicated that a large portion of the methane increase from 2020 to 2022 stemmed from flooding events in equatorial Asia and Africa, which contributed 43% and 30% of the additional atmospheric methane, respectively. Although OH levels did dip during this period, this decline was responsible for only 28% of the surge.
“The heavy rains in these wetland and rice-farming regions likely correspond with the La Niña phenomenon noted from 2020 to early 2023,” Qu explains. “Microorganisms in wetlands produce methane as they digest and decompose organic material without oxygen, meaning that more water in wetlands leads to increased anaerobic microbial activity and consequently, more methane emissions into the atmosphere.”
The researchers believe that enhancing our understanding of wetland emissions is crucial for devising effective mitigation strategies.
“Our findings suggest that the wet tropics have been the primary contributor to rising methane levels since 2010,” Qu adds. “Improved tracking of methane emissions from wetlands and understanding how methane production is affected by rainfall variability are essential to comprehending the influence of precipitation on tropical wetland ecosystems.”
This research is published in the Proceedings of the National Academy of Sciences and was partially funded by NASA’s Early Career Investigator Program under grant 80NSSC24K1049. Qu served as the corresponding author, conducting the research while he was a postdoctoral researcher at Harvard University. Significant contributions were made by Daniel Jacob from Harvard; Anthony Bloom and John Worden from the Jet Propulsion Laboratory at Caltech; Robert Parker from the University of Leicester; and Hartmut Boesch from the University of Bremen, Germany.
