Emissions of methane, a greenhouse gas several times more potent than carbon dioxide, increased at record-high rates between 2020 and 2022. A new study suggests that rather than fossil fuels, microbes were responsible for this recent methane surge.
Until the early 2000s, fossil fuel production drove much of the increase in atmospheric methane, study lead author Sylvia Michel, senior scientist at the University of Colorado Boulder, U.S., told Mongabay by email. Fossil fuels “are still a very large part of the methane budget,” she said. “They just aren’t the cause of the recent increase.”
After a short pause in growth from 1999 to 2006, atmospheric methane concentrations have risen rapidly. Between 2008 and 2014, methane concentrations increased by around 5 parts per billion (ppb) per year, then by 9 ppb per year between 2014 and 2020. From 2020-2022, though, methane went up by around 15 ppb per year.
To find out where that latest surge came from, the study’s researchers analyzed methane in air samples collected from 22 sites globally. They ran the samples through a specialized spectrometer, and used a simple computer model to simulate and track the likely source of the emissions. In the end, the study found microbial sources have been driving increases in methane emissions since 2006, with their contribution especially high since 2020.
“We were surprised by how much the 2020-2022 methane increase could be attributed to microbial sources,” Michel said. These sources include single-celled Archaea, microorganisms that live in oxygen-free environments like wetlands, the guts of cows, rice fields, landfills or waste facilities, she added.
Michel, however, cautioned they can’t differentiate if the recent methane emissions are from natural sources like wetlands or human sources like landfills.
Naveen Chandra from the Research Institute for Global Change in Japan, who was not involved in the research, told Mongabay by email that the study’s findings “align broadly well with what we already know about how microbial processes respond to changes in temperature and rainfall.” Chandra also studies methane emissions.
“It’s widely recognized that microbial sources, such as wetlands and waste sites, release more methane (CH₄) as temperatures rise,” Chandra said. “These sources account for about half of the global methane emissions, so shifts in climate — like higher temperatures or more rainfall — can have a major impact on the amount of methane entering the atmosphere.”
However, what stood out to him was “the study’s estimate that microbial sources may contribute as much as 90% to recent methane growth.”
“This is a surprisingly high number,” he said, adding that it might change if more complex atmospheric processes were included in the modeling.
“If this large contribution proves accurate, it’s a concerning signal,” Chandra said. “With rising global temperatures, we could see an even greater increase in atmospheric methane levels in the future, which would have serious implications for climate change.”
Banner image of a wetland in South Africa, by Rhett A. Butler/Mongabay.
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