Covid-19 Cleared The Skies But Also Supercharged Methane …
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In the spring of 2020, as the COVID-19 pandemic brought global industry and travel nearly to a halt, satellite sensors recorded a dramatic plunge in nitrogen dioxide, a byproduct of internal combustion engines and heavy industry. For a moment, the world’s air was cleaner than it had been in decades.
But then something strange started happening: methane, the second most important anthropogenic greenhouse gas after carbon dioxide, was surging. Its growth rate hit 16.2 parts per billion that year, the highest since systematic records began in the early 1980s. A new study published in the journal Science looked at the complex chemistry of the troposphere (the lowest region of the atmosphere) and found that the two changes are ly connected.
An atmospheric cleaner
Since the late 1960s, we knew that atmospheric methane doesn’t just vanish. It is actively scrubbed from the sky by the hydroxyl radical, a highly reactive molecule that breaks down methane, turning it into water vapor and carbon dioxide. “The problem is that the lifetime of the hydroxyl radical is very short—its lifespan is less than a second” says Shushi Peng, a professor at Peking University, China, and a co-author of the study. To do its job as an atmospheric methane clearing agent, a hydroxyl radical must be constantly replenished through a series of chemical reactions triggered by sunlight. The key ingredients in these reactions are nitrogen oxides, the very pollutants that were drastically reduced when cars stayed in garages and factories went dark in 2020.
When nitrogen oxide levels plummeted by approximately 15 to 20 percent globally during the 2020 lockdowns, the production of the hydroxyl radical slowed to a crawl. Without enough of these to go around, methane molecules that would have normally been destroyed remained in the atmosphere for longer. Peng and his colleagues estimate that the reduction in this methane sink accounted for approximately 80 percent of the massive spike in the methane growth rate seen in 2020. The cleaner our air became, the longer the methane stuck around to warm the planet.
The remaining question, though, was where all this methane was coming from in the first place. Throughout the pandemic, there was speculation that the surge might be caused by super-emitter events in the oil and gas sector, or perhaps a lack of maintenance on leaky infrastructure during lockdowns.
But the new research suggests that the source of these emissions was not what many expected.
The microbial surge
While the weakened atmospheric sink explained the bulk of the 2020 surge, it wasn’t the only factor at play. The remaining 20 percent of the growth, and an even larger portion of the growth in 2021 and 2022, came from an increase in actual emissions from the ground. To track the source of these emissions down, Peng’s team went through tons of data from satellites and various ground monitoring stations.
Methane comes in different isotopic signatures. Methane from fossil fuels natural gas leaks or coal mines is heavier, containing a higher fraction of the stable isotope carbon-13. Conversely, methane produced by microbes found in the guts of livestock, in landfills, and most notably in wetlands, is lighter, enriched in carbon-12.
When the researchers analyzed data from the National Oceanic and Atmospheric Administration global flask network, a worldwide monitoring system tracking the chemical composition of Earth’s atmosphere, they found that the atmospheric methane during the mysterious surge was becoming significantly lighter. This was a smoking gun for biogenic sources. The surge wasn’t coming from pipes or power plants; it was coming from microbes.
La Niña came to play
The timing of the pandemic coincided with a relatively rare meteorological event. La Niña, the cool phase of the El Niño–Southern Oscillation that typically leads to increased rainfall in the tropics, lasted for three consecutive Northern Hemisphere winters (from 2020 to 2023). This made the early 2020s exceptionally wet.
The researchers used satellite data from the Greenhouse Gases Observing Satellite and sophisticated atmospheric models to trace the source of the light methane to vast wetland areas in tropical Africa and Southeast Asia. In regions the Sudd in South Sudan and the Congo Basin, record-breaking rainfall flooded massive swaths of land. In these waterlogged, oxygen-poor environments, microbial methanogens thrived, churning out methane at an accelerated pace.
Peng and his team found that tropical African and Asian wetlands alone were responsible for roughly 30 percent of the global methane emissions increase during the 2020–2022 period.
The clean air paradox
Methane is often touted as the low-hanging fruit of climate policy because it has a shorter atmospheric lifetime than carbon dioxide. For a long time, we thought that if we stopped the infrastructure leaks and other methane emissions today, the atmosphere would clear relatively quickly. But the study done by Peng and his colleagues shows that things might not be that simple. There are two major challenges we must face to solve the methane problem, and both are largely outside of direct human control.
First, there is the threat of climate feedbacks. If warming temperatures and changing precipitation patterns cause a boost in natural wetland emissions, we may find ourselves in a race against a biological source that we cannot simply turn off. The second challenge, arguably even harder to overcome, is the clean air paradox that emerges from the results of Peng’s study.
As we transition away from fossil fuels and improve urban air quality, nitrogen oxide levels will naturally decline—an unequivocal win for public health. But the atmosphere’s natural capacity to scrub methane will also decline.
That’s a piece of science that’s almost sure to get hopelessly distorted in our maelstrom of conflicting politics. Because it means all the coal power plants, V8 cars, and private jets actually purge a greenhouse gas out of the atmosphere, right?
“Not really, because everyone needs clean air,” argues Peng. “It means that we must reduce anthropogenic methane emissions.” If it’s just to compensate for a cleaner atmosphere with less hydroxyl radicals, we’re ly going to need even more aggressive reductions than we previously thought. “I think that’s the only choice for the policy makers,” Peng adds.
Science, 2026. DOI: 10.1126/science.adx8262
Jacek Krywko Associate Writer
Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.
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Arstechnica.com