COVID Lockdowns Triggered a Methane Surge That Scientists Didn’t See Coming

In a twist that underscores the complex web of Earth’s atmospheric chemistry, the dramatic reduction in pollution during the COVID-19 lockdowns of 2020 didn’t just clear the skies—it may have inadvertently accelerated global warming by triggering an unexpected surge in methane levels that continues to concern climate scientists today.

The story begins with what seemed like good news during those early pandemic months: as transportation ground to a halt and industries shuttered, nitrogen oxide emissions plummeted. Cities from Los Angeles to Delhi experienced some of the clearest skies in decades. But beneath this silver lining lurked a chemical cascade that scientists are only now beginning to fully understand.

The Methane Mystery

Methane, while less abundant than carbon dioxide, packs a climate punch that’s approximately 80 times more potent over a 20-year period. What makes this gas particularly concerning is its accelerating growth rate. Since the 1980s, atmospheric methane concentrations have been climbing steadily, initially driven by fossil fuel infrastructure leaks and venting. However, the past two decades have seen an additional surge from biological sources—microbes breaking down organic matter in wetlands, agricultural operations, and landfills.

Then came the pandemic years of 2020-2022, when atmospheric methane levels took an unexpected leap. The increase doubled from roughly 20 million tonnes per year to about 40 million tonnes annually, before settling back to 20 million tonnes in 2023. This dramatic fluctuation puzzled researchers, who expected the economic slowdown to reduce emissions across the board.

The Hidden Chemistry

The answer, according to groundbreaking new research led by Shushi Peng at Peking University, lies in the intricate chemistry of our atmosphere. Nitrogen oxides (NOx), primarily emitted by vehicles, aircraft, and ships, play a crucial role in producing hydroxyl radicals (OH) in the atmosphere. These hydroxyl radicals act as the atmosphere’s “detergent,” breaking down methane and other pollutants.

When NOx emissions dropped during lockdowns, the production of hydroxyl radicals decreased correspondingly. This meant less methane was being removed from the atmosphere, allowing concentrations to build up. It’s a classic case of unintended consequences, where solving one environmental problem exacerbated another.

“It’s like having a hangover or something from our addiction to fossil fuels,” explains Matthew Johnson from the University of Copenhagen. “We’re emitting [methane] pollution and the catalyst at the same time, so if we reduce emissions of the catalyst, the pollution takes over.”

The Numbers Behind the Surge

The research team’s sophisticated modeling revealed that the drop in hydroxyl radicals accounted for a staggering 83% of the variation in methane growth rates during 2020-2021, with levels recovering somewhat in 2022-2023 as economic activity resumed. Aviation emissions remained suppressed through 2021, and transportation and shipping took time to return to pre-pandemic levels, prolonging the atmospheric impact.

The remaining 17% of the methane surge came from increased emissions in natural and agricultural systems. The La Niña climate pattern brought increased precipitation to central Africa, expanding wetlands like the Sudd and Cuvette Centrale regions and boosting their methane output. Similar effects were observed in South and Southeast Asian rice paddies and Arctic wetlands, where warming temperatures enhanced microbial activity.

A Warning for the Future

The implications of this research extend far beyond the pandemic years. As countries like China and India continue their transition to cleaner energy and transportation systems, further reductions in NOx pollution could trigger similar methane surges. Peng warns that “the air will become more and more clean, so it means that we have less and less methane sink in the atmosphere. So we need to reduce more and more anthropogenic emissions.”

This presents a challenging paradox for climate policy: efforts to reduce one type of pollution may inadvertently accelerate another form of climate change. The difficulty of measuring hydroxyl radicals—they’re too short-lived for direct observation—adds another layer of complexity to predicting and managing these atmospheric interactions.

The Path Forward

Regardless of the hydroxyl radical dynamics, one thing remains clear: methane emissions from wetlands are projected to continue rising as global warming increases precipitation and enhances microbial activity in many regions. This means that human-driven methane reductions become even more critical.

Euan Nisbet from Royal Holloway, University of London, and Martin Manning from Victoria University of Wellington, highlight “many potential easy wins” in their commentary accompanying the study. These include capturing methane vented from coal mines, landfills, and sewage treatment facilities—particularly in rapidly developing economies like China and India. The oil and gas industry continues to be a major source of preventable methane leaks worldwide.

“We have to do something, because the system is starting to spin out of control,” Johnson emphasizes. “We’re just seeing that leading edge of increase in methane emissions due to the climate feedback.”

The COVID-19 lockdowns provided an unprecedented natural experiment in atmospheric chemistry, revealing connections between different pollution types that scientists are only beginning to fully understand. As we work to clean our air and combat climate change, this research serves as a crucial reminder that Earth’s systems are interconnected in ways that can produce surprising and sometimes counterintuitive results.

The challenge ahead is clear: as we reduce NOx pollution to improve air quality and public health, we must simultaneously accelerate efforts to cut methane emissions from all sources. The atmosphere’s delicate chemical balance demands nothing less if we hope to avoid triggering further unexpected climate feedbacks in our warming world.

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