Scientists Solve COVID Methane Mystery with Unexpected Atmospheric Chemistry Discovery

The Great COVID Methane Paradox

When the world shut down in 2020, scientists expected greenhouse gas levels to drop across the board. Methane concentrations in the atmosphere surged between 2020 and 2022 at the fastest pace ever recorded, reaching an annual growth peak of about 16.2 parts per billion before easing to around 8.6 parts per billion per year by 2023. This unexpected spike left researchers scrambling for answers to one of the pandemic's most puzzling environmental mysteries.

Six years later, a team of more than 40 scientists has offered an answer to this chemical mystery in a study published last week in Science, pointing to dynamics in the atmosphere and natural areas. Their findings reveal a complex interplay between reduced air pollution and natural climate patterns that created the perfect storm for methane accumulation.

The Atmospheric Cleaning System Breakdown

The answer lies in understanding what scientists call "hydroxyl radicals – highly reactive molecules often described as the atmosphere's 'detergent'." These hydroxyl radicals are present in tiny quantities and have a lifetime of less than a second, but they remove about 85 percent of methane from the atmosphere. They are the "Pac-Man of the atmosphere": "As soon as they see something they eat it and then disappear."

During the pandemic lockdowns, something unexpected happened to this atmospheric cleaning system. OH concentrations decreased by around 1.6 percent in 2020 from the year before, largely because of a fall in nitrogen oxide (NOx) emissions caused by the COVID lockdowns. Around 80 percent of the methane surge was a result of this pollutant reaction, the authors predict. In a cruel irony, cleaner air actually made the atmosphere less efficient at removing methane.

Nature's Perfect Storm

The atmospheric chemistry breakdown was only part of the story. The pandemic coincided with La Niña, a periodic climate event that causes increased rainfall in tropical areas. As regions throughout Africa and Southeast Asia got wetter, they became more ideal environments for methane-producing microbes. Flooded soils and expanded wetlands provided ideal conditions for methane-producing microbes, boosting emissions from wetlands and inland waters. The largest increases were seen in tropical Africa and Southeast Asia, while Arctic wetlands and lakes also released more methane as temperatures rose.

Microbes in wetlands produce methane as they metabolize and break down organic matter anaerobically, or without oxygen. More water storage in wetlands means more anaerobic microbial activity and more release of methane to the atmosphere. This natural process, amplified by unusual climate conditions, contributed significantly to the unprecedented methane spike.

Climate Implications and Future Challenges

The findings expose troubling gaps in our understanding of Earth's climate system. The findings expose important gaps in current methane emission models, many of which underestimated emissions from wetlands during this period. Methane is the second largest contributor to climate warming after carbon dioxide and packs a much stronger punch per tonne. Over a century, a tonne of methane can trap roughly 30 times more heat than a tonne of carbon dioxide, even though methane typically remains in the atmosphere for only about a decade.

Perhaps most concerning is what this means for future climate action. Based on these results, cutting fossil fuel emissions could actually "boost warming because of the methane side of things with the OH radical chemistry." This creates a complex challenge for policymakers trying to balance immediate air quality improvements with long-term climate goals. "As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters and paddy rice systems will increasingly shape near-term climate change."