Hydroxyl Radicals Crashed Methane Surged

The atmosphere has a self-cleaning mechanism, and in 2020, it faltered. Hydroxyl radicals—molecules that scrub methane and other pollutants from the air—declined sharply, triggering the fastest methane surge ever recorded. Between 2019 and 2023, atmospheric methane jumped 55 parts per billion, reaching 1921 ppb by 2023. The peak came in 2021, when concentrations spiked nearly 18 ppb in a single year—an 84% increase over 2019's growth rate.

The culprit wasn't a sudden explosion of emissions. It was chemistry.

The Hydroxyl Paradox

Hydroxyl radicals act as the atmosphere's detergent, breaking down methane molecules before they can trap heat. When OH levels drop, methane lingers. According to research published in Science in February 2026, this decline in atmospheric cleaning power explained 80-85% of the year-to-year variability in methane growth during the surge.

What caused the OH crash? COVID-19 lockdowns. When factories shut down and traffic evaporated, nitrogen oxide emissions plummeted. NOₓ compounds, despite being pollutants themselves, play a complex role in atmospheric chemistry—they help generate hydroxyl radicals through reactions with sunlight and water vapor. Cleaner air meant fewer NOₓ emissions, which meant fewer OH radicals, which meant methane accumulated faster.

The pandemic created an unintended experiment: what happens when you suddenly reduce one type of pollution? The answer involved a cascade of chemical reactions that temporarily weakened the atmosphere's ability to regulate itself. Philippe Ciais of the University of Versailles Saint-Quentin-en-Yvelines, who led the study, found that this chemistry shift—not runaway emissions—drove the spike.

When Wet Gets Wetter

While atmospheric chemistry explains why methane accumulated, climate patterns explain where new emissions came from. From 2020 to 2023, an extended La Niña brought wetter-than-average conditions across tropical regions. Water flooded wetlands, expanded lakes and rivers, and submerged rice paddies. Beneath these waterlogged surfaces, microbes thrived in oxygen-poor environments, producing methane as a metabolic byproduct.

Tropical Africa and Southeast Asia showed the largest emission increases. Arctic wetlands and lakes also contributed as warming temperatures accelerated microbial activity in previously frozen soils. These weren't marginal changes—the wet conditions fundamentally altered how much methane natural and agricultural systems released.

Isotopic evidence confirmed the source. Methane molecules come in different forms depending on their origin. Microbial methane—from wetlands, rice fields, and inland waters—has a distinct isotopic signature compared to fossil fuel methane. The data pointed overwhelmingly to biological sources, not oil and gas leaks or wildfires.

The Rice Field Factor

Natural wetlands weren't the only problem. Managed systems like rice paddies contributed significantly to the surge. Rice cultivation requires flooding fields for months at a time, creating ideal conditions for methane-producing bacteria. As climate patterns shifted and precipitation increased in key agricultural regions, these emissions intensified.

Hanqin Tian, a Boston College professor who contributed to the study, emphasized the connection: "As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change."

This complicates mitigation efforts. Reducing fossil fuel emissions is straightforward policy—regulate extraction, plug leaks, transition energy systems. Controlling methane from flooded ecosystems and agriculture requires different approaches: managing water levels in rice production, restoring degraded wetlands to shift microbial communities, even rethinking where and how rice is grown as climate zones shift.

When Climate Flips the Script

The methane surge wasn't uniform. In 2023, South American wetlands bucked the trend. An extreme El Niño brought drought conditions, drying out previously flooded areas and sharply reducing methane emissions from the region. The contrast with tropical Africa and Southeast Asia—where wet conditions persisted—demonstrated how sensitive these systems are to climate variability.

This sensitivity poses a challenge for prediction. Climate models project overall warming and increased precipitation in many tropical regions, but year-to-year variability will remain high. La Niña and El Niño cycles will continue driving dramatic swings in regional moisture. Each swing will ripple through methane emissions in ways current models struggle to capture.

The research team found that many widely used emission models underestimated wetland and inland-water contributions during the surge. The models missed critical dynamics in how flooding extent, microbial activity, and temperature interact. These gaps aren't academic—they directly affect whether climate targets are achievable.

Rethinking the Methane Pledge

The Global Methane Pledge, launched at COP26, commits signatories to reducing methane emissions 30% by 2030. The initiative focuses heavily on fossil fuels, agriculture, and waste—sources humans directly control. But the recent surge reveals a blind spot: climate-driven sources that respond to temperature and precipitation changes, not policy interventions.

If warming continues and tropical regions experience more frequent wet periods, methane from natural and semi-natural systems could accelerate regardless of human emission cuts. The 2020-2023 surge offered a preview. Even as some countries reduced fossil fuel methane, climate-driven biological sources surged, overwhelming those gains.

The research suggests methane trends will depend as much on climate dynamics as on emission controls. That doesn't mean mitigation efforts are futile—reducing controllable sources remains essential. But it does mean targets need to account for climate feedbacks that current pledges largely ignore.