Pandemic Methane Surge: OH Radical Decline

During the COVID-19 pandemic, as global lockdowns brought travel, industry, and daily life to a near standstill in 2020, many expected a temporary reprieve for the climate: lower emissions of greenhouse gases and pollutants. Carbon dioxide levels did dip noticeably, but methane — the second-most potent greenhouse gas after CO₂ — behaved in the opposite way. Atmospheric methane concentrations surged to record-breaking growth rates, reaching peaks of around 15–16 parts per billion (ppb) per year in 2020–2022, far exceeding the typical 5–10 ppb annual rise seen in prior decades.

This counterintuitive spike puzzled scientists for years. A headline-grabbing recent study published in Science (2026), involving over 40 researchers and drawing on satellite data from the European Space Agency’s Climate Change Initiative, ground observations, and atmospheric modeling, has finally provided a clear explanation. The surge wasn’t primarily from new methane sources exploding during the pandemic. Instead, it stemmed from a temporary disruption in the atmosphere’s natural “self-cleaning” system, triggered paradoxically by the very reductions in human pollution that lockdowns caused.

The Atmosphere’s Invisible Cleanup Crew: Hydroxyl Radicals

Methane (CH₄) doesn’t linger in the atmosphere forever. Its primary removal mechanism is oxidation by hydroxyl radicals (OH) — highly reactive molecules often called the “detergents” or “cleaners” of the troposphere. These OH radicals react with methane to break it down into carbon dioxide and water, limiting how long the gas persists (typically 7–10 years on average).

OH radicals form through complex photochemical reactions involving pollutants like nitrogen oxides (NOₓ, emitted from vehicle exhausts, power plants, and industry), carbon monoxide (CO), and volatile organic compounds. When lockdowns slashed traffic, aviation, shipping, and industrial activity, NOₓ emissions plummeted worldwide. With fewer precursors available, OH concentrations dropped significantly — by around 1.6% or more in key periods.

The result? The atmosphere became less efficient at destroying methane. Even though direct human methane emissions (from fossil fuels, agriculture, landfills, etc.) likely decreased slightly or stayed stable, the gas accumulated faster because less of it was being removed. Models from the study attribute roughly 80–85% of the 2020–2021 methane growth variability — and up to 83% of the peak surge — to this weakened OH sink.

The Amplifying Role of Nature

The remaining portion of the spike (about 20%) came from natural sources boosted by climate patterns. An extended La Niña phase from mid-2020 to mid-2023 brought wetter conditions to northern tropical regions, particularly wetlands in Africa (e.g., areas like South Sudan’s Sudd swamp) and Southeast Asia. Wetter soils and expanded inundated areas fueled methane-producing microbes (methanogens), increasing emissions from wetlands, rivers, lakes, and rice paddies.

This combination — diminished atmospheric cleansing plus enhanced biogenic emissions — drove the unprecedented rise. By 2023, as societies returned to normal patterns, NOₓ levels rebounded, OH concentrations recovered, and methane growth eased back toward pre-pandemic rates (around 8–9 ppb/year).

Why This Matters: A Warning for Cleaner Air Efforts

The phrase “It’s telling us there’s something big going on,” quoted in reports on the phenomenon, captures the unease among researchers. This wasn’t a sign of runaway emissions from human sources getting worse during lockdowns. Rather, it highlights a subtle but powerful feedback in atmospheric chemistry: aggressively cleaning up short-lived pollutants like NOₓ (a major goal for air quality and health) can inadvertently slow methane removal and amplify warming in the short term.

Methane is far more potent than CO₂ on a per-molecule basis over 20 years (about 80 times more), so even temporary buildups accelerate near-term climate impacts like extreme weather and ice melt. This “air pollution paradox” underscores the need for integrated strategies: slashing methane at its sources (e.g., plugging oil/gas leaks, reducing agricultural emissions, managing landfills) while carefully balancing NOₓ reductions to avoid unintended atmospheric side effects.

As global efforts ramp up to meet Paris Agreement goals — including rapid methane cuts pledged at COPs — this COVID-era episode serves as a real-world experiment. It reminds us that Earth’s atmosphere is a finely tuned system where fixing one problem can ripple into another unless we address greenhouse gases holistically and urgently.