Methane spiked after 2020 and the cause was unexpected

One of the biggest drivers was a sharp drop in hydroxyl radicals, which are the main chemicals responsible for breaking methane down in the air. During 2020-2021, this atmospheric clean-up process slowed dramatically. According to the research team, which includes Boston College Professor of Earth and Environmental Science Hanqin Tian, this decline explains about 80 percent of the year-to-year changes in how quickly methane accumulated.

Wet Conditions Fueled Methane Production

At the same time, a prolonged La Niña phase from 2020 to 2023 brought wetter-than-average weather to large parts of the tropics. These conditions expanded flooded landscapes, which are ideal environments for microbes that produce methane. As a result, emissions increased from wetlands, rivers, lakes, and farmed land, adding to the buildup of methane, the second-most important greenhouse gas after carbon monoxide.

Measurements show that atmospheric methane rose by 55 parts per billion between 2019 and 2023, reaching a record level of 1921 ppb in 2023. The fastest growth occurred in 2021, when methane levels increased by nearly 18 ppb. That jump was 84 percent higher than the increase seen in 2019.

"As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change," said Tian. "Our findings highlight that the Global Methane Pledge must account for climate-driven methane sources alongside anthropogenic controls if its mitigation targets are to be achieved."

Natural and Managed Systems Both Matter

The surge was not limited to natural wetlands. Managed environments such as paddy rice fields and inland waters also contributed significantly. According to Tian, who serves as Director of the Center for Earth System Science and Global Sustainability in the Schiller Institute for Integrated Science and Society, these sources are often underrepresented in global methane models.

The largest increases in emissions were observed in tropical Africa and Southeast Asia. Arctic wetlands and lakes also showed notable growth as warmer temperatures boosted microbial activity. In contrast, methane emissions from South American wetlands dropped in 2023 during an extreme El Niño-related drought. This contrast highlights how sensitive methane release is to climate extremes, the report notes.

How Researchers Tracked the Methane Spike

Tian and his colleagues played a key role in identifying and measuring how wetlands, rivers, lakes, reservoirs, and global paddy rice farming contributed to the rapid rise in atmospheric methane. By linking land, freshwater, and atmospheric processes in advanced Earth system models, the Boston College team showed how climate variability amplified emissions across connected ecosystems.

The study also found that fossil fuel use and wildfires played only a small role in the recent methane increase. Chemical fingerprinting indicates that microbial sources, including wetlands, inland waters, reservoirs, and agriculture, were responsible for most of the observed changes.

"By providing the most up-to-date global methane budget through 2023, this research clarifies why atmospheric methane rose so rapidly," said study lead author Philippe Ciais of the University of Versailles Saint-Quentin-en-Yvelines. "It also shows that future methane trends will depend not only on emission controls, but on climate-driven changes in natural and managed methane sources."

Key Findings From the Study

• This early-2020s methane surge was mainly caused by a weakened atmospheric chemistry sink, not runaway emissions.
• A temporary drop in hydroxyl (OH) radicals -- the atmosphere's primary methane "cleanser" -- during 2020-2021 explains about 80-85 percent of the year-to-year variability in methane concentration growth.
• COVID-19-related air pollution changes played a central role.
• Reductions in nitrogen oxides (NOₓ) during pandemic lockdowns reduced OH levels, allowing methane to accumulate faster in the atmosphere.
• Climate-driven wetland emissions amplified the surge.
• Exceptionally wet conditions during a prolonged La Niña (2020-2023) boosted methane emissions from wetlands and inland waters, especially in tropical Africa and Southeast Asia, with additional increases in Arctic regions.
• Fossil fuel and fire emissions were not the main drivers.
• Changes in fossil fuel and biomass-burning methane emissions were comparatively small and cannot explain the observed global methane spike.
• Current bottom-up emission models for natural flooded ecosystems miss critical dynamics.
• Many widely used models underestimated wetland and inland-water emissions and their dynamics during the surge, highlighting urgent gaps in monitoring flooded ecosystems and microbial methane emission processes.