A combination of weakened atmospheric removal and increased emissions from warming wetlands, rivers, lakes, and agricultural land increased atmospheric methane at an unprecedented rate in the early 2020s, an international team of researchers report today in the journal Science.
A sharp decline in hydroxyl radicals – the primary "cleaning agent" that breaks down methane in the atmosphere – during 2020–2021 explains roughly 80 percent of the year-to-year variation in methane accumulation, according to the team, including Boston College Professor of Earth and Environmental Science Hanqin Tian.
At the same time, an extended La Niña period from 2020 to 2023 brought wetter-than-average conditions across much of the tropics, expanding flooded areas and stimulating the production of methane, the second-most important greenhouse gas after carbon monoxide.
Atmospheric methane levels rose by 55 parts per billion between 2019 and 2023, reaching a record 1921 ppb in 2023. The rate of increase peaked in 2021 at nearly 18 ppb, an 84 percent jump compared with 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."
This response extended beyond natural wetlands to include managed systems such as paddy rice fields and inland waters—sources that remain underrepresented in many global methane models, according to Tian, who acts as Director of Center for Earth System Science and Global Sustainability in Schiller Institute for Integrated Science and Society.
The largest emission increases occurred in tropical Africa and Southeast Asia, while Arctic wetlands and lakes also showed significant growth as warming enhanced microbial activity. In contrast, methane emissions from South American wetlands declined in 2023 during an extreme El Niño–related drought, highlighting the sensitivity of methane fluxes to climate extremes, according to the report.
Tian and his team played a central role in identifying and quantifying the contributions of wetlands, rivers, lakes, and reservoirs, and global paddy rice agriculture to this rapid rise in atmospheric methane.
By integrating land, freshwater, and atmospheric processes within advanced Earth system models, the Boston College team helped reveal how climate variability amplified methane emissions across interconnected ecosystems.
Crucially, fossil fuel and wildfire emissions played only a minor role in the recent methane surge. Isotopic evidence confirms that microbial sources – wetlands, rivers, lakes and reservoirs, and agriculture – dominated 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:
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.
