Explaining a global methane spike
A combination of weakened 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 in the journal Science.
A sharp decline in hydroxyl radicals鈥攖he primary 鈥渃leaning agent鈥� that breaks down methane in the atmosphere鈥攄uring 2020鈥�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 Sciences Hanqin Tian.
At the same time, an extended La Ni帽a 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.
AV研究所 Professor of Earth and Environmental Sciences Hanqin Tian (Lee Pellegrini)
Atmospheric methane levels rose by 55 parts per billion between 2019 and 2023, reaching a record 1921 ppb in 2023, according to the researchers. The rate of increase peaked in 2021 at nearly 18 ppb, an 84 percent jump compared with 2019.
鈥淎s the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change,鈥� said Tian. 鈥淥ur 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.鈥�
This response extended beyond natural wetlands to include managed systems such as paddy rice fields and inland waters鈥攕ources that remain underrepresented in many global methane models, according to Tian, who directs the Center for Earth System Science and Global Sustainability in the 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 Ni帽o鈥搑elated drought, highlighting the sensitivity of methane fluxes to climate extremes, according to the report.
Tian and his team, including Senior Research Associate Naiqing Pan and Xing Yu, 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鈥攚etlands, rivers, lakes and reservoirs, and agriculture鈥攄ominated the observed changes.
鈥淏y providing the most up-to-date global methane budget through 2023, this research clarifies why atmospheric methane rose so rapidly,鈥� said study lead author Philippe Ciais of the University of Versailles Saint-Quentin-en-Yvelines. 鈥淚t also shows that future methane trends will depend not only on emission controls, but on climate-driven changes in natural and managed methane sources.鈥�
Key findings:聽
- This early-2020s methane surge was mainly caused by a weakened atmospheric chemistry sink, not runaway emissions.
- A temporary drop in hydroxyl (OH) radicals鈥攖he atmosphere鈥檚 primary methane 鈥渃leanser鈥濃�攄uring 2020鈥�2021 explains about 80鈥�85 percent of the year-to-year variability in methane concentration growth.
- COVID-19鈥搑elated air pollution changes played a central role.
- Reductions in nitrogen oxides (NO鈧�) 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 Ni帽a (2020鈥�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.