BC Scientists Uncover Methane Surge in Early 2020s: A Climate Concern
A recent study by an international team of researchers, published in the journal Science, reveals a concerning trend in atmospheric methane levels. The findings indicate that a combination of weakened atmospheric removal and increased emissions from warming wetlands, rivers, lakes, and agricultural land led to an unprecedented surge in atmospheric methane during the early 2020s.
The research, led by Boston College Professor Hanqin Tian, highlights a sharp decline in hydroxyl radicals, the primary 'cleaning agent' responsible for breaking down methane in the atmosphere, during 2020-2021. This decline accounted for approximately 80% of the year-to-year variation in methane accumulation. Additionally, an extended La Niña period from 2020 to 2023 brought wetter-than-average conditions across the tropics, further contributing to the rise in methane levels.
Atmospheric methane levels rose by 55 parts per billion between 2019 and 2023, reaching a record high of 1921 parts per billion in 2023. The rate of increase peaked in 2021, with a nearly 18 parts per billion jump compared to 2019, an 84% increase.
Professor Tian emphasizes the significance of climate-driven methane sources, stating, 'As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change.' The study also highlights the need to consider managed systems, such as paddy rice fields and inland waters, which have been underrepresented in global methane models.
The largest emission increases were observed in tropical Africa and Southeast Asia, while Arctic wetlands and lakes showed significant growth due to enhanced microbial activity. In contrast, methane emissions from South American wetlands declined in 2023 during an extreme El Niño-related drought, underscoring the sensitivity of methane fluxes to climate extremes.
The Boston College team, including Professor Tian, played a pivotal role in identifying and quantifying the contributions of wetlands, rivers, lakes, reservoirs, and global paddy rice agriculture to the rapid rise in atmospheric methane. By integrating land, freshwater, and atmospheric processes within advanced Earth system models, they revealed how climate variability amplified methane emissions across interconnected ecosystems.
Crucially, the study confirms that fossil fuel and wildfire emissions played a minor role in the recent methane surge. Isotopic evidence indicates that microbial sources, including wetlands, rivers, lakes, reservoirs, and agriculture, dominated the observed changes.
The research provides a comprehensive global methane budget through 2023, clarifying the reasons behind the rapid rise in atmospheric methane. It also emphasizes that future methane trends will depend not only on emission controls but also on climate-driven changes in natural and managed methane sources.
Key findings include:
- The methane surge was primarily caused by a weakened atmospheric chemistry sink, not runaway emissions.
- A temporary drop in hydroxyl (OH) radicals during 2020-2021 explained approximately 80-85% of the year-to-year variability in methane concentration growth.
- COVID-19-related air pollution changes played a significant role.
- Reductions in nitrogen oxides (NOₓ) during pandemic lockdowns reduced OH levels, allowing methane to accumulate faster.
- Climate-driven wetland emissions amplified the surge.
- Wet conditions during the prolonged La Niña period (2020-2023) boosted methane emissions from wetlands and inland waters, particularly in tropical regions.
- Fossil fuel and wildfire emissions were not the main drivers.
- Changes in fossil fuel and biomass-burning methane emissions were minor and could not explain the observed global spike.
- Current emission models for natural flooded ecosystems require improvement to capture critical dynamics.
- Many widely used models underestimated wetland and inland-water emissions during the surge, highlighting the need for urgent improvements in monitoring and understanding these ecosystems and microbial methane emission processes.
