Recent studies have revealed that a significant factor contributing to the rise in atmospheric methane levels was a notable decrease in hydroxyl radicals, the key chemicals responsible for decomposing methane in the atmosphere. The years 2020-2021 saw a dramatic slowdown in this atmospheric cleansing process. Researchers, including Hanqin Tian, a Professor of Earth and Environmental Science at Boston College, noted that this decline accounts for approximately 80 percent of the annual variations in methane accumulation rates.
Wet Conditions Boosted Methane Emissions
Simultaneously, an extended La Niña phase from 2020 to 2023 resulted in wetter-than-normal conditions across vast regions of the tropics. These wet conditions expanded flooded areas, creating ideal habitats for microbes that generate methane. Consequently, emissions surged from wetlands, rivers, lakes, and agricultural lands, contributing to the increase of methane, the second most significant greenhouse gas following carbon dioxide.
Data indicates that atmospheric methane rose by 55 parts per billion from 2019 to 2023, reaching an unprecedented level of 1921 ppb in 2023. The most rapid increase occurred in 2021, with methane levels rising nearly 18 ppb, an increase 84 percent higher than that recorded in 2019.
"As global temperatures rise and conditions become wetter, emissions from wetlands, inland waters, and rice paddies will increasingly influence short-term climate change," stated Tian. "Our research emphasizes that the Global Methane Pledge must consider climate-driven methane sources in addition to anthropogenic factors to meet its mitigation goals."
Importance of Both Natural and Managed Environments
The increase in emissions was not confined to natural wetlands; managed systems like rice paddies and inland waters also played a crucial role. Tian, who directs the Center for Earth System Science and Global Sustainability at the Schiller Institute for Integrated Science and Society, remarked that these sources are frequently overlooked in global methane assessments.
The most significant emission increases were noted in tropical Africa and Southeast Asia, while Arctic wetlands and lakes also experienced notable growth due to warmer temperatures enhancing microbial activity. In contrast, methane emissions from South American wetlands decreased in 2023 amid severe drought conditions related to an extreme El Niño, highlighting the sensitivity of methane release to climate variability.
Research Methodology for Tracking Methane Levels
Tian and his team were instrumental in identifying and quantifying the contributions of wetlands, rivers, lakes, reservoirs, and global rice farming to the rapid rise in atmospheric methane. By integrating land, freshwater, and atmospheric processes within advanced Earth system models, the Boston College researchers illustrated how climate variability intensified emissions across interconnected ecosystems.
The findings also indicated that fossil fuel usage and wildfires had a minimal impact on the recent increase in methane levels. Chemical analysis revealed that microbial sources, particularly from wetlands, inland waters, reservoirs, and agriculture, were primarily responsible for the changes observed.
"By providing an updated global methane budget through 2023, this research clarifies the reasons behind the rapid rise in atmospheric methane," explained Philippe Ciais, the lead author from the University of Versailles Saint-Quentin-en-Yvelines. "It also demonstrates that future trends in methane will depend not only on emission controls but also on climate-induced changes in both natural and managed methane sources."
Key Insights from the Research
- The early 2020s surge in methane was primarily due to a weakened atmospheric chemistry sink rather than excessive emissions.
- A temporary decline in hydroxyl (OH) radicals, the atmosphere's main methane "cleanser," during 2020-2021 accounts for about 80-85 percent of the yearly variability in methane concentration growth.
- Changes in air pollution due to COVID-19 were significant.
- Reduced nitrogen oxides (NOₓ) during lockdowns lowered OH levels, facilitating faster methane accumulation.
- Climate-driven emissions from wetlands exacerbated the surge.
- Exceptional wet conditions during the prolonged La Niña (2020-2023) intensified methane emissions from wetlands and inland waters, especially in tropical regions and the Arctic.
- Fossil fuel and fire emissions were not the primary contributors.
- Variations in methane emissions from fossil fuels and biomass burning were relatively minor and could not explain the global methane spike.
- Current bottom-up emission models for natural flooded ecosystems overlook critical dynamics.
- Many prevalent models underestimated emissions from wetlands and inland waters during the surge, highlighting urgent monitoring gaps in flooded ecosystems and microbial methane emissions.