Methane is a potent greenhouse gas that has about 30 times the impact on global warming per unit mass compared to carbon dioxide over a 100-year lifetime (83 times larger over 20 years). Methane is responsible for 0.5°C of today’s warming representing ~30% of total human-caused warming.1
The concentration of atmospheric methane reached 1922 parts per billion (yearly average) in 2023. This is an increase by a factor of 2.6 compared to the pre-industrial level (722 parts per billion) and the highest value in at least 800,000 years.2
Methane concentrations increased continuously throughout most of the 20th century, primarily driven by anthropogenic industrialization. The rate of increase slowed in the 1990s, and in the early 2000s concentrations appeared to plateau. But beginning in 2007 methane concentrations rose sharply. The highest rate of change in the 40-year observational record occurred between 2020 and 2023.3 Rising methane concentrations oppose any effort to mitigate climate change.
Scientists turn to assessments such as the global methane budget to guide their investigation of the sources for the rise in concentrations.4 Anthropogenic sources include fugitive methane emissions from fossil fuel supply chains, enteric fermentation by ruminants, landfills, rice cultivation, wastewater handling, and manure management. Natural sources include wetlands and inland water systems, termites, oceans, fire, and geologic sources.
The latest global methane budget introduced a new category for ‘indirect anthropogenic emissions,’ which includes elevated methane emissions from human-made reservoirs, nutrient-enriched water bodies such as ponds and lakes, and wetlands experiencing warming due to climate change
Scientists have offered several explanations for the recent rapid increase, including rising anthropogenic emissions from agriculture, landfills, and biomass burning; changes to the atmospheric sink for methane; and increasing emissions from natural sources such as wetlands.5
Wetlands and inland waters are critical ecosystems that significantly influence climate dynamics. These environments serve as substantial carbon sinks, storing large quantities of organic carbon, while also acting as major natural sources of methane. There are strong feedbacks between climate change (via temperature and precipitation) and wetland carbon sequestration and methane emission.
There is an increasing amount of evidence that wetlands are driving part of the recent increase in methane concentrations. This evidence is based on a combination of satellite retrievals of greenhouse gases, global earth system models, and the analysis of different isotopes of carbon present in atmospheric methane. The most common stable isotopes of carbon are ¹²C and ¹³C. Methane-producing organisms (methanogens) thrive in the low-oxygen conditions of wetland soils and other anaerobic environments such as ruminant (livestock) stomachs and manure lagoons. Methanogens preferentially use ¹²C during metabolism. As a result, biogenic methane from wetlands has less ¹³C compared to the so-called fossil methane that is released in the coal, oil, and natural gas supply chains.
The recent rising atmospheric methane concentrations have coincided with an abrupt shift in the stable isotopic signature of methane (δ¹³C-CH4) towards lighter values. This signals a relative shift in the sources of that methane towards biogenic sources such wetlands. Other “biogenic” sources such as cows and rice also carry a similar isotopic signature, and some researchers point to a combination of these sources contributing to the atmospheric rise.
Evidence suggests that tropical wetlands are an important contributor to the recent increase in methane concentrations. Events associated with the El Niño Southern Oscillation (ENSO) cycle produced dramatic shifts in precipitation in the Amazon, Africa, and Asian pantropics that inundated wetlands.6 When wetlands flood, water saturates the soil, depleting available oxygen and creating more anaerobic (oxygen-free) conditions. Elevated inundation paired with higher temperatures, enhances microbial activity, further accelerating methane emissions. Thus, increased inundation and warming-driven microbial processes are intensifying tropical wetland methane emissions.
Current measurements that point to a wetland source are also supported by paleoclimate records. Methane extracted from air bubbles in ice cores and sedimentary data reveals substantial past variability in methane concentrations and isotopic signatures. Evidence points to tropical wetlands as dominant contributors to methane feedbacks during past global warming events, such as glacial/interglacial transitions.7
Methane production increases with rising global temperatures.8 Warmer conditions directly enhance methanogen metabolism in wetland soils, accelerating methane generation. In high-latitude wetlands and permafrost regions, longer thaw seasons extend the annual period of methane emissions. Additionally, rising temperatures melt permafrost, exposing ancient organic carbon that has been locked away for thousands of years. This process fuels microbial decomposition, expands wetland areas, and releases methane into the atmosphere.
We need a much deeper understanding of the role of wetlands in climate change. Estimates of global wetland and inland water emissions represent the largest source of uncertainty in the global methane budget.9 Furthermore, many of the Earth System Models used by the IPCC either omit or inadequately include amplified wetland and permafrost carbon emissions, thus resulting in future temperature trajectories that are artificially low. The response of wetland methane emissions to rising climate change remains poorly understood and is a very active area of research. While emissions are expected to increase, substantial uncertainty persists regarding the timing and magnitude of amplified natural emissions.10
Our understanding of mitigation opportunities for wetland and inland water methane emissions is in its infancy. The obvious and most effective approach to reduce wetland and inland water methane emissions is to lower global temperatures through greenhouse gas mitigation strategies. A range of additional measures need further investigation, including tidal restoration, reduced nutrient loading, the addition of amendments to water bodies, flood management, removal of defunct dams and water bodies, vegetation management, and reduced conversion of certain wetlands to grazing areas.
Danielle Potocek is a Natural Systems Scientist at Spark Climate Solutions. The authors thank Ben Poulter for valuable feedback on this article.
1 International Energy Agency, “Global Methane Tracker 2022,” https://www.iea.org/reports/global-methane-tracker-2022/methane-and-climate-change; McCabe, David and Sarah Smith, “IPCC’s Assessment Report highlights the urgency of sharp reductions in methane,” August 11, 2021, Clean Air task Force, https://www.catf.us/2021/08/ipccs-new-assessment-report-highlights-the-urgency-of-sharp-reductions-in-methane/
2 Jackson, R. B., M. Saunois, A. Martinez, J. G. Canadell, X. Yu, M. Li, B. Poulter, et al. “Human Activities Now Fuel Two-Thirds of Global Methane Emissions.” Environmental Research Letters 19, no. 10 (September 2024): 101002. https://doi.org/10.1088/1748-9326/ad6463.
3 NOAA Global Monitoring Laboratory, “Trends in CH4,” accessed December 11, 2024, https://gml.noaa.gov/ccgg/trends_ch4/
4 Saunois, M., et al., “Global Methane Budget 2000–2020,” (2024) Earth Syst. Sci. Data Discuss. [preprint], https://essd.copernicus.org/preprints/essd-2024-115/
5 Nisbet, Euan G., Martin R. Manning, Ed J. Dlugokencky, Sylvia Englund Michel, Xin Lan, Thomas Röckmann, Hugo A. C. Denier van der Gon, et al. “Atmospheric Methane: Comparison Between Methane’s Record in 2006–2022 and During Glacial Terminations.” Global Biogeochemical Cycles 37, no. 8 (2023): e2023GB007875. https://doi.org/10.1029/2023GB007875.
6 Lin, Xin, Shushi Peng, Philippe Ciais, Didier Hauglustaine, Xin Lan, Gang Liu, Michel Ramonet, et al. “Recent Methane Surges Reveal Heightened Emissions from Tropical Inundated Areas.” Nature Communications 15, no. 1 (December 30, 2024): 10894. https://doi.org/10.1038/s41467-024-55266-y ; Qu, Zhen, Daniel J. Jacob, A. Anthony Bloom, John R. Worden, Robert J. Parker, and Hartmut Boesch.“Inverse Modeling of 2010–2022 Satellite Observations Shows That Inundation of the Wet Tropics Drove the 2020–2022 Methane Surge.” Proceedings of the National Academy of Sciences 121, no. 40 (October 2024): e2402730121. https://doi.org/10.1073/pnas.2402730121.
7 Hopcroft, Peter O., Paul J. Valdes, Fiona M. O’Connor, Jed O. Kaplan, and David J. Beerling. “Understanding the Glacial Methane Cycle.” Nature Communications 8, no. 1 (February 21, 2017): 14383. https://doi.org/10.1038/ncomms14383; Kleinen, Thomas, Sergey Gromov, Benedikt Steil, and Victor Brovkin. “Atmospheric Methane since the Last Glacial Maximum Was Driven by Wetland Sources.” Climate of the Past 19, no. 5 (June 1, 2023): 1081–99. https://doi.org/10.5194/cp-19-1081-2023.
8 Zhang, Zhen, Benjamin Poulter, Joe R. Melton, William J. Riley, George H. Allen, David J. Beerling, Philippe Bousquet, et al. “Ensemble Estimates of Global Wetland Methane Emissions over 2000–2020.” Biogeosciences 22, no. 1 (January 15, 2025): 305–21. https://doi.org/10.5194/bg-22-305-2025; Zhang, Zhen, Benjamin Poulter, Andrew F. Feldman, Qing Ying, Philippe Ciais, Shushi Peng, and Xin Li. “Recent Intensification of Wetland Methane Feedback.” Nature Climate Change 13, no. 5 (May 2023): 430–33. https://doi.org/10.1038/s41558-023-01629-0.
9 Saunois et al., op cit.
10 Rosentreter, Judith A., Alberto V. Borges, Bridget R. Deemer, Meredith A. Holgerson, Shaoda Liu, Chunlin Song, John Melack, et al. “Half of Global Methane Emissions Come from Highly Variable Aquatic Ecosystem Sources.” Nature Geoscience 14, no. 4 (April 2021): 225–30. https://doi.org/10.1038/s41561-021-00715-2.