Methane (CH4) is a hydrocarbon and a major component of natural gas. It is a potent greenhouse gas (GHG), so its presence in the atmosphere affects the earth’s temperature and climate system. Methane belongs to a class of so-called “super pollutants” that simultaneously contribute to climate change and degrade the health of people and ecosystems. It 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 accounts for about 30% of total anthropogenic global warming.1 It also is a precursor for tropospheric ozone, a major component of smog that causes widespread respiratory health problems.2
Anthropogenic methane emissions increased more than 40% from 1970 to 2022 at an average annual rate of about 2100 kilotons per year.3 As a result of increased anthropogenic methane emissions, the methane concentration in the atmosphere is now 2.6 times higher than its pre-industrial (1750) level.4
There are three major source categories for anthropogenic methane emissions: agriculture, the fossil fuel supply chain, and waste handling.
Agriculture accounts for about 38% of total anthropogenic methane emissions. Enteric fermentation alone accounts for 28% of emissions. Enteric fermentation is the digestive process in the rumen, a large “fore-stomach” of ruminant animals. Methane is a byproduct of the fermentation process in the rumen that breaks down food into nutrients that the animal can use. The waterlogged conditions in rice paddies are ideal for microorganisms that produce methane as they break down organic matter. The anaerobic decomposition of organic matter in manure is the other major source of methane emissions in agriculture.
The extraction, processing, and transportation of fossil fuels account for about 36% of total anthropogenic methane emissions. Most of these are fugitive emissions, the unintentional release (leaks) of natural gas during extraction, production, storage, and transportation. They originate from storage tanks, compressors, wells, pressure release valves, and other equipment.
About 11% of anthropogenic methane emissions are released in wastewater management through the anaerobic decomposition of organic matter in sewage and industrial wastewater under oxygen-limited conditions.
The top five country emitters by cumulative volume of anthropogenic methane from 1970 to 2022 were China (10.3%), the United States (9.9%), Russia (9.1%), India (8.4%), and Brazil (4.9%). These countries all have large, fossil fuel, agricultural, industrial, and waste management sectors that are heavy methane emitters.
Countries have distinct methane emission profiles. India and Brazil’s emissions are dominated by enteric fermentation because they are the first and second largest holders of cattle in the world, respectively. China holds the third most cattle, but also has a massive coal industry, mining about one-half of the world’s annual coal output. Emissions from those mines are the single largest contributor to China’s total methane emissions.
The large populations of India (1.4 billion people) and Brazil (216 million people) generate enormous quantities of domestic wastewater. Rapid urbanization concentrates wastewater production in cities where sanitation infrastructure is often inadequate or outdated. Untreated wastewater flows into open drains, rivers, or stagnant pools where anaerobic conditions are ideal for methane production.
About 40% of anthropogenic methane emissions in the United States originate from the oil and gas industry, and most of that is in the form of fugitive emissions from the natural gas supply chain. The nearly 80 million cattle in the United States contribute about 24% of the country’s methane emissions, while its 2600 landfills account for another 13%.
The abatement of methane emissions is a priority for climate policy due to the potency of methane as a greenhouse gas and its approximately nine-year lifetime in the atmosphere.5 This means that, of one ton of methane of methane emitted today, about half will be oxidized (gone) from the atmosphere in 9 years. Only 10% of emissions will remain in the atmosphere after 30 years since the initial release, and methane will be almost completely gone after 50 years.6
The large climate benefit from methane mitigation is reflected by the Global Methane Pledge, an international initiative launched at the COP26 climate summit in 2021.7 Over 150 countries have committed to the pledge and agreed to take voluntary actions to contribute to a collective effort to reduce global methane emissions by at least 30 percent from 2020 levels by 2030. The pledge focuses on curbing emissions from key sectors such as energy, agriculture, and waste. Signatories to the pledge commit to good practice inventory methodologies and collaborative technology deployment and knowledge sharing.
Global CH4 emissions from fossil fuel, agriculture and waste increased over the past decade and call into question how effective voluntary pledges will be. The recent trends of anthropogenic methane emissions are not consistent with the Global Methane Pledge commitment of 30% reductions of 2020 levels by 2030.8
1 Smith, C., et al., 2021, “The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity Supplementary Material. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (V. Masson-Delmotte, V. et al. (eds.), available from https://www.ipcc.ch/.
2 J.J. West, A.M. Fiore, L.W. Horowitz, D.L. Mauzerall, 2006, “Global health benefits of mitigating ozone pollution with methane emission controls,” Proc. Natl. Acad. Sci. U.S.A, 103 (11) 3988-3993, https://doi.org/10.1073/pnas.0600201103
3 All emissions data are from this source: Hoesly, Rachel, Steven J Smith, Noah Prime, Hamza Ahsan, Harrison Suchyta, Patrick O’Rourke, Monica Crippa, et al. “CEDS V_2024_07_08 Release Emission Data.” Zenodo, July 24, 2024, Link
4 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.
5 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.
6 Global Carbon Project, “Briefing on key messages for Global Methane Budget 2024,” September 24, 2024, Link
7 Global Methane Pledge, https://www.globalmethanepledge.org/
8 Global Carbon Project, op.cit.