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Methane is a greenhouse gas that is comprised of one carbon and four hydrogen atoms. It is often abbreviated by its chemical formula CH4. It is the second most common of the greenhouse gases produced by human activities in the United States [1]

Model of a methane molecule: one carbon atom surrounded by four hydrogen atoms

Sources of Methane

Methane has both natural and human produced sources. Natural sources include wetlands, oceans, and volcanoes. Human produced sources include industry, agriculture, and waste management.

Natural sources

  • Wetlands are one of the largest natural sources of methane. The bacteria that help decompose organic matter in the absence of oxygen also emit methane. [2] As wetlands contain large amounts of densely packed organic matter, they abound with methane emissions as the organic matter decays.
  • Oceanic methane is primarily produced by two different methods. Thermogenic methane is produced by organic material degrading in the earth’s heat deep on the seafloor. Biogenic methane is a waste product of microorganisms that eat organic material. Although the methane produced by these different reactions is chemically identical, they have differing stable isotopes (molecules which vary in the number of neutrons) which allow scientists to track how a methane molecule was produced. [3]
  • Methane emissions from volcanoes are generally lower than other sources. It is one of the gases emitted when volcanoes erupt and therefore can be found in areas with high volcanic activity.

Human Sources

Pie-chart of methane emissions in the United States. Credit: EPA[1]

The primary human sources of methane are industry, agriculture, and waste management.

  • In the United States, industrial processes are the largest source of human produced methane. Of the industrial processes, natural gas and petroleum are the largest contributors to methane emissions. Methane is a primary component of natural gas, but not all methane is captured during the production process. Some of it is released into atmosphere during production, processing, storage, and distribution. Methane is also released near oil wells, because methane is one of the gases that forms alongside petroleum. Therefore, petroleum production, refining, and distribution also release methane into the atmosphere. [4]
  • Agriculture is also a major source of methane emissions. Although not as large as industry in the U.S., agriculture is the largest sources of methane emissions worldwide. Animal husbandry is in fact the specific source of methane emissions. A number of common domesticated animals used in agriculture produce methane as a part of their digestive processes; cattle, sheep, goats, and camels are some the primary contributors of methane emissions in agriculture. The animals’ manure that is held in large storage containers (sometimes referred to as lagoons), is another large source of methane emissions.
  • Animal waste is not the only type of waste product that produces methane. Wastewater treatment and landfills also produce methane and are the third largest source of methane emissions in the U.S. [5]

Environmental Impacts of Methane

Methane is an extremely potent greenhouse gas; it is much more effective at trapping heat than carbon dioxide. Fortunately, it stays in the atmosphere for a much shorter time than carbon dioxide. This means that although methane absorbs more energy and traps more heat than carbon dioxide, its affect will last for a much shorter time. Because of its potency, scientists keep track of methane emissions from all over the world and try to determine the patterns of methane emissions to better understand how they will affect humans. [6]


  1. US EPA, C. C. D. (n.d.). Methane Emissions [Overviews & Factsheets,]. Retrieved July 31, 2015, from
  2. US EPA, C. C. D. (n.d.). Methane Emissions [Overviews & Factsheets,]. Retrieved July 31, 2015, from
  3. US Department of Commerce, N. O. and A. A. (n.d.). LopheliaII 2009: Deepwater Coral Expedition: Reefs, Rigs, and Wrecks. Retrieved July 31, 2015, from
  4. US EPA, C. C. D. (n.d.). Methane Emissions [Overviews & Factsheets,]. Retrieved July 31, 2015, from
  5. US EPA, C. C. D. (n.d.). Methane Emissions [Overviews & Factsheets,]. Retrieved July 31, 2015, from
  6. US EPA, C. C. D. (n.d.). Methane Emissions [Overviews & Factsheets,]. Retrieved July 31, 2015, from

Related Links

Methane Emissions|Environmental Protection Agency