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Climate Change

Overview of Greenhouse Gases

Methane Emissions

photo of methane molecule
Properties of Methane
Chemical Formula CH4
Lifetime in Atmosphere 12 years
Global Warming Potential (100-year) 21
U.S. Methane Emissions, By Source
Pie chart of U.S. methane emissions by source. 29 percent is from natural gas and petroleum systems, 25 percent is from enteric fermentation, 18 percent is from landfills, 10 percent is from coal mining, 9 percent is from manure management, and 9 percent is from other sources.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012.

Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2012, CH4 accounted for about 9% of all U.S. greenhouse gas emissions from human activities. Methane is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and the raising of livestock. Natural processes in soil and chemical reactions in the atmosphere help remove CH4 from the atmosphere. Methane's lifetime in the atmosphere is much shorter than carbon dioxide (CO2), but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period.

Globally, over 60% of total CH4 emissions come from human activities. [1] Methane is emitted from industry, agriculture, and waste management activities, described below.

  • Industry. Natural gas and petroleum systems are the largest source of CH4 emissions from industry in the United States. Methane is the primary component of natural gas. Some CH4 is emitted to the atmosphere during the production, processing, storage, transmission, and distribution of natural gas. Because gas is often found alongside petroleum, the production, refinement, transportation, and storage of crude oil is also a source of CH4 emissions. For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks sections on Natural Gas Systems and Petroleum Systems.
  • Agriculture. Domestic livestock such as cattle, buffalo, sheep, goats, and camels produce large amounts of CH4 as part of their normal digestive process. Also, when animals' manure is stored or managed in lagoons or holding tanks, CH4 is produced. Because humans raise these animals for food, the emissions are considered human-related. Globally, the Agriculture sector is the primary source of CH4 emissions. For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks Agriculture chapter.
  • Waste from Homes and Businesses. Methane is generated in landfills as waste decomposes and in the treatment of wastewater. Landfills are the third largest source of CH4 emissions in the United States. For more information see the U.S. Inventory's Waste chapter.

Methane is also emitted from a number of natural sources. Wetlands are the largest source, emitting CH4 from bacteria that decompose organic materials in the absence of oxygen. Smaller sources include termites, oceans, sediments, volcanoes, and wildfires.

To find out more about the role of CH4 in warming the atmosphere, and its sources, visit the Causes of Climate Change page and the Greenhouse Gas Indicators page in the Science section.

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Methane (CH4) emissions in the United States decreased by almost 11% between 1990 and 2012. During this time period, emissions increased from sources associated with agricultural activities, while emissions decreased from sources associated with the exploration and production of natural gas and petroleum products.

U.S. Methane Emissions, 1990-2012
Line graph that shows U.S. methane emissions from 1990 to 2012. The methane emissions hover between 550 and 650 million metric tons of carbon dioxide equivalents from 1990 to 2012 with a slight dip from 1996 to 2004. In 2004, the U.S. methane emissions were just below 600 million metric tons of carbon dioxide equivalents, followed by a slight uptick in 2007 and 2008 and a decrease in 2011 and 2012 back below 600 million metric tons of carbon dioxide equivalents.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012.

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Reducing Methane Emissions

There are a number of ways to reduce methane (CH4) emissions. EPA has a series of voluntary programs for reducing CH4 emissions. Some examples are discussed below.

Examples of Reduction Opportunities for Methane
Emissions Source How Emissions Can be Reduced

Industry

Upgrading the equipment used to produce, store, and transport oil and gas can reduce many of the leaks that contribute to CH4 emissions. Methane from coal mines can also be captured and used for energy. Learn more about the EPA's Natural Gas STAR Program and Coalbed Methane Outreach Program.

Agriculture

Methane can be reduced and captured by altering manure management strategies at livestock operations or animal feeding practices. Learn more about these strategies and EPA's AgSTAR Program.

Waste from Homes and Businesses

Because CH4 emissions from landfill gas are a major source of CH4 emissions in the United States, emission controls that capture landfill CH4 are an effective reduction strategy. Learn more about these opportunities and the EPA's Landfill Methane Outreach Program.

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References

1. EPA (2010). Methane and Nitrous Oxide Emissions from Natural Sources . U.S. Environmental Protection Agency, Washington, DC, USA.

2. U.S. Department of State (2007). Projected Greenhouse Gas Emissions. In: Fourth Climate Action Report to the UN Framework Convention on Climate Change . U.S. Department of State, Washington, DC, USA.

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