Overview of Greenhouse Gases
|Lifetime in Atmosphere||12 years|
|Global Warming Potential (100-year)||21|
Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2011, 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 CO2over a 100-year period.
Globally, over 60% of total CH4 emissions come from human activities.  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 CH4as 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 Changepage and the Greenhouse Gas Indicators page in the Science section.
Emissions and Trends
Methane (CH4) emissions in the United States decreased by 8% between 1990 and 2011. 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.
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.
|Emissions Source||How Emissions Can be Reduced|
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.
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,
end quote from: