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Greenhouse Gas Report: Methane

written by: Edna •edited by: Niki Fears•updated: 11/25/2008

Methane gas is produced naturally in the environment and also through human-related activities.

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    What is methane?

    Methane is a simple alkane, made of one carbon and four hydrogens. It is the main component of natural gas and can be highly combustible if not handled properly. At room temperature, methane is a colorless, odorless gas that is non-toxic in small quantities.

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    Human-related sources of methane

    • About 60% of all global methane emissions are due to human-related activities. Landfills are the largest source of methane in the U.S. and account for 34% of all methane emissions. Methane is generated in landfills and open dumps as waste decomposes under anaerobic conditions.
    • Methane is produced during flooded rice cultivation by the anaerobic (without oxygen) decomposition of organic matter in the soil.
    • Domesticated livestock --cattle, buffalo, sheep, goats, and camels -- produce significant amounts of methane as part of their normal digestive processes. Large amounts of methane are produced in manure lagoons and holding tanks. Manure deposited on pastures or in a dry form, produces very small amounts of methane.
    • Wastewater and sludge from municipal sewage and industrial sources are treated to remove soluble organic matter, suspended solids, pathogenic organisms and chemical contaminants. If the components in the wastewater are processed anaerobically, they produce methane emissions.

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    Natural sources of methane

    • Natural sources of methane are determined by environmental variables such as temperature and precipitation. Wetlands are responsible for approximately 76% of global methane emissions. Wetlands provide an anaerobic habitat for bacteria that produce methane when they break down organic material.
    • Termites account for approximately 11% of the global methane emissions from natural sources. Methane is produced in termites as part of their normal digestive process, and the amount varies among different termite species.
    • Oceans are estimated to be responsible for about 8% of the global methane emissions.Two sources include anaerobic digestion in marine zooplankton and fish, and methanogenisis in sediments and drainage areas along coastal regions.
    • Methane hydrates account for approximately 5% of methane emissions.Hydrates are solid deposits made of water molecules that contain molecules of methane. The solids are found underground in polar regions and in ocean sediments of the outer continental margin throughout the world.
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    How does methane effect the environment?

    Several greenhouse gases are responsible for global warming. Carbon dioxide, also called CO2, is responsible for the most warming. Other contributors include methane, CH4, released from landfills and agriculture, nitrous oxide from fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that would otherwise store CO2.

    Greenhouse gases have different heat-trapping abilities; some trap more heat than CO2. Methane remains in the atomsphere for 9-15 years and is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO2) over a 100-year period. Nitrous oxide is 300 times more powerful than CO2. Other gases, such as chlorofluorocarbons have heat-trapping potential thousands of times greater than CO2. But because their concentrations are much lower than CO2, none of them add as much warmth to the atmosphere as CO2 does.