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Causes of the Greenhouse Gas Methane

Methane is a simple chemical compound made up of one carbon atom and four hydrogen atoms. It is a colorless, odorless gas at room temperature. Methane is a significant greenhouse gas. A greenhouse gas is one which, when released into the atmosphere, absorbs some of the thermal energy radiating from the Earth's surface and transmits that heat back to the Earth and lower atmosphere. Because of this effect, greenhouse gases raise the overall temperature of the Earth and contribute to the problem of global warming. Methane contributes up to about 10 percent of the total greenhouse effect on Earth. There are natural sources of methane emissions, but human activities account for at least half of all methane released into the atmosphere.

Natural Sources
- Approximately half of all methane emissions come from natural sources, unrelated to human activities. Of these, by far the largest contributors are wetlands such as marshes, where bacteria decompose organic material under oxygen-free conditions. These microbes, known as anaerobic bacteria, release methane during the decomposition process. Methane is also produced in much smaller quantities by termites, as part of their natural digestion process, as well as by natural processes occurring in bodies of water such as oceans and rivers. Underground deposits of chemicals known as methane hydrates produce small amounts of methane as they decompose, as do other geological structures, such as mud volcanoes. Finally, wildfires and wild animals also contribute some methane.
Human Sources: Waste
- Decomposition of wastes in landfills accounts for about one quarter of human-generated methane. This occurs because landfills and garbage dumps create ideal conditions for the growth of anaerobic bacteria.
Human Sources: Livestock
- Livestock such as cattle digest their food through a process known as enteric fermentation. This creates a large amount of methane gas inside the animal's digestive system which is exhaled or released as flatulence. As well, manure from livestock held under anaerobic conditions in tanks or ponds also decomposes to release methane. Together, these two sources account for the largest single source of "man-made" methane releases.
Human Sources: Energy
- Natural gas is mostly methane, and the processing of natural gas results in significant releases, making this the third largest human source. Other energy related sources are coal mining, petroleum production and burning of fuels.
Human Sources: Other
- A few other human sources of methane produce significant quantities each year. Treatment of wastewater produces methane as waste sludges decompose via anaerobic bacteria. Flooding of fields for rice cultivation also produces methane from decomposition of organic material in soils. Relatively small amounts of methane also result from burning of crop stubble during agriculture and from the production of iron and steel.

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