From Ecopedia

Overview

Discovered by Alessandro Volta during 1776-1778, methane (CH4) is a commonly occurring chemical compound on earth. Methane, the main constituent of natural gas (87% by volume), is the second major greenhouse gas after carbon dioxide (CO2).^[1]

Methane is found in abundance in the earth’s atmosphere. With a half-life of only 7 years, methane gets eventually oxidized in the atmosphere to produce CO2 and water.

Artificial production of methane is widely undertaken to serve various fuel needs of humans. Man made sources of methane include extraction and transportation of natural gas, agriculture, coal mining and waste disposal among others.

Environmental Impacts

Anthropogenic activities over the past two centuries caused methane to be released in large quantities into the atmosphere, leading to the environmentally disastrous global warming phenomenon. Methane possesses a global warming potential of 25 when compared to carbon dioxide over a period of hundred years. However, methane gas is approximately twenty times much stronger as a greenhouse gas compared to the carbon dioxide gas. ^[2]

Methane’s release by rice paddies, marshland and also by termites and various ruminant animals such as sheep and cattle led to alarming increase in the levels of atmospheric methane.

Anaerobic plant and animal decomposition, a major source of toxic methane emissions, cause methane to be trapped inside the earth’s crust, which finds release during fossil fuel mining activities.

Some major sources of methane emissions include landfills, live stock farming, fossil fuel production, wet rice cultivation, animal wastes, pipeline leakage, sewage disposal, offshore oil as well as coal mining activities.

The excess accumulation of methane in landfills, especially, poses a potentially potent explosion hazard. Old landfill sites, which don not properly ventilate methane, release large amounts of toxic methane gas in to the atmosphere causing dire environmental hazards such as the greenhouse effect.

Methane, however, being a volatile organic compound (VOC), exhibits negligible photochemical reactivity and so contributes little to the formation of environmentally-harmful photochemical smogs. ^[3]

References

1. ↑ http://en.wikipedia.org/wiki/Methane
2. ↑ http://en.wikipedia.org/wiki/Methane
3. ↑ http://www.environment-agency.gov.uk/business/topics/pollution/185.aspx