METHANE
Methane is 21 times more powerful a greenhouse gas than CO2 and is responsible for nearly as much global warming as all other non-CO2 greenhouse gases put together. It has many sources, and lots of potential to cause major damage.
Methane is a clear, odourless gas produced when organic matter decays. It's also produced naturally by farm animals. Humans produce methane in our agricultural and industrial processes. It even comes out of our food waste. Methane has staying power. Each molecule of methane gas hangs in the atmosphere for about twelve years before eventually breaking up.
ANIMAL AGRICULTURE
Animal agriculture produces more than 100 million tons of methane a year.1 Methane production is on the rise, as meat consumption has risen. About 85% of methane from animal agriculture is produced in the digestive processes of livestock.2 Another 15% of animal agricultural methane emissions are released from the large stores of untreated farm animal waste.3
FARMING
Rice paddies are the number-one source of human-produced methane, producing up to 25% of global methane emissions. The warm, waterlogged soil of rice paddies encourages methanogenesis—which happens when a single-celled organism produces both methane and carbon dioxide.4 It's slightly problematic that rice is one of the world's key food staples.
BIOGENIC METHANE
Biogenic methane comes from organic materials as they decompose in oxygen-free environments.5 For example, when you tied up that plastic bag of dog poop. The largest sources are wetlands, livestock, and landfills. Formation of methane in this manner usually takes place close to the surface of the earth, and the methane produced is usually lost into the atmosphere.
FOSSIL FUEL PRODUCTION
When organic material decomposes below the earth's surface, methane often becomes trapped underground in small gaps in the rocks. Mining in these areas allows the methane to escape, and if it's not collected it seeps into the atmosphere. Underground coal seams inevitably contain significant amounts of methane. In some cases it is possible to collect this from the mine and burn it as a fuel; however, in other mines the ventilation system expels it to the atmosphere.
1 Source: www.earthsave.org/globalwarming
2 Source: Ibid.
3 Source: Ibid.
4 Source: http://toxics.usgs.gov/definitions/methanogenesis.html
5 Source: http://www.guardian.co/uk/climatechange/storu0,12374,1684378,00.html