Excuse me! The problem with methane gas

Glossary

accelerator mass spectrometry (AMS). A highly sensitive technique that is used to measure the relative amount of different ions (and often isotopes) in a sample. Accelerated ions are separated by their mass to charge ratio. AMS can be used as a form of carbon dating. By measuring the different isotopes of carbon in a sample, the age of the sample can be determined.

carbon dating. A method of measuring the age of an object that contains carbon. Since living things stop taking up carbon when they die, and carbon-14 decays with a half life of 5,700 years, the amount of carbon-14 remaining in the sample can be used to determine its age.

clathrate. A compound that is formed by the trapping of molecules inside a substance rather than by forming chemical bonds between the two substances. Methane clathrates (also called methane hydrates) consist of methane molecules trapped inside a ‘cage’ of ice crystals. Methane hydrates form under conditions of low temperature and high pressure in deep oceanic sediments, where methane is produced by anaerobic microorganisms.

enteric fermentation. Fermentation that occurs in the digestive system of ruminants such as sheep and cattle. As microbes in the ruminant gut break down food, methane is released. This methane is then released into the atmosphere by the animal, mostly through exhaling or burping.

global warming potential. The global warming strength of one kilogram of a greenhouse gas relative to one kilogram of carbon dioxide over a chosen time period. Global warming potential takes into account the variation in the time that different gases remain in the atmosphere and the ability to absorb radiation.

megatonne (Mt). A megatonne is one million (1,000,000 or 106) tonnes.

methane hydrate. (also called methane clathrate). A substance in which methane is trapped inside a ‘cage’ of ice crystals. Methane hydrates form under conditions of low temperature and high pressure in deep oceanic sediments, where methane is produced by anaerobic microorganisms.

methanogens. Anaerobic microorganisms that use simple organic compounds for energy, producing methane as a by-product. They occur in a range of anaerobic environments including the digestive systems of animals (particularly ruminants and termites) as well as in wetlands, marine sediments and hot springs.

methanotrophs. Microorganisms that use methane for carbon and energy (and so remove methane from the environment). Methanotrophs occur in both aerobic and anaerobic conditions. They are mostly found in soils but also occur in a range of environments associated with methane such as landfill, marshes, rice paddies and the ocean.

permafrost. Permanently frozen ground, as occurs in the polar regions.

ruminant. An animal which chews regurgitated food (cud) and usually has a stomach divided into four compartments, one of which is the rumen. Partially digested food is returned from the stomach to the mouth and chewed, allowing further digestion. Ruminants include cows, sheep, goats and deer. Their digestive system allows them to digest fibrous plant material which would be indigestible to other animals.

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Posted November 2009, edited August 2012.