Atmospheric methane has stabilized at 1999 levels, though livestock numbers have been increasing by an average of about 17 million per year, according to UN FAO data. "At this time there is no relationship between increasing ruminant numbers and changes in atmospheric methane concentrations, a break from previously assumed role of ruminants in greenhouse gases."
Methane is an important subcycle of the carbon cycle. Methane (CH4), like carbon dioxide (CO2), is a transparent, odorless gas. Per gram, methane has about 21 times the greenhouse potential of carbon dioxide, but unlike carbon dioxide it breaks down fairly quickly in the atmosphere.
Methane is produced during anaerobic fermentation of plant material. In the carbon cycle, lignin and cellulose are typically broken down by methanogenic bacteria, such as are present in the digestive systems of ruminant herbivores and termites, and which cannot survive in the presence of oxygen.
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