More on gassy cattle (and sheep)

"Bloat is caused by the slime of starch-fermenting bacteria that entraps fermentation gases. If cattle cannot burp and expel the gas, the rumen can compress the lungs and the animal suffocates."

"You cannot stop a sheep belching or farting, but you can make sure its eructations are less damaging to the environment.
Belches and, to a far lesser degree, farts from sheep, cows and other farm animals account for around 20% of global methane emissions. The gas is a potent source of global warming because, volume for volume, it traps 23 times as much heat as the more plentiful carbon dioxide."

So, if cows and sheep account for 20% of the methane problem, ...

More on gassy cattle (and sheep)

"Bloat is caused by the slime of starch-fermenting bacteria that entraps fermentation gases. If cattle cannot burp and expel the gas, the rumen can compress the lungs and the animal suffocates."

"You cannot stop a sheep belching or farting, but you can make sure its eructations are less damaging to the environment.
Belches and, to a far lesser degree, farts from sheep, cows and other farm animals account for around 20% of global methane emissions. The gas is a potent source of global warming because, volume for volume, it traps 23 times as much heat as the more plentiful carbon dioxide."

So, if cows and sheep account for 20% of the methane problem, how much do you think humans are contributing via burps and farts?

Where does methane come from?

Methane is emitted from a variety of both human-related (anthropogenic) and natural sources. Human-related activities include fossil fuel production, animal husbandry (enteric fermentation in livestock and manure management), rice cultivation, biomass burning, and waste management. These activities release significant quantities of methane to the atmosphere. It is estimated that 60% of global methane emissions are related to human-related activities (IPCC, 2001c). Natural sources of methane include wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies, non-wetland soils, and other sources such as wildfires.

Methane emission levels from a sour...

Where does methane come from?

Methane is emitted from a variety of both human-related (anthropogenic) and natural sources. Human-related activities include fossil fuel production, animal husbandry (enteric fermentation in livestock and manure management), rice cultivation, biomass burning, and waste management. These activities release significant quantities of methane to the atmosphere. It is estimated that 60% of global methane emissions are related to human-related activities (IPCC, 2001c). Natural sources of methane include wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies, non-wetland soils, and other sources such as wildfires.

Methane emission levels from a source can vary significantly from one country or region to another, depending on many factors such as climate, industrial and agricultural production characteristics, energy types and usage, and waste management practices. For example, temperature and moisture have a significant effect on the anaerobic digestion process, which is one of the key biological processes that cause methane emissions in both human-related and natural sources. Also, the implementation of technologies to capture and utilize methane from sources such as landfills, coal mines, and manure management systems affects the emission levels from these sources.

Emission inventories are prepared to determine the contribution from different sources. The following sections present information from inventories of U.S. man-made sources and natural sources of methane globally. For information on international methane emissions from man-made sources, visit the International Analyses Web site.
Human-related Sources

In the United States, the largest methane emissions come from the decomposition of wastes in landfills, ruminant digestion and manure management associated with domestic livestock, natural gas and oil systems, and coal mining. Table 1 shows the level of emissions from individual sources for the years 1990 and 199

Table 1 U.S. Methane Emissions by Source (TgCO2 Equivalents)
Source Category 1990 1997 1998 1999 2000 2001 2002 2003
Landfills 172.2 147.4 138.5 134.0 130.7 126.2 126.8 131.2
Natural Gas Systems 128.3 133.6 131.8 127.4 132.1 131.8 130.6 125.9
Enteric Fermentation 117.9 118.3 116.7 116.8 115.6 114.5 114.6 115.0
Coal Mining 81.9 62.6 62.8 58.9 56.2 55.6 52.4 53.8
Manure Management 31.2 36.4 38.8 38.8 38.1 38.9 39.3 39.1
Wastewater Treatment 24.8 31.7 32.6 33.6 34.3 34.7 35.8 36.8
Petroleum Systems 20.0 18.8 18.5 17.8 17.6 17.4 17.1 17.1
Rice Cultivation 7.1 7.5 7.9 8.3 7.5 7.6 6.8 6.9
Stationary Sources 7.8 7.4 6.9 7.1...

Table 1 U.S. Methane Emissions by Source (TgCO2 Equivalents)
Source Category 1990 1997 1998 1999 2000 2001 2002 2003
Landfills 172.2 147.4 138.5 134.0 130.7 126.2 126.8 131.2
Natural Gas Systems 128.3 133.6 131.8 127.4 132.1 131.8 130.6 125.9
Enteric Fermentation 117.9 118.3 116.7 116.8 115.6 114.5 114.6 115.0
Coal Mining 81.9 62.6 62.8 58.9 56.2 55.6 52.4 53.8
Manure Management 31.2 36.4 38.8 38.8 38.1 38.9 39.3 39.1
Wastewater Treatment 24.8 31.7 32.6 33.6 34.3 34.7 35.8 36.8
Petroleum Systems 20.0 18.8 18.5 17.8 17.6 17.4 17.1 17.1
Rice Cultivation 7.1 7.5 7.9 8.3 7.5 7.6 6.8 6.9
Stationary Sources 7.8 7.4 6.9 7.1 7.3 6.7 6.4 6.7
Abandoned Coal Mines 6.1 8.1 7.2 7.3 7.7 6.9 6.4 6.4
Mobile Sources 4.8 4.0 3.9 3.6 3.4 3.1 2.9 2.7
Petrochemical Production 1.2 1.6 1.7 1.7 1.7 1.4 1.5 1.5
Iron and Steel 1.3 1.3 1.2 1.2 1.2 1.1 1.0 1.0
Agricultural Residue Burning 0.7 0.8 0.8 0.8 0.8 0.8 0.7 0.8
Total for U.S. 605.3 579.5 569.3 557.3 554.2 546.7 542.3 544.9

Source: US Emissions Inventory 2005: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2003