Where do Methane emissions come from?

Methane Emissions report - December 2005

Methane emissions from coal mining, natural gas systems, and landfills represented more than three-fifths of all U.S. methane emissions.


Landfills - #1
Methane emissions from waste management accounted for 31 percent of U.S. anthropogenic methane emissions in 2004. Emissions from this source have fallen by 27 percent from their 1990 level. Landfills represent 92 percent of the methane emissions from waste management in 2004, and they are the largest single source of U.S. anthropogenic methane emissions. Methane emissions from landfills include emissions from both municipal solid waste landfills and industrial landfills. Estimated methane emissions from industrial landfills represent 7 percent of emissions from municipal solid waste landfills.

Due to increased levels of waste disposed in landfills, estimated methane emissions from landfills rose 2.5 percent in 2004, above the 2003 level but still 29 percent below the 1990 level. The dramatic decrease in methane emissions since 1990 is directly attributable to an increase in methane captured at landfills that otherwise would have been emitted to the atmosphere. methane believed to be captured from this source in 2004. In 2004, methane recovery for energy increasingly took the form of direct use of medium-Btu gas in industrial boilers. The acceleration of this practice was driven by higher natural gas prices, which made landfill gas more competitive.

Coal Mines
Methane emissions from coal mines dropped by 30 percent between 1990 and 2004. This decline resulted partly from the increased capture and use of methane from coal mine degasification systems and a shift in production away from some of the Nation’s gassiest underground mines in Central Appalachia.

Mobile Combustion (automobiles, etc)
Mobile combustion in 2004 were up by 0.7 percent from the 2003 level but 22 percent lower than the 1990 level. Methane emissions from passenger cars have declined since 1990 as older vehicles with catalytic converters that are less efficient at destroying methane have been taken off the road. Estimates of methane emissions from mobile sources have been revised downward in the last two annual editions of this report, reflecting a change in the source of data for vehicle miles traveled and a related adjustment in the emission factors for light-duty trucks.

Natural Gas Systems
2004 estimated methane emissions from natural gas systems were down by 0.3 percent from those emitted in 2003.

Petroleum Systems
Methane emissions from petroleum systems dropped from 29.9 MMTCO2e in 1990 to 23.2 MMTCO2e in 2004. Methane emissions from petroleum systems in 2004 are nearly unchanged from their 2003 level and down by 22 percent from their 1990 level.

Stationary Combustion
U.S. methane emissions from stationary combustion in 2004 were down by 6.3 percent from their 2003 level.

Waste generation
Natural gas systems, such as miles of gas transmission and distribution pipeline.

Domestic and Commercial Wastewater Treatment
With the U.S. population growing slowly, methane emissions from domestic and commercial wastewater treatment are estimated to have grown by nearly 1.0 percent between 2003 and 2004 — about 18 percent above the 1990 level. Methane emissions from domestic and commercial wastewater treatment are a function of the share of organic matter in the wastewater stream and the conditions under which it decomposes. Wastewater may be treated aerobically or anaerobically. Because aerobic decomposition does not yield methane, whereas anaerobic decomposition does, the method of treatment is a critical determinant of emissions; however, there is little information available on wastewater treatment methods. Data on flaring or energy recovery from methane generated by wastewater are also sparse. EIA believes that emissions from this source are relatively small, representing less than 3 percent of all U.S. methane emissions in 2004.

Agricultural Sources
Estimated methane emissions from agricultural sources represent 28.5 percent of total U.S. anthropogenic methane emissions. Agricultural methane emissions increased by less than 1 percent from 2003 to 2004, as a small decrease in emissions from enteric fermentation was offset by increases in emissions from animal waste management, rice cultivation, and crop residue burning.

Enteric Fermentation in Domesticated Animals
In 2004, estimated methane emissions from enteric fermentation in domesticated animals declined by 0.8 percent. Because 95 percent of all emissions from enteric fermentation is attributable to cattle, trends in emissions correlate with trends in cattle populations. Between 2003 and 2004, cattle populations were nearly constant, with small declines in all population categories offset somewhat by increases in populations of beef cattle on feedlots. Estimated methane emissions from enteric fermentation in 2004 are 3.7 percent below their 1990 level.

Solid Waste of Domesticated Animals
Estimated methane emissions from the solid waste of domesticated animals increased from 2003 to 2004. The increase reinforced a larger trend over the past decade: in 2004, emissions from the solid waste of domesticated animals were increased 26 percent. Between 1990 and 2004, there was a shift in livestock management to larger facilities, which are believed to be more likely to manage waste using liquid systems that tend to promote methane generation.

Rice Cultivation
Estimated methane emissions from U.S. rice cultivation increased to 12-percent in the number of acres harvested. All U.S. rice-producing States saw increases in acres harvested during 2004, and total methane emissions from rice cultivation in 2004 were 18 percent higher than in 1990.

Burning of Crop Residues
Crop residue burning, the smallest contributor to U.S. methane emissions, represents less than 1 percent of total U.S. methane emissions. Estimated 2004 methane emissions from the burning of crop residues were up by 12 percent from 2003 and 27 percent above their 1990 level. The increase from 2003 to 2004 is attributable mainly to large increases in corn and soybean production.

Chemical Production
The preliminary estimate of methane emissions from U.S. chemical production in 2004 is up by 6 percent from the 2003 level. Methane emissions from chemical production in 2004 were 25 percent above their 1990 level. The increase is attributable to increased production of carbon black, ethylene, and styrene, which more than offset a drop in methanol production.

Iron and Steel Production
With production of pig iron rebounding from a 2-decade low in 2003, methane emissions from iron and steel production rose to an estimated 2.2-percent from 2003 but still 23 percent below their 1990 level.

SOURCE: Energy Information Administration,
Official Energy Statistics from the US government
http://www.eia.doe.gov/oiaf/1605/ggrpt/methane.html