Methane released by coal mining
Coal mining accounts for about 10 percent of US releases of methane (CH4), a potent global warming gas. It is the fourth largest source of methane, following landfills, natural gas systems, and enteric fermentation.
Coal mining releases methane in four ways:
- Underground Mining: In the United States, methane from underground mining operations is typically vented. In some other countries it is also flared.
- Surface Mining: During surface mining, methane is released directly to the atmosphere.
- Post-Mining Activities: Some methane remains in the coal after mining and is released during subsequent processing and transportation.
- Abandoned Mines: Methane emissions from abandoned mines are not quantified and included in U.S. inventory estimates, but may be significant.
Methane plays a significant role in the dynamics of global warming due to the following factors:
- Methane is a relatively potent greenhouse gas with a high global warming potential 72 times that of carbon dioxide (averaged over 20 years) or 25 times that of carbon dioxide (averaged over 100 years), according to the IPCC's Third Assessment Report. (Note that the global warming potential of methane was estimated at 21 times that of carbon dioxide, averaged over 100 years, in the IPCC Second Assessment Report, and the 21 figure is currently used for regulatory purposes in the United States.) Methane in the atmosphere is eventually oxidized, producing carbon dioxide and water. This breakdown accounts for the decline in the global warming potential of methane over longer periods of time.
- CH4 concentrations have more than doubled over the last 150 years.
- According to calculations reported in 2005, methane emissions may account for a third of the climate warming from greenhouse gases between the 1750s and the present, twice the level of previous estimates.
- An average molecule of CH4 lasts around eight to nine years before it gets oxidized into carbon dioxide (CO2) and water (H2O).
Amount of methane released by coal mining
A study by the National Renewable Energy Laboratory estimated that surface mining releases 1.91 grams of methane per kilogram of surface mined coal. The same study estimated that mining releases 4.23 grams of methane per kilogram of underground-mined coal.
As of June 2010, no national limits exist on air pollution from coal mines. On June 17, 2010, in a petition presented to Environmental Protection Agency Administrator Lisa Jackson, a coalition of environmental groups called for new controls over coal mine air pollution. The petition states that coal mines should be held to the Clean Air Act standards in force for gravel mines, coal-fired power plants, coal processing plants, and other sources. The petition also calls on Jackson to adopt strict limits on other dangerous air pollutants released from coal mines, including methane, as well as particulate matter, nitrogen oxide gases, and volatile organic compounds — all toxic air pollutants under the Clean Air Act.
On June 29, 2010, it was announced that underground coal mines, industrial wastewater-treatment systems, and industrial-waste landfills will have to disclose details about methane emissions under a rule finalized by U.S. environmental regulators. The emitters will begin collecting emissions data on Jan. 1, 2011 under the regulation, with the first annual reports due to the U.S. Environmental Protection Agency on March 31, 2012. According to the EPA, the regulation will give the EPA a more global picture of the emissions of methane, which is the primary greenhouse gas emitted by underground coal mines, industrial-size landfills, and wastewater-treatment systems. Underground coal mines will have to track quarterly methane emissions from each ventilation well or shaft, or each centralized monitoring point, among other data. Industrial-waste landfills will have to track annual methane generation and emissions.
The EPA said in May 2013 that mandatory U.S. budget cuts did not leave it with the resources to determine if methane pollution is a significant risk, a necessary step for regulation, and that the coal mines category represents only about 1 percent of total greenhouse gas emissions, according to EPA data.
Related SourceWatch articles
- Coalbed methane
- Marcellus Shale
- The methane time-bomb
- Natural gas as an alternative to coal
- Natural gas transmission leakage rates
- West Virginia and coal
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