Coal recently was eclipsed by natural gas as the nation's top source of energy for electrical power generation. That might seem like a good development, because gas has a reputation as a cleaner fuel that contributes about half as much carbon dioxide to the atmosphere when it's burned as coal does.
But that benefit could be illusory, if even only a small amount of the gas - less than 5 percent of what is removed from the Earth - leaks into the atmosphere while it's being used to produce electricity, according to a newly-published study by University of Colorado, Denver researchers in the journal Climatic Change.
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The problem is that between 70 and 90 percent of natural gas is methane. The latter is 25 times more potent than carbon dioxide as a greenhouse gas emission, according to the U.S. Environmental Protection Agency, though a 2013 study found that it had 34 times the effect of CO2.
The researchers calculated that over a 20 year period, it only takes a leakage rate of 3.9 percent to render natural gas as damaging as coal when it comes to climate change. Over 100 years, the margin does increase to 9.1 percent.
"This study is important because it shows that controlling natural gas leakage is crucial at every step of the supply chain, from drilling to residential distribution," one of the study's authors, associate professor of civil engineering David Mays, said in a press release.
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It seems likely that the threshold set in the study is being exceeded. A 2012 air-sampling study by another UC Denver scientist, Gabrielle Pétron, found that natural-gas drillers in an area known as the Denver-Julesburg Basin were losing about 4 percent of their gas to the atmosphere, even before it's transported through pipelines to electrical power plants.
Here's an EPA database that shows how much methane is being emitted from various facilities across the nation.