This photograph of a natural gas flare was taken in North Dakota. Image courtesy Wikimedia.
A study published Feb. 14 indicates that the nation’s principal air quality regulator is not accurately measuring methane emissions and that conversion of motor vehicles to natural gas and away from diesel fuel is likely to worsen human-caused climate change.
Methane is a greenhouse gas that is far more effective at heat-trapping than is carbon dioxide. According to a website maintained by the U.S. Environmental Protection Agency, “pound for pound, the comparative impact of CH4 on climate change is over 20 times greater than CO2 over a 100-year period.”
That may be an under-estimate. A 2009 paper found that methane has at least 30 times the heat-trapping capability of CO2.
Its prevalence in the atmosphere is now approximately two-and-one-half times what it was during the pre-industrial stage of human history, according to the National Oceanic & Atmospheric Administration, although much less than it was during the first billion or so years of the planet’s existence.
“There does appear to be more methane at the national level than we expect to find,” Adam Brandt, an assistant professor of energy resources engineering at Stanford University and the lead author of this month’s paper, said.
Brandt found that atmospheric emissions of the powerful greenhouse gas are 25-75 percent higher than the U.S. Environmental Protection Agency estimates.
He explained that scientists are not sure of exactly how much of the country’s methane emissions are attributable to the natural gas industry, but that some of it is likely to come from drilling wells, pipelines, and other facilities used to extract and deliver to market a rapidly growing source of energy in the United States.
The cause of the industry’s methane leak problem can be traced to about 50 flawed components of the natural gas production system. This month’s study concluded that about 60 percent of methane leaks can be traced to those flaws.
“The real challenge is, this is a big infrastructure,” Brandt said. “The wells are dispersed across the countryside. There are a lot of pipes, a lot of joints. You’ve got a lot of territory to cover.”
Leaks happen for a variety of reasons. Equipment can be defective, for example, and even when it is operating correctly natural gas that is under pressure can easily escape through hard-to-detect gaps and punctures.
“Anytime you have high pressure gas in a system, it’s going to want to escape,” Brandt said. “It will escape in any hole or crack.”
Some methane is intentionally discharged to the atmosphere.
“There’s a lot of safety equipment, pressure release valves and such, that emit gas when something goes awry,” Brandt explained. “You prevent massive damage and loss of human life by venting gas.”
The problem of unintentional leaks poses financial and logistical challenges to operators. Because the industry’s infrastructure is spread out over a large area, and because leaks can come from very small and hard-to-detect flaws in it, the process of tracking them down and repairing them is expensive.
“These old fashioned ways of finding the leaks, they are labor intensive,” Brandt said. “They want to find them, but it takes lots of time, equipment.”
Human sources of methane account for about 60 percent of total worldwide emissions and the natural gas industry is not the only source of methane pollution of the atmosphere. Livestock, for example, is a major emitter, as are landfills.
Brandt said that his study did not focus on either of these possible avenues of methane pollution.
The paper’s conclusion that EPA may have underestimated the discharge of methane occurring in the United States is consistent with several other recent studies.
One, published last fall in the Proceedings of the National Academy of Sciences, found that total methane emissions in the U.S. were about 50 percent higher than EPA determined during 2007-2008.
Two others that examined local methane emissions in Texas and Utah also concluded that EPA may be inaccurately measuring them.
One commonly advocated mechanism for lowering greenhouse gas pollution is the introduction of natural-gas fueled vehicles. But even as the conversion of petroleum fuels in the vehicles to natural gas can reduce their greenhouse gas emissions by about 30 percent, the production of that natural gas leads to more methane emissions.
“Fueling trucks and buses with natural gas may help local air quality and reduce oil imports, but it is not likely to reduce greenhouse gas emissions,” Brandt said. “Even running passenger cars on natural gas instead of gasoline is probably on the borderline in terms of climate.”
The new study is a synthesis of more than 200 earlier investigations of methane pollution.
Titled “Methane Leakage from North American Natural Gas Systems,” it appears in the Feb. 14 issue of Science.
Graphic courtesy National Oceanic & Atmospheric Administration.