A study funded by a foundation tied to the pioneer of hydraulic fracturing found methane leaks from drilling and transporting natural gas are greater than U.S. estimates, undercutting the fuel’s climate benefits.
Those emissions, 25 percent to 75 percent higher than the estimate used by the U.S. Environmental Protection Agency, would erase the benefits of using natural gas to power vehicles, said the authors of the study to be published today in the journal Science.
“Atmospheric tests covering the entire country indicate emissions around 50 percent more than EPA estimates,” Adam Brandt, an assistant professor at Stanford University and one of the authors, said in a statement.
The research is funded by a foundation set up by George Mitchell, the engineer who pioneered the use of horizontal drilling and hydraulic fracturing, which has unlocked gas in shale resources. Methane, the main component of natural gas, is 21 times more potent at trapping heat in the atmosphere than carbon dioxide, according to the EPA.
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When it’s burned to produce electricity, natural gas emits about half the carbon dioxide, the main gas linked to global warming, as coal. If too much methane escapes during production and transport, that environmental benefit is diminished or lost.
The 16 scientists involved with the research pulled together separate studies that used towers or airplanes to measure methane in the air. Other studies have examined specific areas such as compressor plants, and measured leaks there.
According to the authors, adding the leaks from each component doesn’t provide the full effect of methane being released. In part, that’s because the EPA doesn’t measure natural emissions of methane, such as from wetlands.
The wider studies show methane emissions at 25 percent to 75 percent greater than the EPA estimate, according to a statement from the Cynthia and George Mitchell Foundation describing the results.
Even with the higher estimates of leaks, natural gas still releases less greenhouse gas than coal when calculated over 100 years, the study concluded.
“While I haven’t seen the study, the industry has led efforts to reduce emissions of methane by developing new technologies and equipment, and these efforts are paying off,” Carlton Carroll, a spokesman for the American Petroleum Institute, said in an e-mail. Other “studies show methane emissions are a fraction of estimates from just a few years ago.”
“Methane is natural gas, so capturing more of it helps companies deliver more energy to consumers,” Carroll added. “This creates a built-in incentive to continue reducing emissions.”
For vehicles, the results are different.
“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,” study author Brandt said.
The EPA found that leakage across the entire gas supply chain fell to 1.6 percent in 2011 from 2.4 percent in 2010. For gas to deliver climate benefits over coal, total leakage must remain below 3.2 percent.
Lowering the rate to 1 percent would provide the same climate benefit over the next 20 years as retiring 10 percent of U.S. coal-fired power plants, according to the Environmental Defense Fund, an advocacy group backing cuts in carbon pollution.
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