The amount of methane leaking into the atmosphere from gas and oil operations in the U.S. is far higher than official government estimates, putting at risk the environmental advantages of burning natural gas over coal to make electricity.
A study published in the journal Science last month reports that emissions of the powerful greenhouse gas are roughly 60% greater than what the Environmental Protection Agency thinks they are.
The leaks are equal to 2.3% of gross U.S. gas production, or 13 million metric tons a year. Losses are worth $2 billion annually. That’s enough natural gas to fuel 10 million homes, The New York Times said.
Natural gas, consisting mostly of methane, produces about half the amount of carbon dioxide as coal when it’s burned. Production has boomed in recent years with the rapid growth of hydraulic fracking, making natural gas an attractive substitute for coal. And as utilities have shifted away from coal, emissions have fallen — they’re down by 27% since 2005, The Times said.
When natural gas escapes into the atmosphere, the picture doesn’t look as rosy. Methane has 80 times the global warming potential of carbon dioxide over a 20-year time frame. So, as the leakage rate goes up, the environmental edge that natural gas has enjoyed goes down.
“Natural gas losses are a waste of a limited natural resource (~$2 billion/year), increase global levels of surface ozone pollution, and significantly erode the potential climate benefits of natural gas use,” the authors said. They add that over a 20-year horizon, the climate impact of methane leaks is about the same as carbon dioxide emissions from all U.S. coal plants operating in 2015.
Another study, this one published in the Journal of Industrial Ecology, warns that over a 20-year time frame, power plants using natural gas with a 4% leakage rate have about the same impact on climate as coal plants. If leaks can be kept below 2%, natural gas is still better for the environment than coal.
If there’s some positive news in the Science study, it’s that methane is removed from the atmosphere much faster than carbon dioxide, so emissions can be lowered fairly quickly if sources of the leaks are found and plugged.
Where the leaks come from
Researchers estimate the rate of methane leakage in two ways: with top down (TD) and bottom up (BU) observations. Top-down studies use aircraft, satellites, and tower networks. Bottom-up studies develop estimates by measuring emissions at individual pieces of equipment or facilities, or by taking measurements directly downwind.
“Our BU method and TD measurements yield similar estimates of [methane] emissions in 2015, and both are significantly higher than the corresponding estimate in the U.S. Environmental Protection Agency’s Greenhouse Gas Inventory,” the report says.
The authors said they believe one of the reasons for such a wide discrepancy is that conventional sampling methods “systematically underestimate” the number of equipment malfunctions and leaks. Moving natural gas from production sites to processing plans or transmission pipelines accounts for 20% of total emissions, which are largely overlooked by the EPA.
Emissions could be lowered significantly with the use of well-designed detection and repair systems, the report says. If individual pieces of equipment and whole facilities were operating as designed, emissions would be lower.
The study was a five-year effort led by the Environmental Defense Fund involving more than 140 researchers and 40 institutions, The Times said.
Richard Meyer, managing director of energy analysis for the American Gas Association, said that the new emission estimates amounted to “speculation,” adding, “I have questions about their method and worry that some alternative hypotheses were too readily dismissed.”
An EPA spokesman said in an email, “We are looking forward to reviewing this study.”
Steven Hamburg, the chief scientist with the Environmental Defense Fund, told The Washington Post, “Scientists have uncovered a huge problem, but also an enormous opportunity. Reducing methane emissions from the oil and gas sector is the fastest, most cost-effective way we have to slow the rate of warming today, even as the larger transition to lower-carbon energy continues.”
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