The higher volumes of natural gas leaking from across the industry’s supply chain would be enough to fuel 10 million homes and would be worth an estimated $2 billion, the researchers said.
The study, led by Environmental Defense Fund researchers and including 19 co-authors from 15 institutions, estimated that the leak rate from U.S. oil and gas operations is 2.3 percent, significantly higher than the Environmental Protection Agency’s estimate of 1.4 percent.
While the percentages seem small, methane is a potent greenhouse gas, and the additional emissions would erase the climate advantages of burning natural gas instead of coal during the period when methane’s effects on the climate are most pronounced.
Though half of methane vanishes in 8.3 years, the Environmental Defense Fund says it is still 84 times as powerful as carbon dioxide over 20 years. The EPA uses a broader time frame and says methane’s global warming effect is 28 to 36 times that of carbon dioxide over the course of a century.
“Natural gas losses are a waste of a limited natural resource, increase global levels of surface ozone pollution, and significantly erode the potential climate benefits of natural gas use,” the study’s authors wrote.
They added that, over 20 years, the climate effects of emitting 13 million metric tons of methane annually “roughly equals” the carbon dioxide emissions from all U.S. coal-fired power plants operating in 2015. It would equal about 31 percent of the carbon dioxide emissions from U.S. coal plants over a 100-year time horizon.
“In the short term, the climate impacts of burning coal in a modern plant vs natural gas in a modern plant are similar as a result of the supply chain methane emissions,” Fred Krupp, president of the Environmental Defense Fund, said in an email. But, he added, “over the long term the climate impacts of using gas to generate electricity will be significantly less than those of using coal even with high methane emissions.”
Moreover, he added, “if methane emissions were reduced, which they can be easily, it could deliver significant short term climate benefits as well.”
The study, which relied largely on companies willing to cooperate, cautioned that its estimates could be too low. It said that the worst actors were most likely to opt out of taking part in the study. In addition, the study has not updated measurements of local distribution systems, which could be emitting substantial volumes as well.
The Science study said one possible explanation for the gap between its estimates and the EPA’s is that the federal agency did not adequately count emissions in abnormal conditions. The Science study used an extensive aerial infrared camera survey of about 8,000 production sites in seven U.S. oil and natural gas basins and found that about 4 percent of surveyed sites had one or more observable plumes, with two to seven times the methane emissions from average sites.
The study said the industry could take steps to lower the level of methane emissions. It recommended that companies install less failure-prone systems, carry out on-site leak surveys, re-engineer individual components and processes, and deploy sensors at individual facilities and on towers, aircraft or satellites.
“Scientists have uncovered a huge problem, but also an enormous opportunity,” Defense Fund chief scientist Steven Hamburg, a co-author of the study, said in a statement. “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.”
The study takes an important step in measuring methane leaks, especially from natural operations. In October, the International Energy Agency (IEA) said “methane is a potent greenhouse gas and the uncertainty over the level of methane emitted to the atmosphere raises questions about the extent of the climate benefits that gas can bring.”
It said, “One critical question is the extent to which methane emissions along the gas value chain negate the climate advantages of gas.”
But the IEA also estimated that 40 to 50 percent of current methane emissions could be avoided at no net cost.
“The environmental case for gas does not depend on beating the emissions performance of the most carbon-intensive fuel,” the IEA said, “but in ensuring that its emission intensity is as low as practicable.”