Methane leaks from the US oil and gas industry are 60% greater than official estimates, according to an analysis of previously reported data and new airborne measurements.

Because methane is a potent greenhouse gas, scientists say that the unaccounted-for emissions could have significant impacts on the climate and the country’s economy. The lost gas alone is worth an estimated US$2 billion a year, scientists say.

The analysis ¹ , published on 21 June in Science , is one of the most comprehensive looks yet at methane output from US oil and gas production, and reinforces previous studies that suggested emissions outpaced government estimates. That research prompted the US government to develop regulations that would restrict methane emissions from oil and gas production — rules that US President Donald Trump is now attempting to roll back.

The latest study shows that the US oil and gas supply chain emits about 13 million metric tons of methane, the main component of natural gas, every year. That's much higher than the US Environmental Protection Agency's (EPA's) estimate of about 8 million metric tons.

This discrepancy probably stems from the fact that the EPA’s emissions surveys miss potential sources of methane leaks, such as faulty equipment at oil and gas facilities, says study leader Ramón Alvarez, an atmospheric chemist at the Environmental Defense Fund, a non-profit group in Austin, Texas.

Potent greenhouse gas

Methane warms the planet 80 times as much as CO2 over the first 20 years after it is released. Scientists estimate that the methane in the atmosphere contributes to about 25% of global warming, Alvarez says. “That’s a significant amount.”

If left unchecked, he says, methane emissions from the oil and gas industry could erode the potential climate benefits of using natural gas, which releases far less carbon dioxide and other toxic pollutants than coal when it is burned.

The latest study comes one year after the EPA announced that it would delay the rule that would restrict methane emissions produced by oil and gas drilling operations. The policy, introduced under former president Barack Obama, will not take effect until 2019.

Missing methane

Before 2012, published estimates of the US methane leakage rate ranged from 1% to about 8%, Alvarez says, and the lack of consensus pushed scientists to better characterize those rates in subsequent years. Alvarez and his team pooled data from some of these studies — many of which quantified emissions at individual facilities — and validated the measurements using aircraft surveys. The scientists covered regions that accounted for about 30% of US gas production.

They then extrapolated the figures to estimate methane leaks at the national level. The team concluded that methane emissions in 2015 were about 60% greater than estimates from the EPA’s greenhouse gas inventory: a 2.3% leakage rate compared to the 1.4% estimate from the EPA. “Instead of coming from the well to the pipeline, the gas is escaping through vents or other openings in the system, and it adds up to a lot of emissions,” says Alvarez.

“This is important work,” says Shane Murphy, an atmospheric scientist at the University of Wyoming in Laramie. “They took all these isolated measurements and combined them into something that’s more quantitative.”

The findings reduce the uncertainty around the magnitude of US methane emissions, says Daniel Zimmerle, an energy researcher at Colorado State University in Fort Collins. “I think now it's in the right ballpark,” he says. “But I would be surprised if this would be the final word on the topic.”

Better estimates

Because of methane’s warming potential, a leak rate of 2.3% is concerning, says Robert Howarth, an Earth systems scientist at Cornell University in Ithaca, New York. But he cautions that the study may have underestimated the actual leak rate of methane. Howarth notes that the researchers pulled together a series of measurements that include some obtained with an instrument that — according to the device inventor — produces systematically low numbers ² .

What’s more, Howarth says, the researchers didn’t look at the emissions from gas distribution systems into urban areas, which recent studies suggest are considerable ^{3 , 4 , 5} . Despite the authors’ “optimistic assumptions”, the study “further casts doubt on the wisdom of continuing to use natural gas”, Howarth says.

But Alvarez looks on the bright side. Because a substantial proportion of these leaks is probably due to faulty equipment, he sees a “tremendous opportunity” to reduce methane emissions by developing systems to quickly detect malfunctions at oil and gas facilities and by identifying overlooked ways in which the greenhouse gas escapes into the atmosphere.