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EPA Estimate Undercounts Methane Emissions: Environmentalists (1)

April 17, 2020, 10:00 AMUpdated: April 17, 2020, 6:52 PM

The EPA’s 2020 inventory of greenhouse gas emissions includes a change that sharply undercounts methane emissions from facilities that gather and send natural gas to processing plants and transmission pipelines, environmental groups claim.

Under the change, the Environmental Protection Agency is using emissions estimates taken from individual pieces of equipment, which walks back an Obama-era way of estimating emissions drawn from an entire gathering station site, said Laura Zachary, associate director of energy and climate consulting firm Apogee Economics and Policy.

The new method may be more detailed but less accurate because it can overlook very large emission sources, said David Lyon, a scientist with the Environmental Defense Fund, an advocacy group that has long been pushing for reductions in methane emissions and has worked with the oil and gas industry to try to achieve them.

And Zachary said that while those large emission sources—"super emitters"—are relatively rare, they account for a large portion of total emissions.

‘Could Be Over-Reporting’

But Richard Hyde, executive director of the natural gas company coalition One Future, said it wasn’t apparent to him that the new method imparts any advantage to the gas industry.

“If you’re a distribution company and you have plastic pipe that you use to deliver to individual houses, EPA has a factor that says that pipe is going to leak X amount, no matter if that pipe leaks or not,” Hyde said. “Typically, plastic pipe like that doesn’t necessarily leak because a lot of it is new. But you have to report it to EPA. So there are cases where you could be over-reporting your emissions.”

Todd Staples, president of the Texas Oil and Gas Association, said oil and gas companies in his state are “participating in multiple initiatives that are committed to finding and implementing additional industry-led solutions to improve environmental performance and address climate concerns.”

Methane is a powerful heat-trapping gas, many times more potent than carbon dioxide, the main driver of climate change. Reducing methane leaks is an important part of efforts to slow the rate of global warming.

Calculation Change

The change in the EPA’s method for calculating emissions from natural gas gathering stations was included as part of its greenhouse gas inventory released this week.

The EPA’s Inventory of U.S. Greenhouse Gas Emissions and Sinks is an annual report that tabulates all the greenhouse gases emitted from all man-made sources in the nation. The agency submits it to the United Nations under the U.N. Framework Convention on Climate Change.

An EPA spokeswoman said the agency has made “improvements to specific emission calculations in the natural gas systems category,” as it has in previous years. The new tweaks include improved activity data and emission factors, based on a thorough review of the literature and stakeholder input, she said.

To illustrate the difference between the two approaches, Zachary said the old method reported 2.2 million metric tons of methane emissions from gathering stations in 2017, versus 1.3 million under the method the EPA is now using.

Other factors could be at play behind the sharp drop in reported emissions, such as improvements in gathering technology. But the Environmental Defense Fund’s Lyon said he doubted those effects would be as significant as the numbers reflect, and that any real-world change was actually very minor.

The new method “assumes things are working right and can badly miss the big emissions events when things go wrong,” added Ben Ratner, a senior director at the Environmental Defense Fund. Methane is the primary component of natural gas, and EDF maintains the oil and gas industry is the largest source of human-caused methane emissions.

EPA Responds

The EPA spokeswoman said the agency routinely assesses new studies for data that could inform inventory updates. It also conducts a “multiphase process including expert review and stakeholder engagement during inventory development, and public review” of its inventory.

The study upon which EPA’s new method is based also has proved effective at catching large methane emitters, according to the spokeswoman. For example, it found that 50% or more of emissions come from the largest 5% of emitters, she said.

The agency spokeswoman further said the new method uses onsite measurements taken from 180 gathering stations, compared with 114 in the previous data source.

Lyon countered that the onsite measurement approach only counts emissions from individual pieces of equipment, and often underestimates total methane releases by excluding emissions from sources that are overlooked or can’t be accurately quantified due to safety or technical limitations.

Anthony Marchese, associate dean at Colorado State University’s Walter Scott Jr. School of Engineering, principal investigator on the study that formed the basis for the old method, and co-principal investigator on the study that underpinned the new method, said the EPA’s new approach yields a lower emissions estimate partly because it draws on a higher proportion of small gathering stations that emit at an overall lower rate.

He also said the new method could miss “episodic emissions or other unmeasured emissions that would have been captured” if site-level measurements were also made. But those effects are likely to be small, Marchese said, because his team made careful, real-world measurements that fed into the new formula the EPA is using.

Lyon agreed that the study team has extensive experience and isn’t likely to overlook emissions that occurred while they were onsite, but questioned if enough measurements were made to fully account for episodic emissions. He also called on the EPA to compare data between the two methods to determine the size of the disparity.

Aaron Padilla, manager of climate and environmental, social, and governance policy at the American Petroleum Institute, said only that API “supports accurate data on greenhouse gas emissions, including methane, from all emitting sectors.” He also said that in recent years methane emissions relative to production have declined.

(Adds detail about Marchese's involvement in 19th paragraph; corrects number of gathering stations in 17th paragraph.)

To contact the reporter on this story: Stephen Lee in Washington at

To contact the editors responsible for this story: Gregory Henderson at; Renee Schoof at