More Than Half of U.S. Landfills May Be Methane ‘Super-Emitters,’ Study Finds

Aerial observations of hundreds of large landfills across 18 states found they are leaking 40 percent more methane than is reported to the EPA

An aerial image of a landfill with a heat map showing methane emissions
Methane plumes observed at a Louisiana landfill during the study. More than 14 percent of U.S. methane emissions were reported to have come from landfills in 2021. Arizona State University

Landfills in the United States are larger sources of methane than previously thought—according to a new study, more than half of these facilities are methane “super-emitters,” releasing more than 100 kilograms of the potent greenhouse gas each hour.

Researchers used aircraft to conduct a survey of methane emissions from hundreds of large landfills across the country. They found that on average, emission rates were 1.4 times higher than what has been recorded in the Environmental Protection Agency’s Greenhouse Gas Reporting Program, according to a statement from Arizona State University (ASU), a collaborator in the research.

The findings demonstrate that climate change mitigation policies need to include improved monitoring of landfill emissions, the researchers wrote last week in the journal Science.

“Airborne data such as these verify what we’ve been seeing on the ground for decades,” Rob Jackson, an environmental scientist at Stanford University who did not contribute to the findings, tells CNN’s Rachel Ramirez.

In 2018, Americans sent around 146.1 million tons of waste to landfills, according to the EPA. As organic material in landfills decomposes, it releases gas, and around half of that is methane.

A powerful greenhouse gas, methane traps 80 times as much heat as carbon dioxide does in a 20-year period. It’s also hazardous to breathe—exposure to methane causes an estimated one million premature deaths each year, according to the United Nations Environment Program. But compared to carbon dioxide, methane is shorter-lived in the atmosphere—so cutting methane emissions can provide a quicker way to slow climate change.

“Addressing these high emission sources and mitigating persistent landfill sources offers a strong potential for climate benefit,” study lead author Dan Cusworth, a climate scientist with the nonprofit Carbon Mapper, says in the statement. “The ability to precisely identify leaks is an efficient way to make quick progress on methane reduction at landfills, which could be critical for slowing global warming.”

view out an airplane window
A view from the aircraft during an aerial survey of methane emissions from U.S. landfills. Arizona State University

An estimated 50 to 65 percent of global methane emissions come from human activities, per the EPA. And landfill emissions are the third-largest source of human-generated methane in the U.S., accounting for more than 14 percent of this pollution in 2021.

But Cusworth tells Business Insider’s Catherine Boudreau that these estimates are based on computer models rather than observations. Facilities are required to perform surveys on the ground four times per year, but Cusworth tells Grist’s Sachi Kitajima Mulkey that such surveys aren’t as frequent or precise as they need to be.

“Those types of measurements really are not designed to do anything in terms of emissions,” and are just for detecting methane “hotspots,” Cusworth says to CNN.

For the new study, the researchers made observations across 18 states from two aircraft, measuring methane leaks using imaging spectrometers. Between 2016 and 2022, they studied 20 percent of the country’s approximately 1,200 total open landfills. The effort was the most comprehensive study to-date of point sources of methane emissions from the waste sector, the authors write.

dark-colored airplane flying low with a building in the background
One of the two aircraft that used Earth-mapping technology to measure emissions in the study. Arizona State University

They found that 52 percent of the sites had significant, or “super-emitting,” point source emissions of methane, and when they returned weeks and months later, they found emissions persisting at many landfills. Plumes continued for months or years at 60 percent of emitting sites, per the statement.

The researchers also found plenty of hotspots leaking more than the Clean Air Act’s limit of 500 parts per million, per Grist.

Overall, the emissions detected in the study far outweighed those reported to the EPA—exceeding reported levels by 40 percent on average.

The findings point to the need for more comprehensive monitoring of emissions, per the statement. Remote sensing from satellites, aircraft and drones can better measure emissions from landfills. And recent innovations in methane valve caps and leak sensors can help reduce emissions at their source, writes Grist.

“In the waste sector, specifically, we know what technologies to implement—we’ve known for a number of years. They’re feasible, readily available, and a number of them are actually quite cost effective,” Kait Siegel, who is the waste sector manager for the methane pollution team at the Clean Air Task Force and was not involved in the study, tells Grist. “We need to have regulations in place.”

The Environmental Defense Fund launched a satellite on March 4 to measure methane emissions from the oil and gas sector. Carbon Mapper is also working with the NASA Jet Propulsion Laboratory to launch additional satellites that will track carbon dioxide and methane from oil and gas sites and landfills, per Business Insider.

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