A long-term study of a single New Jersey landfill suggests that methane emissions from U.S. landfills may be substantially higher than official government figures show, with implications for how the country tracks one of its most potent greenhouse gases.
The study was conducted by researchers at Columbia University's Lamont-Doherty Earth Observatory, part of the Columbia Climate School. It was published in the journal Environmental Science and Technology.
Methane is a greenhouse gas significantly more powerful than carbon dioxide. One ton of methane carries the warming potential of about 28 tons of carbon dioxide. In 2022, the most recent year for which official U.S. data exist, methane made up roughly 12 percent of the country's total greenhouse gas emissions. Landfills account for an estimated 17 percent of U.S. methane emissions, making them one of the largest single sources.
The U.S. Environmental Protection Agency currently estimates landfill methane emissions using two primary methods. One projects emissions based on a landfill's total waste, adjusted for gas captured on-site. The other extrapolates whole-landfill figures from those gas-capture readings. Both approaches have long been questioned by scientists who use satellites and aircraft to measure actual emissions from above, and those independent measurements have consistently come in higher than EPA estimates.
But satellite and aircraft measurements have their own limitations. Satellites can be blocked by clouds or thrown off by water vapor, which is a particular problem near wetlands where many landfills sit. Both methods also produce only snapshots rather than continuous data. Ground-level sensors, meanwhile, sample only small areas and can miss localized hotspots where methane concentrations are especially high.
"If you take all of the evidence, it's pretty clear that the EPA estimates are too low," said Andrew Hallward-Driemeier, a researcher at Lamont and a Ph.D. candidate in Earth and Environmental Sciences who led the study.
To address the gap, his team developed a method using two and a half years of continuous methane readings collected from a monitoring tower operated by Rutgers University, located near a landfill in East Brunswick, New Jersey. The continuous data allowed the researchers to build year-round emission estimates rather than relying on periodic snapshots.
Their results aligned with emission levels detected by two separate aircraft flying over the same site, lending credibility to the tower-based approach. The agreement between ground and air measurements strengthens the case that the EPA's current calculation methods are undercounting real-world emissions.
"We wanted to come up with a methodology that uses continuous measurements to give year-round estimates of emissions," Hallward-Driemeier said.
The study adds to a growing body of evidence that methane accounting in the U.S. needs revision, particularly for landfills, which are spread across the country and often located near population centers.
