Methane emissions from US urban areas 'widely' underestimated, satellite observations suggest
Parts of the U.S. may be emitting much more of one of the most potent greenhouse gases than previously thought, according to new research.
Satellite observations suggest that methane emissions in urban areas may be "widely underestimated" – up to 80% higher than noted in the U.S. Environmental Protection Agency's Greenhouse Gas Inventory, an annual report that accounts for total greenhouse gas emissions and carbon sinks for all man-made sources in the U.S., according to a paper published Wednesday in Science.
Researchers analyzed satellite images taken by the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel-5P satellite and found that emissions from 12 major urban areas – New York City, Los Angeles, Chicago, Philadelphia, Dallas, Miami, Houston, Washington, D.C., Atlanta, Boston, Detroit and Cincinnati – were emitting up to 80% more methane than reported by the EPA, according to the study.
The finding suggests that urban sources of methane, such as landfills and natural gas infrastructure, play a larger role in near-term climate warming than previously realized, Xiaolin Wang, a postdoctoral researcher in atmospheric science at Harvard University and lead author of the paper, told ABC News.
The EPA is not able to comment on external studies, a spokesperson told ABC News.
Urban areas have complex, population-driven methane sources, including landfills, natural gas distribution systems, wastewater treatment plants and residential combustion, Wang said.
In the U.S., these sources account for one-quarter of total anthropogenic, or human-caused, methane emissions, according to the most recent EPA Greenhouse Gas Inventory, which covers the years 1990-2022.
A colorless, odorless, highly flammable hydrocarbon that is a primary component of natural gas, methane is the second-most abundant anthropogenic greenhouse gas, after carbon dioxide, according to the EPA, and is more than 28 times as potent as carbon dioxide at trapping heat in the atmosphere. Methane sources include "landfills, oil and natural gas systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial processes," according to the EPA.
About 45% of net global warming today is caused by anthropogenic methane emissions, according to the World Resources Institute, which notes that methane is considered a "super pollutant" because of its impact on global warming.
Methane emissions often go underreported, Amy Townsend-Small, a professor of environmental studies at the University of Cincinnati, told ABC News.
A "key reason" for this underreporting is landfill emissions, Wang said, adding that "in many cities, gas collection systems are not capturing as much methane as expected." This is due to wide variances in the efficiency of the gas-collection systems, according to the report.
Additionally, the EPA often relies on industry self-reporting of emissions without any independent verification, Robert Haworth, Atkinson Professor of Ecology & Environmental Biology at Cornell University, told ABC News.
"Methane is incredibly powerful greenhouse gas," Haworth added.
"Measuring urban methane emissions is important because we cannot manage what we cannot accurately quantify," Wang said. "Satellite observations allow us to detect methane from space and consistently quantify emissions across entire urban areas."
Fortunately, methane emissions can be easily mitigated with existing technologies, the experts said. Some cities, such as Los Angeles, are performing "much better" with methane capture due to California's efforts to reduce landfill emissions through enhanced gas collection and control measures, Wang said.
"It's actually possible for these landfills to harvest the methane for good – and they can make money on it" in the form of fuel, Townsend-Small said.
This is not the first time that satellite observations show that official methane emission estimates are "much too low," Daniel Varon, a professor at the Massachusetts Institute of Technology's Department of Aeronautics and Astronautics, told ABC News.
"We've seen that time and time again in the oil and gas sector, for example, and we're seeing it now for landfills," said Varon, who specializes in satellite remote-sensing of atmospheric conditions.
The countries that are the biggest emitters of methane are China, the U.S., Russia, Brazil, Indonesia, Nigeria and Mexico, according to the EPA. These countries are estimated to be responsible for more than half of all human-caused methane emissions.
"By improving how cities track and manage emissions, there is a real opportunity to make meaningful climate progress in the near term," Wang said.
