Highlights
- Methane emissions associated with natural gas were equivalent to about 1.7% of the methane delivered through the system.
- That loss amounts to nearly $300 million worth of natural gas purchased, but unused, each year.
- Reducing methane emissions offers a significant near-term opportunity for climate mitigation
GeorgeLouis / English WikipediaMethane emissions from the New York City metropolitan area are largely driven by natural gas use, according to
a new study published today in
Atmospheric Chemistry and Physics by researchers at the
Lamont-Doherty Earth Observatory, part of the Columbia Climate School. The findings may offer cities an overlooked pathway for reduce methane emissions while potentially saving consumers millions of dollars lost to wasted natural gas.The researchers estimate that methane emissions associated with natural gas were approximately 1.7% of all gas delivered through the system. These emissions represent a substantial amount of fuel NYC consumers are paying for but not fully using, equivalent to nearly $300 million of natural gas, based on 2023 and 2024 retail prices.Methane is a powerful greenhouse gas, with more than 80 times the global warming potential of carbon dioxide over a 20-year timescale. Because methane remains in the atmosphere for only about a decade, cutting its emissions may be a quick way to slow near-term global warming.This chart shows monthly natural gas delivered in 2023 and 2024 to New York City and northeastern New Jersey (horizontal axis) against measured natural gas methane emissions (vertical axis). Red diamonds represent heating months and orange diamonds represent cooling months. The dotted line indicates a steady 1.7% natural gas loss rate throughout the seasons.“This study shifts the focus from underground pipeline leaks as a source of methane emissions to how natural gas is used in buildings, particularly how efficiently appliances burn it,” said lead author
Yuwei Zhao, a PhD student in Columbia’s Department of Earth and Environmental Sciences.
A new picture of New York City’s methane emissionsThe study provides the first monthly analysis tracking methane emissions before and after natural gas reaches customers in the NYC metropolitan area. The researchers’ methods enabled them to distinguish between natural gas released without combustion—either from leaks in underground utility pipes or from building appliances—and inefficiently burned gas from heating and cooling systems.To track those emissions, the researchers analyzed two years of hourly methane observations from the Mineola Tower, a National Institute of Standards and Technology monitoring site on Long Island. The tower is positioned to sample air flowing out of Manhattan and western Long Island during westerly winds. The study team used data from January 2023 through December 2024 to capture seasonal patterns.Zhao and her colleagues also conducted intensive measurement campaigns at the tower in summer 2023 and winter 2024, measuring methane, ethane and carbon monoxide at high frequency. This allowed them to chemically identify and separate raw natural gas leaks from the incomplete combustion occurring in buildings.The measurements revealed a distinct seasonal cycle: methane emissions peaked during the winter heating season, declined through spring and rose again during the summer cooling season, before increasing further during the following heating season. Natural gas accounted for 99% of total methane emissions in February and 98% in May, and 85% to 88% during the summer cooling months.“We expected winter heating to dominate methane emissions, but the summertime signal showed us that we need to be tracking these emissions year-round,” said co-author
Róisín Commane, Associate Professor in Columbia’s Department of Earth and Environmental Sciences and a researcher at the Lamont-Doherty Earth Observatory. Some large buildings use natural gas-powered cooling systems, which may help explain why methane emissions rose again during the summer months.While the researchers detected methane from wetlands, wastewater treatment plants and landfills, these biogenic sources played a minor role in the region. Among the methane traced to natural gas, incomplete combustion was the dominant signal detected at the Mineola Tower in both the heating and cooling seasons. The researchers identified incomplete combustion by looking for a correlation between methane and carbon monoxide, which is produced when natural gas does not burn completely. By contrast, natural gas leaks that occur before the gas reaches customers would not have a combustion signature. Only 6% of the identified natural gas plumes in winter and 7% in summer showed no combustion signature, indicating that pipeline leaks were detected less frequently at the tower than methane associated with incomplete combustion.Scatter plots compare methane (y-axis) with incomplete combustion intensity (x-axis) over 5-minute windows. The purple dots represent natural gas plumes. Most of these plumes show strong signals of incomplete combustion that closely track increases in methane. This close relationship helped the study team identify inefficient natural gas combustion as the source of much of the observed methane, rather than leaks from utility pipes.Methane emissions also closely tracked real-time natural gas deliveries across the study area, further supporting the conclusion that emissions were driven mainly by natural gas use after it reaches customers.
Rethinking urban methane emissionsThe findings may help explain why methane emissions estimated from observations in the New York metropolitan area have exceeded national and global inventory estimates. Previous studies estimated two to five times more methane emissions in the area than those inventories accounted for. Despite efforts to fix pipeline leaks, methane emissions in cities have remained higher than expected, suggesting that important sources were being overlooked. The authors say inefficient use of natural gas, including incomplete combustion, accounts for much of the missing methane and should be incorporated into future calculations.The findings also have implications for a warming climate. Rising temperatures and more frequent and intense extreme weather are expected to increase demand for both heating and cooling. Without a transition to cleaner energy sources, greater use of natural gas to meet that demand could lead to higher methane emissions in urban areas. Reducing these emissions could offer a significant near-term opportunity for climate mitigation.The study was coauthored by Andrew Hallward-Driemeier, Department of Earth and Environmental Sciences; Luke D. Schiferl, Lamont-Doherty Earth Observatory; Trey Maddaleno, University of Minnesota; Michael P. Vermeuel, Purdue University; Dylan B. Millet, University of Minnesota; and Delphine Farmer, Colorado State University.The research was supported by the New York State Energy Research and Development Authority.
