A Columbia team traces New York City's methane mainly to gas that burns badly indoors

The separation rests on carbon monoxide. Gas that escapes without burning brings none of it along; gas that burns badly does, because carbon monoxide is what natural gas produces when it fails to burn completely ^[10]. So a methane plume that arrives at the tower correlated with carbon monoxide came out of a flame. During two intensive campaigns, in summer 2023 and winter 2024, the team measured methane, ethane and carbon monoxide at high frequency, which let them chemically sort raw gas from incomplete combustion ^[9].

The no-combustion category is broader than pipes. It covers leaks in underground utility mains and gas vented from building appliances without ever igniting ^[7]. Only 6% of identified plumes in winter and 7% in summer fell into it, leaving 94% and 93% with a combustion signature ^[11][2]. Those are counts of plumes at a single site, and a plume count is not a mass balance: two hundred badly tuned boilers and one large main leak can register as two hundred detections against one. The study's own wording is about frequency, reporting that pipeline leaks were detected less often at the tower than methane tied to incomplete combustion ^[11].

The $300 million is a retail valuation, which means it is money customers in the region already paid ^[3]. Over whatever period the figure covers, a 1.7% loss rate priced at the same retail level implies roughly $17.6 billion of gas delivered ^[1]. Methane carries more than 80 times the 20-year warming potential of carbon dioxide and clears the atmosphere in about a decade ^[4].

"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 Ph.D. student in Columbia's Department of Earth and Environmental Sciences ^[5]. The published account describes an overlooked pathway for cities and potential savings for consumers, without an estimate of what reducing appliance losses would cost ^[20].

Natural gas made up 99% of total methane in February and 98% in May, falling to between 85% and 88% in the cooling months ^[14]. Everything else, including the wetlands, wastewater plants and landfills the team detected, therefore tops out at 12 to 15% of the total in summer ^[3][17]. "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 Roisin Commane, an associate professor at Columbia and a researcher at Lamont-Doherty ^[15]. Some large buildings run natural gas-powered cooling, which the authors say may help explain the summer rise ^[16].

This is the first monthly analysis to track methane before and after the gas reaches customers in the metropolitan area ^[6]. Across the study area, emissions closely followed real-time natural gas deliveries, which the authors take as support for emissions driven mainly by use downstream of the meter ^[18].