SOURCE: Science

DATE: July 19, 2019

SNIP: Natural gas, long touted as a cleaner burning alternative to coal, has a leakage problem. A new study has found that leaks of methane, the main ingredient in natural gas and itself a potent greenhouse gas, are twice as big as official tallies suggest in major cities along the U.S. eastern seaboard. The study suggests many of these fugitive leaks come from homes and businesses—and could represent a far bigger problem than leaks from the industrial extraction of the fossil fuel itself.

When burned for heat or power, methane emits less carbon dioxide (CO2) than fossil fuels such as coal. But when leaked directly into the atmosphere, its warming effect can be dozens of times stronger than CO2, depending on the time scale over which the warming is measured.

The new findings come courtesy of data gathered by aircraft over six U.S. cities: Washington, D.C.; Baltimore, Maryland; Philadelphia, Pennsylvania; New York City; Providence; and Boston. In 2018, researchers flew at altitudes between 300 and 800 meters and measured concentrations of methane, ethane, CO2, and carbon monoxide, among other gases.

The ethane measurements were clues to likely sources of the methane leaks, says Eric Kort, an atmospheric scientist at the University of Michigan in Ann Arbor and co-author of the new study.

The team’s analyses suggest the five biggest urban areas studied—which together include about 12% of the nation’s population—emit about 890,000 tons of methane each year, the researchers report this week in Geophysical Research Letters. The vast majority of that, at least 750,000 tons, comes from methane leaks from homes, businesses, and gas distribution infrastructure, rather than natural sources and other human-driven sources such as landfills. For comparison, the team notes, that’s well over triple the amount emitted by gas production in the Bakken shale formation in the U.S. Midwest.

It’s also much more than the amounts estimated by the Environmental Protection Agency (EPA). A 2016 report suggested methane emissions in the six major urban areas the researchers studied totaled only 370,000 tons.