Inventories sharply underestimate the quantity of methane wafting from six large US cities.

Some of the largest US cities emit more than double the amount of the potent greenhouse gas methane than had been estimated, as shown by air samples collected on research flights.

Methane is burnt in homes as fuel for heating and cooking. It is known to leak from distribution pipes and appliances, but such leakage isn't closely monitored in urban centres.

Eric Kort and Genevieve Plant at the University of Michigan in Ann Arbor and their colleagues sampled the air down wind of 6 large cities, including Washington DC and New York City, on 20 research flights in 2018. They found that these cities collectively emit almost one million tonnes of methane per year — more than twice the amount reported in existing inventories.

Fugitive natural gas that had leaked from supply lines and homes made up the bulk of the observed emissions. Estimates of methane leaks from the gas supply chain in the United States should be revised upwards to account for urban losses, the team says.