Gas flares don’t burn off as much methane as they should – to the tune of 3 million cars’ worth of pollution.

Science News looks gas flares, the open flames used to burn off leaking natural gas and to convert methane to CO2 directly at oil fields. They find that they’re less effective than promised, and that the difference between what they do burn and what they should be burning is the same as if 3 million extra cars starting driving around, giving off climate-warming greenhouse gases:

The industry and the U.S. government assumed those flares worked at 98 percent efficiency. But previous studies said that might be too optimistic, says Genevieve Plant, an atmospheric scientist at the University of Michigan in Ann Arbor ….

Plant and her colleagues sent planes to sample air over more than 300 flares in the Bakken Basin in North Dakota and the Permian and Eagle Ford basins in Texas, which account for more than 80 percent of the flaring in the country. The samples showed five times as much methane unburned than previously estimated.

Half of the difference is due to flares that aren’t burning. “We expected that flares might show a range of efficiencies, but we did not expect to see so many unlit flares,” Plant says. Between 3 and 5 percent of flares weren’t working at all. If those fires were lit, and 98 percent efficiency achieved, the result could remove the equivalent of about 13 million metric tons of carbon from the atmosphere.

You can read more of Plant’s research here, in Science.