Gas cookers leak methane even when turned off, study finds

According to a new report, gas stoves release significant amounts of methane when turned on and even when turned off, adding to the growing debate about the effects of gas-powered appliances on human health and climate change.

The small study – based on measurements of cooktops, ovens and broilers in 53 homes in California – estimated that the stoves emit between 0.8 and 1.3% of the natural gas they consume in the form of unburned methane, a potent greenhouse gas. In a typical year, three-quarters of those emissions occur when appliances are turned off, the study showed, which could suggest leaks in fittings and connections to gas service lines.

Over a 20-year period, emissions from stoves across the United States could have the same global warming effect as half a million gas-powered cars, the study found.

“People are so attached to their stoves, said Eric D. Lebel, senior researcher at the nonprofit PSE Healthy Energy Research Institute and lead author of the study, which was published Thursday in the journal Environmental. Science & Technology. “There’s something human about cooking on a gas stove, over an open flame.”

But growing evidence, he said, suggests that stoves “harm both health and the climate”.

A growing number of US cities, mostly in blue states like California and Massachusetts, are moving homes away from gas cooking and heating. Last month, New York City banned gas hookups in all new buildings. But at least 20 mostly red states have banned cities from restricting gas use, often with backing from natural gas companies and utilities that view electrification as a threat to their bottom line.

There were more than 40 million gas stoves in US households in 2015, the latest year for which there are detailed data from government surveys. In total, homes and buildings are responsible for about 13% of greenhouse gas emissions in the United States.

Methane is the main component of natural gas, and if not combusted when released, it can warm the Earth more than 80 times more than the same amount of carbon dioxide over a 20-year period. Methane also contributes to ground-level ozone pollution, which can cause respiratory problems and other health problems.

Methane leaks from oil and gas facilities have drawn increasing attention in recent years, and efforts are underway to plug thousands of inactive, methane-spewing oil and gas wells across the country. But less research has been done on emissions inside residences, said Rob Jackson, a geologist at Stanford University who worked on the new study.

Dr. Lebel, Dr. Jackson, and two co-authors have used plastic sheeting to seal kitchens in private homes, Airbnb rentals, and properties for sale or rent. They found that, on average, lighting a burner on a gas stove emitted about the same amount of methane as leaving it on and burning for 10 minutes. Gas ovens emitted methane at a higher rate than cooktop burners, they found, because ovens cycle their main burner on and off periodically to maintain the set temperature.

The researchers also measured emissions over periods of five to 10 minutes when the stoves were off, although they did not attempt to identify the sources of these leaks.

“It’s almost an inevitable byproduct of the natural gas supply chain,” Dr. Jackson said. “Every fitting, every fitting has the potential to leak, especially over time, as stoves sit there for years.”

None of the gas leaks measured by the researchers had a concentration that could cause explosions, Dr Lebel said.

The researchers found that when it comes to methane emissions, old stoves performed no differently than new ones. The more expensive models also did not outperform the cheaper ones.

They did, however, acknowledge that they would have liked to carry out tests in more homes owned by people who could not afford to replace or maintain old appliances. This would help their findings better capture the disproportionate impacts of gas emissions on low-income families, they said.

Methane levels in the atmosphere have skyrocketed in recent years, and scientists don’t fully understand why, said Kathryn McKain, a researcher at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory, who doesn’t has not worked on the new study.

More methane appears to end up in the air than represented by the gas infrastructure on the ground. Appliances, Dr. McKain said, are “just one piece of the puzzle.”

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