Gas-burning stoves in kitchens across America may pose a greater risk to the planet and public health than previously thought, new research suggests.

The appliances release far more of the potent planet-warming gas methane than the Environmental Protection Agency estimates, Stanford University scientists found in a study published Thursday in the journal Environmental Science and Technology. The appliances also emit significant amounts of nitrogen dioxide, a pollutant that can trigger asthma and other respiratory conditions.

Scientists and climate activists have increasingly urged homeowners to switch to all-electric stoves, water boilers and other appliances, even as the natural gas industry fights in New York and across the country to keep the signature blue flames of gas-burning stoves as a staple in American homes.

“If you have the financial ability to swap out a gas stovetop for an electric induction cooktop, I do think it’s a good idea,” said Rob Jackson, a Stanford earth science professor and co-author of the study. “It’s a good idea for the planet and for air quality.”

Nationally, more than one-third of households — about 40 million homes — cook with natural gas. In California, 60% of households favor the popular fuel.

The researchers in Thursday’s study measured emissions from stoves in 53 homes across seven California counties. They used their findings to estimate that methane emissions from gas stoves in the United States have a comparable climate impact to about 500,000 gas-powered cars driven for a year, Jackson said.

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Methane, the main component of natural gas, is the second-largest contributor to climate change among greenhouse gases. Although it dissipates more quickly than carbon dioxide, it is more than 80 times as powerful in the first 20 years after it is released into the atmosphere.

The researchers also found that more than three-quarters of the methane emissions occurred when the gas stoves were turned off, suggesting that leaks persist even when the appliances are not being used for cooking or heating. Emissions of nitrogen dioxide, meanwhile, were more closely correlated with the amount of gas burned.

Tim Carroll, an EPA spokesman, noted that the agency previously has not included emissions from inside homes and buildings, known as “post-meter” emissions, in its Greenhouse Gas Inventory, an annual report on every sector of the U.S. economy. But the agency plans to update its approach.

“EPA looks forward to reviewing the new study,” Carroll said in an email. “While post-meter leak emissions (including leak emissions from stoves) are not currently included in the GHG Inventory, EPA plans to incorporate an estimate for these post-meter emissions in the upcoming 2022 GHG Inventory.”

The American Gas Association, a trade group that represents more than 200 companies, has defended the industry’s efforts to reduce its climate impact, noting that total methane emissions from natural gas systems have declined 16% from 1990 to 2019 and that residential natural gas use amounts to only a small portion of U.S. emissions.

“We are committed to going even further by investing nearly $30 billion each year to modernize our system and $4.3 million every day to help our customers and communities shrink their carbon footprint through energy efficiency improvements,” Karen Harbert, the association’s president and chief executive officer, said in a statement.

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The group added that agencies such as the EPA and the Consumer Product Safety Commission “closely monitor and have evaluated homes with natural gas piping and natural gas appliances and have never taken action to limit their use.”

The EPA does not regulate indoor air pollution because it lacks the authority to do so under the Clean Air Act, which covers only sources such as automobiles, power plants and other industrial facilities.

But in 2018, the EPA set a one-hour outdoor exposure limit of 100 parts per billion for nitrogen dioxide, a common pollutant that forms when fossil fuels such as oil, gas and coal are burned at high temperatures. Exposure can have a range of harmful effects on the lungs, including increased asthma attacks and inflammation of the airways, according to the American Lung Association.

Thursday’s study found that families who don’t use their range hoods or who have poor ventilation can surpass the one-hour outdoor standard within a few minutes of stove usage, particularly in more cramped kitchens, which are more common in poorer communities.

“It’s definitely an environmental justice issue because lower-income households are more susceptible,” said Eric Lebel, a senior scientist at PSE Healthy Energy, a research institute in Oakland, Calif., who worked on the study as a graduate student at Stanford.

New York City last month became the largest municipality in the country to ban gas use in new buildings, overcoming opposition from the fossil fuel industry and real estate developers. The New York City Council, a majority-Democratic body, voted to require new buildings under seven stories to go electric by December 2023. Taller buildings have until 2027.

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In recent years, gas bans have spread from liberal enclaves in California to bigger cities across the country, including Boston, Denver and Seattle. Last week, New York Gov. Kathy Hochul proposed the first statewide gas ban by 2027, a move that climate activists cheered while calling for a faster timeline.

The gas industry has waged a campaign in statehouses across the country to preempt such bans, arguing that they deny consumers choice of a reliable fuel. Republican-controlled legislatures in Southern states including Alabama, Kentucky and Texas have passed industry-backed bills to prevent cities from restricting fossil fuel use.

Frank Maisano, an energy policy expert at Bracewell, a law and lobbying firm, who has worked with gas industry clients, criticized the methodology of Thursday’s study.

The researchers conducted the study by “wrapping kitchens in plastic, which is in no way a realistic measure of the circumstances in a typical home,” Maisano said in an email. “It is too bad that we aren’t trying to find out more important things about indoor air quality rather than pushing a political agenda centered on electrification.”

The study’s authors said they stand by their findings, which went through a rigorous peer-review process. Jackson added that he hopes the conclusions persuade some Americans to ditch gas stoves for induction cooktops, which can boil a pot of water in nearly half the time of a conventional burner, despite often costing more upfront.

“Some people have an affinity for gas stoves,” he said, “but if we could just get them to try electric cooktops, they would never go back.”