The evidence is growing: Your gas stove is a menace to the climate, and could very well be harming your health.
A new peer-reviewed study published on Thursday by Stanford University researchers found that as much as 1.3% of the gas used in typical U.S. stoves could be leaking into the atmosphere unburned. While that might not sound like a lot, when multiplied across all the households that cook with natural gas in the United States, the researchers estimate that stoves may be contributing the same amount to climate change each year as half a million gasoline-powered cars. And they found that three-quarters of the emissions leak out when the stoves aren't even turned on.
The natural gas that people use for cooking is primarily composed of methane, a greenhouse gas. When methane is combusted in your oven or on the stovetop, carbon dioxide is released. But when methane leaks out without being burned, it has a much greater short-term warming effect than carbon dioxide. Over the first 20 years that it hangs in the atmosphere, methane is 86 times more powerful at heating up the planet than CO2.
The past decade has seen a growing body of research into the climate impacts of the natural gas industry, finding that methane is leaking out of wellheads, pipelines, and other infrastructure used to drill for natural gas and move it around the country. But there has been far less investigation into what happens once the gas reaches your home.
"There are over 3 million miles of gas pipelines in the U.S., and when we are looking at a gas stove, we are basically looking at the end of a pipeline," said Brady Seals, a manager in the Carbon-Free Buildings program at RMI, a clean energy advocacy group, who was not directly involved in the research. "We need a full climate and health accounting of these seemingly innocent gas stoves."
Eric Lebel, the lead author of the study, told Grist that the team had previously investigated methane emissions from hot water heaters and was surprised to learn that the appliances leaked the most methane when they were shut off. So next Lebel wanted to see if the same held true for other household appliances.
The authors studied stoves in 53 homes in California that came from 18 different brands and ranged from 3 to 30 years old. They partitioned off each kitchen with plastic sheets and measured the amount of methane and nitrogen oxides that were emitted from the burners and oven when they were both in use and shut off.
All but four of the stoves leaked at least 10 milligrams of methane per hour when they were off, "suggesting that most stoves and associated nearby piping leak some methane continuously," the authors wrote. The rate of methane emissions while using the burners was about 4.5 times higher than while the stoves were off. And simply turning a burner on and off released the same amount of methane as keeping the burner on for 10 minutes — however, stoves that used a pilot light leaked a lot more than those that had an electric ignition system.
The new study documented similar levels of methane leakage as a study published in 2019 using a different method, as well as a study published in 2018 by researchers from Lawrence Berkeley National Laboratory. Zachary Merrin, a research engineer at the University of Illinois' Indoor Climate Research and Training program who published the 2019 study, said in an email that the field is still in its infancy, and that there's no agreed-upon method yet to quantify these residential methane emissions. But Merrin said he found it "reassuring" that all three studies arrived at similar conclusions.
The new study also suggests that the U.S. Environmental Protection Agency is underestimating residential methane emissions. The amount of methane the researchers found leaking out of stoves alone was 15% higher than the agency's estimate for all residential emissions in 2019.
Lebel assured Grist that the amount of methane leaked by stoves does not pose an immediate safety hazard. Methane does, however, contribute to decreased air quality locally by increasing concentrations of tropospheric ozone, a component of smog. Smog can worsen the severity of respiratory illnesses such as bronchitis and emphysema and trigger asthma attacks, particularly in children, the elderly, and people with existing lung problems. And methane emissions contribute to the climate crisis and the health threats that come with it — illness driven by heat waves, disease tied to insect and bacteria outbreaks, premature death linked to extreme weather events, and more.
The authors also measured nitrogen oxides, health-damaging air pollutants that were released when the stoves were turned on. They found that in a house with poor ventilation or where the range hood was not used while cooking, the indoor level of nitrogen dioxide could exceed the EPA's outdoor standard within minutes. Nitrogen oxides have immediate consequences for human health. "It's a respiratory irritant that's been associated mainly with asthma and premature death," Jonathan Buonocore, a research scientist at Harvard's Center for Climate, Health, and the Global Environment who was not involved in the study, told Grist.
The study's health-related findings aren't new; researchers have known for some time now that gas-burning stoves release pollutants that can impact human health. But Buonocore said that the study's efforts to monitor and inventory the exact quantity of these gases and pollutants emitted by individual stoves could unlock a new line of health research. Buonocore said he hopes future studies will look at a larger sample size of stoves, not just in California but across the U.S., and take a deeper look at what happens to pollutants produced by these stoves when kitchens aren't sealed off. "There's definitely a hazard here that's been underappreciated, and the next step would be to figure out what the exposures are under normal use," he said. Lebel said future research also needs to look at whether the risks of stove emissions are amplified in low-income homes with smaller kitchens and poor ventilation.
The good news is there is an electric alternative to gas, and it's not those loathsome electric coils that take forever to get hot. Induction cooktops are a newer technology that use an electromagnetic field to heat up pots and pans. Fans of induction cooking rave about their precision, how fast they can boil water, and how quickly they cool down after you shut them off.
If you want or need to keep using gas, make sure you turn on the range hood if it's not automatic. If you don't have one, or if it's not vented to the outdoors, open a window to improve ventilation. Merrin also said to keep an eye on the flames: It's a good sign if your burners show a steady blue flame, but orange flames are a sign of incomplete combustion and likely an increase in methane, nitrogen oxides, and carbon monoxide. "People can help their stove perform better by keeping the surface and the burners clean, making sure the burner caps are centered and well seated, and fixing any issues with the igniters if the stove is not lighting quickly or completely," he said.