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Gas stoves leak significant amounts of methane when ignited or even turned off, adding to the growing debate over the effects of gas-fired appliances on human health and climate change, according to a new report.

Based on measurements from stoves, ovens and broilers in 53 California homes, the small study estimates that stoves emit between 0.8 and 1.3 percent of the natural gas they consume as unburned methane, a potent greenhouse gas. The study showed that during a typical year, three-quarters of these emissions occur when devices are turned off, which could indicate leaky fittings and connections with gas service lines.

The study estimates that over a 20-year period, emissions from stoves in the United States could have the same effect on heating the planet as half a million gas-powered cars.

“People are very attached to their stoves,” said Eric D. Lebel, a senior scientist at the nonprofit research institute PSE Healthy Energy and lead author of the study, published Thursday in the journal Environmental Science and Technology. “There’s something human about cooking over a gas stove over fire.”

But more and more evidence suggests that stoves are “harming health and climate at the same time,” he said.

A growing number of American cities are largely located in blue states such as California and Massachusetts. change house from gas-powered cooking and heating. New York last month prohibited gas connections in all new buildings. But at least 20 states, mostly red, have prevented cities from restricting gas use, often with the backing of gas companies and utilities, who see electrification as a threat to their profitability.

In 2015, the last year for which detailed data from government surveys are available, American households had more than 40 million gas stoves. In general, houses and buildings are responsible estimated 13 percent America’s greenhouse gas emissions

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

methane leaks oil and gas installations has received increased attention in recent years, and efforts are underway to shut down thousands of inactive, methane-emitting oil and gas wells across the country. But less research has been done on emissions from homes, said Rob Jackson, an earth scientist at Stanford University who worked on the new study.

Dr. Lebel, Dr. Jackson and two co-authors have used plastic sheets to seal kitchens in private homes, Airbnb rentals, and properties for sale or rental. They found that on average, igniting a burner in a gas stove emits the same amount of methane as leaving it on and burning it for 10 minutes. Gas ovens emit higher rates of methane than stove burners because ovens periodically ignite and extinguish their main burners to maintain the set temperature.

The researchers also measured emissions over periods of five to 10 minutes with the furnaces turned off, although they did not try to pinpoint the sources of the leaks.

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

Dr. Lebel said that none of the gas leaks the researchers measured were at a concentration that could cause an explosion.

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.

However, they agreed that they would like to run more home tests on people who can’t afford to replace or maintain older devices. This, they said, will help their results better capture the disproportionate effects of gas emissions on low-income families.

Kathryn McKain, a researcher at the National Oceanic and Atmospheric Administration’s Earth Systems Research Laboratory, who did not work on the new study, said atmospheric methane levels have skyrocketed in recent years, and scientists don’t fully understand why.

More methane seems to end up in the air than gas consumption on the ground accounts for. Dr. McKain said home appliances are “just one piece of the puzzle.”