Natural gas stoves have negative climate impacts: researchers

Stanford University – A new study from Stanford University has revealed that natural gas-burning stoves inside homes in the United States have a much greater impact on the climate than previously thought.

Researchers found that the amount of methane emitted from gas stoves in the U.S. has the warming effect of carbon dioxide emitted from 500,000 gasoline-burning cars. While most of the emissions occur while the stove is off, stoves also emit dangerous levels of nitrogen oxides, a toxic air pollutant, during combustion.

The findings, published in Environmental Science & Technology, come as legislators in numerous U.S. municipalities and at least one state – New York – weigh banning natural gas hookups from new construction.

“Surprisingly, there are very few measurements of how much natural gas escapes into the air from inside homes and buildings through leaks and incomplete combustion from appliances,” said study lead author Eric Lebel, who conducted the research as a graduate student in Stanford’s School of Earth, Energy and Environmental Sciences. “It’s probably the part of natural gas emissions we understand the least about, and it can have a big impact on both climate and indoor air quality.”

An overlooked contributor to a growing problem

Although carbon dioxide is more abundant in the atmosphere, methane’s global warming potential is about 86 times as great over a 20-year period and at least 25 times as great a century after its release. Methane also threatens air quality by increasing the concentration of tropospheric ozone, exposure to which causes an estimated one million premature deaths annually worldwide due to respiratory illnesses. Methane’s relative concentration has grown more than twice as fast as that of carbon dioxide since the beginning of the Industrial Revolution because of human-driven emissions. Over one-third of U.S. households – more than 40 million homes – cook with gas.

Findings and implications

To better understand cooking appliances’ potential climate and health impacts, the researchers measured methane and nitrogen oxides released in 53 homes in California, not only during combustion, ignition and extinguishment, but also while the appliance was off, something most previous studies had not done. Their study included 18 brands of gas cooktops and stoves ranging in age from three to 30 years.

The highest emitters were cooktops that ignited using a pilot light instead of a built-in electronic sparker. Methane emissions from the puffs of gas emitted while igniting and extinguishing a burner were on average equivalent to the amount of unburned methane emitted during about 10 minutes of cooking with the burner. Interestingly, the researchers found no evidence of a relationship between the age or cost of a stove and its emissions. Most surprising of all, more than three-quarters of methane emissions occurred while stoves were off, suggesting that gas fittings and connections to the stove and in-home gas lines are responsible for most emissions, regardless of how much the stove is used.

Overall, the researchers estimated that natural gas stoves emit up to 1.3 percent of the gas they use as unburned methane. While the U.S. Environmental Protection Agency (EPA) does not report emissions from specific residential natural gas appliances, it does report methane emissions for residential appliances collectively. From stoves alone, the researchers estimated total methane emissions to be substantially more than the emissions currently reported by the EPA for all residential sources.

“Switching to electric stoves will cut greenhouse gas emissions and indoor air pollution,” said study senior author Rob Jackson, professor of Earth System Science at Stanford.