Study: Methane Emissions From Gas Stoves Have Climate Impact of 500,000 Cars

They actually leak more methane when they are off than when they are on.

This gas cooktop leaks more methane when it is off than it does when on.
This gas cooktop leaks more methane when it is off than it does when on.

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Treehugger has long complained about gas stoves, mostly about the products of combustion from burning methane—because that is what "natural" gas mostly is—including particulate matter, nitrogen oxides, carbon monoxide, and, of course, carbon dioxide and its impact on indoor air quality. One thing we never considered was the direct emissions of methane, or unburned natural gas. But Eric Lebel, the lead author of a new study from Stanford University, says in a press release: “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.”

The study, published in the journal Environmental Science & Technology, measured the full gamut of emissions from gas ranges and the results are surprising: up to 1.3% of the gas that is piped to a stove is released unburned. That doesn't sound like much, but it adds up. The researchers write: "We estimate that natural gas stoves emit 0.9% to 1.3% of the gas they use as unburned methane and that total U.S. stove emissions are 28.1 Gg [gigagram, or one million kilograms] CH4 [methane] [per] yr... Using a 20-year timescale for the lifetime of methane, these emissions are comparable in climate impact to the emissions of approximately 500,000 cars."

Burning methane produces a lot of CO2 which has a global warming potential (GWP) of one. Methane has a GWP that is 86 times as great over a 20-year period, so leaking methane is far worse for the climate than burning methane.

The researchers built zip-wall enclosures with plastic sheets to partition the kitchen from the surrounding space because, of course, these are probably typical California open kitchens where the products of combustion go all over the house, having exhaust hoods that we have described as the most screwed up, badly designed, inappropriately used appliance in your home. They used a neat technique to measure the volume of the enclosure, releasing a known amount of ethane into the space and measuring its dilution. The researchers noted in the study: "We found this method to be more straightforward for estimating kitchen volume than taking measurements of chamber dimensions, which proved challenging with cabinetry and non-standard configurations of many modern kitchens."

They measured the emissions in 53 homes that had 18 different brands of stoves that were between three and 30 years old. According to the press release:

"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."

Interestingly, the researchers found no relationship between total methane emissions and stove cost or age, although it is only older stoves that have pilot lights instead of piezoelectric sparkers.

The researchers conclude the press release by asking questions that we have been raising on Treehugger for years. “I don’t want to breathe any extra nitrogen oxides, carbon monoxide or formaldehyde,” said study senior author Rob Jackson. “Why not reduce the risk entirely? Switching to electric stoves will cut greenhouse gas emissions and indoor air pollution.”

It is difficult to get people to give up their stoves, especially when the gas industry is dropping big money on Instagram influencers and the previous American Secretary of Energy wanted to rename the stuff as Freedom Gas.

But it seems that every week there is new research about how much methane leaks along the whole supply chain from the fracking to the meter on our homes, how bad it is for the health of occupants, and now with this study, how bad our gas stoves are for the climate. It really is time to go induction.

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