Natural gas is widely hailed as cleaner than other fossil fuels, but new research says using it -- instead of diesel -- to power trucks and buses could actually exacerbate global warming over a 100-year period.
Diesel engines are relatively fuel-efficient, while the natural gas infrastructure leaks more heat-trapping methane than federal or industry data suggest, says a study by 16 scientists from federal laboratories and seven universities including Stanford, Harvard and MIT.
"There's lots of reasons to shift from diesel," says lead author Adam Brandt of Stanford, adding diesel buses are "stinky" and natural gas ones may help cut oil imports and improve air quality. But from a climate perspective, "it's not likely to reduce greenhouse gas emissions." Burning natural gas emits less carbon dioxide than burning diesel, but the drilling and production of natural gas leaks methane, a potent greenhouse gas. Those leaks offset natural gas' CO2 benefit.
"Even running passenger cars on natural gas instead of gasoline is probably on the borderline in terms of climate," he says. His research, a review of 200-plus studies, appears in the newest edition of the journal Science.
An industry group disagrees. Richard Kolodziej, president of Natural Gas Vehicles for America, says a 2007 report by the California Energy Commission calculated that on a well-to-wheel basis -- which includes extraction and distribution -- natural gas in vehicles emits 22% fewer greenhouse gases than diesel and 29% fewer than conventional gasoline.
Brandt says his analysis is based on greenhouse-gas calculations from a 2012 study led by Ramon Alvarez of the Environmental Defense Fund, a private research group. Alvarez's team said switching buses and trucks from diesel to natural gas might not help the climate over a 100-year period if 1.7% or more of methane is leaked in producing and using natural gas. The Environmental Protection Agency says 1.5% is leaked, an estimate Brandt says is about 50% too low.
The new research says natural gas is still -- despite methane leaks -- better for the climate long-term than coal as a way to generate electricity.
The production of natural gas is booming in the United States, and President Obama welcomed it in his 2014 State of the Union Address as "bridge fuel that can power our economy with less of the carbon pollution that causes climate change."
The authors call on the natural gas industry to clean up its leaks. Fortunately for gas companies, they say a few leaks probably account for much of the problem, so repairs are doable. An earlier study of about 75,000 components at processing plants found just 50 faulty ones were behind nearly 60% of the leaked gas.
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