A new study to be published Friday in the journal Science says the Environmental Protection Agency and other organizations have underestimated natural gas emissions in the country overall. "Atmospheric tests covering the entire country indicate emissions around 50 percent more than the EPA estimates. And that's a moderate estimate," lead author and Stanford University professor Adam Brandt says in a news release. The study said it "does not try to attribute percentages of the excess emissions to natural gas, oil, coal, agriculture, landfills, etc., because emissions rates for most sources are so uncertain."
However, it also concludes that:
- Generating electricity by burning gas rather than coal reduces the total greenhouse effect over 100 years. That gain has long been contested by some researchers.
- Replacing big diesel engines on over-the-road truck and bus fleets "probably makes the globe warmer, because diesel engines are relatively clean" and it is "improbable" natural gas versions could improve enough to beat diesel.
- Replacing gasoline in passenger cars with natural gas as a fuel "is probably borderline in terms of climate," Brandt said.
Addressing "some recent studies showing very high methane emissions in regions with considerable natural gas infrastructure," the authors also conclude that those measures "are not representative of the entire gas system." Eric Kort, a coauthor of the study, said: "If these studies were representative of even 25 percent of the natural gas industry, then that would account for almost all the excess methane noted in continental scale studies. Observations have shown this to be unlikely." The group's news release didn't say which studies it was referring to, but in 2012 researchers in Colorado estimated that producers in the Denver-Julesburg Basin were losing 4 percent of their gas. The study also questions the results of an unnamed study last year that directly measured emissions at natural gas production sites, saying only six of 30 companies approached decided to participate, which could lead to self-selection of better performers.
"Fortunately for gas companies, a few leaks in the gas system probably account for much of the problem and could be repaired," study authors said. Emissions of methane, the principal component of natural gas, are important because the gas has a powerful greenhouse effect -- about 30 times more than the same amount of carbon dioxide, the study said. The study was funded by a grant from the Cynthia and George Mitchell Foundation through a grant to Novim, a not-for-profit formed in 2007 by scientists and engineers at the Kavli Institute for Theoretical Physics at the University of California at Santa Barbara.
-- Jim Fuquay