But a new study by a group of scientists from various federal labs as well as MIT, Stanford, Harvard and four other universities is throwing that optimism into question. If anything, natural gas "is not likely to reduce greenhouse gas emissions," cautions the study's lead author Adam Brandt, of Stanford. At best, switching a car from gasoline to CNG is "on the borderline in terms of (the benefits to) the climate," he says.
The problem isn't actually with natural gas itself, the researchers emphasize. It's with the way the fuel is produced.
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Like petroleum, natural gas is sourced from underground deposits, often from the same wells. For many years, a sizable amount of the gas was "flared," or burned off at the well site, because of either low demand or because of the difficulty of transporting it to markets where it could be used.
More pipelines are being built and other transport methods—such as specially designed supertankers—have become available.
And just in time. The energy industry has been rapidly expanding the use of so-called fracking, sending a mix of lubricants and other materials into wells to crack rock formations and thereby access vast underground stores of oil and natural gas that had long been considered out of reach.
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Fracking has plenty of critics who blame it for everything from localized earthquakes to water pollution. But now they may have another cause to rally around. The problem is that some of the gas generated from drilling is leaking into the atmosphere at the wellhead. How much is a matter of debate.
The U.S. Environmental Protection Agency sets the figure at about 1.5 percent of the total gas released by drilling. Stanford's Brandt says his data suggest it could be well over 2 percent.
A separate 2012 study by the Environmental Defense Fund warned that those leaks at the wellhead could actually result in a long-term increase of global warming gases.