Cornell University biogeochemist Robert Howarth had heard it dozens of times: Natural gas was the green fuel.

As horizontal drilling, also known as hydrofracking, swept across Texas and Arkansas and into the gas-rich regions of New York and Pennsylvania, that claim became more and more widespread.

And it wasn't just coming from the gas companies. Journalists repeated the statement in their numerous reports on the radio and in newspapers. Small-town mayors in gas-rich areas touted the importance of getting off foreign oil and onto a beneficial energy source. Even environmental groups talked about shale gas reserves as a clean, green energy - if nothing else, a bridge fuel to bring the nation closer to renewable sources such as wind and solar.

Howarth, who has been researching environmental questions for close to 30 years, decided to investigate the claim. In a paper that came out in late April, he and co-authors Anthony Ingraffea, a Cornell engineer, and research assistant Renee Santoro, a former Washington Post fact-checker, delivered a blow to the gas industry's claims - and in the process encountered a geyser of criticism.

Howarth's report stated that methane emissions from wells drilled using hydrofracking were at least 30 percent greater than those coming from conventional natural gas wells, and perhaps twice as much. It also stated that methane had a far greater potential to contribute to global warming than carbon dioxide, particularly over the first few decades after the emissions occurred.

The most crucial time for methane leakage is after the drillers bore down into the shale formation to create fissures and then pump in water and chemicals to coax out the gas, but before they actually suck the gas out. That period can be as long as two weeks. During that time, Howarth said, methane escapes because the gas companies say it is not yet economical to capture it.

In short, the report concluded that natural gas as a fuel, in terms of greenhouse gas emissions, was not a better alternative than coal, and in fact, could be far worse.

"It's been widely reported as a green fuel, and there's virtually no scientific basis for it," Howarth said of shale gas. "A lot of green groups have bought into it, and it's an important part of the industry's business plan - it does burn cleaner, it puts out less carbon dioxide and mercury than coal. But natural gas is methane, and methane is a potent greenhouse gas, and it's the greenhouse gas footprint that matters - I do think natural gas is worse for the greenhouse gas footprint."

The natural gas companies began the assault on The Cornell researchers' report even before it was published in Climatic Change, a journal housed at Stanford University. A draft report was leaked three days before the revised version came out; Howarth says he has no idea how, as the only copy was on his own computer.

Energy In Depth, an industry publication, asked this question on its blog: "All kidding aside, is this guy insane?" It also derided Ingraffea, a respected engineer who wrote his dissertation on hydrofracking in the 1970s, as a "rock-mechanics specialist." The blog also presented video of Howarth "leading a protest" at an EPA fracking meeting in Binghamton. In fact, the video shows Howarth speaking to a crowd and saying that fracking needs more study.

The American Natural Gas Association referred to him as "debunked professor Robert Howarth," and talked about how he went to Washington, DC, to "trot out his baseless claim that somehow natural gas is actually a less clean fuel."

Those organizations criticize Howarth for using scant data, for making his predictions using a 20-year time horizon instead of a 100-year one to reach his conclusions and for not factoring in the methane leaks in coal production.

Representatives from the Council on Foreign Relations, the National Resources Defense Council and the Massachusetts Institute of Technology's Energy Initiative also questioned the authors' methodology.

In a presentation to the Chesapeake Bay Program's Scientific and Technical Advisory Committee in June, Howarth acknowledged several times that the data was "lousy," in part because the industry refuses to release more figures because they say emissions information is proprietary.

Howarth had said previously that he erred in not including methane emissions from coal, but that wouldn't change his conclusions. He also did not apologize for using the 20-year time horizon because, "if you're worried about climate change, you want to at least look at the short-term time horizon."

Howarth characterized the paper's estimates as conservative. To reach their conclusions, the authors used data from recent reports released by the EPA, the Governmental Accountability Office and the American Petroleum Institute. They also mined data from gas company financial reports and state data from Texas, which has a longer history with hydrofracking than the states in the Marcellus Shale region.

The report comes amid a barrage of scrutiny over hyrdofracking, much of it stemming from accidents in Pennsylvania that have contaminated the drinking water supply and resulted in fish kills. New York's attorney general recently sued the EPA and other federal agencies, accusing them of violating the National Environmental Policy Act in allowing hydrofracking in the Delaware River basin.

A collection of environmental groups, among them the Chesapeake Bay Foundation, recently implored President Barack Obama and his scientific advisers to take a comprehensive look at the cumulative air, water and land impacts before allowing any more drilling. While many state forests and public lands allow drilling, the U.S. Forest Service recently announced that no hydrofracking would be allowed in the George Washington National Forest in the Shenandoah Valley.

Howarth, who is the New York governor's representative to the Bay Program's Scientific and Technical Advisory Committee, said he hoped that committee members would take a closer look at natural gas hydrofracking.

"The amount of production that has gone on to date is a fraction of what's predicted," he said. "I would love to see STAC think about what the water quality implications are…it would be great to look at what it would mean for the Bay."