If you were going to craft a saga with natural gas as the protagonist (bear with us here) it would go something like this: Natural gas, once described by experts as “the neglected stepchild of the climate debate,” is thought to be in decline when, suddenly, bountiful resources are discovered in shale rock deposits that crisscross the country, a mile underneath our feet.

Seemingly overnight, the fuel becomes wildly popular and is feted as a cheap, abundant and clean-burning alternative to environmentalists’ bête noire, coal. A simple equation emerges: replace coal-fired electricity with natural gas for an easy win on greenhouse gas reductions.

Then, a study from Cornell University, co-authored by Professor Robert Howarth, claims to expose natural gas as a pretender. The study finds that the “lifecycle” emissions from extracting, transporting and burning natural gas – methane, its principal component and a potent greenhouse gas, leaks every step of the way – make it more damaging to the climate than coal in some circumstances. Howarth is particularly critical of emissions from the drilling process called hydraulic fracturing, or fracking. Energy experts, both in industry and academia, assail the study as incomplete and worse, sloppy. Still, the controversies cast a shadow on natural gas.

So, where does gas go from here?

Old coal plants will “disappear”

Despite its dramatic ups and downs, many experts believe that natural gas is the best hope for curbing greenhouse gas emissions before 2020 – a “bridge” to a low-emissions future.

And these gains by natural gas will likely come at coal’s expense, particularly in the U.S.

“The U.S. is at a bit of a turning point,” said David Hone, the climate change adviser for oil giant Shell, during a recent interview. “It has a relatively old fleet of coal-fired generating stations and there have to be decisions about how to retrofit them or whether to keep them at all. I think you’ll see that a lot of them will disappear.“

A recent report by The Brattle Group, an economic consultancy, found that up to 67 gigawatts (GW) of coal-fired power plants could go dark by 2020. The report concluded that natural gas-fired plants, which emit about 1,135 lbs of carbon dioxide per megawatt hour (MWh) – about half the emissions of coal – would fill the gap.

The environmental effects of this power shift could be dramatic. Hone argues that if an additional 35 GW of coal-fired electricity goes offline in favor of natural gas, the U.S. could forego 400 million metric tons of carbon dioxide annually (other estimates are more conservative).

These emissions savings would bring the U.S. about one-third of the way to President Obama’s unofficial emissions reduction target of 17 percent below 2005 levels by 2020. The gas switch has the additional benefit of being relatively cheap, Hone said.

Other energy experts endorse this approach.

Henry Jacoby, a co-chair of the M.I.T. Energy Initiative’s 2010 report, “The Future of Natural Gas,” notes that the capacity to generate more electricity from natural gas already exists because of overbuilding of gas turbines in combined cycle in the 1990s. Natural gas represents about 40 percent of the total installed generation capacity in the U.S. but produces only 21 percent of the electricity, according to the report.

“You could, with a very small capital investment, have an effect on the carbon emissions of the [electricity] system,” Jacoby said.

Critics: Industry must address concerns

Before the fuel can be embraced on a large scale, experts say the natural gas industry must improve its environmental practices and reassure the public.

“The gas industry has not been very good at building public trust,” said Michael Levi, a fellow on energy and environment at the Council on Foreign Relations. “When somebody comes out with a study that says they’re not being straight, people believe that.”

Levi has been an ardent critic of the Howarth study and believes in the potential of natural gas. But he has written that some in the industry have responded poorly to criticism and he has urged gas producers to embrace constructive regulation of drilling practices.

The gas industry could start with close monitoring of lifecycle methane emissions and coordinated action to mitigate the leaks, said Dan Lashof, the director of the National Resources Defense Fund’s Climate Center.

Lashof said that while he has reservations about the Howarth study, other studies done by the U.S. Environmental Protection Agency have documented significant methane emissions from natural gas. (Another study by the Post Carbon Institute has backed Howarth’s claims.)

But there are environmental concerns beyond methane emissions that keep the environmental community from embracing natural gas, Lashof added. He cited, for example, the environmental impact from chemicals in fracking fluid, which are exempt from the U.S. Safe Drinking Water Act.

“It’s very hard to consider any energy source as environmentally friendly if the producers are seeking exemptions from bedrock environmental standards,” Lashof said.

A spokeswoman for America’s Natural Gas Alliance (ANGA), an industry group, responded that the alliance joined several other natural gas groups in supporting a state-by-state registry that would disclose contents of hydraulic fracturing fluids.

Asked about lifecycle methane emissions, ANGA’s executive vice president, Tom Amontree, responded by attacking the Howarth study.

“It is hardly the type of scientific research that should cast doubt on the widely-accepted clean benefits of natural gas, and we are working aggressively to educate the public on the facts,” he said. “At a pivotal time in America’s energy future, it’s crucial that the conversation remain centered on facts, not misleading studies.”

“The main weapon against coal is gas”

Benjamin Schlesinger, a Bethesda, Md.-based consultant to the natural gas industry, said it’s optimistic to think that natural gas will replace all of the departing coal plants.

But he notes that gas prices are already competitive with coal and likely won’t go up, even if demand increases, because there is so much latent production.

If gas doesn’t pick up the slack for coal, there aren’t many appetizing alternatives. Wind, solar power and other renewables are starting from such a small base that they will not be able to edge out fossil fuel generation in the coming decades. At best, they will be able to absorb the increase in electricity demand, according to Shell’s Hone.

“I just don’t see renewables as really being in contention with gas at all,” said Mark Thurber, the associate director for research at Stanford’s Program on Energy and Sustainable Development.

Still, in order to take the opportunity to promote gas, experts say the industry must be willing to accept regulation and environmental groups must be willing to embrace another fossil fuel as an alternative to coal.

As Levi, from the Council on Foreign Relations, notes, the “main weapon against coal is cheap gas.”

Top image: Sunset over the Fisk power plant. Courtesy/Flickr user Vxla