The shale gas extraction industry is still in its infancy in Europe, but in the United States the practice has been going on since the 1990s. And depending upon whom you ask, the enormous deposits of natural gas running underneath the country either represent the future of U.S. energy security or a dire threat to the environment.

As European countries grapple with how -- and in some cases, whether -- to exploit their own natural-gas deposits, the U.S. experience with the relatively new technique of hydraulic fracturing, or "fracking" -- the controversial but effective method of extracting gas from rock buried a kilometer or more underground -- is being watched carefully.

Horror stories of foul-smelling drinking water, kitchen faucets that spurt flames, ponds with no fish life, and chronic illnesses in people who live near drilling sites have led some to conclude that in its eagerness to feed America's  huge energy appetite, the shale-gas industry is taking unacceptable risks with human health and the environment.

In France, lawmakers are so alarmed at what they’ve seen and heard that the country's parliament has given preliminary approval to a new law banning hydraulic fracturing and withdrawing permits that have already been issued.

First-Time Filmmaker

Nothing has galvanized shale-gas opponents in the United States and raised fears abroad more than the 2010 documentary "Gasland."

After a gas company asked Josh Fox for permission to drill on his land in Pennsylvania, the first-time filmmaker investigated claims from people all over the country who live near drilling sites. He interviewed them, took water samples, looked at the money changing hands, and concluded that wherever drilling is taking place, the air, water, and the people are suffering.

Political instability in oil-producing countries and rising fuel prices are driving the need for domestic energy sources, and supporters of shale gas are thrilled by estimates that the United States could hold enough natural gas to last the next 100 years, even at current rates of energy consumption. By contrast, proven American oil reserves won't last another decade.

Before the shale-gas boom took off a few years ago, renewable energy sources like solar and wind power were growing in popularity. Now, natural gas is being touted as a clean fuel, with advocates arguing that it burns as much as 50 percent cleaner than coal because it releases less carbon dioxide into the atmosphere.

President Barack Obama has called natural gas "the standard" for clean energy and has asked publicly, "Are we doing everything we can to develop" U.S. shale deposits?

That's the wrong question to be asking, according to opponents like Brady Russell of the environmental group Clean Water Action.

"When people compare natural gas to other forms of energy production, and they talk about how clean it is, all they mean is the greenhouse-gas effects," Russell says. "They’re not talking about the rest of the effects of hydrofracking. And we see those as so destructive that when you put it all together, it’s just the newest, latest form of dirty fossil-fuel energy that we really just need to move on from."

Drilling Underway Across America

Russell is based in Pennsylvania, where some of the United States' most intensive shale-gas extraction occurs in the Marcellus Shale field, which has been compared to Saudi Arabia in terms of its energy production potential.

Natural gas trapped in shale rock is extracted by sending a drill hundreds of meters down, underneath groundwater aquifers, and then horizontally through the shale-rock bed. A mixture of water and chemicals is injected into the shale, which creates tiny fractures through which bubbles of methane gas are released. The gas travels to the surface and is captured in storage tanks above ground and is then burned to create electricity.

Drilling is under way in at least 30 states, and as operations have increased so, too, have the industry’s opponents. They point to studies that show methane  gas released from the rock isn’t always captured at the surface and sometimes leaks into the atmosphere and drinking water supplies; that the fracking fluid isn't always treated and disposed of properly; and that the chemicals used in the process have spilled onto the ground and poisoned the surrounding land.

But not all shale skeptics in the United States are environmental activists. The New York state attorney general recently filed a lawsuit to force the federal government to do an environmental-impact study of hydraulic fracking in the Delaware River watershed, which provides drinking water to 5 percent of the country. And in April, a group of lawmakers in Congress released a report that accused several energy companies of sending cancer-causing chemicals into gas wells in more than a dozen states.

That's partly why activists like Russell of Clean Water Action say the industry can't be trusted.

"Given the opportunity, fossil-fuel industries always will take as little care as they can possible get away with," Russell says. "Whatever the least they can do is, that’s what they’ll do, because they don’t care about protecting the environment, they don’t care about leaving things as they once were before the industry came there. They want to make as much money as possible, and being less careful yields higher profit margins."

Bad Headlines

One of the largest gas companies in Pennsylvania is Chesapeake Energy, which has been the source of headline-grabbing accidents. In April, one of its gas wells blew out and sent thousands of gallons of fracking fluid into the ground. In 2009, a similar spill killed surrounding trees and fish life. Local families have been told to avoid drinking their own well water.

To counter the bad press, Chesapeake has produced a series of television ads that portray it as a major state employer and a company that takes its safety record seriously.

In fact, regulation of shale-gas extraction varies widely from state to state and compared to the oversight of other industries like coal and nuclear is considered weak.

Ed Reed, senior editor at Scotland-based NewsBase Ltd., which tracks global energy developments, says the U.S. industry has been able to evolve so rapidly partly because the country's environmental standards are "lax." France's cautious approach is aimed at staving off U.S. mistakes, but it will mean slower progress, he says.

"Now, looking at places like France, which has placed this moratorium on hydraulic fracturing -- that’s going to be a problem, as well," Reed says. "I think knowing what we know, and looking at the American example, it's going to be very hard to carry out the same level of processes at the same intensity."    

Base Fears On Facts

Some advocates of shale-gas extraction, like Terry Engelder, a professor of geosciences at Pennsylvania State University, say people are right to be concerned about accidents within the industry but need to base their fears on facts and not emotions, like a bias against fossil fuels.

Engelder became an important figure in the shale-gas industry in 2008 when he discovered that the value of natural gas underneath economically depressed Pennsylvania stood at around $1 trillion.  

He says the controversy has become so heated that the two sides "are really speaking past one another without really trying to really understand what the opportunity is, what the risks are, and how these risks can be managed."

Engelder and other supporters of shale-gas extraction say it has a key role to play in keeping the United States' energy appetite satisfied for decades to come and reducing reliance on foreign imports. He also believes that industry practices are improving, states are moving to tighten regulations, and the rewards outweigh the risks.

"You can, I think, compare it quite favorably with the aircraft industry or the automobile industry," Engelder says. "There are automobile accidents that kill people, [and] there are airplane accidents that kill people, and the public has come to understand the risk associated with driving a car or flying in an airplane. And the public, I think, has yet to appreciate the actually relatively low risk that hydraulic-fracturing -- and I’m using this in the broad sense of the term -- gas production presents relative to its rewards."

Clean Water Action's Russell says groups like his don't think they’ll be able to stop the shale-gas boom, so they're putting their energy toward raising public awareness of its risks and urging states to adopt tougher oversight standards.

His advice to Europeans who are looking warily across the Atlantic at America’s experience is to get out ahead of the industry.

"Don't let the drillers come in and start operating before you've built a good solid regulatory framework," Russell says, "so that you've got inspectors who are keeping an eye on drills, you're doing a good job establishing baseline tests for your water supplies to verify that they aren't contaminated before drilling, so that you know that if they’re contaminated afterward that it was drilling that did it."

European winters are always going to be cold, he says, so there's no rush to start before it's safe.