Quick, name the most significant American innovation of the past ten years. How about hydraulic fracturing?

A workman marks the pipes used in Chesapeake Energy's hydraulic fracturing, or fracking site in Carroll County Monday, October 17, 2011. (Gus Chan/The Plain Dealer)

Okay, that's not an entirely new invention. As T. Boone Pickens has pointed out, people have been using pressurized fluid to split open rocks underground since the 1940s. But it wasn't until very recently that the U.S. natural gas industry, with support from the Energy Department, managed to refine fracking techniques in order to drill horizontally into shale rock and extract natural gas and oil. Lots and lots of natural gas and oil.

In the past few years, the shale gas boom has upended the U.S. energy landscape. With large and small companies drilling wells around the country, cheap natural gas is now displacing coal as the nation's top source of electricity. That, in turn, has helped contribute to a drop in U.S. carbon-dioxide output: According to the International Energy Agency, the United States has cut its emissions 7.7 percent since 2006, more than any other country or region in the world. (A natural gas plant emits about half the carbon-dioxide that a coal plant does, although fracking for gas can release heat-trapping methane.)

That's a major turn of events. But, for now, the fracking boom has largely been confined to the United States. Other nations, from China to Australia to France, also have vast shale formations that contain "unconventional" natural gas and oil. But they've barely started tapping those resources, either because of technical hurdles or political obstacles.

Could that change in the years ahead? Perhaps. Consider France. By some estimates, the Paris Basin, located near the country's capital, contains more than 100 billion barrels of crude oil trapped within its rocks. But after Canada's Vermilion Energy drilled two exploratory wells in the region in 2010, the French legislature banned hydraulic fracturing altogether. Farmers in the region worried that the chemicals used in fracking could contaminate the water supplies. As a result, French energy companies are barred from even poking around.

Recently, however, the French government has shown signs of changing its mind. “It’s not a banned subject,” Industry Minister Arnaud Montebourg said on Thursday, according to Bloomberg Businessweek. “We must confront it. For the moment, there is no government position.” In June, Environment and Energy Minister Delphine Batho said France's ban on fracking was "not open" to discussion. But Montebourg quietly rebuked her, saying, "That's just her opinion." It seems that the allure of vast fossil fuels is getting harder for France to ignore.

Then there's the rest of Europe. Britain may have vast offshore gas reserves. Poland, too, has large shale gas deposits. But right now, Europe's fracking industry is still in its infancy. The IEA notes (pdf) that drilling a well in Poland costs about $12 million to set up, three times as much as it costs to drill in Texas' Barnett shale, because "the drilling and service industry is much less developed." In the years ahead, the gas industry in Europe is hoping that advanced techniques imported from the United States could help nudge down those costs.

Source: International Energy Agency

Fracking could also catch on in China, eventually. Jenny Mandel recently wrote a long and comprehensive piece in E&E News on the country's growing interest in U.S. shale gas technology. China is a tantalizing landscape for drillers — the country has an estimated 1,275 trillion cubic feet of "technically recoverable" gas, compared with 862 trillion cubic feet in the United States. But fracking has been slow going. The geology is much more difficult to work in — many of China's shale formations are far deeper underground — and the lack of private property rights has hindered development. (Meanwhile, the biggest shale gas prize lies in the Tarim Basin out west in the Xinjiang Uighur autonomous province. But water is hard to come by in that arid region — and fracking needs plenty of water.)

So it may be some time before other countries join the fracking frenzy. The potential is there: The IEA estimates that, by 2035, worldwide production of unconventional natural gas could triple, to 1.6 trillion cubic meters. That would require "more than one million new unconventional gas wells worldwide between now and 2035, twice the total number of gas wells currently producing in the United States." But this is also a high-end scenario, and there are all sorts of reasons, from political to technological, why it might not happen. (The IEA, for its part, argues that drilling companies need to address controversial issues like water contamination and air pollution. Otherwise, protests and local opposition could bog down the expansion of fracking.)

P.S. By the way, the IEA has also taken a look at what a shale gas boom would mean for global warming. Technically, there would be some environmental benefits (especially if companies managed to plug the methane leaks from their wells) as natural gas edged out coal. But if this was the only change made to our energy system, we'd still be on track for a very hot future:

The Golden Rules Case puts CO2 emissions on a long-term trajectory consistent with stabilising the atmospheric concentration of greenhouse-gas emissions at around 650 parts per million, a trajectory consistent with a probable temperature rise of more than 3.5 degrees Celsius (°C) in the long term, well above the widely accepted 2°C target.

In other words, if the world simply experienced a boom in gas fracking and didn't make any other attempts to limit greenhouse gases, we'd be on pace for a level of global warming that Tyndall Center director Kevin Anderson says is "likely to be beyond 'adaptation', is devastating to the majority of ecosystems and has a high probability of not being stable."

Or, in the dry bureaucratic language of the IEA, "natural gas cannot on its own provide the answer to the challenge of climate change."