Which has done more in the last five years to cut America's greenhouse-gas emissions and slow the pace of global warming?
1) Development of renewable energy such as wind and solar.
2) Increasing the fuel efficiency of vehicles, especially through hybrid technology.
You see where this is headed.
The equation of national energy use can be tough to parse. As energy consultant Geoffrey Styles says, it has many "moving parts."
But you can make a reasonable argument that fracking, or hydraulic fracturing -- the recently developed process of springing gas and oil from previously impenetrable rock formations -- has done more than any other policy or technology in the last few years (except, perhaps, for our disastrous recession) to slow the production of greenhouse gases.
How? By producing abundant, cheap natural gas. That gas has replaced a lot of coal in generating electricity, while releasing only half the carbon dioxide.
Partly for that reason, the United States has outpaced "green" Europe in reducing greenhouse-gas emissions. As America has raced to frack new gas fields, Europe has held back. France and Bulgaria outlawed fracking last year. The Czech government is preparing a moratorium on new shale-gas exploration. As Germany phases out nuclear power, it is increasing its use of coal.
The United States could follow Europe's lead if the opponents to fracking have too much sway. And that would be too bad, for the economy and the environment.
"I do think that climate change is a problem," says Styles, the principal of GSW Strategy Group. He spent 22 years at Texaco and also consults on alternative-energy strategies. "But I think that we would be foolish to turn our backs on this tremendous opportunity that we've been handed."
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So far, the debate over fracking has focused on its intense local effects. Above the Marcellus shale formation in Pennsylvania, farmers and suburbanites fret about potential contamination of water wells, unintended seepage of methane, and drilling pads carved from the wooded hills. Ironically, Pennsylvania was the birthplace of the oil industry. Think Quaker State and Pennzoil. "What's different," says Styles, "is that it is now being done in closer proximity to people, in places that haven't seen a drilling rig in a couple of generations."
Meanwhile, in southeastern Minnesota and southwestern Wisconsin, small-town residents complain about the noise and dust from mining and hauling frac sand, the crush-resistant round-grained silica sand forced down wells with water and various chemicals to free oil and gas. Wabasha residents just lost in their bid to derail a proposal to build a frac-sand rail shipping hub. Now, trucks will make as many as 600 trips a day to deliver sand from nearby mines for transport to North Dakota and Texas.
Of course, no one wants to live next to a drilling rig or sand mine. "But who wants to live next to anything?" asks Styles. "This is a fundamental problem in our society. Frac sand is just a microcosm. All these things we depend on -- long-distance transmission lines, all kinds of mines, factories, power plants -- none of us wants any of this stuff close to us."
The International Energy Agency, among others, recognizes that local conflict could jam up energy development. "Numerous hurdles need to be overcome, not least the social and environmental concerns associated with [gas] extraction," says the IEA, which has recommended "golden rules," such as establishing baseline data to measure environmental effects, giving priority to water protection, and encouraging environmental regulation.
That's small consolation, perhaps, if a company is drilling beneath your home, or if truck traffic rattles your windows. But the protests over water pollution, noise and dust overlook the truly huge consequences of fracking -- both the good and the bad.
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The good: Fracking is transforming the energy industry -- for the better.
Very recently, coal generated 53 percent of the nation's electricity. And coal certainly ranks among the worst possible energy sources when it comes to greenhouse-gas production. Not only that, but coal mining is itself destructive and dangerous. And burning coal produces particulates that are estimated to kill thousands each year, just in the United States.
What a difference a few years of fracking can make. According to the U.S. Department of Energy, cheap natural gas has reduced coal's share of the power-generation market from 43 percent to 37 percent -- in just the last year.
"The reduction in coal use is remarkable," says Styles. "The increase in shale-gas production is almost unprecedented. I can't remember any recent energy development that has come on this quickly. Renewables get so much attention, but the increase in production from shale gas dwarfs everything that's been added from wind and solar and all of that in the last few years."
In fact, since 2007, natural gas has added about three times as much electrical generation capacity as wind, solar and geothermal combined, says Styles. Why is that important? Because most of that generation by gas comes at the expense of coal.
And this is just in the United States, remember. Keep in mind that China consumes more coal than any other country and has the greatest demand for more energy. According to the IEA, by 2035 China will add more electrical generating capacity than currently exists in the United States and Japan combined. But China also appears to have great reserves of frackable natural gas and is eager to exploit them. Replacing some of that coal with natural gas would have a huge benefit to the world's climate.
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But here's the bad. This, too, is overlooked in the hyperlocal tussles over fracking.
A cheap, almost infinitely abundant fossil fuel is like a high-rate credit card -- handy in a pinch, but tough to pay off once you've come to rely on it.
Natural gas, after all, is still a fossil fuel. Burning it produces greenhouse gases. And even the IEA predicts that vigorous natural-gas development will only slow greenhouse-gas production. It won't stop or reverse it: "Natural gas cannot on its own provide the answer to the challenge of climate change."
So the question is this: Gifted with abundant, cheap gas, how will we ever transition to a low-carbon economy? As even the IEA acknowledges, abundant cheap gas can make it hard for renewables to find traction in a competitive market. And with no worries for energy, will countries such as the United States do even less than they have so far to find alternatives to fossil fuel?
Clearly, a solution will have to come from a combination of greater efficiency, conservation, and new energy technology, all helped along by some measure of subsidies for clean energy and disincentives for fossil fuels.
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Styles is pinning his hopes on technology. Current renewables aren't ready yet to replace fossil fuels, even with incentives. "We need a new generation of these things," he says. "That will take time. In the meantime, to keep our economy going, we need oil and gas. All of a sudden, we've got this tremendous bonanza of shale gas. This is a tremendous opportunity. The timing is fortuitous. This stuff can buy us the time that we need to develop the renewable technologies that are really going to do the job."
We need something that is obviously better and cheaper than the technology it replaces -- something that will have the transforming effect of kerosene replacing whale oil, of cars superseding horse-drawn wagons, of natural gas displacing coal. "Look at how rapidly the iPhone has taken over that segment of communications," says Styles. "You need that kind of dynamic, and I think technology will deliver that.
"People are ingenious," he says. "The idea that we would never be able to come up with a renewable-energy technology that could beat fossil fuels at their own game -- I think that's just selling people short."
As one oil industry wag said, the Stone Age didn't end because we ran out of stones. It ended because we found something better. And the same will be true of the fossil-fuel age.
But until we do find that something better, we have to buy time. Fracking -- along with sensible incentives, conservation and measured use of existing renewables -- will help.
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Greg Breining writes about science, nature and travel. He is the author of "Paddle North: Canoeing the Boundary Waters-Quetico Wilderness" and "Wild Shore: Exploring Lake Superior by Kayak."