Both John McCain and Barack Obama have expressed support for a new type of coal-burning technology that would reduce its impact on the environment. Is clean coal really possible?

What is clean coal?
An oxymoron—for now, at least. The idea of clean coal is immensely appealing—especially on the political stump—because coal is relatively cheap, and America has so much of it. (As it happens, two of the biggest coal-producing states, Pennsylvania and Ohio, are “swing” states in this election.) At current consumption rates, the U.S. has enough coal to last more than 250 years. Coal, unfortunately, is the most carbon-intensive fuel we use. Worldwide, burning coal produces nearly 40 percent of carbon dioxide emissions, the chief contributor to global warming. The coal and electric power industries often use the phrase “clean coal” to refer to existing technologies that have taken the majority of sulfur dioxide, carbon monoxide, and nitrogen oxide out of emissions from coal-powered electric plants. But while smokestack scrubbers and other clean-coal applications have addressed the 20th-century threat of acid rain, they offer little defense against the 21st-century threat of climate change. That’s why some entrepreneurs and scientists are touting a new kind of clean-coal technology.

What is the new technology?
It’s called carbon capture and storage, or CCS. In theory, CCS could reduce CO2 emissions by as much as 90 percent. Essentially, the process involves capturing a plant’s carbon emissions before they escape into the atmosphere and then storing them where they can do no harm. But even proponents don’t expect the process to be commercially viable for at least a decade. And the development of storage facilities—and the means to transport CO2 to them—is enormously challenging. No such infrastructure currently exists.

Where would the CO2 be stored?
Scientists are researching a variety of options, from injecting large quantities of CO2 underground into depleted oil fields to burying it in sandstone beneath the North Sea. One study estimates that 300 years’ worth of emissions from Pennsylvania’s 79 coal-fired electricity plants could be stored in the state’s saline formations. Some geologists have even suggested that the gas could be injected into volcanic basalt, a common rock found beneath an 85,000-square-mile expanse of Western states; scientists theorize that the CO2’s interaction with basalt could turn the CO2 into a harmless mineral. No matter what form it took, CO2 storage would be daunting. The U.S. produces nearly 2 billion tons of CO2 annually from coal-fired plants, and questions remain about how stable the CO2 would be underground. Any leakage, of course, would defeat the whole purpose of storage.

Are there other obstacles?
Yes. Not only would it cost billions of dollars to build such plants, but the process of capturing carbon is itself incredibly energy-intensive, so it would dramatically lower the productivity of the power plants that use it. Proponents say the technology is viable—it just needs investment and a strong push from the federal government. “We’re not technologically ready to build all the infrastructure now,” says engineer Howard Herzog of the Massachusetts Institute of Technology, “but we know enough to start.”
Why isn’t clean-coal technology more advanced?
The desire for cheap power has trumped all other concerns. As a result, utilities and power companies have had little incentive to take on the cost of engineering and building new, state-of-the-art plants that would make environmentalists happy. Only a dozen coal-fired plants have been built in the U.S. since 1990, and none is “clean.” The picture is even less encouraging abroad. To provide electricity for their rapidly growing middle classes, China is powering up new coal plants at the rate of one a week, and India is not far behind. Neither country is deeply concerned about CO2 emissions, and the new plants remain a long way from “clean.” The same is true of new plants coming on line in Italy, Germany, Great Britain, and the Czech Republic.

Can existing coal-fired plants be turned green?
That appears to be extremely unlikely. Newer, so-called supercritical coal plants convert coal to energy about a third more efficiently than older plants do. But they still produce enormous amounts of CO2 emissions. And even if CCS technologies advance at a rapid pace, it won’t be easy or cheap to retrofit even the most recently built plants to capture their carbon emissions. That’s why many environmentalists and climate-change experts favor investment in other alternative energy technologies, such as wind and solar, rather than increasing the world’s reliance on coal. “Building new coal-fired plants is ill-conceived,” said James Hansen of NASA’s Goddard Institute for Space Studies. “We need a moratorium on coal now.”

So is clean coal a mere pipe dream?
Not necessarily. With many technologies competing to lead the way to a green future, and no obvious winner emerging, clean coal remains in the mix. Coal is not only cheap but plentiful. So figuring out how to make it clean would be quite a boon. By 2030, the nation’s electricity consumption will grow 40 percent, the U.S. Energy Information Administration estimates. Unless that demand is significantly constrained, the power will have to come from somewhere. “There is no silver bullet here,” said James Rogers, chief executive of Duke Energy. “What we need is more like silver buckshot, a lot of things working together.”

An inauspicious beginning
In 2003, the Bush administration launched a public-private consortium called FutureGen to create a first-generation commercial-scale CCS plant. Plans called for a 275-megawatt coal plant that would produce energy from gasified coal and then pump the plant’s CO2 emissions thousands of feet below ground into rock formations. The Department of Energy agreed to provide three-quarters of the estimated $1.8 billion cost. But because of its technical complexity and environmental sensitivity, progress on the project was slow. It took four years just to find a site for the plant, in Mattoon, Ill., and by then, building costs had risen sharply. Earlier this year, citing the mounting costs, the DOE announced it was pulling out of the project. The episode did little to reassure clean-coal skeptics. “It may not work in the end,” said Jeffrey Sachs, director of Columbia University’s Earth Institute. “And if it is not viable, the situation, with respect to climate change, is much more dire.”