Coal is the most carbon-intensive of all fossil fuels: For every ton you burn, three tons of carbon dioxide are created. As everyone knows, CO2 is the main greenhouse gas responsible for heating up the planet. Globally, coal is responsible for about 40 percent of all CO2 emissions. In America we burn more than a billion tons of coal a year, mostly to generate electricity. A big coal-fired power plant typically emits as much CO2 in a single year as a million SUVs. China burns nearly twice as much coal as we do (although less than half as much per capita) and is erecting a new coal plant every ten days. In addition, rising oil prices are boosting demand for plants that can transform coal into liquid fuels like diesel. If the world’s appetite for coal continues unabated, the consequences are easy to predict: We’re cooked.

Fortunately, there’s a technological solution on the horizon. It’s called carbon capture and storage. On paper, it sounds simple. As coal is burned, remove the CO2 with a scrubber or other device, pressurize it into a supercritical liquid that’s roughly the consistency of oil, then pump it underground. Depleted oil and gas wells make good storage sites, as do deep saline aquifers 2,000 feet or so underground. You can even pipe the CO2 offshore and inject it under the ocean floor. In theory, the CO2 will stay buried in these spots for thousands of years, thereby allowing us to continue burning coal without trashing the earth’s climate. Indeed, the promise of this technology is at the heart of every discussion about “clean coal” these days, as well as the Bush Administration’s FutureGen initiative, the $1.7 billion coal plant the Energy Department is building in partnership with a dozen or so electric power and coal companies. FutureGen, which will convert coal into electricity and hydrogen, the much-hyped fuel of the future, is scheduled to go online in 2012 (although there are doubters–within the power industry, it’s dubbed by some as “NeverGen”). Politically the point of FutureGen is to make clear that this dirty black rock–the very symbol of nineteenth-century industrialism–can be spiffed up for the twenty-first century.

It’s a hopeful story, and one that any 2008 presidential candidate who wants to carry Big Coal swing states like Illinois, Pennsylvania, West Virginia, Wyoming and Ohio is sure to embrace. And why not? It would certainly make America’s energy problems easier to solve if “clean coal” was more than a PR slogan. As high-profile, politically ambitious coal boosters like Montana Governor Brian Schweitzer never tire of pointing out, America is “the Saudi Arabia of coal.” Oil wells in the Middle East may be running dry, but America is blessed with a 250-year supply of black rocks (at current rates of consumption–and never mind the environmental havoc caused by getting that coal out of the ground). If the CO2 problem can be solved, the argument goes, energy independence won’t be far behind.

Unfortunately, this story is more complex than the coal boosters suggest. Squirting CO2 into old oil wells is no big deal–the oil and gas industry does it all the time to help push out stubborn reserves. But capturing billions of tons of CO2 from power plants and pumping it underground–and doing it safely, on a massive global scale, both in the West and the developing world–is another thing altogether. And the politics of this undertaking is even more daunting than the technology. Big Coal is an industry that has thrived for 100 years by fighting off change, isolating itself from market forces and generally depending on political muscle to get its way. The notion that this industry will embrace this challenge is akin to believing your 70-year-old gin-splattered uncle when he tells you he’s taken his last drink. Getting him to sober up can be done, but it requires radical intervention.

The technological issues involved with capturing and storing CO2 are not trivial. Unlike other pollutants, like sulfur dioxide and nitrogen oxides, which are relatively easy to remove with a scrubber on the smokestack of a pulverized-coal plant, CO2 emerges in a diffuse stream that’s difficult to filter. In fact, nobody has figured out a good way to capture CO2 from a smokestack that isn’t prohibitively expensive and doesn’t reduce the efficiency of the plant by as much as 30 percent. Other possibilities, such as burning the coal in pure oxygen, may someday make the job of capturing CO2 easier, but this technology is nowhere near ready for prime time.

It’s more likely that capturing CO2 will require shifting to an entirely new kind of plant, called IGCC, or “integrated gasification combined cycle,” which uses heat and pressure to transform coal into a synthetic gas that can then be burned to generate power. The advantages of IGCC are many, including the fact that CO2 can be removed during the gasification process, when the volume of the gas is much smaller than it is when it is released up the stack of a conventional coal plant. The disadvantage of IGCC is that it is new and different, and this is an industry that fights anything new and different. In any case, the important point is that the ability to capture CO2 is likely to apply only to new coal plants. Retrofitting the thousands of existing coal plants is a pipe dream. If and when the world gets serious about dealing with global warming, these plants will likely have to be bulldozed.

For the sake of argument, however, let’s assume a brilliant entrepreneur invents a cheap, efficient way to capture CO2 from existing coal plants (lots of people are working on it). And let’s put aside the fact that before it can be buried, the CO2 must be compressed into a supercritical fluid–not hard to do, but the process can use up to 10 percent of the energy created by burning the coal in the first place. The important question is: Can we bury enough to make a difference?

According to the popular “wedge theory” of Princeton professors Stephen Pacala and Robert Socolow, capturing and burying 1 billion tons of carbon from coal plants by 2050 would contribute one-seventh of the reduction they estimate we need to achieve to stabilize the earth’s climate. One billion tons of carbon is equivalent to 3.6 billion tons of CO2, or more than twice the annual CO2 emissions from coal plants in America today. What would it mean to capture and bury 3.6 billion tons of CO2?

There are three carbon capture and storage projects in operation in the world right now (all are used for enhanced oil and gas recovery; storing the CO2 is secondary). The most significant is in Sleipner, Norway, where Statoil has been pumping 1 million tons of CO2 into a reservoir beneath the North Sea each year since 1996. It is an enormous engineering project, deploying one of the largest offshore platforms in the world. But compared with the engineering effort that would be required to stabilize the climate, it’s inconsequential. It would take ten Sleipner-size CO2 storage projects to offset the annual emissions of a single large coal plant.

Lynn Orr, a petroleum engineer who directs the Global Climate and Energy Project at Stanford University, estimates that to store a billion tons of carbon underground, the total inflow of CO2 would be roughly equal to the total outflow of oil and gas today. The magnitude of the engineering challenge is not necessarily an argument against doing it. But it is an argument against seeing underground carbon storage as a simple, easy solution to CO2 emissions from coal.

It’s unlikely anyone will be laying thousands of miles of CO2 pipelines anytime soon, however. Until a significant cost is attached to dumping greenhouse gases into the atmosphere, no corporation will go to the trouble and expense of burying much CO2. In the United States most studies suggest that until the price hits $25 to $30 per ton of CO2 emitted (either through a straight carbon tax or a market-based cap-and-trade program similar to the one now used to reduce sulfur dioxide emissions from coal plants), power companies will find it cheaper to continue dumping CO2 into the atmosphere than to try to capture and bury it.

Not surprisingly, for the past two decades Big Coal has worked hard to deny the existence of global warming and to undermine any legislation that would put a price on carbon. Today, even the dinosaurs of the industry know that carbon legislation is inevitable; the game now is to delay legislation and to make sure that when it does pass, the cost of carbon stays as low as possible for as long as possible. So get ready for years of talk about the promise of carbon capture and storage but very little action.

In fact, the prospect of carbon legislation has created a perverse incentive for big power companies like Dynegy and Wisconsin Energy to throw up another generation of old-style coal burners that offer little hope of ever capturing and burying CO2. The companies are betting that with the help of a little muscle in Washington, the emissions of these new plants will be grandfathered in by coming legislation. That loophole is relatively easy for Congress to close, however.

Far more complex is figuring out a policy that will drive power companies to begin capturing and storing CO2 in the decade or so before high carbon prices kick in. David Hawkins, director of the climate center for the Natural Resources Defense Council, advocates the creation of a CO2 emissions standard for coal plants, arguing that such a standard, modeled on a measure passed last year in California requiring electricity generators to meet the state’s goals for CO2 reductions, could be implemented quickly and would push coal burners to experiment with capture and storage today.

Big Coal has good reason to fear a crackdown on CO2. Coal’s ace in the hole has always been that it’s cheap. Of course, coal is cheap in the same way that fast food is cheap–because all the health and environmental costs are offloaded onto the public and not included in the bottom line. But when a price tag is attached to CO2 emissions, that calculation will change. A new study from MIT estimates that deploying carbon capture and storage will raise the wholesale price of electricity from new coal plants by 50 percent (this may be a conservative estimate–other studies have put the price nearly twice as high). If the price of coal-fired power increases 50 percent, a lot of people will ask, Why bother?

Venture capitalist Vinod Khosla, who is leading Silicon Valley’s charge into clean energy, believes the balance toward renewables is shifting quickly. “I think we’re at the beginning of a whole new innovation cycle,” says Khosla, adding, “If you’re a rational financial investor, and you did your homework, you wouldn’t fund a coal plant.”

The real wild card in this whole scenario, however, may be public opinion. Most Americans have never heard of underground CO2 storage, and it’s far from clear how they will feel about living above giant pools of CO2. The liquefied carbon gas is buoyant underground and can migrate through cracks in the earth and around old well heads, pooling in unexpected places. This is troublesome because CO2 is an asphyxiant–in concentrations above 20 percent it can cause a person to lose consciousness in a breath or two. At Mammoth Mountain, California, where CO2 naturally seeps up through the ground, skiers have died when they tumbled into CO2 pockets that had built up in hollows in the snow. In theory, you could enter a basement flooded with CO2 and because it’s an invisible, odorless gas, you wouldn’t know it was there. Also there’s the slight but not insignificant risk of a geyserlike eruption of CO2 from an underground storage facility, which in a populated area could be devastating.

Another public health concern is the release of toxic heavy metals. When CO2 is pumped into underground aquifers, it makes the water more acidic. Acidic water dissolves certain types of rocks, releasing minerals and nasty stuff like arsenic and uranium, which can then seep into drinking water.

Who will be the carbon police? For power companies CO2 is waste, and capturing and burying it is nothing more than high-tech garbage dumping. They will obviously be interested in getting rid of it as cheaply as possible. Given the coal and electric power industry’s history of regulatory abuse, making sure this is done safely and responsibly is going to require a new breed of watchdog. A related issue–and one that I’ve heard raised by a number of power industry CEOs–is liability. If a micro-seep of CO2 asphyxiates five girls having a slumber party in a basement in Illinois, who is going to be held accountable? Monitoring and verifying the integrity of CO2 storage is also important from the standpoint of actually solving the problem of global warming–what’s the point of going to the trouble and expense of pumping CO2 underground if it seeps back out a year later? Even tiny leaks undermine the value of burying carbon; some experts estimate that an annual leakage rate of 1 percent could add $850 billion per year to overall costs by 2095. On small-scale pilot projects, seepage can be monitored with various high-tech diagnostic tools, including 4-D seismic imaging. But if carbon capture and storage is going to be deployed on a global scale, these problems grow exponentially. “We don’t even believe China’s GDP numbers,” says Joe Romm, the author of Hell and High Water, a new book about global warming. “Who is going to be the certifying body that double-checks to make sure they’re storing as much CO2 as they say they are?”

In a world determined to tackle global warming, none of these problems are insurmountable. Nor are they an excuse to delay legislation that will drive big cuts in greenhouse gas emissions. Clearly, every ton of CO2 that is safely locked underground is a step in the right direction. But the notion that coal is the solution to America’s energy problems is a technological fantasy on par with the dream of a manned mission to Mars.

By all means, let’s praise innovative companies that take risks with new technology, and let’s boost federal funding for carbon capture and storage research–the more we know about the costs and risks of burying CO2 the better. But let’s not lose sight of the big picture here. Coal is the fuel of the past, not the future. The sooner we muster up the courage to admit that, the sooner the revolution can begin.