Editor's Note: This is the fifth in a series of five features on carbon capture and storage, running daily from April 6 to April 10, 2009.

Human activity results in the emission of some 30 billion metric tons of climate change–causing carbon dioxide (CO2) per year. About half of the greenhouse gas is absorbed by the world's oceans and plants, among other natural processes, but the rest lingers in the atmosphere for a century or more, driving up annual CO2 concentrations by around two parts per million (ppm).

Those atmospheric concentrations have climbed from roughly 280 ppm in the 18th century before the widespread burning of fossil fuels to 386 ppm today—and continue to rise. According to the Natural Resources Defense Council (NRDC), the coal-fired power plants built or planned since the turn of the 21st century will emit more carbon dioxide than all human coal-burning since the dawn of the Industrial Age: 660 billion metric tons over the next 25 years versus 524 billion metric tons emitted between 1751 and 2000.

"The next 25 years of investment would produce 26 percent more emissions than all previous human use of coal," says George Peridas, a mechanical engineer and scientist at NRDC in San Francisco. "This is a massive legacy and we cannot afford to let that happen."

Environmental groups like the NRDC, Environmental Defense Fund (EDF), Union of Concerned Scientists, and Clean Air Task Force (CATF) are pushing lawmakers to implement the kinds of policy—such as a cap-and-trade scheme to limit CO2 emissions—that would lead to widespread to adoption of  carbon capture and storage (CCS) technology.

"Environmentalists are talking about coal not because we love coal," says EDF's director of business relationships Mark Brownstein. "It's because we have to deal with coal in order to achieve the kind of CO2 reductions we need to make in the time frame we need to make them."

Most environmental groups agree that global greenhouse gas emissions must be reduced by at least 80 percent below 1990 levels by mid-century, a goal also shared by the Obama administration. But they differ on how that can be achieved. The Sierra Club and Greenpeace, for example, oppose CCS technology, preferring to push for more power derived from renewable resources, such as wind and solar energy.

CCS supporters, however, believe the technology is vital to reducing emissions quickly. "If we don't address the problem of coal, it's game over for climate change," says John Thompson, director of the coal transition project for CATF. The NRDC, for example, supports paying utilities $90 for every metric ton of CO2 buried at the first three gigawatts worth of coal-fired power plants with full CCS.

And that's because CCS is expensive. Today, three types of technology can capture CO2 at a power plant. One, as at Schwarze Pumpe in Germany, involves the oxyfuel process: burning coal in pure oxygen to produce a CO2-rich emission stream. The second uses various forms of chemistry—in the form of amine or ammonia scrubbers, special membranes or ionic liquids—to pull CO2 out of a more mixed set of exhaust gases. The third is gasification, in which liquid or solid fuels are first turned into synthetic natural gas, the most common being integrated gasification combined cycle (IGCC) technology; CO2 from the conversion of the gas can be siphoned off.

The primary problem with all of them is cost. Simply put, it costs money—and energy—to capture the CO2, ranging from as little as $5 a metric ton at natural gas projects like In Salah in Algeria to more than $90 a metric ton for certain gasification technologies. "The majority of cost for CCS is the first 'C': capture," says research engineer Howard Herzog at the Massachusetts Institute of Technology (M.I.T.).

The U.S. Department of Energy (DoE) estimated in May 2007 that a new power plant burning pulverized coal and equipped with amine scrubbers to capture 90 percent of the CO2 would make electricity at a cost of more than $114 per megawatt-hour (compared to just $63 per MWh without CO2 capture). A similar integrated gasification combined cycle (IGCC) plant—in which coal is turned to gas before being burned—capturing the same amount would produce electricity for roughly $103 per MWh. For the consumer, the extra cost of carbon capture would therefore amount to about $0.04 a kilowatt-hour.

The DoE hopes to bring that price down. "In terms of total cost, they want to shoot for $10 per metric ton of CO2," says CO2 sequestration project leader Rajesh Pawar of Los Alamos National Laboratory in New Mexico. "We are closer to the $50 per ton range right now."

Governments and utilities around the world are beginning to make plans to build more such expensive power plants. Vattenfall will expand the Schwarze Pumpe operation and convert several commercial boilers in power plants such as Janschwalde in Germany and Nordjylland in Denmark for CCS by 2015, according to Vattenfall's CCS spokesman Staffan Gortz. Statoil Hydro is building a CCS research site at its Mongstad refinery in Norway and France's Total has retrofitted a natural gas-burning power plant in Lacq with oxyfuel technology. And Australia and China are both building what will become zero-emissions coal-fired power plants using IGCC, dubbed ZeroGen and GreenGen, respectively.

"[China] is adding about one [coal] gasifier a month and has been doing so for four years," CATF's Kurt Waltzer says. "Since all of those gasifiers are in the business of making chemicals, fuels and fertilizers, they're all doing carbon capture. And what I suspect is China is doing more CO2 capture than anyone else. But all of that is being vented."

The Obama administration may even resurrect the FutureGen project—a 275 MW IGCC power plant that would capture 90 percent of its greenhouse gas emissions; the Bush administration had canceled it because of spiraling costs (which may have been miscalculated). The DoE has also offered at least $8 billion in loan guarantees for coal-fired power plants with CCS.

As a result, commercial CCS projects are springing up in the U.S. as well. Duke Energy is spending $2.35 billion to build a 630-MW IGCC power plant in Edwardsport, Ind. that may become the first commercial CCS project in the country—although it would be designed to capture only about 18 percent of the CO2 it will generate in 2013. "It is our goal to make this one of the first demonstrations of CCS at a working power plant," says Angeline Protogere, a Duke spokesperson. "Coal powers about half the nation's electricity and we have to find ways to burn it cleanly."

Of course, such a demonstration plant will not address some of the other issues vilifying coal use, such as mountaintop-removal mining to get at coal seams or the toxic coal ash left over after burning. And all (or nearly all) of the greenhouse gas would need to be captured for a coal-fired power plant to be climate-friendly. But IGCC is capable of removing 90 percent or more of the CO2. "Our request is to look at 18 percent capture and sequestration," Protogere says. "That doesn't preclude going back and asking for a higher level later on."

Duke is not alone. American Electric Power will begin capturing just over 3 percent of the 8.5 million metric tons of CO2 emitted by its 1,300-MW Mountaineer Power Plant in West Virginia later this year and injecting the CO2 nearly two miles (3.2 kilometers)  underground. The Erora Group plans to build a 630-MW IGCC power plant with CCS dubbed Cash Creek in Henderson County, Ky. Summit Power has proposed to build a 170-MW IGCC power plant in West Texas that would capture 80 percent of its CO2 emissions. BP and Southern Company have projects as well.

But previous plants, such as two proposed by the utility NRG in New York and Delaware, have fallen by the wayside. They were killed by the high cost of the technology and a lack of federal policy—a cap-and-trade program, a carbon tax or some other mechanism effectively setting a price on CO2 pollution—to make them economically feasible, notes Caroline Angoorly, head of environmental markets at JP Morgan Chase, who formerly lead development of these projects at NRG.

Nevertheless, Oklahoma-based Tenaska is planning for two plants. One $3.5-billion plant in Taylorville, Ill., would gasify the high-sulfur local coals before capturing at least 50 percent of the CO2. Another $3.5-billion plant planned for Sweetwater, Tex., would burn pulverized coal to generate 600 MW of electricity while capturing its 5.75 million metric tons of emissions postcombustion with amine or ammonia scrubbers or, possibly, with advanced membranes that separate CO2 from other flue gases.

If postcombustion capture can be demonstrated commercially, "then the market for those existing coal-fired power plants is very large. There are at least two billion tons of domestic emissions from pulverized coal power plants," says Greg Kunkel, Tenaska's vice president for environmental affairs. "You can't tackle the larger problem [of climate change] unless you deal with those plants in some way."

And CCS can be equally well applied to other CO2-intensive industries: cement production, steel making and aluminum smelting, among others. They can even be combined with the burning of plant matter to create a "carbon negative" fuel that when burned removes more CO2 from the air than it puts in.

"CCS is [also] about these really large natural gas fields in Indonesia and Malaysia that have as much as 50 percent CO2 by content. It's just like Sleipner but even higher concentrations that are going to vent the CO2 to the atmosphere for want of $20 per metric ton of CO2," says engineer James Dooley, senior research scientist at the Pacific Northwest National Laboratory. "[Coal] is the biggest market but, in the near term and in the developing world, CCS can reduce emissions from other sectors—and that has benefit."

But it is going to take time: research engineer Howard Herzog of the Massachusetts Institute of Technology estimates that the first new CCS coal plant in the U.S. won't be completed before 2015. "We may have by 2020 a handful, maybe even close to 10," he says. "If your goal is 80 percent cuts [in CO2 emissions] by 2050, then it's not big enough."

And it is also going to take money—at least $20 billion over the next decade, according to International Energy Agency estimates. Even industry group the American Coalition for Clean Coal Electricity estimates it will cost $17 billion for CCS to be available by 2025.

"We're going to have to do it, the same as adding wind, solar, nuclear power and conservation," says Julio Friedmann, leader of the carbon management program at Lawrence Livermore National Laboratory. "It's a climate imperative so let's get on with it."

After all, "for every five years of inaction, it requires an extra gigaton of reductions," says Gardiner Hill, manager of technology and engineering for CCS at BP's alternative energy arm. "Unless we get started now, we don't get the advantage of CCS and the emission reductions we need."