Burning coal provides half the electricity in the U.S. and one third of greenhouse gas emissions worldwide. Capturing that carbon dioxide and storing it will be essential if climate change induced by such pollution is to be averted, according to reports from the U.N. Intergovernmental Panel on Climate Change and the Massachusetts Institute of Technology. Dubbed carbon capture and storage (or carbon sequestration), such technology will be fully demonstrated for the first time near Mattoon in southeastern Illinois, the FutureGen Alliance (a public–private partnership to build a prototype clean-coal plant) announced.

"[Mattoon] has a reliable and assured water source. It has excellent geologic structure and conditions for carbon sequestration," says Lawrence Pacheco, a spokesman for the alliance of 14 of the largest coal burners and miners in the world, including American Electric Power in Columbus, Ohio, Australia-based BHP Billiton and China Huaneng Group headquartered in Beijing. "The goal is to break ground in 2009 and be operational in 2012."

The $1.5 billion power plant is expected to produce 275 megawatts of electricity by turning coal into gas, thereby removing impurities including CO2, and burning the resulting pure gas to turn turbines to produce power. Some of the power generated would be used to compress the CO2 and pump it deep underground to be permanently stored in saline aquifers. "It will never come out," says geologist Susan Hovorka of the University of Texas at Austin, who has been conducting carbon sequestration feasibility experiments. "It's moving through the tiny pores between the sand grains and it gets smeared, like grease on a tie."

Hovorka's initial experiments at an oil field northeast of Houston have shown that the CO2 behaves as expected, remaining trapped in the geologic formation. But it does have impacts, such as leaching out minerals in the rocks and corroding well equipment. "If you put undiluted weak acid into your plumbing, it will eat holes in it," Hovorka notes. "We observed that and it's not unexpected."

But despite some commercial demonstrations of such carbon sequestration technology, largely to help recover more oil from depleted fields, none have approached anywhere near the scale necessary to significantly impact the 9.3 billion metric tons of CO2—and rising—emitted every year from burning coal. The largest such project, the Sleipner West gas field under the North Sea, injects roughly one million metric tons of CO2 per year. "The issue on the sequestration side is making sure one can do it on a very large scale," says M.I.T. physicist Ernest Moniz. "Gasification looks today to be the lowest-cost option with carbon capture [but] there is no plant that integrates gasification with capture and sequestration."

The FutureGen power plant aims to fill that hole but has struggled with delays and mounting costs as the materials to build such a power plant become more expensive. The FutureGen Alliance therefore decided to announce the siting of the proposed plant over the objections of its primary government backer, the U.S. Department of Energy (DOE), which concurrently announced plans to demonstrate the feasibility of carbon sequestration in the deep geology of the region by injecting one million metric tons of CO2. "As the [DOE] has discussed with the FutureGen Alliance for the past several months, projected cost overruns require a reassessment of FutureGen's design," James Slutz, DOE's acting principal deputy assistant security for fossil energy, said in a statement.

"The Alliance has been sticking to a very aggressive schedule and timeline. They wanted to stick to that," Pacheco says. "They felt it was appropriate and important to make this announcement."

Given the scope of the climate change challenge, moving forward quickly is key. "Unless we get confidence for large-scale sequestration in a decade, it's going to be extremely difficult to get what we need by mid-century," Moniz says. "It's like a mortgage. It gets us out of the problem in the 21st century."