In Iceland, scientists are transforming carbon dioxide into rock, cleaning the air of harmful emissions that cause global warming. The technology imitates a natural process that can take thousands of years, injecting CO2 into porous basalt rock where it mineralizes, catching it forever.

"With this method, we have actually changed the time scale dramatically," says geologist Sandra Osk Snaebjornsdottir. Snaebjornsdottir is working on Iceland's CarbFix project with researchers and engineers from utility company Reykjavik Energy, the University of Iceland, France's National Centre for Scientific Research (CNRS), and Columbia University.

In Iceland, a country of geysers, glaciers, and volcanoes, at least half of the energy produced comes from geothermal sources. That's a goldmine for CarbFix researchers, who've turned the Hellisheidi geothermal power plant; one of the world's biggest-into their own laboratory. The plant, located on the Hengill volcano in southwestern Iceland, sits on a layer of basalt rock formed from cooled lava and has access to virtually unlimited amounts of water. The plant pumps up the water underneath the volcano to run six turbines providing electricity and heat to the capital, Reykjavik, about 30 kilometers away. The CO2 from the plant is meanwhile captured from the steam, liquified into condensate, then dissolved in large amounts of water.

"So basically we are just making soda water out of the CO2," says project director Edda Sif Aradottir.

The water is piped several kilometers to an area where grey, igloo-shaped domes dot a lunar-like landscape. Here the water is injected under high pressure into the rock 1,000 meters under the ground. The solution fills the rock's cavities and begins the solidification process-a chemical reaction that occurs when the gas comes in contact with the calcium, magnesium, and iron in the basalt.

"Almost all of the injected CO2 was mineralized within two years in our pilot injection," Snaebjornsdottir says. Once the CO2 is turned to rock, it's pretty much captured there for good.

"If you have a volcanic eruption...and you heat up the rock to very high temperatures, then some of the minerals will break down and maybe dissolve in water," says University of Iceland geochemist Sigurdur Gislason. But, he noted, "this is the safest and most stable form of storing carbon". The last volcanic eruption here was a thousand years ago.

The CarbFix project reduces the plant's carbon dioxide emissions by a third, which amounts to 12,000 tons of CO2 captured and stored at a cost of about 25 dollars a ton. By comparison, Iceland's volcanoes spew out between one and two million tons of carbon dioxide each year.

The main drawback of the method is that it requires large volumes of desalted water, which, while abundant in Iceland, is rare in many other parts of the planet. Around 25 tons of water are needed for each ton of carbon dioxide injected. "That is the Achilles' heel of this method," says Snaebjornsdottir.

"I agree that the process uses a lot of water, but we gain a lot by permanently getting rid of CO2 that otherwise would be floating around the atmosphere," says Aradottir.

Experiments are currently underway to adapt the method to saltwater.