Volcanic rocks deep beneath the sea off the coast of California, Oregon and Washington State might prove one of the best places to store the carbon dioxide emissions that are causing global warming, a new study finds. In fact, the very instability that causes earthquakes and eruptions adds an extra layer of protection to keep the CO2 from ever escaping.

The U.N. Intergovernmental Panel on Climate Change (IPCC) and other experts, including the G8 (Group of Eight) leaders of the world's richest nations, have called carbon capture and storage a critical tool in the fight against climate change. In essence, such technology catches the CO2 and other pollutants emitted when coal or other fossil fuels are burned. It is then compressed into a liquid and, theoretically, pumped deep beneath the surface to be permanently trapped.

Such technologies have been demonstrated on a small scale to enhance the recovery of oil from tapped out fields; pumping down the CO2 pushes up more of the black gold. But geophysicist David Goldberg of Columbia University's Lamont–Doherty Earth Observatory in Palisades, N.Y., and his colleagues found that pumping such CO2 into basalt rock beneath the ocean floor might be a better solution.

Specifically, liquid CO2 is heavier than the water above it at 8,850 feet (2,700 meters) or more under the surface, meaning any leaks would never bubble back into the atmosphere. Further, the CO2 mixes with the volcanically warmed water below the surface and undergoes chemical reactions within the basalt (the black rock created from rapidly cooling lava) to form carbonate compounds—otherwise known as chalk—effectively locking up the greenhouse gas in mineral form. The 650-foot (200-meter) layer of marine sediment on top of the basalt rock acts as yet another barrier. "You have three superimposed trapping mechanisms to keep your CO2 below the sea bottom and out of the atmosphere," Goldberg says. "It's insurance on insurance on insurance."

The researchers estimate, conservatively, that at least 229 billion tons (208 billion metric tons) of carbon could be stored in the basalt formations of the Juan de Fuca Plate 100 miles (160 kilometers) off the U.S. west coast in this way—or the equivalent of 122 years of all U.S. emissions of 1.9 billion tons (1.7 billion metric tons) annually.

It is unlikely that all of the CO2 emitted in the U.S. could ever be captured and transported—whether by pipeline or tanker—to the west coast for injection, but local coal-fired power plants might be able to take advantage of the formation.

"On the one hand you wouldn't want to bet the future of U.S. climate policy on it until one has done more work, but on the other hand it looks quite promising," says engineer M. Granger Morgan of Carnegie Mellon University, a carbon sequestration expert. "In contrast to CO2 injected in the ground, which is buoyant, in this case it won't be buoyant."

Such formations are also potentially accessible in many parts of the world, according to Goldberg, who is currently researching the global resource. The next step will be a small pilot project during which researchers plan to inject some CO2 into the undersea formation and see what happens—a process that will take at least three years. Also, colleagues in Iceland will begin pumping CO2 from a power plant into similar basalt formation later this year, but on land. "The volumes [of storage] we're talking about are huge and the problem is huge," Goldberg says. "The prize is very large here with this option. It's worth a serious look."