Curbing Emissions Won't Be Enough

Cost is unknown, but a back-of-the-envelope calculation yields $80 to $100 per ton of carbon captured. That compares to $25 or so per ton that proponents of a carbon tax believe would deter emissions enough to stabilize the atmosphere, and as much as $75 per ton under some proposed cap-and-trade systems. But Lackner believes "it's worth looking at things that start out even five times too expensive." The IPCC, in a 2005 report on carbon capture and storage, concluded that it "has the potential to reduce overall mitigation costs and increase flexibility" in reducing greenhouse gases.

Even cheaper than drawing carbon dioxide out of the atmosphere is capturing it from power plants before it heads for the sky. GreenFuel Technologies Corp., in Cambridge, Mass., has invented a process for treating power-plant exhaust to remove a large fraction of the CO₂. The basic technology is 3.5 billion years old—that's when organisms first began photosynthesizing—and all it takes is a greenhouse and a trough filled with algae. A prototype is under construction at a 1,000-megawatt natural-gas-fueled power plant outside Phoenix run by Arizona Public Service. Built to full capacity—which would require about 8,000 acres—it could absorb as much as 80 percent of CO₂ emissions during daylight hours. With ethanol or biodiesel as byproducts, an algae installation could actually be a profit center, says GreenFuel CEO Cary Bullock.

The U.S. Department of Energy is working on ways to grab CO₂ from coal burned for electricity. Existing technology can reduce CO₂ emissions from coal-fired or natural-gas power plants by 80 to 90 percent, estimates the IPCC. That translates to an extra penny to a nickel per kilowatt hour of electricity (now 3 to 6 cents). But scientists at the National Energy Technology Laboratory in Pittsburgh, the lead DOE center for carbon capture and storage, think they can slash that to an added cost of no more than 10 percent, says Sean Plasynski, who manages the lab's carbon program. Energy efficiency and some renewables are cheaper now, but if the climate begins to tip out of control, then carbon capture and storage can provide a planet-saving insurance policy.

Earth has no shortage of places to stow the stuff, starting with depleted oil and natural-gas fields as well as the deep ocean. By one estimate, the storage capacity exceeds 545 billion tons of carbon, or 70 years' worth at current emissions levels. There are three commercial projects already, one off Norway in the North Sea, one in Canada and one in Algeria, each storing 1 to 2 million tons of CO₂ a year. The DOE lab plans test injections of 1,000 to 500,000 tons at 25 sites in the United States.

If the world had gotten serious about controlling greenhouse emissions in ... well, take your pick: in 1988, when NASA climatologist James Hansen testified before Congress that that summer's heat wave and drought were signs of global warming; in 2001, when the National Academy of Sciences told the Bush administration that human-induced climate change was underway and could be severe, we wouldn't have to think about strewing giant carbon-sucking towers across the land. But it didn't, so we do.

© 2007