The Science of Curbing Emissions

The Science of Curbing Emissions

Like many people who are scrambling for ways to stave off climate disaster, Klaus Lackner is thinking trees. But not the kind with green leaves and roots, and certainly not the sweet little specimens that "carbon offset" purveyors hawk as a way to balance out the carbon dioxide emitted when you tool around town in a Hummer. Lackner, a professor of geophysics at Columbia University, is helping to design a synthetic tree. It would stand roughly 1,000 feet tall with a footprint a little bigger than a football field, and be crisscrossed with scaffolding holding liquid sodium hydroxide, which is best known as lye. For in addition to cleaning drains, sodium hydroxide has a chemical property that promises to be in great demand if, as seems likely, the nations of the world fall short of stabilizing the atmosphere's load of greenhouse gases: it sucks carbon dioxide out of the air.

A new phrase has emerged in the debate over climate change: managing the unavoidable. To grasp "unavoidable," consider a few simple numbers. Before the Industrial Revolution, the atmosphere held 280 parts per million of carbon dioxide (CO2). We are now at 380 and climbing. Since the 1992 Rio Convention on Climate Change, which obligated its signatories (including the United States) to inventory their greenhouse-gas emissions and devise plans to control them, global emissions have risen from 6 billion metric tons of carbon to 7.3 billion in 2003, 7.85 billion in 2005 and an estimated 8 billion last year, says Gregg Marland of Oak Ridge National Laboratory. Combine that pathetic record with another number: molecules of carbon dioxide stay in the atmosphere as long as 200 years; yes, carbon dioxide molecules belched out by Model Ts are still up there. As a result, "incremental reductions in CO2 emissions" as called for by the 1997 Kyoto Treaty and legislation pending in Congress "will not stabilize atmospheric CO2 levels," argues climate researcher Wallace Broecker of Lamont-Doherty Earth Observatory, part of Columbia. "They only slow the rate of increase."

As we head toward 450, 550, even 750ppm this century—according to projections by the Intergovernmental Panel on Climate Change (IPCC)—environmental leaders are therefore getting serious about carbon capture and storage. The idea is to suck carbon out of the ambient air or—even more feasible—out of power plants where it's produced, and store it in the deep ocean or in depleted oil and natural-gas fields. The U.S. Department of Energy is spending $100 million this year for R&D on carbon storage, up from $1 million in 1997. Just before his death in 2006, Gary Comer, founder of Lands' End, funded a start-up company in Tucson, Ariz., called Global Research Technologies to develop ways to pull CO2 out of the air. In February, Sir Richard Branson, chairman of the Virgin Group, and Al Gore announced the creation of a $25 million prize for devising a way of, as Branson put it, "removing the lethal amount of CO2 from the Earth's atmosphere."

Gore's involvement was notable. Until recently, environmental activists viewed carbon capture and storage as an evil scheme (probably hatched by the Bush administration) to let SUVs and coal-fired power plants keep polluting. But with emissions rising and plans to cut them alarmingly slow to kick in—especially in China, which accounts for half the rise in emissions since 1992—"we are now facing a planetary emergency," Gore said in announcing the prize.

The growing interest in carbon capture also reflects the fact that the climate we have at 380ppm of CO2 is dire enough that even the inevitable 450ppm—perhaps 40 years away—looks scarier than it once did. Hurricane Katrina happened at 380. Glaciers are melting and coral reefs are dying at 380. The 2003 heat wave in Europe, which killed an estimated 35,000 people, happened at 380. The seas are rising at 380. Arctic sea ice is vanishing at 380; according to an analysis in the journal Science last month, by 2040 the Arctic may have zero summer sea ice. However you feel about polar bears not having floating platforms from which to hunt seals, the vanishing ice will shift wind patterns in a way that intensifies midlatitude storms, increasing wintertime precipitation over Western and Southern Europe, but reduces rainfall in the American West. Since 1998 that region has been mired in a historic drought. According to a study led by Lamont-Doherty's Richard Seager to be published in Science, the Dust Bowl drought of the 1930s "will become the new climatology of the American Southwest."

Enter Lackner's synthetic, carbon-sucking tree. It is only conceptual, but he calculates that an area of sodium hydroxide the size of a television screen (not a 103-inch plasma behemoth but the 20-inch diagonal that people found just fine once upon a time) would soak up an amount of carbon equivalent to what one American is responsible for emitting. Or, to use another comparison, one tree could absorb about as much as 15,000 cars emit. Paired with a windmill, the carbon-capture tree would generate about 3 megawatts of power, Lackner calculates, making the operation self-sufficient in energy. "The carbon-capture efficiency is better than a [living] tree," he says. "We can, with such a system, collect a significant fraction of the carbon from the air." Carbon capture from the air has the advantage of removing this pollutant no matter where it came from—cars, planes, factories, power plants. No other carbon-capture technology now on the drawing boards would work on moving sources, such as cars and planes.

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.

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