Giant carbon vacuums could cool Earth

Tall metal structures would scrub the greenhouse gas from the air.

from the April 19, 2007 edition

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As for cost, in the long run, Lackner foresees a price of $30 per ton of CO2 captured, about 25 cents on the gallon at the pump. "There is actually something positive to be said with 'Look, you don't have to change anything; you just have to pay the bill,' " he says.

The major cost would be in the chemistry, says Lackner. He initially proposed sodium hydroxide, or lye, which, when wet, snatches CO2 from the atmosphere. (Global Research Technologies claims to have pioneered another method employing a compound much less caustic than lye, says company president Wright.) Separating the CO2 is the costly part, says Lackner, requiring temperatures of 900 degrees C. But this type of cost is not without precedent, he points out. For every unit of energy used at your home's electrical outlet, three have been spent at the plant, for example. The real issue, says Lackner, is not the energy consumed but the CO2 emitted. He estimates that for every ton of CO2 he captures, he'll generate another 0.4 ton. But because this process will take place at a plant, where emissions are concentrated relative to air, it will be easily captured.

Robert Williams, a research scientist at Princeton University in New Jersey, thinks Lackner's research is important for the long term, but short-term steps are still needed. And there are possibilities in using what is already available. Instead of burning only coal at electricity plants, for example, combust biomass as well. Fast-growing and easily cultivable plants like prairie or switch grasses could be used. They've already captured CO2 from the atmosphere, and by capturing the CO2 at the flue, you end up with net negative emissions. "Mother Nature knows how to take the carbon dioxide out of the atmosphere," he says. "We can put it underground."

But Gary Rochelle, professor of chemical engineering at the University of Texas, Austin, thinks projects like Lackner's are a distraction at a critical time. More effort should be made toward retrofitting older plants, he says. And more resources should be directed toward perfecting the technology of coal-gasification plants, which allows for easier CO2 capture. "There are other lower hanging fruit alternatives to deal with the carbon dioxide problem that we need to do now," he says.

 

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