Mar 162012
 
English: Macro photograph of coca-cola bubbles...

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The idea of pulling carbon dioxide out of the atmosphere is a beguiling one.

Could it ever become real?

THOSE who worry about global warming have a simple answer to the problem. Simple in theory, that is: stop pumping carbon dioxide into the atmosphere. In practice that is rather hard to do. But there is another approach. Having put the stuff into the air, take it out.

One proven way of doing this is photosynthesis. Measures to nurture and expand the world’s forests come high on the agenda of environmental proposals. But new forests take up a lot of land. How about a high-tech alternative: capturing the CO2 from air by artificial means and tucking it away in the Earth’s crust?

Klaus Lackner, a physicist at Columbia University, started talking about this a decade ago. Peter Eisenberger, also of Columbia, and David Keith, until recently of the University of Calgary, in Canada, and now at Harvard, have taken up the idea as well. All three have formed companies aimed at doing it, with the help of some intrigued billionaires. Dr Lackner was patronised by the late Gary Comer, founder of Lands’ End, a large clothing company. Dr Eisenberger’s backer is Edgar Bronfman, whose fortune came from Seagram, a now defunct distiller. And Dr Keith has Bill Gates.

But there is a limit to what even an enthusiastic green billionaire can afford—and many observers think that air capture lies well beyond it. A report published last year by the American Physical Society (APS) put the cost of extracting and storing carbon dioxide using an air-capture system based on known technology at between $600 and $800 a tonne. That is about 80 times the current price of European carbon credits. At such prices it would take tens of trillions of dollars to deal with a year’s worth of carbon-dioxide emissions. And some think the APS’s estimates of costs are on the low side.

It was in large part to argue about that estimate that air-capture enthusiasts and their critics met in Calgary on March 7th-8th. The discussions were detailed, mostly civil, sometimes heated. They did not arrive at a meeting of minds, but they did demonstrate that the way people think about air capture is shifting. What was once seen as a way of tucking CO2 away for good is now increasingly thought of as a way of packaging it up for people willing to pay for it—including oil companies eager to sell more oil.

The billionaire boys’ club

Air-capture schemes revolve round a process of reversible absorption. First, a stream of air is run over the absorbing material in question, which pulls CO2 out of it. Then the absorber is processed to release the CO2, allowing the device to go back to work and the CO2 to be disposed of.

Dr Lackner’s version uses layers of Teflon or paper covered with a resin that absorbs carbon dioxide when dry and gives it up when moist. Dr Eisenberger’s proposal employs ceramic blocks similar to those found in a car’s catalytic converter. These, like Dr Lackner’s sheets, are coated with chemicals that take in and release carbon dioxide according to the circumstances. In Dr Eisenberger’s case, though, the crucial circumstance is temperature. The blocks absorb CO2 when they are cool and re-emit it when they are hot.

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