Direct air capture of CO2 to fight global warming is too expensive to be feasible
December 09, 2011

Using existing technology to "scrub" carbon dioxide directly from the atmosphere is far costlier than capturing emissions directly from the smokestacks of coal-burning power plants, reports a paper published this week in the Proceedings of the National Academy of Sciences.

The study, authored by researchers from Stanford and MIT, found that air-capture of CO2 would cost 10-20 times that of carbon capture from "large centralized sources such as power plants, cement plants, fertilizer plants and refineries." The current cost of such capture at centralized sources is $50-100 per metric ton.

"Direct air capture sounds great in theory," said Stanford energy and environmental researcher Jennifer Wilcox in a statement. "In reality, though, a lot of energy is required, and using fossil-based energy sources to capture and regenerate the carbon dioxide could readily result in more carbon dioxide entering the atmosphere than is captured.

Nigel Sizer, a scientist at the World Resources Institute (WRI), wryly noted that the world already has a cheap way to absorb carbon dioxide directly from the air: trees. Tropical forests absorb more than a billion tons (3.7 billion tons of CO2) of carbon per year.
"For direct air capture to be feasible, carbon-free energy, such as solar or wind, is required. But that carbon-free energy would be used more cost effectively to replace CO2-emitting power plants."

The researchers note that concentrations of CO2 in the air are 300 times lower than in the smokestack of a coal-fired power plant.

"The lower atmospheric concentration makes removal from air much more expensive than removing CO2 directly from the flue gases at the source," Wilcox said.

While technology could help make scrubbers more efficient, the economics seems to still favor targeting major emissions sources.

"It's possible to come up with air-scrubbing systems that appear to be feasible. But if you look at empirical data – how engineers look at this, with real-world efficiencies – you don't find many reasons to be hopeful," explained said co-author Howard Herzog of the MIT Energy Initiative.

The study concludes the best path for reducing atmospheric carbon dioxide is to directly cut emissions.

"Ultimately, society needs to move completely away from carbon-based energy resources," said Wilcox.

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CITATION: (December 09, 2011).

Direct air capture of CO2 to fight global warming is too expensive to be feasible.