Removing CO2 from air not viable technology, study concludes

A committee of 13 experts – led by Princeton engineer Robert Socolow and BP chemist Michael Desmond – has issued a report under the auspices of the American Physical Society (APS) suggesting that technologies for removing carbon dioxide directly from the air are unlikely to offer an economically feasible way to slow human-driven climate change for several decades.

Socolow, a professor of mechanical and aerospace engineering at Princeton, said of the report:

We humans should not kid ourselves that we can pour all the carbon dioxide we wish into the atmosphere right now and pull it out later at little cost.

The group looked at technologies known as Direct Air Capture (DAC), which would involve using chemicals to absorb carbon dioxide from the open air, concentrating the carbon dioxide, and then storing it safely underground.

In essence, the committee found that such a strategy would be far more expensive than simply preventing the emission of the carbon dioxide in the first place. Making optimistic assumptions about initial DAC technologies, the committee concluded that, from the evidence it had seen, building and operating a system would cost at least $600 per metric ton of carbon dioxide removed from the atmosphere for a system that could work today. In comparison, removing carbon dioxide from the flue gas of a coal-fired power plant would cost about $80 per ton.

As a result, the group concluded, DAC is not likely to become worthwhile until nearly all the significant point sources of carbon dioxide are eliminated.

Socolow said:

We ought to be developing plans to bring to an end the carbon dioxide emissions at every coal and natural gas power plant on the planet.

Beyond using electricity more efficiently, one option is to modify plants so their emissions are kept from the atmosphere, he said. Experts call this sort of modification carbon capture and storage, or CCS. It involves separating and compressing CO2 from the power plant exhaust and storing it underground. CCS technology is also largely unproven, although tests are ongoing. Socolow said yet another option is to shut down plants entirely and replace them with low-carbon alternatives. He said:

We don’t have to do this job overnight. But the technologies we studied in this report, capable of removing carbon dioxide from the air, are not a substitute for addressing power plants directly.

The possibility of using DAC has arisen in policy discussions that contemplate a so-called “overshoot” strategy in which the target level of carbon dioxide in the atmosphere is exceeded and then reduced later through use of some air capture technology. In its report, the group noted:

No demonstration or pilot-scale DAC system has yet been deployed anywhere on earth, and it is entirely possible that no DAC concept under discussion today or yet to be invented will actually succeed in practice. Nonetheless, DAC has entered policy discussions and deserves close analysis.

Socolow noted that while the contents of the report serve as a warning against complacency, the experience of developing the report offers grounds for optimism:

The message of hope is that smart scientists and engineers are getting more and more interested in energy and climate problems.

The committee that worked on this problem included both senior researchers and researchers starting their careers, and both industry experts and academics. The review process elicited contributions from 30 to 40 others. Everyone was a volunteer. Leading this project convinced me that scientists and engineers are poised to provide many creative strategies to reduce the risks of dangerous climate change.

Bottom line: An American Physical Society study – led by Princeton engineer Robert Socolow and BP chemist Michael Desmond – concluded that removing CO2 from the air using Direct Air Capture (DAC) technology would not be a viable option until all significant point sources of CO2 have been modified or eliminated.

Prior to this, the possibility of using DAC has arisen in policy discussions that contemplate a so-called “overshoot” strategy in which the target level of carbon dioxide in the atmosphere is exceeded and then reduced later through use of some air capture technology. Socolow spoke of another technology to reduce carbon emissions at the sites of power plants. This technology – called carbon capture and storage, or CCS – is also in the development stage. CCS involves first capturing the CO2 emitted from power plants and then storing that CO2 underground.

Via Princeton

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