Direct air capture of carbon dioxide -- more and less than meets the eye

The American Physical Society released a report last week on direct air capture of carbon dioxide by essentially running ambient air over a chemical sorbent that binds the ambient carbon dioxide, thereby removing it from the air and preventing it from warming the planet. It has been pointed out that the advantage of such an approach is that unlike emissions reductions, it can be deployed unilaterally or by a "coalition of the willing" to reduce the ambient concentration of CO2, without having to worry so much about what China or other supposedly climate recalcitrants or doing, making it a "backstop technology." The APS report is somewhat skeptical, having found that the costs of direct air capture to be in the neighborhood of $600 per ton of CO2, but it is quite possibly much less, as University of Calgary researcher David Keith has estimated it to be only 50% more than post-combustion carbon capture and storage. In fact, Keith has issued a response to the APS report that challenges some of the perhaps unnecessarily conservative assumptions made in the APS report.

For climate policy wonks, the development of air capture is heartening in that it offers the potential to insulate the climate change problem from the comedic vicissitudes of domestic politics and international climate negotiations. If this one technology can be developed, then there is no need to have subsequent Monty Python conferences such as Copenhagen, and no need to fret about what other countries do. As I have written, the emissions mitigation question has up to now posed mostly strategic questions; what the US (China) or Canada should do has everything to do with what China (the US and Canada) will do. What if we could avoid these inconvenient strategic questions? Air capture offers not only the prospect of avoiding strategic problems, but also potentially un-doing some of the harm that we have already done. With an effective greenhouse life of about a century, just reducing emissions right now does nothing about the existing stock of emissions, which may already be too high.

But there is still also less than meets the eye. Development of air capture technology and deployment is still going to be costly. One country, or a coalition of the willing, undertaking development and deployment is very likely not going to be a magic bullet to the climate change problem. With development of air capture technology, there will likely be little incentive for countries to reduce consumption to reduce greenhouse gas emissions. Imagine the US (China), sucking CO2 out of the air just fast enough to keep pace with emissions from China (the US). Is that likely to be politically sellable?

For that reason, two things must accompany air capture: a carbon price, preferably in the form of a carbon tax, and a truly global collaborative effort on development of air capture technology. Were a carbon tax in place, then the capture of CO2 from the ambient air would, under a sensible policy, qualify for a subsidy, as a mirror image of the carbon tax. And with global cooperation of air capture R&D, there is not only the prospect of international buy-in, but also better economies of scale in R&D spending. While air capture R&D may not seem worthwhile from an individual country's perspective, that cost-benefit analysis changes if a cooperative agreement to share research is reached, so that the costs remain the same, but the potential benefits are doubled, or trebled, in accordance with the number of countries on board with the R&D effort. That is presumably one driver for a US-China carbon capture and storage partnership between the Pacific Northwest National Lab and the Chinese Academy of Sciences. But even more importantly, a joint global research effort is necessary so that all of the major emitting countries can have some buy-in to the idea of reducing ambient GHG concentrations. For air capture to have a chance at success, there can be no leakage (in the economic sense).