“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,” said Robert Socolow, professor of mechanical and aerospace engineering at Princeton University.
Mr. Socolow led a committee of 13 experts who came up with the report “Direct Air Capture of CO2 with Chemicals” recently released by the American Physical Society.
The committee looked into direct air capture of carbon dioxide, a technology for removing carbon dioxide from the atmosphere through the use of chemical sorbents.
In a direct air capture system, or D.A.C., ambient air flows over the carbon sorbent which removes the carbon dioxide. The greenhouse gas is then released as a concentrated stream for disposal or reuse, while the sorbent is regenerated and the air released back into the atmosphere.
The technology is similar to the established technology of carbon dioxide scrubbers used for capturing and the emissions of coal power stations. The difference is that it removes carbon dioxide from ambient air, while carbon dioxide scrubbers concentrate on small point areas such as the flue gas stream of a coal power plant.
An example of a potential direct air capture device is being developed at the University of Calgary in Canada. Climate change scientist David Keith developed a tower-like air capture structure that contains sodium hydroxide – a common carbon absorbing material used in existing carbon scrubbing technology.
Expensive technology
While the idea of being able to remove carbon dioxide directly from the atmosphere is appealing, solving the problem of reducing emissions already in the air as well as that still being created, Mr. Socolow’s study found that it is far more expensive than simply preventing emissions in the first place.
The committee concludes that, from the evidence it has seen, building and operating a direct air capture system would cost at least $600 for the sake of removing a metric ton of carbon dioxide. And with this, building a system big enough to compensate for the emission of a 1,000-megawatt coal power plant would require 30 kilometers of equipment.
In this case, established carbon dioxide scrubbing technology would be a better and less expensive alternative, costing about $80 per ton.
While the study conceded that direct air capture eventually might have a role to play in countering some decentralized carbon dioxide emissions, such as those from buildings or vehicles, it might prove too costly for at least the next few decades.
The study concludes that if direct air capture must be deployed, it should be done at a cautious pace.
“We ought to be developing plants to bring to an end the carbon dioxide emissions at every coal and natural gas power plant on the planet,” said Mr. Socolow.
He recommends the more efficient use of energy and modifying plants so their emissions are kept from the atmosphere, or even shutting them down entirely and replacing them with low-carbon alternatives.
«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,» Mr. Socolow added.
Last year, the Carnegie Institution for Science published a study that also concluded that trying to “clean up” the atmosphere from carbon dioxide already emitted would not be enough to combat the effect of rising carbon dioxide levels on the climate.
Through a series of earth model simulations, the Carnegie scientists studied the effects of the removal of human-emitted carbon dioxide from the atmosphere.
They found that for every 100 billion tons of carbon removed, average global temperatures would only drop by 0.16 degrees Celsius (0.28 degrees Fahrenheit).
The study also looked into the effect extracting carbon dioxide from the air would have and found that in order to keep carbon dioxide at low levels, the process would have to continue for many decades.
