Schematic representation of a 1 m2 intake area contactor capturing 20 tCO2/yr. Image: The American Physical Society
Technologies for removing carbon dioxide from the atmosphere are
unlikely to offer an economically feasible way to slow human-driven climate
change for several decades, according to a report issued by the American
Physical Society and led by Princeton engineer
“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 Socolow, a professor of mechanical and aerospace engineering.
The report, issued by a committee of 13 experts, was co-chaired by
Socolow and Michael Desmond, a chemist at BP. The group looked at technologies
known as “Direct Air Capture,” or 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
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. Building a system big
enough to compensate for the emissions of a 1,000-megawatt coal power plant
would require 30 km of equipment. 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
“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,” Socolow said. Beyond using electricity more efficiently, options
are to modify plants so their emissions are kept from the atmosphere or to shut
them down 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,” Socolow added.
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 that, “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,” Socolow said.
“The committee that worked on this problem included both
senior researchers and researchers starting their careers, and both industry
experts and academics,” he continued. “The review process elicited
contributions from thirty to forty 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.”
The DAC assessment began when it was authorized
by the American Physical Society’s Panel of Public Affairs in 2008. Socolow’s
first co-chair was William Brinkman, who was then a senior research physicist
at Princeton and now directs the Office of
Science at the Department of Energy. They convened a meeting of experts at
Princeton in March 2009, but then Brinkman’s move to Washington required him to step down from
the group. Socolow continued the project, first with co-chair Arun Majumdar,
who stepped down to direct the Department of Energy’s Advanced Research
Projects Agency-Energy initiative, then with Desmond.