During the past few years, some of world’s brightest minds have become fascinated with a seemingly simple idea: Easing the threat of climate change by pulling carbon dioxide out of the air.
The concept is entirely different from capturing and sequestering carbon dioxide from power plants and other big polluters before it enters the air. Rather, the aim would be to remove the gas from the planet’s ambient air, where it exists in low concentrations everywhere.
In 2007, the British billionaire Richard Branson and former US vice president Al Gore created a US$25 million prize for the first creator of such a technology and millions of US dollars in venture capital have since flowed to start-up companies tackling the problem.
However, a new study casts serious doubts on whether such efforts will ever yield an economically viable tool for fighting global warming. The study, released last Monday by the American Physical Society, the world’s largest group of physicists, finds that while removing carbon dioxide from ambient air is technically feasible, the cost is likely to remain prohibitively high.
The report concluded it would cost at least US$660 a tonne to capture carbon dioxide from the air, compared with an estimated cost of about US$88 a ton to capture the gas from a power plant.
The most significant hurdle is the extremely low concentrations of carbon dioxide in air, compared with the stream from a coal-fired power plant or other large emitter, said Robert Socolow, a Princeton physicist and a co-chairman of the report.
The flue gas from a coal plant is roughly 10 percent carbon dioxide, while carbon in the ambient air is about four-hundredths of a percentage point.
“We have to deal with our centralized power sources first,” Socolow said. “This is not an assignment for the next few decades.”
The conclusion was greeted with dismay by several leading scientists who have championed air capture as a climate change solution.
Wallace Broecker, a professor of physics at Columbia University and a pioneering climate change researcher, said it was premature to write off the technology, which was still in its infancy.
“It’s something that’s so promising, it’s a crime not to explore it,” he said.
“The cost depends on how widely it’s implemented,” Broecker added. “The first computers cost a fortune and now they cost almost nothing.”
Developing a workable system to capture and sequester carbon emissions directly from power plants is far more pressing, said Michael Desmond, a chemist and senior internal consultant at BP, who served as co-chairman of the report.
“You’ve got to get your entire electric infrastructure decarbonized,” Desmond said. “It’s only there where air capture starts to make sense.”
The development of carbon capture technology for power plants and other large emissions sources has made significant strides in recent years and a US federal stimulus package included billions of US dollars for research and demonstration projects.
However, wide-scale deployment in the US will almost certainly require the passage of federal climate legislation setting a price for carbon dioxide emissions — such legislation failed to clear the US Senate last year and is unlikely to be revived anytime soon.
Spending on carbon capture from ambient air, by contrast, has been far more modest, totaling just tens of millions of US dollars. Kilimanjaro Energy, a California-based start-up and one of the leading developers of ambient air carbon-capture technology, for instance, has spent just more than US$11 million on research and development, the firm’s president Nathaniel David said.
The idea of capturing carbon in ambient air has found some bipartisan support in the US Senate, where a bill to reward researchers who develop carbon-removal technology was reintroduced last month with a Republican sponsor.
Klaus Lackner, a physicist and director of the Lenfest Center for Sustainable Energy at Columbia University’s Earth Institute, who has worked on the technology, criticized the American Physical Society study as too narrowly focused, saying it had only analyzed outdated technology.
Lackner said his design, which uses a plastic that absorbs carbon dioxide when dry and releases it to the air when wet, would eventually be capable of capturing the gas for far less than US$660 a tonne.
“I can assure you that if I believed it would cost [US$660 a tonne], I would have given up long ago,” he said.
David also said the report had failed to take into account the use of captured carbon dioxide as a feedstock for biofuels, like those made from algae.
“What we’re into is making fuels,” he said. “If you can grab CO2 from the atmosphere and can do it economically, you can find yourself in the midst of the fuel business.”
Desmond said his group had struggled to get sufficient data from private companies engaged in research into direct air capture. In the absence of data, claims that the process could be done cheaply were almost impossible to verify, he said.
“In the big scheme of things, those numbers don’t seem credible,” he said. “That’s my concern.”
Other analysts had mixed views. In an e-mail, Sasha Mackler, director for energy innovation at the Bipartisan Policy Center, a Washington-based institute, agreed that direct air capture of carbon dioxide was probably decades away from making economic sense. However, the market for alternative fuels could make the process far more profitable than forecast in the report, Mackler said.
“We are at far too early a stage to predict how this field will emerge in the years ahead,” she said. “Now is not the time to be taking options off the table.”