A team of scientists from Harvard University and the company Carbon Engineering announced on Thursday that they have found a method to cheaply and directly pull carbon-dioxide pollution out of the atmosphere.
If their technique is successfully implemented at scale, it could transform how humanity thinks about the problem of climate change. It could give people a decisive new tool in the race against a warming planet, but could also unsettle the issue’s delicate politics, making it all the harder for society to adapt.
Their research seems almost to smuggle technologies out of the realm of science fiction and into the real. It suggests that people will soon be able to produce gasoline and jet fuel from little more than limestone, hydrogen, and air. It hints at the eventual construction of a vast, industrial-scale network of carbon scrubbers, capable of removing greenhouse gases directly from the atmosphere.
Above all, the new technique is noteworthy because it promises to remove carbon dioxide cheaply. As recently as 2011, a panel of experts estimated that it would cost at least $600 to remove a metric ton of carbon dioxide from the atmosphere.
The new paper says it can remove the same ton for as little as $94, and for no more than $232. At those rates, it would cost between $1 and $2.50 to remove the carbon dioxide released by burning a gallon of gasoline in a modern car.
The team published their results Thursday morning in Joule, a new American scientific journal printed by the same publisher behind the biology journal Cell.
“What we’ve done is build a [direct-air capture] process that is—as much as possible—built on existing processes and technologies that are widespread in the world,” said David Keith, a professor of applied physics at Harvard and the lead author of the new study. “That’s why we think we have a reasonable possibility of scaling up.”
Keith is also a founder and executive chairman of Carbon Engineering, a Bill Gates–funded company that has studied how to directly remove carbon dioxide from the atmosphere.
Carbon Engineering says the technique unveiled today has already been implemented at its small, pilot plant in Squamish, British Columbia. It is currently seeking funding to build an industrial-scale version of the plant, which Keith says it can complete by 2021.
Their technique, while chemically complicated, does not rely on unprecedented science. In effect, Keith and his colleagues have grafted a cooling tower onto a paper mill. It has three major steps.
First, outside air is sucked into the factory’s “contactors” and exposed to an alkaline liquid. These contactors resemble industrial cooling towers: They have large fans to inhale air from the outside world, and they’re lined with corrugated plastic structures that allow as much air as possible to come into contact with the liquid. In a cooling tower, the air is meant to cool the liquid; but in this design, the air is meant to come into contact with the strong base. “CO2 is a weak acid, so it wants to be in the base,” said Keith.
Second, the now-watery liquid (containing carbon dioxide) is brought into the factory, where it undergoes a series of chemical reactions to separate the base from the acid. The liquid is frozen into solid pellets, slowly heated, and converted into a slurry. Again, these techniques have been borrowed from elsewhere in chemical industry: “Taking CO2 out of a carbonate solution is what almost every paper mill in the world does,” Keith told me.
Finally, the carbon dioxide is combined with hydrogen and converted into liquid fuels, including gasoline, diesel, and jet fuel. This is in some ways the most conventional aspect of the process: Oil companies convert hydrocarbon gases into liquid fuels every day, using a set of chemical reactions called the Fischer-Tropsch process. But it’s key to Carbon Engineering’s business: It means the company can produce carbon-neutral hydrocarbons.
What does that mean? Consider an example: If you were to burn Carbon Engineering’s gas in your car, you would release carbon-dioxide pollution out of your tailpipe and into Earth’s atmosphere. But as this carbon dioxide came from the air in the first place, these emissions would not introduce any new CO2 to the atmosphere. Nor would any new oil have to be mined to power your car.
Eventually, a similar process could be used to sequester greenhouse gases. Instead of converting carbon dioxide into a liquid fuel, Carbon Engineering could pump it deep into the ground, reducing the amount of heat-trapping gas in the atmosphere. But such a technique wouldn’t give Carbon Engineering any product to sell, and there are no buyers stepping up to front the effort, for now.
“The main, near-term market is making carbon-neutral hydrocarbon fuels,” Keith told me. “We see this as a technology for decarbonizing transportation.”
Speaking from Cambridge, Massachusetts, on Wednesday, Keith said he was “pretty optimistic” about climate change. “The reason is that the market for these low-carbon fuels is much, much better than they were a few years ago. At the same time, low-carbon power—electricity generated by solar and wind—has just gotten much cheaper.”
Outside experts said they were encouraged by Keith and his colleagues’ approach, but cautioned that it would take time to examine every cost estimate and engineering advance in the paper. The consensus response was something like: Hmm! I hope this works!
“I don’t question that the range of costs they report are valid. I think the lower end of $100 per ton of CO2 produced through their approach is probably doable in five years or so and that their higher end of $250 per [ton of] CO2 is more doable with their technology today,” says Jennifer Wilcox, an associate professor at the Colorado School of Mines.
“The improvements that Carbon Engineering have made all seem appropriate, and I am comfortable that their estimated costs are within the window of what I would expect from such improvements,” says Roger Aines, a senior scientist at Lawrence Livermore National Laboratory’s energy program.
“The strongest part of this paper, in my opinion, is the fact that they’ve actually tested the technology in a prototype plant for a few years. That’s a big deal, and offers a proof of principle that’s way stronger than simple calculations or computational models,” says Scott Hersey, an assistant professor of chemical engineering at Olin College.
Caldeira said that the paper offered hope for the trickiest parts of the economy to adapt to climate change. “This suggests that the hardest-to-decarbonize parts of the economy (e.g. steel, cement manufacture, long-distance air travel, etc.) might continue just as they are now, and we just pay for CO2 removal,” he told me.
He continued: “Depending on how you count things, global GDP is somewhere in the neighborhood of $75 to $110 trillion. So, to remove all of this CO2 would be something like 3 to 5 percent of global GDP (if the $100 a ton number is right). This puts an upper bound on how expensive it could be to solve the climate problem, because there are lots of ways to reduce emissions for less than $100 a ton.”
Keith said it was important to still stop emitting carbon-dioxide pollution where feasible. “My view is we should stick to trying to cut emissions first. As a voter, my view is it’s cheaper not to emit a ton of [carbon dioxide] than it is to emit it and recapture it.”
“But once emissions are heading downhill and we’re heading back down to zero—which maybe could be 10 or 15 years from now—then I’m happy to see more large-scale removal of carbon dioxide.”
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