The DAC facilities themselves will need to scale as quickly as possible. To be able to remove a mere 2 to 2.5 gigatons of carbon a year by 2050—a fraction of the amount that will help get us to the Paris goals—we’d need around 800. But to truly make a dent in the skyrocketing CO2 levels, we’d need to build them much faster. We’re talking 4,000 to 9,000 plants by the year 2075, and beyond 10,000 by the end of the century, at which point we could theoretically be sequestering up to 27 gigatons of carbon a year. “It shows, in effect, that you have a really long, slow, gradual scale-up as the industry grows through 2050,” says Hanna. “Then once it sort of grows to a massive size, then it’s really easy to add a lot of plants quickly, because you have this huge industrial base for the industry.”
But there are some important caveats to consider, because Hanna and his colleagues are modeling a nascent technology rife with unknowns. For instance, they have to make informed assumptions about how much energy the future plants might use, which determines their operation costs. “The other big unknown,” Hanna says, “is how the performance of the system could actually improve, and how the costs of the systems would decline over time, given firms’ experience with building the technology.”
Plus, global politics could make a mess of DAC’s rollout: If all humans share the same atmosphere, why would one country pay to research and deploy the technology if their neighbor doesn’t pay a penny? “It’s nice to approach things about climate change as if they’re just technological problems—if we get the cost right, if we get the technology right,” says Louisiana State University environmental scientist Brian Snyder, who wasn’t involved in this new work. “But they are inherently political problems, and we’ve got to solve that simultaneously.” (In their paper, Hanna and his colleagues call for help from political scientists to study the challenges of international cooperation here.)
Yet another outstanding question: What do you do with that carbon once you’ve captured it? One option is to pump it underground, sealing it away forever. Economically, that’s a bit fraught, because you’re spending money to run your facility, but then throwing away your product instead of selling it. That means DAC will require government subsidies to be economically feasible. A nation could assign an inherent value to capturing carbon and slowing climate change, and dedicate some of its own funding to taking a financial loss—at least in the near term—for an environmental good.
Researchers are also working on turning captured carbon into new fuels, which could make that initial government investment in DAC lucrative. That sounds, well, counterproductive, since we’d be burning the fuel and putting the carbon right back into the atmosphere. But the idea is to use such a fuel to make hard-to-decarbonize industries carbon-neutral. Airliners and cargo ships, for instance, are too massive to run on current solar technologies. Making them essentially reburn fuel that’s on its second life means there’s less demand for fossil fuels pulled right out of the ground.
If these industries burn fuels made from captured CO2, they’ll still pollute, but at least they’ll be polluting with carbon that was previously in the atmosphere. “The real effective role of negative emissions is for this long tail of hard-to-decarbonize sectors,” says Zeke Hausfather, a climate scientist and the director of climate and energy at the Breakthrough Institute, which advocates for climate action. (He wasn’t involved in this new research.) “Aviation, agriculture—things where we’re still going to be emitting carbon well into the 2050s, and perhaps after that.”