The climate emergency demands that we dramatically and rapidly cut emissions. There’s no substitute for that, full stop. But it also demands a technological revolution to reverse years of out-of-control emissions: The UN’s Intergovernmental Panel on Climate Change notes that if we want to meet the Paris climate agreement’s most optimistic goal of limiting warming to 1.5 C above preindustrial levels, we have to deploy some sort of negative emissions technologies.
One promising technique is known as direct air capture (DAC), machines that scrub the atmosphere of CO2. Early versions of these facilities already exist: One firm called Carbon Engineering has been developing the technology for over a decade. DAC facilities use giant fans to suck in air, which then passes over special plastic surfaces, where it reacts with a chemical solution that binds to the CO2. The air leaves the facility minus the carbon.
But what might the wide-scale deployment of DAC look like? In a recent paper in the journal Nature Communications, a team of researchers crunched the numbers, arguing that it’s feasible for humanity to embark on a wartime-style crash deployment of a global network of machines that sequester carbon.
“We think there's sort of a dearth of conversation generally, but also in the academic literature, around emergency responses to the climate crisis,” says Ryan Hanna, an energy systems researcher at the UC San Diego and lead author on the paper.
Typically, climate scientists run big, complicated models about the most economically optimal ways to decarbonize. “That envisions this very technocratic, manicured, highly granular transition,” Hanna says, “which doesn't really reflect the way transitions actually occur in reality.” So Hanna and his colleagues sketched out an alternate vision: Imagine what would happen if humanity invested in DAC like we’d invest in another World War.
The researchers broke their modelling into three parts. The first was an estimate of how much governments would need to pay for DAC plants. This would include appropriating crisis-level funding to pay private firms to build the facilities, and to pay the companies for storing the carbon they’d be capturing. The second piece of the modelling looked at how fast the plant rollout could scale using already-existing energy supplies like hydropower. (You wouldn’t want to use fossil fuels to run them, obviously.)
And the last part was a climate model, representing the entire Earth system, including oceans and the atmosphere. This showed how global temperatures would change if a mass deployment of DAC facilities turned down the solution that binds to the CO2. The air leaves the facility minus the carbon.
The researchers found that with an annual investment of between one and two per cent of the global gross domestic product, humanity could scale up a DAC network to remove around 2.3 gigatons of CO2 annually by the year 2050. (For perspective, total global emissions are currently around 40 gigatons a year.)
Yet another outstanding question: What do you do with that carbon once you’ve captured it? #climatecrisis #climatechange
Bolster wetlands and plant trees
That’s about 400 times the amount of CO2 humanity currently sequesters, so we’re talking about a massive scale-up. Still, “relative to what the integrated assessment models tell us we should do by 2050, it's actually quite small,” says Hanna. We need to remove something like five to nine gigatons of CO2 per year by 2050 to meet the Paris Agreement’s 1.5 C goal.
“What that tells us is that we need more than just a single means of negative emissions,” Hanna adds. For instance, we could also bolster wetlands and plant trees to naturally sequester carbon.
The DAC facilities themselves will need to scale as quickly as possible. To be able to remove a mere two 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 modelling 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 co-operation 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.
Turning captured carbon into new fuels
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.”
Another option is for a corporation to pay a DAC facility to sequester CO2 underground on its behalf, so the company can boast about being carbon-negative or neutral. That might encourage nations to subsidize the development of DAC technology, or they might buy the tech from other countries to jump-start their own carbon-capture industries. Which is all to say, the solution might be to give in to the unfettered capitalism that got us into this mess.
But to be very clear: DAC is not a miraculous cure for climate change. Hanna’s team’s modelling found that even with a massive buildup of this technology, the world will still warm by 2.5 C by the year 2100 if we don't bring down greenhouse gas emissions. Humanity must invest in ways to dramatically reduce those emissions, and fast.
“We still have to vigorously pursue emission reductions,” says Janos Pasztor, executive director of the Carnegie Climate Governance Initiative, who wasn’t involved in this new work. “Otherwise, the amount of DAC we're going to have to do is going to be huge. And it's going to be forever before we reach our temperature goals.”
Negative-emissions technologies carry with them a moral hazard: the temptation to keep emitting CO2 as usual and to use DAC as a crutch.
“The problem with that, of course,” says Hausfather, “is that if you say, ‘OK, we're going to have very slow emission reductions today, because we're going to assume we'll have all this cool technology 60 years from now that'll solve the problem for us’ — we might not have this cool technology 60 years from now that'll solve the problem for us. And so you might end up in a world much warmer than you want it.”
The wartime-like deployment of DAC infrastructure that Hanna and his colleagues envision is going to cost a lot of money, all for a technology that we can’t yet say for sure will actually be feasible at a global scale. But, Hanna says, a climate emergency demands an emergency response. “In the long run over the century, if we're going to address the climate (crisis), we're going to invest just incredible amounts of dollars into solving the problem,” he says.
If we invest heavily now in DAC — in conjunction with a frenzied effort to reduce emissions — we can determine its potential while simultaneously driving down its cost. “That's a different mindset than, I think, conventionally what we're used to,” Hanna says.