Each frame contains hundreds of white polymer strips filled with resins that bind with carbon dioxide molecules. The strips form a kind of sail, designed to snatch the greenhouse gas out of the air as wind blows through the contraption.

Crucially, that same material releases the carbon dioxide when wet. To make that happen, Lackner’s device retracts its frames into their container, which then fills with water. The gas can next be collected and put to other uses, and the process can begin again.

Lackner and his colleagues at Arizona State University’s Center for Negative Carbon Emissions have built a simple machine with a grand purpose: capturing and recycling carbon dioxide to ease the effects of climate change. He envisions forests of them stretching across the countryside, sucking up billions of tons of it from the atmosphere.

Lackner, 66, with receding silver hair, has now been working on the problem for two decades. In 1999, as a particle physicist at Los Alamos National Laboratory, he wrote the first scientific paper exploring the feasibility of combating climate change by pulling carbon dioxide out of the air. His was a lonely voice for years. But a growing crowd has come around to his thinking as the world struggles to slash climate emissions fast enough to prevent catastrophic warming. Lackner’s work has helped inspire a handful of direct-air-­capture startups, including one of his own, and a growing body of scientific literature. “It’s hard to think of another field that is so much the product of a single person’s thinking and advocacy,” says David Keith, a Harvard professor who cofounded another of those startups, Carbon Engineering. “Klaus was pivotal in making the argument that [direct air capture] could be developed at a scale relevant to the carbon-climate problem.”

No one, including Lackner, really knows whether the scheme will work. The chemistry is easy enough. But can we really construct anywhere near enough carbon removal machines to make a dent in climate change? Who will pay for them? And what are we going to do with all the carbon dioxide they collect?

The latest prototype unfolds to grab carbon from the air. Klaus Lackner pioneered the field of direct air capture. Spencer Lowell

Lackner readily acknowledges the unknowns but believes that the cheaper the process gets, the more feasible it becomes. “If I tell you, ‘You could solve the carbon problem for $1,000 a ton,’ we will say, ‘Climate change is a hoax,’” Lackner says. “But if it’s $5 a ton, or $1 a ton, we’ll say, ‘Why haven’t we fixed it yet?’”

Narrowing our options

The concentration of carbon dioxide in the atmosphere is approaching 410 parts per million. That has already driven global temperatures nearly 1 ˚C above pre-­industrial levels and intensified droughts, wildfires, and other natural disasters. Those dangers will only compound as emissions continue to rise.

Some scientific critics found Lackner’s projections not just wrong but dangerous. A pair of critical papers in 2011 sounded to many like a death knell for direct air capture. Lackner was undaunted.

The latest assessment from the UN’s Intergovernmental Panel on Climate Change found that there’s no way to limit or return global warming to 1.5 ˚C without removing somewhere between 100 billion and a trillion metric tons of carbon dioxide by the end of the century. On the high end, that means reversing nearly three decades of global emissions at the current rate.

There are a handful of ways to draw carbon dioxide out of the atmosphere. They include planting lots of trees, restoring grasslands and other areas that naturally hold carbon in soils, and using carbon dioxide–sucking plants and other forms of biomass as a fuel source but capturing any emissions when they’re used (a process known as bio-energy with carbon capture and storage).

But a report from the US National Academies in October found that these approaches alone probably won’t be enough to prevent 2˚C of warming—at least, not if we want to eat. That’s because the amount of land required to capture that much carbon dioxide would come at the cost of a huge amount of agricultural food production.

A close-up view of the carbon-capturing materials in a grass-like configuration, an earlier design that releases carbon dioxide when placed in a greenhouse. Spencer Lowell

The appeal of direct-air-capture devices like the ones Lackner and others are developing is that they can suck out the same amount of carbon dioxide on far less land. The big problem is that right now it’s much cheaper to plant a tree. At the current cost of around $600 per ton, capturing a trillion tons would run some $600 trillion, more than seven times the world’s annual GDP.

In a paper last summer, Harvard’s Keith calculated that the direct-air-capture system he helped design could eventually cost less than $100 a ton at full scale. Carbon Engineering, based in British Columbia, is in the process of expanding its pilot plant to increase production of synthetic fuels, created by combining the captured carbon dioxide with hydrogen. These, in turn, will be converted into forms of diesel and jet fuel that are considered carbon neutral, since they don’t require digging up additional fossil fuels.

If Keith’s method can capture carbon dioxide for $100 a ton, these synthetic fuels could be sold profitably in markets with public policy support, such as California, with its renewable-fuel standards, or the European Union, under its updated Renewable Energy Directive. The hope is that these kinds of early opportunities will help scale up the technology, drive down costs further, and open additional markets.

Other startups, including Switzerland-based Climeworks and Global Thermostat of New York, think they can achieve similar or even lower costs. They are exploring markets like the soda industry and greenhouses, which use air enriched with carbon dioxide to fertilize plants.

However, selling carbon dioxide isn’t an easy proposition.

Global demand is relatively small: on the order of a few hundred million tons per year, a fraction of the tens of billions that eventually need to be removed annually, according to the National Academies study. Moreover, most of that demand is for enhanced oil recovery, a technique that forces compressed carbon dioxide into wells to free up the last drips of oil, which only makes the climate problem worse.

A critical question for the carbon-­capture startups is how much the market for carbon dioxide could grow. Dozens of businesses are exploring new ways of putting it to work. They include California-based Opus12, which is using carbon dioxide to produce chemicals and polymers, and CarbonCure of Nova Scotia, which is working with more than 100 concrete manufacturers to convert carbon dioxide into calcium carbonate that gets trapped in the concrete as it sets.

A 2016 report by the Global CO2 Initiative estimated that the market for products that could use carbon dioxide—including liquid fuels, polymers, methanol, and concrete—could reach $800 billion by 2030. Those industries could put to use some 7 billion metric tons per year—about 15% of annual global emissions.

Such projections are extremely optimistic, though. And even if such a vast transformation of multiple sectors actually occurs, it will still leave huge amounts of captured carbon dioxide that will need to be permanently stored underground.

The hundreds of polymer strips form a kind of sail that grabs carbon dioxide molecules as wind blows air through the device. Lackner peers through an early model of an air-capture device, with the carbon-trapping materials shaped into a grid. Spencer Lowell

That’s only going to happen if society decides to pay for it, and some are skeptical we ever will. Capturing carbon dioxide out of the air—which means plucking a single molecule from amid nearly 2,500 others—is one of the most energy-intensive and expensive ways we could dream up of grappling with climate change. “Direct air capture is more expensive than avoiding emissions, but right now we’re not even willing to spend the additional money to do that,” says Ken Caldeira, a climate scientist at the Carnegie Institution. “So the idea that we’re going to get to negative civilization-­scale emissions through air capture, to me, just seems like a fantasy.”

Robot-making robots

On a summer night in 1992, while Lackner was a researcher at Los Alamos National Laboratory, he and a fellow particle physicist were having a beer and complaining about the lack of big, bold ideas in science. One or two drinks later, they had one of their own: What would become possible if machines could build machines? How big and fast could you manufacture things?

They quickly realized that the only way the scheme would work is if you designed robots that dug up all their own raw materials from dirt, constructed solar panels to power the process—and made ever more copies of themselves.

The next morning, Lackner and his friend, Christopher Wendt of the University of Wisconsin–Madison, decided they had an idea worth exploring. They eventually published a paper working out the math and exploring several applications, including self-replicating robots that could capture massive amounts of carbon dioxide and convert it into carbonate rock.

“My argument has always been we need to be passive,” Lackner says. “We want to be a tree standing in the wind and have the CO2 carried to us.”

The robot armada, solar arrays, carbon-­converting machines, and piles of rock would all grow exponentially, reaching “continental size in less than a decade,” the paper concluded. Converting 20% of the carbon dioxide in the atmosphere would generate a layer of rock 50 centimeters (20 inches) thick covering a million square kilometers (390,000 square miles)—an area the size of Egypt.

The hitch, of course, is that self-­replicating machines don’t exist. Lackner moved on from that part of the plan, and briefly focused on solar power as a replacement for fossil fuels. But the more he studied the problem, the more he came to believe that renewable sources would struggle to compete with the price, abundance, and energy density of coal, oil, and gasoline.

“This suggested to me that fossil-­fuel-based power will not just roll over and die,” he says. But perhaps if carbon removal technologies were cheap enough, he thought, you could “force fossil-fuel providers to clean up after themselves.”

A few years later, Lackner published a paper titled “Carbon Dioxide Extraction from Air: Is It an Option?” He argued that it was technically feasible and might be possible for as little as $15 a ton. (He now believes the price floor is probably between $30 and $50 a ton.)

In 2001 Lackner moved to Columbia University, where he cofounded Global Research Technologies, the first effort to commercialize direct air capture. Gary Comer, founder of the clothing and furniture company Lands’ End, handed the company $8 million of what Lackner describes as “adventure capital, not venture capital.”

The company built a small prototype but soon ran out of money. A group of investors bought the controlling interest, moved it to San Francisco, and renamed it Kilimanjaro Energy. Lackner served as an advisor and board member. But it quietly closed its doors after failing to raise more money.

Despite these failures, Lackner continued to try to figure out how to do air capture cheaply and efficiently. He’s published more than 100 scientific papers and editorials on the subject, and applied for more than two dozen patents.

Some scientific critics, however, found Lackner’s projections not just wrong but also dangerous. They feared that claiming direct air capture could be done cheaply and easily would reduce the pressure to slash emissions. In 2011, a pair of studies concluded that the technology would cost between $600 and $1,000 a ton.

Howard Herzog, a senior researcher at the MIT Energy Initiative, who coauthored one of the studies, took the added step of suggesting that “some purveyors” of the technology were “snake-oil salesmen.” In an interview last year, Herzog told me he was mainly talking about Lackner. “He was the one who was really out there,” he says.

Many read the two papers’ conclusions as a death knell for direct air capture. Lackner stood firm, telling the journal Nature after the first of the studies was published: “They proved that one specific way to capture carbon dioxide from air is expensive. If you study penguins, you might jump to the conclusion that birds can’t fly.”

Spencer Lowell

In 2014, he and his Global Research Technologies cofounder, Allen Wright, established the Center for Negative Carbon Emissions at Arizona State, where they’ve continued to try to get their own fledgling to take flight.

Planting synthetic forests

At the heart of the Center for Negative Carbon Emissions’ design is a particular type of commercially available anion-­exchange resin. As wind carries carbon dioxide in the air across those polymer strips, negatively charged ions bind with the gas molecules and convert them into bicarbonate—the main compound in baking soda and antacids.

The machine then retracts, pulling those saturated strips back into the container and pumping it full of water. The water begins converting the bicarbonate molecules into carbonate ions.

As the water drains away, those compounds become unstable and turn back into carbon dioxide in the air within the container. The now carbon dioxide–rich air can then be sucked out through a tube, and into an adjacent set of tanks.

Since carbon dioxide is relatively dilute in the air, most other direct capture approaches employ large fans to blow air over the binding materials to trap more of the gas. They then employ heat to drive the subsequent reactions that release the carbon dioxide. Both these steps use more energy. In contrast, Lackner says, his and Wright’s approach just requires a little electricity to extend and retract the machine, pump the water, and vacuum out the air.

“My argument has always been we need to be passive,” Lackner says. “We want to be a tree standing in the wind and have the CO2 carried to us.”

But there are big drawbacks to this method. It works only when the wind is blowing and makes sense only in dry areas, since humidity allows the carbon dioxide to escape. Moreover, the concentration of captured carbon in the resulting gas is less than 5%, compared with around 98% from a Carbon Engineering or Climeworks facility.

A critical question for carbon-­capture startups is how much the market for carbon dioxide could grow. Dozens of businesses are exploring new ways of putting it to work.

That low level is fine for fertilizing plants in greenhouses. But that’s a tiny market, and Lackner has grander designs.

He envisions thousands of these machines plucking carbon dioxide from the sky in some dry and hot part of the world, while adjacent solar panels drive an electrolysis process that extracts hydrogen from water. The carbon dioxide and hydrogen could then be combined on site to produce thousands of barrels a day of synthetic fuel, which could be sold for heating or transportation, or used to feed the electric grid when renewables like wind and solar flag.

That plan, however, poses several challenges. Electrolysis is still very expensive. And they’d need to compress the carbon dioxide to the necessary concentration while removing water vapor, nitrogen, and oxygen.

That can be done, but it could substantially increase costs and energy needs. “This is a big, important piece that he’s glossing over a bit,” says Jennifer Wilcox, a professor at Worcester Polytechnic Institute and coauthor of the National Academies report.

Some believe Lackner’s strengths as a theorist and big-picture guy haven’t served him as well in translating those ideas into the necessary advances in materials science and chemistry. Notably, the Center for Negative Carbon Emissions project is trailing well behind Carbon Engineering, Climeworks, and Global Thermostat, which are amassing capital, hiring staffs, and building out demonstration if not commercial-scale facilities.

But Lackner remains confident that his approach will be less expensive than competing ones. “I can lay it out unit process by unit process, and in terms of first principles, at every step we’re a little cheaper,” he says.

Deep trouble