Just over a century ago in Ludwigshafen, Germany, a scientist named Carl Bosch assembled a team of engineers to exploit a new technique in chemistry. A year earlier, another German chemist, Fritz Haber, hit upon a process to pull nitrogen (N) from the air and combine it with hydrogen (H) to produce tiny amounts of ammonia (NH₃). But Haber’s process was delicate, requiring the maintenance of high temperatures and high pressure. Bosch wanted to figure out how to adapt Haber’s discovery for commercial purposes — as we would say today, to “scale it up.” Anyone looking at the state of manufacturing in Europe around 1910, Bosch observed, could see that the task was daunting: The technology simply didn’t exist.
Over the next decade, however, Bosch and his team overcame a multitude of technological and metallurgical challenges. He chronicled them in his 1932 acceptance speech for the Nobel Prize for Chemistry — an honor he won because the Haber-Bosch process, as it came to be known, changed the world. His breakthrough made possible the production of ammonia on an industrial scale, providing the world with cheap and abundant fertilizer. The scientist and historian Vaclav Smil called Haber-Bosch “the most important technical invention of the 20th century.” Bosch had effectively removed the historical bounds on crop yields, so much so that he was widely credited with making “bread from air.” By some estimates, Bosch’s work made possible the lives of more than two billion human beings over the last 100 years.
What the Haber-Bosch method had going for it, from the very start, was a ready market. Fertilizer was already in high demand, but it came primarily from limited natural reserves in far-flung locales — bird droppings scraped from remote islands near Peru, for instance, or mineral stores of nitrogen dug out of the Chilean desert. Because synthetic ammonia competed with existing products, it was able to follow a timeworn pattern of innovation. In much the same way that LEDs have supplanted fluorescent and incandescent bulbs (which in turn had displaced kerosene lamps and wax candles), a novel product or process often replaces something already in demand. If it is better or cheaper — and especially if it is better and cheaper — it usually wins in the marketplace. Haber-Bosch did exactly that.
It may now be that another gas — carbon dioxide (CO₂) — can be removed from the air for commercial purposes, and that its removal could have a profound effect on the future of humanity. But it’s almost certainly too soon to say for sure. One sunny morning last October, several engineers from a Swiss firm called Climeworks ambled onto the roof of a power-generating waste-incineration plant in Hinwil, a village about 30 minutes outside Zurich. The technicians had in front of them 12 large devices, stacked in two rows of six, that resembled oversize front-loading clothes dryers. These were “direct air capture” machines, which soon would begin collecting carbon dioxide from air drawn in through their central ducts. Once trapped, the CO₂ would then be siphoned into large tanks and trucked to a local Coca-Cola bottler, where it would become the fizz in a soft drink.
The machines themselves require a significant amount of energy. They depend on electric fans to pull air into the ducts and over a special material, known as a sorbent, laced with granules that chemically bind with CO₂; periodic blasts of heat then release the captured gas from the sorbent, with customized software managing the whole catch-and-release cycle. Climeworks had installed the machines on the roof of the power plant to tap into the plant’s low-carbon electricity and the heat from its incineration system. A few dozen yards away from the new installation sat an older stack of Climeworks machines, 18 in total, that had been whirring on the same rooftop for more than a year. So far, these machines had captured about 1,000 metric tons (or about 1,100 short tons) of carbon dioxide from the air and fed it, by pipeline, to an enormous greenhouse nearby, where it was plumping up tomatoes, eggplants and mâche. During a tour of the greenhouse, Paul Ruser, the manager, suggested I taste the results. “Here, try one,” he said, handing me a crisp, ripe cucumber he plucked from a nearby vine. It was the finest direct-air-capture cucumber I’d ever had.
Climeworks’s rooftop plant represents something new in the world: the first direct-air-capture venture in history seeking to sell CO₂ by the ton. When the company’s founders, Christoph Gebald and Jan Wurzbacher, began openly discussing their plans to build a business several years ago, they faced a deluge of skepticism. “I would say nine out of 10 people reacted critically,” Gebald told me. “The first thing they said was: ‘This will never work technically.’ And finally in 2017 we convinced them it works technically, since we built the big plant in Hinwil. But once we convinced them that it works technically, they would say, ‘Well, it will never work economically.’ ”
For the moment, skeptics of Climeworks’s business plan are correct: The company is not turning a profit. To build and install the 18 units at Hinwil, hand-assembled in a second-floor workshop in Zurich, cost between $3 million and $4 million, which is the primary reason it costs the firm between $500 and $600 to remove a metric ton of CO₂ from the air. Even as the company has attracted about $50 million in private investments and grants, it faces the same daunting task that confronted Carl Bosch a century ago: How much can it bring costs down? And how fast can it scale up?
Gebald and Wurzbacher believe the way to gain a commercial foothold is to sell their expensive CO₂ to agriculture or beverage companies. Not only do these companies require CO₂ anyway, some also seem willing to pay a premium for a vital ingredient they can use to help market their products as eco-friendly.
Still, greenhouses and soda bubbles together represent a small global market — perhaps six million metric tons of CO₂ annually. And Gebald and Wurzbacher did not get into carbon capture to grow mâche or put bubbles in Fanta. They believe that over the next seven years they can bring expenses down to a level that would enable them to sell CO₂ into more lucrative markets. Air-captured CO₂ can be combined with hydrogen and then fashioned into any kind of fossil-fuel substitute you want. Instead of making bread from air, you can make fuels from air. Already, Climeworks and another company, Carbon Engineering, which is based in British Columbia, have moved aggressively on this idea; the Canadians have even lined up investors (including Bill Gates) to produce synthetic fuel at large industrial plants from air-captured CO₂.
The ultimate goal for air capture, however, isn’t to turn it into a product — at least not in the traditional sense. What Gebald and Wurzbacher really want to do is to pull vast amounts of CO₂ out of the atmosphere and bury it, forever, deep underground, and sell that service as an offset. Climeworks’s captured CO₂ has already been injected deep into rock formations beneath Iceland; by the end of the year, the firm intends to deploy 50 units near Reykjavik to expand the operation. But at that point the company will be moving into uncharted economic territory — purveyors of a service that seems desperately needed to help slow climate change but does not, at present, replace anything on the consumer or industrial landscape. To complicate matters, a ton of buried CO₂ is not something that human beings or governments have shown much demand for. And so companies like Climeworks face a quandary: How do you sell something that never existed before, something that may never be cheap, into a market that is not yet real?
Even the most enthusiastic believers in direct air capture stop short of describing it as a miracle technology. It’s more frequently described as an old idea — “scrubbers” that remove CO₂ have been used in submarines since at least the 1950s — that is being radically upgraded for a variety of new applications. It’s arguably the case, in fact, that when it comes to reducing our carbon emissions, direct air capture will be seen as an option that’s too expensive and too modest in impact. “The only way that direct air capture becomes meaningful is if we do all the other things we need to do promptly,” Hal Harvey, a California energy analyst who studies climate-friendly technologies and policies, told me recently. Harvey and others make the case that the biggest, fastest and cheapest gains in addressing atmospheric carbon will come from switching our power grid to renewable energy or low-carbon electricity; from transitioning to electric vehicles and imposing stricter mileage regulations on gas-powered cars and trucks; and from requiring more energy-efficient buildings and appliances. In short, the best way to start making progress toward a decarbonized world is not to rev up millions of air capture machines right now. It’s to stop putting CO₂ in the atmosphere in the first place.
The future of carbon mitigation, however, is on a countdown timer, as atmospheric CO₂ concentrations have continued to rise. If the nations of the world were to continue on the current track, it would be impossible to meet the objectives of the 2016 Paris Agreement, which set a goal limiting warming to 2 degrees Celsius or, ideally, 1.5 degrees. And it would usher in a world of misery and economic hardship. Already, temperatures in some regions have climbed more than 1 degree Celsius, as a report by the Intergovernmental Panel on Climate Change noted last October. These temperature increases have led to an increase in droughts, heat waves, floods and biodiversity losses and make the chaos of 2 or 3 degrees’ additional warming seem inconceivable. A further problem is that maintaining today’s emissions path for too long runs the risk of doing irreparable damage to the earth’s ecosystems — causing harm that no amount of technological innovation can make right. “There is no reverse gear for natural systems,” Harvey says. “If they go, they go. If we defrost the tundra, it’s game over.” The same might be said for the Greenland and West Antarctic ice sheets, or our coral reefs. Such resources have an asymmetry in their natural architectures: They can take thousands or millions of years to form, but could reach conditions of catastrophic decline in just a few decades.
At the moment, global CO₂ emissions are about 37 billion metric tons per year, and we’re on track to raise temperatures by 3 degrees Celsius by 2100. To have a shot at maintaining a climate suitable for humans, the world’s nations most likely have to reduce CO₂ emissions drastically from the current level — to perhaps 15 billion or 20 billion metric tons per year by 2030; then, through some kind of unprecedented political and industrial effort, we need to bring carbon emissions to zero by around 2050. In this context, Climeworks’s effort to collect 1,000 metric tons of CO₂ on a rooftop near Zurich might seem like bailing out the ocean one bucket at a time. Conceptually, however, it’s important. Last year’s I.P.C.C. report noted that it may be impossible to limit warming to 1.5 degrees by 2100 through only a rapid switch to clean energy, electric cars and the like. To preserve a livable environment we may also need to extract CO₂ from the atmosphere. As Wurzbacher put it, “if you take all these numbers from the I.P.C.C., you end up with something like eight to 10 billion tons — gigatons — of CO₂ that need to be removed from the air every year, if we are serious about 1.5 or 2 degrees.”
There happens to be a name for things that can do this kind of extraction work: negative-emissions technologies, or NETs. Some NETs, like trees and plants, predate us and probably don’t deserve the label. Through photosynthesis, our forests take extraordinary amounts of carbon dioxide from the atmosphere, and if we were to magnify efforts to reforest clear-cut areas — or plant new groves, a process known as afforestation — we could absorb billions more metric tons of carbon in future years. What’s more, we could grow crops specifically to absorb CO₂ and then burn them for power generation, with the intention of capturing the power-plant emissions and pumping them underground, a process known as bioenergy with carbon capture and storage, or BECCS. Other negative-emissions technologies include manipulating farmland soil or coastal wetlands so they will trap more atmospheric carbon and grinding up mineral formations so they will absorb CO₂ more readily, a process known as “enhanced weathering.”
Negative emissions can be thought of as a form of time travel. Ever since the Industrial Revolution, human societies have produced an excess of CO₂, by taking carbon stores from deep inside the earth — in the form of coal, oil and gas — and from stores aboveground (mostly wood), then putting it into the atmosphere by burning it. It has become imperative to reverse the process — that is, take CO₂ out of the air and either restore it deep inside the earth or contain it within new surface ecosystems. This is certainly easier to prescribe than achieve. “All of negative emission is hard — even afforestation or reforestation,” Sally Benson, a professor of energy-resources engineering at Stanford, explains. “It’s not about saying, ‘I want to plant a tree.’ It’s about saying, ‘We want to plant a billion trees.’ ” Nevertheless, such practices offer a glimmer of hope for meeting future emissions targets. “We have to come to grips with the fact that we waited too long and that we took some options off the table,” Michael Oppenheimer, a Princeton scientist who studies climate and policy, told me. As a result, NETs no longer seem to be just interesting ideas; they look like necessities. And as it happens, the Climeworks machines on the rooftop do the work each year of about 36,000 trees.
“The idea of bringing direct air capture up to 10 billion tons by the middle or later part of the century is such a herculean task it would require an industrial scale-up the likes of which the world has never seen,” Princeton’s Stephen Pacala told me. And yet Pacala wasn’t pessimistic about making a start. He seemed to think it was necessary for the federal government to begin with significant research and investments in the technology — to see how far and fast it could move forward, so that it’s ready as soon as possible. At Climeworks, Gebald and Wurzbacher spoke in similar terms, asserting that the conversations around climate challenges are moving beyond the choice between clean energy or carbon removal. Both will be necessary.
Gebald and Wurzbacher seem less assured about the future of global policy than on the mechanics of scaling up. Some of that, they made clear, was related to their outlook as engineers, to what they’ve gathered from observing companies like Audi and Apple. If the last century has proved anything, it’s that society is not always intent on acting quickly, at least in the political realm, to clean up our environment. But we’ve proved very good at building technology in mass quantities and making products and devices better and cheaper — especially when there’s money to be made. For now, Gebald and Wurzbacher seemed to regard the climate challenge in mathematical terms. How many gigatons needed to be removed? How much would it cost per ton? How many Climeworks machines were required? Even if the figures were enormous, even if they appeared impossible, to see the future their way was to redefine the problem, to move away from the narrative of loss, to forget the multiplying stories of dying reefs and threatened coastlines — and to begin to imagine other possibilities.