“Taking CO2 out of a gas stream, that’s not rocket science,” Wurzbacher told me. “And it’s also not new. People have filtered CO2 out of gas streams for the last fifty years, just for other applications.” On submarines, for instance, the carbon dioxide the crew breathes out has to be sucked from the air; otherwise, it will build up to dangerous levels.
But it’s one thing to be able to pull carbon out of the air and quite another to be able to pull this off at scale. Burning fossil fuels generates energy. Capturing CO2 from the air requires energy. So long as this energy comes from burning fossil fuels, it will add to the carbon that has to be captured.
A second major challenge is disposal. Once captured, CO2 has to go somewhere, and where it goes has to be secure. “The good thing about basaltic rock is it’s so easy to explain,” Wurzbacher observed. “If someone asks you, ‘Hey, but is it really safe?’ the answer is very simple: within two years it’s stone, one kilometer underground. Period.” suitable underground storage sites aren’t rare, but they aren’t common, either, meaning that, should large-scale capture plants ever be built, they’ll either have to be located in places with the right geology or the CO2 will have to be shipped long distances.
Finally, there’s the issue of cost. Pulling CO2 from the air takes money. Right now, a lot of money. Climeworks charges $1,000 a ton to turn subscribers’ emissions to stone. I used up my allotment of twelve hundred pounds to fly one-way to Reykjavík, leaving all the rest of my emissions, including those from my return trip and my flight to Switzerland, floating loose. Wurzbacher assured me that, as more capture units went up, the price would come down; within a decade or so, he predicted, it would fall to around $100 per ton. Were emissions taxed at a comparable rate, then the math could work out: Basically, a ton extracted would be a ton that could avoid the tax. But who’s going to spend that when carbon can still be dumped in the air for free? Even at $100 a ton, burying a billion tons of CO2—a small percentage of the world’s annual output—would run to $100 billion.*
“Maybe we are too early,” Wurzbacher mused, when I asked whether the world was prepared to pay for direct air capture. “Maybe we’re just right. Maybe we’re too late. No one knows.”
* * *
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Just as there are lots of ways to add CO2 to the air, there are lots of ways—potentially—to remove it.
A technique known as “enhanced weathering” is a sort of upside-down version of the project I toured at the Hellisheiði Power Station. Instead of injecting CO2 deep into rock, the idea is to bring the rock up to the surface to meet the CO2. Basalt could be mined, crushed, and then spread over croplands in hot, humid parts of the world. The crushed stone would react with carbon dioxide, drawing it out of the air. Alternatively, it’s been proposed that olivine, a greenish mineral that’s common in volcanic rock, could be ground up and dissolved in the oceans. This would induce the seas to absorb more CO2 and, as an added benefit, combat ocean acidification.
Another family of negative-emissions technologies, or NETs, takes its cue from biology. Plants absorb carbon dioxide while they’re growing; then, when they rot, they return that CO2 to the air. Grow a new forest and it will draw down carbon until it reaches maturity. A recent study by Swiss researchers estimated that planting a trillion trees could remove two hundred billion tons of carbon from the atmosphere over the next several decades. Other researchers argued that this figure overstated the case by a factor of ten or even more. Nevertheless, they observed, the capacity of new forests to sequester carbon was “still substantial.”
To deal with the rot problem, all sorts of preservation techniques have been proposed. One entails cutting down mature trees and burying them in trenches; in the absence of oxygen, the trees’ decay—and the release of CO2—would be forestalled. Another scheme involves collecting crop residues, like cornstalks, and dumping them deep into the ocean; in the dark, cold depths, the waste material would decay very gradually or perhaps not at all. As strange as these ideas may sound, they, too, take their inspiration from nature. In the Carboniferous period, vast quantities of plant material got flooded and buried. The eventual result was coal, which, had it been left in the ground, would have held on to its carbon more or less forever.
Reforestation, when combined with underground injection, yields a technique that’s become known as BECCS (pronounced “becks”), short for “bioenergy with carbon capture and storage.” The models employed by the IPCC are extremely partial to BECCS, which offers negative emissions and electrical power at the same time—a have-your-cake-and-eat-it-too arrangement that, in climate-math terms, is tough to beat.
With BECCS the idea is to plant trees (or some other crop) that can pull carbon from the air. The trees are then burned to produce electricity and the resulting CO2 is captured from the smokestack and shoved underground. (The world’s first BECCS pilot project launched in 2019, at a power plant in northern England that runs off wood pellets.)
With all of these alternatives, the challenge is much the same as with direct air capture: scale. Ning Zeng is a professor at the University of Maryland and the author of the “wood harvest and storage” concept. He has calculated that to sequester five billion tons of carbon per year, ten million tree-burial trenches, each the size of an Olympic swimming pool, would be required. “Assuming it takes a crew of ten people (with machinery) one week to dig a trench,” he has written, “two hundred thousand crews (two million workers) and sets of machinery would be needed.”
According to a recent study by a team of German scientists, to remove a billion tons of CO2 through “enhanced weathering,” approximately three billion tons of basalt would have to be mined, crushed, and transported. “While this is a very large amount” of rock to mine, grind, and ship, the authors noted, it is less than global coal production, which totals some eight billion tons per year.
For the trillion-tree project, something on the order of 3.5 million square miles of new forest would be needed. That’s an expanse of woods roughly the size of the United States, including Alaska. Take that much arable land out of production and millions could be pushed toward starvation. As O. Táíwò, a professor at Georgetown, put it recently, there’s a danger of moving “two steps backward in justice for every gigaton step forward.” But it’s not clear that using uncultivated land would be any safer. Trees are dark, so if, say, tundra were converted to forest, it would increase the amount of energy being absorbed by the earth, thus contributing to global warming and defeating the purpose. One way around this problem might be to genetically engineer lighter-colored trees, using CRISPR. So far as I know, no one has yet proposed this, but it seems only a matter of time.
* * *
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A couple of years before Climeworks launched its “pioneer” program in Iceland, the company opened its first direct-air-capture operation, atop a garbage incinerator in Switzerland. “Climeworks makes history,” the company declared.
One afternoon while I was in Zurich, I went to visit the “history-making” operation with Climeworks’ communications manager, Louise Charles. We took a train and then a bus out to the town of Hinwil, about twenty miles southeast of the city. As we walked up the access road to the incinerator, a huge box of a building with a candy-striped smokestack, a truck rolled by filled with rubbish. In the entrance hall, we paused to admire a series of artworks, also made of rubbish. Several men were seated before video monitors that displayed more rubbish. We signed the visitors’ log and took a service elevator up to the top floor.
On the roof of the incinerator were eighteen capture units just like the one at the Hellisheiði plant. These were arranged in three rows, which were stacked one above the other, like children’s blocks. A metal placard, aimed at visiting school groups, explained the Climeworks operation in pictures. It showed a garbage truck pulling up to the incinerator, which was depicted with little flames inside. One pipe, labeled Waste Heat,
led from the flames to the stack of capture units. (Using waste heat from the incinerator allows Climeworks to sidestep the it-takes-emissions-to-catch-emissions trap.) A second pipe, labeled Concentrated CO2, led from the units to a greenhouse filled with floating vegetables.
Climeworks’ carbon dioxide removal system uses a two-step process.
From the roof, I could see in the distance the actual greenhouses where the CO2 was headed. Charles had arranged for us to tour those as well, but she’d recently had knee surgery and was hobbling painfully, so I walked over alone. I was met at the entrance by the manager of the complex, Paul Ruser. Without Charles to translate, we had to make do with a hodgepodge of English and German.
Ruser told me—or at least I think he told me—that the greenhouses covered an area of eleven acres: an entire farm, under glass. Outside, it was sweater weather; inside, it was summertime. Bumblebees, which had been imported in boxes, buzzed around groggily. Twelve-foot-tall cucumber vines rose out of small bricks of potting soil. The cucumbers—a miniature variety the Swiss call Snack-Gurken—had just been picked and were piled high in bins. Ruser pointed out a black plastic tube running along the floor. This, he explained, was carrying CO2 from the Climeworks units.
“All plants need CO2,” Ruser observed. “And if you supply more to them, they become stronger.” Eggplants in particular, he said, thrive on lots of carbon dioxide; for their sake, he might crank the level way up, to as much as a thousand parts per million—more than double the level in the outside world. He needed to be careful, though. He was paying Climeworks for the piped-in CO2, so he had to make every molecule count: “I have to figure out the level that’s going to be profitable.”
Carbon dioxide removal may be essential; it’s already built into the calculations of the IPCC. Under the current order, however, it’s also economically infeasible. How do you go about creating a $100 billion industry for a product no one wants to buy? The eggplants and the Snack-Gurken represented an admittedly jury-rigged solution. By selling its CO2 to the greenhouses, Climeworks had secured a revenue stream to underwrite its capture units. The catch was that the captured carbon was only briefly being captured. Whoever snacked on the Snack-Gurken would liberate the CO2 that had gone into producing them.
From more little bricks of dirt, cherry tomato plants stretched to the roof in helical coils. The tomatoes, just a day or two from harvest, were perfect, in that greenhouse tomato-y sort of way. Ruser picked a couple and handed them to me. The burning trash, the acres of glass, the boxes of bumblebees, the vegetables raised on chemicals and captured CO2—was it all totally cool or totally crazy? I paused for a second, then popped the tomatoes into my mouth.
Skip Notes
* There are two ways to measure quantities of CO2: by accounting for either the full weight of the carbon dioxide or just the weight of the carbon. In this chapter, I am generally using the former measure, as is Climeworks, but many scientific publications use the latter. I have tried to distinguish the two by referring to a “ton of carbon dioxide” when I mean the full weight, and a “ton of carbon” when I mean the alternative. One ton of carbon dioxide translates into roughly a quarter of a ton of carbon; thus, annual global emissions are either about forty billion tons of CO2 or ten billion tons of carbon.
2
The Volcanic Explosivity Index was developed in the 1980s as sort of a cousin to the Richter scale. The index runs from zero, for a gentle burp of an eruption, to eight, for a “mega-colossal,” epoch-making catastrophe. Like its better-known relative, the VEI is logarithmic, so, for example, an eruption has a magnitude of four if it produces more than a hundred million cubic meters of ejecta and a magnitude of five if it produces more than a billion. In recorded history, there have been only a handful of magnitude sevens (a hundred billion cubic meters) and no eruptions of magnitude eight. Among the sevens, the most recent—and, hence, the best chronicled—is the eruption of Mount Tambora, on the Indonesian island of Sumbawa.
Tambora fired its first warning shots on the evening of April 5, 1815. People across the region reported hearing loud booms, which they attributed to cannon fire. Five days later, the mountain issued a column of smoke and lava that reached a height of twenty-five miles. Ten thousand people were killed more or less immediately—burned to cinders by the clouds of molten rock and searing vapor that raced down the slopes. One survivor reported seeing “a body of liquid fire, extending itself in every direction.” So much dust was thrown into the air that, it’s said, day turned to night. According to a British sea captain whose ship was anchored two hundred and fifty miles to the north of Tambora, “It was impossible to see your hand when held up close to the eye.” Crops on Sumbawa and the neighboring island of Lombok were buried under ash, leaving tens of thousands more to perish from starvation.
The eruption of Mount Tambora left an enormous crater.
These deaths were just the beginning. Along with ash, Tambora released more than a hundred million tons of gas and fine particles, which remained suspended in the atmosphere for years, drifting around the world on stratospheric winds. The haze itself was invisible; its results were just the opposite. Sunsets in Europe glowed eerily in blue and red, an effect recorded in private diaries and in the works of painters like Caspar David Friedrich and J.M.W. Turner.
Europe’s weather turned gray and cold. In what is probably the world’s most famous summer share, Lord Byron rented a villa on Lake Geneva in June 1816, with Percy and Mary Shelley as his housemates. Confined indoors by the season’s ceaseless rain, they decided to write ghost stories, an exercise that gave birth to Frankenstein. That same summer, Byron composed his poem “Darkness,” which runs, in part:
Morn came and went—and came, and brought no day,
And men forgot their passions in the dread
Of this their desolation; and all hearts
Were chill’d into a selfish prayer for light.
The grim weather caused harvests to fail from Ireland to Italy. Traveling through the Rhineland, the military tactician Carl von Clausewitz saw “ruined figures, scarcely resembling men, prowling around the fields,” searching for something edible among the “half-rotten potatoes.” In Switzerland, hungry crowds destroyed bakeries; in England, protesters marching under the banner Bread or Blood clashed with police.
How many people starved to death is unclear; some estimates put the figure in the millions. Hunger prompted many Europeans to immigrate to the United States, but conditions on the other side of the Atlantic, it turned out, weren’t much better. In New England, 1816 became known as the “year without a summer” or “eighteen-hundred-and-froze-to-death.” In mid-June it was so cold in central Vermont that foot-long icicles dripped from the eaves. “The very face of nature,” opined the Vermont Mirror, “appears to be shrouded in a death-like gloom.” On July 8, there was frost as far south as Richmond, Virginia. Chester Dewey, a professor at Williams College, in Williamstown, Massachusetts, where I happen to live, recorded a freeze on August 22 that killed the cucumber crop. A harder freeze on August 29 killed most of the corn.
* * *
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“What a volcano does is put sulfur dioxide into the stratosphere,” Frank Keutsch said. “And that gets oxidized on the scale of weeks to sulfuric acid.
“Sulfuric acid,” he continued, “is a very sticky molecule. And it starts making particulate matter—concentrated sulfuric acid droplets—usually smaller than one micron. These aerosols stay in the stratosphere on the timescale of a few years. And they scatter sunlight back to space.” The result is lower temperatures, fantastic sunsets, and, on occasion, famine.
Keutsch is a burly man with floppy black hair and a lilting German accent. (He grew up near Stuttgart.) On a lovely late-winter day I went to visit him in his office in Cambridge, which is decorated with pictures of and by his kids. A chemist by training, Keutsch is one of the leading s
cientists with Harvard’s Solar Geoengineering Research Program, an effort funded, in part, by Bill Gates.
The premise behind solar geoengineering—or, as it’s sometimes more soothingly called, “solar radiation management”—is that if volcanoes can cool the world, people can, too. Throw a gazillion reflective particles into the stratosphere and less sunlight will reach the planet. Temperatures will stop rising—or at least not rise as much—and disaster will be averted.
Even in an age of electrified rivers and redesigned rodents, solar geoengineering is out there. It has been described as “dangerous beyond belief,” “a broad highway to hell,” “unimaginably drastic,” and also as “inevitable.”
“I thought the idea was entirely crazy and quite disconcerting,” Keutsch told me. What brought him around was fear.
“The thing I worry about is that in ten or fifteen years, people could go out in the street and demand from decision-makers, ‘You guys need to take action now!’ ” he said. “We have this integrated CO2 problem that you can’t do anything about very quickly. So if there’s pressure from the public to do something fast, my concern is that there will be no tools at hand other than stratospheric geoengineering. And if we start doing research at that point, I am concerned it’s too late, because with stratospheric geoengineering, you’re interfering with a highly complex system. I will add that there are a number of people who do not agree with this.
“When I started this, I was perhaps, oddly, not as worried about it,” he observed a few minutes later. “Because the idea that geoengineering would actually happen seemed quite remote. But, over the years, as I see our lack of action on climate, I sometimes get quite anxious that this may actually happen. And I feel quite a lot of pressure from that.”
Under a White Sky Page 14
