seventeen the unthinkable
climate engineering

There are two more backup options for climate change that we should have in our pocket. Neither of them is a sustainable solution, but either might play a vital role in the coming decades of transitioning away from fossil energy.

The first is to contain the problem of carbon dioxide, by capturing it from power plants or from the open air, and storing it in some form where it won’t warm the planet or acidify the seas.

The second is to reflect some of the energy of the sun back into space, reducing the warming of the planet.

Containing the Problem

In eastern Germany, between Berlin and Dresden, is the town of Schwarze Pumpe. Since September 2008, German energy company Vattenfall has been operating an experimental power plant in the town. The coal-fired plant produces 30 megawatts of power, making it a baby compared to its 1,600 megawatt cousin nearby. What’s unique about the planet is that it emits virtually no carbon dioxide into the atmosphere. Instead, the CO₂ produced by burning the coal is captured, condensed into a liquid, and injected into container trucks. Those trucks transport the liquefied CO₂ to a site outside the town of Ketzin, just west of Berlin.

At the Ketzin site, the liquefied CO₂ is inserted into something rather like the opposite of an oil or natural gas well. Rather than pull fossil fuels out of the ground, the equipment at the site pumps the liquid CO₂ half a mile down, into a natural sandstone cavern capped by a 700-foot-thick layer of impermeable clay, with additional layers of sandstone and clay, above that. There, if all goes well, the CO₂ will remain trapped for millions of years.¹

The Schwarze Pumpe/Ketzin project runs at a tiny scale, capturing less than 100,000 tons of CO₂ per year, compared to the more than 30 billion tons of CO₂ that humanity emits each year. Its goal is to prove that the technology, carbon capture and sequestration, works.

And it does appear to work, though not without its challenges. Carbon capture requires extra energy and extra equipment. That means greater costs. A landmark paper from Harvard, surveying all current carbon capture proposals estimated that the first projects would cost roughly $100–$150 per ton of CO₂ captured, dropping over time to a range of $30–$50 per ton as experience and scale brought costs down.²

At that long-run cost, the cost of coal electricity would rise by 3 to 5 cents per kilowatt hour, and natural gas electricity by about half that.

The more options we have to address climate, the better. Batteries or next-generation nuclear power may provide us baseload power for the times when the sun isn’t shining and the wind isn’t blowing. Or they may be slower to develop than we expect. Judging by the current course and speed, it will still be twenty years before battery technologies have matured to the point that they can handle the grid’s needs for overnight power at a reasonable cost. And if unexpected hiccups appear, it could take longer.

Carbon sequestration would give us a way to meet that baseload power need for those intervening decades.

The challenge is enormous. Because CO₂ is only a third carbon by weight, and condenses down to a liquid that is only about half as dense as oil and a third as dense as coal, the total volume of liquid CO₂ that would need to be pumped underground to capture all of the world’s carbon emissions is on the order of ten times as much as all the oil the world pumps out of the ground today. Building that infrastructure would require a massive initial outlay of capital, manpower, and energy, to build ships, pipelines, wellheads, pumps, and so on to move and sequester that carbon, none of which will happen quickly.

In addition to the difficulty of the task, storing high-pressure carbon dioxide underground brings with it the danger of leaks into drinking water or back into the air. A 2010 Duke study, for instance, found that in some areas, high levels of CO₂ deep underground could slowly bubble into drinking water, bringing with them dangerous heavy metals.³ Even worse would be a catastrophic release of major amounts of carbon dioxide. In addition to undoing the benefit of capturing CO₂ underground, a leak of a large amount could be deadly. In 1986, the release of a large amount of CO₂ in a natural reservoir under Lake Nyos in Congo suffocated 1,700 nearby villagers, killing them.⁴

Even so, the U.S. Environmental Protection Agency, the International Energy Agency, and the UN’s Intergovernmental Panel on Climate Change all believe that there are enough natural caverns and reservoirs far from water sources and fault lines to store at least one trillion tons of CO₂, and possibly as much as ten trillion. The proof of principle is existing oil and natural gas fields, which have held hydrocarbons under similar or higher pressures for millions or tens of millions of years. We know geological formations are capable of that. What we need to do is select them carefully. If the EPA, IEA, and IPPC’s projections of at least one trillion tons of safe CO₂ storage capacity underground are correct, then there’s enough storage underground, if we can make use of it, to delay further CO₂ buildup in the atmosphere for at least another thirty years at current rates of emissions, and possibly much longer. At the high end of estimates, those geological formations could store all the emissions humanity will produce in the twenty-first century.

Spurred on by the challenges of underground storage of liquid CO₂, researchers have proposed new ideas over the last few years. As limestone weathers, it absorbs carbon dioxide from the atmosphere, in a process that takes millennia but that captures the carbon for millions of years. Some proposals, called “advanced weathering,” involve chemically accelerating that process to speed up the rate at which CO₂ can be absorbed into the earth’s crust. The authors of one such proposal from Harvard estimate that it would use roughly 400 kilowatt hours per ton of CO₂ sequestered, increasing energy costs by around 25 percent.⁵

Another approach, proposed by Greg Rau at the University of California, Santa Cruz, involves running the carbon dioxide plumes of power plants through a mixture of sea water and crushed limestone, which it will react with to create calcium bicarbonate, which can then be injected back into the oceans without raising ocean acidity, a process that should be cheap in terms of energy but that may only work near large bodies of water.⁶

Yet another approach, championed by a venture-backed company called Calera, would use waste CO₂ from power plants, combined with waste water and fly ash from coal, to manufacture cement that would bind up the carbon dioxide for its lifetime. Calera points out that the world consumes more than twelve billion tons of cement each year, enough to capture virtually all of the CO₂ emissions from today’s power plants.⁷

For most of these approaches, it’s simply too early to know how they’ll pan out. Carbon sequestration in underground formations is the furthest advanced, yet also presents risks in storage and challenges in the scale of operations needed. The more recently proposed solutions don’t have the risk of CO₂ suddenly escaping underground storage. They look attractive, but are far younger and far less tested. Yet the more such ideas we try, the more likely it is that we’ll hit upon a solution that works cheaply, safely, and at a volume high enough to make a dent.

The more options we have, the better.

The Elephant in the Room

For the last million years, the amount of carbon dioxide in the atmosphere never went above 280 parts per million. We are now at 390 ppm. Opinions differ on the level that we can safely stabilize at without a major risk of hitting a climate tipping point. The most talked-about number right now is 450 ppm, a level that would keep average planetary warming below 2 degrees Celsius, or 3.6 degrees Fahrenheit. Others, concerned that we’re already in uncharted waters, and by the evidence of methane release from melting tundra and from the Arctic seabed, are urging a return to a level around 350 ppm, lower than today, but still higher than the planet has seen during the lifetime of our species.

The elephant in the room is this: We’re not going to halt the accumulation of carbon dioxide in our atmosphere at 350 ppm or even 450 ppm, even with the most aggressive ramp up of clean energy we could imagine.

In 2010, three eminent climate scientists wrote a paper in Science posing the question “what if we stopped building CO₂ emitting devices today?” That is to say, what if, in 2010, we’d put a halt to the construction of all coal and natural gas plants and all gasoline-powered cars, trucks, and planes. Their answer was that we’d reach 430 ppm. And today, the world hasn’t stopped building coal or natural gas plants, or cars, trucks, and planes. Deployment of all of those is going faster than ever.

The world needs energy. People need it to come out of poverty, to achieve the type of comfort and health that we have in the rich countries of the world. They’re going to keep clamoring for electricity, for cars and trucks, for manufactured goods. We will, eventually, replace the way that we provide that energy. But even in the most optimistic scenario I can muster, the world as a whole will keep building new coal-fired power plants until at least 2020, and quite possibly longer. We’ll keep growing the number of cars on the world’s streets for a lot longer than that.

Clean energy will eventually win out. The issue is one of time. And right now, it looks like it won’t be fast enough to avoid the danger zone. Indeed, we may be in that danger zone already.

In 2009, U.S. energy secretary and Nobel Prize winner Steven Chu echoed this when he told Rolling Stone, “The fact is, we’re not going to level out at 450 ppm. . . . I hope we hit 550 ppm. Who knows?”⁸

So we need one more tool in our tool belt. I’ve argued since the beginning of this book that the way to think about climate and energy isn’t in terms of certainty—it’s in terms of risk and the need to insure against that risk. We need one more piece of insurance. We need a way to cool the planet, either globally, or in select parts.

One approach is to use carbon sequestration to capture CO₂ from the open air. That would allow us to collect CO₂ that’s built up from past years of burning fossil fuels, and from current emissions of cars, trucks, and planes. There’s wide disagreement about how feasible CO₂ capture from the open air is. The physics indicates that it’s definitely possible to do with a relatively small amount of energy. At the theoretically best possible efficiency, using 4–8 percent of the energy originally released by burning fossil fuels, we could capture and compress the CO₂ they emitted. Some people question whether coming anywhere near that is practical, but in other areas of science and engineering we’ve come within a factor of 2 of the best efficiency the laws of physics allow. If we can do that again, we can capture old emissions at a cost of 8–16 percent of the energy we gained from burning them in the first place. If the climate situation becomes dire, it may make more sense to use wind, solar, and nuclear to capture carbon dioxide, either from power plants or from open air, than to replace current coal and natural gas plants. A one-gigawatt nuclear reactor or solar or wind farm could capture and sequester the carbon released from six similar-capacity coal plants or twelve similar-capacity natural gas plants.

And if those plants have already been shut down, or are already sequestering their own carbon emissions, then, every year of operating that solar, nuclear, or wind installation could recapture the cumulative carbon emissions of six years of a similar-sized coal plant or twelve years of a similar-sized natural gas plant.

These systems haven’t been built. This is just theory at the moment. But it’s a capability we should invest in, as a backup we may well need at some point in the future. It’s an area that we should be aggressively funding the research in. It’s an area that we need to be sure our carbon prices support. Every ton of CO₂ pulled out of the atmosphere should be rewarded by a bounty. The same price it costs to emit a ton of CO₂ is the price that should be paid to anyone who improves our atmospheric commons by sucking CO₂ out of it. If we put that profit incentive in place, do the research on safety and sustainability of carbon sequestration, and invest in early basic research to bootstrap the field, then we’ll see innovation bloom. And if some day we need to use this technology—which is not at all unlikely—then we’ll be happy that we nurtured it well in advance.

The Solar Shield

In the early morning hours of June 12, 1991, Mount Pinatubo erupted in an explosion ten times larger than that of Mount St. Helens. The eruption sent a column of superheated steam and ash 12 miles high into the atmosphere above the Philippines. Friction from the column ignited lightning storms in the sky. The explosion was so powerful that it knocked out the seismographs at Clark Air Force Base, 20 miles away. A cloud of ash covering 50,000 square miles descended on the Philippines, bringing total darkness to much of the country’s largest island, Luzon.

Over the next two years, the eruption of Mt. Pinatubo did something else. It cooled the Northern Hemisphere of the planet by nearly a degree Fahrenheit. In the ash released by the volcano were an estimated 17 million tons of small sulfur dioxide particles that reached the upper atmosphere, and then lingered there for the next two years. Once in the stratosphere, those particles were too high up to cause acid rain. But they did alter the environment in another way: they reflected just a small fraction of the sun’s light back into space, thus cooling the planet.

In 2006, Nobel Prize–winning chemist Paul Crutzen, who won his Nobel for work on the ozone hole, proposed a radical idea in the journal Climate Change: We could use the cooling effect of aerosols in the upper atmosphere to fight climate change.⁹ The idea was controversial enough that many climate scientists argued against publication. Had it been proposed by anyone with less credibility than Crutzen, the idea might have been dismissed as science fiction. But with a Nobel Prize winner as the source, the idea had to be at least looked at it. Since then, dozens of scientists have proposed variations on the idea.

The idea of reflecting more sunlight into space by injecting small particles into the stratosphere—solar radiation management, as it’s called—is deeply imperfect. The particles will only stay in the atmosphere for a year or two, meaning that we’d need to constantly keep injecting new particles if we want to keep the cooling effect. Even if we cool the planet in this way, the buildup of small particles in the upper atmosphere will cause changes to rainfall patterns, with results that aren’t fully predictable. If sulfur dioxide is used, there’s a chance that some of it will drift down low enough to cause acid rain before it’s destroyed in the upper atmosphere.

Most seriously, solar radiation management doesn’t slow down ocean acidification. The CO₂ we emit still ends up dissolving in seawater to create carbonic acid, which breaks down coral reefs and the calcifying phytoplankton at the bottom of the ocean food chain. If we keep pumping CO₂ into the atmosphere and compensating for it by pumping aerosols into the upper atmosphere, we’ll eventually kill off much of the life in the ocean.

For these reasons, many climate scientists and activists—maybe most of them—oppose this approach.

But the dangers of solar radiation management have to be weighed against the dangers it guards against. In the Arctic, we’re at risk of hitting a climate tipping point. As the tundra thaws, buried vegetable matter decays and releases methane. As the ice cap over the Arctic Sea melts, it exposes dark water underneath that absorbs more sunlight, warming the shallow sea above a trillion tons of frozen methane. It’s a ticking time bomb.

We can’t depend on solar radiation management forever. It’s not a full solution to the climate problem. But using it selectively, to cool the Arctic and stabilize the methane there, would reduce the risk of hitting a climate tipping point. It’d lower the risk of tremendously more carbon entering the atmosphere, and eventually finding its way into the oceans. It could be a very useful part of our global insurance plan.

What we need now is further research into both carbon sequestration from the air and techniques to reflect more sunlight into space. We don’t want to be forced to use either, but we’d rather have them and not need them, then need them and not have them.