Environment Science & Environment

November 10, 2009

A Rock That Helps Out In a Hard Place

If only some incredibly common rock would just sit around and suck up carbon dioxide all day. Oh, there is one. Why aren’t we excited about it?

By Sam Kornell

Folded into the mountains of northern Oman is a rare burst of peridotite rock. Viewed from above, its black-and-white striations make it look like a great scoop of marble fudge ice cream has been slathered across the earth.

In January 2008, a Columbia University doctoral student named Sam Krevor traveled to Oman to study the peridotite. For three showerless weeks he and a team of researchers surveyed, observed and catalogued the rock, camping under the stars and subsisting on an unlikely diet of cabbage and canned shellfish (nonperishable food items not being a staple of Omani grocery stores).

What were they looking for? The answer is as intriguing as it is unexpected. Peridotite, it turns out, absorbs carbon dioxide, and according to Krevor it potentially represents one of the greatest — if most bafflingly ignored — solutions to climate change in the world.

Originating deep in the earth, peridotite is a part of a family — “ultramafic rock” — that reacts naturally with CO₂ to form solid minerals. Last May, Krevor was the lead author of a study identifying and mapping enough ultramafic rock in the United States to sequester an enormous amount of carbon dioxide. Taking into account various land-use constraints — private property, proximity to cities, national and state parks — he and his fellow researchers found storage potential for 500 years of the country’s CO₂ emissions.

So it’s a mystery of current climate studies that the U.S. Department of Energy, the country’s largest single source of funding into clean energy research and development, has awarded just one small grant, in 2003, to researchers studying mineral sequestration.

“It’s very striking,” Krevor said. “This is a technology that’s a potential game changer, and there’s been very little research done in the area.”

Scientists have long mulled various strategies for capturing and storing greenhouse gas, thus far with limited practical success. In recent years, even the idea of sequestering carbon dioxide has become a source of contention. Some experts are skeptical that large amounts of CO₂ can be sucked out of the air and stored safely and permanently, and they worry that “carbon capture” technology could be used to justify the continued expansion of coal power plants, among the most profligate sources of carbon emissions in the world.

And yet the pace of climate change is now so rapid that sequestration may be necessary to avert catastrophe. Even if strong international agreements to reduce global carbon emissions are signed in the near future — a not-at-all-certain prospect — there may now be so much greenhouse gas caked into the atmosphere that actively removing it from circulation is necessary to avoid violent upheaval in weather and temperature patterns across the globe.

“Unless we’re able to capture and store CO₂ at a reasonable price, we’re in huge trouble,” says Wally Broecker, a professor and scientist at Columbia University. One of the world’s foremost authorities on climate change — he coined the term “global warming” in 1975 — Broecker worries that without major changes in the global energy infrastructure the world is headed toward climate disaster.

Broecker isn’t a Cassandra: A few days after I spoke with him, the Met Office, the leading climate laboratory of the British government, issued a report finding that without a substantial reduction in carbon emissions, within 50 years global average temperatures will rise by up to 10 degrees Fahrenheit, with much of the United States warming by between 13 and 18F — a change which, scientists agree, would make large parts of the Earth more or less unlivable, including large parts of the American Southwest. (By contrast, climate observers hope action now can keep the world’s heating to 3.6 degrees F.)

Broecker believes that solar power will eventually become the world’s primary energy source, but because it will take time before solar can directly compete with coal and oil, carbon sequestration is an essential stopgap measure to curb climate change.

“There are only three energy sources that can supply the bulk of the world’s needs: nuclear power, solar power and fossil fuel,” he said. “I have a hard time believing nuclear is going to run the world. Solar is going to eventually come down in price and then it will run the world, but that will take time. And so in the meantime, we’re going to have to learn to capture and store CO₂.”

Sequestration efforts in the U.S. and Europe have so far focused on geologic storage -capturing the CO₂ at power plants and piping it, in gaseous form, into massive underground wells in, say, Nevada. “Air capture,” a less researched field, would suck CO₂ directly out of the atmosphere.

According to Krevor, using ultramafic rock to store CO₂ — which scientists call “mineral sequestration” — has a couple of major advantages over other forms of carbon storage. For one thing, silicate rock, of which ultramafic rock is a subset, is the second most common mineral in the crust of the Earth, which gives it vast storage capacity. For another, it’s safe. Once carbon dioxide is incorporated into the chemical structure of ultramafic rock, it’s there to stay.

“There are no other forms of carbon as stable as carbonate rocks,” Krevor said.

The problem Krevor and other researchers must surmount is that ultramafic rock sequesters CO₂ very slowly — over tens of thousands of years. “This process is important on geological time scales in buffering the CO₂ concentration of the atmosphere, but on a year-to-year time scale it doesn’t keep up,” he said. “So the question is: Is there a way to speed the process up so that it’s fast enough to counteract the emissions from industrial processes?”

In 2003, a group of researchers at the Albany Research Center, a laboratory in Oregon funded by the Department of Energy, attempted to answer that question. They focused on two traditional methods of accelerating chemical reactions in minerals — pulverizing them into tiny particles, and heating them to extreme temperatures. Both methods worked, but there was a problem: They required so much energy to enact that they produced more CO₂ than they sequestered.

After the ARC study was published, the Department of Energy effectively cut off funding into mineral sequestration research. The decision was based on a simple equation — the cost, in energy and money, appeared to outweigh the benefit. But according to Krevor, the goal of the ARC study was not to find the best way to accelerate mineral sequestration, but simply to prove it could be done. It was supposed to be the first step — “proof of concept” — but funding never arrived to develop step two.

At Columbia, Krevor studied, and eventually wrote his dissertation about, developing a catalyst to speed up the process. The idea is straightforward: If researchers can find a chemical that will accelerate mineral carbonation without itself being consumed or altered in the reaction, they should be able to mine ultramafic rock and use it in chemical reactors to sequester enormous quantities of heat-trapping CO₂.

If such a catalyst were found, Krevor said, it would be a cheap, profoundly safe and environmentally friendly way to combat global warming — a means to transform much of the Earth’s crust into a huge carbon depository. “Any greenhouse gas technology is going to be evaluated by four factors: Cost, capacity, permanence and benign environmental impact,” he said. “If you were able to find a catalyst that would make this process work quickly and cheaply, you’d have everything.”

Klaus Lackner, a professor of geophysics at Columbia who was Krevor’s doctoral adviser, and who was one of the first to suggest ultramafic rock as a climate solution, said the lack of funding for mineral sequestration is the result of “a fairly conscious decision that the center of gravity should be injecting CO₂ into the ground. [The scientific community] has decided, for better or for worse, to put all of our eggs into one basket.”

Lackner and Krevor both took pains to note that they support developing methods to safely store CO₂ underground. Indeed, Krevor is now a post-doctoral researcher at Stanford, where he is studying geologic sequestration. But both men pointed out that the safety and permanence of mineral sequestration makes it an attractive alternative to traditional geologic sequestration.

“If you store CO₂ as a gas, you are ultimately responsible, virtually indefinitely, for ensuring that that gas doesn’t come back into the air,” Lackner said. “The more you put underground, the greater the responsibility, because if it begins to leak it would be disastrous.”

What’s more, both worry that there is simply not enough room underground to store the amount of CO₂ necessary to curb global warming over the long run. “We run the risk that 20, 30, 40 or 50 years from now, we’ll run out of space,” Lackner said. “The challenge we face right now” — with climate change — “is so big that I’m uncomfortable with the idea of investing entirely in this technology with the possibility that in 50 years it’s over.”

Krevor readily concedes that a cheap chemical catalyst may not be found. But he argues that the potential benefits of mineral sequestration are so great, and the danger climate change poses so dire, that it’s senseless not to fund research into it.

“I understand that there’s a very good chance that nothing could be found,” he said. “But in science, and especially in the development of technology, you can really never say never. And what’s really more illustrative to look at is not whether there’s any inherent reason it could happen, so much as is there an inherent reason why it can’t happen, and the answer in this case is absolutely not. There’s no law of physics that says this is impossible.”

Lackner echoed Krevor. As exciting as many new clean energy technologies are, he said, the bare reality is that the world is still far from having a fully viable substitute for coal and oil.

“We do not know how to provide the energy the world needs. We may have some good ideas, we may have some guesses, but if you tell me that energy consumption over the next 100 years will quadruple, which it easily will do, there is no good way right now to provide that energy without creating environmental havoc.

“It is very, very clear that we already have far more CO₂ in the air than we can afford. That must be addressed, and we are not yet accepting, in public view, in public policy and in funding, how dire the situation is.”

Insufficient research funding is the working scientist’s perennial complaint. But considering how much money the federal government has already extended toward dubious climate solutions like biofuel, and considering how overwhelming the need to develop big solutions to climate change has become, it’s difficult to understand why mineral sequestration — the potential merits of which are so impressive — hasn’t garnered more attention.

As Krevor put it, “If the cost of the process were low enough, we’d be doing it today.”

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