FEATURE

The Carbon Eaters

One Columbia researcher thinks a solution to global warming could lie beneath our feet.

by Douglas Quenqua Published Fall 2013
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Peter Kelemen with a chunk of rock covered in carbonate. / Contour by Getty Images

The first time Peter Kelemen visited the mountains of northern Oman, a craggy stretch of rock that pushed up through the earth’s surface ninety million years ago, he was disappointed to find cracks filled with carbonate, obscuring much of the landscape.

To him, it might as well have been Wite-Out, redacting millions of years of geological history. “When I would come to an outcrop full of all these white veins, I would turn and run the other way,” says Kelemen, a geochemist at Columbia’s Lamont-Doherty Earth Observatory.

In a spring in Wadi Sudar, Oman wherever water has run over a rock called peridotite, a crust of carbonate has formed. / Oman photos by Kevin KrajickIt was 1994, and Kelemen had traveled to the desert Sultanate of Oman to study a coarse-grained, greenish rock called peridotite. The main constituent of the earth’s mantle, peridotite is normally hidden ten miles or more below ground. But a series of tectonic flukes under the Arabian Peninsula pushed a big chunk of mantle upward, forming the Hajar Mountains and making this one of the few places in the world where peridotite is accessible to scientists. Kelemen hoped that by studying the rock’s chemical composition he could reveal secrets about the extraordinarily hot, pressurized, and unstable subterranean world from which it came. The problem was that wherever peridotite had come into contact with carbon dioxide, the two had reacted to form a limestone-like solid. Much of the peridotite exposed to air or water was thus converted into a chalky substance, making it difficult for scientists to find clean samples.

“If our goal had been to study how carbon dioxide interacts with these rocks, this would have been great,” says Kelemen. “But we wanted to understand processes in the mantle. And the carbonate-filled cracks were obliterating the evidence.”

When Kelemen returned to Oman in 2007 for the first time in a few years, however, it was the carbonate he was looking for. Politicians and scientists in the United States had been buzzing about an ambitious plan to slow global warming by sucking carbon dioxide out of the air and storing it underground. One challenge was finding a safe place to lock it away.

Kelemen had a hunch his old nemesis could help. “These rocks suddenly seemed worth sampling,” he says. “Whereas once I bemoaned how they react with carbon dioxide, now I wanted to know: how much of the stuff could they take? And how fast?”

Mantle Pieces

The Hajar Mountains on the Arabian Peninsula were created when a piece of the earth’s mantle thrusted upward from ten miles underground.Since the Industrial Revolution, the amount of carbon dioxide in Earth’s atmosphere has risen more than 40 percent, sealing in heat and wreaking havoc with our climate. The problem grows worse with every pound of fossil fuel we burn to fly, drive, watch television, or wash our clothes.

But what if there were a way to siphon that excess carbon dioxide right out of the air and stash it somewhere forever? The idea is known as carbon capture and storage, and while it may sound like wishful thinking, it’s won some prominent backers. Howard Herzog, a senior research engineer at the MIT Energy Initiative, says that developing a practical storage method is “critical for a secure, clean energy future.” President Obama has supported carbon capture since his first national campaign, and included in his 2009 federal stimulus package $3.4 billion for developing it.

“This rock from the earth’s interior is out of equilibrium with our atmosphere, and hungry for carbon dioxide. We want to take advantage of that.” — Peter Kelemen

To pull the carbon out of the air, researchers have devised some creative, if still speculative, solutions. Columbia physicist Klaus Lackner is working on giant synthetic trees that would absorb carbon dioxide like real trees do, but at a much greater rate. Harvard physicist David Keith has built a machine that sucks air through a thirty-foot-long chamber and extracts carbon dioxide using water laced with sodium hydroxide.

But what to do with the gas once it’s been captured? Some suggest compressing it into a liquid and injecting it into depleted oil wells, gas reservoirs, and other cavities underground. But critics warn that it could escape and cause damage to soil and water. Others suggest selling it to oil drillers, who use it to float oil out of the ground, or even selling it to carbonated-beverage manufacturers. But all the soda in the world isn’t going to use up the billions of tons of CO2 that scientists hope to pull from the air.

Kelemen is not a climate scientist, nor did he have much professional interest in global warming until a few years ago. But his experience working in Oman — since 1994 he has returned there regularly — gave him unique insight into the chemistry of carbon dioxide and rock. He knew that those streaks of carbonate that he had avoided occurred when magnesium and calcium in the mantle rock sucked up carbon dioxide from air and water, storing it, he says, “as an inert, harmless mineral.” He thought: what if peridotite could be made to do that on a massive scale? It might make the perfect storage facility.

Geologists had noticed that peridotite soaks up carbon dioxide long before Kelemen visited Oman. But most believed the process was impractical for large-scale sequestration. “I was told that people had thought about it and concluded that it was not practical because it was too slow,” Kelemen says. He was pretty sure they were wrong. “It didn’t match my intuition,” he says. “I had seen things that made me think the reactions could happen within hours.” 

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