Trapping Carbon Dioxide Below the Earth

Tuesday, Nov. 4, 2008 | The world should hope Mark Zumberge’s experiment keeps working.

Off the Norwegian coast, deep beneath the turbulent North Sea, Zumberge, a Scripps Institution of Oceanography geophysicist, is monitoring one of the world’s only efforts to trap carbon dioxide, to keep it from entering Earth’s atmosphere and exacerbating climate change. The process is called carbon sequestration.

His experiment’s success holds significant implications for a world that is beginning to classify carbon dioxide, the major man-made contributor to the planet’s warming climate, as a pollutant. The test also holds considerable meaning for the United States, a country heavily dependent on coal, a chief source of the nation’s carbon dioxide emissions.

Because if mankind is going to tuck carbon dioxide away deep beneath the ocean floor to keep it out of the atmosphere, it had better stay there. Zumberge, who’s based in La Jolla, is keeping an eye on the world’s first sequestration project to make sure it is.

In 1996, StatoilHydro, a Norwegian oil and gas company, launched the world’s first large-scale carbon sequestration project off Norway’s coast, where Zumberge has been studying. The company, Norway’s largest gas producer, was drilling for natural gas off the country’s coast.

Natural gas deposits beneath the ocean floor aren’t purely natural gas. They also contain a small percentage of carbon dioxide, which must be removed before the gas heads to customers to be burned in heaters and stoves. Historically, companies simply released the carbon into the environment.

But Norway instituted a $49-per-ton tax on carbon dioxide emissions from natural gas production in 1991. (A ton of carbon dioxide is as many molecules as you could cram in about six oil barrels.) So StatoilHydro has an incentive to prevent the gas — 1 million tons annually — from escaping into the atmosphere.

And that’s where Zumberge comes in.

StatoilHydro has been stripping carbon dioxide from the natural gas it produces and pumping it deep beneath the sea floor. The carbon is sequestered — trapped — in a rock formation underneath the ocean’s bottom. Zumberge monitors it to make sure the carbon dioxide is staying put.

StatoilHydro’s gas-producing platform off Norway’s coast is fortuitously located near something called the Utsira formation — a huge layer of sand that’s capped by a dome-shaped layer of impermeable shale almost as thick as a football field. It’s like a rock lid that stretches hundreds of miles. StatoilHydro pumps carbon dioxide beneath the lid. And because carbon dioxide is lighter than water, the buoyant gas gets trapped beneath — essentially forming an upside-down lake of carbon dioxide that should stay put for thousands of years. StatoilHydro says the formation has enough capacity to store 600 years’ worth of emissions from all of Europe’s power plants.

Click the image above to see an illustration of how StatoilHydro pumps carbon dioxide beneath the Norwegian sea floor. Image Courtesy of: StatoilHydro

But for carbon sequestration to be a viable solution in the fight against climate change, the carbon pumped into the deep needs to stay there.

It’s not exactly easy to figure out whether carbon dioxide is staying trapped beneath a football-field-thick layer of shale hundreds of feet below one of the world’s coldest, most storm-tossed stretches of ocean.

So Zumberge must monitor tiny changes in gravity along the seafloor to make sure the carbon is staying put. He visits Norway every few years to check gravity at 30 spots on the seafloor above the carbon trap. The reason that StatoilHydro turns to him? He and his colleagues at Scripps are the only scientists in the world who do this type of research. They’ve historically used it to find gas and oil deposits.

Their experiments are expensive. Spending weeks floating in a ship off the Norwegian coast costs between $500,000 and $750,000 each time. But measuring gravity there is the key to knowing how much carbon dioxide is trapped beneath the surface.

Here’s why: As carbon dioxide displaces water below the surface, it causes infinitesimally small changes in gravity. Less-dense carbon dioxide displaces more-dense water.

How much gravity exists at any place on earth depends on how much stuff is underneath you pulling you toward the earth’s center. So decreasing the amount of mass beneath the surface — by pumping in carbon dioxide — decreases gravity. It’s not a change you could feel if you were standing there — it’s measured in gravity’s ninth decimal place.

Since 2002, Zumberge and his Scripps colleague Glenn Sasagawa have traveled twice to Norway — they’ll return again for a month next summer — to monitor the project’s progress, along with a StatoilHydro scientist, Ola Eiken. Since they know how much carbon dioxide is being sequestered, they know how gravity should change.

“We should eventually see a clear signal,” Zumberge said. “Right now we see a little tiny, tiny signal that’s barely in the data.”

The changes that have been monitored to date have shown the carbon dioxide is accumulating as expected — a positive sign that it’s not leaking out.

Zumberge’s experiment has been funded not only by StatoilHydro but also the U.S. Energy Department, highlighting the potential implications a successful test have for this country, which relies heavily on coal to keep the lights on.

If the new president fulfills his promise to adopt climate-change legislation that would cap the country’s carbon emissions (both Barack Obama and John McCain agree on the need), effective ways to sequester carbon would be an enormous boon for the United States’ coal industry. Coal is one of the country’s most abundant and inexpensive energy sources. It’s also dirty. While coal provides 48 percent of the country’s electricity, it creates 83 percent of the greenhouse gases associated with electricity production.

If proven viable, sequestration is not likely to become prolific in Southern California or San Diego, which gets 10 percent of its electricity from coal-fired sources. (No coal plants operate in the San Diego area, which gets more than half of its power from cleaner-burning natural gas.)

But it could potentially be used throughout states that are heavily dependent on coal. Experts caution, though, that sequestering carbon isn’t a cure-all. In a world that produces 7 billion tons of carbon dioxide annually, tucking it all away won’t be the sole solution to climate change. Some states don’t have the necessary geology. Dangers exist, too, that sequestered carbon may escape. An underwater store of carbon dioxide blew out of Lake Nyos in Cameroon in 1986, asphyxiating and killing 1,700 nearby villagers.

As climate change is addressed, sequestration may play a role, though the world will also have to cut the amount of carbon dioxide it produces in the first place.

“[Sequestration] is appealing,” said Andrew Dickson, a marine chemistry professor at Scripps, who has not participated in Zumberge’s experiment. But even sequestering all of Europe’s carbon emissions from electricity production off Norway’s coast wouldn’t solve climate change, he said. It would “change the timing of the problem and not the scale of the problem. This is bound to contribute, but I think we need a machine gun belt of silver bullets — not a single item.”

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