SCI-TECH & AGRI

How Oman’s rocks could help save the planet

Carbonate veins formed when water with dissolved carbon dioxide flowed through rocks, in Oman.Vincent Fournier/NYTVINCENT FOURNIER  

In the arid vastness of this corner of the Arabian Peninsula, out where goats and the occasional camel roam, rocks form the backdrop practically every way you look.

But the stark outcrops and craggy ridges are more than just scenery. Some of these rocks are hard at work, naturally reacting with carbon dioxide from the atmosphere and turning it into stone.

Veins of white carbonate minerals run through slabs of dark rock like fat marbling a steak. Carbonate surrounds pebbles and cobbles, turning ordinary gravel into natural mosaics.

Even pooled spring water that has bubbled up through the rocks reacts with CO2 to produce an ice-like crust of carbonate that, if broken, re-forms within days.

Scientists say that if this natural process, called carbon mineralisation, could be harnessed, accelerated and applied inexpensively on a huge scale — admittedly some very big “ifs” — it could help fight climate change. Rocks could remove some of the billions of tons of heat-trapping carbon dioxide that humans have pumped into the air since the beginning of the Industrial Age.

And by turning that carbon dioxide into stone, the rocks in Oman would ensure that the gas stayed out of the atmosphere forever.

“Solid carbonate minerals aren’t going anyplace,” said Peter B. Kelemen, a geologist at Columbia University’s Lamont-Doherty Earth Observatory who has been studying the rocks here for more than two decades.

Capturing and storing carbon dioxide, is drawing increased interest. The Intergovernmental Panel on Climate Change says that deploying such technology is essential to efforts to rein in global warming. But the idea has barely caught on: There are fewer than 20 large-scale projects in operation around the world, and they remove carbon dioxide from the burning of fossil fuels at power plants or from other industrial processes and store it as gas underground.

What Kelemen and others have in mind is removing carbon dioxide that is already in the air, to halt or reverse the gradual increase in atmospheric carbon dioxide concentration.

Although many researchers dismiss direct-air capture as logistically or economically impractical, especially given the billions of tons of gas that would have to be removed to have an impact, some say it may have to be considered if other efforts to counter global warming are ineffective.

If billions of tons of CO2 are to be turned to stone, there are few places in the world more suitable than Oman, a sultanate with a population of 4 million and an economy based on oil and, increasingly, tourism.

The carbon-capturing formations here, consisting largely of a rock called peridotite, are in a slice of oceanic crust and the mantle layer below it that was thrust up on land by tectonic forces nearly 100 million years ago. Erosion has resulted in a patchy zone about 200 miles long, up to 25 miles wide and several miles thick in the northern part of the country, including here in the outskirts of Ibra, a dusty inland city of 50,000. Even the bustling capital, Muscat, on the Gulf of Oman, has a pocket of peridotite practically overlooking Sultan Qaboos bin Said’s palace.

Peridotite normally is miles below the earth’s surface. When the rocks are exposed to air or water as they are here, Kelemen said, they are like a giant battery with a lot of chemical potential. “They’re really, really far from equilibrium with the atmosphere and surface water,” he said.

The rocks are so extensive, Kelemen said, that if it was somehow possible to fully use them they could store hundreds of years of CO2 emissions. More realistically, he said, Oman could store at least a billion tons of CO2 annually. (Current yearly worldwide emissions are close to 40 billion tons.)

While the formations here are special, they are not unique. Similar though smaller ones are found in Northern California, Papua New Guinea and Albania, among other places.

The rocks here may be capable of capturing a lot of carbon dioxide, but the challenge is doing it much faster than nature, in huge amounts and at low enough cost to make it more than a pipe dream.

One possibility, Kelemen said, would be to drill pairs of wells and pump water with dissolved CO2 into one of them. As the water traveled through the rock formation carbonate would form; when it reached the other well the water, now depleted of CO2, would be pumped out. The process could be repeated over and over.

Experiments and eventually pilot projects are needed to better understand and optimise this process and others, Kelemen said, but so far Omani officials have been reluctant to grant the necessary permits.

The researchers may need to go elsewhere, like California, where the rocks are less accessible but the state government has set ambitious targets for reducing emissions and is open to new ways to meet them.

NY Times