Scientists have turned carbon dioxide into stone in a matter of months by pumping it deep underground, offering a revolutionary new way of storing the greenhouse gas to tackle climate change.

The pioneering experiment in Iceland mixed CO{-2}emissions with water and pumped it hundreds of metres underground into volcanic basalt rock — where it rapidly turned into a solid.

“We need to deal with rising carbon emissions. This is the ultimate permanent storage — turn them back to stone,” said Juerg Matter, lead author of the study, which was published Thursday in the journal Science . Carbon dioxide is a key factor in global warming, and experts have long called for innovative “carbon capture and storage” solutions.

Attempt in aquifers

Previous attempts to inject CO{-2}into sandstone soils or deep saline aquifers have struggled, as they relied on capping rocks to hold the gas down — triggering fears it could eventually leak.

In contrast, the Carbfix project at Iceland’s Hellisheidi plant — the world’s largest geothermal facility, which powers Reykjavik — sought to solidify the CO2.

The plant produces 40,000 tons of CO{-2}a year — just five percent of the emissions of a similarly sized coal plant, but still significant. In 2012, they began pumping 250 tons of CO{-2}mixed with water underground.

Scientists had feared it could take hundreds or even thousands of years for the mildly acidic liquid to solidify. But 95 per cent of the injected mixture — which they had tagged with tracer chemicals in order to check it didn’t leak out — had became chalky white stone within two years.

“It was a very welcome surprise,” said Edda Aradottir, who heads the project for Reykjavik Energy.

Encouraged by the success, the company has scaled up the project and from this summer will be burying some 10,000 tonnes of CO{-2}each year, Ms. Aradottir said.

“This means that we can pump down large amounts of CO{-2}and store it in a very safe way over a very short period of time,” said study co-author Martin Stute, a hydrologist at Columbia University’s Earth Observatory.

“In the future, we could think of using this for power plants in places where there’s a lot of basalt — and there are many such places.”

“It’s what we hoped for ... and in some ways better,” said David Goldberg, a Columbia University geophysicist who wasn’t part of the team but praised it. “What’s going on here is a natural process being accelerated.”

A 2014 report by the Intergovernmental Panel on Climate Change warned that without carbon sequestration technology, adequately limiting global warming could prove impossible.

On seafloors

Basalt makes up most of the world’s seafloors and approximately 10 per cent of continental rocks, according to the study’s researchers.

A porous, blackish rock, basalt is rich in calcium, iron and magnesium, minerals researchers said are needed to solidify carbon for storage.

“Carbon capture is not the silver bullet, but it can contribute significantly to reducing carbon dioxide emissions,” Mr. Matter said. — AFP/AP