Storing carbon underground? There's less room than we thought, new study suggests

Many countries, including Canada, ar counting on some sort of resistance c storage to stay fresh planet-warming greenhouse gases out of the atmosphere and avoid the most catastrophic climate projections.

But a study published this week in the journal Nature is raising a new issue with what is already a mostly unproven technology. 

The study, led by researchers in the U.K., Austria and the U.S., analyzed a wider range of risk factors than conventional assessments of carbon storage potential. 

They found that globally, about 1,460 billion tonnes of carbon dioxide can be safely stored underground. That's significantly less than current projections of around 12,000 billion tonnes. That means using all the safe areas for carbon storage would cut global warming by only 0.7 C, much less than previous estimates of around 6 C.

"If we consider carbon storage to be a scarce resource, which based on our assessment it should be, then countries should be very explicit about how they plan to use it in order to meet their climate pledges" said Matthew Gidden, associate research professor at the University of Maryland's Center for Global Sustainability and lead author of the study.

Interest in removing and storing carbon has been growing as climate modeling increasingly suggests lowering our current emissions alone will not be enough to keep warming to safe levels. In Canada, the federal government is offering a tax credit to support carbon capture and storage projects, projected to cost taxpayers up to $5.7 billion until 2028. The U.S. And Europe also have massive programs to support the technology. 

"As [the study authors] point out, if we act to reduce emissions now, we probably have enough storage, but that ceases to be true really, really soon," said Rob Anex, professor at the University of Wisconsin – Madison who researches carbon capture technology.

"Global emission rates are so high that the window of time in which geologic storage is practical is shutting really, really fast." 

Gidden said most engineering studies looking into carbon storage focus on technical potential — the engineering or technically-feasible amount of carbon can be collected and stored underground in sedimentary rock. His team took a different approach: taking into account numerous risks like the closeness to towns and cities, sensitive ecosystems and protected wildlife areas, and seismically active zones. 

They also assumed carbon storage would not happen beyond a depth of 2.5 kilometres, based on their assessment of current technology, and excluded some nascent storage technologies. Some researchers say that might be too limiting, considering how quickly carbon storage technology is improving.

"They have very valid reasons for picking these depth ranges based on previous literature and studies that they cite. But I don't think this is necessarily a hard cut-off," said Anna Littlefield, a researcher at the Payne Institute for Public Policy at the Colorado School of Mines, focused on the energy transition. 

Kate Moran, president and CEO of Ocean Networks Canada, an oceans research observatory, is working on a project exploring carbon storage in basalt rock below the seabed. She says CO2 reacts with basalt to turn from gas into a solid, making it a more appealing way to store carbon compared to a gaseous form that may leak. 

"The capacity is huge," Moran said. "The basin we're studying, Cascadia basin, we think there's at least just at least 200 gigatons available in this one location off the West Coast of Canada."

B.C. Program aims to capture carbon and push it underwater

Anex, meanwhile, says the study's carbon storage projections may be too rosy considering the financial challenges of building up storage capacity quickly enough to address rising global temperatures.

"To scale up fast is just almost unimaginably expensive. And that competition for capital competes with lots of other social needs," he said, adding that the study assumed that a lot of the carbon would be transported great distances, over land in pipelines or shipped, to where it would be stored, raising costs and the potential for public opposition. 

Still, the space available for storage may not be the biggest hurdle.

"There's a lot of geological space there. And this study sort of says, well, there's not as much as you thought, comma, but there's still a lot, period," said Dave Sawyer, principal economist at the think-tank Canadian Climate Institute.

The real challenge, experts say, is demonstrating that carbon capture and storage can actually work at a large enough scale to offset emissions. Pilot projects in Canada and abroad have often seen mixed results.

Littlefield said that if the main problem with carbon storage was just that we were running out of storage capacity, that would be a good place to be for the industry.

"Because right now we're just still trying to get successful projects up and running," she said.

Gidden said one of the messages of the study is about the so-called overshoot theory — where climate scientists believe the world will overshoot 1.5 C of warming but later, through carbon storage technology, be able to bring temperatures back down (the world is currently at around 1.3 C of warming above pre-industrial levels).

"[If] we know that there's a limit in terms of how much carbon we can store, then there's a possibility we won't be able to return to 1.5 degrees," he said.

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