Salt is one of the oldest and most famous preservatives around. But could it be used to preserve carbon deep underground for thousands of years? Researchers believe it can, and that it just might offer a way forward in combating the atmospheric carbon levels that are leading the planet into an unprecedented climate crisis.

With greenhouse gas emissions like carbon dioxide continuing to increase, and climate feedback loops partially caused by these emissions accelerating, finding ways to suck carbon out of the air is more crucial than ever. The problem is that direct air capture (DAC) technologies such as the quick and efficient one developed by researchers from Tokyo Metropolitan University last year, can be quite costly to build and maintain.

For example, at the world’s largest carbon capture plant, which is slated to open in Wyoming this year, grabbing one tonne of carbon out of the air will cost US$600, although the developers of that project hope to eventually bring the cost down to the hundred-dollar range. Even at $100 per tonne, considering that we need to remove nearly one billion tonnes of carbon from the atmosphere per year to meet current climate goals, the cost will be mighty.

So that has left scientists scrambling to find other ways to get the carbon out of the air in a more cost-effective way. Earlier this year, scientists at MIT proposed a relatively inexpensive way to remove carbon from the world’s oceans so that they could soak up more carbon from the atmosphere, and last year chemists at the University of California Berkeley proposed using a cheap material called melamine to grab carbon from smokestacks and tailpipes.

Another affordable way to capture carbon from the air is through what’s known as agro-sequestration. While it might sound like something a petulant tween might do when having a bad day, the technique actually involves growing crops (such as certain grasses) that sequester carbon, and then burying those crops deep in the ground. The problem is that when bacteria starts to break down those crops, the carbon will be re-released into the atmosphere.

Seeking to overcome this hurdle, scientists at Berkeley have come up with a simple solution: salt. By first drying the crops and then burying them in biomass pits lined with two-millimeter-thick layers of polyethylene, then adding salt, the crops could hold onto their carbon store for centuries underground.

“There are significant questions concerning long-term sequestration for many of these recently popularized nature- and agriculturally-based technologies,” said Harry Deckman, co-author of a new study on the method. “The agro-sequestration approach we’re proposing can stably sequester the carbon in dried salted biomass for thousands of years, with less cost and higher carbon efficiency than these other air-capture technologies.”

Unlike DAC technologies, the researchers say their solution would cost only about $60 per tonne of captured and sequestered carbon dioxide. What’s more, the process would be carbon-negative, as for each tonne of dry biomass, two tonnes of carbon dioxide could be sequestered.

The team put together a list of high-productivity plants, and say that the majority can be grown on marginal farmland, most of which isn’t currently being used to grow crops. They also say that a 1-hectare pit could hold material from 10,000 hectares of biomass. Using those calculations, the researchers say that it would take only one-fifteenth of the world’s croplands, forests, and pastures to sequester half the world’s greenhouse emissions.

“To remove all the carbon that’s produced would require a lot of farmland, but it’s an amount of farmland that is actually available,” said Yablonovitch. “This would be a great boon to farmers, as there is farmland that is currently underutilized.”

The study has been published in the journal, PNAS.

Source: UC Berkeley