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Salted crops can provide cost-effective carbon capture say researchers

Cost effective carbon capture is currently a bit of a myth. But could arguably Earth’s oldest preservative, salt, provide a solution to lock atmospheric carbon deep underground?

Carbon removal is now deemed essential to stay within all theoretical pathways of 1.5C warming, says the IPCC’s AR6 Synthesis Report.

Depending on how effectively we transition the most pollutant industries away from fossil fuels, we’ll need to actively sequester somewhere between 5 gigatons to 16 gigatons a year by the mid-century.

Proposed methods to do so range between weird, wonderful, and woefully useless. Some highlights covered by Thred in recent years include ocean cloud bleaching, scattering moon dust around the Earth’s atmosphere, and even creating carbon-filled shampoo from a hotel’s circular shower system.

Whether born from pure enthusiasm or the best quantitative science, the vast majority of carbon capture projects have one unfortunate commonality: they’re just too expensive. That’s not to say that all avenues can’t be low cost, however, and researchers have been buoyed by a recent milestone involving salt.

For some time scientists have been testing a process called agro-sequestration, in which carbon hungry crops of grass (like switchgrass and miscanthus) are used to draw emissions from the air over time before eventually being buried deep underground.

Avoiding expensive technology and maintenance, this method has long been explored as a potential game-changer, though a fatal flaw has prevented its promise from materialising.

Prior to a recent breakthrough, when bacteria broke down grass biomaterial samples within the soil, its sequestered carbon was re-released back into the atmosphere.

Seeking to overcome this hurdle in a new study, scientists at Berkeley turned to arguably history’s oldest preservative, salt. During a revised field test, they laid carbon-gorged grass cuttings within biomass pits and coated them in salt. The change proved vital, as the grass remained entirely preserved over months along with all isolated carbon.

‘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,’ the study’s co-author Harry Deckman concluded.

On the latter, the world’s largest carbon capture plant is soon slated to open in Wyoming with the aim of sequestering 5 million metric tons of CO2 every year by 2030. Deemed by many as an unrealistic prospect – given $600 is the current cost per every ton of sequestered carbon – the company is eventually striving for $100-per-ton using experimental materials.

Unlike direct air capture technology, Berkley’s researchers claim their agro-sequestration method can already deliver significantly better value at just $60 per ton of CO2 – meaning the process would also be carbon negative, as each ton of dry biomass reportedly captures around two tons of emissions.

Moving swiftly, the team has already drafted a list of high-productivity plants, of which the majority can be theoretically grown on marginal land and barren farmland. They assert that a 1-hectare salt-pit would hold material from 10,000 hectares of biomass.

Under this productivity ratio alone, calculations show that one-fifteenth of the world’s croplands, forests, and pastures could conceal half of the planet’s total GHG emissions.

These figures obviously represent the very best case scenario and put us back in pie-in-the-sky territory, given the logistics of securing so much land. Even on a much smaller scale, nonetheless, there is reason to be excited and optimistic about carbon capture’s natural, low cost boon already.