Adding crushed volcanic rock to arable land across the world – regardless of climate – could help to remove billons of tonnes of carbon from the air each year, say scientists.
Previous research has shown rain captures carbon dioxide from the air as it falls, then reacts with volcanic rock, locking in carbon.
The process, called rock weathering, usually takes millions of years, but by crushing the rock into dust, the process is sped up.
This ‘enhanced’ rock weathering could store as much as 215bn tons of carbon dioxide over the next 75 years if it is spread across farmland around the world, scientists have suggested, but until now there had been little research into how effective the process could be in arid climates.
In a study published in the journal Environmental Research Communications, researchers at the University of California, Davies, and Cornell University carried out field testing in extreme drought conditions.
In trials, scientists applied crushed silicate — metabasalt and olivine, two byproducts of mining — across five acres of fallowed cornfield from December 2020 to February 2021, a period when California was experiencing 41% less rain than its historical average.
During the testing period, the researchers analysed soil moisture and pH to identify bicarbonate, which is produced when silicate materials react with dissolved carbon dioxide.
From their analysis, they found that plots with crushed rock stored 0.15 tons of carbon dioxide per hectare, compared with plots without crushed rock.
While different rates of carbon can be removed in different environments, if the amount of carbon in the study was removed across the whole of California’s cropland, it would equate to taking 350,000 cars off the road each year, the researchers said.
“While humid, acidic environments encapsulate far greater enhanced weathering potential overall, this study in a Mediterranean climate during a historic drought suggests we may expand the margins of where enhanced weathering technology might operate into global arid lands,” they added.
