Using Crushed Rock to Tackle Climate Change

My last article focused on the need for large-scale carbon sequestration with a look at a project in northern British Columbia that shows promise for meeting this challenge. Its approach takes biodiverse seed packets enveloped in biochar for nutrients and moisture retention and uses drones to spread these casings over wide areas to regenerate forests. This method of reseeding forests works especially well in remote, inaccessible terrain where replanting by hand is impossible.

Forests, or more specifically, the growing of trees, have been scientifically proven to pull carbon dioxide from the atmosphere. The calculations of some scientists, however, suggest that this natural process cannot achieve the scale of carbon drawdown required to offset our ever-growing carbon emissions. They cite the availability of land for forest restoration being the limiting factor. Consequently, another natural process is being considered to enhance and accelerate the storing of carbon not only in forests but on farms as well. This process occurs when rain dissolves the carbon dioxide that is present in air, creating a weak carbonic acid. If this acid falls on basalt rock, it reacts to form a carbonic mineral (calcium carbonate) that locks up the dissolved carbon for hundreds of thousands of years.

Basalt is the most common rock found on Earth’s surface. It is formed primarily from volcanic eruptions. Various forms of basalt are widely used in construction as aggregate in asphalt and concrete mixes and as base layers for highways and railroads. Although dense, this igneous rock crushes easily. Once pulverized into dust, it can be spread relatively inexpensively on forest and farmland, making it readily available for rain to wash carbon out of the air and accelerate the process of sequestration. The understanding of this process, called “enhanced weathering,” is not new, but because it speeds up a natural process, it has only recently been explored for its potential to offset human-made emissions that are causing climate change.

The Future Forest Company, a recent start-up company, is conducting a trial of this sped-up weathering approach on a large birch and oak forest on the Isle of Mull in Scotland. Results of the trial will be known soon. If the data show the expected increase in carbon sequestering, then this accelerated weathering process could potentially capture gigatons of carbon dioxide when applied to forests and on farms around the world. Reseeding of forests is still needed, but enhanced weathering can supplement forest restoration and be applied to farmland as well.

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