For farming, the latest climate fix isn’t especially high tech or glossy. By spreading rock dust over large swatches of land, carbon dioxide could be trapped in transformed, scrubbing it from the atmosphere. If this technique, called enhanced weathering, were to be employed around the world, scientists estimate two billion tons of carbon dioxide could be removed from the atmosphere each year.
In a paper published in the journal Nature July 8, researchers at the University of Sheffield laid out the potential costs and impact of the process. If the three countries that emit the most carbon dioxide —China, the United States and India—adopted the practice, one billion metric tons could be scrubbed from the air.
Enhanced weathering essentially speeds up natural processes of erosion and chemical reactions using newly introduced minerals. During the process, rocks are crushed and transported to farmland, where they are spread over a large area once a year, reports Lyndsey Layton at the Washington Post. When it rains, water dissolves silicate or carbonate materials in the dust. This cycle causes carbon dioxide to be pulled from the atmosphere into the solution, forming bicarbonate ions. Over time, these ions are washed into the ocean and form carbonate minerals, trapping the carbon for at least 100,000 years.
Though the technique could be applied to any large swatch of land, many farms are already equipped to spread rock dust due to the common practice of enriching cropland with crushed lime, writes Nathanael Johnson at Grist. The minerals in the crushed rock could further fertilize soil, as long as metals and organic materials are not added to crop fields.
“Spreading rock dust on agricultural land is a straightforward, practical CO2 drawdown approach with the potential to boost soil health and food production,” David Beerling, director of the Leverhulme Centre for Climate Change Mitigation and lead author of the study, tells the Washington Post. “Our analyses reveal the big emitting nations — China, the U.S., India — have the greatest potential to do this, emphasizing their need to step up to the challenge.”
To meet the guidelines in the United Nations Climate Change Paris Agreement, some scientists claim at least ten gigatons of CO2 must be extracted from the atmosphere each year, the authors write. If the global surface temperature were to cross 3.6 Fahrenheit above preindustrial levels, scientists warn that the effects would be irreversible.
“We have passed the safe level of greenhouse gases,” James Hansen, a partner in the study and a climate scientist at Columbia University’s Earth Institute, tells the Washington Post. “Cutting fossil fuel emissions is crucial, but we must also extract atmospheric CO2 with safe, secure and scalable carbon dioxide removal strategies to bend the global CO2 curve and limit future climate change.”
Other methods of removing CO2 from the air include sequestration, in which CO2 from a factory is absorbed into a liquid or solid and stored. Enhanced weathering bears about the same cost, but has added agricultural benefits.
However, in order to meet the expected demand for rock dust, mining and grinding operations could require the same amount of energy as 10 to 30 percent of the CO2 captured, the study reports. To mitigate this, excess rock from industrial projects could be crushed and spread to limit the need for new mining.
The authors write that their plan offers “opportunities to align agriculture and climate policy,” but acknowledge that “success will depend upon overcoming political and social inertia.”
Spreading rock dust on half the farmland in the U.S. would cost $176 per ton of carbon and $225 annually per American. That’s pricey compared to clean energy solutions that directly cut emissions. Solar farms, for instance, cost less than $40 per ton of emissions cut, according to Grist.
To clear the atmosphere of greenhouse gasses to the degree necessary over the next several decades, the international community will have to remove existing carbon in addition to cutting new emissions, the Intergovernmental Panel on Climate Change notes.