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Spreading rock dust on farmland could capture surprisingly large amounts of CO2, fast

The technology and infrastructure already exist—and the strategy could provide a substantial income source for farmers.
July 17, 2020

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Sprinkling rock dust across cropland could draw down two billion tons, or more, of carbon dioxide from the atmosphere each year. Paired with other mitigation approaches, that could play a huge role in helping us achieve the goals of the Paris Climate Agreement by 2050. 

This seemingly outlandish idea actually relies on a well-known geological feature: rock weathering. When rock is weathered through rainfall or high temperatures, it involves a chemical reaction that results in carbon being pulled down from the air, turned into a carbonate, and stored. 

But the new University of Sheffield-led study is the first to consider this technique as a mitigation tool at the national and global scale—and to tally up the surprisingly large planetary-scale benefits this approach could have.

The researchers looked at basalt, a widespread volcanic rock that has high weathering potential. They found that, incidentally, the three countries with the greatest potential for carbon-capture through basalt dust were also the highest-emitting countries in the world: China, the United States, and India. Collectively, these countries could remove between half a billion and two billion tonnes of CO2 from the atmosphere each year. That’s enabled by the large areas of cropland and warm weather in these countries, which accelerates rock weathering. Following on from those, Brazil and Indonesia were also found to have large capturing potential, mainly thanks to the vast extent of their croplands in those countries. 

But even in countries with smaller land areas, the potential of rock dust to bring down emissions was noteworthy: of all European countries, the five with the greatest potential for rock weathering could offset almost one-third of all the current emissions from all of Europe. Of the five highest European emitters, three of those had the best potential for locking away carbon in farmland rock dust—demonstrating the potential of this effect, not only at regional but national scales.

This highlights a core purpose of the study: by exploring this question at the national scale, the researchers illustrate how useful carbon-capturing rock dust would be for individual countries to reach their nationally-determined contributions—the emissions reduction pledges that nations made to meet the goals of the Paris Climate Agreement. For instance, rock dust could help Indonesia, Canada, and Mexico meet 40% of their currently pledged emissions target by 2030. India, France and Spain could reach 40% of their targeted emissions cuts. And in Brazil—likely on account of its expansive farmland area—rock dust could actually offset 100% of its pledged emissions cut over the next 10 years.

An obvious question is how countries would acquire all this rock to shower over their crops. An interesting revelation the researchers share in their study is that many countries already have large deposits of rock dust available: basalt rock dust is a common byproduct of mining, and it has been accumulating for decades around the world. Usually, it’s simply stockpiled and stands unused, or it’s dumped into landfills, its potential wasted. Dust could also come from sources other than basalt rock, the researchers note. Iron and steel mining produce dust byproducts that could be substitutes for regular basalt. The existing global supply of dust would therefore substantially limit the need to mine more from virgin rock. 

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As it turns out, the researchers discovered that the high-emitting nations of China and India have the highest potential dust supplies available—enough to meet their full dust demand, and aligning conveniently with their greater need to bring down CO2 emissions. 

Compared to other similarly-effective drawdown efforts, rock dust also holds unique appeal. Applying rock dust to cropland could de-acidify soils and enrich them with mineral nutrients—boosting food security on depleted farmland. Dust spreading is something some farmers already do (usually using limestone) to reverse soil acidification from intensive land use—so, many are already familiar with this practice. Unlike some other mitigation strategies, this one doesn’t compete with agriculture for land—which is another way to safeguard food security. What’s more, the researchers note that much of the dust would also eventually be flushed by rainfall into rivers and eventually the ocean, where it would create a permanent carbon sink. 

Crucially, this approach could also provide a substantial income source for farmers: the researchers calculate that a ton of carbon captured in rock dust could pay between $80 and $160 to landowners—comparable to the pricing of existing carbon capture strategies. 

The researchers issue a single, very important warning alongside their findings: that the quick-fix nature of the solution shouldn’t distract from the larger and more important goal of reducing global emissions, in the first place. The researchers are very clear that this technique won’t be valuable in isolation; it should be one among a fleet of approaches for reducing emissions, and drawing them down from the atmosphere. 

Still, it holds unique power as a tool we can roll out rapidly to start tackling climate change in the short term, they maintain. “The technology and infrastructure already exist to adapt these practices to utilize basalt rock dust,” the researchers say. “This offers a potentially rapid transition in agricultural practices to help capture CO2 at large scale.”

Source: Beerling et. al. “Potential for large-scale CO2 removal via enhanced rock weathering with croplands.” Nature . 2020. 
Image: via Kenneth Allen


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