Rock dusting on farms: a puzzling climate solution

The simple act of sprinkling rock dust – an abundant mining byproduct – on farmland could capture the 45% of the carbon dioxide needed to help the UK meet its 2050 net goals.

This new number from a recent study adds to a growing body of evidence looking at the power of minerals to lower carbon, while also regenerating agricultural soils.

In fact, rocks are some of the largest carbon sinks on our planet. This capture occurs through a process called chemical weathering, in which atmospheric carbon dioxide breaks down in raindrops, forming carbonic acid, which reacts with rock minerals and causes them to crack and “weather.” During this process, carbon also changes form and is trapped in sediments as bicarbonate: this effectively strips it from the atmosphere and keeps it circulating in terrestrial and ocean systems for long periods of time.

Chemical weathering occurs on naturally slow time scales, because rocks take centuries to decompose. But, we can speed up this process by crushing it, exposing the minerals and creating a greater surface area for weathering to occur and thus the minerals absorbing carbon dioxide. This is the idea behind rock dust, which researchers have been exploring for several years as a way to quickly capture more carbon dioxide.

In fact, the latest study is based on research by the same experts who published work in 2020 to estimate the regression potential of shale dust in several countries around the world; their new paper homes in the UK, where they are discovering the unrecognized potential of this approach to achieve zero-zero country goals.

To make this discovery, they developed a model to test how much CO2 would be captured if we applied it across UK farmland, taking into account elements such as varied soil conditions and changing rates of weathering (due to regional climatic differences) across the UK. Specifically, the researchers looked at basalt, a widely available mining by-product that contains rapidly weathering minerals. Their model also included the costs of mining emissions and then spreading the rock powder over the fields.

Despite this, the potential for shale dust to offset the country’s emissions was enormous: by 2050, it could remove up to 30 million tons of carbon dioxide from the atmosphere each year, capturing nearly half – 45% – of the emissions it needs. The UK is conquering from its atmosphere, if it hopes to reach its 2050 net goals.

The researchers also showed that the mineral’s long-term decline potential means that with successive applications of rock dust to agricultural land, the amount of carbon dioxide captured cumulatively could reach 800 million tons by 2070.

These findings emerge as the debate grows about technologies that remove carbon dioxide directly from the air. Reducing global emissions remains a priority for climate action. But with the goals of controlling global temperatures by 2050 inches alarmingly close to us, many now see an urgent need for innovations that remove carbon dioxide directly from our atmosphere.

But these solutions are controversial, in part because the space is occupied largely by high-tech and expensive innovations like live-air capture technologies, which some accuse of distracting from accessible solutions that are already within our reach.

But the benefit of shale dust as a carbon removal method is that it’s a low-tech solution that’s also pretty much ready to implement, the researchers say. They also use food production for their benefits, rather than competing with crops for space — as some other large-scale decarbonization projects might do, they point out. However, this baffling solution has so far been ignored in UK climate policy.

The increasing status of rock dust as a climate solution requires farmers to buy, who can be gained by the obvious co-benefits that rock dust can bring to their lands: rock dust not only captures carbon, but also delivers nutrients and minerals back into the soil that can reduce the need for Fertilizer, significantly reduces costs.

The public may also need persuasion, especially since access to the required quantities of basalt to cover farmland in the UK will require a few new basalt mines, and the mines are flashpoints for public opinion. The researchers caution that this extraction will need to be carefully managed to meet the needs of sustainability and society.

But whether or not they find a foothold in UK policy, they hope for now their model will provide a “blueprint” for other countries to start exploring the benefits of farm shale dust. “This easy-to-implement technology could technically be transformative for the use of agriculture to mitigate climate change.”

Burling et al. “Possibility of significant carbon withdrawal from improved rock weathering in the UK.” natural earth sciences. 2022.

Photo: Tom Fisk from Pexels

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