Spreading rock dust on farms: an attractive climate solution

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

This new figure from a recent study adds to a growing body of evidence on the power of minerals to extract carbon, while replenishing agricultural soils.

In fact, rocks are among the greatest carbon sinks on our planet. This capture occurs through a process called chemical weathering, whereby atmospheric CO2 dissolves in raindrops, forming carbonic acid, which reacts with minerals in the rock and causes them to break down and “weather” them. During this process, carbon also changes form and becomes fixed in sediments as bicarbonate: this effectively removes it from the atmosphere and keeps it circulating in land and ocean systems for long periods of time.

Chemical weathering occurs on naturally slow timescales because rocks take centuries to break down. But, we can speed up this process by crushing them, which exposes the minerals and creates a larger surface area for weathering to occur and therefore for the minerals to absorb CO2. That’s the idea behind rock dust, which researchers have been exploring for several years as a way to quickly capture more CO2.

In fact, the recent study builds on research from the same experts who published work in 2020 estimating the drawdown potential of rock dust in several countries around the world; their new paper is set in the UK, where they discover the unrecognized potential of this approach to achieve the country’s net zero goals.

To make this discovery, they developed a model to test how much CO2 could be captured if we applied it to all of UK farmland, taking into account things like various soil conditions and humidity levels. variable 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 incorporated the emission costs of mining and then spreading this rock dust on the fields.

Despite this, the potential for rock dust to offset the country’s emissions was enormous: by 2050, it could remove up to 30 million tonnes of CO2 from the atmosphere each year, capturing almost half (45 %) of the emissions the UK needs to overcome from its atmosphere, if it hopes to meet its 2050 net zero targets.

The potential for sustainable mineral uptake means that with successive applications of rock dust to agricultural land, the amount of CO2 captured could reach up to 800 million tonnes by 2070, the researchers also showed.

These findings are emerging as the case for technologies that directly remove carbon dioxide from the air grows. Reducing global emissions remains the priority for climate action. But as the goals of reigning over global temperatures by 2050 inches creep alarmingly closer to us, many now see an urgent need for innovations that also directly remove carbon dioxide from our atmosphere.

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

But the advantage of rock dusting as a carbon removal method is that it’s a crude solution, which is also pretty much ready for implementation, the researchers say. It also uses food production to gain its benefits, rather than competing with crops for space, as other large-scale carbon removal projects might, they note. And yet, this tantalizing solution has so far been overlooked in UK climate policy.

Raising the status of rock dust as a climate solution will require buy-in from farmers, who might be persuaded by the clear co-benefits that rock dust could bring to their land: rock dust not only captures carbon , but also puts nutrients and minerals into the soil, which can reduce the need for fertilizer, dramatically reducing costs.

The public, too, may need some convincing, especially since to reach the quantities of basalt required to cover UK farmland will require a few new basalt mines, and the mines are hotspots for l ‘public opinion. This extraction should be carefully managed to meet sustainability and community needs, the researchers warn.

But whether or not it finds a place in UK policy, they hope for now that their model will provide a ‘blueprint’ for other countries to start exploring the benefits of rock dust on farms. “This technically simple-to-implement technology could prove transformative for using agriculture to mitigate climate change.”

Beerling and. al. “Substantial carbon uptake potential through enhanced rock weathering in the UK.” nature geoscience. 2022.

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