UK soils could absorb an additional 6-30 million tonnes of carbon dioxide a year – thanks to a little rock dust.
According to a study published in natural geosciences, the ancient technique of enhanced rock weathering could meet nearly half of the UK’s carbon removal needs and improve agricultural soils in the process.
It would also be a method of carbon dioxide removal at an attractive price: around £200 (A$350) per tonne of CO2 for now, and likely to drop by 2050. This makes it one of the cheapest negative emission technologies.
Enhanced rock weathering, or basalt weathering, involves scattering crushed rock on agricultural soils. The rocks should be silicates, with lots of calcium and magnesium.
This process makes the soil more alkaline – and therefore more likely to react with carbon dioxide in the air, turning it into carbonates and keeping it out of the atmosphere. The method can also reduce the amount of nitrous oxide (another greenhouse gas) and reverse soil acidification. This has the added benefit of reducing farmers’ reliance on fertilizers.
According to the researchers’ modelling, widespread rock weathering on UK farms could remove 6-30 million tonnes of CO2 every year, up to 2050. The UK currently emits around 300 million tonnes of CO2 every year, it is therefore an important part.
In fact, researchers claim that improving rock weathering could account for 45% of the UK’s carbon removal budget (i.e. the amount of carbon dioxide that needs to be removed from the atmosphere to achieve a net zero emissions goal, assuming that some processes are still going to cause emissions).
And, unlike other forms of carbon dioxide removal, the technology relies on existing infrastructure and processes. Although it takes energy and money to mine the rocks and grind them to dust, the researchers found that savings in fertilizers and agricultural productivity were responsible.
In fact, according to the document, the main problem is to get the communities to accept the method. This endeavor would require the involvement of the national government, right down to individual farmers.
“Reaching our net zero targets will require massive changes to the way farming and land in the UK is managed,” says co-author Professor Nick Pidgeon, director of the Understanding Risk group at the Cardiff University, UK.
“For this transformation to succeed, we will need to fully engage rural communities and farmers in this important journey.”
Prof Budiman Minasny, a soil-landscape modeling researcher at the University of Sydney who was not involved in the study, says enhanced rock weathering is an “attractive” and “long advocated” method.
But he thinks it’s a less viable option for Australia – and there are other logistical and environmental factors to consider, even for the UK.
“The weathering process is very slow, especially in arid areas, and so the effect might not be as fast as it was simulated,” says Minasny.
“While there are potentials in highly weathered soils in Australia, applying crushed basalt is not a practical thing to do in Australia, where soil carbon sequestration has much more potential.”
He points out that transporting rock from mine to farm isn’t necessarily a smooth process either. In a previous study, researchers estimated that this project would require about 40 tons of rock dust per hectare per year.
“In practice, there are a lot of challenges, about feasibility and other environmental effects – for example, where to find and finely grind that large amount of rock and how to transport it and apply that amount,” says Minasny.
He adds that if insufficiently mixed, rock dust and soil can cause dust pollution. The rocks, meanwhile, could also contain toxic metals that could seep into the ground and waterways. Authorities should pay attention to the content of rock dust.
- Published in partnership with the Royal Institution of Australia’s Cosmos magazine. To see cosmosmagazine.com.