Scattering rock dust on crops could soak up billions of tons of CO2

With traditional carbon sinks like the Amazon rainforest facing an uncertain future, scientists are looking to get creative with their efforts to slow the buildup of CO2 in the atmosphere. A new study out of the University of Sheffield makes a case for a technique known as enhanced rock weathering, which essentially involves supercharging soil’s ability to remove CO2 from the atmosphere by sprinkling it with rock dust.

Just like other geoengineering technologies such as cloud seeding and machines that suck carbon out of the air, enhanced rock weathering is a technique designed to reduce the amount of carbon dioxide in the atmosphere. Rocks naturally absorb CO2 as they break down in the environment, and enhanced rock weathering is a way of enhancing this process by first pulverizing them to increase their surface area, and then adding the dust to soils to accelerate the sequestration process.

The University of Sheffield team has completed what it says is the first nation-by-nation assessment of what this technique could achieve in terms of carbon dioxide drawdown if applied to the world’s croplands. To do this, the researchers developed a model that accounts for varying carbon dioxide removal potential among the nations, along with the costs involved.

Through its analysis, the team found that globally, enhanced rock weathering could draw as much as two billion tonnes of carbon dioxide from the air each year. This is more than the amount of CO2 emitted through global aviation and shipping combined, and around half of Europe’s current total emissions.

The world’s biggest CO2 emitters – China, the US and India – are the countries with the largest potential, with the capacity to remove one billion tonnes of CO2 each year alone. The researchers say this could be accomplished at a comparable price to other proposed CO2 removal strategies, with a cost of around US$80 to $180 per tonne.

While other countries like Indonesia and Brazil have a carbon footprint 10 to 20 times lower than the US and China, their climates and vast croplands make them highly suitable to the task of carbon dioxide removal via enhanced rock weathering, according to the team.

As for where the pulverized rocks will come from, the researchers suggest sourcing them from waste materials produced by various industries. It could come from the silicate rock dust left over from mining operations, for example, while the silicate by-products of iron and steel manufacturing could also be recycled for these purposes.

Critically, the researchers note that the technique wouldn’t be too difficult to deploy as farmers often use additives such as agricultural lime to treat their soils anyway. The team is calling for governments to establish national inventories of rock dust, and to incentivize the practice of applying it to crops.

“The practice of spreading crushed rock to improve soil pH is commonplace in many agricultural regions worldwide,” says Professor Steven Banwart, a partner in the study and Director of the Global Food and Environment Institute. “The technology and infrastructure already exist to adapt these practices to utilize basalt rock dust. This offers a potentially rapid transition in agricultural practices to help capture CO2 at large scale.”

The research was published in the journal Nature.

Source: University of Sheffield

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