Rock dust on croplands could remove billions of tonnes of carbon dioxide from the atmosphere

The study conducted by Sheffield University’s Leverhulme Centre for Climate Change Mitigation, found that adding rock dust to farmland could remove the carbon dioxide equivalent of more than the current total emissions from global aviation and shipping combined.

The carbon dioxide produced by both industry’s is roughly equal to half of Europe’s current total emissions.

Published in weekly journal Nature, the study reveals how spreading finely crushed basalt, a natural volcanic rock, on fields can boost the soil’s ability to extract CO2 from the air.

The scientists have demonstrated the method’s potential for carbon drawdown by major economies, and identified the costs and engineering challenges of scaling up the approach to help meet ambitious global CO2 removal targets.

Led by experts at the University of Sheffield’s Leverhulme Centre for Climate Change Mitigation with Professor Steven Banwart from the University of Leeds as a principal author, the analysis captures some of the uncertainties in enhanced weathering CO2.

It has also helped to identify the additional areas of uncertainty that future work needs to address specifically through large-scale field trials.

Encouragingly, despite China, the United States and India emitting the highest level of CO2 fossil fuels, they also have the highest potential for CO2 drawdown using rock dust on croplands.

All three nations have a combined potential of approximately 1 billion tonnes of CO2 per year from the atmosphere, at a cost comparable to that of other proposed carbon dioxide removal strategies (US$80-180 per tonne of CO2).

Indonesia and Brazil, whose CO2 emissions are 10-20 times lower than the US and China, were also found to have relatively high CO2 removal potential due to their extensive agricultural lands, and climates accelerating the efficiency of rock weathering.

Professor Steven Banwart, a partner in the study and Director of the Global Food and Environment Institute at Leeds, said: “The practice of spreading crushed rock to improve soil pH is commonplace in many agricultural regions worldwide.

“The technology and infrastructure already exist to adapt these practices to utilise basalt rock dust. This offers a potentially rapid transition in agricultural practices to help capture CO2 at large scale.”

Meeting the Paris Agreement’s goal of limiting global heating to below 2 degree Celsius above pre-industrial levels requires drastic cuts in emissions, as well as the active removal of between two and 10 billion tonnes of CO2 from the atmosphere each year to achieve net-zero emissions by 2050.

This new research provides a detailed initial assessment of enhanced rock weathering, a large-scale CO2 removal strategy that could make a major contribution to this effort. 

The scientists suggest that meeting the demand for rock dust to undertake large-scale CO2 drawdown might be achieved by using stockpiles of silicate rock dust left over from the mining industry, and are calling for governments to develop national inventories of these materials.

Calcium-rich silicate by-products of iron and steel manufacturing, as well as waste cement from construction and demolition, could also be processed and used in this way, improving the sustainability of these industries.

These materials are usually recycled as low value aggregate, stockpiled at production sites or disposed of in landfills.

China and India could supply the rock dust necessary for large-scale CO2 drawdown with their croplands using entirely recycled materials in the coming decades.

The technique would be straightforward to implement for farmers, who already tend to add agricultural lime to their soils. The researchers are calling for policy innovation that could support multiple UN Sustainable Development Goals using this technology.

Government incentives to encourage agricultural application of rock dust could improve soil and farm livelihoods, as well as reduce CO2, potentially benefiting the world’s 2.5 billion smallholders and reducing poverty and hunger.

Professor David Beerling, Director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield and lead author of the study, said that the process is “straightforward” and offers a potential boost to “soil health and food production”.

“Carbon dioxide drawdown strategies that can scale up and are compatible with existing land uses are urgently required to combat climate change, alongside deep and sustained emissions cuts,” he said.

“Our analyses reveal the big emitting nations – China, the US, India – have the greatest potential to do this, emphasising their need to step up to the challenge. Large-scale Research Development and Demonstration programmes, similar to those being pioneered by our Leverhulme Centre, are needed to evaluate the efficacy of this technology in the field.”

Professor James Hansen, a partner in the study and Director of the Climate Science, Awareness and Solutions Program at Columbia University’s Earth Institute, said: “We have passed the safe level of greenhouse gases. Cutting fossil fuel emissions is crucial, but we must also extract atmospheric CO2 with safe, secure and scalable carbon dioxide removal strategies to bend the global CO2 curve and limit future climate change.

“The advantage of CO2 removal with crushed silicate rocks is that it could restore deteriorating top-soils, which underpin food security for billions of people, thereby incentivising deployment.”

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