Enhanced Rock Weathering Could Help Crops Remove 2 Billion Tonnes of CO₂ Each Year

Cutting the carbon dioxide (CO₂) released into the atmosphere dramatically is the most effective response to the climate crisis. However, drawing CO₂ out of the air could also have a major impact, and scientists have identified a method that could substantially increase the amount of CO₂ absorbed by crops.

The method involves applying crushed rock dust, setting off a process called enhanced rock weathering (ERW). Minerals in the fine rock fragments chemically bind to the CO₂ that rainwater naturally collects as it falls to the ground.

The resulting bicarbonate is then carried away, becoming stored in the soil or eventually reaching the ocean.

Although rock weathering occurs naturally, using finer rock particles accelerates the process so that it can take place within months.

Enhanced rock weathering could remove CO₂ from farmland

The researchers calculated that rolling out this straightforward crop treatment globally could remove 2 billion tonnes of CO₂ each year.

That is roughly equivalent to the amount of CO₂ released annually by the aviation and shipping sectors.

"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," says David Beerling, the director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield in the UK.

"Spreading rock dust on agricultural land is a straightforward, practical CO₂ drawdown approach with the potential to boost soil health and food production."

For their assessment, the team produced detailed gridded maps covering global farmland and the weather conditions affecting it. They examined costs, engineering obstacles and CO₂ removal capacity on a country-by-country basis.

They also accounted for local soil quality and the energy needed to transport rock dust to individual sites. After all, there would be little value in extracting CO₂ from the air if delivering the required material to farmers generated even greater emissions.

Global deployment and existing farming infrastructure

The scientists believe the 2 billion tonne target could be achieved by 2050 if there is coordinated action worldwide. Though the strategy presents challenges, it has several advantages, including the fact that farmers already use a comparable practice.

"The practice of spreading crushed rock to improve soil pH is commonplace in many agricultural regions worldwide," says Steven Banwart, director of the Global Food and Environment Institute at the University of Leeds in the UK.

"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."

The approach brings several additional benefits. It could slow the loss of topsoil, lower the acidity of rainwater and oceans, and make use of stockpiled silicate rock dust from mining, alongside construction by-products.

Scientists have investigated the concept for several years, but this is the first in-depth study of ERW's possible worldwide costs and effects. According to the researchers, countries with the greatest CO₂ emissions, including the US and India, could remove the largest quantities of carbon dioxide because they have extensive agricultural sectors and suitable climates.

Challenges for rock dust carbon removal

Nevertheless, the undertaking would remain enormous. Work across farms worldwide would require careful coordination, substantial funding would be essential, and applying rock dust to crops would unfortunately be far from sufficient on its own to solve the problem.

In addition, this detailed model must now be tested under real-world conditions to support its findings and identify any possible unintended effects.

Even so, the need for options such as this has rarely been greater.

"We have passed the safe level of greenhouse gases," says climatologist James Hansen, from Columbia University.

"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 research has been published in Nature.