Crushed Rock Could Help Tackle Climate Change — But How Effective Is It?
From sugarcane fields in Brazil to tea plantations in India, a new climate solution is taking root — literally. Known as Enhanced Rock Weathering (ERW), the technique involves spreading finely crushed rock, often basalt, across farmland to accelerate the natural process of carbon capture.
The idea is simple: weathering — the natural breakdown of rock by weak acids like carbonic acid formed from carbon dioxide and water — removes CO₂ from the atmosphere over time. ERW speeds this up using crushed, fast-weathering rocks to increase surface area and, in theory, maximize CO₂ absorption.
A Growing Industry
ERW is attracting significant interest from companies looking to offset carbon emissions. Airlines, tech firms, and fashion brands are purchasing carbon credits from ERW initiatives to meet their climate pledges.
In 2024, an ERW startup in India, Mati Carbon, won the $50 million X Prize for carbon removal. That same year, Google struck the world’s largest ERW deal for 200,000 tons of carbon removal credits with startup Terradot, which also sold 90,000 tons for $27 million to another corporate buyer group including H&M.
Does It Actually Work?
Scientific opinion is cautiously optimistic — but with caveats.
One U.S. study estimated that applying 50 tonnes of basalt per hectare annually could remove up to 10.5 tonnes of CO₂ per hectare over four years. However, field trials in Malaysia and Australia have found significantly lower carbon capture rates, raising concerns over overly optimistic modeling.
“It’s clear we’ve overestimated the amount and speed of carbon capture in some trials,” said soil scientist Paul Nelson of James Cook University.
Measurement Challenges
Measuring carbon capture through ERW is complex. The most common method tracks the release of cations — positively charged ions — which signal that weathering has occurred. But cations are released regardless of which acid initiates the reaction, meaning they don’t necessarily prove that CO₂ was captured.
“There’s no doubt this process works,” said Wolfram Buss, a researcher at the Australian National University. “But if we want precise data on how much carbon is removed, we need better funding and more research.”
More Than Just Carbon
Beyond carbon capture, ERW offers agricultural benefits. Basalt can improve soil quality, increase alkalinity, and provide nutrients that boost crop yields. The rock is also widely available and often a byproduct of mining, making it cost-effective.
Even when ERW doesn’t capture carbon directly, it may still reduce indirect emissions. By neutralizing soil acidity, the crushed rock can prevent acid runoff into waterways — a process that would otherwise trigger CO₂ release downstream.
Risks and Uncertainties
While generally considered safe, ERW comes with risks. Some rocks contain heavy metals, posing contamination hazards. The fine rock dust also requires protective handling. The biggest risk, however, is overestimating carbon capture and issuing credits that don’t reflect real reductions — leading to “phantom offsets” that allow emitters to pollute more than they should.
Where It’s Happening
ERW projects are underway across Europe, North and South America, and Asia. In early 2024, a project in Brazil issued the first verified carbon removal credits from ERW, marking a milestone for the technology. The technique is being tested in a wide range of agricultural contexts, from soy and maize fields in the U.S. to tea estates in India’s Darjeeling region.
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