Rock Solid Solution? How Crushed Stone Could Combat Climate Change

Can Crushed Rock Help Cool the Planet? A Look at Enhanced Rock Weathering.

From Brazil’s sugar plantations to India’s tea estates, farmers around the world are turning to a surprising ally in the fight against climate change: crushed rock. This method, known as Enhanced Rock Weathering (ERW), involves spreading finely ground volcanic rock like basalt over farmland. The idea is to accelerate a natural process — the breakdown of rock by rainwater and carbon dioxide — to capture and store CO₂ from the atmosphere.

How ERW Works
Weathering occurs when carbon dioxide in the air or soil dissolves in water to form a weak acid, which breaks down rocks and locks away CO₂ as bicarbonates that eventually turn into limestone. ERW boosts this process by using fast-weathering rocks and increasing their surface area through grinding.

Promise and Pitfalls
ERW is being hailed as a scalable carbon removal solution, with tech firms, airlines, and fashion brands already buying carbon credits from such projects to offset their emissions. However, experts caution that ERW’s effectiveness varies widely.

A U.S. study suggested that applying 50 tonnes of basalt per hectare could remove up to 10.5 tonnes of CO₂ per hectare over four years. But field trials in Malaysia and Australia showed much lower removal rates. “So far, we’ve seen that some of the earlier estimates were overly optimistic,” said Paul Nelson, a soil scientist at James Cook University.

A Challenge to Measure
Tracking how much carbon is actually removed is tricky. Scientists typically measure cations — positively charged ions released during weathering — but these can be produced even when CO₂ isn’t captured, such as when stronger acids in the soil are involved.

Despite these challenges, researchers say the science is sound — it just needs more study and precise monitoring. “There’s no question that ERW works,” said Wolfram Buss, a carbon removal expert at the Australian National University. “But we need more research to know exactly how well.”

Added Benefits
Besides carbon removal, ERW may improve soil health, boost crop yields, and help neutralize harmful soil acids. Even when it doesn’t lock in carbon directly, it can prevent future emissions by stopping acid runoff from reaching rivers and oceans — where it would otherwise trigger the release of CO₂.

Basalt is also cheap and plentiful, often a byproduct of quarrying.

Caution and Oversight
The biggest concern with ERW isn’t safety — though some rocks may contain heavy metals, and handling fine dust requires protection — but accountability. If companies buy credits based on carbon capture estimates that turn out to be wrong, it could lead to a net increase in emissions, undermining climate goals.

Global Rollout
Projects are now underway worldwide — from soy and corn fields in the U.S. to highlands in India. In Brazil, one ERW project recently issued the first verified carbon removal credits. India-based startup Mati Carbon even won the $50 million X Prize for carbon removal this year.

In December, Google signed the world’s largest ERW deal to date, securing 200,000 tons of carbon credits from startup Terradot, which also sold 90,000 tons for $27 million to a group representing companies like H&M.