New Scientist highlighted a growing body of research suggesting that spreading crushed basalt on farmland could absorb up to 1 billion tonnes of CO₂. Field trials in Queensland, Australia, are among the latest to generate real data. Nations like Brazil are already deploying enhanced rock weathering (ERW) at scale, partly because crushed silicate rock also reduces fertiliser costs.

Big number. Important caveat: “could” is doing a lot of work in that headline.

What CDI’s Research Actually Shows

CDI runs the world’s largest greenhouse EW experiment — over 400 lysimeters, 2+ years of data, roughly 1 million CO₂ readings through Project Carbdown. What we’ve learned tempers the enthusiasm with specifics:

Soil type determines everything. Acidic soils are where ERW works best. High-pH soils hit saturation and produce minimal additional weathering. A global “1 billion tonnes” number obscures massive variability by geography and soil chemistry.

Cation retention is the elephant in the room. In Year 1, CDI’s data shows 10–50× more cations retained in soil than exported as alkalinity. Measuring only what leaves the field drastically underestimates total weathering — but also means the carbon isn’t in the ocean yet, and the permanence timeline is longer than simple models suggest.

MRV is the bottleneck, not the rocks. Carbon-based MRV methods have fundamental limitations for field EW. CDI advocates for cation-based or total alkalinity-based approaches. Electrical conductivity (EC) tracks alkalinity well at macro scale but breaks down at treatment level, as our Part 7 research demonstrated.

The Honest Take

ERW absolutely has billion-tonne potential. The geology is right, the co-benefits (soil pH, reduced fertiliser needs, crop yields) are real, and deployment on farmland avoids the land-use conflicts that plague afforestation.

But getting from “potential” to “verified, permanent removal” requires solving the measurement problem. How much CO₂ did this specific field application actually remove? When? How permanently? Those questions need multi-pool, multi-year monitoring — exactly what CDI is building.

The rocks work. Proving they worked — that’s the hard part.

Sources: New Scientist, CDI Research

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