Rock - Enhanced Weathering

Enhanced rock weathering (ERW) may become one of the largest carbon removal pathways on Earth. The Global Rock C-Sink Standard was the first to certify ERW projects - and the only one honest enough to distinguish between what can be certified today and the carbon drawn down by weathering but cannot yet be reliably measured and predicted.

The Global Rock C-Sink Standard was developed by the Ithaka Institute and published in version 1.0 in December 2023. It was by then the first certification standard for carbon dioxide removal through enhanced rock weathering (ERW). When finely ground silicate rock is applied to cropland, it reacts with dissolved CO₂ in the soil solution, binding atmospheric carbon as bicarbonate. This dissolved inorganic carbon is transported via groundwater and rivers to the ocean, where it remains stable for millennia and contributes to counteracting ocean acidification.

The standard certifies that a defined amount of rock powder with known mineralogical properties was applied to a specified piece of land, in an agronomically sound manner, with a fully documented life-cycle greenhouse gas balance that proves the project is net-negative. It certifies the C-Sink potential — the maximum amount of CO₂ that will be removed once the rock has fully weathered.

What it does not certify is the actual rate of weathering. This is the critical distinction from other ERW certification schemes. A generally accepted, peer-reviewed method for the ex-post quantification of CDR through enhanced rock weathering does not yet exist. Models that claim to predict weathering rates remain insufficiently reliable. Rather than issuing tradeable carbon removal credits based on predictions that cannot be verified, the Global Rock C-Sink Standard takes a different approach: it documents everything that can be documented now — rock properties, soil conditions, climate data, application method, emissions — and holds the certified C-Sink potential in reserve until a robust quantification method has been developed, validated, and accredited.

Once such a method exists, projects that were documented according to the standard can be retroactively converted from C-Sink potential to certified, tradeable carbon removals. Projects that were not documented to this standard cannot be retroactively certified. This means that farmers and project developers who apply rock powder today under the Global Rock C-Sink framework are building a verifiable record that will gain value the moment the science catches up — without pretending the science is already there.

In 2022–2023, the Ithaka Institute, the Carbon Drawdown Initiative, and Carbon Standards International ran a prototype project with nine farmers applying 1,200 tonnes of basanite rock powder in Germany, testing the feasibility and economics of certified ERW in practice. The experience from this project directly shaped the current standard.

Enhanced rock weathering does not compete for land. Applied to existing cropland, it delivers agricultural co-benefits: silicate rock powder provides macro- and micronutrients, raises soil pH in acidic soils, and stabilises soil organic carbon. The standard and its certification are operated by Carbon Standards International. The Ithaka Institute develops and curates the standard.

Link to Global Rock C-Sink Standard v1.0 (PDF)

Link to Carbon Standards International for further information.