Enhanced rock weathering carbon removal

Verified certificates representing one tonne of CO2 durably removed from the atmosphere by spreading crushed silicate rock on farmland. The carbon is locked into stable bicarbonate, and credits are issued by registries such as Isometric and Puro.earth after measurement and verification, then retired in a buyer's name as proof of removal.

Tens of thousands of years. Once CO2 is converted into dissolved bicarbonate and carried to the ocean, it joins the sea’s enormous alkalinity store on a geological timescale, with about 90% retained over roughly 10,000 years. The storage is geochemical, so no fire, drought or land-use reversal can release it, which puts ERW alongside direct air capture at the durable end of the spectrum.

This is the method’s hardest part and its live scientific debate. Removal is not metered directly; it is inferred from how much rock has dissolved, measured through paired soil and water sampling combined with geochemical models. The leading protocols credit conservatively and deduct downstream losses, and measurement credibility is the attribute Senken weighs most heavily before listing any ERW project.

Reputable projects use silicate rocks such as basalt that are screened for heavy metals and applied at agronomic rates, much like agricultural lime. Basalt carries far lower nickel and chromium than the ultramafic rocks the industry avoids, and feedstock screening and application limits are pass-or-fail criteria in the standards and in Senken’s own review.

Roughly €185 to €300 per tonne of CO2, indicatively, which places it in the middle of the durable market: more than nature-based methods, well below direct air capture. Large disclosed offtakes have cleared at the top of and above that band, because measurement-heavy early supply commands a premium. Deal structure matters as much as geography.

A removal. It takes CO2 out of the atmosphere and locks it into stable bicarbonate that would not otherwise have formed at that rate, distinct from avoidance credits that pay to prevent emissions elsewhere. Under the Oxford Offsetting Principles it counts as removal with long-lived, geochemical storage, the most durable end of the spectrum.

Faster than nature, but not instant. Crushed basalt weathers over several years after spreading, with the reaction back-loaded across roughly a decade and dependent on climate, soil and grain size. Warm, wet regions weather fastest, which is why many projects favour tropical farmland in Brazil and India.

Because heat, moisture and acidic soils dissolve silicate rock far faster, so a tonne of basalt removes its carbon in years rather than decades. That is why the suppliers with the strongest verified-delivery records, in Brazil and India, are tropical, while temperate projects weather more slowly per tonne spread and lean on logistics or faster-weathering feedstocks to compensate.

Yes, for neutralising residual emissions. ERW qualifies as durable, long-lived carbon removal under the SBTi Corporate Net-Zero Standard, and Version 2.0 (published June 2026) leans further into exactly the long-lived storage that enhanced weathering provides. It does not substitute for reducing your own emissions, because nothing does.

Not yet. The EU Carbon Removals Certification Framework adopted its first permanent-removal methodologies, for direct air capture, bioenergy with carbon capture and biochar, in force from May 2026. A dedicated enhanced weathering methodology is still in technical scoping, so CRCF eligibility is emerging; credits remain fully reportable under CSRD ESRS E1-7 in the meantime.

Every project is scored across 600+ data points in Senken’s Sustainability Integrity Index, and fewer than 5% pass. For enhanced weathering the heaviest-weighted dimension is measurement credibility, because that is where the method stands or falls. Senken rejects projects whose accounting leans on optimistic modelling, and delivers audit-ready documentation with every purchase.

Both, in different roles. Biochar delivers verified tonnes at scale today at a lower price, with soil and community co-benefits. Enhanced weathering offers longer, geological-scale permanence on working farmland, but at an earlier stage of measurement and delivery. A common pattern is bulk tonnes from biochar with a deliberate enhanced weathering allocation for maximum durability.