Rocks have always absorbed carbon dioxide as they weather, but slowly. Enhanced rock weathering (ERW) speeds that up by grinding suitable rock and spreading it where it can react. It promises very long storage at a lower cost than machines, with one big catch: proving how much carbon a field actually removed. This page covers how it works, how it is credited and what to check. It is part of our guide to carbon credit project types.
How enhanced weathering works
Puro.earth describes ERW as fast-tracking natural rock weathering by crushing large silicate rocks into fine particles, or gathering residual rock from other processes, and applying it to soilSource 2. Removal speeds up by choosing the most reactive rock types, increasing the rock’s surface area and applying it to suitable soils and climatesSource 2.
As the rock dissolves, it reacts with CO₂ in soil water. The carbon ends up stored in dissolved form, which rivers can carry to the sea, or in new minerals. Isometric’s protocol requires long-duration storage of CO₂ in seawater and/or soilSource 4.
The IPCC groups carbon dioxide removal processes as biological, geochemical or chemicalSource 6; enhanced weathering is a geochemical one. Puro.earth argues the method can scale because the resources required are abundant across the globe and rock mining, grinding and spreading are established technologiesSource 2.
Most projects so far are on farmland. Puro.earth lists agricultural co-benefits, including improved soil fertility and crop yield and reduced reliance on fertilisersSource 2.
Matched shop
Buy engineered removal credits
- Registry serial numbers
- Retirement certificate
- Project documentation
Removal, not avoidance
ERW produces removal credits: the CO₂ comes out of the atmosphere and is stored. The Oxford Offsetting Principles describe carbon removal to the geosphere as including converting atmospheric carbon into rock through remineralisationSource 7, and class mineralised storage among the options with a low risk of reversalSource 7.
Read removal vs avoidance credits for how removals compare with reduction credits.
How permanent is it?
Storage is one of ERW’s strengths.
- Puro.earth states its methodology provides carbon removal permanence of 1,000+ years, calling ERW one of the most permanent forms of carbon removal, with little risk of reversalSource 2.
- Isometric requires storage estimated at 1,000 yearsSource 4.
- The Oxford Principles say mineralising carbon into a stable form can store it for centuries to millenniaSource 7.
The measurement problem
The harder question is how much CO₂ was removed in the first place. The reaction happens slowly, spread across large fields, and some of the effect is lost along the way. Standards have responded by tightening their rules.
- Two methods, one check. Puro.earth’s November 2025 update describes seven eligible measurement approaches and requires projects to combine two: one to quantify the stored CO₂ and one to validate it. It also requires rigorous use of control plotsSource 3.
- Losses. The update accounts for losses such as secondary mineral formation, cation adsorption, plant uptake, weathering by acids other than carbonic acid, and losses in rivers and the oceanSource 3. Isometric’s protocol likewise deducts plant uptake, new carbonate minerals and non-carbonic acid weathering, and applies a retention factor for river and ocean processesSource 4.
- Uncertainty discounts. Puro.earth now applies an uncertainty discountSource 3. Isometric credits projects at the 30th percentile of their estimated removal by default, or the 40th percentile if they pass an optional validation stepSource 4.
Why percentiles matter
Crediting at the 30th percentile means a project is credited for a figure it is about 70% likely to have reached or exceeded, not its best guess. That builds caution into each tonne you buy.
What do enhanced weathering credits cost?
We have not found an openly published average transaction price for ERW credits, so we don’t quote one; our price snapshot leaves engineered removals other than biochar out for the same reason. For context, Ecosystem Marketplace reports that removal credits averaged $19.50 per tonne in 2024 and biochar over $160Source 8. Check our carbon credit prices page for updates.
Risks and integrity issues
- Measurement uncertainty is the main risk, as above. Ask which quantification approaches a project used and what discount was applied.
- Life-cycle emissions. Mining, grinding and transporting rock all emit CO₂. Puro.earth says environmental stressors and emissions are measured and verified by third-party auditors at each stepSource 2.
- Scale. The IPCC notes that CDR methods vary widely in maturity, cost, risks and governance needs, and that scaling them up depends on addressing feasibility and sustainability constraintsSource 6.
Rock spread is not carbon removed
Tonnes of rock applied are not tonnes of CO₂ removed. A credible seller can show measured removal, the losses deducted and the registry record for the issued credits.
Standards and methodologies
Scrolls sideways to show every column.
| Programme | Methodology | Notes |
|---|---|---|
 Puro.earth | Enhanced Rock Weathering (2025 edition) | Two-method quantification, uncertainty discount |
 Isometric | Enhanced Weathering in Agriculture, v1.2 | Credits at 30th or 40th percentile |
Logos identify the organisations named; no endorsement is implied.As of Oct 2026
Puro.earth says its 2025 update aligns the methodology with its General Rules and the ICVCM Core Carbon PrinciplesSource 3. The ICVCM’s October 2025 batch of carbon removal approvals covered DAC, biomass storage and concrete carbonation methodologies, not enhanced weatheringSource 5.
Buying enhanced weathering credits
- Ask how removal was measured, which losses were deducted and what uncertainty discount applies.
- Check whether credits are issued or sold ahead of measurement.
- Verify retirement in the registry; our guide to how to verify carbon credits explains how.
Compare ERW with biochar and direct air capture, or see how buyers blend removal types in a portfolio approach.