Enhanced Rock Weathering Methodology
Enhanced Rock Weathering Methodology

We at are delighted to launch the world's first Enhanced Rock Weathering (ERW) carbon crediting methodology!

Enhanced rock weathering (ERW) is a process that aims to accelerate natural rock weathering during which carbon dioxide reacts with rocks. CO2 is removed from the atmosphere and converted to bicarbonates and/or carbonates. As a carbon removal method, ERW involves finely grinding down silicate rocks to increase their surface area and spreading them over soil. Utilizing natural rainfall and rock chemical reactions, it results in the long-term storage of large amounts of carbon dioxide, for thousands of years.

The Enhanced Rock Weathering Puro Standard methodology was co-created using the latest science by a working group of carbon market experts, project developers and scientific researchers, and was approved by’s Advisory Board after a period of public consultation. It is available for projects who want to monetize their carbon removal activities with CO2 Removal Certificates, CORCs, and for corporations who want to compensate for carbon emissions and contribute to the scaling of this carbon removal method.

As a carbon removal method ERW has multiple strengths:

  • Huge scalability potential - suitable rock types, such as olivine and basalt, and well-established supporting industries for rock mining, grinding and spreading exist across the globe
  • Carbon sequestration volume potential of over a billion tons per year
  • Permanent carbon sequestration of over 10,000 years with low reversal risk
  • No dependency on biomass feedstocks
  • Positive impact beyond carbon removal - particularly in agriculture as it can counteract soil acidity and increase soil fertility, build plant resistance against pests and diseases, and improve crop water retention, potentially increasing crop resilience to drought.

ERW can be carried out in terrestrial (soils), coastal and aquatic environments. This methodology only considers the application of rock in terrestrial environments.

Point of creation of the CORC

During the development of the ERW methodology, several options for the point of creation of the carbon removal certificates (CORCs) were considered. These options ranged from fully ex-post issuance (CORCs issued only once the sequestration has already happened and was empirically demonstrated) to various methods of issuance based on simulated results. In the end, the fully ex-post issuance was chosen and all CORCs are issued after field-data measurements validate simulations.

While the methodology does not outright require or endorse any particular funding methods for projects, it is noted that the funding gaps associated with the long return periods need to be bridged with, for example Pre-CORCs (essentially prepayments for possible future CORCs, for which no removal claims can be made), the project’s own equity, or various other means of funding.

Safety first

The safety focus of this methodology allows ERW projects and supporting corporate CORC buyers to start operations with confidence, delivering more data needed to scale ERW as a carbon removal solution, globally.

During the weathering of silicate rocks, elements are released into the soil, like calcium and magnesium, which are needed for carbon removal. Depending on the individual rock chemistry and mineralogy, it can also include elements that above certain levels are considered as contaminants. Once the silicate rock is applied to the soil it cannot be undone. Therefore, we require serious consideration of the risks before any activity is undertaken.

The working group defined environmental safeguards aligned with the latest science to ensure little to no environmental impact. Where there is no local regulation guiding threshold levels of potentially toxic elements, such as heavy metals, EU thresholds for inorganic soil improvers will be used. Where there is a local regulation that differs to those set by the EU, local thresholds should be followed but if EU threshold limits are more stringent a contextual justification is required.

Projects are also required to perform laboratory tests of samples to establish toxicity baselines, in both ground rock and application site soils, before and after spreading.

Eligibility requirements

Aspiring ERW projects that want to be issued CORCs need to submit their quantification approach for consideration by the Puro Standard, with the following requirements. To see how these align to the IC-VCM Core Carbon Principles, please see the methodology document below.

Suppliers must provide convincing evidence demonstrating that the project would not have occurred in the absence of the incentive created by carbon credit revenues. The Puro Standard relies on investment analysis which is the leading method to measure financial additionality.

Life Cycle Assessment
We require the full scope of a project’s emissions, from cradle-to-grave, including sourcing or mining of materials, processing of silicate rock, crushing of production, transportation, and application-related emissions. The producer must demonstrate net negativity with results from a life cycle assessment.

The life cycle assessment (LCA) shall follow the general guidelines of the ISO standards 14040/44 for LCAs, unless otherwise specified:

Simulated weathering
The estimated amount of removed carbon from the ERW project activity will need to be presented via a simulated weathering result. The result of which will then need to be validated with post-application measuring and reporting.

Accepted land types include acidic arable and forest lands where no effects on water resources can occur and degraded sites can be considered where restoration of the land is needed along with CO₂ removal.

Carbon content determination
ERW in soils leads to the formation of both carbonates and bicarbonates, in variable proportions determined by local environmental conditions. The carbonate minerals form part of the soil, and CO₂ remains stably sequestered in soils. The bicarbonates are dissolved in the soil water and can ultimately reach river streams and oceans, where CO₂ remains stable. In both forms, the permanence of the carbon storage arising from enhanced rock weathering is deemed to be guaranteed for 10,000 years with little risk of reversibility, either by human or natural activity.

We require each project to report the performance of CO₂ removal volumes and submit the report annually for third-party verification to prevent any uncertainty of over-crediting.

Rock type
The mineral composition of rocks affects the rate of weathering. The most suitable rocks usually contain minerals with high amounts of magnesium and calcium.

Rock particles size
The rate of mineral dissolution is proportional to the surface area of the rock, thereby, rock crushing, and grinding improve the rate of enhanced rock weathering.

Environmental and climatic conditions
The acidity of soils, availability of water and temperature can all impact the rate of silicate dissolution and therefore accelerate the rate of weathering and carbon removal. The methodology supports ERW in optimal warm tropical regions that are known for their highly weathered and acidic soils. 

Rock toxicity levels
All rock materials considered for ERW will be analyzed for potential toxic contaminants to ensure minimal environmental impact will occur from the weathering process. We also require projects to perform laboratory tests of application site soil samples to establish baselines.

Sourcing of rocks
Silicate rocks must be sourced in accordance with local regulations, in particular mining regulations. Where relevant, suppliers will be required to provide proof of any exploitation permit, land use right, or environmental permits, as well as certification of operations.

The residual rocks from other processes, such as basaltic or cement kiln dust, can be beneficially used for ERW and are supported under the methodology.

Application site
An environmental risk assessment as well as a proper analysis of food safety must be completed before the decision to apply weathering rock material at the potential application site can be considered. The supplier must also provide evidence regarding the right or authorization to spread the silicate rock onto the application site.

Local communities
Suppliers are required to provide evidence of how they gathered informed consent from local communities for the operation of ERW. They also need to provide evidence that such communities were informed on the acceptability limits for contaminants as well as any possible environmental risks associated with the ERW activity both at the specific site of application and in the receiving catchment during stakeholder consultations. Engagement with local communities will need to be maintained in an ongoing and transparent manner throughout the project’s lifetime. Evidence will also be required as proof that the project will not operate on land that has been identified as culturally sensitive or cause community displacement.

Occupational hazards
The supplier will be required to present measures taken for occupational health and safety hazards during operation or the ERW activity. The activities such as crushing, grinding, and spreading shall be performed in accordance with local regulations on noise limits and dust emission limits.

Surrounding ecosystems
Suppliers must demonstrate evidence that projects have a low risk of any negative impact on the surrounding ecosystems including soil health, biodiversity, water, and air pollution. Furthermore, suppliers will be required to submit follow-up reports on the impact on crop quality and yield after the application of silicate rock to agricultural soils.

Carbon removal certification and verification

Under the Puro Standard, all carbon removal suppliers go through a rigorous verification process to confirm that their products and processes are truly carbon net-negative. The ERW supplier must complete a full Lifecycle Assessment (LCA) to measure total project emissions which will then be audited by third-party assessors who visit the production facility, validate the accuracy of data, and issue an audit statement.

Once silicate rocks are applied to the soil, the ERW supplier is required to measure and verify the volume of removed carbon annually for as long as it wishes to be issued CO₂ removal certificates (CORCs). 

Consultation feedback

The Public Consultation took place in October, 2022. All respondents were encouraging and welcomed the work, and how comprehensive the methodology is. Feedback received tackled mainly: environmental risk assessment procedures; carbon accounting rules for ERW; and modelling and measuring ERW in field. The working group further elaborated on these aspects, making the methodology more precise. A summary of development dates and public consultation feedback can be found here

Enhanced rock weathering has been considered for decades to remove atmospheric carbon dioxide, yet it had not been included in any existing carbon crediting standard, so we are very excited to see how far we can scale Enhanced Rock Weathering within the carbon markets! 📈

Find more info by downloading the methodology and interactive ERW brochure, reading the press release and watching the webinars from the working group and AirMiners.

Methodology document

Press release

Interactive ERW Brochure

Watch the methodology presentation of the working group to the Puro Standard Advisory Board:


Watch the AirMiners webinar on Monitoring, Reporting and Verification of Enhanced Rock Weathering moderated by our VP of Methodologies, Leonard Smith.


If you are a project developer or potential supplier of Enhanced Rock Weathering in Soil carbon removal, please contact us.

If you are interested in buying CORCs from a Enhanced Rock Weathering in Soil project, get started here

Are you ready to include carbon removal in your climate actions? Welcome to learn more about carbon removal suppliers at and don't hesitate to contact us. 

4th Carbon Removal Ecosystem Meeting - Watch the recording!
4th Carbon Removal Ecosystem Meeting - Watch the recording!

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