On January 20, 2026, Isometric issued the world’s first verified River Alkalinty Enhancement (RAE) carbon dioxide removal (CDR) credits to CarbonRun. The 76.69 credits mark the first verified RAE issuance globally and demonstrate that the pathway can deliver measurable, permanent carbon removal.
RAE addresses carbon emissions by accelerating the Earth’s natural weathering process. Finely crushed limestone is dissolved into river water, where it reacts with acidic carbon dioxide to form stable carbonate and bicarbonate ions. This reaction prevents carbon dioxide from being released into the atmosphere. These stable ions are carried downstream to the ocean, where the carbon is safely stored for tens of thousands of years.
This explainer walks through how these world-first credits were quantified.
Project background
CarbonRun’s Kvina River Project operates on the Kvina River in southern Norway, a 73 km watercourse draining approximately 1,560 km² to Frafjorden, which opens to the North Sea. The project employs RAE by dosing calcium carbonate slurry at the Nyland site, located 15.6 km upstream from the river mouth.
The Kvina River basin has historically experienced acidification, resulting in low pH values (pH 4.5-5.2) that have made the river unsuitable for salmon populations. Since the 1990s, Norway has operated an extensive river liming program to address acidification. River liming involves adding alkaline feedstock, in this case, a calcium carbonate slurry, to the river.
The river system has been limed since 1994 to mitigate acidification, particularly episodic low pH and elevated aluminium levels that can threaten salmon and other aquatic life. This liming is conducted through multiple dosing stations using a baseline liming regime designed to support salmon spawning cycles. While the baseline pH targets for this liming (6.0-6.4) meet Norwegian water quality standards for acidified rivers, water quality targets recommend pH above 6.5.
CarbonRun’s Kvina River Project augmented the existing dosing operations from June 10 to September 15, 2025 (97 days), targeting elevated pH conditions to a target pH of 7.0. The project dosed approximately 1749 tonnes of calcium carbonate in total, with 1480 tonnes representing additional dosing above the baseline liming requirements.
The monitoring network comprises two primary sites: a reference station at Little Ana (LA) on a tributary of the Kvina River where baseline liming continued unchanged, and a downstream site at Kloster (KL), positioned near the river mouth where the alkalinity is monitored as the river flows into the fjord. For the full monitoring plan and additional details on ecosystem safety, see the Project Design Document (PDD).
With this context established, the quantification approach can be understood in full.
Quantification approach
Isometric’s River Alkalinity Enhancement Protocol outlines the requirements to quantify gross atmospheric carbon dioxide removal. Below is an overview of how it was applied to CarbonRun’s project. See Section 8.0 of the protocol for more details on the quantification approach.
Net CDR was calculated as:
Dissolved Inorganic Carbon (DIC) export in project scenario* ocean retention factor - DIC export in baseline scenario* ocean retention factor - counterfactual feedstock weathering - carbon content in additional feedstock dose - project emissions - uncertainty
DIC export in the project scenario
DIC export in the project scenario is the total amount of DIC that is delivered from the Kvina River to the ocean. It is directly measured at the river mouth using a combination of weekly grab samples for water chemistry analysis and in situ sensors for discharge and temperature. The measured Total Alkalinity (TA) and pH was used to calculate DIC using PyCO2SYS.
To ensure a signal above environmental noise was measured, statistical tests were used to confirm the measured DIC in the project scenario significantly exceeded the predicted baseline DIC (p < 0.05).
DIC export in baseline scenario
To determine the amount of DIC measured from the Kvina River that is attributable to the project, the baseline amount of DIC export without the project must be estimated and subtracted.
To do this, two short-range river forecast models were built to predict baseline pH and alkalinity at KL (near the river mouth) from observations at LA (where business-as-usual liming occurred). These linear models are trained on historical data dating back to 2011. A number of safeguards were applied to the baseline model to ensure robust science:
- The models could only be used when predictors remained within training data ranges
- The root mean square error from model validation needed to be used in uncertainty propagation
- A post-project model validation was conducted to confirm the model could predict the most recent baseline conditions
The predicted TA and pH from the short-range river forecast models were used to calculate DIC using PyCO2SYS.
Ocean retention factor
Not all alkalinity exported to the ocean is guaranteed to result in permanent carbon dioxide storage—some may be released back to the atmosphere depending on the river water and seawater chemistry. This release must be subtracted to ensure the net carbon removal is accurately quantified.
The ocean retention factor represents the percentage of DIC that will stay durably stored in the ocean. Using a thermodynamic equilibrium model, the DIC conditions at the river mouth are used to estimate ocean conditions. This conservatively quantifies how much carbon dioxide would be lost following ocean equilibration.
Counterfactual feedstock weathering
In the absence of the project, the additional feedstock would have been discharged in a submarine tailings pile, of which some of the additional feedstock would have weathered naturally. This must be subtracted to ensure the project is additional. To do this, three counterfactual weathering pathways were considered:
- Dissolution prior to ocean discharge,
- Dissolution of fine feedstock particles in the water column, and
- Metabolic dissolution of bulk feedstock by organic sediments in a submarine tailings pile
Feedstock dissolution over 100 years was estimated for each of these pathways, and the dissolved feedstock was assumed to achieve full atmospheric carbon dioxide removal potential:
- Dissolution prior to ocean discharge was determined using geochemical modeling and operational information about mixing with freshwater or acidity at the feedstock processing site.
- Fine particles in the water column were assumed to be 100% dissolved.
- Metabolic dissolution was determined using geochemical modeling, constrained by fjord water column measurements and sediment core data.
More information can be found in Section E.17 of the PDD.
Carbon content in additional feedstock
Since CarbonRun used calcium carbonate as a feedstock, the dissolution of the feedstock itself contributes carbon to the river. The carbon from the feedstock would not be in the river without the project, so it must be subtracted from the DIC measured in the river.
Historical dosing data from 2023-2024 was used to establish the baseline (business-as-usual) alkalinity addition that would have occurred without CarbonRun’s intervention and the additional feedstock. The carbon content in the feedstock was determined through elemental analysis during feedstock characterization.
Project emissions
Emissions related to project activities were quantified according to Section 7.4.4 of the protocol—which aligns with best practices from ISO standards—and subtracted from the gross carbon removal. This includes emissions related to feedstock production and transport, site operations and monitoring, and personnel transportation and accommodation.
Uncertainty
To credit accurately and conservatively, the net carbon removal calculation must account for uncertainty in the underlying measurements and models.
The following sources of uncertainty were quantified and used to calculate an overall uncertainty value using Monte Carlo simulations. Monte Carlo simulations repeat the same calculation thousands of times using slightly different values spanning the range of uncertainty for each parameter to produce an overall probability distribution for the net carbon removal. One standard deviation is subtracted from the mean carbon removal quantification to ensure conservatism.
The following parameters were included in the uncertainty assessment:
- Uncertainty in mass of total feedstock dosed
- Uncertainty in mass of baseline feedstock dosed
- Uncertainty in the feedstock carbon fraction
- Uncertainty in river discharge
- Uncertainty in DIC in the project scenario
- Uncertainty in DIC in the baseline scenario
- Uncertainty in ocean retention factor
- Alkalinity production and transportation emissions
- Operational energy use emissions
Why this matters
The issuance of the world’s first RAE credits demonstrates that this pathway can deliver measurable, verifiable, and permanent carbon dioxide removal while providing important co-benefits to river ecosystems. The data and insights from these first credits will accelerate RAE's development as a pathway with the potential to remove millions of tonnes of carbon dioxide from the atmosphere each year.
Learn more
You can explore the credits on the Isometric Registry, along with associated source documents including the Validation and Verification Report and PDD, for more details on this project. Isometric welcomes continued discussion and any questions or comments. Please get in touch at contact@isometric.com.
