New Study Demonstrates Measurable Carbon Removal Through Enhanced Weathering in a Temperate Climate

UNDO has released a new scientific study that demonstrates measurable carbon dioxide removal (CDR) through enhanced weathering in a temperate climate.

The ongoing study, conducted over 1.5 years at a field site in Scotland, shows that enhanced weathering can achieve statistically significant CDR even under cooler, wetter conditions.

This paper, currently available as a preprint submitted to Frontiers in Climate, strengthens the real-world evidence base for enhanced rock weathering (ERW) and highlights the importance of rigorous field monitoring.

Enhanced Rock Weathering Captures CO₂ in Real-World Field Conditions

Enhanced rock weathering (ERW) is a nature-based carbon removal solution that accelerates the natural process of rock dissolution to capture additional atmospheric CO₂.

By spreading crushed silicate rock, such as basalt, onto agricultural land, chemical reactions that dissolve the rock also transform carbon dioxide into stable bicarbonate ions, which are eventually transported to the oceans for long-term storage.

UNDO’s approach to ERW is grounded in building a credible evidence base through field-based validation and real-world MRV.

While theoretical models have projected the large-scale potential of ERW, delivering measurable, verifiable carbon removal in real-world conditions is critical for building trust, securing investment, and scaling this essential climate solution.

This latest study offers one of the clearest demonstrations to date that ERW can deliver measurable CO₂ removal at field scale in a temperate, agricultural setting.

The Field Trial Design

The field trial took place on a grassland pasture used for occasional grazing at the Dumyat Estate near Stirling, Scotland.

The local climate is classified as “temperate oceanic”, with a mean annual temperature during the study of 8.2°C and an average daily precipitation surplus (precipitation minus evapotranspiration) of 2.8 mm/day.

The experimental setup included four large plots (48 x 100 metres each), treated with varying application rates of crushed basalt:

– 0 tonnes per hectare (control plot)

– 23 tonnes per hectare

– 78 tonnes per hectare

 – 126 tonnes per hectare

Basalt was surface-applied using a commercial agricultural spreader and hand-sieved in central monitoring zones, where porewater was collected, to ensure uniformity.

Importantly, the basalt used was relatively coarse-grained (D50 = c.1 mm) and had a measured specific surface area of 0.917 m²/g.

While this design reflects practical, farmer-ready deployment, the coarser material and surface-only application likely contributed to slower weathering rates compared to finely crushed or soil-incorporated feedstocks.

Direct Evidence of Carbon Dioxide Removal

To assess potential carbon dioxide removal (pCDR), the team focused on two key measurement approaches:

1. Direct pCDR —  estimated bicarbonate fluxes from cation and anion balances in soil porewater.

2. Inferred pCDR — estimating changes based on soil cation exchange pools.

Porewater Sampling and Results

Porewater samplers (known as rhizons) were installed at 5 cm and 10 cm depths in each plot.

Porewater was collected approximately every two weeks, whenever soil moisture allowed, providing one of the most detailed porewater datasets for enhanced weathering in a temperate field setting.

By analysing the concentration of major base cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and anions, and inferring subsequent bicarbonate levels, researchers could estimate how much carbon was being removed and in the process of being transported through the soil system.

After 1.5 years of weathering, the results showed significant direct pCDR at 5 cm depth:

– 78 t/ha basalt → 0.33 ± 0.11 tonnes CO₂ per hectare

– 126 t/ha basalt → 0.53 ± 0.13 tonnes CO₂ per hectare

– An increase in measured CO₂ removal was observed at higher basalt application rates in the 5 cm soil layer.

A linear trend was observed, and when normalised to the mass of rock applied, for both application densities:

 – 42 kilograms of CO₂ removed per tonne of basalt applied per hectare (0.0042 tCO₂/ha/tRock).

These findings are consistent with the mid-range of results from other global enhanced weathering field trials, confirming that even coarse, surface-applied basalt in temperate climates can deliver measurable carbon removal over relatively short timescales.

No significant pCDR was detected at the 10 cm depth, suggesting that much of the weathering signal remains concentrated in the shallow soil layers during the early years of deployment.

It is also important to note that sampling was conducted at discrete time intervals, so some cation fluxes may have been missed. As a result, these reported values likely represent a conservative estimate of total CDR at the site. This underlines the need for additional MRV approaches, such as total cation analysis (TCA), or different pore water measurement techniques, that can capture time-integrated signals across all relevant pools.

The Importance of Real-World Monitoring

UNDO’s monitoring, reporting, and verification (MRV) approach integrates porewater chemistry with precipitation surplus data to calculate bicarbonate flux. This method provides a robust, high-resolution measure of potential carbon removal, grounded in actual field conditions.

The study highlights why frequent sampling is so important.

Porewater bicarbonate concentrations fluctuated significantly over the year, reflecting rainfall patterns and seasonal soil dynamics.

By sampling every two weeks rather than relying solely on annual average precipitation surplus, the team was able to capture these critical variations.

This type of high-resolution, field-based data is essential for developing MRV protocols that reflect real conditions and satisfy the expectations of buyers and regulators as the CDR market matures.

Theory vs Practice: Bridging the Gap

One of the key findings of the study was the comparison between theoretical maximum CDR and real-world results.

Using the rock’s chemistry, the theoretical maximum carbon removal potential (known as the Epot value) was calculated.

Around 1–2% of the theoretical maximum potential was observed in the measured porewater fluxes over the 1.5-year study period. However, this reflects only one component of the full CDR signal.

This reinforces the importance of grounding carbon removal projections in real-world field data, which accounts for variability in soil, climate, and operational conditions.

Factors such as:

– Coarse particle size

– Rock dissolution kinetic limits

– Surface-only application

– Soil moisture availability

– Soil pH and temperature dynamics

All affect how quickly and how much weathering occurs in practice.

By comparing measured porewater results to theoretical models, UNDO is helping to establish realistic benchmarks for ERW, supporting the credibility and transparency needed to scale the industry responsibly.

Looking Ahead

The results also offer insights for future research into enhanced weathering optimisation, including:

– Exploring the effects of different particle sizes on weathering rates.

– Investigating whether soil incorporation might further enhance dissolution in certain conditions.

– Continuous water flux monitoring (e.g., with passive drainage meters) could further improve MRV accuracy.

While the measured CO₂ removal may seem modest in absolute terms, it is important to remember:

– The basalt was coarse and surface-applied – realistic for early-stage deployment.

– Weathering continues beyond the 1.5-year study window, meaning that cumulative CO₂ removal will likely grow over time.

– The durability of carbon storage through enhanced weathering exceeds thousands to tens of thousands of years.

By advancing the field evidence base for ERW through high-quality research and open data, UNDO is helping unlock a scalable, scientifically robust solution for durable carbon removal.

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