Enhanced rock weathering

In plain language

Certain rocks react with carbon dioxide over time. When rain falls on crushed silicate rock, the rock dissolves slowly, and the dissolved minerals can react with CO2 from the air to form bicarbonate. That bicarbonate can be carried away in drainage water and stored in the sea, or it can form carbonate minerals in the soil. Spreading crushed rock on fields is a way to speed this natural process up, because the rock dust has a large surface area and farmland is already tilled and fertilised.

The open questions are how much CO2 is really removed, and how that can be proven. Trials so far show removal in the soil and water, but the amounts are small per hectare and hard to measure. Some trials also report higher crop yields, which may help farmers adopt the method. Carbon removal credits have started to be issued, but the way removal is counted is still being tested.

Technical explanation

Enhanced rock weathering (ERW) uses fast-reacting silicate minerals, such as those in basalt or wollastonite, that are ground to a fine grain size and spread on land. Dissolution consumes protons and CO2 and releases divalent cations such as calcium, magnesium and sodium. Where these cations are transported to the ocean as bicarbonate, the carbon is removed on a long timescale. Field studies typically estimate removal from a charge-balance calculation on the bicarbonate in porewater, from losses of base cations from the soil, or from soil carbonate accumulation, and then compare the result with a theoretical maximum calculated from rock chemistry.

The Corn Belt trial published by Beerling and colleagues (2024) applied crushed basalt at 50 tonnes per hectare each autumn over four seasons and gives a conservative time-integrated cumulative CDR potential of 10.5 ± 3.8 t CO2 per hectare. The Scottish trial by McBride and colleagues (2025) used porewater sampling on pasture and reported direct removal of 0.33 to 0.53 t CO2 per hectare at 5 cm depth after about 1.5 years, at application rates of 78 and 126 tonnes per hectare, before a 22% deduction for outgassing and losses that the authors apply later. Those rates are above normal farm spreading, and the study had no plot replication.

Model studies give much larger potentials. Strefler and colleagues (2018) estimated that global cropland could remove as much as 4.9 Gt CO2 per year with basalt, and as much as 95 Gt CO2 per year with dunite, using a 20 µm grain size in the main text. Their basalt cost estimate was about US$200 per tonne of CO2, against about US$60 for dunite. Credits are verified under registry protocols. The Isometric protocol requires direct soil and porewater measurements against control plots, and Puro.earth has a land-based methodology that does not restrict rock type.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• Most removal figures are calculated from soil and porewater chemistry rather than measured directly; the Scottish trial's removal figures are calculated from porewater chemistry and reduced by a 22% deduction for outgassing and losses (McBride and colleagues, 2025).
• Field trials are few and short. The Scottish trial had no plot replication and ran for about 1.5 years; the Corn Belt trial ran for four years (Beerling and colleagues, 2024).
• Reported removal differs between sources for the same trial. The University of Sheffield press release gives 'around 3-4 tonnes' of CO2 per hectare per year for the Corn Belt trial, while the PNAS abstract gives 10.5 ± 3.8 t CO2 per hectare cumulative over four years, which is about 2.6 t per hectare per year if spread evenly.
• Model estimates of global potential depend heavily on weathering rate and grain size. The headline figures from Strefler and colleagues (2018) assume a 20 µm grain size in the main text.
• The Corn Belt trial reported no significant rise in trace metal content in maize or soybean grain, but reported rises in molybdenum (about fourfold) and copper (about 35%) with the treatment (Beerling and colleagues, 2024). Health and plant-toxicity effects at scale are not covered by the sources used for this profile.
• The Puro.earth methodology does not specify or exclude rock types, and the summary of its page reviewed here does not describe how net removal or uncertainty is quantified; the methodology document itself was not read for this profile (CarbonCredits.com, 2022).

Possible future uses

Timeline

1. 19 Feb 2018Beerling and colleagues publish 'Farming with crops and rocks to address global climate, food and soil security' in Nature Plants (vol. 4, pp. 138-147). Sources: [2]
2. 5 Mar 2018Strefler and colleagues publish a techno-economic model in Environmental Research Letters giving a cropland potential of 4.9 Gt CO2 per year for basalt. Sources: [3]
3. Oct 2022Puro.earth's enhanced rock weathering methodology is open for public consultation, with the consultation running until 17 October 2022. Sources: [7]
4. 22 Feb 2024Beerling and colleagues publish the four-year US Corn Belt trial in PNAS, reporting 12 to 16% higher maize and soybean yields and a cumulative removal estimate of 10.5 ± 3.8 t CO2 per hectare. Sources: [1], [5]
5. 6 Jan 2025Isometric reports 235.53 ex-post enhanced weathering credits from InPlanet's Serra da Mantiqueira project in Brazil, delivered to Adyen through ClimeFi, and describes them as the first independently verified enhanced weathering credits. Sources: [6]
6. 5 Sept 2025McBride and colleagues publish a Scottish pasture trial in Frontiers in Climate, reporting direct removal of 0.33 to 0.53 t CO2 per hectare at 5 cm depth after about 1.5 years at the two highest application rates. Sources: [4]

Futures this could help bring about

How far away?

Farmland that pulls CO2 out of the air with crushed rock

Pilots · 3 of 7 steps done

Related breakthroughs

• Field trial on Scottish pasture estimates CO2 removal from basalt using porewater (5 Sept 2025)

Glossary

Enhanced rock weathering

Spreading finely crushed silicate rock on land so that it dissolves faster and takes up CO2 from the air.

Silicate rock

Rock made mostly of silicate minerals, such as basalt, that release calcium and magnesium when they dissolve.

Porewater

Water held in the spaces between soil particles, which can be sampled to measure dissolved carbon and minerals.

Bicarbonate

A dissolved form of carbon, produced when CO2 reacts with water and minerals, that can be carried to the ocean and stored.

Sources

1. peer reviewed paper
   Enhanced weathering in the US Corn Belt delivers carbon removal with agronomic benefits
   David J. Beerling, Dimitar Z. Epihov, Ilsa B. Kantola et al.. Proceedings of the National Academy of Sciences, 22 Feb 2024. DOI: 10.1073/pnas.2319436121. Accessed 21 Oct 2026.
2. peer reviewed paper
   Farming with crops and rocks to address global climate, food and soil security
   D. J. Beerling, J. R. Leake, S. P. Long et al.. Nature Plants, 19 Feb 2018. DOI: 10.1038/s41477-018-0108-y. Accessed 21 Oct 2026.
3. peer reviewed paper
   Potential and costs of carbon dioxide removal by enhanced weathering of rocks
   Jessica Strefler, Thorben Amann, Nico Bauer et al.. Environmental Research Letters, 5 Mar 2018. DOI: 10.1088/1748-9326/aaa9c4. Accessed 21 Oct 2026.
4. peer reviewed paper
   Quantifying potential carbon dioxide removal via enhanced weathering using porewater from a field trial in Scotland
   Amy L. McBride, Kirstine Skov, Peter Wade et al.. Frontiers in Climate, 5 Sept 2025. DOI: 10.3389/fclim.2025.1606574. Accessed 21 Oct 2026.
5. university press release
   Field trials reveal crushed rock boosts carbon removal and improves crop yields
   University of Sheffield, 26 Feb 2024. Accessed 21 Oct 2026.
6. company announcement
   World's first independently verified enhanced weathering credits
   Isometric, 6 Jan 2025. Accessed 21 Oct 2026.
7. news
   Puro.earth enhanced rock weathering methodology
   CarbonCredits.com, 6 Oct 2022. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.