How Much CO₂ Can Enhanced Weathering Really Remove? - Derry

Cornell University geochemist Louis Derry joins @geoengineering1 to discuss a fundamental question for enhanced rock weathering: how much of the alkalinity generated in soils actually makes it through watersheds to the ocean? Derry argues that many studies and commercial MRV approaches focus on the top 10-30 cm of soil, potentially missing critical processes along the full flow path, including ion exchange in acidic soils, secondary clay formation, acidity generation and carbonate precipitation, which can reduce alkalinity export before it reaches streams.

He highlights hydrological constraints, arguing that limited runoff and realistic alkalinity concentrations make proposed removal rates of 5-10 tonnes of CO₂ per hectare per year difficult to achieve across typical row-crop regions. Drawing on natural basaltic catchments and experimental systems, he points to estimates of global basalt weathering of ~0.1-0.2 Gt CO₂/yr, suggesting gigaton-scale enhanced weathering projections are overoptimistic, with co-benefits more credible than large-scale CDR.

Paper Discussed: Derry, L. A., Maher, K., & Chadwick, O. A. (2026). Critical zone processes limit alkalinity export from natural basaltic systems. Nature, 1–6. https://doi.org/10.1038/s41586-026-10936-3

Related article: Limitations on carbon dioxide uptake by enhanced weathering - Springer Nature Research Communities

https://communities.springernature.com/posts/limitations-on-carbon-dioxide-uptake-by-enhanced-weathering

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