Enhanced rock weathering (ERW) is a proposed carbon dioxide removal (CDR) approach that speeds up the slow geochemical reactions by which silicate and carbonate rocks absorb CO₂ from the atmosphere. In nature, rainwater containing dissolved CO₂ reacts with rocks like basalt and olivine to form bicarbonate ions, which are eventually carried to the ocean and stored as dissolved inorganic carbon or precipitated as carbonate minerals. This process normally takes thousands to millions of years and is a key regulator of Earth's long-term carbon cycle.
ERW accelerates the reaction by grinding silicate rock into fine powder and spreading it across large surface areas, most commonly agricultural fields. The increased surface area allows weathering to occur on timescales of years rather than millennia. Basalt is the most frequently studied feedstock because it is abundant, contains useful nutrients like calcium and magnesium, and avoids the nickel and chromium contamination risks associated with olivine.
Beyond carbon removal, proponents argue ERW offers co-benefits for farmers: raising soil pH (similar to agricultural lime), releasing plant nutrients, and potentially improving crop yields. A 2020 study in Nature by Beerling et al. estimated that large-scale deployment across cropland in major emitting countries could remove between 0.5 and 2 gigatons of CO₂ per year by 2050, though at substantial cost.
Significant uncertainties remain. Open questions include actual field-scale removal rates, the energy and emissions cost of mining and grinding rock, transport logistics, monitoring and verification (MRV) of removed carbon, and ecological effects of trace metals. ERW currently lacks an established methodology under the major voluntary carbon registries, though companies including Lithos Carbon, UNDO, and Eion have begun selling ERW credits to buyers such as Frontier and Stripe. The IPCC's Sixth Assessment Report (2022) lists ERW among emerging CDR options but notes low technology readiness and limited empirical evidence at scale.
Example
In 2023, Frontier — a carbon removal buyer coalition backed by Stripe, Alphabet, and Meta — signed offtake agreements with Lithos Carbon to purchase enhanced rock weathering credits generated by spreading crushed basalt on US farmland.
Frequently asked questions
Direct air capture uses engineered chemical systems and machinery to pull CO₂ from ambient air, while ERW relies on natural geochemical reactions between crushed rock and CO₂ dissolved in rainwater or soil moisture. ERW is generally cheaper per ton but slower and harder to measure.
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