Challenges and opportunities in scaling enhanced weathering for carbon dioxide removal

Terrestrial enhanced weathering (EW) on agricultural lands is a proposed carbon dioxide removal (CDR) technology involving the amendment of soils with crushed base cation-rich rocks, such as basalt. Over a quarter of a billion dollars have been raised by commercial EW start-ups across the globe, accelerating the deployment of EW at scale. In this Review, we outline the scientific knowledge and policy requirements for scaling EW. The global CDR potential of EW is 0.5–2 Gt CO2 year by 2050. Tracking carbon as it is transferred from soils (cradle) to the oceans (grave), fully considering and quantifying lag times in CDR and developing a robust framework of monitoring, reporting and verification of CDR are all important for understanding the performance of EW deployments. Policies aimed at incentivizing responsible deployment and gaining acceptability among directly impacted communities, such as agriculture, are essential to sustainable and long-term growth of EW. High initial prices, the lack of consistent methodology for issuing carbon credits and lifecycle carbon emissions associated with a deployment are the main challenges of scaling EW through the voluntary carbon market. Future research needs to explore the co-deployment of EW and other CDR technologies and utilize long-term (>10 years) instrumented EW field trials to evaluate processes that regulate CDR efficiency and agronomic and economic co-benefits. Commercial investment in enhanced rock weathering for carbon dioxide removal on agricultural lands is growing rapidly. This Review explores the potential of large-scale deployment, outlining the challenges faced in science, policy and governance to scale the technology.