Enhanced weathering strategies for stabilizing climate and averting ocean acidification

The chemical breakdown of rocks can be enhanced by spreading silicate granules over land. Research suggests that this measure, which increases the rate at which CO2 is locked up in ocean carbonates, could lower atmospheric CO2 by 30–300 ppm by 2100. Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions1,2,3,4,5. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling6,7,8 driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation)9,10 indicates that enhanced weathering could lower atmospheric CO2 by 30–300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m−2 yr−1) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems11,12,13,14. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions15.