Carbon capture and storage via enhanced carbonate weathering coupled with aquatic photosynthesis: Potential, cost, and advantages

Abstract

The application of crushed rock powders to terrestrial or marine ecosystems (termed enhanced rock weathering, ERW) is regarded as an effective carbon dioxide removal (CDR) mechanism for mitigating ongoing climate change. As a potential ERW material, carbonate is characterized by rapid dissolution kinetics and is environmentally friendly. However, the CDR potential, cost, and effectiveness of carbonate-based ERW implementation are not well explored. Using a carbonate equilibrium equation, and the CMIP6 (Coupled Model Intercomparison Project Phase 6) GCM (Global Climate Model) and LCA (Life Cycle Assessment) models, here we analyze the CDR potential, carbon footprint, and cost of a carbonate-based RW strategy (so-called enhanced carbonate weathering, ECW). We estimated that the current global potential carbon removal (PCR) of ECW could reach ∼2.66 (Representative Concentration Pathway (RCP) 4.5) and ∼ 2.82 (RCP8.5) Gt CO₂ a⁻¹, and that the cumulative CO₂ removal by the end of this century could reach 241.32 Gt CO₂ a⁻¹ (RCP4.5) and 246.64 Gt CO₂ a⁻¹ (RCP8.5). This could potentially neutralize ∼23.11 % (RCP4.5) and ∼ 23.62 % (RCP8.5) of future global carbon dioxide emissions. We also found that the global CDR potential of ECW can respond sensitively to global environmental perturbations, and that the CDR potential in the future will generally increase in high-latitude regions due to global climate change. We compared the cost of enhanced silicate weathering (ESW) with ECW implementations for seven major countries with high CDR potential and found that the cost per mol of CO₂ removal by ECW is 1.33–2.07 times lower than that for ESW. While the stability of dissolved inorganic carbon (DIC) is debated in many studies, we suggest that the new approach represented by ECW should consider the role of aquatic photosynthesis. Overall, the biological pump induced by aquatic photosynthesis is significant for increasing the carbon storage of ECW in inland waters. For future ERW implementation, we stress the need to develop an Enhanced Coupled Carbonate Weathering plus aquatic photosynthesis strategy (ECCW) that can both offset the negative effect of CO₂ degassing and also increase the total CDR of ECW to a greater degree than expected. ECCW remains in the developmental stage, and its large-scale implementation requires further laboratory and field experiments to determine its CDR-efficiency and environmental effects and risks.