Life Cycle Perspective-Based Modeling Assessment of Ocean Alkalinity Enhancement.

The removal of carbon dioxide from the atmosphere via ocean alkalinity enhancement (OAE) is proposed and discussed to mitigate climate change. We modeled the life cycles of four types of OAE technologies (ocean liming, accelerated weathering of limestone, mineral carbonation-ocean liming, and coastal enhanced weathering) in an Earth system model and investigated their environmental impacts. When the OAE is simulated to operate from the year 2030 to 2099 in 12 different coastal areas, the carbon emissions generated from the OAE's mining, processing, transportation, and dumping can significantly offset their carbon sequestration effects, causing specific OAE technologies unable to reduce atmospheric CO2. Among all four OAE technologies, coastal enhanced weathering exhibits the best overall carbon removal effectiveness, while the North Atlantic has the highest potential to store OAE-captured CO2. All OAE runs have an OAE-induced oceanic carbon leakage into the atmosphere, especially when clean energy is utilized to power the OAE activities, highlighting the necessity to consider the carbon removal additionality, permanency, and leakage performance for robust modeling assessment.