Life cycle impact on climate change caused by metal production from deep sea manganese nodules versus land-based deposits

At the "UN Climate Change Conference" (COP27), France called for a ban on deep sea mining. The topic has gained momentum over the last years as some businesspeople and politicians are promoting the mining of manganese nodules as a less CO2-intensive way to meet the rising demand for the battery metals nickel, copper, cobalt and manganese. In this study, we modelled the impact on climate change caused by metal production from manganese nodules vs. mining on land. The total climate impact of producing these metals from manganese nodules (similar to 2.0 kg CO(2)eq/kg dry nodules) compared to current land-based projects is about 27% lower. Comparing it to values reported in the literature by industry associations and by the ecoinvent database, the climate impact from manganese nodules is about 16% lower or 28% higher, respectively. Based on their monetary values, the allocation of the total climate impact to each metal assigns the highest contribution to FeMn. Our research shows that producing Ni, Cu, Co and FeMn from manganese nodules could lead to higher or lower impact on climate change depending on the model input data and methodological choices. The authors share the opinion that climate change should not be the central argument regarding the realization of manganese nodule projects. The discussion should instead explicitly include further environmental impacts, e.g., biodiversity or plumes as well as economic considerations.