Comparative life cycle assessment of CO2 removal solutions, including ocean liming, based on different energy sources and carbon storage methods

The deployment of a wide range of carbon dioxide removal approaches is essential to limit global warming to well below 2 ◦C. Ocean liming (OL) combines CO2 removal with the co-benefit of ocean acidification mitigation. This study evaluates four configurations of a process for removing atmospheric CO2 including OL. They combine two energy sources (i.e. woody biomass and renewable electricity) to produce slaked lime, and two methods for the storage of CO2 generated by the process (i.e. in underground geological formations and as bicarbonates in the sea via pH-equilibrated ocean alkalinization). The environmental impacts of the different configurations are evaluated through the life cycle assessment methodology. Results reveal efficiencies of carbon dioxide removal (i.e. the ratio between the net CO2 equivalent removal and the gross amount of removed CO2) in the range 85–92% for scenarios using the Italian electricity mix projected for 2050, and 93–96% for those using biomass. Therefore, all scenarios achieve net CO2 removal and the carbon penalty due to materials and energy used in the processes does not undermine the feasibility of OL. However, trade-offs are noted between climate change and other impact categories, such as land use. The proposed process configurations capitalize on existing technologies but require the integration of effective CO2 capture and storage to prevent emissions during calcination. Among these, the pH-equilibrated approach emerges as a promising alternative for CO2 storage, especially in regions where geological storage is not available.