Identifying life cycle greenhouse gas emission factors for utilizing green hydrogen as fuel on marine vessels considering various shipping scenarios

Unlike fossil-based fuels, green hydrogen offers a viable pathway for ships to meet decarbonization targets set by international regulatory frameworks, including IMO’s 2023 Greenhouse Gas (GHG) Strategy. However, its environmental benefits are highly dependent on upstream processes such as electricity source, production technology, liquefaction, transportation, and distribution pathways. While IMO’s 2024 Life Cycle Assessment (LCA) Guidelines provide Tank-to-Wake emission factors for fossil-based marine fuels, consistent Well-to-Tank GHG intensity data for hydrogen remain limited. This study addresses this gap by conducting a comparative life cycle GHG emissions assessment of replacing marine diesel oil (MDO) with green hydrogen on a high-speed passenger ferry. Unlike previous maritime hydrogen LCA studies, the proposed framework explicitly incorporates long-distance LH2 transportation and alternative boil-off gas management strategies within the Well-to-Wake assessment framework, enabling the derivation of transport-distance-based emission factors and hydrogen Well-to-Tank GHG intensity values. Three hydrogen supply pathways are evaluated: (i) international delivery with boil-off hydrogen release to the atmosphere, (ii) international delivery with onboard boil-off hydrogen utilization, and (iii) on-site solar-based hydrogen production. The results indicate that replacing MDO with green hydrogen reduces life cycle GHG emissions by 75.2%, 79.0%, and 82.3%, respectively. Shipping-related emissions account for 15.6–28.0% of total hydrogen life cycle emissions, while onboard utilization of boil-off hydrogen reduces shipping-related emissions by 52.6% compared with atmospheric release. The study further derives hydrogen Well-to-Tank GHG intensities of 26.7–37.1 g CO₂eq/MJ and transport-distance-based emission factors of 306.9–359.9 g CO₂eq/t H₂·nm. These findings provide valuable input for future maritime decarbonization policies and hydrogen supply chain assessments.