A Review of Life Cycle Assessment for Marine Alternative Fuels: Methodology, Multidimensional Evaluation, and Decarbonization Pathways

Driven by global climate goals and stringent shipping decarbonization policies led by the International Maritime Organization (IMO) and the European Union, green alternative fuels have become a key pathway toward net-zero shipping. Life cycle assessment (LCA) is essential for quantifying the environmental performance of marine fuels and supporting fuel selection, policy making, and industrial deployment. However, existing studies still diverge in system boundary setting, emission factor selection, and methodological frameworks, leading to considerable discrepancies in reported fuel performance and constraining their large-scale deployment. This review synthesizes recent advances in the LCA of marine alternative fuels. It summarizes the physicochemical properties, energy conversion efficiency, propulsion configurations, and deployment status of mainstream options, including LNG, methanol, ammonia, hydrogen, biofuels, and battery power. It then outlines the standardized LCA framework for marine fuels, represented by the IMO 2024 Fuel LCA Guidelines and the well-to-wake (WtW) accounting framework. On this basis, it compares the environmental, economic, technical, and social performance of these fuels and discusses the major methodological debates and remaining challenges. Finally, it identifies future research priorities, including methodological standardization, integrated multidimensional assessment, and uncertainty analysis. These findings can inform the selection of shipping decarbonization pathways and further marine fuel LCA development.