A Systematic Review on Maritime Decarbonization: The Synthesis, Implications, and Strategies of a Decade of Alternative Fuels for Shipping

The maritime industry faces an unprecedented challenge to achieve the net-zero emissions goal by or around 2050. While numerous alternative fuels are undergoing intense evaluation, the industry remains trapped in a profound ‘technological deadlock’ driven by the irreconcilable trade-offs of current options, where fuel might offer excellent environmental profiles but fail on economic viability or safety acceptance. This study addresses this uncertainty by systematically reviewing 39 studies published from 2015 to 2025 that evaluated alternative fuels for the shipping industry using various criteria. Unlike traditional reviews, this study employs a horizontal synthesis across environmental, economic, technical, safety, and social criteria. By cross-examining these fragmented dimensions, this study maps the core friction points that prevent the scalable deployment of alternative fuels. The synthesis indicates that the regulatory framework should shift from static measures to dynamic, phased carbon pricing to address the immediate green premium of alternative fuels. Additionally, the analysis points to a looming global human capital bottleneck and a significant geographic risk of a two-tier global fleet. Most significantly, this study consolidates a decade of marine fuel evaluations into a practical, strategic fuel-deployment matrix that provides industry managers and global policymakers with a clear roadmap to overcome decision-making inertia and safely guide the maritime transition.