A critical review of pathways, fuels, and challenges to achieving decarbonization strategies in the maritime sector
The maritime sector accounts for approximately 3% of global CO2 emissions and remains among the most difficult industries to decarbonize because of its continued reliance on fossil fuels. Therefore, a comprehensive assessment of current pathways toward maritime decarbonization by critically analyzing regulatory frameworks, energy-efficiency technologies, alternative fuels, techno-economic factors, and prospective transition strategies is provided in this work. Initially, it examines the influence of international climate policies and emission-reduction targets on the transformation of maritime energy systems, followed by an evaluation of technical and operational measures for improving efficiency, such as hull optimization, energy-saving technologies, wind-assisted propulsion, digitalization, and intelligent voyage planning. The review then systematically compares the characteristics, benefits, limitations, and commercialization prospects of major alternative marine fuels, including liquefied natural gas, methanol, hydrogen, ammonia, biofuels, and synthetic e-fuels, considering key factors such as energy density, storage requirements, safety, infrastructure maturity, lifecycle greenhouse gas emissions, and scalability. In addition, well-to-wake environmental performance, bunkering infrastructure, economic constraints, fuel availability, and renewable electricity demand associated with large-scale fuel adoption are critically assessed. The findings indicate that no individual fuel or technology is sufficient to achieve full maritime decarbonization. Instead, a coordinated portfolio of measures integrating operational efficiency improvements, diverse alternative fuels, digital technologies, enabling regulatory frameworks, and significant investment in renewable energy infrastructure will be essential. Finally, the review highlights major research gaps, safety concerns, and policy priorities that can facilitate the development of resilient, economically feasible, and environmentally sustainable pathways aiming to achieve maritime decarbonization by 2050.