A review of life cycle assessment studies of maritime fuels: Critical insights, gaps, and recommendations

The shift from fossil-based to alternative fuels has been identified as a means of reducing the maritime transportation sector's environmental footprint. However, deciding which alternative fuels will make up the future fuel mix requires comprehensive knowledge on the environmental impacts of these fuels, which can be assessed using life cycle assessment (LCA). A detailed review of 43 peer-reviewed scientific articles of maritime fuel LCAs was performed according to i) their coverage of fuels and fuel technologies, ii) the methodological choices made when conducting these LCAs, and iii) the transparency when documenting them. It was found that, despite an increasing focus on alternative, non-fossil fuels, there is no clear picture of the potential impacts of future fuel mixes due to a lack of transparent disclosure of the methodological choices and assumptions. Additionally, only 8 of the reviewed articles (19 %) provide a complete life cycle inventory. Uncertainty analyses, which are a key methodological element of LCAs and particularly relevant for emerging fuels and technologies, are only included in 16 % of the reviewed articles. Consequently, current LCA studies of maritime fuels are unable to provide clear guidance on the potential environmental impacts of maritime fuels, in particular those relating to emerging fuel types. To support this need and enhance the reliability of decision-making regarding fuel choices, practical recommendations for future maritime fuel LCAs are provided. These include a focus on emerging fuels for long-distance shipping, increased transparency in reporting choices and assumptions, and inclusion of key methodological elements such as uncertainty analyses.