Environmental assessment of present and future marine fuels

Our globalised world is connected by shipping, an industry powered by one of heaviest and dirtiest products of refining: heavy fuel oil. Tougher environmental regulations are now challenging the industry to take action. Ship-owners and operators are faced with the choice of installing exhaust gas cleaning technologies or switching to a different fuel altogether. The primary purpose of this thesis was to assess the environmental performance of present and future marine fuels and to evaluate potential methods and tools for their assessment.Two different system approaches are used in this study: life cycle assessment (LCA) and global energy systems modelling. LCA is a well-established method for assessing the environmental performance of fuels. This type of assessment was complemented with the use of the Global Energy Transition (GET) model to investigate cost-effective fuel choices based on a global stabilisation of CO2 emissions and the global competition for primary energy sources. The GET model includes all energy sectors and considers the interactions among them, but it is limited in scope to CO2 emissions and costs. The LCAs involve a holistic systems perspective that includes the entire life cycle and various types of environmental impacts, but they are limited to analyses of one product or service at a time. These methods provide insights that are both contradictory and complementary.This study concludes that there is substantial potential for reducing the environmental impact of shipping through a change in fuel types and/or the use of exhaust abatement technologies. A switch from heavy fuel oil to any of the alternatives investigated in this study reduces the overall environmental impact of marine fuels. The GET model indicates that it is cost-effective to phase out the use of crude oil-based fuels in the shipping sector and replace these fuels with the use of natural gas-based fuels during the next few decades. Based on the LCA results, the use of biofuels may be one possible way to reduce the impact of shipping on the climate, but biofuels may only be a cost-effective fuel in shipping if the corresponding annual available bioenergy resources are sufficiently large. Three important implications are highlighted: the importance of reducing the NOX emissions from marine engines, the need to regulate the methane slip from gas engines and the fact that a change in fuels may not reduce the impact of shipping on the climate