Consequential Life Cycle Assessment of Fuels for Shipping

While the maritime transportation sector is responsible for the movement of up to 90% of the world’s goods, it is also responsible for 3% of global GHG emissions. The awareness of the effects of these emissions has led to regulations on decreasing emissions from fuel combustion, and changing to low-carbon or carbon-free fuels has been identified as a critical means of achieving these targets. A variety of alternative fuels for shipping have been identified as promising, although there is
no consensus yet on what the future fuel mix looks like.

Life cycle assessments (LCAs) have been used to support decision-making in various sectors, and several life cycle assessments of maritime fuels have been conducted and published in scientific journals, with many of these focused on conventional fuel oils. Despite an increasing representation of alternative maritime fuel LCAs in literature, the existing literature is limited in its inclusion of critical elements and transparency in reporting methodological choices and assumptions.
The diversity of fuel types and fuel production pathways, coupled with inconsistent LCAs on these fuels complicate decisionmaking regarding fuel choice.

In this work, consequential LCA is applied to a range of different maritime fuel scenarios, to demonstrate how to address the existing gaps in literature. The system boundaries include both production and combustion of the fuels. The function unit is chosen as 1 tonne of cargo transported 1 kilometer (1 tkm) to address differences in fuel energy density. Multiple literature sources of data are used to provide a range of potential impacts for several different impact categories. Additionally, the results of the environmental life cycle assessment scenarios are contexualised with regards to regulatory frameworks and certification schemes for fuels, such as the EU’s Renewable Energy Directive (RED) and the the Low Carbon Fuel Standard (LCFS).
It is expected that the outcomes of this study will provide guidance to LCA practitioners and decision-makers for i) how to conduct comprehensive LCAs of alternative maritime fuels, and ii) decision support regarding fuel choice and the expected ranges for the various fuels.