Key issues in LCA methodology for marine fuels
The International Maritime Organization (IMO) is in the process of developing life-cycle analysis (LCA) guidelines for fuels under its greenhouse gas (GHG) reduction strategy. There are many considerations and methodological decisions when doing an LCA, particularly when assessing transport fuels, and it is critical that the LCA accounting that is ultimately adopted be comprehensive enough to align with IMO’s climate goals. This paper highlights key decisions by comparing the different LCA methodologies of five existing fuel policies and then assessing the life-cycle GHG emissions of four marine fuels—soybean biodiesel, used cooking oil (UCO)-based renewable diesel, e-methanol, and hydrogen—across a variety of LCA scopes and assumptions.
The results illustrate the importance of understanding the reason for the life-cycle carbon accounting of fuels. For one, fuels that have zero tank-to-wake or direct emissions can have substantial upstream production emissions that are not counted when assessing only tank-to-wake emissions. Additionally, while indirect effects are uncertain and difficult to estimate, they might be large enough to greatly affect the estimated GHG savings of some fuel pathways, and assuming a value of zero on the basis of uncertainty is not necessarily a neutral decision. To avoid the adoption of high-emitting fuels in an effort to decarbonize maritime transportation, the IMO can adopt full life-cycle well-to-wake GHG accounting for policies related to fuel operational use such as the Carbon Intensity Indicator and potential future policies like the GHG Fuel Standard. Such accounting would be consistent with other major fuels policies that assess the indirect emissions attributable to fuels.