Uncertainty in life cycle greenhouse gas emissions of sustainable aviation fuels from vegetable oils

Abstract

Sustainable aviation fuel (SAF) is one of the most promising short-to medium-term term options to mitigate greenhouse gas (GHG) emissions from aviation. Life cycle assessment (LCA) is commonly used to estimate GHG emissions from SAF in comparison to fossil kerosene. While there are several studies reporting the GHG emissions from SAF, uncertainty in the results is not always addressed in a comprehensive way.In this work, GHG emissions of hydroprocessed esters and fatty acids (HEFA) fuels derived from jatropha (Jatropha curcas), pennycress (Thlaspi arvense), castor (Ricinus communis), energy tobacco (Nicotiana tabacum, Solaris) and Salicornia (Salicornia bigelovii) oils were estimated. A stochastic methodology was employed where parametric uncertainty was propagated using Monte Carlo simulations. Uncertainty due to methodological choices was incorporated through scenario analyses. Emissions from direct land use change (DLUC) and the associated uncertainty were assessed under the IPCC Tier 1 approach by considering alternative land use transitions per feedstock.Analyzed HEFA pathways provide GHG emissions benefits (34–65%) in comparison to fossil kerosene when DLUC emissions are not considered. Parametric uncertainty yields up to 26% deviation from the median well-to-wake GHG emissions. Changing the allocation choice for the oil extraction step, from the base assumption of energy-based allocation to mass- or market-based, can impact the results by up to 46%. DLUC is a more significant source of uncertainty than both parametric uncertainty and allocation assumptions in the analysis. DLUC emissions negate any GHG savings from HEFA fuels if forests or natural shrublands are lost.