Assessing the sustainability implications of alternative aviation fuels

This working paper provides background and analysis to help identify how an effective policy for alternative aviation fuels could distinguish among fuels that can deliver deep greenhouse (GHG) reductions and those that cannot. It provides an overview of the life-cycle GHG emissions attributable to the production of sustainable aviation fuels (SAFs) from a variety of conversion processes and feedstocks. Taking into account each fuel pathway’s GHG emissions and other sustainability considerations, the analysis assesses which SAF pathways are likely to play a meaningful role in European climate policy.

The analysis finds that wide variation in climate impacts across different SAF feedstocks and conversion technologies illustrates that simply displacing petroleum jet fuel with any alternative jet fuel will be insufficient to drive deep decarbonization in aviation. It is critical that European policies incentivize those fuels which offer the highest GHG savings estimated on a life-cycle basis.

In particular, hydroprocessed esters and fatty acid (HEFA) fuels are often made from feedstocks with high, indirect life-cycle emissions that undermine their supposed greenhouse gas savings. In contrast, many fuels made from by-products, wastes, and residues can offer substantial carbon savings but may be more difficult to produce. Strong sustainability protections will be necessary to ensure that SAF policies do not undermine their goals by diverting feedstocks with high-value existing uses. Similarly, we find that electrofuels will not be able to generate meaningful GHG reductions without corresponding protections to ensure they are produced using additional, renewable electricity.

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