Sustainable aircraft fuels are designed to reduce the environmental impact of aviation. There are so many of them that it’s difficult to know what they really mean. It’s hard to know whether they’re really more eco-friendly. We will be forced to navigate their multiplicity to answer two questions: are sustainable aviation fuels truly sustainable? And are they eco-friendly?
Let's start first with sustainability. “The level of sustainability of SAF is assessed by taking into account the entire life cycle, from production to use, and comparing greenhouse gas emissions to conventional fuels,” says Charlotte de Lorgeril, Energy Partner at Sia Partners. “It depends on several factors, including raw materials used, production methods, GHG emissions and impact on land use. Their sustainability depends on the way in which these raw materials [those from which they are created, editor's note] are cultivated and transformed. Biofuels can negatively impact land use and food security if produced on a large scale, but sustainable approaches aim to use uncultivated land or agricultural waste for production.”
Indeed, since the fuels we’re discussing here remain alternatives to kerosene intended to burn in an engine, they’re only sustainable in terms of their production. And therefore, they’re only relatively sustainable compared to the fossil fuels which currently power planes. If using kerosene is dramatic, that of SAF is a little less so. Unfortunately nothing more. Moreover, even in terms of production, sustainable aviation fuels are far from perfect. And for good reason: there’s no point in producing an alternative fuel made from beets if it deprives the world of arable land that could be used to feed humans. Or creating a supposedly sustainable synthetic fuel by electrolysis which uses non-sustainable electricity.
The eco-credentials of these fuels are debated. As de Lorgeril explains: “They’re presented by some, notably industry players, as a potential solution to reduce the carbon footprint of the aviation industry. But the ecological impacts of SAF are still controversial,” she explains. “The pluses of SAF from an ecological point of view lie in the fact that they’re produced in part from renewable resources, particularly from biomass and waste. This is advantageous from the point of view of CO2 emissions: a fuel produced from agricultural resources has a lower carbon footprint than a fossil fuel, because the carbon released during the combustion of the fuel is carbon previously stored in biomass. We therefore add less net CO2 to the atmosphere.”
“Depending on the raw materials used, we have to distinguish conventional SAF (called first generation) made using food crops (soybean, palm, rapeseed, sunflower) or sugar (beet, corn), from advanced SAF (called second generation) which use of biomass (forest or agricultural residues) or organic waste (used cooking oil, animal fat, municipal waste). First generation SAFs remain high CO2 emitters (1 to 1.5 times more than conventional kerosene) taking into account the cultivation of raw materials, while second generation SAFs can reduce emissions by 20% to 80% of CO2 compared to conventional kerosene.” In short, the results of certain SAFs are rather good even if, as de Lorgeril reminds us, “the adjective ‘ecological’ can be subject to interpretation and depends on the perspective and specific sustainability criteria.”
Finally, the sustainability and ecological credentials of SAF depend on the amount the aviation industry uses. Can they really maintain these qualities if we use them on a large scale? Are we going to need to produce enough so that all the planes in the world fly with them, rather than with the kerosene mixture? Nonetheless, they will probably always be cleaner than oil mined from the centre of the other. But does that still make it a good solution? The jury is out.
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