Source: The Conversation – UK – By Ben Purvis, Research Associate, Sustainability Assessment, University of Sheffield
The UK chancellor, Rachel Reeves, has described so-called sustainable aviation fuel (SAF) as a “game changer”. As she announced government support for a series of airport expansions, she said that the fuel “can reduce carbon emissions from flying by 70%”.
This number is misleading. Optimistic estimates do suggest that fully replacing fossil jet fuel with its sustainable alternative could lead to total savings of around 70%. But it will be hard to produce enough SAF to make a difference on that sort of scale. Even if the UK meets its ambitious targets, an annual saving of 7% by 2030 is more plausible.
SAF is synthetic liquid fuel derived from something other than fossil fuels. These inputs have to be processed into a liquid that can be burned safely while also storing a lot of energy for its weight, since minimising weight is crucial. This is why long-haul electric battery-powered planes are unlikely to take off any time soon.
The UK classifies three major pathways for creating sustainable aviation fuel. It can be derived from oils or fats, including used cooking oil or tallow. It can come from other sorts of material, such as municipal solid waste, agricultural residues, or sewage. Or it can be made from hydrogen and captured carbon using renewable electricity.
SAF can also be produced from bioenergy crops, and products such as palm oil. However the UK won’t certify it as sustainable, due to concerns about land use and impacts on wildlife.
Emissions that would have occurred anyway
Burning SAF actually emits a similar amount of CO₂ to fossil jet fuel. Instead, most savings come from how we account for the waste and renewable energy that is used to produce it.
Jenya Smyk/shutterstock
SAF fundamentally relies on assumptions that if waste or energy crops were not used to make this fuel, they would be incinerated, would degrade, or would in some way release their embodied carbon anyway. In the case of fuel derived from renewable energy and captured carbon, it assumes that carbon came from the atmosphere in the first place. This allows these emissions to be deducted from the total impact of SAF, leading to lower emissions than conventional aviation fuel.
Is sustainable aviation fuel even sustainable?
Estimates of how much greenhouse gas SAF could cut vary greatly due to the many different ways it can be produced, and the complexities of accounting for emissions across the entire life cycle from waste, to fuel production, to plane engine. A 2023 review by the Royal Society illustrates this nicely. It found SAF could at best produce effectively negative emissions (a 111% reduction), while at worst it could be more carbon intensive than fossil kerosene jet fuel (a 69% increase).
While policy incentives are likely to encourage increased production, there remain serious concerns that will need to be addressed before SAF can become a serious competitor for conventional jet fuel. There are hard limits to the amount of used cooking oil available for instance, and the use of other feedstocks is still in its infancy.
Meanwhile any renewable energy used to make the fuel will have to compete with growing demand from electric vehicles, AI data centres and more. And there are big worries the industry simply won’t be profitable enough to attract initial capital investment, let alone take on its well-established rival.
UK SAF production
Coming into effect in January, the UK’s SAF mandate sets legal obligations for aviation fuel suppliers in the UK to progressively increase proportions of sustainable fuel, from 2% of total jet fuel in 2025 to 10% in 2030, and 22% in 2040.
This is one of a growing number of commitments globally, including RefuelEU, and the US SAF grand challenge, which seek to increase demand and encourage more investment in production.
As of 2023, 97% of the UK’s supply is derived from used cooking oil, with the rest from food waste. Only 8% of this cooking oil is sourced from the UK, with most being imported from China and Malaysia. The UK also comprises 16% of the global SAF market, despite representing only 1% of total passengers.
Currently, the only commercial producer of SAF in the UK is the Phillips 66 Humber Refinery which processes used cooking oil. The previous government allocated £135 million of funding to nine projects, aiming to have five plants under construction by 2025. Despite several projects selecting sites, at the time of writing none appear to be under construction.
In an industry with razor-thin profit margins, SAF remains considerably more expensive than conventional aviation fuel. With potential producers filing for bankruptcy and companies including Shell pulling out due to profitability concerns, the market is looking rocky.
A 7% saving is more plausible
Let us assume that Rachel Reeves’ 70% saving is deliverable if fossil jet fuel was fully replaced with SAF. That’s optimistic in itself, but not beyond the realms of possibility.
Getting hold of that much sustainable fuel is less plausible, however – the total demand for jet fuel in the UK is more than ten times the current global production of SAF. But let’s assume that the rocky global market can deliver the UK’s ambitious demand of 10% SAF use by 2030.
Reeves’ figure then becomes an optimistic value of 7% savings across the UK industry. If we then correct for anticipated growth of passenger numbers, assuming plans for airport expansion, those savings are likely to vanish.
While SAF has a role to play in decarbonisation, growth sits in clear opposition to its impacts and potential. If the UK has any hope of meeting its climate targets, it should instead be seeking alternatives to flying where possible.
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Ben Purvis receives funding from the Grantham Foundation for the Protection of the Environment.
– ref. There isn’t enough ‘sustainable’ aviation fuel to make a dent in our emissions – and there won’t be for years – https://theconversation.com/there-isnt-enough-sustainable-aviation-fuel-to-make-a-dent-in-our-emissions-and-there-wont-be-for-years-249270
