The aviation industry’s reliance on Sustainable Aviation Fuel (SAF) as its medium-term decarbonisation strategy is under increasing scrutiny. While the UK government is targeting 1.2 million tonnes of SAF production by 2030, evidence suggests this strategy risks delaying urgent climate action.
HIGH-LEVEL SUMMARY
CURRENT CONTEXT
Global aviation emissions are growing, and the UK is one of the highest per-capita emitters. While industry and policy has focused on promoting Sustainable Aviation Fuel (SAF) as the primary medium-term solution for decarbonisation, there are serious concerns about its scalability, sustainability, and effectiveness in reducing the climate impact of aviation within the necessary timeframe.
PRACTICAL CONSTRAINTS
Research has shown that SAF availability will be constrained by competition for limited resources across sectors and geographies. There are also technical limitations – SAF cannot be legally used in aircraft engines without blending it with conventional jet fuel, at no more than 10-50% content. Additionally, SAF also does not prevent the formation of condensation trails (contrails), which may cause more warming than carbon dioxide (CO2) emissions themselves, limiting the potential climate benefits.
MANAGING DEMAND
Taking immediate measures to manage aviation demand at source, rather than committing to airport expansion based on the promise of future technological solutions, remains the most credible path to reducing the climate impact of aviation.
BACKGROUND
GLOBAL EMISSIONS PROBLEM
International flights contribute 2% of global CO2 emissions, but the total global warming impact is around 4 per cent due to effects such as contrails and nitrogen oxide emissions. Commercial aviation emissions are growing year on year and reached a record high in 2024.
UK EMISSIONS PROBLEM
Within the UK, aviation is responsible for 7 per cent of CO2 emissions, of which international flights account for 93%. The UK is one of the highest per-capita aviation emitters, though this impact is driven by a small minority – only 15% of UK residents take 70% of flights.
TIMESCALE PROBLEM
Despite the growing climate impact, the deployment of zero or low-emission flight technologies is several decades away. Hydrogen and electric planes are not expected to be viable for long-haul flights (which produce 71% of global emissions) until after 2050, and even targets for shorter routes are being pushed back due to concerns around technology development and infrastructure availability. This leaves SAF as the primary fuel option proposed for the next several decades.
WHAT IS SAF?
SAF is a catch-all term for any non-traditional jet fuel that is compatible with existing engines when blended with fossil fuel. It can be derived from household or agricultural waste, used cooking oil, or by combining captured CO2 with hydrogen. SAF must always be blended with traditional jet fuel, at no more than a 50% ratio.
SCALE
Currently, the UK has just one operational SAF plant, with eight more aiming to begin operations before 2030. If these plants are built on schedule, their combined output will nevertheless generate only half of the Government target of 1.2 million tonnes of SAF per year by 2030. This will create a reliance on SAF imports at a time when other major markets will also be competing for resources to meet their own decarbonisation targets.
KEY POINTS
CONCERNS
There is strong evidence that aviation decarbonisation cannot be addressed by SAF alone. Both academia and industry are highlighting concerns about the ability to sustainably provide the volume of SAF needed, within the urgent timescale to meet climate goals, outlined in the following points.
BIO COMPETITION
Aviation is not the only sector relying on bio-based fuels as a decarbonisation measure. Other sectors including heat, energy, road and marine transport also expect to use the same feedstock in their decarbonisation pathway. The UK produces around 250 million litres of used cooking oil each year, most of which is used to feed livestock, fuel road transport, and make products such as soap, make-up, and detergents. This competition is fierce, but the Royal Society has estimated that even if 80 per cent of the UK’s cooking oil was repurposed for jet fuel, it would still only fuel 0.6 per cent of flights.
ALTERNATIVES TO BIO
Alternative ways to produce SAF without using biological material are also facing challenges. Synthetic fuels (eFuels) require enormous amounts of electricity to produce. The US Department of Energy estimates that powering all US domestic flights on eFuel would use ‘85 per cent of the current total U.S. electricity generation’. At a time when all sectors need to decarbonise, this raises serious questions about whether aviation is the best and fairest use of these limited resources and energy.
CLIMATE IMPLICATIONS
The ability of SAF to significantly reduce aviation’s climate impact is also under question. While the UK mandate requires SAF to have a CO2 emissions reduction of 40% compared to fossil fuels, recent research has indicated that condensation trails (contrails) formed by planes may cause more warming than the CO2 emissions themselves. As SAF use does not prevent contrail formation, the actual climate benefit of switching to SAF may be much less than estimated.
COST BARRIERS
The cost of SAF has been highlighted by the industry as a major barrier to uptake. Current SAF prices typically between 2-5 times higher than traditional jet fuel, and industry leaders including the CEOs of Shell and British Airways have acknowledged these costs will likely be passed directly to passengers.
ECONOMIC MISCONCEPTIONS
Claims about the economic benefits of aviation growth and airport expansion are not supported by recent evidence. Research by the New Economics Foundation has shown that increasing passenger numbers over the last two decades has led to no net job creation, but instead has resulted in stagnant business travel, a decline in real wages in the sector, and a reduction in domestic tourism. The major outcome has been significant growth in outbound leisure travel, which in fact removes spending from the UK economy. These findings undermine a key justification for aviation expansion.
URGENT TIMEFRAME. Most crucially, the urgency of the climate crisis requires immediate action. Multiple climate tipping points have already been crossed, global wildfires and floods are increasing in severity and frequency, and we are approaching the 1.5 C limit enshrined in the Paris Agreement faster than any models predicted. Using the future potential of SAF to justify airport expansion delays climate action to a dangerous point of no return. In this key moment, we cannot afford to pursue strategies that defer emissions reductions to an uncertain future – particularly when evidence shows these strategies may be flawed and immediate alternatives are within our grasp.
CALL FOR ACTION
DEMAND MANAGEMENT
Implement measures to reduce demand, limiting aviation emissions at source. Actions could include the introduction of a frequent flyer levy and increasing domestic air passenger duty in line with international rates, but at the minimum they must include a moratorium on airport capacity expansion.
SUSTAINABLE ALTERNATIVES
Invest in high-speed rail infrastructure and transport networks, including international links. This would also support the domestic tourism industry, which has been negatively impacted by the proliferation of cheap, short-haul flights.
HONEST ASSESSMENT
Accept and communicate honestly about the decarbonisation challenge in aviation. Both industry and policymakers must acknowledge that technological solutions alone cannot address aviation emissions in the timeframe required by climate science, and the Government’s own legally binding climate targets. Policy measures must be developed based on the total climate and warming impact, rather than a sole focus on CO2.
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