Sustainable Aviation Fuels are the future and the future only
Aviation is behind the curve. As sectors like electricity, road transport, and industry are making significant progress towards decarbonisation, commercial aviationʼs share of global emissions is set to rise. This is an industry whose emissions are prohibitively costly to reduce given currently available technology, currentlyaccounting for 2-3% of the worldʼs CO2 emissions. However, the statistic neglects private jet usage, with Taylor Swiftʼs alone translating into more than 8300 tonnes of CO2 in 2022, relative to the 0.001 tonne the average flier emits.
If sustainable aviation fuel (SAF) had powered her flights, her emissions could have been reduced by 80% if SAF were fully compatible with existing aircraft, and by 40% if blended with kerosene. This is because SAF is sourced from biomass and waste-base feedstock: waste fats and oils, municipal solid waste, wood and agricultural residue, sewage sludge, food wastes, and animal manure. The other, more incipient production method uses green hydrogen by capturing carbon directly from the air, creating synthetic SAF. While private jet-owners do not use SAF because private flights are not regulated, even in the regulated commercial sector, sustainable fuel only amounts to 0.1% of total commercial airline fuel. Here the hurdles are more complex, as high technology and production costs and a scarcity of carbon-neutral feedstock – the raw material used to produce SAF industrially – limit SAFʼs role in decarbonising aviation in the short term. Giving priority to the development of SAF could thus mean less funding towards industries whose decarbonisation has more readily available solutions.
Figure 1: Carbon life cycle of SAF.
The Need for SAF
From 1990 until 2019, flight demand has quadrupled, while the energy used for these flights halved. This energy efficiency came from technological developments and a higher passenger load factor (a higher percentage of occupied plane seats), rather than improvements in jet fuel. The carbon intensity of the fuel, or how much CO2 is emitted per kilowatt-hour of electricity has not changed, despite aviation being the most carbon-intensive transportation sector. So as demand for air flight increases, the fuel consumed and its emissions increase proportionally. Therefore, new solutions should seek beyond the efficiency gains of the past 30 years.
Though battery-powered planes can become substitutes for short-haul flights in the future, liquid hydrogenʼs potential to replace long-haul fuel is limited to when it will become technologically viable. This is where biogenic SAF comes in. Its drop-in character makes it the only medium-term solution to maintain air services over six hours, as it is compatible with existing commercial fleets. It can substitute petroleum-based fuel without any modifications to engines, airframes, and the fuel supply chain at the airports. Scaling it up becomes even more imperative considering long-haul accounts for more than 50% of CO2 emissions from aviation, despite comprising just 6% of flights departing European airports. Current SAF production capacity is only at 10% of what is required to meet the EU mandate in 2030, but increasing production comes at a substantial cost: feedstock collection and delivery renders SAF 2-5 times more expensive than kerosene.
The Current State of SAF
Most natural SAF sources come from waste streams already in use by other industries, and whose supply is increasingly scarce. SAFʼs potential to reduce emissions by 80% was evaluated using a small variety of feedstock, including ones that are not yet deployed industrially or are limited in volume. For the aviation industry to grow, the amount of SAF needed outpaces the available feedstock required to produce it, due to physical constraints on land and renewable energy. The fuel of the new generation will thus have to come from a much broader range of feedstocks. Additionally, for SAFs to not have adverse effects on agriculture, land use, water availability, or biodiversity, they must be locally sourced. For example, the UK would have to primarily produce fuels based on plant dry matter and forestry residues, as importing sustainable fuels would generate a carbon footprint that is higher than the fossil fuel alternative.
Even if the feedstock problem did not exist, the fact that commercial airlines are already nearing peak efficiency in technology and operations means that the added cost of using SAF has the potential to render their bottom lines negative. This creates uncertainty regarding the type of SAF that airlines will prefer in the future, which also poses a risk for SAF suppliers who already face immense sunk costs. The fact that a large enough SAF production plant has not been constructed further explains why it is challenging for SAF manufactures to attract traditional investors. HEFA – the most commercially viable SAF production method as of today – suffers most from the feedstock constraint, while the promising Power-to-Liquid (PtL) method – the synthetic e-fuel production solution to this problem – bears 5–8 times the cost of conventional jet fuel. To mitigate this SAF production risk, aircraft operators are now considering off-take agreements, where they agree to buy a portion of the SAF suppliersʼ future output for a longer period of time.
Unfortunately still, the most optimistic projection shows that even maximum SAF production will only constitute 5.5% of 2030 European jet fuel demand. As demand for SAF is expected to increase over time, its potential to displace conventional fuel is low if not for strong government intervention. The low availability of the best-performing feedstock and the infancy of the e-fuel industry mean that SAF production alone cannot achieve the EU aviation sectorʼs long-term greenhouse gas reduction goals. Thus, the fact that every unit of biomass or electricity dedicated to SAF is lost to other uses becomes ever more important. For example, consuming electricity to produce e-kerosene represents an opportunity cost of decarbonising the electricity sector itself. Against this backdrop, governments face policy and energy trade-offs.
Figure 3: Estimated annual SAF production and percentage of jet fuel demand that could be displaced.
The Distributive Effects (or Lack Thereof)
Aviation only accounts for 2.5% of carbon emissions because a majority of people in the world do not fly. The proportion of people from high-income countries that fly at least once a year is 40%, compared to only 0.7% from low-income countries. Waypoint 2050, the aviation industryʼs report on its strategy towards net zero emissions, highlights that air transport growth will widen access to flight and thus enhance global social justice. However, given only a minute proportion of frequent flyers – 1% of all passengers – account for 50% of all air travel emissions, the industryʼs trickle-down expectations of achieving justice should be given more scrutiny.
SAFs are considered sustainable because their emissions are offset by the carbon they absorb during production, but they burn the same as kerosene; there is always more carbon in the atmosphere as long as biomass is burned. This is why life-cycle carbon saving – the total amount of carbon that would have been emitted throughout the phases of a productʼs life – is often likened to a carbon offset, rather than a carbon reduction. For CO2 to be reduced from the atmosphere, cumulative emissions from SAF should be lower than all alternative courses of action that would have happened to the biomass if not burning for energy, such as forest protection. Expanding aviation by allocating investment and research efforts towards SAF would mean fewer subsidies towards more accessible and sustainable travel alternatives, such as railways. Therefore, the inequalities of flying mean that the people who benefit from the growth of the industry are different from those who often ncur the price: the high environmental and health toll disproportionately affects vulnerable communities.
This is compounded by the rising amount of private jet flights, which in Europe increased by 64% in 2022 and doubled the amount of CO2 emissions compared to 2021. The extent to which gains in sustainability in the aviation sector will be achieved will also depend on the use of fossil jet fuel in private flights, which are up to 14 times more polluting per passenger. This issue remains unaddressed by global aviation commitments: The Paris Agreement tackles commercial fuel alone, while the EU Emissions Trading System (EU ETS) exempts private aircraft from paying a carbon price.
The EU’s stance
The SAF’s role in driving air travel to net zero is decided by the coordination of some key stakeholders.
The Directorate-General for Mobility and Transport (DG MOVE) develops policies and oversees their implementation in reducing greenhouse gas emissions in the transportation sector. In particular, Directorate E on Aviation focuses on enabling technological progress, ensuring the functioning of the EUʼs internal air services market, and coordinating agreements with the external market.
The European Union Aviation Safety Agency (EASA) is an agency of the European Commission that collects data regarding the provision of SAF by suppliers and the use of SAF by airline operators at the main EU airports. It tracks the amount of SAF bought at the Union level, its origin, and the compliance status of each airline. It also facilitates partnerships between Member States and SAF initiatives such as Clean Skies for Tomorrow.
The International Civil Aviation Organization (ICAO) is an agency of the United Nations that facilitates airspace cooperation between the 193 countries involved. It devises the sustainability criteria for SAF (CORSIA) and assists Member States in deploying SAF through training activities, feasibility studies, and information sharing.
In April 2023, the European Parliament amended the EU ETS to gradually eliminate free allowances given to the aviation industry by 2026. EU ETS caps the total amount of greenhouse gas that airlines can emit through allowances – rights to emit one tonne of CO2 – that the aviation sector previously received for free. From 2024 onwards, airlines will have to transition towards trading them on the market. Additionally, 20 million of these allowances are now specifically reserved for commercial airlines that increase their SAF use. However, carbon trading is widely seen as a justification for harmful behaviour rather than a systemic remedy to the problem. Airlines compensating for polluting activities by paying for them shifts the moral responsibility for carbon reduction to someone else, and carbon credits usually come from carbon offsetting projects whose quality varies and is not guaranteed.
Later in 2023, the EU adopted the ReFuelEU Aviation package to complete the ʻFit for 55ʼ legislation. It mandates that the minimum share of total SAF employed be 2% in 2025, increasing periodically to ultimately reach 63% in 2050. However, airlines have expressed concerns that there is currently not enough SAF on the market to achieve proposed targets. The high SAF goal, absent complementary policies, may encourage more widespread biofuel use. Increased demand for biofuels provides an economic incentive for forests and grasslands to be cut and ploughed under to plant SAF crops, so that existing cropland would not be diverted away from food production. In addition to destroying habitats, exploiting previously unused land releases the carbon stored in trees and soil into the air, which would negate the greenhouse gas savings that biofuels would bring. This is why the package phases out fuels that have a high impact on indirect land use change (ILUC) by 2030.
Member States can only devise and implement policies limited to flights departing their airports. For example, France banned short-haul flights that can be covered by rail in less than 2.5 hours. Norway requires fuel suppliers to stick to a 0.5% minimum content of advanced biofuel, to grow to 30% by 2030. Sweden established a target to reduce greenhouse gas emissions to promote SAF adoption, while the UK dedicated GBP 165 million to SAF development projects, following up on its 2022 Jet Zero pledge.
However, the costs of environmental impact today are still paid voluntarily by conscious passengers in the form of green taxes on flight tickets. Given the urgency of the climate crisis, voluntary action is not enough. Using SAF at scale presents itself as a promising pathway towards achieving net zero emission air travel. But reaching that goal implies large subsidies towards SAF deployment, and the moral conundrum of financing privately owned enterprises with public funds raises the question of the lack of community control over them. As the net climate benefit and the constraints of SAF uptake are increasingly questioned from a wider system perspective, ideas outside technological innovation are also explored. Fiscal measures – mandatory carbon taxes and frequent flyer levies – as well as capping long-haul flights and reducing growth in operations can reduce demand for flying. It is important to question the social purpose of the air travel industry, whether it justifies the environmental costs and investments into mitigating them, and how these costs and benefits are distributed socially and geographically.
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