Sustainable aviation fuels: powering aviation to net zero


There is currently no zero emissions technology. As a result, we all need to fly less, was the observation of Cait Hewitt, policy director at Aviation Environment Federation, speaking at the CAPA Airline Leader Summit - 'Airlines in Transition 2022' in Apr-2022.

This view is not uncommon, even though aviation was the first industry with a global decarbonisation strategy. The industry adopted a target to halve emissions by 2050 back in 2009. Its leading participants are now more ambitious, aiming for net zero by 2050.

Aviation has long had four pillars in its decarbonisation strategy: new technology, sustainable aviation fuels (SAF), operations/infrastructure and economic measures. This is an 'eggs in many baskets' approach, but SAF must make the biggest contribution to the 2050 net zero goal.

SAFs are not created equal – the performance varies. Both carrot and stick – incentives and regulation – are needed to ramp up SAF production, but the first 10% will be the hardest and riskiest.

Meanwhile, global governments must back aviation industry participants by adopting the 2050 net zero target at the ICAO General Assembly in Sep-2022.


  • SAF must make the biggest contribution to the 2050 net zero goal.
  • Different SAFs have a different climate performance based on a full life cycle analysis of greenhouse gas reductions.
  • Both incentives and regulation are needed to ramp up SAF production – but the first 10% will be the hardest and riskiest.
  • Global governments must back net zero through ICAO.

SAF must make the biggest contribution to the 2050 net zero goal

New aircraft/engine technology is unlikely to deliver new sustainable propulsion methods (electric or hydrogen-powered) beyond short haul flights by 2050, and operational efficiency gains can only reduce the growth in emissions.

This means that SAF must make the biggest contribution towards net zero in 2050, with economic measures offsetting the remaining shortfall.

IATA expects SAF to contribute 65% of the reduction in emissions needed to achieve net zero in 2050, while European aviation's 'Destination 2050' modelled SAF's contribution at 34%.

The details and pathways to net zero vary, but all industry participants agree that SAF production will be critical and needs to scale up rapidly.

Three technologies for SAF production

Broadly, there are three technologies for producing SAF, but all of them are significantly more expensive than existing jet fuel (ranging from approximately 2.5 times to approximately 8 times).

  • Hydroprocessed esters and fatty acids (HEFA): a technique using vegetable oils and fats, is the most immediate and least expensive;
  • Alcohol-to-jet: a more technologically advanced process, which converts alcohols into fuel and is the middle option in terms of cost;
  • Electrofuels (also known as power-to-liquid): created by electrolysis of water to create hydrogen and then combining it with carbon monoxide created from captured CO2. This forms hydrocarbons that can be mixed with jet fuel to power existing aircraft engines. Electrofuels are often cited as being one of the best forms of SAF in terms of (Greenhouse Gas) reduction, but are the most expensive.

Not all SAFs are equal

One of the important nuances in any consideration of SAF is the climate performance of each type of fuel. This must be based on a full life cycle analysis of its greenhouse gas (GHG) reductions – from feedstock extraction and processing to combustion (also known as well-to-wake emissions).

This must take into account the impact of diverting the feedstock from other uses, in addition to the production pathway and feedstock.

Well-to-wake emissions for SAFs from non-crop feedstocks relative to petroleum jet fuel baseline


For example, a crucial consideration in the production of electrofuels is that the electricity used to create the hydrogen must be from a renewable (i.e. emissions-free) source if this form of SAF is to achieve genuine GHG reduction.

Using European grid-average electricity would generate more GHG than the use of existing fossil fuel, according to a 2021 paper by The International Council on Clean Transportation (ICCT).

This brings huge challenges: for example, the UK would need to build a new wind turbine every three days until 2050 to achieve 100% electrofuel.

Carrot and stick needed to ramp up SAF production

SAF currently represents only an extremely small fraction of aviation fuel (0.05% of jet fuel use in the EU, according to the European Commission in 2021).

There is a 'chicken and egg' problem that demand is held back by the high cost of SAF production, which also inhibits the investment needed to produce at scales that would bring costs down.

A combination of carrot (incentives) and stick (regulation) is needed to stimulate growth in the production and use of SAF.

Incentives will need to include government support, such as tax breaks for investment and a price stability mechanism of the sort that had helped to drive the offshore wind energy sector.

The UK has a contract for a difference mechanism for price stability, which will be helpful to those investing in SAF production.

Regulation includes mandates setting targets for the proportion of SAF usage over time. This is already on the way in the EU through its 'ReFuelEU' initiative, and the UK is also working on a SAF mandate. Neither is yet finalised or implemented.

In addition, clarity is needed from regulators on feedstock compliance. Countries have different approaches to the related carbon credits.

"The first 10% is the hardest"

Speaking at the CAPA Airline Leader Summit - 'Airlines in Transition 2022' in Apr-2022, Jonathon Counsell, IAG Group head of sustainability, said: "the first 10% is the hardest as it carries the highest risk".

After that, once the concept is seen to be commercially viable, market dynamics should kick in.

SAF production plants are being planned. The UK may have 14 plants in the next 10 years, while more than 20 are planned across the EU and more than 40 in the US.

IAG is committed to achieving 10% of its fuel from SAFs by 2030, and the leading US airlines are targeting 15% through the industry body Airlines for America.

Both of these targets are much more ambitious than the EU's ReFuelEU proposal of 5% and the Destination 2050 roadmap, which envisages 6% of jet fuel coming from SAF in 2030.

Perhaps more importantly, ICCT's 2021 paper estimated that the resource base would be sufficient to support 5.5% of projected 2030 jet fuel demand.

Global governments must back net zero through ICAO

Aviation industry participants are in broad agreement over the goal of net zero for 2050, adopted by European aviation in Feb-2021 and by the world airline trade body IATA in Oct-2021.

IATA's Director Fuel, Alexander Kueper, said at the CAPA Airline Leader Summit - 'Airlines in Transition 2022' that net zero could be achieved, although "flying might be a bit more expensive".

However, the commitment also needs to be backed by governments all across the globe.

The only way to achieve this is through the International Civil Aviation Organisation (ICAO), an agency of the United Nations. ICAO has welcomed the aviation industry's net zero target, but has not yet adopted it.

This requires a general assembly of ICAO's 193 member states, which will next take place in Sep-2022. The general assembly will be asked to adopt a long term net zero target and commit to a global ambition on SAF.

Aviation needs a "positive reinforcing loop"

Meanwhile, there is a growing body of public opinion which believes that less flying is the only way to reduce emissions.

Aviation Environment Federation's Ms Hewitt argued that SAF is a form of offset, not a reduction in emissions. In the absence of zero emissions technology, the only solution to growing emissions is to fly less, she said to a roomful of aviation professionals.

Moreover, some voices in governments are calling for downward management of demand in aviation.

Christina Cassotis, CEO of Allegheny County Airport Authority, which manages Pittsburgh International Airport in Pennsylvania, stressed at the CAPA Airline Leader Summit - 'Airlines in Transition 2022'  that aviation must improve its communication of what it has already done and what it will do to achieve net zero, "or it will be taxed".

Ms Cassotis said that the industry could create either a "negative reinforcing loop or a positive reinforcing loop". She had a stark warning: "Take away air service and you take away an economy".

Aviation emissions are an explosive issue for the airline industry and the mountain to climb has become even taller than it was before COVID-19

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