If you are a frequent flyer, your travel habits may well be responsible for the largest share of your personal CO2 emissions. Aviation accounts for approximately 2-3% of global greenhouse gas emissions annually. Demand for air travel is expected to grow, particularly as incomes rise in emerging economies where people fly far less than in Europe, where I am based. For example, in 2018 the average Brit emitted almost 450 kg of CO2 flying – 75 times more than the average Nigerian.
And those metrics don’t even reflect the full extent of aviation’s climate impacts: contrails – the long, thin artificial clouds formed by planes – also induce warming under certain weather conditions.
This makes reducing aviation’s climate impacts a complex and urgent challenge and one that we can only win by betting on innovation – and not just technological innovation but also new approaches to operational efficiencies and travel behaviour. We need to fly only when there are no other viable options, and when we do, we need to fly sustainably. To achieve this, we need new fuels to decarbonise the planes of the present, while accelerating the path to market for the zero-carbon planes of the future.
Unless we change the sector’s emissions trajectory, the combination of increasing demand and the slow adoption of clean technologies could push the sector’s emissions to up to a quarter of the world’s total emissions by 2050. This would be catastrophic.
The challenge of decarbonizing aviation
Aviation is incredibly hard to decarbonize from a technological perspective. Reducing emissions will require the development and deployment of clean technologies across each market segment. We need to accelerate the path to market for the zero-carbon planes of the future with electric and hydrogen-powered aircraft, key solutions to decarbonize regional and short-haul flights.
In contrast, decarbonising long-haul aviation will be more challenging, as these planes are much bigger and travel longer distances—making them particularly CO2-intensive. Much of the technological challenge comes down to energy density, an area where fossil fuels are difficult to beat. Planes carry all the energy they need to reach their destination in the form of liquid fuels. These fuels are burned throughout the flight, progressively making the plane lighter and extending its range. And even figuring out the right technology to store all that clean energy on a plane wouldn’t be enough.
Large planes also need engines that can deliver a lot of energy at once: an Airbus A380’s engines produce more than 200 MW at take-off, similar to a medium-sized power plant. Additionally, the average lifespan of a commercial plane is several decades, making it unrealistic to rapidly replace existing planes at scale.
Enter sustainable aviation fuels (SAF), a clean alternative made from renewable biomass and waste resources that are functionally identical to oil-based jet fuel but with a fraction of its carbon emissions. Decarbonising aviation today, with aircraft currently in use around the world, will only be possible with sustainable aviation fuels.
What are sustainable aviation fuels?
Sustainable aviation fuels (SAF) are made from various low-carbon feedstocks, including agricultural waste, industrial carbon emissions, clean hydrogen and clean electricity. Compared to traditional jet fuel from crude oil, SAFs can drastically cut greenhouse gas emissions over their entire lifecycle while also enhancing local air quality around airports by reducing conventional pollutants like particulate matter.
There are two major SAF families, biofuels and synthetic fuels, which differ according to the feedstock type. Biofuels are produced from biomass, while synthetic fuels are produced from CO2 and clean hydrogen. When synthetic fuels are produced using electrolytic hydrogen—made from water and clean power—they are called e-fuels, PtL fuels, or e-SAF.
Synthetic fuels are the missing piece in the SAF puzzle
A fuel will only be as sustainable as the feedstock it is produced from, and standards for what’s sustainable vary widely across regions. Europe tends to adopt stricter criteria, especially for biomass, compared to regions like the Americas or Southeast Asia. However, sustainability alone isn’t enough—new fuels must also scale effectively to impact global emissions and eventually compete economically. Although SAF production doubled between 2022 and 2023, it still makes up less than 0.2% of global aviation fuel demand.
Today’s SAF is mainly derived from used cooking oil (UCO) via HEFA processing – a solution that is severely limited by feedstock availability, which is now mainly imported from China. Other advanced biofuels share similar limitations in the availability of sustainable feedstock – a challenge being tackled by entrepreneurs around the world, such as Viridos and Nova Pangea.
Synthetic fuels, on the other hand, can offer very low emissions (over 90% less than fossil jet fuel), scalability, and future cost-reduction potential – making them a necessary complement to sustainable biofuels. Synthetic fuels are produced from clean hydrogen and CO2. They enhance energy security, particularly in oil-dependent regions like Europe, and can both reduce contrails and improve airport air quality. They can be potentially be produced on-site, allowing for logistic flexibility in situations where supply lines may be constrained, such as military operations.
In Europe, synthetic fuels, especially eSAF from electrolytic hydrogen, are a technological priority and market opportunity. However, synthetic fuels face significant challenges: high costs and extreme energy and CO2 demands – two major technological challenges to scale, and that should guide our approach to progressive deployment.
Compared to most biofuels, the technologies needed to produce synthetic fuel are less mature and green premiums remain very high. Yet as renewable energy, electrolyzer technology, and production processes scale, eSAF costs are expected to decline. This path forward requires diverse advancements: new, more efficient pathways for fuel production from hydrogen and CO2, improved electrolyzers, and new sustainable energy sources, such as geologic hydrogen, a form of primary hydrogen that doesn’t rely on vast clean power resources.
Scaling synthetic fuels will also depend on our ability to deploy direct air capture (DAC) technologies, to extract CO2 from the atmosphere and use it to produce synthetic fuels, and to tackle the sector’s residual emissions – as no low-carbon fuel reduces emissions by 100%. The economics of continuing to use fossil fuels and DAC to offset the emissions may look more interesting in the short term than synthetic fuels, as long as oil prices remain manageable and refinery economics stable. But following this path is a risky bet if we see the day when cars and trucks no longer run on gasoline and diesel, leaving jet fuel to cover most refining and oil extraction costs.
What’s next for sustainable aviation fuels?
The path to decarbonizing aviation is both challenging and urgent, but sustainable aviation fuels offer a viable solution to reducing emissions. As demand for air travel rises, significant technological advances, feedstock availability, and economic scalability will be critical for expanding the use of SAF.
In my next piece, I’ll discuss the innovators and leaders at the forefront of SAF innovation and the policy efforts needed for widespread adoption – including the newly launched Project SkyPower and their efforts to accelerate final investment decisions for large-scale e-SAF plants.
