De onderkant van een vliegtuig tegen een lucht met wolken en zon
“If we cannot scale up sustainable aviation, then perhaps we have to scale back unsustainable aviation.” (Foto: Kevin Woblick/Unsplash)

TU Delft should have more critical discussions about the urgency and scalability challenges of the energy transition, argues master student Antonio Küng.

(This opinion piece is based on many sources. Relevant links can be found at the bottom of the article.)

Last month, Jos Wassink’s article on this website estimated that the Netherlands would not generate enough wind power by 2030 to meet the hydrogen demand of a fleet of sustainable Dreamliners. This sparked my engineering curiosity and got me wondering, if not by 2030, then when can we fly sustainably?

Wind power aside, one major obstacle to achieving green aviation is simply that sustainable Dreamliners with 330 seats don’t exist, at least not now. None of the current projects, including ZeroAvia, HAPSS and the Airbus ZEROe, will be available within the next five to 10 years, and all of them will have significantly fewer seats than existing commercial airliners. Considering market adoption rates, both Airbus and Boeing expect that most commercial airliners will continue to rely on traditional jet engines until at least 2050.

The year 2050 sounds familiar because by then the world needs to have reached net-zero emissions, and developed countries preferably by 2040. Even more so, the latest published Intergovernmental Panel on Climate Change (IPCC) report states that to stay below 1.5°C or 2°C of warming, emissions need to peak by 2025. Achieving this requires ‘rapid, deep and, in most cases, immediate greenhouse gas emission reductions in all sectors this decade’.

Zero emission aircraft will not be available at scale by 2030, and yet we still have to drastically reduce emissions if we want to avoid the worst effects of climate change. Is it possible then to compensate for ever-growing jet engine emissions instead? In theory, we can already achieve net-zero emissions today with carbon offsets. However, in practice, the carbon offset market is mostly voluntary, highly unregulated and of questionable effectiveness. Again, not a scalable solution.

Instead, the silver bullet appears to be Sustainable Aviation Fuels (SAF). Both KLM and IATA rely heavily on SAF to reach their 2050 net-zero goals. But global SAF production today is less than 1% of total jet fuel demand, and the Royal NLR does not hold out much hope that SAF production will be sufficiently scaled up by 2050. Even carbon capture, our desperate last resort against carbon emissions, suffers from exactly the same scalability problems.

‘There is a rapidly closing window of opportunity’

So when will we be able to fly sustainably? Not in this decade it appears. As engineers, we of course have faith in solving these problems eventually. But ‘eventually’ is not enough, and engineers also need to face the time constraints they are dealing with. As the IPCC states, ‘There is a rapidly closing window of opportunity to secure a liveable and sustainable future for all’.

If we cannot scale up sustainable aviation, then perhaps we have to scale back unsustainable aviation. As stated by the European Federation for Transport and Environment, the priority for this decade must be to reduce demand. This is the most effective measure that can be taken before 2030, and it can realistically be achieved by simply getting rid of the generous state subsidies that keep the market price of polluting activities artificially low.

In Europe at large, airlines do not have to pay excise tax on kerosine or sales tax on tickets. For the Netherlands, this amounts to EUR 2.1 billion a year in tax exemptions, enough money to cover the costs of all national passenger train tickets. These tax exemptions are especially inequitable considering that only 1% of the world’s population is responsible for 50% of all aviation emissions. And this while the 80% of human beings that have never even been on a plane still have to bear the costs of climate change.

I hardly expect KLM to advocate for higher taxes and fewer flights, quite the opposite. After all, companies whose bottom line is intrinsically linked to burning fossil fuels have little incentive to decarbonise, although some within TU Delft seem to think otherwise. What I would expect though is that a technical university like TU Delft has more critical discussions about the urgency and scalability challenges of the energy transition. Jos Wassink’s article is a great example of this, and I hope that we can integrate these discussions into TU Delft's curriculum.

So when discussing emission reductions, remember to not only ask “How much?” but also “How quickly?”. The answer to the former needs to be “A lot”, and the answer to the latter “Right now”.

Antonio Küng is a master student at the Faculty of Aerospace Engineering. Also read his previous letter on this website.

Relevant Links:

Airbus tells EU hydrogen won't be widely used in planes before 2050 in Reuters.

New climate report: UN chief demands EU, US set new targets in Politico.

Synthesis Report of the IPCC Sixth Assessment Report (AR6)Summary for Policymakers.

1.5 or 2 degrees Celsius of additional global warming: Does it make a difference? in Yale Climate Connections.

Revealed: more than 90% of rainforest carbon offsets by biggest certifier are worthless, analysis shows in The Guardian.

Sustainable aviation fuel on the KLM website.

Our Commitment to Fly Net Zero by 2050 on the IATA website.

Fact Sheet Sustainable Alternatives To Kerosene by Royal NLR and TU Delft.

Feedstocks for sustainable aviation fuels in the Netherlands by Royal NLR.

Carbon removal hype is becoming a dangerous distraction in MIT Technology Review.

Roadmap to climate neutral aviation in Europe by Transport & Environment.

Absurd: The Netherlands supports major polluters with 8 billion euros per year (in Dutch) by Milieudefensie.

True Price – The real price of a plane ticket (in Dutch) by Natuur & Milieu.

Will the Netherlands also experiment with cheap trains? (in Dutch) in NOS.

The global scale, distribution and growth of aviation: Implications for climate change by S. Gössling and A. Humpe, November 2022,

KLM, Delta sue Dutch government over Schiphol flight cuts in Associated Press News.

Stranded assets could exact steep costs on fossil energy producers and investors in MIT News.