The cost of climate-neutral aviation in the future

Aviation currently contributes to about four percent of the global warming that has been observed. As demand for flights is likely to continue to increase, researchers and governments are looking for solutions to make aviation climate-neutral by 2050 at the latest. The majority of experts agree that air fares will become more expensive as a result. But how much more? There is also some debate about which technology is best for decarbonising aviation.

According to a new study by researchers at ETH Zurich and the Paul Scherrer Institute published in the journal Nature Communications, air fares could rise by around 50 percent compared to current prices if synthetic fuels were to replace the fossil fuel kerosene throughout the world by 2050.

“When looking at this potential increase, it should be taken into account that air fares have fallen by over 40 percent in the last 25 years,” says Anthony Patt, ETH Professor of Climate Policy and co-author of the study. “If this trend were to continue, a climate-neutral flight in 2050 would cost roughly the same as a flight today.”

Two technological approaches

The authors of the study compare two approaches for reducing the climate-damaging effects of aviation. In the first, aeroplanes continue to use petroleum-based kerosene. However, an equivalent amount of CO₂ is extracted from the atmosphere as that emitted by the jet engines, for example by filtering it directly from the air and storing it underground. The ETH spin-off Climeworks launched this technology onto the market a few years ago.

In the second approach, airlines replace an increasing amount of kerosene with synthetic fuel without the need to modify turbines or aircraft. This fuel is produced from captured CO₂ combined with sustainably produced hydrogen, the latter produced from water either using electricity or with a solar reactor. The latter technology was developed at ETH Zurich and brought to market by the ETH spin-off Synhelion.

Synthetic fuels the cheaper option

The researchers show that synthetic fuels would be the cheaper option if air traffic continues to increase. The reason for this is that aviation’s impact on the climate is not limited to CO₂ emissions. “As a result of condensation trails and other non-CO₂ effects, such as those relating to the release of soot particles or nitrogen oxides, the overall impact of aviation on the climate can be up to three times greater than that of CO₂ emissions alone,” says Nicoletta Brazzola, lead author of the study and post-doctoral researcher in the Professorship for Climate Policy at ETH Zurich.

Unlike the warming from CO₂ emissions, which lasts for centuries, the non-CO₂ effects are short-lived, and hence respond immediately to the volume of aviation. As the volume of aviation grows, these short-lived effects can rise quite quickly. Truly climate neutral aviation requires offsetting these non-CO₂ effects with additional removal of CO₂ from the air.

Synthetic fuels have one significant advantage: they burn more cleanly than fossil kerosene and cause far fewer damaging non-CO₂ effects. This also means that less additional CO₂ needs to be removed compared to an aircraft fuelled with fossil kerosene. The researchers explain that this works out cheaper. In the case of an emit-and-compensate approach based on kerosene, ticket prices would be around 55 to 75 percent higher than they are today. With synthetic fuels, they would only go up by 45 to 60 percent.

A rocky road ahead

However, Brazzola, the author of the study, believes that the road to climate-neutral aviation will not be a straightforward one. “To achieve climate-neutral aviation, we will need to massively scale up supply of these fuels, producing large quantities of green hydrogen and building CO₂ transport and storage infrastructure,” says the ETH researcher. “This will be an unprecedented challenge.”

The actual cost of producing synthetic fuel depends on the price of its energy inputs, with solar and wind offering the lowest costs. The least expensive inputs, in sufficient quantities to serve the global market, are to be found outside of Europe.

“We would expect to see global production chains for synthetic fuels rather than European ones. This global market makes the renewable energies required for the production of these fuels a lot cheaper,” says ETH Professor Patt. For example, large solar energy plants could be located in areas of Northern Africa or the Arabian Peninsula that are exposed to a lot of sunshine. There are also other countries with significant potential for renewable energies, such as the USA, South Africa, Chile and Australia.

CO₂ and kerosene need to be more expensive

The key question for Patt is whether the volume of sustainable kerosene will increase quickly enough, as the market is still very small at present. The ETH professor believes that the right political conditions will play a vital role in this. For example, a law came into effect in the EU in 2025 that initially requires two percent sustainable fuel to be blended into fossil kerosene. This is to increase to 70 percent by 2050. A similar regulation is set to come into effect in Switzerland in 2026. “These measures are a step in the right direction, but they need to be expanded further. The price of CO₂ would also have to go up to make fossil kerosene more expensive and therefore more unattractive,” says Patt.