Sustainable flying in 2050? Why the airlines’ promises don’t work

Zurich Airport called last Sunday a “record day” since the pandemic: During the first weekend of Zurich’s school holidays, the airport registered more than 100,000 passengers – in a single day. And according to the airport, it shouldn’t be the only peak day in the summer holidays where this figure is broken.

During the hot months, the Swiss prefer to travel by plane. In general, the number of flights per capita in this country is about twice as high as in our neighboring countries Germany and Austria. One or the other traveler will probably be embarrassed to fly, as it is well known that flying harms the climate.

The aviation industry promises that this bad conscience will soon be superfluous. Thanks to new technologies, flying should be CO₂ neutral by 2050. As Swiss boss Dieter Vranckx recently said in Radio SRF’s “Tagessprach”, “There should be no more flying shame in the future, because we are greener on the road.”

Is that really realistic? Or is the promise of green flying like a castle in the air? This question has been explored in a new study by researchers from ETH Zurich and the Paul Scherrer Institute (PSI), which was published in the journal “Nature Communications”. The results can be summarized in three messages: one good, one bad, and one thought-provoking.

The good news: the researchers think the goal of climate-neutral flying is ambitious, but not entirely impossible. They also see technological progress, for example in the development of sustainable fuels, as a reason for hope.

The bad news: Just a clean ride is not enough. To meet the climate targets, global air traffic must decrease – and current projections suggest that this is highly unlikely. According to calculations by the umbrella organization Iata, global passenger traffic will more than double by 2040 – to about 9 billion passengers per year.

And the thought-provoking message: there is an urgent need for a unified definition of what is actually meant by climate neutrality while flying. Because that is far from clear at the moment. The calculations usually focus on the pure CO2 emissions that arise when fuel is burned.

However, according to the researchers’ calculations, these are only for a fraction of the total climate effect. Much more important – but often only imprecisely or not at all included in the climate targets – are the so-called “non-CO2 effects”.

The planes also emit several other substances, such as nitrogen oxides and soot, which react to form ozone and methane, as well as water vapor. This forms vapor trails and clouds, which reflect heat rays back to the earth, heating it up.

It is true that these substances break down relatively quickly, while CO2 remains in the atmosphere for decades or even centuries. But their accumulation is problematic, explains co-author Viola Becattini: “Due to the increase in air traffic, the substances accumulate instead of quickly disappearing. In this way they develop their enormous cash potential over a longer period of time.” This regardless of whether the aircraft use fossil or clean fuel. On the other hand, one thing especially helps: less air traffic.

The realization that non-CO2 effects have a major climate impact is not new. But it has been massively underexposed in the public discourse so far. The topic is still relatively poorly researched scientifically, as the Swiss Academy of Sciences stated in an April 2021 factsheet.

The problem: It is difficult to determine what the non-CO2 effects are. On the one hand, they are highly dependent on factors such as flight altitude, geographical location, time of day and weather situation. On the other hand, the calculation changes depending on whether the effect is considered over 20, 50 or 100 years, depending on technical developments and depending on how much air traffic increases or decreases.

When asked, the Swiss airline also emphasized that it was aware that the “general impact of air traffic on the climate is not limited to the effect of CO2”. The Lufthansa subsidiary points out that the “climate effects of non-CO2 emissions are scientifically little known”. The level of knowledge does not yet allow for quantification and therefore does not allow “target setting and accurate derivation of control measures”.

The Swiss and the Lufthansa Group would participate in research projects that “specifically examine and evaluate non-CO2 impacts,” the airline continues. “This with the overarching goal of creating transparency and also implementing appropriate reduction measures in the field of non-CO2 emissions.” However, Swiss does not answer what these research projects entail in concrete terms.

The conclusion of the investigation is unlikely to please Swiss and the other airlines. It says: if aviation wants to be climate neutral by 2050, air traffic must decrease annually by 0.2 to 0.8 percent compared to now – depending on whether fossil or sustainable fuel is used. Just new drives, climate-friendly fuels and filtering CO₂ from the atmosphere to store it underground are not enough.

Meanwhile, airlines are placing all their hopes – as well as their PR strategies – on new technologies. Researchers around the world are working to replace conventional petroleum-based drives, for example with electric batteries, fuel cells or the direct combustion of hydrogen. But these technologies are still in their infancy. Until now they were completely unsuitable for large aircraft. In addition, there is the problem with hydrogen combustion, for example, that the harmful non-CO2 climate effects increase as a result.

Then the sustainable fuels remain. Artificial kerosene made from CO2 and water is intended to replace fossil fuels. If renewable energy is used in production, it is practically climate neutral.

At the moment, however, production volumes are nowhere near sufficient to meet the future sharply rising demand. In addition, production is many times more energy-intensive than conventional kerosene – which is why clean fuel is also four to seven times more expensive.

Flying more climate-friendly therefore costs more resources and money. The airlines have also recognized this. Many of them offer the possibility to “compensate” for CO₂ emissions at an additional cost. But as co-author Romain Sacchi explains, this is window dressing: “Many of these compensatory measures are ineffective.” To compensate for all climate effects, airline tickets would have to cost three times as much as they do now.

The criticism of the “flight compensation” has reached Swiss. As the airline writes, it has not offered this label “for a while”. The website now speaks of “compensation” instead of “compensation” for the emissions. For an additional charge, Swiss customers can book a “green fare” – at least on flights within Europe. This allows it to invest in the use of sustainable fuels and in climate protection projects. According to Swiss, CO₂ emissions are reduced by 20 percent and the remaining 80 percent is ‘balanced’. (aargauerzeitung.ch)