How Contrails Harm the Climate

In recent years, studies have been conducted to explore how air masses that lead to the formation of particularly persistent contrails can be avoided. Since there is currently a lack of alternatives to the combustion engine, this could be a relatively straightforward approach to quickly reduce the significant environmental impact of air traffic. Nevertheless, a controversy has now arisen.

How do contrails form?

The trails form when water vapor from the aircraft engines meets cold air and condenses into ice crystals. These attach to the soot particles also emitted by the turbines. At low temperatures and high humidity, the trails are particularly long-lasting and can develop into artificial cirrus clouds. This occurs mainly at high altitudes of at least ten kilometers, the usual cruising altitude of commercial aircraft.

How harmful are contrails to the environment?

This depends on several circumstances - including the time of day. Like natural clouds, their artificial counterparts trap warm air masses in lower layers of the atmosphere. This is especially a problem at night. During the day, however, the artificial clouds can even shield the Earth from the sun's heat rays. The climate impact also depends on the season and the geographical position of the aircraft.

What are the possibilities for avoiding contrails?

In addition to alternative fuels with fewer soot particles, route optimization seems particularly suitable for reducing contrails. The airplanes would have to take detours with additional kerosene consumption to avoid humid high-altitude air layers. The respective environmental effects of the routes must be measured and offset against each other. For fuels, the scientists from Future Cleantech Architects (FCA) recommend the targeted use of sustainably produced synthetic fuels (SAF) on flights where a particularly high number of contrails are expected.

Are detours with higher kerosene consumption worthwhile?

The European environmental organization Transport & Environment assumes that only three percent of all flights are responsible for 80 percent of climate-damaging contrails. Their routes, especially over the North Atlantic, would need to be changed in small sections, with the jets consuming five percent or less additional fuel. The benefit for the climate is said to be 15 to 40 times greater than the disadvantage of the additionally burned kerosene. In practice, these figures have hardly been substantiated so far.

What Problems Are There in Implementation?

The German Aerospace Center (DLR) is running the research project "D-Kult", in which more than 100 regular flights of German companies were rerouted in 2024 to avoid contrails. The flights in question had to be selected and planned with great personnel effort at Lufthansa, Condor, and DHL, among others. There is a lack of reliable data for automated flight planning, such as weather along the entire route. Participants say that reliable statements about actually avoided climate effects are not yet possible.

Very large detours were not planned because it would have endangered the stability of the entire network. Even small delays can lead to major problems and additional necessary flights if slots are missed or night flight limits are exceeded, warns Tuifly, which is also involved. The German Air Traffic Control (DFS) also points to the congested airspace in Europe and over the Atlantic: Changes to original flight plans into so-called Yo-Yo routes (up and down) would inevitably lead to domino effects and result in increased coordination efforts by the controllers.

What Is the European Union Planning?

Since the beginning of the year, the EU has required European airlines to determine and report the non-CO2 effects of their European flights. However, according to the German industry association BDL, the necessary reporting system "NEATS" (Non-CO2 Aviation Effects Tracking System) will only be fully available by the end of the year. In terms of content, the instrument is currently a "black box" for the airlines, criticizes BDL Managing Director Joachim Lang. Due to a lack of research results, the expected NEATS results on climate impact are not reliable and are rather set too high due to conservative assumptions.

Why Does the Aviation Industry Want a Postponement?

The BDL fears an additional burden for European airlines in competition with providers from Turkey or the Arab region, for example. The EU wants to integrate the non-CO2 effects into the already existing emissions trading for CO2 certificates. This would mean that airlines would have to obtain and pay for "pollution rights" for contrails in addition to those for kerosene. It is also unclear who would pay for the additional fuel for climate-friendly detours. Here, the BDL demands a moratorium until more reliable studies are available. These are to come, among other things, from the already approved follow-up project SD-KULT, which is to start in 2026.

(APA/Red)

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