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Air Traffic Controllers can help reduce the climate impact of contrails

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European air navigation service providers can play an outsized role in tackling the climate impacts of flying by developing, implementing and perfecting contrail avoidance protocols, writes Denis Bilyarski.

Denis Bilyarski is an aviation decarbonisation and climate safety researcher.

As millions of Europeans are preparing for holiday travel or looking back at it, delays have become the norm in the flying experience.

Around 40 percent of flights in Europe were delayed in June. When announcements get made at the gate, Air Traffic Control – or ATC – often gets “credited”, especially when industrial action is involved.

Europe-wide ATC strikes, however, while always possible, have not materialised so far. And while flights over France were impacted in early summer by action involving all public employees, a close look at stats published reveals that they were not the main reason behind these delays.

Neither were the airspace closures that European air traffic controllers helped mitigate when military exercises were unfolding over the continent.

Instead, bad weather was by far the most common reason behind the nearly 60,000 hours of total delays reported in June.

And while this would be considered the norm in a mode of transport highly dependent on favourable meteorology, the trend is clear: more instances of adverse weather encountered both in-flight and at airports.

So much so that a working group led by Eurocontrol and ACI issued a special briefing to European aviation stakeholders on preparing for adverse weather events this summer – based on experiences from the last one.

It arrived just in time for what is so far proving to be a season of shattered temperature records and violent storms across much of the continent. Its publication also shows that historic datasets and standard procedures are not always as relevant in a changing climate.

Unsurprisingly, the impacts the climate crisis is having on air transport are not as often discussed as the role the sector plays in driving it.

The now established scientific consensus that the problem goes beyond CO2 has prompted the EU to start work on a set of Monitoring, Reporting and Verification (MRV) guidelines for aviation non-CO2 effects, with a view of incorporating them under its ETS scheme.

Clouds forming from condensation trails – known as contrail cirrus – account for the biggest share of the warming. While the transition to advanced jet fuels from non-fossil origin – also known as SAF – holds promise in reducing climate impacts stemming from both CO2 and contrails, their current rate of uptake is broadly deemed to be too slow.

This has led to research on more direct methods to reduce radiative forcing linked to contrails. Early August saw an announcement by Google that its AI technology was used in a trial to help pilots on a number of American Airlines flights avoid contrails forming behind them.

As it often happens, Europe did it first but almost no one noticed.

In May, the results from the first real-world trial of persistent contrail formation avoidance involving thousands of passenger flights above Belgium, the Netherlands and northern Germany over the course of several months in 2021 were published.

Conducted by Eurocontrol and DLR, the experiment consisted of air traffic controllers making small adjustments to the altitude aircraft fly at, seeking to keep them away from areas where temperature and humidity levels were identified to make contrail formation more likely – essentially the same procedure as Google’s trial but on a bigger scale and without the help of AI.

To be clear, both report that prediction accuracy for persistent contrails will need to improve, something that current advances in computing power and weather system modelling are bound to bring about. For now, the findings validate the concept of navigational contrail avoidance as a viable means of reducing aviation non-CO2 impacts.

Importantly, they show that European air navigation service providers can play an outsized role in tackling the climate impacts of flying by developing, implementing and perfecting contrail avoidance protocols.

The policy perspective is that this can be seen as a “middle way” alternative to the command-and-control approaches to addressing aviation emissions that the sector so often opposes.

After all, what air traffic controllers do best is help guide flights safely through the skies to their destination. They can do exactly that for the airline industry’s climate neutrality journey, despite the delays and expected turbulence ahead.



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