Curbing Contrails

Emirates is preparing to test the notion of flying aircraft through low humidity layers of the atmosphere.
Credit: Joe Pries

Debates about how to reduce aviation’s climate change impact tend to focus on new fuels and propulsion technologies – or simply on reducing the amount we fly.

Whatever the argument, the focus is always on reducing carbon dioxide emissions, but a parallel approach may also be possible.

This is because some studies estimate that more than half of aviation’s global warming effect is from contrails, with the rest coming from CO2 and other turbofan emissions, notes a recent New Scientist story.

It is possible to design engines that produce much smaller contrails, but given the impracticalities of doing so in any useful timetable, a more feasible approach is to alter the height that aircraft fly at.

Low-humidity layers of the atmosphere produce fewer, smaller contrails and directing aircraft to fly through these layers could be feasible.

Emirates is preparing to test the idea in conjunction with British technology company SATAVIA, which feeds weather data into its software to predict where the ideal layers lie.

The technology is designed to work on a global scale, although directing all aircraft to constantly shift altitude would likely be unsafe, and might even offset any gains from contrail reduction with higher emissions.

However, a study of flights over Japan found that most of the contrail warming was cause by just 2% of flights, so targeting the small fraction of flights that produce the longest-lasting contrails may be a viable approach.

Nonetheless, the warming effects of contrails is still subject to a significant margin of error, and is also still far from clear how balance their relatively short-term effects against the long-term build-up of CO2  - and is correspondent warming effect – in the atmosphere.

Thus the focus on CO2 is here to stay, but it will be worth keeping an eye on progress on other fronts.

Alex Derber

Alex Derber, a UK-based aviation journalist, is editor of the Engine Yearbook and a contributor to Aviation Week and Inside MRO.