The Hitchhiker’s Guide to the Galaxy says 42 is the answer. But what is the question?

For Dr Marc Stettler it’s how to alter the course of climate change.

Could a small tweak to flight paths significantly reduce global warming? Dr Marc Stettler, Senior Lecturer in the Department of Civil and Environmental Engineering, believes so.
Along with his colleagues in Imperial’s Transport and Environment Laboratory, he’s working on what he calls “the fastest way for aviation to reduce its overall climate impact”.
His focus is contrails, the white streaks that form in an aeroplane’s wake when water vapour condenses on to soot particles and freezes as ice crystals. While the majority evaporate, some linger and form a barrier that traps heat that would otherwise escape the Earth’s atmosphere.

Existing efforts to curb aircraft-related climate change focus on reducing or offsetting carbon dioxide emissions, but Stettler says these will take decades to implement, may work less well than expected and could be expensive. His research, based on in-depth analysis of flight data from Japanese airspace, weather and flight trajectories, breaks new ground in the finding that one small change could have huge impact.

“We found that two per cent of flights contribute 80 per cent of the warming effect related to contrails,” he says. The research suggests that making a minor change to these flights’ trajectories could be transformative, as it is possible to avoid the thin layers of the atmosphere where the (cold and humid) weather conditions are just right for contrails to persist.
The next step is getting the aviation industry on board. However, Stettler points out that if just one forward-thinking airline started considering contrails at the flight-planning stages, it would set a trend. “It’s a small change that could have a really big effect and very quickly – within five years if there is an appetite to do it.”
Mitigating the Climate Forcing of Aircraft Contrails by Small-Scale Diversions and Technology Adoption by Roger Teoh, Ulrich Schumann, Arnab Majumdar, and Marc E.J. Stettler was published in February 2020 in Environmental Science and Technology.
Dr Stettler leads the Transport and Environment Laboratory (@TransEnvLab_IC) at Imperial.