Reduce climate impact by flying more

By flying longer distances we can reduce the climate impact of aviation, according to visiting Professor Volker Grewe. Exactly how so he will investigate with TU Delft colleagues starting from March.

Flying longer distances to spare the environment may sound strange. Obviously, airplanes will emit more carbon dioxide. This gas, however, is not the most significant contributor to climate change caused by aviation. Rather, the theory goes, contrails are. These large condensation trails in the sky form when planes fly through freezing cold, moist air. The exhaust condenses and gives rise to clouds.

These clouds cause both cooling and warming. Condensation trails reflect sunlight back into space and cool the earth, but they also trap infrared light, causing the earth to warm. Scientists think that the warming effect is stronger than the cooling.

Because of the way the earth curves, you can add small extra distances onto the flight to avoid vast contrails. By doing so on a flight to New York from Amsterdam, for example, you would only add about 22 kilometers to the journey.

This is one of the conclusions from the REACT4C research project, which ended last year and focussed on rerouting options to reduce the climate impact of transatlantic flights.

"We found that is possible in some cases to reduce the climate impact by 25 per cent while only increasing the cost for the airline company by 0.5 per cent", said Grewe, who is professor at the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Oberpfaffenhofen (Germany).

Grewe will be appointed professor at TU Delft next year, at the Faculty of Aerospace Engineering (section Aircraft Noise and Climate Effects). He will then expand on the REACT4C project. He received European funding for a new project called ‘Future Air Traffic Management for Climate’ to investigate the feasibility of rerouting flights in the European sky.

In their previous research Grewe and his colleagues at the DLR and the Center for International Climate and Environmental Research Oslo, the Department of Meteorology of the University of Reading (UK) and Eurocontrol in Brussels, combined a detailed climate-chemistry model with an air traffic model to calculate maps of the climate impact of localized emissions – so-called climate cost functions. They did this for one typical weather situation in the North Atlantic for winter and one for summer.

"These calculations are very complex and require intensive supercomputing. We used about two million CPU-hours for testing and the final simulations," said Grewe.

For rerouting to be successful, a much faster way of determining the ideal flight path must become available for airline companies. That is why in the follow up project Grewe wants to work on climate cost functions based on algorithms. These should result in much faster calculations of the alternative routes.

Grewe can't stress enough the importance of strategic flying. "Aviation contributes to climate change by roughly five per cent. Only one third arises from CO2 emissions. The rest comes mainly from contrails and NOx emissions."

Whether airline companies will adopt new routes remains to be seen. Half a per cent extra costs seems little. But then again airline companies work with very small profit margins. Grewe hopes that rerouting will become standard practice due to legislation or new self-regulatory mechanisms in aviation.