Non-CO₂ emissions responsible for 66% net aviation impact on climate

October 1st 2022

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A recent University of Bristol report argues revised air traffic control procedures and aircraft operations could reduce the climate impact of aviation by as much as 20% in the next five to 10 years. Read More » Lead author of the report, Kieran Tait, said aircraft non-CO₂ emissions are responsible for more than 66% of aviation’s net climate impact, but due to a policy focus on decarbonization, mitigation of these emissions often is overlooked.

“Flight route climate optimal routing, to avoid climate sensitive regions, and formation flight, where two aircraft separated by two kilometres fly one behind the other, could hold the key to drastically reducing aviation’s climate impact.”

The two main contributors to aviation’s non-CO₂ climate impact – aircraft condensation trails (contrails) and emission of nitrogen oxides (NOx). The warming effect of non-CO₂ emissions strongly depends on the chemical and meteorological state of the atmosphere at the instant they are released.

Contrails account for 51% of aviation’s total climate impact, the study said. Where the air is very cold and humid, the water vapour in the contrails condenses around particulates to form ice crystals trapping heat and producing a net warming effect.

Similarly, emissions of NOx react with chemicals in the atmosphere to generate ozone and reduce methane. However, the generation of ozone tends to outweigh the methane reduction, leading to a net warming effect.

“While climate optimal routing may require a longer flight, and therefore an additional 1%-2% fuel burn, avoiding climate sensitive areas could reduce the overall climate impact of a flight by around 20%,” Tait wrote.

In formation flight, the follower aircraft flies in the wake of the leader aircraft, receiving an up wash reducing required lift and resulting in a 5% - 8% decrease in fuel burn. It has the additional benefit of the overlapping of aircraft exhaust plumes and the accumulation of emissions contained within them.

“The next step is to analyse global air traffic data to identify high density airspace hotspots, for example along flight corridors, where implementation of the formation flight concept would be most appropriate,” Tait said.

Associate Professor of Aerospace Engineering at the University, Dr. Steve Bullock, said “aviation had a lot to gain from adopting these findings, making small but crucial changes to air traffic control and aircraft operations that will have such a significant impact.”

The Department of Aerospace Engineering at the University of Bristol has several links with industry leaders including Airbus and Rolls-Royce.