Relating the climate impact of trans-Atlantic flights to typical north Atlantic weather patterns

Aircraft contribute to climate change through emissions of carbon dioxide, oxides of nitrogen, water vapour and formation of persistent contrails. Both the aircraft routing and subsequent climate impact are dependent on the large-scale weather pattern. It may therefore be possible to reduce aircraft climate impact by defining climate-optimal aircraft routes; this is being investigated by the European REACT4C project for trans-Atlantic flights. To better understand the links between the weather, aircraft routes and climate impact, we first identify five typically occurring north Atlantic weather patterns for the winter season, using 21 years of ERA-Interim re-analysis data. These weather patterns are characterised by the strength and location of the upper-level jet stream, leading to time-optimal aircraft routes different from the great circle. We demonstrate that the expected climate impact also varies according to the weather pattern, with a particular focus on cold ice-supersaturated areas where persistent contrails would form. The distribution of cold ice-supersaturated regions varies both by weather pattern and altitude. Along time-optimal routes through these weather patterns the probability of persistent contrail formation is 1-10%. This can increase or decrease with height, depending on the weather pattern, indicating it is not possible to mitigate contrail climate impact simply by flying higher.