Reducing the climate change impacts of aviation by restricting cruise altitudes

Two of the ways in which air travel affects climate are the emission of carbon dioxide and the creation of high-altitude contrails. The latter have been found to potentially play a major role in climate change accounting for the largest impact from the aviation sector. One possible strategy for reducing the impact of air travel on climate change is to significantly reduce the formation of contrails. This can be achieved by limiting the cruise altitude of aircraft, although the benefits would be dependent upon seasonal effects. If implemented, this sort of policy could severely constrain air space capacity, especially in parts of Europe. In addition, carbon emissions would likely be higher due to less efficient aircraft operation at lower cruise altitudes, which would offset some of the benefits of eliminating contrail formation. This paper describes an analysis of these trade-offs using the RAMS air space simulation model as applied to European airspace. This model simulates the flight paths and altitudes of each aircraft and is here used to calculate emissions of carbon dioxide and changes in the journey time. For a 1-day Western European traffic sample, calculations suggest annual mean CO 2 emissions would be less than 4% higher if cruise altitudes were restricted to prevent contrail formation. The change in journey time depended on aircraft type and route, but average changes remained less than 1 minute. Our analysis demonstrates that altitude restrictions on commercial aircraft could be an effective means of reducing climate change impacts, though it will be necessary to mitigate the increased controller workload conflicts that this will generate.