Flying low and slow: Application of algorithmic climate change functions to assess the climate mitigation potential of reduced cruise altitudes and speeds on different days

The climate effect from aviation's non-CO2 emissions such as contrail cirrus, water vapor and nitrogen oxide induced ozone and methane changes depend on emission location and time. Among other approaches, the resulting climate effect can be reduced by lowering cruise flight levels. However, aircraft typically aim to fly at optimum altitudes and perform step climbs with increasing flight length to enhance fuel efficiency and reduce operating cost, what also limits climate effect from CO2 emissions. To account for this contradicting correlation and to reduce the overall climate effect of flights, the additional fuel consumption at lower flight altitudes can be compensated by also reducing flight speeds. Therefore, this study analyzes the mitigation potential of flying lower and slower with regard to the overall climate effect along flight trajectories. Specifically, actually flown point profiles are combined with related meteorological parameters to evaluate the effect from reduced cruise altitudes and speeds with an updated set of prototype algorithmic climate change functions. Different case studies show varying effects for individual days during different seasons and significant mitigation potentials due to flying lower and slower can be observed (up to 9 % on a summer day and 16 % on a winter day). A sensitivity study to explore uncertainties with regard to the quantification of contrail effects is performed as well as an investigation on possible economic consequences in terms of changes in direct operating cost and eco-efficient solutions.