Potential to reduce the climate impact of aviation by flight level changes

Abstract

This paper discusses various strategies to reduce the global warming from aircraft by contrail formation and carbon dioxide emissions. In particular, we discuss the impact of changes of the flight level, typically 2000 ft (610 m) up or down. Previous studies suggested reducing contrail formation by flying lower generally or by flying higher or lower at the actual level with minimum relative humidity. This paper introduces a more efficient strategy which selects optimized routes based on the climate impact of contrails and fuel consumption along these routes. By preferred flights in atmospheric regions where contrails cool, an aircraft routing can be designed with minimum or even negative climate impact. For the fleet as a whole the climate impact is measured in terms of its radiative forcing RF. For individual flights, the climate impact is measured by the amount of energy induced into the Earth-atmosphere system per unit flight distance, which we call the energy forcing EF. Both RF and EF for contrails and CO2 can be combined into a global mean surface temperature increase for a given time horizon. This paper describes the basic principles and quantifies the potential impacts using the recently developed Contrail Cirrus Simulation Prediction tool (CoCiP).