Climate impact of air traffic emissions in dependency of the emission location and altitude

Within the present work, the dependency of air traffic climate effects with respect to the emission location and altitude is investigated by means of the three-dimensional chemistry-climate-model ECHAM4.L39(DLR)/CHEM/ATTILA. Numerous simulations employing idealized aircraft-like emissions are carried out to systematically study effects of air traffic on contrail coverage, water vapour, ozone and methane and air traffic induced radiative forcing with respect to the emission location and altitude. For the composition of present day air traffic emissions, the overall radiative forcing from non-CO2 effects increases strongly with emission altitude and slightly from the extra-tropics to the tropics, with the largest potential contributions resulting from ozone and stratospheric water vapour. The results of these idealized simulations are used to test whether the climate impact of a realistic air traffic inventory can be reconstructed by linearly recombining these pre-calculated idealized data. This methodology may be particularly useful for the optimization of flight paths with respect to minimum climate impact, as this off-line reconstruction of air traffic perturbations could bypass time consuming global three-dimensional simulations. Perturbations determined by the linear recombination indeed compare well with effects determined by comprehensive chemistry-climate-model simulations. Furthermore, the findings indicate a high potential to reduce non-CO2 air traffic climate effects through optimized flight routing.