Future development of contrail cover, optical depth, and radiative forcing: Impacts of increasing air traffic and climate change

Abstract

The future development of contrails is investigated considering changes in air traffic and aircraft technology as well as climate change by means of a contrail parameterization developed for the ECHAM general circulation model. Time slice simulations show an increase in global annual mean contrail cover from 0.06% in 1992, to 0.14% in 2015, and to 0.22% in 2050. In the northern extratropics, the enhancement of contrail cover is mainly determined by the growth of aviation. In the Tropics, contrail cover is, additionally, highly affected by climate change. In order to quantify the effect of systematic errors in the model climate on contrail cover, offline diagnostic studies are also performed. These studies suggest an underestimation of global contrail cover in the ECHAM simulations by a factor of about 0.8-0.9. The effect of the bias in the model climate is strongest in tropical latitudes. The temporal development of the simulated contrail radiative forcing is most closely related to total contrail cover, although the mean optical depth is found to increase in a warmer climate. Our best estimate is an increase of global annual mean radiative forcing from 3.5 mW m-2 in 1992, to 9.4 mW m-2 in 2015, and to 14.8 mW m-2 in 2050. Uncertainties in contrail radiative forcing mainly arise from uncertainties in microphysical and optical properties such as particle shape, particle size, and optical depth.