Are contrail cirrus climate effects predictable?

The climate impact of aviation may be minimized by selecting routes with minimum warming from contrail cirrus and CO2. Such an approach requires sufficient scientific understanding. Moreover, it requires accurate predictions of contrails forming for the planned and possible alternative flight routes together with fuel consumption and radiative forcing. During the Mid-Latitude Cirrus experiment (ML-CIRRUS) in March/April 2014, contrail-cirrus predictions were performed quasi operationally by the Contrail Cirrus Prediction model CoCiP. Here we present comparisons to observations. Contrail cirrus optical depth, a basic input for radiative forcing calculation, is shown to be predictable to some degree depending on several parameters. Most important are accurate numerical weather prediction input for the time period from departure until about one day after arrival, fuel consumption along the various alternative routes, and soot particle number emissions. In addition some open issues of basic understanding will be identified