On contrail climate sensitivity

In equilibrium climate change simulations with a global climate model we estimate the climate sensitivity parameter to contrail cirrus to be 0.43 K/(Wm^-2), only about 60% of the corresponding value for a CO₂ forcing. The spatial pattern of the surface temperature response is much smoother than the forcing pattern of contrails with little correlation between both. As the thermal inertia of the climate system causes a marked delay of the transient response, only about 30% of the equilibrium surface warming to be expected from some aircraft induced radiative forcing is actually realised for aviation increase rates typical for the 1990s. Our findings do not confirm recent results of a dominating influence of contrail cirrus on temperature change over the United States between 1975 and 1994.