Estimating the climate impact of linear contrails using the UK Met Office climate model

The HadGEM2 global climate model is employed to investigate some of the linear contrail effects on climate. Our study parameterizes linear contrails as a thin layer of aerosol. We find that at 100 times the air traffic of year 2000, linear contrails would change the equilibrium global-mean temperature by +0.13 K, corresponding to a climate sensitivity of 0.3 K/(Wm(-2)) and a climate efficacy of 31% (significantly smaller than the only previously published estimate of 59%). Our model suggests that contrails cause a slight warming of the surface and, as noted by most global warming modelling studies, land areas are affected more than the oceans. Also, unlike the contrail coverage and radiative forcing, the contrail temperature change response is not geographically correlated with air traffic patterns. In terms of the contrail impact on precipitation, the main feature is the northern shift of the Inter-Tropical Convergence Zone. Finally, our model strongly indicates that the contrail impact on both the diurnal temperature range and regional climate is significantly smaller than some earlier studies suggested.