Wanula Dreaming: Not having read the original paper I wouldn’t know, however a quick stab in the dark: We are not discussing cloud in its lower level liquid droplet form, we are talking about a thin layer of ice crystals. Assuming these are good at reflecting infrared but have a high transmission of shorter wavelength higher energy electro-magnetic radiation, overall you would have a net gain of energy underneath the contrails (even though blocking solar emitted I.R.) – as the shorter wavelength (more energetic..) radiation will be absorbed by the earth surface and re-emitted at longer wavelengths e.g. infrared, which would be reflected by the contrails. The figure quoted in the full article was something like 0.1% total cover of contrails on the Earth at the moment…
Just found this on the NOAA site: 'While thick, dark clouds can block UV radiation, puffy or thin-layered clouds do not'
Wino: That is very cool...it is amazing to think aircraft can make that much difference to the temperature variation.
Tom.