Interesting, because there has been debate around contrails on ET since the beginning. Famously, 9/11, by grounding planes and leaving the sky clear of contrails for a time, was supposed to have provided an observable drop in temperature. But the researchers here say:

Contrail Blanket Warms Earth | Climate Change & Clouds & Aviation | LiveScience

Like natural clouds, contrails have contradictory effects on the Earth's surface temperature. Their ice crystals reflect solar light, decreasing the amount of light and heat that reach the Earth's surface, but at the same time they trap long-wave radiation (such as infrared light) coming from the other direction, preventing it from heading into space after it gets reflected off the ground. This heats the planet's surface.   

Article by Burkhardt and Kärcher available free at Nature Climate Change.