Contrails are real. But they aren't motivated like people think they are
When 9-11 shut down flights for 3 days, it actually got hotter. This is what the initial studies said.
Of course the climate change folks can't let that stand and are going back to revise to say contrails bad.
Can aircraft trails affect climate? : Nature News
"Two studies1,2 noted that when planes stopped flying on 11–14 September 2001, the average daily temperature range in the United States rose markedly, exceeding the three-day periods before and after by an average of 1.8 °C. The unusual size of the shift, says David Travis of the University of Wisconsin–Whitewater, who led both of the earlier studies, implied that an absence of contrails gave the temperature range a significant boost. But that idea, he says, was "more like a hypothesis" than a firm conclusion."