| There was no smoke or contrails behind the craft, and it made no noise in the perfectly clear sky. |
| The reason, it turns out, is that American airspace was shut down, and no airplanes means no contrails. |
| The thick, twisting contrails still prevented any visual sightings. |
| A couple years ago, I was fascinated to hear about the possibility that airplane contrails have an effect on the weather. |
| Although this complicates global warming arguments, it offers further evidence that contrails do affect climate in some way. |
| Higher and farther to the west the contrails of the aircraft bent around the mountains and merged with the clouds, pointing north. |
