‘Contrails present a bit of a dilemma for cloudspotters. On the one hand, they are both interesting to observe and often very beautiful. …. On the other hand, there is growing evidence that the preponderance of contrails is having a significant impact on the temperatures down on the ground, and yes – you guessed it – the overall effect seems to be a warming one.’ The Cloudspotter’s Guide, Gavin Pretor-Pinney, 2006
Photo: Silver Spring, Maryland, USA, April 2011