In this article, Clifford Carnicom make some bold claims: http://www.carnicominstitute.org/articles/model1.htm If we give Carnicom the benefit of the doubt and assume most of this science is correct, then the conclusion he reaches is that: - First the water vapor freezes, because it's so cold - Then it melts and evaporates, because the sun is so hot So why doesn't is just freeze again, because it's so cold? The condensation nuclei still exist, and are now considerably cooler than when they exited the engine. He also makes the distinction between clouds and contrails, saying clouds form on smaller condensation nuclei (0.1 to 0.2 microns). To suport this he quotes Goethe MB - Ground Based Passive Remote Sensing of Ice Clouds with Scattered Solar Radiation in the Near Infrared - Max Planck Inst Meteorol, which gives a particle size of 30-200 microns. However that Goethe study is not measuring nuclei (the tiny seed at the heart of an ice crystal), it's measuring the actual fully grown ice crystals. The condensation nuclei for contrails that come from the exhaust are basically soot and other byproducts of combustion, having a size of 0.1 microns or less. Hence they will behave exactly the same as clouds. If carnicom has proven here that contrails cannot persist and spread, then, since clouds must start out small and spread to a larger size, he has also proven that cirrus clouds cannot even exist at all. Then in a second article, The RH Deception http://www.carnicom.com/rh1.htm He claims that if the relative humidity is between 70% and 100% then contrails should dissipate in about ten seconds, because at 10% relative humidity it would dissipate in two seconds. This is nonsense for two reasons. 1) Evaporation or melting time does not scale like that. It's as if he claimed that since ice melts in ten seconds at 100 degrees, and in five seconds at 50 degrees, then it should melt in about two seconds at zero degrees. Of course it's not actually going to melt at all. 2) If Relative Humidity with respect to water is between 70% and 100% then relative humidity with respect to ice is always above 100%. In that environment ice cannot sublimate. In fact it will always accrete more ice, and the ice crystals will grow bigger, causing the contrail to spread.