Over time humanity went from accepting the weather to predicting the weather, to actively controlling it. Sure, passenger airplanes still produce vapor trails like we were taught in school, which remain or disappear based on the weather conditions at that height, and they do not have room to do anything else.
But modern Internet has provided us with up-to-date information of ships and airplanes, and this shows some interesting patterns: sometimes an airplane will just fly a regular pattern of parallel lines, covering a large part of the sky over a given patch of land. And we are not talking about cropdusting here!
You might think I am making it up, but I have personally seen whether control taking place: during an outdoor event, the sky was clear blue, with ample sunlight. While we were enjoying an icecream, suddenly the sky started showing a hatch pattern of chemtrails. This very rapidly expanded from mere trails into a total cloud cover that totally blocked the sun!