I'm out of the loop, didn't the government admit this stuff a few years ago?
I was at a presentation in Croatia recently about weather modification in Yugoslavia. This is considered public knowledge there. When Yugoslavia fell apart, Croatia was no longer permitted to engage in weather modification.
The main method discussed was the use of small rockets. It was used for agricultural purposes.
The problem is the unsubstantiated logical leap from "weather modification is possible" to "contrails behind commercial aircraft are secretly dispersing chemicals in order to control weather".
If I was an evil government figure trying to secretly control weather, there are better ways of doing that (e.g. drones, rockets) than orchestrating a conspiracy that requires hundreds of thousands of people to stay quiet for decades.