Thanks for everyone's input. I think Fabo's post is the one that most got my attention.
Now there of course is technology to alter weather... specifically, to make clouds rain before they want to. Has to do with shooting iodium crystales (or something of that kind) into clouds so they go off before, or alternatively, still away from, the big day. I have read about it being delivered by planes, but in more of shovel-it-out-of-cargo-door fashion, or shot up the cloud by the means of rocketry. Hardly stuff you could just push through a jet engine.
It is true that newer planes are better at doing contrails. It might also be true that the engines exhaust gasses are just more prone to it due better burning and whatnot, but you have to consider that nowadays, airplanes are more likely to be found in flight levels better suited for contrail forming than some 20 years ago (compare optimal FL of 737NG is often FL400ish, A320 FL370ish even on shorter hops, while 737 Classic would mostly only go as high as 330,340)
It occurs to me that most pilots and companies probably would not want to throw mysterious additives into their Jet-A just to cropdust a community. I mean, hey, these pilots fly over their families too, right? Not to mention possible wear on engines and fuel systems if they have to push weird stuff through the engines to make "chemtrails".
And I agree. G-man's post is ace!
