I find the "Chemtrails" people are an interesting sub-group to study. It looks as if they've woven whole cloth from a few stray threads - a whole conspiracy theory based on not very much at all, or a fallacious interpretation of perceived phenomena. Firstly, I can't help thinking there are easier, cheaper, less elaborate and more effective methods of mind-control and behavioural modification available to any malevolent people who would obtain benefit from reprogramming our minds. Look at News International/SKY/FOX-TV, for instance. Two; most of us know next to bugger all about what goes on in the sky. This includes a lot of meteorologists. If pushed, I could put names to maybe three different types of cloud before I have to go and look it up. Three: of course there's a lot more activity going on up there than there was fifty or sixty years ago. In 1945 there were only a handful of jet aircraft and the effective ceiling for any sort of plane was around thirty thousand feet with only a specialised handful able to get any higher. So contrails - as opposed to "chemtrails" - are a fairly recent phenomena dating from the first high-altitude bombers in the 1940's. Very hot engines at twenty-five thousand feet putting out an exhaust WILL create vapour trails in the sky. As the number of planes up there exponentially increased, then of course there are going to be a hell of a lot more contrails up there. And for all I know that amount of jet engine exhaust residue - which only really has one direction to go in - might have long-lasting effects on people down here. But to say it's being done deliberately, as opposed to it being just incidental background pollution, is stretching things.
That's not to say it's never been attempted - look at attempts to seed clouds and force rain to happen where it's needed - and I wouldn't put it past certain government agencies to conduct feasiblilty studies. (and then to decide it's inefficient and fuctionally useless). After all, if any war came to this, air-delivery from above would be used to spread chemical weapons (Agent Orange in Vietnam). I just think to allege it happens on the claimed vast scale beggars belief. It'd be horrendously expensive, you'd need a whole secret infrastructure depending on absolute secrecy (whistle-blowers? Credible ones?) to make the stuff and fit the planes, and it sounds incredibly inefficient as a delivery system - how much of it would be wasted on seas, deserts and uninhabited areas? And why haven't aviation engineers working on maintaining civil planes broken silence, and reported on the strange equipment secretly fitted to civilian airliners - which must be useless dead weight adding to their running costs? (What surcharge would Ryanair put on the chemtrail delivery systems fittted to its fleet?)
The more you try to anayse it, the more the chimera of "chemtrails" vanishes. Yet enough otherwise rational people still believe and cannot be shaken from their belief. This in itself is an interesting Fortean study - what makes them predisposed to believe?