I first noticed the lingering trails en masse in Southern California in 1993 or 1994. The first ones appeared occaisionally as up to about six parallel lines heading north past the horizon. That was in 1981, right after Reagan (Bush) assumed control, and opened the treasury floodgates on the military. (There is a Bush behind every terrorist!) Somewhere around 1995 a random caller on talkradio said the trails were scalar weapons tests. As in, they act as antennae or lenses for electromagnetic energy pumped out by HAARP and its sister transmitters in Australia, and Russia.
The trails enhance and control the location of standing waves. Standing waves are integral to scalar weapons technology. The frequencies involved are 6-8Hz. This is the resonant frequency for radio waves bouncing around the planet. By pinging the transmitter every time the signal bounces back to you, the amplitude grows. Just like Tesla's famous device that could bring down a building just by taping on it at the right frequency. Or like pushing a child on a swing so it goes higher every time. By using two or more transmitters, interference patterns are created. This is what causes standing waves. On this global scale, they can certainly cause earthquakes, even trigger volcanoes!
But it gets worse. This frequency range, probably not coincidentally, is the same as Theta brainwaves. These are associated with visionary, dreamlike states, reached in deep meditation, or when waking or falling asleep. Not recommended while operating heavy machinery!
Incidently, your nervous system also pumps spinal fluid as this same frequency! It's called sacral nutatiion. This frequency is considered subsonic. The lowest note in a pipe organ is 7Hz. It can be felt, if not heard. It is about as fast as you can count numbers in your head. Or the rate at which individual drumbeats blend into a drumroll.
Electromagnetic effects of persistent trails are just the tip of the iceberg of different itches the spraying program scratches, or can scratch, if you happen to be a genocidal, dope peddling, MIC CEO. Or a cadre of same.
It has been established that high altitude jet trails act like cirrus clouds, and actually cause global warming.  
Toss chemical and biological warfare agents into the mix, and it gets pretty stupid to just stick your head in the sand!