Chemtrailing and aerosolizing the atmosphere with barium and aluminum salts (and other unknowns) is a highly covert operation and may not be wise to discuss here. These "persistent contrails" aka chemtrails, did not exist before late 96' See: Operation Cloverleaf
Normal contrails (ice condensing on the tips of the wings of an aircraft, occurrs in high atmospheric altitudes of + 30,000 ft. They dissipate in under a minute as well. Chemtrails persist at much lower altitudes, last all day and turn blue skies cloudy. It has nothing to do with global warming and has everything to do with secret testing. Don't believe? look up in the sky every day this week and you will see operations in real time at least a few times.
See: Aerosol Operations
http://www.youtube.com/watch?v=lBjDSNWiuKQ
Chemtrails of Death:
http://www.youtube.com/watch?v=lBjDSNWiuKQ
AND:
http://www.carnicom.com/
Its staring you right in the face, thats all I am saying on this topic. Please don't reply and smear untill you research it. I was very skeptical at first too. But clearly, there is now something in our pretty skies