They don't. Its the exhaust from the plane, and the hot air from the jets causing water to condense into clouds.
Some conspiracies about chemtrails are that the trails are left behind when nuclear radiation takes over and area. If you have the radiation on you, then you are contagious.
Over 7.6 million people worldwide.
Over 200,000 people worldwide.
Over 30 million people worldwide.
Over 151,000,000 worldwide as of April 2008
Over 500 million people worldwide have a Facebook Account.
over 1 billion people worldwide, or around 16% of the world.
No se cabron
over 1/2 a million people watch it worldwide !!
Get Over It grossed $19,860,259 worldwide.
Mandarin Chinese is the language spoken by over 1 billion people worldwide.
Over 100 million have been sold worldwide as of July 2012.