What ARE CHEMTRAILS used for?

Question

Please, no 'standard responses' here, serious answers only.

Answer 1

Wikipedia covers it nicely:

The chemtrail theory is a group of conspiracy theories regarding unnatural vapor trails in the sky which allegedly hold "chemicals." Chemtrails form when certain aircraft (in certain places and at certain times), leave behind contrails thought to be laden with "chemicals." Contrails are formed by condensation of water vapor in the aircraft's exhausts.

Proponents of the theories maintain that some trails have an appearance and quality different from those of normal water-based contrails, i.e. that chemtrails are not consistent with the known properties of contrails. The general unifying factor is the generally conspiratorial belief that some kind of chemical or biological agent is being secretly released. The term "chemtrail" should not be confused with other forms of aerial dumping (e.g. crop dusting, cloud seeding or aerial firefighting). It specifically refers to systematic, high-altitude dumping of unknown substances for some undisclosed purpose resulting in the appearance of these supposed chemtrails.

Among the theories proposed for the purpose of the alleged "chemtrails" are: atmospheric and weather modification, biological warfare, mind control or occult purposes. They are also theorized to be part of a system to counter the effects of global warming, to create a cheap wireless communications network for the military, or to create a more sophisticated radar system (for both defensive and scientific application).[