What effects do contrails have on the environment:

Local climate:

And planet wide:

Also whats everyones thoughts on the mysterious chemtrails?
Hears more chemtrail info:
http://www.sciforums.com/showthread.php?s=&postid=396015#post396015

PS:Contrails are regular plane trails and Chemtrails are unknown. :)

So-called chemtrails are actually ordinary contrails which are expanding in the upper atmosphere due to abnormally still conditions and the presence of air at or near the condensation point;

the passage of air through the engines and over the wingtips of the plane in question forms tiny ice cystals behind the plane called a con trail; these usually sublime and disappear but if the air at that level is at or near the condensation point these tiny crystals will seed new larger crystals and form a long, thin, expanding cloud which may persist for hours and lower the ground temperature.

They do not contain chemicals of any kind apart from the jet exhaust.

Without the original contrail acting as a seed, it is likely that ordinary cirrus or cirrostratus clouds would have formed spontaneously anyway, so the net effect on the climate is negligible.
__________________
SF worldbuilding at
http://www.orionsarm.com/main.html

I don't think it would have much any effect at all.