Sonia,
When you mentioned contrail pollution, it put me in mind of what happened after 9/11. Most aircraft were grounded for a week, and the skys cleared up.
Here is a link to a very interesting article on Global Dimming and the Greenhouse Effect.
http://www.bbc.co.uk/sn/tvradio/prog...ng_trans.shtml
It seems that we are damned if we do and damned if we don't.