There was a study conducted on the effects of jet airplane contrails, composed of water vapor and CO. They are ineffect, artificial clouds. Those performing the study believed the contrails would cause a dimming of sunlight, as records indicated it was cooler during the day and warmer at night, generally speaking, over the last century. There was no "control" sample, however.

Then, on 9/11, when all air traffic was grounded for a few days, the temperature went back up a few degrees and "normalized". It was interesting to hear about, just a short on the "Science" channel or something.

I saw the movie yesterday. Science aside, it was entertaining.