September 11th gave some scientists the opportunity to measure the effects of jet planes on environmental temperature [here].

Their conclusion: Without jets or contrails, the clear skies boosted the temperature swing between daytime highs and nighttime lows by about 3 degrees nationwide.

The article goes on to say that it is unknown how this might affect global warming.

Well, of course it is unknown how this might affect global warming. Scientists don't really know how anything affects global warming. It's a complex, non-linear system. Our intuition is misleading when we try to predict the effects of different phenomena on the global climate, because relative effects can interact with each other in bizarre ways.
2:52:31 PM