The big effect of airtraffic was immediately obvious to me living under J-80 at the date in question. You'd look up and instead of seeing several bands of contrails streaking E-W, there was nothing but blue skies. Jets create contrails. Contrails provide a non-trivial amount of cloud cover. Clouds reflect sunlight.
This effect has little to do with global warming. The NASA guy whom the administration tried to muzzle was the one pointing out the very close correlation between mean temperature on earth and atmospheric CO2 levels.
Global warming is really gonna screw up civilized living, but it by itself probably won't knock off the human population.
Even without global warming, we've got some really interesting times ahead: the whole world is built on cheap non-renewal energy, and we use these to sustain extremely high population in general, and high population densities. It's questionable that we'll "find some other" equally cheap energy source once we restore to the atmosphere all the CO2 that's been stored over the last who knows how many hundreds of millions of years.
As mammals, when resources get scarce, elevated intraspecies aggression is a result. As mammals armed with nukes and biological weapons, things can get dicy.
If I could send a message to what humans there may be 2 centuries from now, it would be, "It was a great party -- sorry about the mess!"
