For those under 30yrs old, I don't expect them to remember the blue skies with no contrails in the sky. In fact, it use to be so unusual (in LA at least) that when I was a kid we always knew when Edwards Airforce Base was shooting off missiles cuz it would like persistant trails. At no other time did any of the contrails left by airplanes blanket the sky...but this is now the norm.
For those over 30...can you honestly remember a sky that had 20+ lines running all over the sky and then them merging and turning into a gigantic cloud cover?