When I was a mere child in the early 50s, I recall seeing jet aircraft making very long contrails in a clear sky. I later figured out these were B-52s during test flights out of the Boeing plant in Seattle. B-52s flew at 50,000 feet. Most airliners at that time were flying at 35,000 feet, where contrails are less persistent.
Only the first one is true. And contrails are an inevitable result of using hydrocarbon fuels at high altitude.
Contrails were certainly around in the mid-60's when I was a small boy....
When I was a mere child in the early 50s, I recall seeing jet aircraft making very long contrails in a clear sky. I later figured out these were B-52s during test flights out of the Boeing plant in Seattle. B-52s flew at 50,000 feet. Most airliners at that time were flying at 35,000 feet, where contrails are less persistent.
Interesting, I was a decade after being born in 58