On my morning walk Monday I couldn't help but notice the contrails, short for "condensation" trails because that is exactly what they are: water vapor from airplanes that condense in the cold air above.
Airplane engines release an exhaust of water vapor, carbon dioxide, sulfur, carbon monoxide, and other particles, the only one of which matters to contrails is the water vapor. Right now, the air up there is around 10 degrees, plenty cold to turn that water vapor into ice crystals.
That's exactly what you're seeing, trails of ice crystals against a calm sky. If the humidity is high (and it is--you'll remember the fog we had Monday) then the contrails will last a while, sometimes hours, where if the humidity is low then the dry air will cause the trails to evaporate pretty quickly.
What's interesting to scientists about all this is that contrails do affect the climate--after all, they are 'clouds' in a sense and clouds affect incoming solar radiation. As important, these jets do release Carbon Dioxide and a recent assessment assigned 3.5% of carbon dioxide releases due to human activity to airplanes.
Despite the big problems with the Boeing Max 8 that has been in the news, this plane is not only more fuel efficient but reduces carbon dioxide emissions by 14-20% compared to older planes.
You can read much more about contrails right here in a report from the FAA. And, yes, I know all about the hoax of Chemtrails and found it interesting that Edward Snowden (the CIA whistleblower) says he went searching deep into the CIA files for the truth about chemtrails and found nothing. Same with Aliens.
In the meantime, when you take that morning walk be sure to look up to the sky....it's a fascinating place!