The main way to tell whether something is a regular contrail, and something that MAY be, and that's still a may, is that regular contrails, formed from condensation of water or ice in the exhaust stream of the jet, usually dissipate in a few minutes. Those ever enlarging and seemingly never to disappear contrails are definitely suspicious, but if my memory is correct, I remember seeing those back in the 1970's, and other than the cloud seeding experiments back then, I don't know what would have been the reason to do it, since back then, "global cooling" was the fear.
See comment further above. Persistent contrails have been around since the 50s. It is all a matter of being formed at high-er altitudes, where the air is more saturated and it is difficult for a cloud to dissipate. Just a fact of airplanes being able to fly at higher altitudes due to better engines.
Depending on wind and humidity, a normal contrail can persist for 15-20 minutes, easy. Other days you can watch them disappear in seconds. Other days the plane doesn't leave a visible contrail.
The main way to tell whether something is a regular contrail, and something that MAY be, and that's still a may, is that regular contrails, formed from condensation of water or ice in the exhaust stream of the jet, usually dissipate in a few minutes. Those ever enlarging and seemingly never to disappear contrails are definitely suspicious, but if my memory is correct, I remember seeing those back in the 1970's, and other than the cloud seeding experiments back then, I don't know what would have been the reason to do it, since back then, "global cooling" was the fear.
See comment further above. Persistent contrails have been around since the 50s. It is all a matter of being formed at high-er altitudes, where the air is more saturated and it is difficult for a cloud to dissipate. Just a fact of airplanes being able to fly at higher altitudes due to better engines.
Depending on wind and humidity, a normal contrail can persist for 15-20 minutes, easy. Other days you can watch them disappear in seconds. Other days the plane doesn't leave a visible contrail.
Where I live, they can last the whole day, slowly spreading in width. More the norm than not. The last few days have been especially noteworthy.