Some people believe that persistent contrails are actually evidence of a secret government spraying program called “chemtrails”, which was begun in the 1990s, for some purpose such as weather control, population control or more exotic purposes.

A common claim made by those believers is that it is only in recent years that chemtrails have persisted, and back when they were young (usually implying sometime before the 90’s), they remembered “blue skies”, which they don’t see any more.

I live (in 2007) in Los Angeles. The sky is generally blue here. In fact it’s blue about 300 days of the year. It’s often hazy in the morning. But I’d say the sky is blue, and if asked to recall what the color of the sky was, I think I’d say blue, especially if I were recalling a day at the beach or some such thing.

Were the skies different before 1980? Personal memory is not a good yardstick, so perhaps the photographic record. Now, until recently most of the photos people put online were from digital cameras, and hence quite recent. But now the older folks are starting to scan in their old photos, so we get things like this album:


http://picasaweb.google.com/WynnWagner/WynnSFirstPhotoBatch
This is a batch of photos from the 1960’s and earlier. While there is not much that looks like a contrail in any of the photos, there are a LOT of photos that show the kind of hazy sky that chemtrailers believe did not exist when they were young. In fact, nearly all the “blue sky” shots show some form of haze or cirrus clouds. The only time a sky approachs the “deep blue” of chemtrailers childhood imagination is when the camera is pointed nearly straight up, such as in the photo of the South Dakota capitol. Even there, you get the haze.

So why no persistent contrails? Well, it’s not just no persistent contrails in the photos, it’s no contrails at all. In fact, there are no planes in the sky!

Here are some more albums of old photos
1979 http://picasaweb.google.com/photos.hall/Crete1979
1980 http://picasaweb.google.com/kldelpha/TripWest1980

Back to the claims of the chemtrailers. Are the skys different now? Sure, there is more air traffic, hence more contrails. But is there evidence of this? Look on picasaweb at people’s vacation photos. You see blue skies, hazy skies, cloudy skies. You really don’t see many contrails.

Look for photos of places that people consider to be hotbeds of chemtrail activity. Any place you are familiar with, say San Diego. Look for photos of San Diego. How many have contrails in them? Almost none.

What does this mean? It means confirmation bias, it means selective memory. Most of the time the sky is hazy. Most of the time it does not have persistent contrails in it.

Sometimes, of course, they do. We can be selective with the past as well as the present. We don’t remember them because they are rare, but they are there:

Applegate Lake, 1981, persistent contrail above the horizon.

1970s – Two parallel contrails, with a third being formed

1969, morning contrails that will spread and cover the sky: