People who think that there is something wrong with the world sometimes point to the sky and say it's different. It was bluer a decade ago, and certainly bluer when they were children. Was it bluer? Probably not. Probably what they have is simply a memory of bluer skies, a memory that natuarally gets more intense with age, because that's what memories of color do. Look at the research: http://www.opticsinfobase.org/josa/abstract.cfm?uri=josa-50-1-73 And sky was bluer in your recollection. The colors in your memory tend to be brighter and more colorful than they are in reality, or in the photos you take. 30 or 40 years ago our color memories were magnified by one of the the most popular film around at that time: Kodachrome. The way the film responded to colors gave them an overly saturated look. Blues looked bluer. But we did not mind, because that's how we remembered them. For us older folk, these are the holidays, the vacations of our youth. (image source: http://intelligenttravel.nationalgeographic.com/2009/06/25/kodachrome_tourism/) But over time the Kodachrome reinforces our color memory, and we start to think that indeed everything was more colorful in our childhood. The vibrancy of our past increases with the passing of time. The present naturally seems pale in comparison. And it's not just memory - your color vision actually does fade with time. http://www.allaboutvision.com/over60/vision-changes.htm So with these two effects combined, it's no wonder people think the sky was bluer when they were younger. [Update] There is some evidence of a slight whitening over the 20 years from 1996 to 2007, see post #73. However, it's does not seem like this would be something people would notice, with natural variation, and the other factors mentioned.