There are people who study the reduced sunlight that gets through our now-hazy skies.
1st man: "I'm really old."
2nd man: "How old are you?
1st man: "I'm so old I can remember when the skies were really blue." I am so old that I remember when pollution used to rise from chimneys. Now it falls from the sky. But we really did have days of intensely blue skies.
Just the memories of a sentimental old cat? Hardly. Since, in many people, opinion-propaganda is used to formulate their ideas, we'll just talk about those who measure things.
In the days of film photography, we often used light meters. We measured available light.
Those who generate solar power have noticed a decline of 20% in solar radiation reaching their solar cells. If you are living off the grid, or generating a large portion of the electrical power of an entire nation, such losses are important.
Please don't think I have a plan to make the skies blue again. "If we only get together, we can reverse this trend." That sort of thing. Write to your congressman? That is what wastebaskets and computer delete systems are for. Besides, I don't want to lose my Pessimist license.
So why write about this at all? I collect negative data on how the world is being mis-managed, and I just wanted to show you something from my collection.