I Did Not Know That...

Kevin Drum has a bit of environmental trivia that, well, isn't that trivial.

Did you know that in the three days following 9/11 the average temperature range across the United States (the difference between the daytime high and the nighttime low) rose one degree Centigrade? That's the biggest, fastest climate change ever observed.

The reason, it turns out, is that American airspace was shut down, and no airplanes means no contrails. Since contrails absorb sunlight, getting rid of them allows more sunlight to reach the ground and causes a rise in surface temperature. When planes started flying again temperatures went back down.

As this BBC report says, this is a dramatic example of an effect called Global Dimming, something that scientists have recently concluded is far larger than they previously thought: since 1950, increased amounts of soot and ash have reduced the amount of sunlight reaching the surface of the earth by an astonishing 10-30% in various parts of the world.

The interesting part is that the effects of this phenomenon are diminished -canceled out, if you will- by the effects of global warming.

Just as an aside, I found the lack of contrails on 9/11 and the days after a moment to remember. I have always been a sky watcher, day and night, and I have always sort of resented contrails. They are visual pollution. Given our geographic location here in Central Illinois, seeing contrails overhead is entirely unavoidable. I understand they are a part of our modern world and all that and I have flown many times in planes leaving the same contrails. Still, all my life I wondered what it would be like not to see them. Unfortunately, it took horrible circumstances to get my wish.