Reminds me of an interesting thing I'd read back years and years ago. Apparently, during 9/11 when all the planes were grounded for nearly a week, it provided researchers on climate change an unparalleled opportunity to study the effect of contrails on the environment. According to their research, on the three days where there were no contrails whatsoever in the US -- thus reduced particles in the sky -- the mean temperature of the entire country rose three degrees.

Kinda scary, what we're doing to our planet.