Yesterday, I flew from Chicago to San Jose as a part of my recent East Coast family adventure.
About 165 minutes into the flight (somewhere over Nevada or Utah?), I opened the window shade to see and hear a military jet pass by our plane from South to North some distance below us (thousands of feet below, but not tens of thousands). Close enough that I could hear it.
That certainly caught my attention. After that, I saw two more plans and numerous contrails all at about the same distance the 33,000 foot cruising altitude of my plane.
Looking out at the sky, there was this disgusting thick brown layer of jet exhaust for as far as the eye could see. It seemed to last for a good 45 minutes.
It made me wonder about exactly what aircraft exhaust does to the environment. There were articles about the post 9/11 grounding of aircraft indicating a noticeable improvement in quality of the air over the north east in the days that followed.
In particular, how much worse (or not) is military aircraft exhaust than civilian aircraft. Civilian aircraft are optimized for fuel efficiency and that generally means that the fuel is burned off as much as possible in the interest of producing forward thrust. Military aircraft certainly benefit from fuel efficiency, but weight, power, and maneuverability optimizations likely change the equation considerably. Furthermore, the military has a long long history of not really giving a rat's ass about the environment.
Coincidentally, Boing Boing posted an article about airplane exhaust and the environment.