It's tough when two worldchanging philosophies conflict. On the one hand, we strongly believe that (as a general rule) international travel is a Good Thing. It can broaden intellectual horizons, letting one experience life in a wholly different culture, reminding one that the world does not end at one's nation's borders. As a perspective-shaking epiphany, it's not quite the same as seeing the Earth from space, but it's as close as most of us can come for now.
Unfortunately, airplanes -- the most practical means of international travel -- are not environmentally benign. We've mentioned before the greenhouse gas problem from air travel (and the hope that a shift to biofuels will reduce the footprint), but another issue of increasing concern are the contrails left by planes flying through cold reaches of the atmosphere. NASA research suggests that contrails can add significantly to greenhouse heat-trapping. The picture at right -- click it for a larger version -- shows a single day's contrails over the southeastern US.
To help ongoing research into the effects of contrails, NASA is promoting a contrail-counting effort as part of their "Earth Science Week" education project. Today (October 14th) and tomorrow (October 15th), students, teachers, parents and other interested citizens are asked to count the contrails they see and enter a report at NASA. A similar count was done on Earth Day 2004; the results and initial analysis are now available online.
(Thanks for the tip, Bernard!)
I dont know about counting them - the east/west highway in the sky goes directly over Chicago - I have looked up, esp. in winter, and could likely see at least 20 fresh trails. By the end of the day it would be near impossible to get anything else done!
On a side note - I find them beautiful, abstract line drawings in the sky. Like the intense particulate inspired orange sunsets we now get reflecting all over the skyscrapers, in a strange way pollution can be visually stimulating.