I remember reading that the flight ban following the September 11 attacks affected the weather. What was that all about?
All commercial aircraft across the United States and Canada were grounded for three days following the terrorist attacks of September 11, 2001. That constituted a gigantic unplanned weather experiment, one consequence of which was a demonstration that high-altitude jet condensation trails affect surface temperatures. Water vapor in jet exhaust condenses into a thin veil of ice-crystal clouds that lowers daytime and raises nighttime temperatures slightly in very high-traffic jet corridors.
In the absence of those clouds during the three days of grounded jet traffic, the spread between daily high and low temperatures increased by 2 degrees.