A couple years ago, I was fascinated to hear about the possibility that airplane contrails have an effect on the weather. Those seemingly harmless puffy lines in the sky can expand into impressive cloud cover. But do they significantly change the weather? Climatologists looked at the data from September 11-13, when most jet traffic was grounded. The difference between daytime and nighttime temperatures increased in areas where there is normally heavy contrail traffic. Within those regions of heavy air traffic, the smaller differences between day and night temperatures could affect the environment. For example, maple trees need temperature changes in order to produce sap. In another study, a scientists observed single contrails produced by military jets that were allowed to fly during those days. “He witnessed six contrails, each no wider than an airplane wing, evolve in a matter of hours into cloud banks that covered 20,000 square kilometers.” I bet this doesn’t help the reasons why it always seems to rain on weekends.