Climate researchers have long debated the effect of airplane contrails on the average ground temperature.  They theorized that contrails prevented sunlight from hitting the ground and warming the lower atmosphere.  But while each individual contrail could, in theory, create a slight shadow over a wide area, it was impossible to really gauge the effect of these ubiquitous clouds on the overall climate unless people literally stopped flying for several days.

Of course, this is exactly what happened during the week of September 11, 2001.  And researchers subsequently discovered that contrails did affect climate after all.  As CNN reported at the time, the average temperature volatility in the US actually rose significantly:

“During the three-day commercial flight hiatus, when the artificial clouds known as contrails all but disappeared, the variations in high and low temperatures increased by 1.1 degrees Celsius (2 degrees Fahrenheit) each day, said meteorological researchers.”

The recent moves by the SEC and FSA to curtail shorting of financial stocks provides researchers with a similarly unique opportunity to examine the effect of this equally ubiquitous phenomenon.

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