Contrails affect weather, study finds

Newsday

An unexpected experiment -- the sudden three-day grounding of air traffic after last September's terrorist attacks -- shows that high altitude jet contrails are having an important impact on temperatures, scientists said last week.

Because thousands of commercial flights were canceled after the disaster, the researchers said, a thin blanket of cirrus clouds that often forms from water vapor exiting jet engines in high-traffic corridors was absent. The lack of clouds allowed daytime temperatures at ground level to rise and nighttime temperatures to fall.

The researchers said the loss of cloud cover caused by the grounding of commercial planes led to a 1.98-degree increase in the difference between the highest day temperature and lowest night temperature over the United States. Their report showing the human impact on temperature was published in Thursday's issue of Nature.

"This is the first really concrete evidence that jet contrails are influencing temperature," said climatologist David Travis at the University of Wisconsin, lead author of the study. "Prior to now, most of the evidence was circumstantial."

The high-altitude cirrus clouds are thought to reduce heating during the day by blocking some sunlight, and prevent cooling at night by keeping infrared energy from radiating away into space. The result is less difference between day and night temperatures.