Jets’ Vapors, Temperature Linked
An unexpected experiment--the sudden three-day grounding of air traffic after last September’s terrorist attacks on New York and the Pentagon--shows that high-altitude jet contrails are having an important effect on temperatures, scientists said Wednesday.
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 3.5-degree Fahrenheit 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 today’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.... No one had actually looked at temperature data to see if we could detect a contrail influence.”
Atmospheric scientist Stan Chagnon, who spent his career at the University of Illinois studying the cirrus cloud phenomenon, stated: “Here is the proof, baby. It’s right there. It’s irrefutable proof of the effect of contrails on climate.”
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 of a difference between day and night temperatures.
For about 50 years scientists have tried to understand whether contrails from aircraft are doing anything. More than 30 years ago, atmospheric scientist Walter Orr Roberts, founder of the National Center for Atmospheric Research in Boulder, Colo., was showing time-lapse movies illustrating how the thin white stripes from jets spread out--and sometimes cover much of the sky.
In the new research after Sept. 11, Travis and colleagues from Pennsylvania State University gathered data on maximum and minimum day and night temperatures from 4,000 weather stations within the 48 coterminous states. They looked back as far as 1971, comparing those data to the recent three-day no-flight period.
