for National Geographic News
Moving flight times from night to day could reduce air travel's contributions to global warming, a new study suggests.
Scheduling more daytime flights may lessen the impact of contrailsthe visible streaks of condensation that many planes leave in their wake.
The role of contrails in climate change is still under study, but some scientists believe that they contribute to the greenhouse effect by trapping heat in Earth's atmosphere.
Nicola Stuber, first author of the study, to be published in tomorrow's edition of the journal Nature, suggests that contrails' overall impact on climate change is similar in scope to that of aircrafts' carbon dioxide (CO2) emissions over a hundred-year period.
Aircraft are believed to be responsible for 2 to 3 percent of human CO2 emissions. Like other high, thin clouds, contrails reflect sunlight back into space and cool the planet.
However, they also trap energy in Earth's atmosphere and boost the warming effect, the study says.
(See National Geographic magazine's "Global Warning: Signs From Earth.")
Stuber and other scientists believe that the effect of the contrails is significant.
"On average the greenhouse warming effect dominates [the effects of contrails]," said Stuber, a meteorologist at England's University of Reading.
Global Warming and Contrails
This warming effect is far greater for contrails left by night flights, Stuber added.
"The solar cooling effect [wherein contrails reflect the sun's rays back into space] only happens during the day, when the sun is up," she explained.
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