- As more and more commercial jets fill the skies over
the next half century, the cloud-like plumes from their exhausts may play
a bigger role in changing our climate, according to a new study.
- "Contrails could be playing a role in the future
once airplanes proliferate like cars," says David Doelling a NASA
scientist and one of the authors of the paper in the July 1 issue of Geophysical
- The researchers point to increased growth in contrails
as airplanes begin to crowd the skies of southeast Asia and cruise at higher
altitudes. Contrails -- short for condensed trails -- form when the air
is particularly humid.
- The concern, says Doelling, is that contrails can help
cirrus clouds grow. Cirrus clouds, which trap the sun's heat and reflect
it back to Earth, are thought to be major players in the global climate
- And contrails, he says, can also form cirrus clouds by
themselves. "We've seen pictures of contrails over an hour, and all
of a sudden they become a cloud," he says.
- Ironically, cleaner-burning jet engines are one of the
reasons for the anticipated growth in contrails.
- According to an April report on aviation by the U.N.'s
Intergovernmental Panel on Climate Change, while these engines reduce the
amount of polluting particles and gases, they boost the amount of water
vapor going into the air, helping contrails form.
- One possible approach to dealing with this issue, notes
Stephen Ackerman, an associate professor of Atmospheric and Oceanic Sciences
at the University of Wisconsin-Madison, is better control of passenger
- "If we know atmospheric regions where contrails
form, we can direct aircraft around those regions. But the aircraft industry
may not like that, because it may not be the shortest route," he says.
- Contrails also help researchers get a better handle on
the entire science of climate change, he notes, because of their role in
- "One of the problems we have in understanding climate
change is understanding how clouds form, and contrails allow us to look
at that right away because of their ability to generate a cloud,"