Increasing Jet Contrail
Volume May Change Climate
By Harvey Black
Discovery News Brief

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 Research Letters.
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 change game.
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 jet routes.
"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 cloud formation.
"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," Ackerman says.