Q: You sometimes hear of

contrails. What are they?

A: Contrails are what appear

to be long lines of clouds high

in the sky and they are formed

from jet aircraft exhaust, Brent

McRoberts of Texas A&M University


“Contrails are created when

very cold air freezes the warm

and humid engine exhaust,” he

said. “Air temperatures where

contrails are formed are usually

minus 40 degrees or colder.

Contrails could be compared

to exhaling in winter and seeing

your breath because it’s so

cold. When water vapor from

the exhaust hits the cold air,

ice crystals develop and they

produce a contrail.”

Q: Do contrails affect the


A: This is a question that

is beginning to be ser iously

debated worldwide, McRoberts


“More and more scientists

believe contrails act like natural

cirrus clouds and they block out

solar energy from above and

keep in the heat from below,”

he added. “One study shows that

contrails cover about 1 percent

of the Earth’s surface, but in

heavy air traffic areas, as much

as 20 percent.”

“Another study shows that

lower atmospher ic temperatures

across North America rose

almost 0.5 degree per decade

from 1975 to 1994, which is

why some researchers believe

contrails have an impact on climate

change over long periods

of time,” McRoberts said.

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2010-12-02 digital edition

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