Scientists believe that contrails turn into larger cloud
banks that substantially
alter the atmosphere's heat balance. They may even an
important role in shaping our weather.
Scientists have long suspected this may be true, but haven?t
been able to test it until 911, when the FAA grounded
commercial flights nationwide for three days following the
terrorist air attacks. They have now discovered that the
American climate was noticeably different during those three
days.
A team of climatologists say that temperatures in the United
States fluctuated by 1.2 degrees Celsius more when
airplanes were grounded than when normal flight patterns
prevailed. That is, planes in the sky decrease the variability
between day and nighttime temperatures. More air travel,
the researchers means less meteorological difference
between noon and midnight. This research provides one of
the strongest indicators that air travel itself changes our
climate.
"We actually found a much greater change in temperature
range for parts of the country that normally get the greatest
contrail coverage," says David J. Travis, of the University of
Wisconsin in Whitewater. Large contrails, he says, only form
when the cruising-altitude atmosphere is both sufficiently
moist and sufficiently cool (somewhere in the range of minus
40 to minus 65 degrees Celsius). The skies above the
Southwest are typically too dry, and the skies above the
deep South are too hot for extended contrail coverage.
These factors, plus the varying density of air traffic over
different parts of the country, combine to make the skies in
the Midwest and Northeast -- and, to a lesser extent, the
Pacific Northwest -- particularly filled with contrails. In
such
contrail-heavy parts of the country, Travis' team found that
during September 11-13, the difference between day and
night temperatures increased even more. The Midwest and
Northeast experienced a "contrail effect" of 3 degrees
Celsius, more than twice the national average.
Travis says that the new data does not suggest that contrails
make global warming either better or worse. Other research
has suggested that contrails have a global-warming effect.
But Travis' data addresses variability beween day and night
temperatures, not an overall warming or cooling trend. "It
complicates the debate," he says.
Conclusions are more certain on the regional scale. As air
traffic increases over some regions of the world, the
increased density of contrails will likely bring even smaller
differences between daytime and nighttime temperatures,
and that will alter the local environment.
Cranberry bogs and citrus orchards, for instance, require a
combination of cool nights and warm days for optimum yield.
And in the spring, sugar maples don't produce sap if daily
temperatures don't fluctuate enough. Some insects are
particularly sensitive to changes in day and night
temperature variations. And changes in insect populations
can in turn have some unexpected aftershocks.
Patrick Minnis of NASA's Langley Research Center in
Hampton, Virginia, says Travis' results confirm his own
studies on contrails. "Having this data set made the
relationship a little more definitive," Minnis says.
Instead of studying the lack of airborne jets during the FAA's
three-day moratorium, Minnis looked at the few aircraft that
were in the skies -- military jets and transport planes.
In a usually packed air corridor around Washington, D.C.,
Minnis followed satellite images of a lone contrail flying over
the mid-Atlantic states on September 12. The three days of
grounded air travel provided him a unique opportunity to
model the evolution of a single contrail where normally
scores or hundreds would be found.
He saw six contrails, each no wider than an airplane wing,
evolve in a matter of hours into cloud banks that covered
20,000 square kilometers. "This is a once-in-a-lifetime
opportunity to measure these contrail effects," Travis
says. "Or, at least, we can only hope it's once in a lifetime."
How have other cultures coped with end times? Read ?A
Hitchhikers Guide to Armageddon? by David Hatcher
Childress, click here.
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