Longer flights could reduce climate impact of contrails (Wired UK)


A contrail, or “condensation trail”

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Climatologists at the University of Reading have
discovered
 that a slight lengthening of flight routes
could reduce aviation’s climate impact.

There has been concern for many years over the extent to which
thin contrails (condensation trails of artificial cloud left by
aeroplanes) affect the Earth’s climate. These contrails are
triggered by the water vapour emitted from the exhaust of aircraft
into cold air, or through changes in air pressure around the
wings. Just like regular clouds, they are made up of water in
a suspension of tiny droplets or ice crystals.

Despite their frail appearance in the sky, contrails tend to be
long-lived and spread out into thin, bright clouds that can be up
to 150 kilometres in length.

These high-altitude clouds have both warming and cooling effects
on the climate, as they reflect both sunlight back into space and
heat back down to the surface. In recent years, however, a
consensus has built that the warming effect is more significant
than the cooling.

Some researchers have suggested that planes fly at a lower
altitude to avoid the cooler air, but this means burning
significantly more fuel (as the air isn’t so thin) and the
resulting CO2 emissions may offset any reductions in the
clouds.

Instead, Emma Irvine at the University of Reading investigated
whether re-routing flight paths to avoid colder areas would reduce
contrail formation while allowing planes to remain at the optimum
flying altitude.

“You think that you have to do some really huge distance to
avoid these contrails,” Irvine told
BBC News
. “But because of the way the Earth curves you
can actually have quite small extra distances added onto the flight
to avoid some really large contrails.”

She found that a flight from London to New York would need to
add just 22km to its journey to avoid large contrails. “The key
things you need to know are the temperature of the air and how
moist it is, these are things we forecast at the moment, so the
information is already in there,” said Irvine. “Whether the
forecasts are accurate enough to do this is another question.”

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Her work was published in Environmental
Research Letters
.

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19 June 2014 | 5:00 pm – Source: wired.co.uk
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