"There was even a paper suggeting that commercial flights should be limited
to 20,000 feet. I cant remember why."
Because engine exhaust contrails are formed above 20,000 ft. The atmosphere
has to be cold enough to rapidly freeze the water vapor into ice crystals
before it can evaporate. If flights were restricted to below 20,000 ft, the
increased use of fuel would offset some of the benefit gained by not having
the contrails, but the main disadvantage would be the longer travel time
required. The flights would also be a lot bumpier and the skyways more
crowded. Time still equals money. Global warming is not yet part of that
equation. In the TV series Fringe, the people of a parallel universe
avoided all this by not ever developing air transportation for mass
transport. Instead, they rely on airships. A quaint, but impractical idea.
http://en.wikipedia.org/wiki/Contrail
"The main byproducts of hydrocarbon fuel combustion are carbon dioxide and
water vapor. At high altitudes this water vapour emerges into a cold
environment, and the local increase in water vapor can push the water
content of the air past saturation point. The vapour then condenses into
tiny water droplets and/or deposits into ice. These millions of tiny water
droplets and/or ice crystals form the vapour trail or contrails. The vapor's
need to condense accounts for the contrail forming some way behind the
aircraft's engines. At high altitudes, supercooled water vapor requires a
trigger to encourage deposition or condensation. The exhaust particles in
the aircraft's exhaust act as this trigger, causing the trapped vapor to
rapidly turn to ice crystals. Exhaust vapour trails or contrails usually
occur above 8000 metres (26,000 feet), and only if the temperature there is
below ?40 蚓 (?40 蚌).[3]"
----- Original Message -----
From: "John Gorman" <[email protected]>
To: <[email protected]>; "Geoengineering"
<[email protected]>
Sent: Thursday, March 31, 2011 4:06
Subject: Re: [geo] Contrails bad?
My idea for stratosheric aerosol generated from aircraft fuel (1) came
from reading papers showing the warming during the three day period after
9-11 when there were no contrails over the US.
That was long before I had heard the word geoengineering or about
volcanoes, SO2, Alan Robock or Paul Crutzen. -or this group!
I later heard that there were other papers suggesting that contrails
caused warming. I put some effort into trying to work out which was
correct but eventually gave up , concluding that there were equal numbers
of papers suggesting that contrails caused warming or cooling. I very much
doubt that this has added more than one bit of paper to one side of the
balance.
There was even a paper suggeting that commercial flights should be limited
to 20,000 feet. I cant remember why.
john gorman
(1) www.naturaljointmobility.info/grantproposal09.htm
----- Original Message -----
From: "John Nissen" <[email protected]>
To: "Geoengineering" <[email protected]>
Sent: Wednesday, March 30, 2011 11:04 PM
Subject: [geo] Contrails bad?
http://planetark.org/wen/61626
John
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