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Global Warming Contrails

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Global Warming Contrails

Old 17th Oct 2002, 20:53
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Post Global Warming Contrails

There is an interesting article in this weeks ‘New Scientist.’ The article discusses the conclusion of a study by Imperial College, London: that contrails reflect enough I.R. radiation back to earth that by 2050 (assuming current air travel growth rates), contrails will cause more global warming than the carbon dioxide produced by the engines. According to the Intergovernmental Panel on Climate Change (IPCC) currently contrails contribute a similar amount to global warming directly through I.R. reflection as the engines do through CO2 production. The upshot of this is that flying aircraft at lower altitudes (FL240-310) where contrails do not generally form will cause less global warming, even though there would be a higher fuel burn. Bizarre, eh? Here is a link to the shortened online article:
http://www.newscientist.com/news/news.jsp?id=ns99992926
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Old 17th Oct 2002, 21:54
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Question

Sure, contrails and clouds trap heat and act like a blanket, but don´t these clouds also prevent the earth from warming up more, by refexting sunlight ?

If the production of CO2 is reduced and clouds shield the earth from sunlight, the netto result might be a decrease in temperature.
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Old 17th Oct 2002, 22:11
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There was a study done in the US during the 9/11 shutdown. The effect of taking the aicraft out of the sky was to increase the daily variatoin in temperature by 5 degrees or so. (thats +5 in the day and -5 at night) because of the loss of cirrus clouds.

Furthermore, as Airforce one was the only thing flying they were able to track it by the moisture in the upper atmosphere. I remeber thinking during the shut down, MY GOD THE SKY IS BLUE for the 4 days of the shut down. Didn't see a single cirruc cloud. Aparrently it was that way all over the country.

Cheers
Wino
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Old 17th Oct 2002, 22:45
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Wanula Dreaming: Not having read the original paper I wouldn’t know, however a quick stab in the dark: We are not discussing cloud in its lower level liquid droplet form, we are talking about a thin layer of ice crystals. Assuming these are good at reflecting infrared but have a high transmission of shorter wavelength higher energy electro-magnetic radiation, overall you would have a net gain of energy underneath the contrails (even though blocking solar emitted I.R.) – as the shorter wavelength (more energetic..) radiation will be absorbed by the earth surface and re-emitted at longer wavelengths e.g. infrared, which would be reflected by the contrails. The figure quoted in the full article was something like 0.1% total cover of contrails on the Earth at the moment…
Just found this on the NOAA site: 'While thick, dark clouds can block UV radiation, puffy or thin-layered clouds do not'
Wino: That is very cool...it is amazing to think aircraft can make that much difference to the temperature variation.
Tom.
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Old 18th Oct 2002, 15:42
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In any case: One day a nuclear winter will take care of global warming.
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Old 18th Oct 2002, 16:33
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So you'll be an optimist then GlueBall?
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Old 18th Oct 2002, 19:46
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THX for the info Tom !

I remember seeing a TV program in which a global cooling was predicted for as far as cloud cover is concerned.

As you pointed out, contrail clouds trap heat, but an increase in global temperature will cause more evaporation. This in turn will increase the global coverage of lower level liquid droplet clouds which will (hopefully ) cool down the planet.

Sort of like Glueballs nuclear winter...but then a bit milder.
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Old 18th Oct 2002, 20:35
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One of the points which used to be made was that high flying aircraft are in the stratosphere, where weather systems don't reach.

Consequently the deposits from aircraft would remain and accumulate in this layer.

The observations after 911 seem to indicate the stratosphere somehow became clearer in four short days, so it would appear that aircraft deposits do infact get reabsorbed in the troposphere, and are therefore not too damaging long term.

No doubt this is an oversimplified or just plain wrong interpretation, so I await other interpretation of the observations.
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Old 22nd Oct 2002, 13:20
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Wink

that contrails reflect enough I.R. radiation back to earth that by 2050 (assuming current air travel growth rates), contrails will cause more global warming than the carbon dioxide produced by the engines.
...... AND, of course, assuming that oil reserves will last until 2050.
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