Do contrails warm or cool?

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john gorman

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Jul 14, 2019, 8:40:24 AM7/14/19
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The report that got me into this was a research paper showing that the lack of contrails just after 911 allowed a warming of the atmosphere. So I came up with an idea to increase and simulate the cooling effect of contrails. At the time I had never heard of the this group or the word geoengineering.

 

I now see in a recent post that contrails warm the earth.

 

Which is correct?

 

John Gorman

 

 

Seb Eastham

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Jul 14, 2019, 10:15:55 AM7/14/19
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Hi John ,

Inconveniently, they do both. They reflect and scatter incoming solar radiation (cooling effect) but also absorb outgoing longwave (warming). At night they are purely warming, but during the day the net effect can be either - depending strongly on whether there are clouds beneath them (decreases cooling benefit), the surface albedo (sea is dark so contrail benefits are greater), and the surface temperature. Kärcher wrote an excellent review article in 2018 (Formation and radiative forcing of contrail cirrus) covering the degree of uncertainty in all this - since we have very poor records of total coverage and properties, the exact balance between warming and cooling is also highly uncertain.

Regards,

Seb

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Alan Robock

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Jul 14, 2019, 10:47:18 AM7/14/19
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The reported warming after 9/11 was actually a change in diurnal temperature range. Kalkstein and Balling found that it was just clear weather and not lack of contrails. https://www.int-res.com/articles/cr2002/cr2004/26/c026p001.pdf

Alan

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Alan Robock

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Jul 14, 2019, 10:51:24 AM7/14/19
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See also https://www.nature.com/news/2008/081231/full/news.2008.1335.html for a discussion of several papers on this. 


Alan

Alan Robock, Distinguished Professor
   Associate Editor, Reviews of Geophysics
Department of Environmental Sciences                    Phone: +1-848-932-5751
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Stephen Salter

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Jul 15, 2019, 4:45:35 AM7/15/19
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Alan

1. How can you tell the difference between clear weather and no contrails? 

2. Do contrails affect weather clarity?

3. Is there a reason why it was the clearest of clear weather for 30 years?

Stephen

Emeritus Professor of Engineering Design. School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland S.Sa...@ed.ac.uk, Tel +44 (0)131 650 5704, WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change

Alan Robock

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Jul 15, 2019, 9:06:05 AM7/15/19
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2.  What is clarity?

3.  Where? When?  I have never heard this claim before. Please show us the data. 

Alan

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Stephen Salter

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Jul 15, 2019, 10:32:23 AM7/15/19
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Alan

1.  The contrailscience site you give is an excellent source about detecting contrails but my question was how you can tell no contrails from very clear skies.  I show two pictures below.  Which is which?


2. I suggest that clarity is 'clearness' in skies, language and optics.

3. The mention of  a factor 30 was in the 2002 Nature paper.

https://www.nature.com/articles/418601aSnips are

Snips are:


A relevant factor might be the financial consequences of a reduced permission to burn hydrocarbons in the atmosphere.

A possibly relevant paper is attached.

Stephen





Emeritus Professor of Engineering Design. School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland S.Sa...@ed.ac.uk, Tel +44 (0)131 650 5704, Cell 07795 203 195, WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change
Salter hydrogen planes.pdf

Dave Stanley

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Jul 25, 2019, 3:57:35 PM7/25/19
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Alan/Stephen, I follow the geoengineering site as an environmentalist particularly interested in global warming. Also particularly interested in this contrail issue – as an ex-fighter pilot many years ago.
My recollection is that contrails are also, under certain Met conditions, emitted by piston engined aircraft within the troposphere, and of course  jet engines in the stratosphere. Understand the point about uncertainty as to the net global warming effect of contrails.
However, I understand that water vapour is responsible for around 65% of the greenhouse effect. 
And that has temperature decreases with altitude within the troposphere but increases in the stratosphere there is little exchange of air mass between the two?
Does this therefore imply that aircraft flying within the stratosphere and burning fossil fuels are increasing both water vapour and carbon dioxide levels in the stratosphere?

Suggests that the global warming impact exceeds that of straightforward CO2 emitted per kilogram of fuel? Or is this allegedly account for with the IPCC 1.8 X factor? 

Impact in ozone in the stratosphere?


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Dave

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On 15 Jul 2019, at 15:31, Stephen Salter <S.Sa...@ed.ac.uk> wrote:

Alan

1.  The contrailscience site you give is an excellent source about detecting contrails but my question was how you can tell no contrails from very clear skies.  I show two pictures below.  Which is which?


<ifefmhjolbchfpci.png>

2. I suggest that clarity is 'clearness' in skies, language and optics.

3. The mention of  a factor 30 was in the 2002 Nature paper.

https://www.nature.com/articles/418601aSnips are

Snips are:

<jdbnmchnbhkkdmjm.png>

<aplcnimkomblkdag.png>


For more options, visit https://groups.google.com/d/optout.
<Salter hydrogen planes.pdf>
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.

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Stephen Salter

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Jul 26, 2019, 4:38:02 AM7/26/19
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Dave

Water vapour is indeed a strong greenhouse gas and retains about 2.5 times more  heat  but fortunately it condenses back to liquid much more easily than CO2.

Kevin Trenberth 1987 gives the average mass of water in the atmosphere as 1.46 x 10^16 kg which you can compare with annual jet fuel consumption. This would be a liquid level of 2.86 centimetre of the earth's surface. This amount will increase as we warm the sea. Most of it is quite low in the atmosphere. 

The evaporation /condensation residence time is about 10 days so the water comes out very easily.  Let me know if you would like papers about a way that might do this removal by cooling the sea surface. The method would also help Arctic ice, coral, hurricanes, sea level rise but nobody seems to want to do any of these. 

Stephen




Emeritus Professor of Engineering Design. School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3DW, Scotland S.Sa...@ed.ac.uk, Tel +44 (0)131 650 5704, Cell 07795 203 195, WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change

Dave Stanley

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Jul 28, 2019, 5:24:09 AM7/28/19
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Many thanks Stephen and Alan for taking the trouble to reply. It was an idle/curious enquiry – should’ve guessed it would be an incredibly complex issue.
I am a bit more into global warming/carbon/cycle/ecosystem/soils and food/farming.  On Climate Change and complexity, When talking on the carbon cycle like to quote Christine Jones – Australian soil scientist – “ five years ago we thought we understood about 5% of how the soil ecosystem functions, now we know quite a bit more and realise we only understand 1%”


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Dave

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