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billiards
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Joined: 21 Jul 2007
Posts: 79
Location: London, UK
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 Posted: Tue Aug 28, 2007 4:39 pm Post subject: Exam Question |
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Hi people! Back from my holidays in Barcelona and Leeds, had a fantastic time, hope you didn't miss me too much 
Was tidying my desk and stumbled across an exam paper I took last year, there's one question (that I chose not to do in the exam) that I think is quite interesting - so I will share it here and would love to see some answers/comments.
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A neswpaper recently claimed that the effect of heat released by fuel burning was being ignored in global warming predictions. Investigate this claim by determining the time taken for a small increase deltaT in temperature of the atmospheric column to radiate to space. By treating the atmosphere as a column of density p and thickness h, show that its temperature T satisfies
dT/dt=-sigma.T4/cpph
Use this equation to determine the time taken for the atmosphere to equilibrate. Comment on your answer.
Stefan's constant, sigma=5.7*10-8 J m-2 K-1 s-1
Specific heat of air, cp=1005 J kg-1 K-1
Density of air at 273 K = 1.3 kg m -3
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scpg02
Joined: 22 Jul 2007
Posts: 221
Location: Sacramento
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| Posted: Tue Aug 28, 2007 7:45 pm Post subject: |
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You were gone? 
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sneez
Joined: 11 Aug 2007
Posts: 13
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| Posted: Tue Sep 04, 2007 6:46 pm Post subject: |
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| Quote: | A neswpaper recently claimed that the effect of heat released by fuel burning was being ignored in global warming predictions. Investigate this claim by determining the time taken for a small increase deltaT in temperature of the atmospheric column to radiate to space. By treating the atmosphere as a column of density p and thickness h, show that its temperature T satisfies
dT/dt=-sigma.T4/cpph
Use this equation to determine the time taken for the atmosphere to equilibrate. Comment on your answer.
Stefan's constant, sigma=5.7*10-8 J m-2 K-1 s-1
Specific heat of air, cp=1005 J kg-1 K-1
Density of air at 273 K = 1.3 kg m -3
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dQ/dt = emissivity*sigma*area*T^4 ------>radiative heating
dQ= m*cp*dT ----->definition of specific heat (m=mass)
V=m/rho ------>relationship between mass and density
let V= A*h -area time hight => m=A*h*rho
then:
dT/dt = [ emissivity*sigma*area*T^4 ] / [m* cp]
hence: dT/dt = [ emissivity*sigmaT^4 ] / [h*rho*cp] ------->the areas divide out
Integrating we would get time inverselly proportional to Temp. Thats quite interesting, so let me hear if I made a mistake here. |
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Andre
Joined: 21 Jul 2007
Posts: 291
Location: Germany - The Nederlands
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| Posted: Tue Sep 04, 2007 7:15 pm Post subject: |
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here is the empirical outcome:
http://www.knmi.nl/~laatdej/2006joc1292.pdf
| Quote: | ...We confirm the presence of a temperature change–industrialization correlation by analyzing the data with an additional statistical method and further confirm the absence of the above correlation in climate model simulations of enhanced GHG warming. Our findings thus provide an important test of climate model performance on regional scales.
These findings suggest that over the last two decades non-GHG anthropogenic processes have also contributed significantly to surface temperature changes. We identify one process that potentially could contribute to the observed temperature patterns, although there certainly may be other processes involve... |
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Derek
Joined: 12 Dec 2007
Posts: 7
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| Posted: Sat Dec 15, 2007 10:49 pm Post subject: |
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Hi All,
I just knew there was a reason why I did not become a scientist.....
To answer the exam questions means spouting and "proving" AGW rubbish.
What happened to the idea that the earth can loose 5 times more heat than we and it can generate / recieve.
It's like trying to prove a flea deciedes which direction the dog goes in.
In would have to be an enourmous, totally unrealistic flea wouldn't it.
A flea called "an IPCC approved climate model" no doubt... 
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scpg02
Joined: 22 Jul 2007
Posts: 221
Location: Sacramento
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| Posted: Sun Dec 16, 2007 12:35 am Post subject: |
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| Derek wrote: |
A flea called "an IPCC approved climate model" no doubt... |
Sucking the blood of the tax payer.
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