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Post by douglavers on Nov 26, 2014 19:15:08 GMT
I think the "greenhouse effect" as applied in a closed car or greenhouse is quite easy to understand.
Basically, trapped local heat which normally dissipates by convection, but this is not possible.
The "greenhouse effect" as applied in our atmosphere is vastly more complicated.
Multiple gases, multiple pressure & temperature layers, clouds .................All absorbing, emitting or reflecting furiously.
A few thoughts:
On a clear night, ground cools really fast - open radiation windows to outer space are available Hence, the availability of atmospheric "radiation windows" are really important - forget comments about radiation from the top of the atmosphere
How could the Ordovician Glaciation ever happen with CO2 greater than 4000ppm
What physical process triggered the end of any particular ice age - prima facie the increased albedo of our planet should have kept temperatures really low
A decent theory has to be able to explain extreme conditions, and how they can change.
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Post by nonentropic on Nov 26, 2014 19:32:33 GMT
All this highlights that the principle problem with the CAGW hypothesis is the feedback factor that is used to determine the ultimate impact of a rising level of CO2. The science is settled that CO2 is a "greenhouse gas" but the science of whether it will deliver CAGW or just some AGW is very much unsettled.
The half life of specific frequencies of IR at different CO2 levels in the atmosphere tends to suggest that without a feedback well above 1 the CAGW story is dead. The very existence of the world as we see it and knowing the huge changes that the atmosphere has endured tends to support a number much lower. This is however an empirical observation rather than the more popular computer model based science.
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Post by douglavers on Nov 27, 2014 6:06:44 GMT
Nonentropic
"The half life of specific frequencies of IR at different CO2 levels in the atmosphere"
Sorry, I don't understand. Please explain
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Post by nonentropic on Nov 27, 2014 7:12:44 GMT
The absorbency is related to travel path length and that is impacted by particulate or molecular density.
so more CO2 more absorption. the half life is the 50% reduction over distance/density.
thus a log relationship.
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Post by Ratty on Nov 27, 2014 21:47:03 GMT
The absorbency is related to travel path length and that is impacted by particulate or molecular density. so more CO2 more absorption. the half life is the 50% reduction over distance/density. thus a log relationship. Nonentropic, do you know of a reference that a layman might understand?
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Post by duwayne on Nov 28, 2014 3:09:31 GMT
Duwayne I have an original article in pdf format. Admittedly it is from 2007, but the science has not changed!! For fun, I have added a CO2/Geologic Eras file. Douglavers, I can't track down either of the above references. Could you cut and paste a few sentences from these references which support your claims as referenced below? "Unfortunately, the first 20 ppm absorbs about half the radiation that CO2 is capable of absorbing. The next 20 ppm absorbs another half, and so on. By the time one reaches 400 ppm, that means that about 99.999% of the radiation that carbon dioxide can ever absorb has already happened."
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Post by sigurdur on Nov 28, 2014 3:36:14 GMT
Duwayne asked a straight forward question. If one wanted to incorporate other variables, that changes the outcome and also becomes very complicated.
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Post by douglavers on Nov 28, 2014 6:25:36 GMT
Duwayne
Article I posted stated that "The first 20 ppm [of CO2] has a greater effect than the next 400 ppm"
I approximated that to 50 % absorbance for the first 20 ppm, for simplicity.
The relationship is actually logarithmic [ Beers Law, I think].
By the time one reaches 400 ppm, that means that about 99.999% of the radiation that carbon dioxide can ever absorb has already happened. [(1-0.5^20 as %], as an approximation.
As a crude analogy, it is like looking through panes of smoked glass, each of which absorbs 50% of the incident radiation. Not much gets through 20 panes stacked together.
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Post by nautonnier on Nov 28, 2014 14:21:20 GMT
This post from Steve Goddard's site is around a year old but I thought I would repost it here to muddy the waters "........The whole theory of a CO2 greenhouse effect is wrong yet the ignorant masses in academia have gone to great lengths trying to prove it with one lie and false study after another, mainly because the people pushing the global warming hoax are funded by the government who needs to report what it does to the IPCC to further their “cause”. I’m retired so I don’t need to keep my mouth shut anymore. Kept my mouth shut for 40 years, now I will tell you, not one single IR astronomer gives a rats arse about CO2...... "Read the whole post it's worth it. There is a tendency to accept the assumptions of the protagonists of AGW and then argue based on those same assumptions rather than go back to first principles and make sure that all the assumptions made are actually soundly based. Whenever I read a paper the very first thing I look for are the assumptions and simplifications as those are where the gross errors or 'fiddles' are usually buried. The complex maths after that where the mathematicians always look and nit-pick is almost always correct.
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Post by duwayne on Nov 28, 2014 15:38:41 GMT
As Sigurdur noted I was asking for someone to check my calculation based on the assumption that CO2 effect on temperature declines in a logarithmic fashion. I was pretty sure that if that assumption was correct my calculation was correct and I appreciate Sigurdur independently verifying that calculation.
As to whether that logarithmic assumption is correct, I know it is stated as fact by warmists and skeptics alike. But I've always had a question whether that assumption is true for all cases. If there were 1 molecule of CO2 in the atmosphere, a second molecule would seem to be likely to have almost the same effect as the first molecule since because of the curvature of the earth it will rarely be in position to suffer any interference from or interfere with molecule number 1. Certainly, in my mind it wouldn't take 2 molecules to have the same effect as the first molecule.
on the other end of the scale, if enough CO2 is added to the atmosphere, say enough that 3/4 of the radiation is trapped, then no matter how much CO2 is added it can't have the same effect as the the preceeding CO2 had. The maximum effect is to trap all the remaining radiation or 1/4 of the original radiation.
If the logarithmic assumption is not true for all cases, is it true for the current case?
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Post by nautonnier on Nov 28, 2014 16:14:19 GMT
Duwayne, The normal reply is that CO2 is a 'well mixed gas' and therefore the assumption is that the concentration in PPM can be taken as the same worldwide. This of course is another assumption and the Japanese CO2 sensing satellite does show considerable variation. But not to the reductio ad absurdum of two lonely CO2 molecules somewhere in the atmosphere But you can start at say 20 ppm (with all plant life dead) and then work your way through the physics from there.
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Post by sigurdur on Nov 28, 2014 20:21:53 GMT
The important thing to note is ppmv. Ppm is pretty commonly used but really means nothing. The (v) is critical. As explained in another thread, 30% of the volume of the atmosphere is located in the 1st 10,000. However, in that 10,000 ft co2 means nothing as the small band it actually occupied in regards to radiation is like a speck of dust on an elephants ass.
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