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quote: I'm using Celsius, not Kelvin - 0.6C equates to 1K. Its not the first time you failed to read my post properly.
LKW, Kelvin is Celsius plus 273. So 0.6C difference is the same as 0.6K difference. 0.6C is approximately 1 Fahrenheit - maybe that is where the confusion is. 3.7W forcing gives 1C, or 1K difference in temperature (or 1.8 F) using basic stephan boltzmann physics. Thanks for the Eemian link, I'll have a look when I have time. Yes I did say I would try to find out myself. I was commenting on Phlipper claiming I would try and change the subject. |
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quote: Originally posted by Lost in Kate Winslet:
I'm using Celsius, not Kelvin - 0.6C equates to 1K. Its not the first time you failed to read my post properly.
Now that is funny. You manage to display ignorance of a fundamental unit of measurement whilst accusing someone else of not reading your post properly! A change of 0.6°C = a change of 0.6K. An absolute temperature of 0.6°C = 273.75K. |
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Steve_M quote: Son of Mulder, one of the things that that diagram that you posted the other day brought home to me was exactly how much influence the greenhouse gases had. I assumed that it was the increase in the total amount of surface emissions with increase in CO2 that was relevant, but as the diagram shows, about 90% of the infrared emission is absorbed by the atmosphere.
Yes, amazing isn't it. I was starting with the surface for my investigations because it's relatively simple. One thing I'm still not clear about is why the back radiation is as much as 324 W/M^2. Given that when a photon of energy is emitted from the atmosphere there is a greater area for it to miss the earth than to hit the earth. Hence one would expect the outgoing radiation from this source to be greater than 324, so adding the reflected 107+324 would gives at least 431 which is bigger than the 342 arriving. Any idea what's going on here as it's clearly not true? |
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quote: Hence one would expect the outgoing radiation from this source to be greater than 324, so adding the reflected 107+324 would gives at least 431 which is bigger than the 342 arriving. Any idea what's going on here as it's clearly not true?
The chance of a photon from the atmosphere heading towards earth is not much less than 0.5 since the atmosphere is only 10 or so miles thick. Looking up from the earth, the earth sees the warmer side of this greenhouse "fog" and space sees the cold side. Hence, there is more radiation downwards than upwards. For example, a layer of atmosphere at, say 1 mile up will be at, say 0C (colder than the surface. Half the energy it emits goes down, and half goes up. But the half that goes up has a better chance of being absorbed again before it reaches space than the half going down has of reaching the earth. |
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Steve_M
OK I've sussed it in principal. Say 64 photons leave the surface and get absorbed by the atmosphere at 100 meters. 32 come down and 32 continue up again and get absorbed at 200 meters. Then 16 come down to 100 meters and 16 go up to 300 meters. Then 8 come down to ground and 8 go back to 200 meters. The 4 come back to 100 meters and 4 go the 300 meters. Then 2 come back to earth so of the 64 that left the surface 32+8+2=42 come back to the surface.
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Son of Mulder.
I hate to but in, but I think the system is more chaotic than that.
A photon may be emitted in any direction. Thus, emission has random direction and is not vectored towards, or away from, the Earth.
Is this not so?
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Suricat quote: A photon may be emitted in any direction. Thus, emission has random direction and is not vectored towards, or away from, the Earth.
Is this not so?
Thats why I used the phrase 'in principal'. Although there will be countless photons in all directions it can still be reduced to a counting game to understand why the back radistion is much higher than simply assuming only 50% would return to the surface. |
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Son of Mulder.
Point taken.
So the statistical probability of the photon achieving atmospheric escape is positively affected by its increased altitude, but also negatively dependant upon its local pressure (closeness of local molecules [high pressure - less probability as less distance travelled]).
I think that these calculations will be a nightmare for you, especially when a spectral frequency will affect some molecules and not others, but it could define an altitude band for the radiation point of a set (limited) frequency band and show the true surface area of Earth radiation for that frequency.
Good luck.
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quote: Originally posted by Steve_M: quote: I'm using Celsius, not Kelvin - 0.6C equates to 1K. Its not the first time you failed to read my post properly.
LKW, Kelvin is Celsius plus 273. So 0.6C difference is the same as 0.6K difference. 0.6C is approximately 1 Fahrenheit - maybe that is where the confusion is. 3.7W forcing gives 1C, or 1K difference in temperature (or 1.8 F) using basic stephan boltzmann physics. Thanks for the Eemian link, I'll have a look when I have time. Yes I did say I would try to find out myself. I was commenting on Phlipper claiming I would try and change the subject.
Apologies Steve, definitely a brainfart moment. Having looked up Stephan Boltzmann, based on an ideal state, 3.7w/m2 equates to 1.01C based on my maths. What interesting about the 3.7w/m2 forcing is that it appears to be based on a one-shell model. A two-shell model would reduce the amount of forcing. I've read an argument that the one-shell model is too simplistic in terms of representing the Earth's atmosphere. |
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Suricat, quote: I think that these calculations will be a nightmare for you, especially when a spectral frequency will affect some molecules and not others, but it could define an altitude band for the radiation point of a set (limited) frequency band and show the true surface area of Earth radiation for that frequency.
I agree but I know enough maths to know that it can be done (will have been done?) by someone with the time, the necessary data, knowledge of the physics, integral calculus, probability and a computer so I'm now comfortable with the surface balance. Now onwards and upwards into the atmosphere. |
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I find the easiest way to remember the celsius/fahrenheit relationship is that 28 deg C is 82 deg F. Then I don't get the signs wrong in the 5/9ths and 32 equation.
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quote: What interesting about the 3.7w/m2 forcing is that it appears to be based on a one-shell model. A two-shell model would reduce the amount of forcing. I've read an argument that the one-shell model is too simplistic in terms of representing the Earth's atmosphere.
Clearly the one shell model is simplistic, but the forcing is an input to this, or any, model, so does not change with the addition of shells. A quick back of the envelope calculation shows also, that the addition of shells doesn't change the results of the sensitivity calculation (the amount of warming). A real climate model obviously has very many levels and simulates the physics and dynamics of the atmosphere, showing up the feedbacks from water vapour that double or triple the sensitivity of the temperature to increased CO2. |
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I note that discussions of the Eemian sea level rises seem to be concerned as to the relative contribution of the relative size of the Greenland ice sheet or the West Antarctic ice sheet to the change in sea level since then. It reminds me of a couple of things. Firstly, that I was told that the Greenland ice sheet is not a "given" in our current climate. ie. that if it vanished tomorrow, it wouldn't grow back. Actually, there is a report of this finding here: environment.newscientist.com/channel/earth/climate-change/dn4864 Secondly, that much of the Western Antarctic ice is below sea level (ie. the top of it is above sea-level, but if you drilled down, you'd hit rock below sea level), but is held stable by conveniently placed ridges. Slightly different ocean currents or slightly different orography could perhaps have resulted in it being smaller in previous interglacials, or have caused it to melt quickly. The following paper has evidence of rapid Eemian sea-level rises: www.sciencemag.org/cgi/content/abstract/311/5768/1747 |
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quote: The following paper has evidence of rapid Eemian sea-level rises: www.sciencemag.org/cgi/content/abstract/311/5768/1747
Got hold of this paper. It's reasonably on topic as a good example of a possibility of accelerated impacts of GW if not an acceleration of GW itself. Basically it says that orbital wobbles mean that during the last interglacial (130000 years ago) the northern hemisphere got more summer sunlight, which would have led to some melting of Greenland which would add 2-4m to the ocean levels. However, 4m is at the low end of the sea-level rise thought to have existed then, suggesting that the Western Antarctic Ice Sheet (WAIS) probably also contributed to sea level rise. They ran models of the two periods, including the differences in solar insolation, and the models showed that the temperatures at the time of the LIG Greenland melting phase would be reached within this century given 1% per year rise in CO2. They speculated on the possible causes of the purported WAIS melt thus: quote: Given that there was no positive summer (melt-season) insolation anomaly at high southern latitudes in the several millennia before 129,000 years ago, it appears that two factors may have led to a LIG collapse of the WAIS (or perhaps portions of the EAIS). The first may have been the sea-level rise associated with ...GIS melting, and...shallow ocean warming around and under the Antarctic ice shelves that buttress portions of the Antarctic Ice Sheet. Sea-level rise seems to have had minor effects on the WAIS during the most recent deglaciation, but perhaps the greater speed of sea-level rise into the LIG compared with that from the Last Glacial Maximum (ca. 21,000 years ago) played a role by reducing the ability of isostatic rebound after grounding-line retreat to shallow sub ice-shelf cavities and promote regrounding. As for the subsurface warming of south polar oceans, our LIG simulation showed modest (generally less than 0.5° but up to 1°C) warming in the upper 200 m of the ocean (Fig. 3) that would have further weakened ice shelves by thinning them from below... Heat transport beneath ice shelves is highly complex, so caution is required, but the LIG may provide a conservative constraint on the future dynamics of the Antarctic Ice Sheet and particularly the WAIS. Moreover, the same parts of the Antarctic Ice Sheet may prove vulnerable even given increased precipitation
Finally, though, they note: quote: Even in the absence of more-realistic models of ice-sheet behavior, it remains that ice sheets have contributed meters above modern sea level in response to modest warming, with peak rates of sea-level rise possibly exceeding 1 m/century. Current knowledge cannot rule out a return to such conditions in response to continued GHG emissions.
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