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Post by jimcripwell on Jun 7, 2009 11:19:32 GMT
glc writes "You're not necessarily wrong, but the other "ways" don't matter (as far this issue is concerned) . Ultimately incoming solar energy is balanced by the emittance of outgoing LW radiation. The earth receives, on average, 235 w/m2 of solar energy. In order to maintain equilibrium it emits 235 w/m2 LW radiation. Some of this is emitted directly from the surface - some from different layers of the atmosphere. In the CO2 band this is at higher altitudes. How energy reaches these layers is irrelevant."
Wow! And some radiation passes from the earth to outer space without being affected at all. And there are all sorts of other complications. This is only in the CO2 band. There is all the rest of the spectrum. You state " How energy reaches these layers is irrelevant." I cannot follow this. I cannot say I dont believe you, because I dont understand it. Can you give me a really good reference where I can read all about this, so I can understand it?
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Post by glc on Jun 7, 2009 13:13:53 GMT
Look, they are just asking you to show your work. Unless you went to one of those fancy free-form schools in Marin County, you must have been required by your arithmetic teachers to show your work. If you guys want us to bend over and take a multi-trillion dollar reaming to allegedly save the planet, you should at least be willing to show us the calculations. I gave a link to the calculation(s). The basic equation of radiative transfer is the Schwarzchild equation, i.e. dI = -Ikr dz + Bkrdz where I is the radiation intensity ; k is the absorption coefficient; r is the density of the absorbing/emitting gas; B is the planck function. By simple integration this equation can be rearranged into an expression for I as follows I = I 0(exp(-krz)) + B[1 - exp(-krz)] where I 0 is the incident radiation passing through an absorbing layer of thickness z. This, then, is the basic equation. Now then can I just stick some numbers in to produce an answer which is what you appear to want? No I can't The reason being that the terms in the equation are not constant. For example r (density) varies with altitude. Also k is dependant on wavelength as are terms in the Planck function (B). This means numerous line by line calculations need to be done across the emitting spectrum at different temperature and pressure levels throughout the atmosphere. Now can I direct you Jack Barrett's site here www.barrettbellamyclimate.com/page45.htm where you will find an explanation and discussion which is considerably more informative than I am able to provide.
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Post by dmapel on Jun 7, 2009 13:18:11 GMT
I said: jimcripwell asked for an explanation on why radiative transfer models are suitable to estimate radiative forcing. Seems simple enough.
soclod: "Well no it doesn't. That sounds like it could possibly be an essay question at degree level climatology. I don't think anyone here has the expertize to answer it."
Nobody expected you to explain it. You certainly have not shown any signs of doing so yet. Jim is asking for a reference. Either an explanation exists, or it doesn't. Seems simple enough. What convinced you that the estimates of radiative forcing are correct? Make yourself useful and provide a link. jimcripwell: “ I could easily understand a paper by Gunnar Myhre that explains why radiative transfer models are suitable to estimate radiative forcing. This paper, so far as I have been able to find out, does not exist.”
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Post by dmapel on Jun 7, 2009 13:20:53 GMT
glc: "where you will find an explanation and discussion which is considerably more informative than I am able to provide."
Thank you
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Post by glc on Jun 7, 2009 13:50:58 GMT
Wow! And some radiation passes from the earth to outer space without being affected at all. Yes - it's known as the IR window. About 40 w/m2 which is outside the absorption bands of the main ghgs is emitted directly to space. And there are all sorts of other complications. This is only in the CO2 band. There is all the rest of the spectrum. The IR window is in the "rest of the spectrum". Absorption is quite apparent in the CO2 band. This link shows a typical spectrum with the various regions labelled www.barrettbellamyclimate.com/page16.htmNote the IR window (~800 to ~1200 wavenumber). Here emittance occurs at just over 280 K (blue line), i.e. ground temperature. In the "CO2 band" emittance to space is at a much higher (and colder level). You state " How energy reaches these layers is irrelevant." I cannot follow this. I cannot say I dont believe you, because I dont understand it. My explanation is clumsy but I can't think how best to put it. Try this: The earth (including it's atmosphere) receives an average of ~235 w/m2 solar energy. To maintain a roughly stable temperature 235 w/m2 is emitted by radiation (nothing else) from the top of the atmosphere. Right so we have 235 coming in and 235 going out. Incoming = Outgoing = 235 w/m2. Between the earth and the TOA there are a lot of other things going on which distribute heat towards the poles and up through the atmosphere, but it is only by radiation that the system, as a whole, maintains equilibrium. That's what I meant by being irrelevant. Convection, for example, allows the earth's surface to cool but it cannot transport heat into space.
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Post by nautonnier on Jun 7, 2009 14:07:05 GMT
JimC, Nautonnier I think you might be getting hung up on the RF definition. It's true that if we perform a Modtran run which calculates the change in forcing due to a doubling of CO2, say, then we are effectively instantaneously dumping ~300 ppm of CO2 into the atmosphere while keeping tropospheric temperatures and other factors constant. It's the same with laboratory experiments, i.e. we can transmit radiation through different concentrations of gases. Obviously this doesn't happen in the real world. As CO2 is added troposphere temperatures to the change in RF will respond which - may invoke other feedbacks (both positive and negative). You are using the feedback uncertainty to cast doubt on the whole basic theory. Sure - things might not pan in a totally predictable fashion but there's no reason to think that the ~3.7 w/m2 (~1.2 deg C) is not a reasonably robust result. Ignoring feedbacks can either of you explain why you think the result of the 'instantaneous' calculation will be appreciably different to the result from the gradual increase. "Ignoring feedbacks can either of you explain why you think the result of the 'instantaneous' calculation will be appreciably different to the result from the gradual increase. "glc - do you not see the logic fault in your statement above? This is precisely how the maths is being done - ignore all feedbacks by making the troposphere be unperturbed and magically double CO 2 - and that is precisely why JimG and I are saying it is unreal. So to restate what you wrote above: "Ignoring that the calculation is unreal show why you think the calculation is unreal" It is the total lack of feedbacks both positive and negative AND the feedbacks to those feedback responses, that make the value that you generate unreal as a way of calculating the effect of CO 2 in a real-world atmosphere. Your statement is as nonsensical as saying 'ignoring Archimedes principle why does this iron bar not float?'
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Post by nautonnier on Jun 7, 2009 14:16:11 GMT
So far as my reading tells me, radiative forcing reacts with all four ways in which energy is transmitted through the atmosphere; not just radiation. glc, do you agree with this, or am I wrong?Jim You're not necessarily wrong, but the other "ways" don't matter (as far this issue is concerned) . Ultimately incoming solar energy is balanced by the emittance of outgoing LW radiation. The earth receives, on average, 235 w/m2 of solar energy. In order to maintain equilibrium it emits 235 w/m2 LW radiation. Some of this is emitted directly from the surface - some from different layers of the atmosphere. In the CO2 band this is at higher altitudes. How energy reaches these layers is irrelevant. The key point is: How much energy enters earth's climate system and how much energy leaves earth's climate system. and the only way it leaves is by radiation. If we are looking at WM -2 then first you have to define the 'surface' whose surface area you are measuring. It would appear to me that in most cases all the radiative forcing is being measured at the tropopause. Therefore we are not looking at the surface area of the Earth but the surface area of the tropopause. There seems to be a considerable degree of imprecision in the statements that are being made. This is getting to the level that it appears close to deliberate obfuscation. Has anyone anywhere measured total global heat content? This would be far more correct metric than using atmospheric temperatures when we are apparently wanting to identify the heat content of the entire globe as measured out to the tropopause.
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Post by nautonnier on Jun 7, 2009 14:23:54 GMT
So as JimG has said you are using a hypothetical world not a real one - and therefore the results of the calculations while perhaps interesting results, cannot be taken as relating to the real world. In the case that you state (solar output increasing) then I would expect to see _negative_ feedback mechanisms of increased cloudiness in particular convective weather increasing albedo and carrying heat up from the surface. Feedback comes after the forcing. Afterall if there is no forcing there is nothing for the feedback to act upon. There are instant doubling experiments and gradual doubling experiments, not just the first. Again the radiative forcing is distinct from the climates response to it. "Feedback comes after the forcing. Afterall if there is no forcing there is nothing for the feedback to act upon."Feedbacks will start as the forcing starts - they don't wait until all the forcing has finished then take their turn. If negative feedbacks are more powerful than the forcing then the effect of the forcing is in the opposite sense to the sense that was applied. If you do not understand the physics and complexity of all the feedbacks you can have NO IDEA of the effect of your forcing. It is the ignorance of and (sometimes willful) disregard of these feedbacks that make me believe less and less of what AGW proponents are saying however earnest and good intentioned they are.
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Post by jimcripwell on Jun 7, 2009 14:54:58 GMT
glc writes "My explanation is clumsy "
I agree. What I asked for was a reference that explains this in scientific terms. Surely for something that is this important for the whole business of AGW there must be a proper reference.
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Post by socold on Jun 7, 2009 15:29:38 GMT
Feedback comes after the forcing. Afterall if there is no forcing there is nothing for the feedback to act upon. There are instant doubling experiments and gradual doubling experiments, not just the first. Again the radiative forcing is distinct from the climates response to it. "Feedback comes after the forcing. Afterall if there is no forcing there is nothing for the feedback to act upon."Feedbacks will start as the forcing starts - they don't wait until all the forcing has finished then take their turn. Feedbacks are proportional to forcing. If you have no forcing, the feedback aint gonna be doing anything. The forcing for say doubling co2 or increasing solar output 2% is independent of feedbacks and therefore the climate's response. No negative feedbacks would simply dampen the climate response to any unit of forcing, not negate it. Obviously, but it's the forcing that is being calculated, not it's effect.
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Post by icefisher on Jun 7, 2009 17:22:58 GMT
Do you accept that the increase in CO2 atmospheric concentrations will impede the flow of energy from the earth's "climate system" to space. You can't seem to get off of first base GLC and go for second. Look I have answered this question directly to you on multiple occasions. I have agreed there is a certain amount of minimal warming that CO2 provides. I even agree that it is very much likely that the amount of warming that CO2 provides is greater than certain other gases that could be added to the atmosphere. You even tried to model it a week or so ago and I pointed out all you modeled was a model of additional gas, any gas, to the atmosphere which is also going to increase the temperature of the earth in relationship to how much gas you add to the current amount of gas in the atmosphere. Is CO2 an important gas in the atmosphere? Well it obviously is in its role of supporting life on the planet. Whether it is as a gas that provides a significant bulk of the current additional 30 degree warmth to the planet I am not convinced. When I first took an apprenticeship to become a CPA fresh out of getting a degree, my employer gave us an indoctrination. In that indoctrination was an important lesson that might be applicable to the vast majority of gases in the atmsophere (99%). The story was about a bank software developer that created an interest rate calculation software for a banking system that shaved the rounded mils off each calculation by always rounding down to the nearest penny and depositing the excess in an account controlled by the software developer. The maximum cost for any individual account holder was about $1.80 spread over 360 daily interest calculations per year. . . .even if it was a million dollar account; but with a bank with a 100 thousand accounts this was a big deal. (making up the numbers here as this was a long time ago) Fact is every molecule in the atmosphere intercepts at least small amounts of both visible light coming in and longwave infrared going out and converts some of that to energy. To claim it doesn't is unfounded. To claim it doesn't emit IR is also unfounded. That would be tantamount to a claim that if you had a contained warm bag of gas in space in a bag transparent to IR it would never cool. That does not compute. Cools slowly does compute. I think the problem here is some of this stuff is difficult to experiment upon and measure. While it cools slowly and may be unimportant in relationship to CO2 when dealing with equal amounts of gas, that is not relevant in relationship to our atmosphere. The energy capture of the dominant gases in the atmosphere are very small on a molecule for molecule basis but in relationship to the fact that in some areas of the atmosphere this is mixed in at a rate of 99.96% of the atmosphere (in the reaches above water vapor) it doesn't need to be but a very small amount to overwhelmingly provide the greenhouse affects for the earth in relationship to what CO2 provides. I doubt we can come close to measuring the radiation effects of CO2 anywhere near to the level of accuracy that would be necessary to establish that in the lab. Thus even if one can estimate the radiation efficiency of CO2 maybe within 99.9%(probably a gross exaggeration in itself) one has no basis to claim that CO2 is even the dominant greenhouse gas in the upper troposphere yet. What we are dealing with are exacting calculations of infintessimally small amounts of a gas and we have coarse theories about how all this works. Yeah GLC you could be absolutely right but what I think folks are saying is "show me" and not many folks around here are not convinced you can't.
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Post by nautonnier on Jun 7, 2009 17:42:59 GMT
"Feedback comes after the forcing. Afterall if there is no forcing there is nothing for the feedback to act upon."Feedbacks will start as the forcing starts - they don't wait until all the forcing has finished then take their turn. Feedbacks are proportional to forcing. If you have no forcing, the feedback aint gonna be doing anything. The forcing for say doubling co2 or increasing solar output 2% is independent of feedbacks and therefore the climate's response. No negative feedbacks would simply dampen the climate response to any unit of forcing, not negate it. Obviously, but it's the forcing that is being calculated, not it's effect. "Feedbacks are proportional to forcing. If you have no forcing, the feedback aint gonna be doing anything. The forcing for say doubling co2 or increasing solar output 2% is independent of feedbacks and therefore the climate's response."
This is totally untrue. The climate is a chaotic system - feedbacks need not be proportional in anyway at all and they definitely will not be simple they may be part of a chain of system responses to the input or to the system reaction to the input.. You have a very simplistic view of the climate. "No negative feedbacks would simply dampen the climate response to any unit of forcing, not negate it."Again an extremely simplistic view of a chaotic system. But I suppose you can be forgiven as you don't believe in ANY negative feedbacks. An input into a chaotic system at the 'right time' can move the system from one 'attractor' to another stable state around another attractor. The way the Earth moves from ice-age to inter-glacial seems to be this kind of change. "Obviously, but it's the forcing that is being calculated, not it's effect."But it is the effect of the forcing that AGW proponents are waving in front of politicians to scare them into killing industries and taxing other businesses into bankruptcy. Of COURSE it is the effect that you are calculating - you are the one SoCold that keeps on telling us of an ice free Arctic - that's an effect not a forcing! So we have a hypothetical forcing based on impossible assumptions used to calculate effects based on simplistic to unreal views of the climate - which are then used to scare the populace and empower the politicians and enrich the climate scientists and the 'cap and trade' scheme and 'in the green for profit' companies like Al Gore's and GE.
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Post by glc on Jun 7, 2009 17:56:17 GMT
glc writes "My explanation is clumsy "
I agree. What I asked for was a reference that explains this in scientific terms. Surely for something that is this important for the whole business of AGW there must be a proper reference.
Explains what, Jim?
Look, let's start from the beginning. We are adding CO2 to the atmosphere. At current rates, CO2 concentrations will double from 1900 levels sometime during the next ~100 years. It would be useful to know what the effect of this will be.
So how do you suggest we achieve this?
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Post by icefisher on Jun 7, 2009 18:11:01 GMT
Feedbacks are proportional to forcing. If you have no forcing, the feedback aint gonna be doing anything. The forcing for say doubling co2 or increasing solar output 2% is independent of feedbacks and therefore the climate's response. Logically lets look at the primary feedback, evaporation of water. We know if you have water on the ground and the air becomes warmer you get more evaporation and thus more water vapor in the atmosphere. The AGW feedback principle here states that this is a positive feedback because water vapor acts as a greenhouse gas trapping more heat in the atmosphere. So why does not such an event trigger runaway warming or at least say 100% humidity in the atmosphere world wide? The answer seems common sense enough, namely that the water cycle itself overpowers its own negative feedback of increased greenhouse effect. The water cycle is in fact a cooling system just as it appears to be when one sprays water on a hot surface by moving heat upwards to an escape point in the atmosphere. What you can be correct in saying is you will generate some warming despite the feedback as the feedback does not exist unless you have the initial forcing; but this does not get you an inch closer to claiming how much additional warming. It could be very very very very very very minor additional warming despite initially strong strong strong strong strong strong forcings. 10 years ago when it appeared warming was driving upwards and nobody was talking about ocean oscillations this was looking like a minority argument. But that has all changed. Today the most likely descriptions of what has been going on can be seen in the graphs from Don Easterbrook and Dr Akasofu. These papers, whether you agree with them or not, take the air out of the urgency behind curbing CO2 emissions short of significant new additional warming (which I take to mean more than a decade of warming by way of the arguments of the AGW advocates around here) Also as I noted in my reply to GLC we don't even know if CO2 is an important greenhouse gas in the quantities it exists in our atmosphere. The nice things about GCMs is you create one that seems to match what has happened then watch it crash and burn and go back to the drawing board. The fact folks are instead trying to draw epicycles around their models to explain the failure of their models to predict I think bespeaks of human nature rather than science.
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Post by glc on Jun 7, 2009 18:23:49 GMT
"Ignoring feedbacks can either of you explain why you think the result of the 'instantaneous' calculation will be appreciably different to the result "
glc - do you not see the logic fault in your statement above?
No. Because the calculations I am referring to don't include feedbacks. I don't believe feedback is significant. The models on the other hand do include feedbacks and perform the calculations over thousands of time intervals , so they do actually replicate the real world better.
This is precisely how the maths is being done - ignore all feedbacks by making the troposphere be unperturbed and magically double CO2 - and that is precisely why JimG and I are saying it is unreal.
I'll ask you again why do you think that the effect of the gradual increase will be appreciably different to the theorectical instantaneous increase.
You and Jim are getting confused by the definition of Radiative Forcing. All that means is the radiative transfer equations use current temperature and pressure values to calculate an estimate of the total forcing due to a doubling of CO2. We could do the calculations incrementally and re-adjust the temperatures each time, but then we would have a Climate Model.
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