The greenhouse effect is real. If there were no greenhouse gases in the atmosphere, earth would be a cold place. Compare Mars versus Venus – Mars has minimal greenhouse gas molecules in its’ atmosphere due to low atmospheric pressure, and is cold. By contrast, Venus has a lot of greenhouse gas molecules in its’ atmosphere, and is very hot. Temperature increases as greenhouse gas concentration increases. These are undisputed facts.
outgoing radiation = incoming radiation – changes in oceanic heat content
The image below from AER Research explains the radiative balance.
http://www.aer.com/scienceResearch/rc/rc.html
About 30% of the incoming shortwave radiation (SW) is reflected by clouds and from the earth’s surface. 20% is absorbed by clouds and re-emitted back into space as longwave (LW) radiation. The other 50% reaches the earth’s surface and warms us. All of that 50% eventually makes it back out into space as LW radiation, through intermediate processes of convection, conduction or radiation. As greenhouse gas concentration increases, the total number of collisions with GHG molecules increases. This makes it more difficult for LW radiation to escape. In order to maintain equilibrium, the temperature has to increase. Higher temperatures mean higher energies, which in turn increase the frequency of emission events. Thus the incoming/outgoing balance is maintained.
Click for larger image
http://www.aer.com/scienceResearch/rc/m-proj/lbl_clrt_mls.html
The important greenhouse gases are: H2O, CO2, O3, N2O, CO and CH4. The reason why the desert can get very cold at night is because of a lack of water vapor. The same is true for Antarctica. The extreme cold in Antarctica is due to high albedo and a lack of water vapor and clouds in the atmosphere, which results in almost all of the incoming radiation returning immediately to space.
An earth with no CO2 would be very cold. The first few tens of PPM produce a strong warming effect, and increases after that are incremental. It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks. So the debate is not about the greenhouse effect, it is about the feedbacks.
Suppose that the amount of reflected SW from clouds increases from 20% to 21%? That would cause a significant cooling effect. Thus the ability of GCM models to model future temperatures is largely dependent on the ability to model future clouds. Cloud modeling is acknowledged to be currently one of the weakest links in the GCMs. Given the sensitivity to clouds, it is perhaps surprising that some high profile climate scientists are willing to claim that 6C+ temperature rises are established science.
So the bottom line is that the greenhouse effect is real. Increasing CO2 will increase temperatures. If you want to make a knowledgeable argument, learn about the feedbacks. That is where the disagreement lies.
I have finally realised why I have found this particular discussion so confusing. Steven began by trying to explain a simplified model of the badly named greenhouse effect. I generally agree with his description but he was not entirely explicit about the simplifying assumptions that he was making. This left him open to the “ah but what about..” comments which then tended to presage highly simplistic arguments about a far more complex model.
So at the risk of being boring I will be explicit.
We can consider the greenhouse effect in isolation if we assume that all other variables which affect climate are constant. These are:-
Cosmic variables – sun’s output, earth’s distance from and inclination to the sun, Solar wind, cosmic rays etc.
Geophysical variables – earth’s albedo (% of sun’s energy reflected by surface) , volcanic and geothermal activity etc.
Climate variables – energy stored in oceans land and atmosphere, vertical and horizontal non radiative heat transport (winds, sea currents, convection, evaporatation etc.) amount and location of clouds, aerosols humidity etc.
Any other variables you can think of other than the concentration of CO2.
This may seem ridiculous but only if all these variables are considered constant can you consider the affect of CO2 in isolation. I have effectively created a “Groundhog day” where every day is identical. Instead of using this to seduce my colleague I am going to change the CO2 concentration to see what would happen.
Steve gave a good description of the basic physics but I will give a slightly different slant on it which might be helpful.
In this scenario where everything is constant the temperature will also be constant. What would this temperature be?
For the temperature to be constant the energy absorbed by the earth has to be equal to the energy radiated into space.
The energy absorbed is mainly short wave radiation characteristic of the sun’s high temperature.
The energy radiated is long wave radiation characteristic of the earth’s low temperature.
The amount of energy radiated at any particular wavelength will depend on the emissivity and temperature of the surface which emits the photon into space.
For about half the spectrum these photons are emitted from the earth and therefore the temperature can be considered to be about 300K.
The other half of the spectrum is absorbed by the atmosphere and then reradiated into space from high altitude.
Water is the main factor here. Because its concentrations are high near the surface and considerably less at high altitude the effective height at which radiation into space takes place is only a few kilometres above the surface. Temperature reduces with altitude so the effective temperature is about 270K.
CO2 is more evenly distributed and is a powerful absorber albeit in a small frequency band between 14 and 18 micron compared with the total spectrum which is mainly between 6 and 50 micron. The effective height of this radiation layer is about 8km according to Hadley but the satellite data I have places it much higher. The effective temperature might be as low as 225K.
Because radiation is proportional to the 4th power of the absolute temperature the 10% reduction in the temperature of the water molecules radiating into space (compared with the surface) results in a reduction in energy loss reduction of about 1/3 for those wavelengths.
For CO2 the reduction in temperature is 25% so the energy loss reduction is more like 60%.
These reductions in energy losses at the characteristic absorption frequencies of water and CO2 (and to a lesser extent ozone and methane etc.) means that the energy losses at the other wavelengths have to increase to compensate. Again if all other things are constant the only way this can happen is if the temperature of the surface rises. This is the so called greenhouse effect. However silly the name, the effect is real.
So, back to our “Groundhog” experiment. What would happen if we increased the amount of CO2? The number of absorptions and re-radiations would increase as Steve describes but ultimately the key issue is that, at a given height, the probability that a photon would be directly radiated into space reduces. This means that the effective radiating surface must move to a greater (less dense) altitude. This implies lower temperatures and therefore further reduced losses. Therefore the surface has to increase in temperature to compensate. Thus the greenhouse effect still impacts even when the CO2 absorption bands are saturated.
This is the “incontrovertible” evidence that the AGWs propound. However it does not take a genius to see that all the other variables are not constant. It is also obvious that 60% of the total effect that CO2 can have has already happened. More importantly the level at which CO2 radiates is approaching the tropopause where further increases in height would not lead to reductions in temperature. Some research would suggest that the height of the tropopause is increasing to accommodate a temperature drop but I am yet to be convinced by the data.
So I agree with Steve. Don’t try and argue that the greenhouse effect is not real because you are on a loser. The real argument is that history demonstrates that the effect is swamped by all the other variables. The AGWs are then left with one argument which has some validity. Whereas all the other variables are cyclical and would average to zero over time the effect of CO2 is permanent.
My feeling about this is that we are living in a golden age. Temperatures are high compared with the average over the past million years although it has been warmer. If we are doing something that increases the average temperature by about 1 or 2 degreesC (which is what the science really suggests might happen over the next centuary) then all to the good. It might just keep us in the manner to which we have become accustomed.
Steven Goddard (09:20:12) :
Gary Gulrud,
You wrote: Back-radiation has no practical consequence of heating the surface whatever.
I bicycle year round day and night, and am quite certain that my hands stay warmer on cloudy nights in the winter – due to back radiation from the clouds.
jae (09:34:15) :
Maybe it’s because water vapor has four times the thermal capacity of the rest of the air?
—
Also, as the air is more humid on a cloudy night, the perspiration generated by the effort of cycling evapoates slower, and hence reduces skin temperature rather less, and many many more factors –
NOT JUST THE OBSESSION WITH A RADIATIVE EXPLANATION OF LIFE, THE UNIVERSE AND EVERYTHING! SURELY THERE IS MORE TO LIFE THAN THIS!
As has been pointed out before on this site, the sun’s emissions in the IR band are as large as in the visible band, so it seems the sun is not too hot (proud?) to emit low frequencies.
AM
One annoying thing in debates like this is the continual appearance of few wild guesses that keep being presented as facts or “evidence” in debates like this:
1. The continual assertion about “observational evidence” for the effect of increased CO2. All such observations in fact are ambiguous, with cause and effect difficult to determine, yet a lot of scientists have nevertheless given an opinion that certain effects must have been due to CO2. They managed this feat by excluding or ignoring all other possibilities. Yet their knowledge about these other possibilities is ludicrously minimal (which is even admitted by the IPCC). The arguments rest entirely on “we can’t think of anything else”. This flawed opinion then somehow becomes stated as “evidence”. Well it just isn’t! Should we accept it as expert opinion anyway? Only if some real evidence appears!
2. The idea that ice age cycling can be explained by CO2 amplification but by no other means. Obviously there must be some kind of amplification involved but whether this is CO2 is merely guesswork. In fact CO2 can explain the heating quite well but it can’t explain the cooling at all. And that is the illogical part of the feedback theory that AGWers just ritually ignore. In fact datawise that idea that CO2 acts alone has been debunked by Lowell Stott’s real evidence. Severinghaus on RC guesstimated a mere 30% effect from CO2, without of course telling us too much where the rest came from. Of course it could have conceivable been a negligible effect. When you don’t bother to look for any other factors then you surely don’t find them.
3. The idea that any demonstration of increased water vapour in the atmosphere – either the postulated 2% by Trenberth or that ridiculously short trend analysis by Dessler – means that the high CO2 amplification factor has been proven. Yet as Lindzen argues, higher water vapour can mean cooling as well as heating so you need to look at the actual temperatures for the evidence. Is it there in the temperatures? Well no it isn’t. And of course then the various hand-waves come into play – ozone depletion (lately Steig), brown clouds (Ramanathan), weather noise (everyone), the sun (Hansen), dubious statistical error overlaps and observational errors (Santer et al.). It’s all a big guessing game where the conclusion is pre-determined by bias. These expert scientists know the excess warming should be there so it must surely be masked by something else. Whereas the more logical explanation is that the basic theory of CO2 amplification is likely wrong.
I’d agree with Steven that the 1.2C degrees for no-feedback doubling, has to be conceded even if that is dubious too (due to the gross simplifications involved). But without focusing specifically on the much weaker feedback issue you can be picked off too easily as a knee-jerk contrarian. Whereas all we want is the real truth – not biased opinions presented as truth.
Potential double accounting?
This: http://www.globalwarmingskeptics.info/phpbb3/viewtopic.php?f=5&t=585&st=0&sk=t&sd=a
Claims that the CO2 measurements are done with IR that can not distinguish th CO2 absorption from other GHGs absorption signatures. IF true, this would assert that we actually measure “IR absorbent gas” rather than CO2, then we separately measure methane et. al. and add those GHGs to the CO2 measure to get total GHGs.
This looks to me like a double accounting. Does anyone know how they get the CO2 measure to only measure CO2, given that it’s really an IR measure?
AD NAUSEUM to Joel Shore,
Joel Shore,
You did not reply to my post on Gavin Schmidt et al 2005 quoted thusly:
“Tropospheric warming is a robust feature of climate model simulations driven
by historical increases in greenhouse gases (1–3). Maximum warming is predicted
to occur in the middle and upper tropical troposphere.”
http://www.osti.gov/energycitations/servlets/purl/881407-xk2Sdg/881407.PDF
Your statement, and those being bandied about the various pro-AGW blogs are now back pedaling. With that, you are saying GCM predictions are mistaken?
If your version is correct, why then have Schmidt, Santer and the usual suspects been attempting to a) discredit satellite data and b) show models in agreement with observations? Surely you are aware of the serious “problems” with Santer et al 2008?
You can’t have it both ways. Are GCM predictions, which are driven by increases in GHG emissions, correct or not?
Chico (22:08:27) :
Finally a discussion on the physics of the Greenhouse Effect. I have a few observations and questions.
I agree. It is interesting to see all the different approaches by people here. I am personally more interested by the instantaneous physical effect.
2) Phil’s Makes a very powerful point that an excited CO2 molecule will almost certainly transfer its ‘excess’ energy to surrounding O2 and N2 molecules. This is *very* important because O2 and N2 don’t principally radiate at a frequency that is absorbed by traditional Greenhouse gases. Correct me if I am wrong but it is O2 microwave radiation that satellites observe to infer the temperature of the Earth’s atmosphere (i.e. RSS and UAH). Although Phil also suggests that O2 and N2 don’t radiate? I thought all mater above absolute zero temperature radiates?
Is it possible that H²O and N² molecules (given their number) could also re-transfert some energy to CO² molecules by collision?
To Phil,
you apparently has some knowledge in physic (at the molecular level). Could you provide a (or point to a detailed) heat/energy analysis of the influence of the re-radiated LW photon by CO² molecules on both the surface and the atmosphere right above the surface? My own analysis above is meaningless and I think it is the central problem of the GH effect (if any). Thanks in advance.
Bye,
TMTisFree
David Porter (01:27:35)
David you can construct a graph for yourself that is similar in form to the graphs in the top post, but is more representative of the climate sensitivity in relation to a very large amount of scientific evidence.
This puts the likely middle of the range value of the climate sensitivity (the temperature rise at equilibrium upon doubling atmospheric CO2) near 3 oC.
A suitable equation is:
T = (3.0/log(2))*(log(C))-9.39
This gives the temperature at equilibrium within a climate sensitivity of 3.0, normalised to a temperature of 15 oC at an atmospheric CO2 concentration (pre-industrial) of 280 ppm. The “log(2)” relates to the fact that the 3.0 is the temperature rise upon doubling, “C” is the atmospheric CO2 concentration and “log(C)” defines the logarithmic dependence of the temp rise on increased atmospheric CO2.
You can use a different value for the climate sensitivity but you’ll then need to re-normalize the 280 ppm value to 15 oC (by adding/subtracting the appropriate offset – we could do a better equation to normalize this automatically!). Use the appropriate tool in your graphing package to construct a set of data for “C”.
Note that the graph in the top post is additionally misleading in two further ways:
ONE: The Y-axis label (“Estimated temperature”) isn’t estimated temperature at all, but is the estimated temperature rise at equilibrium. For example, when the Earth’s temperature was “nearish equilibrium” at the preindustrial level of around 280 ppm, the temperature couldn’t have been 5 oC, 7 oC and 12 oC all at the same time! I’ve normalized my data to a pre-industrial (280 ppm) “temperature” of 15 oC, but you could normalize to a different pre-industrial temperature if you felt like it.
TWO: by plotting the data starting at a completely unrealistic value for [CO2] near zero the graphs appear to have virtually flattened from around 250 ppm [CO2] upwards, especially for the vastly unrealistically low values for the climate sensitivity. To determine what the equilibrium temperature response looks like within a 3 oC climate sensitivity under conditions that are meaningful for consideration of current and future emissions, plot the data for a [CO2] range from 250 ppm (say) to 1200 ppm (say) to encompass the [CO2] range of real world relevance.
I asked a question above to those that are here often and was ignored. Please someone take my question up. Educate me.
I said:
Something was mentioned twice here that was never addressed by the normal folk that inhabit this site –
Pressure.
Does the temperature of Venus, Mars Jupiter atmosphere at 1ATM correlate to earth’s average temperature after adjusting for distance from the sun?
If it does, and I’ve now read two websites not related to climate science that say that it does, then the big…..OH…moment for me is that pressure regulates temperature more than any thing and that the ocean accounts for the rest of earth’s temperature variations over time – noting that the earths overall temperature doesn ‘t actually fluctuate by that much).
Also it says that SG’s comments about Venus and Mars are really misleading to say the least, which as a long time reader here, is disappointing.
Can someone clarify? Leif would be a prime candidate to answer because what I said would go along perfectly with his tireless shouts that IT’S NOT THE SUN! Which I believe
With regard to the supposed greenhouse effect, does rainfall affect the balance?
How much atmospheric carbon dioxide and atmospheric heat is removed by precipitation?
The old desert cooler(before aircon) was quite good at taking away atmospheric heat.
Does this constant removal affect the calculations in any meaningful way and has it been inculuded in the calculations?
Perhaps a quarter of the earths surface is being rained on any given day so this must take a considerable amount of CO2 and heat from the atmosphere and dump it either into the ocean cycle or the biomass cycle.
Steve Goddard writes ‘higher GHG densities force the temperature up’. He goes on to say that this is not disputed.
This is wrong. He has played a linguistic trick.
The statement, that for planetary atmospheres ‘higher densities force temperatures up’ is based on well established physical theories.
By adding GHG, standing for ‘greenhouse gases’, he introduces a new, different and greatly disputed theory.
There is no greenhouse effect. It is no use saying, ‘OK, CO2 does cause warming, lets get paid for discussing how much’.
It is good to be sceptical especially of a warmist guest posting
EM Smith,
Doesn’t most of the corn grown in Nebraska get fed to cows and belched out as GHG?
Reed Coray (22:32:19) :
Reed,
Thank you for your response. I’ll try to address your points as best I may.
Firstly, on the matter of labels (‘alarmist’, ‘denier’, etc.), I agree with you that this is an issue on both sides. I think there are some alarmists about (people deliberately misrepresenting or exaggerating the likelihood of calamitous outcomes) and also think there are some denialists around (people deliberately misrepresenting or exaggerating to the opposite effect).
Let’s just presume that we fall into neither camp :-). Though I would certainly accept that I am alarmed by the risks, my intention is not to exaggerate.
Simon is right, I don’t know the history of AGW theory very well; and undoubtedly, Simon’s description of some scientists was right on. But if Simon is trying to convince me that when Al Gore first presented his slide show, Al (and others like him) knew that the initial temperature rises were not CO2 induced and carefully mentioned as much every time he gave his presentation, I can’t, or more correctly, won’t believe it.
I’d be very surprised if he didn’t know, but I guess you’re right that he didn’t ‘carefully mention’ it (I’ve only watched it once, a while ago. What I remember as being ‘alarmist’, IMV, was the implication that multi-metre sea level rises might be imminent which, at the time at least, was not a fair view). But, as is oft repeated here, Gore is not a scientist. I’m not an apologist for him anyway, but I could pick out just as many ‘glosses’ from the public presentations of people like Bob Carter, for example.
In response to my question: “So the AGW alarmists have increasing CO2 levels acting as both an originating and a feedback phenomenon. I’d like to know which if either is correct.” Sinom answered: “Both”. When I asked: “if both, then what stopped runaway global warming in the past?” Simon answered: “The temperature feedback is less than the input.”
That answer is confusing to me because I thought the AGW supporters agree that the temperature changes from a doubling of CO2 by itself is at most 1.2 degrees, but the “feedbacks” will amplify this change by at least three degrees and somewhere I’ve read by as much as seven degrees.” And since the temperature effect as a function of CO2 level is logarithmic, more of the temperature change will occur early in the doubling process rather than later. As such I don’t understand how Simon can answer: “The temperature feedback is less than the input.” If Simon wants to talk about absolute temperatures, not temperature change, then he has a point. But I thought AGW theory was best described in terms of changes to a nominal level. This is in part why I want to see a clear diagram of the system inputs, outputs, feed forward, and feedback mechanisms.
It wasn’t my clearest ever answer, so I’ll try again (I should have maybe written “the temperature change from one circuit of the feedbacks is less than the temperature change from the input alone”). In the case of increased CO2 concentration giving rise to increased IR absorption giving rise to temperature gain (allow the premise for now!) giving rise to increased CO2 concentration as the ocean buffer changes, then that is a simple feedback loop. In this case, I understand that the GHG feedback will be markedly less than the GHG input, except perhaps in the case of methane clathrate release. In the case of CO2 ~ temperature increase ~ water vapour increase ~ temperature increase then there is, so far, a feedback to the system, though not to the original input. There will also be some feedback to the original input from further warming of the ocean buffer, but again it will be smaller than the original. For a given input, the system adjusts to a new state of unstable equilibrium. To simplify, an input of 1 which has a total feedback rate of 75% would give rise to an equilibrium output of 0.75/(1-0.75), = 3.
And for what it is worth, the stability of a linear, time-invariant system with feedbacks is defined by the location of the system’s “poles” not by the system’s input. [For discrete-time systems, any pole on or outside the unit circle means the system is unstable. For a continuous-time system, poles on the vertical axis or in the “right half-plane” make the system unstable.] In turn, the location of a system’s poles are a function of its feedback loops, not the system’s input. Even for a large input, the system output may initially be small compared to the input but over time the system output will grow without bound.
Well, I don’ think the climate is a linear, time-invariant system, and nor is it simply deterministic! But anyway, I think you are considering a system above where the input is maintained. In the climate case, where the input of increased IR absorption is considered, we may also conclude that if that input were to be maintained (and eventually, of course, the planet would run out of capacity to ‘feed’ it) then the output would continue to accumulate. The calculation of the outcome from doubling CO2 is simply that, though – an assessment of equilibrium temperature response to that doubling alone.
Simon’s answer confuses me. First he says “They are not – at least, not fully”–meaning the larger delta temperature changes at the system output are “not fully” fed back to the system input. By “not fully” does he mean the output temperatures are not fed back to the system input but to an intermediate point in the system; or does he mean only a portion of the output temperatures are fed back to the system input; or both? The lack of precision of his answer is one of the reasons I want to see of “circuit diagram” for climate model used by AGW supporters.
Ok, try again. There is no ‘larger temperature delta’ consequent upon a temperature input for one ‘circuit’ of any feedback loop. If there were then, of course, the system would be subject to explosive feedback. The larger temperature delta is the addition of all feedback over time and is not fed back in total, since it is only the change in temperature that feeds back and not the absolute temperature. By ‘not fully’ I meant simply that the feedback rate, in response to any temperature change, is less than 1.
Then after answering “not fully”, Simon then mentions methane gas and opines that Dr. Hansen just might have had a “full feedback” in mind for methane gas. If someone can clarify what’s going on, I’d appreciated it.
I had in mind the ‘clathrate gun hypothesis’ –
http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
Finally, when I mentioned that I’d like to see a circuit diagram of the AGW theory, Simon responded: “I’d recommend Chapter 8 of the AR4. It may not be quite in the form you want, but you can figure out answers to your questions” ….I didn’t see anything that even remotely resembled a circuit diagram.
No, as I wanted to indicate, it’s not in the form you want, but it does include the figures for various feedback assessments (p. 629 on) along with discussion. I’m not aware of a ‘circuit diagram’ presentation as such, so I was suggesting that the best one might do is to figure it out from the discussion of the modelling.
I hope I’ve clarified my views further.
Smokey (17:23:56) :
Smokey, a useful aspect of science is that one can relieve oneself from tedious arguments (“my Pofessor is more important than yours!) and address the evidence.
It’s not clear where the data for Lindzen’s climate sensitivity in the graph in the top post comes from (someone apparently created the graph on a site called “junk science” apparently). However we know from Lindzen’s earlier papers that his interpretations of low climate sensitivity values arose partly from his model in which moist (cumulus) convection that should increase with atmospheric warming under enhanced CO2 concentrations, might cause a drying of the upper troposphere[***]. This proposed drying would be a negative feedback that would partly offset the positive feedback from enhanced water vapour at lower altitudes.
Now we know that this interpretation was incorrect. We can measure the water content of the troposphere (upper and all) and determine that in the real world the upper troposphere is moistening (as models predict in fact)[*****]. So we reject Lindzen’s failed hypothesis in this particular respect, since it is shown not to be correct. There’s no problem with that. It’s part of science. However what we shouldn’t do is to retain analyses that we know to be incorrect because we happen to like their implications.
[***]e.g. Lindzen RS (1990) Some Coolness Concerning Global Warming Bull. Am. Meteorol Soc. 71, 288-299
[*****]e.g. Soden BJ, et al (2005) The radiative signature of upper tropospheric moistening Science 310, 841-844
Santer BD et al. (2007) Identification of human-induced changes in atmospheric moisture content. Proc. Natl. Acad. Sci. USA 104, 15248-15253
Brogniez H and Pierrehumbert RT (2007) Intercomparison of tropical tropospheric humidity in GCMs with AMSU-B water vapor data. Geophys. Res. Lett. 34, art #L17912
Buehler SA (2008) An upper tropospheric humidity data set from operational satellite microwave data. J. Geophys. Res. 113, art #D14110
Gettelman A and Fu, Q. (2008) Observed and simulated upper-tropospheric water vapor feedback . J. Climate 21, 3282-3289
pft (16:12:01) :
“and the more CO2 there is, the less effect it has. ” should have said “and the more CO2 there is, the less affect more CO2 has”
Not exactly (saith the grammar policeman).
Excellent discussion. I am wondering if you have a way to explain this to people in a general way that would attract a more serious public discussion than whether or not global warming is a reality.
Phil,
Your explanations are appreciated, but appear to be missing something important. If the CO2 is losing all of it’s excitation energy in nanoseconds near the surface, how can there be excited CO2 at 1mb altitudes?
According to this chart, the 15um absorption spectrum is saturated.
http://www.globalwarmingart.com/wiki/Image:Atmospheric_Transmission_png
@ur momisugly Leif Svalgaard (08:15:03) :
“…any energy CO2 absorbs [most of it coming from below] is immediately re-emitted, half up into space and lost and half downwards back to the surface. The surface thus heats up and warms the air by conduction and convection.”
Wouldn’t it be more correct to say that the ground heats up faster, and/or cools more slowly?
(I know you know all this stuff, but I find it easier to understand if I look at it this way)
If we were at steady state, with energy emitted=energy absorbed, the ground and air would be maxed out and no change would occur. So, every day from sunrise to sometime in the afternoon the earth warms up, and from then till the next sunrise the earth cools. We never, fortunately, achieve ‘steady state’.
So, the ground warms faster because of GHG’s, and it does that because when it re-radiates the sun’s energy back into space, some of that energy is absorbed by the atmosphere and half is re-radiated back to earth. BUT that is only half of what the earth radiated out, so it can’t “warm” the earth.
If you give me two dollars, and I give you back one, you aren’t richer than you were before you gave me the 2, though you are less poor. The same with the energy arriving from the sun. In a fixed time, the earth receives, say 10, of which it gives 2 to the air, and the air gives one back 1, so the earth now has 9, as opposed to only 8 if the air didn’t give any back.
The involvement of the air, then, isn’t to warm the ground, but to slow it’s cooling, which will in turn keep the air warmer for a longer time. The question then is, how much longer and what difference does it make? I.e., how much does increased [CO2] slow the heat loss – and if water vapor does the same thing, and does it so much more effectively than CO2, why are we worried about CO2?
ASIDE – the plot of earth’s climate history is often used as a demonstration of how CO2 has been higher in the past, but what strikes me about that figure is how there seems to be a maximum temperature of 22DegC which has NEVER (except for a single blip) been exceeded, and how we are currently no where near that max. If that means the earth CAN’T get any hotter than 22DegC, no matter how much CO2
JamesG says:
Welcome to the world of science. Of course, all observational data has problems and is subject to different interpretations, which is why it is important to have a broad array of different data and a lot of different analyses, which is what we have.
First of all, people have been studying the ice ages for a long time and have looked at a wide variety of explanations. In fact, your own statement about Severinghaus shows that there are other factors that have not only be considered but in fact are understood to contribute significantly.
Second of all, in answer to your implied question, most of the rest of the forcing comes from the change in albedo due to the ice sheet advances and recessions. There is also a little bit of contribution from changes in aerosol levels in the atmosphere although I can’t remember which way that goes. The orbital Milankovitch oscillations that trigger these cycles contribute only a very small amount to global mean forcing although they play a vital role in causing the advance and recession in the ice sheets that lead to the considerable forcing due to the albedo change.
Third of all, your question about how we know that CO2 contributes about 1/3 of the change rather than being negligible is a good one (and something I once wondered to). The answer is that you are missing at least one important piece of the puzzle: As Steve Goddard’s discussion explains, we know very well the radiative forcing due to the change in CO2. We also have reasonable estimates of the radiative forcing due to the albedo change, the small forcing due to aerosol changes, and the very small forcing due to the orbital oscillations. From this, we have a good estimate of the total forcing in W/m^2. We also have reasonably good estimates for the global mean temperature change. By dividing this global temperature change by the forcing, we get an estimate of the climate sensitivity: ~0.75 C / [W/m^2]. Since doubling CO2 gives a forcing of 4 W/m^2, this implies a climate sensitivity of about 3 C per doubling.
Note that if we simply did what you suggest and assumed that CO2 had a negligible effect and excluded its contribution to the forcings, we would get an even higher estimate for the climate sensitivity than ~0.75 C / [W/m^2] because it would have then taken less W/m^2 to produce the observed temperature change. Of course, our calculation would also not be self-consistent since this result for the sensitivity together with the known radiative forcing due to CO2 would imply that in fact CO2 does play a non-negligible role, contrary to our original assumption.
The only conceivable way to pull a much lower climate sensitivity out of the ice age – interglacial cycles is to come up with some huge forcing that we are missing (or claim that we are vastly underestimating the albedo forcing)…Or claim that the whole concept of radiative forcings breaks down in a very dramatic way. And, of course, this still leaves us with difficulties in explaining other paleoclimate events, the eruption of Mt Pinatubo, etc.
As a final note, I have presented one piece of the puzzle here. But, there are other pieces. For example, I believe that the role of greenhouse gases is necessary in order to explain the synchronicity of the ice age – interglacial cycles in the two hemispheres. I.e., if you have only the other forcings, climate models tend to have difficulty producing the approximately synchronous rise in temperature seen in both hemispheres. This is additional evidence for the role of the greenhouse gases in the ice age – interglacial cycles.
When I see some evidence that the atmosphere has actually warmed above the level where most of the latent heat of evaporation is released I will start to take some interest in the possibility of a ‘greenhouse effect’. Till then, I will attribute the warming of the near surface atmosphere (the only part that has actually warmed) to the increase in ocean temperature and evaporation.
The land does not store heat and as Bill Illis very sensibly remarked:
“I think everyone could benefit from understanding the greenhouse effect operates at a timescale of hours. It operates at the speed of light and at the speed of quantum physics.
It is just a delay of several hours in the time in takes for the Sun’s energy from the current day and the previous day to escape into space.”
Now, that is good common sense. But is it hours or just minutes? And if any net addition to the surface temperature is lost before sun-up the next day, who cares.
In any case I know in my bones that this summer is just not warm enough.
Allan M,
At 20F, humidity is very low, and perspiration is essentially non-existent. Also, high clouds are not necessarily associated with low altitude humidity but they do produce a lot of back radiation.
@ur momisugly Leif Svalgaard (08:15:03) :
“…any energy CO2 absorbs [most of it coming from below] is immediately re-emitted, half up into space and lost and half downwards back to the surface. The surface thus heats up and warms the air by conduction and convection.”
Wouldn’t it be more correct to say that the ground heats up faster, and/or cools more slowly?
(I know you know all this stuff, but I find it easier to understand if I look at it this way)
If we were at steady state, with energy emitted=energy absorbed, the ground and air would be maxed out and no change would occur. So, every day from sunrise to sometime in the afternoon the earth warms up, and from then till the next sunrise the earth cools. It seems we never achieve ‘steady state’?
So, because we aren’t at steady state, the ground warms. And, it does so faster than it would in a vacuum, or with a radiation transparent gas, presumably because of GHG’s, and it does that because when it re-radiates the sun’s energy back into space, some of that energy is absorbed by the atmosphere and half is re-radiated back to earth. BUT what is re-radiated back is only half of what the earth radiated out, so that energy can’t “warm” the earth.
If you give me two dollars, and I give you back one, you aren’t richer than you were before you gave me the 2, though you are less poor.
http://www.dailymotion.com/video/x44j0l_abbott-costello-the-loan_shortfilms
The same with the energy arriving from the sun. In a fixed time, the earth receives, say 10, of which it gives 2 to the air, and the air gives back 1, so the earth now has 9, as opposed to only 8 if the air didn’t give any back.
The involvement of the air, then, isn’t to warm the ground, but to slow it’s cooling, which will in turn keep the air warmer for a longer time. The question then is, how much longer and what difference does it make? I.e., how much does increased [CO2] slow the heat loss? – And if water vapor does the same thing, and does it so much more effectively than CO2, why are we worried about CO2?
ASIDE – this plot of earth’s climate history…
http://net33.com/images/earth_co2_temp_history_millions.gif
…is often used as a demonstration of how CO2 has been higher in the past, but what strikes me about that figure is how (1) there seems to be a maximum temperature of 22DegC which (2)has NEVER (except for a single blip) been exceeded, and how (3) we are currently nowhere near that max. If that means the earth CAN’T get any hotter than 22DegC, no matter how much CO2 is added to the atmosphere, and (4) the earth has survived that temperature throughout MOST of it’s history, we must question the motives (and/or intelligence?) of those who tell us it will be a disaster.
I’ll grant that perhaps the scientific community does not put as much emphasis in the climate models as do the laymen, including the press and the politicians, do.
Many people feel the term ‘alarmist’ is insulting, but it’s a very proper description of Gore, Lauri David, Sharon Begley and Seth Borenstein. Unfortunately, I’ll have to put that label on Dr. Hansen as well.
Most of these people aren’t scientists, but Hansen is (or at least used to be) as scientist who relies heavily upon his models as the basis for his prophecies of doom.
Laymen also tend to label Mann’s fictitious hockey stick as climate model, which it is not.
Regardless, the evidentiary support for the models is quite weak. I’ll also repeat my assertion that the GC Models forecast global warming because that’s what they are programmed to do.
Mike Borgelt (01:42:52) :
I’m not sure of the mass of CO2 psm compared with Earth but that is more or less irrelevant. The surface gas pressure is more important for the atmospheric energy content psm. Surface pressure on Mars varies wildly but it’s thought to be about 7.0 to 8.0 millibars average. Compare this to 1000 millibars for Earth. The Mars atmosphere has considerably less capacity for energy retention than Earth.
Provided the planetary model is just for Mars then yes we should be able to model what role CO2 plays in it’s climate.
Surface temperature and atmospheric temperature are two different things. According to the source I’m using The Mean surface temperature is -63°C and the Maximum surface temperature 20°C. I find it difficult to imagine that CO2 would add 50 to 25 percent to the surface temps unless we invoke the IPCCs magic molecule hypothesis.
Source for my reply here.
http://www.solarviews.com/eng/mars.htm
AJ Abrams (05:06:05) :
Does the temperature of Venus, Mars Jupiter atmosphere at 1ATM correlate to earth’s average temperature after adjusting for distance from the sun?
We simply do not have the data yet for this. In a couple hundred years when we have temperature records for the other planets the answer will be obvious.
E.M.Smith:
“Does anyone know how they get the CO2 measure to only measure CO2, given that it’s really an IR measure?”
They alternate ‘known samples’ with their in situ readings. They attempt to rid the sample of H2O with an ‘cold trap’.
Moreover, their ‘peak emissivities’ over the narrow absorption bands co-opt the term, derived to express the relation of the ideal black body with real materials, renaming this empirical constant “total emissivity”. The original relation is not maintained in any fashion.