Also of Interest
The temperature at the inner wall surface is lower than the interior room temperature. It is important to maximize absorption, particularly if one is trying to save money by reducing the daily dose of Suboxone. What light source should I use for illumination? Your general analysis is spot on. Thank you Dr Junig!
I am sure it must be possible to get a reasonable estimate of this effect without writing a GCM model and solving radiative transfer equations etc - and I will try to do it. That said - the effect is generally agreed to be around 1 degree maximum.
The alarmists however have tuned the models to include scary feedbacks to pump this up to degrees. I think the evidence is now coming in that this is a gross exaggeration.
Clearly there are vested interests in keeping the scare story going. Your statement above seems to imply that the ppm of CO2 emitting and absorbing photons in the top atmospheric layer represents some sort of gatekeeping effect. The upper atmosphere emits black body IR across a broad spectrum of wavelengths. There is no significant amount of water vapor at that altitude http: Any heat CO2 captures at or above that height would warm the surrounding air and increase the black body radiation of all of the components at that altitude, so the only net effect is a huge decrease of net emission in the CO2 absorption bands, with a corresponding increase across the remainder of the black body spectrum.
If there were any significant observed temperature changes at any level of the atmosphere due to CO2, it would be front page news and there would be no need for climate hysterics to massage surface station temperature data. That is not really true. At a given height the flux of IR upwards is equal to the sum of emissions from all levels below the given height including that directly from the surface, plus the emission from the given level upwards.
The rate of emission depends on the local temperature, and this rate for a given wavelength is determined by the Planck distribution for that temperature. This is usually called local thermodynamic equilibrium. How is the lapse rate maintained? What really happens is that radiative heating absorption from below for any given layer tends to increase the lapse rate away from the adiabatic lapse rate.
This then increases convection to restore the lapse rate to the stable adiabatoc rate. Eventually there are so few absorbing molecules left that the lapse rate peters out. This is essentially the tropopause. It would indeed be very interesting to compare temperature soundings from the s to those of today to see whether the tropopause has really increased in height as a result of higher CO2 concentrations!
Nitrogen and Oxygen are not magically exempt from emitting thermal radiation. ALL matter loses heat through thermal radiation. But even taking your position that only the greenhouse gases are significant sources of radiation, then my statement is still correct. The emission profile from any layer of atmosphere would be exactly the same as the aggregate absorption profile of the greenhouse gases in that layer.
The profile looking downward from 30, ft. On first glance, that big opaque spot around 15 um looking down from space looks worrisome. But all it is showing is that the average temperature of the CO2 visible from space is much cooler than the average temperature of most all the other gases.
So yes, there is heat being emitted by CO2 in the colder layers above those containing water vapor. There is too much transfer of heat to other gases and therefore other outgoing wavelengths. CO2 has been in or near total saturation from about ppm. Whereas any time you add heat you increase the water vapor in the atmosphere on a water planet. Thanks for the timely and thoughtful reply, but, I have to disagree:. Yes, I have seen this argument for increased CO2 impact before.
I have dismissed itsas specious, but, have not worked it out in detail. It seems to display a failure to understand the basic thermodynamics of atmospheric CO2 radiations, especially with regard to the certain fact that each molecule of CO2 radiates isotropically. What gets absorbed by CO2, regardless of altitude, cannot be more gone than gone.
I will try to work that all out and get back to you. But that is moot anyway because we can go back to my approx. I am left still wondering how arguments such as you have referenced can still be made when they amount to claiming that the differential impact of CO2 increases as the amount of CO2 increases; that 1XCO2 causes less warming than does going from 1X to 2X.
What is your ref. I have seen several versions of it and would like to analyze the particular one you refer to. Even your own site, wherein I find. I am not saying that such does not exist. I am merely saying that I cannot find it, and, should it exist, I would greatly appreciate having it pointed out. Although the human contribution to outgoing CO2 flux is small why-the-co2-increase-is-man-made-part CO2 concentrations have been increasing slowly for 50 years as confirmed by measured in Maona Loa.
Although there still may also be a natural increase in CO2 in the atmosphere caused by the ocean warming, most people are convinced that the main component is man. It is a cumulative effect which will eventually reverse when in years fossil fuels run out. Thereafter CO2 levels will likely fall.
However all this does not mean that AGW is proved. An observed relatively minor increases in global temperatures of about 0. This is still just a theory which needs experimental evidence. There are other drivers of climate apart from CO2 and climate feedbacks are unproven and could even be negative.
There is no physical evidence of this at all. Simple logic based on the conservation of matter says that it is mathematically impossible. This absurd claim that somehow the atmosphere selects out fossil fuel CO2 from natural CO2 is key to the whole AGW argument and is made repeatedly.
The most rudimentary knowledge of physical chemistry and of statistical thermodynamics shows it to be patently absurd. You have a tank filling from two streams of water, stream A and stream B. In the tank the streams become completely mixed. Do you say, in contradiction to the 2nd Law, that somehow, in the tank's mixture of A and B, B separates from A and the tank magically accumulates water that came from B in preference to water that came from A?
All that matters is how long it takes to reach equilibrium again if the amount exchanged between the biosphere and the atmosphere each year increases by a small amount. Left to itself the Earth would return to an equilibrium concentration say after a massive volcanic eruption.
All that would happen is that vegetation and plancton would bloom in the medium term to absorb any small excess. I have read everything on the subject including Dr. If we merely double CO2 concentrations, then the added CO2 will mix within the existing atmosphere.
It does not seem like this added amount can make much of a difference in the point in the upper atmosphere where newly radiated infrared energy can escape? If this band did grow in height, then the argument stated would make sense? Does the air pressure at sea level change? What does make sense is that the added CO2 leads to additional thermal energy at the lower altitudes and this eventually mixes throughout the atmosphere. This energy is absorbed within lower altitude band.
The fact that the entire atmosphere is opaque in these bands is not relevant to the process. The lower denser air gets warmer first. I agree that what really matters is whether the effective height in the atmosphere where IR radiation escapes into space is the crucial factor.
It is always assumed that extra CO2 diffuses rapidly isotropically throughout the atmosphere. I also find this difficult to believe have not seen any data showing the actual increase of CO2 levels at different heights. How water reacts to forcing from CO2 is crucial to the whole debate. Does extra evaporation lead to more clouds thereby increasing albedo?
Do more clouds produce more rain leading to lower H2O levels in the upper atmosphere? If so then H2O feedback is negative and there will be just 0. How can emissions from China be immediately observed at the South Pole. I think that the real reason for seasonal changes is the assymetry of water coverage between SH and NH. This is more likely the cause of seasonal changes and long term CO2 levels are driven by Ocean dynamics.
Clive, Thank you for reviewing these points. I am a firm believer that anthrogenic factors have given rise to much of the recent global increase in temperature. I am disappointed how virulent comments become when one asks to connect the dots on the global warming subject.
I have been trying to understand the large attribution of the effect of CO2 on the forcing function for warming. I had to come to a similar conclusion that the widening of the absorption band for the higher concentration fell far short of the 1.
You struck a chord descibing the attribution as a circular argument. My inclination is that the CO2 concentration is a clear data set that shows the effect of industrialization, etc. The global temperature rise follows that rise with a reasonable correlation and the infrared absorption can plausibly describe an increase.
My opinion I know the expressions is that a reasonable correlation can be drawn using the global population, the global power consumption which contributes CO2 , the world cattle population, etc in place of the CO2 concentration and come up with the same conclusions. I fear the environmentmental engineering projects spending a great deal of effort and energy at carbon sequestration, etc having unintended consequences but having no effect on the temperature rise.
I agree that the indoctrination of children that climate change is dangerous and caused by our evil lifestyle is unproductive. Clive, I truly appreciate the effort you put into deriving this. I have a very hard time accepting science which not grounded in classical or in this case, quantum physics. I look forward to following your additional insights into other physical explanations of climate complexities.
I have agraph which plots temperature increments against increments of CO2 in ppm starting at 20ppm and goes to ppm with the temperature increments declining exponentially.
Which means only the first 20ppm of CO2 has a significant affect. I calculated the temperature response to CO2 levels using radiative transfer. I got following result:. Anthony Watts has a version of this bar chart on his page, Jo Nova on hers. Clive provides the data in the more conventional format.
From simply the concentration of CO2, it is an easy point to make that the atmosphere is optically opaque to infrared at concentrations well below any historical levels. Therefore all the heat radiating from the surface of the earth is absorbed by the small amount of CO2 whether it is or or ppm. The point is then made that additional CO2 does not contribute anything to warming the atmosphere. Unfortunately, as Clive has described, the effect of CO2 on warming is a consequence of the temperature gradient in the atmosphere.
At the thin, outer layers of the atmosphere, the number of atoms in a given volume result in it being effectively transparent. As you go deeper into the atmosphere, the density rises to the point where it is effectively opaque at the CO2 infrared wavelengths.
The CO2 in the atmosphere at this level would radiate out to space and below this level it would be absorbed or reflected within the atmosphere. In the blog post referenced above, Clive describes the exact physics of the phenomenon which, in turn, can be converted into the plot of surface temperature versus concentration, below.
Thank you Clive, and thank all of you who have commented. The question is cause, effect, or co-indicator and of course subtler feedbacks. I found a Watts per Sq M number the range I found was 1.
Surface area of the earth: Heck, for that mater let us use 10 Watts per Sq. I started wondering how does that compare to the heat energy released from hydrocarbons burning. First I just looked at total electricity production. The numbers were easy to find. The production of electricity in was 20,TWh. Electricity is not the only hydrocarbon source of heat, and atmospheric CO2 is only an averaged indication of hydrocarbon use.
I found some graphs. The heat produced by burning hydrocarbons would be offset by the fact that more sunlight will be absorbed by plants as the CO2 goes up, and the sugar production by plants is a cooling process. In a stable planet this would be the case, however there has simultaneously been a process of deforestation and desertification going on.
Unless we know where the has been an increase or decrease in planetry biomass it is not safe to assume that this relationship holds. I made this video that proves that catastrophic global warming will never happen, and that climate sensitivity is much lower than some claim:. I have not read all these comments, so possibly another has written what I now write here.
Not to put too fine a point on it, but the statement that the effective radiating layer achieved by adding CO2 occurs at a higher and thus lower temperature is inconsistent with fundamental physics. The input is defined by the Sun and its distance from the Earth, the Earth simply responds. Supposedly, such detailed calculations are made routinely with every climate model, but how accurately they are made is opaque, perhaps even to the modeler, who may himself not understand the details. After all, he is likely an expert on climate, not on spectroscopy.
Reading this and dozens of others climate posts I think all can agree with W. Clive, as a science person I have some general points that I think other science people might be asking. If the answer to that is near yes, considering that all agree that additive CO2 has fast diminishing sensitivity if not already negligible, how can models be prediction more rise in the next years than we saw in the last ?
If scientists are really expecting water vapor positive feedback to amplify warming on what hypotheses did or climate stabilize in past inter-glacial periods at current temperature or warmer by several degrees than present, rather than run away to a Venus. Some of these periods significantly gained CO2 after their warm stabilization and nevertheless cascaded back into glaciation with high CO2 that only slowly diminished thousands of years later.
Do you agree with any of this physics? Also, if higher temp puts more vapor in the air there will not only be more clouds but they will be more transpiration of heat, and the vapor can absorb the CO2 heat and relay it out in lower IR frequencies that are CO2 transparent. Perhaps these feedbacks and others are what has saved life from frying in the last 2 billion years. Models assume natural forcing is mostly insignificant except volcanoes, and that all net forcing since is anthropogenic.
Amazingly these efts in the models cancel out to result in an essentially simple CO2 log forcing! Doubling CO2 and basic physics eliquidassets.
Your analysis is very helpful. But — I want to question some specific text — and you can perhaps rewrite the sentence with other wording to help me better understand. In Argument 1, you write: I am completely lost. I assume that some part of the sentence or paragraph is missing. You are taking the effort to tell the reader not to forget some important point — but the point is lost, due to the sentence making no sense. In addition Cloud cover must depend on evaporation reducing albedo so the end result is complex and not included in models.
Wording poor I agree. I woke up one morning a few months ago and realised that assumptions about CO2 and global warming could not be right. I reasoned that CO2 makes up a tiny fraction of the atmosphere and that the atmosphere is dwarfed by the oceans, so it is not possible for CO2 to have such an enormous effect. This would represent preindustrial levels of CO2. An increase in CO2 levels to 0.
Finding objective information about climate and atmospheric heat has proved difficult, so I am grateful to everyone in this forum for contributions. The principles of physics hold, so now I can the science my students. There is a very simple problem with your math: Our satellite measurements of the stratosphere are quite good over the past 25 years or so anyway.
Barry, nobody is monitoring what the temp in the stratosphere is otherwise people would have known that: Pagan beliefs are for confusing people, not to inform. Here is the truth: More research on the lines of Harries Imperial College could provide a more definitive answer. Just Google Harries spectrum. I have just read an Harris article, but do not know if it is the salient one. I agree that this is the sort of physics that is important and that understanding what happens to energy in the atmosphere is the crux, but would suggest that drawing conclusions from the outgoing spectrum is flawed.
If I look at my bank balance, it tells me nothing about income or expenditure. Similarly analysing outgoing radiation tells me nothing about incoming radiation which we know fluctuates , or how that radiation was changed before readmittance.
I would love to see a complete energy audit of what happens to all energy coming to the earth and emanating from geophysical processes on the earth. Energy is mutable in systems, so energy of one wavelength once absorbed is often re-emitted in another wavelength e. If anyone knows of analysis of this nature, I would love to read it. What happens instead in that basic physical model is that:.
But then the article goes on to explain that the temperature drop at the higher radiating altitude does not actually happen, since surface temperature increases. To summarize results of the basic model: CO2 concentration doubles through the atmosphere; surface temperature goes up, and the earth radiates more as a result; this extra radiation gets absorbed by the lower half of the troposphere; so in the upper section of the troposphere, nothing has changed temperature-wise — the effective radiating temperature is still the same in equilibrium since it has to compensate the constant amount coming in from the sun.
Rayleigh or Mie scattering which give us blue sky. Rather, it appears to be the following process. The fundamental element is absorption and re-emission of infrared radiation by a carbon dioxide molecules as described and illustrated here: The re-emitted radiation then encounters another carbon dioxide molecule and the process is repeated multiple times. In a secondary process, a carbon dioxide molecule, after it has absorbed an infrared photon and started vibrating, but before it has the chance to give up that energy by re-emission, may collide with another gas molecule, transferring the energy to it, in kinetic form, and raising the temperature of the gas.
The body of gas, like all hot bodies, emits radiation, which increases with temperature. However, this is not the same phenomenon as direct re-emission by the carbon dioxide molecule. The extent of this secondary process is not clear, i. It then re-emits far infrared radiation again — upwards only. The process is repeated multiple times in theory, an infinite number. Each time, half the amount of radiation comes back down to earth, so there is a convergent geometric series. This seems a more plausible model than radiation suddenly reaching a critical height at which it can escape into space.
Although radiative energy is transferred upwards through collisions, this is not the reason for the lapse rate. The lapse rate is caused by convection. In a sense the atmosphere is a heat engine powered by the sun. Heat from the surface flows through the atmosphere to the tropopause where it radiates to space. The amount of CO2 and water vapour determines the height at which the mean free path for absorption is larger than the atmosphere above it.
That average height is at K to balance energy in and out. If the height increases then so must the surface temperature.
All things equal it increases by about 1C for each doubling of CO2. So if CO2 quadrupled to over ppm the tee rapture would rise by 2C. Richard and Clive thanks for posts. Can anyone direct me to original papers about energy transfers in gas, particularly the atmosphere. At a basic level what happens to an energised gas molecule? How long does an individual molecule retain energy and how much of that energy is dissipated via collisions and how much radiated?
If a CO2 molecule collides with an N2 molecule how much energy transfers to the N2 molecule and how is that transferred energy then dissipated? There must be half lives for energy retention. Does energy transferred to N2 then eventually radiate to space at a different frequency to CO2 frequency?
My understanding is that in a gas energy principally transfers through collisions and only small proportions through radiation, so given the ratio of CO2 to N2 and O2 it would seem likely that most radiative energy absorbed by CO2 would quickly transfer to other molecules and ultimately be re-emitted in another wavelength?
Another thought I have had since it has been such a cold May and June in Scotland is that since convection is the principal mechanism for energy transfers in the atmosphere, any heating in the lower atmosphere will be counter balanced by cold currents descending from the upper atmosphere. Rather than warming being a consequence of heating, more wind would be the effect? Is the earth getting windier? The first comment to make is that we never hear this crucial explanation in the popular descriptions of the greenhouse effect.
That is, however, because those communicating with the public have concluded, probably correctly, that their knowledge of science and their capacity for focus is SO meager that the correction explanation would be lose of them. I have also inserted some words in square brackets to provide a bit more explanation. A common fallacy in thinking about the effect of doubled CO2 on climate is to assume that the additional greenhouse gas warms the surface by leaving the atmospheric temperature unchanged, but increasing the downward radiation into the surface by making the atmosphere a better infrared emitter.
A corollary of this fallacy would be that increasing CO2 would not increase temperature of the lower atmosphere if the lower atmosphere is already essentially opaque in the infrared, as is nearly the case in the tropics today, owning to the high water vapor content of the boundary layer.
This throws the top-of-atmosphere budget out of balance, and the atmosphere must warm-up in order to restore [radiative] balance [due to the Blackbody Law]. The increased temperature of the whole troposphere increases all the energy fluxes into the surface, not just the radiative fluxes. Further, if one is in a regime where the surface fluxes tightly couple the surface temperatures to the overlying air temperature, there is no need to explicitly consider the surface balance in determining how much the surface warms.
Surface and overlying atmosphere simply warm in concert, and the trop-of-atmosphere balance rules the roost. Ray also goes on to point out that Arrhenius got this all right, as did Callendar and Plass , and then Manabe Ray does not point it out, but I will: Others did not, e. Plass did not get it right. It would appear to me to be very helpful to describe the radiative effect of additional ppm CO2 or so based on the 5 W per m2, as a percentage of the roughly W per m2 of incident solar radiation e.
Many people have a feeling for percentages if not all the science behind global climate change and this may help a debate. That is about the same as the energy density removed from the atmosphere by a wind farm. In that respect it is noticeable how the the largest cloud cover is over the warmest tropical oceans in summer months. The physics explanation is that tropospheric carbon dioxide heat blankets exponentially double in halving time increments.
The greenhouse effect is cumulative. Heat is trapped between the ocean surface and the tropospheric heat blankets. CO2 loads the gun; the solar cycle pulls the trigger. Since the millennium, the CO2 heat blanket effect dominates over the solar cycle heat input.
Oceans are stratified with warm freshwater over cold salty water; heated from above, there is no convection.
Wind-driven and geostrophic near-surface currents, in eleven counter-rotating ocean gyres, transport heat and nutrients polewards. At high latitudes, tropical-origin seawater basal melts floating ice. Freeze-brine carries cold salty water to abyssal depths. This is different from the ocean conveyor model. Land evaporation, dependent on windspeed and relative humidity, is mis-used in current climate models. On this basis, a recent peer-reviewed publication computed equatorial evaporation equal at midnight and midday!
This is based on century-long daily sea surface temperature records. It was found on a student cruise between Tahiti and Hawaii where surface and 3m temperatures and salinities were measured hourly. A sign change in the seawater density equation reverses the impact of increasing salinity on density.
By a quirk in the seawater density equation water warmer than 36 parts per thousand and 28C does not sink. It forms a westward thickening subsurface layer along the equator.
It contributes to the 30C western and eastern Pacific warm pools. Climate sensitivity is a nonsense. The doubling CO2 heat trap is also seen in the exponential doubling decrease in Arctic floating ice volumes. The carbon dioxide heat trap is far more serious than current thinking assumes. Hopefully this is wrong. It is hard to argue for many long daily sea surface temperature and salinity measurements and ice volumes The latest full text articles are online at: Let me point out that the amount of electromagnetic energy, whether incoming or outgoing, converted into atmospheric heating next to the major portion which is via surface contact is many orders of magnitude greater for H2O in the form of vapour or liquid than by CO2.
The absorption bandwidth for a water droplet is, dependent on size, virtually continuous. As increasing earth temperature increases both forms of H2O, it is clear the greenhouse gas theory does not need CO2 to cause global warming! Also, more water vapour means more cloud cover — and incidentally more reflection and re-radiation as well. It would also add to the discussion to note that a blanket does not keep you warm in any way which is related to the atmosphere, it prevents the energy generated internally in the body from escaping by a thermal barrier, that is what raises bodily temperature.
But only for energy radiated by CO2. Hardly a significant change. This changes the wavelength of the vibrational modes. CO2, H2O and O3 lie all within the thermal planck spectrum for earth temperatures whereas O2 and N2 are are much shorter wavelengths — typical of those on the surface of the sun. They emit and absorb IR photons in thermal equilibrium with the surrounding air molecules. The temperature at a given height up to about 10, m is determined by thermodynamics — the adiabatic moist lapse rate and not by radiation.
This scale is set by the surface temperature. This cools off the top of the troposphere and sets the scale. The earth remains approximately in energy balance so that the energy lost to space equals the absorbed incoming solar radiation. The surface temperature approximately is then determined by the lapse rate. For the atmosphere to radiate from a higher altitude in general, due to an increase in the number of molecules in the atmosphere, its pressure would have gone up.
All mater above 0K emits heat energy, not just CO2, so But none the less the atmosphere emits upwards as a black body at all the frequencies you would expect of a black body at that temperature. Only some of those frequencies are impacted by CO2 so I believe what I say is valid; that either atmospheric pressure has gone up in line with the entire atmosphere emitting from a higher, and colder level, or it is only CO2 molecules that are now emitting from higher and colder levels, in which case any increase in heat retention must be relative to the increase in only CO2.
Because of conversation depth, replying to myself ConcernedCitizen: Not so for the outgoing. And, also as Clive described, the only part of the atmosphere that radiates and dumps energy is the top. The partial pressure of CO2 has gone up because we have emitted more, but it is such a small percentage of atmosphere that its effect upon atmospheric pressure is negligible compared to fluctuations in lapse rate and weather.
My understanding of this theory is that by adding CO2 we have thickened the atmosphere, causing it to radiate from a higher, colder altitude. This would of course entail an increase in surface pressure. For instance, if the top of a square meter column of air rises, but the density of the air within it goes down, there is a way that can be done so that the total mass of the air in the column does not change, and so there would be no pressure change.
If a photon emitted 9. The emission of a photon by a CO2 molecule can be done by two ways, correct me if I am wrong: CO2 is removing energy in this case, taking ke, converting it to a photon, and emitting it out to space.
In the first case the energy in the photon has to be the same when its emitted, so it is immaterial whether the photon is absorbed ad emitted by a hundred CO2 molecules arranged vertically, passing the photon up and out to space.
As I wrote, there will be some pressure change due to increases in CO2, albeit small. Sure, because the per unit volume amount of CO2 over all the atmosphere is higher. Accordingly, the emissive layer that succeeds is closer to the edge where there is no CO2. How does a photon, emitted by a CO2 molecule at say 9.
It depends on the wavelength energy of the photon. Most simply escape directly to space. Only a few in the central 15 micron line are absorbed by CO2 molecules higher up. None of this changes the temperature of the emitting layer which is dominated by the thermal energy of the surrounding air molecules. Eventually radiation loss to space becomes large enough to stop convection. That is the tropopause. I am not sure the about the source of confusion CC is experiencing.
The top of atmosphere concept is elucidating for me. For IR wavelengths within the absorption and transmission bands, the atmosphere will attenuate the IR photons from the surface to space as a function of the concentration. CO2 is concentrated enough that the atmosphere would appear opaque. Looking from space the surface features of the earth would be obscured—the earth would look like a gaseous sphere. This is the only energy that can escape from earth to space of that wavelength.
As the concentration of the emitting gas increases, the TOA is extended higher in the atmosphere. Thermal equilibrium at that altitude is at a lower temperature so less IR is transmitted. I think this is the only correct way to think about the GHE. Using this simple model I was able to calculated the radiative forcing of CO2, and understand the IR spectrum as measured from space.
You migfht be interested in these posts. CO2 Greenhouse effect demystified. Convection and Latent heat drive the thermodynamics of heat loss from the surface and generate the lapse rate.
Greenhouse gases just set the scale height of radiative cooling to space. Back radiation is a complete red herring which explains nothing. I think the co2 saturation story should be or could be the main scientific base to start a global campaing againts agw, if not too late.
I am not strong enough scientificly to detect technical flaw to this thread. Here in Québec our Prime Minister returned from Paris with totally new green policy, stopping any emerging oil exploration and full of new green taxing policy.
I thing we can stop, or at least modify, the trend. But we must start with soud scientific arguments like I founb here. Knut Angstrom was a relative of the great Angstrom, but not the same. There are two great links at:. Almost all scientific paper I read take for granted ipcc co2 radiative forcing, witch is suspected to be originating from a circular processus.
The way i proceed is examine arguments thoses whose views differ from ipcc one and try to judge at merit. Not an easy task, but quite interesting. Thank you for links reference. A good thing is to check out online courses, and textbooks. The reason why CO2 forcing only grows logarithmically with concentration is because the central absorption lines are already saturated.
These are spectra I calculated using this model. Yes, and, uh, so? Did not say central lines contributed any more. But, facts are, especially around per cm, there are lots and lots of lines.
That was a detail I deferred in my comment. And, if you will recall, only half of the warming is CO2. The other half is from knock-on effects from water vapor, due to greater carrying capacity of atmosphere.
Reference to text cited earlier: I agree with you. This book is a masterpiece. I have it at home — but it is perhaps a bit heavy for your average punter. Calculating CO2 forcing is not simple nor straightforward. But yes it has been done and the answer is known.
Even then you have to make some assumptions such as a standard lapse rate. Feedbacks are a second order effect whose effects are not known. What about the umbrella effect? What is the cooling effect? However, as you indicate there should be reduced sensitivity with increasing CO2, so the likely forcing should be less! Moreover, have you considered the reduction in incoming solar near IR. Thanks for your consideration and ….
And to the degree the basic model back of the envelope one, not GCMs fits the data, which it does pretty well, I call that a win. The wave number of corresponds to a wavelength of 15 microns. Where there is no absorption there is NO emmission.
The heat of Venus and the climate on Venus may be understood if you consider the strength of the emr including gamma rays to be many times greater than earth because of its closeness to the sun. Then look at the slowness of the orbit. On earth near the equator a 48 hour day might cause temperatures above the boiling of water. On venus with a much stronger emr, the day is times as long as ours. Some rocks actually boil.
Because Venus is large enough to hold an atmosphere and half of the planet is not exposed to the sun, the enormous winds between hot and cold areas are created. Gamma rays and Xrays are absorbed by solids. The gases are a side effect. What gases absorb is irrelevant. What have you learned about the fudge factor? Is it derived from the cirular argument expressed above? No it is not a circular argument -I got that wrong.
I finally ended up writing my own radiative transfer code to derive the greenhouse effect. I was then able to get about the same logarithmic result. Any doubts about Climate Change? It does not necessarily follow. You must specify the mechanism by which the level shifts higher in the atmosphere. Shifting it higher in the atmosphere requires energy. Moreover, it would be a positive feedback — increasing temperature, lofting the CO2 higher, increasing the temperature, and so on.
Eventually, the CO2 would achieve escape velocity, and launch itself beyond Earthly influence. All that really says is that the density of air falls with height. So if CO2 as a percentage of air rises from 0.
This is still an argument lacking a mechanism. Density alone does not provide height. If you took the Sun away, the entire atmosphere would collapse into a solid mass at the surface — very dense, in relative terms, but with hardly any height at all.
You must have an energy source to sustain the particles at higher altitude. The diurnal bulge is quite sensitive to solar activity, with the center of mass extending further outward by hundreds of km when solar activity is high see figure 2. The extra energy from the Sun is what sustains the atmosphere at those higher altitudes. Clive — thank you for spelling out the crux of the AGM argument as I understand your explanation — a decrease in radiative energy loss with decreasing T as one goes higher in the atmosphere.
What about the decrease in absorption that occurs as the temperature drops because of a reduction in doppler broadening sharpening of the IR absorption band? However, I found an archived copy of it here: It seems that one has to do the calculation to get a good appreciation of how sensitive the IR absorption is to [CO2]. I got frustrated and so I made up my own simple model see appendix below.
It is immediately clear from the solutions to the rate equations that the value of the reaction cross-section for IR absorption per molecule of CO2 is critical as one might expect. It is clear that the absorption is not saturated in the wings of the absorption bands for increasingly smaller absorption cross-sections. There will be a range of cross-section values that are important from the perspective of additional photon absorption for the levels of [CO2] that are relevant to the atmosphere I should determine that sometime.
My problem is getting good, tabulated, cross-section data for the IR wavelengths of interest. Naturally, the IR absorption cross-section spectra will also vary with height in the atmosphere temperature and pressure dependence bur even values at STP will be useful for bounding the assessment problem. Can anyone point me to a good source of easily accessible tabulated cross-section data? Appendix — The differential equations describing the steady-state passage and dissipation of photons in the atmosphere per cubic metre are: P0 and P1 are the numbers of photons that are free and bound respectively.
Solution of these equations gives the number of free photons as a function of height. It is assumed that any photon that is free at km is lost to outer space. I am not convinced about the black-body radiation argument: Being a failed physicist I would want to see some experimental data showing the effect of temperature on photon emission — does that exist?
This is the correct approach that you describe. The important ones on earth are the vibrational excitation quantum lines in the 15 micron band. I think the local thermodynamic equilibrium of the atmosphere is important because CO2 molecules can also be excited by collisions. Here is my simple picture. The surface radiates as a black body at temperature Ts.
Only triatomic molecules have vibrational quantum excitation modes in the Infrared. H2O has a rather broad wavelength spectra whereas CO2 has just 3 main bands, but on earth only the 15 micron band is significant. Gravity generates an exponential falloff of density with height. By inhibiting the direct radiative heat loss from the surface to space, the atmosphere generates itself a lapse rate.
This is because convection begins to move heat up through the lower atmosphere more efficiently than radiation. Only with a convective atmosphere under gravity can the greenhouse effect work. For each wavelength in the CO2 band there is an effective emission height where the mean-free path for IR photons is greater than all overlying layers. IR photons from this level radiate directly to space. Likewise for O3, although Clouds complicate H2O.
These actually get smeared out by pressure broadening. The central line cross-section is so high that it currently emits from the stratosphere where temperature increases with height. This means that this wavelength actually cools the planet with increasing CO2 levels. You can actually see this in Nimbus spectra. A simple excel spreadsheet model that approximates the GHE can be downloaded from this post.
You have helped a great deal, but I still have questions. As you stated, the absorption length for the current concentration of CO2 is around 25 meters. What happens to the thermalized energy? I would guess convection and water vapor transport it upwards. I understand that radiation is the only way for all this energy to exit to space. Water vapor must be a major radiator. Any help tying this all together would be appreciated. I think the trick is the following.
This is because by far the easiest way to move heat upwards is through evaporation from the oceans and convection to where it can radiate freely. That is why we have thunderstorms and weather due to Coriolis forces.
Net radiative losses occur at high latitudes to offset net absorption in the equator. As CO2 increases the tropopause should get higher.
However, as you rightly say water vapour is the ace card. No-one really knows how clouds and H2O will play out. Clouds reduce albedo cooling the earth, whereas H2O water vapour enhances the greenhouse effect. My hunch is that water is the ultimate negative feedback because otherwise the oceans would have boiled away billions of years ago.
The greenhouse effect works because the lapse rate usually makes the atmosphere cooler at any location than the radiation profile it is being exposed to. This gradient continues to the tropospause where Clive rightly points out that the stratosphere temperature then increases with height, but only during the daytime. At night the lapse rate would continue cooler at higher elevation to space.
I agree, however, that water transpiration, clouds and convection dominate the regulation of atmospheric temperature. The areas where there is little water vapor, like at the poles, deserts and the tropopause, then CO2 can have an amplified role. There is still matching emission, but just from GHG in equilibrium with ambient, not matched to the particular absorption event.
It says emissivity equals absorptivity. What is actually absorbed and emitted depends on incident intensity for absorption and temperature for emission. That sounds like what I tried to articulate. The emission profile is identical to the absorption profile when there is a local thermal equilibrium. Temperature, of course, is a measure of mean molecular kinetic energy. This is a property of the gas as a whole, not of a molecule. The higher the gas pressure the more convection collisions will dominate over radiation to determine an instantaneous molecular state.
Imagine a gas at K sealed within a perfectly insulated and infinitely thin balloon. Now transport the ballon into outer space. If the gas is argon then it will remain at K for ever. However, if the gas contains. The Infrared Spectrum of Argon R. You are of course correct: A building with no windows and no CO2… Consider a building with modest insulation that is heated at a constant rate from inside. Assume that the building is insulated equally well everywhere resulting in a uniform temperature of the outer surface.
In steady state there is a higher temperature inside the building compared to the fixed exterior temperature. The temperature at the outer wall surface is higher than the exterior temperature. The temperature at the inner wall surface is lower than the interior room temperature. These temperature differences maintain an export of heat at the same rate at which the interior is heated. A building with no windows but with CO2… If now the heat resistance CO2 of the walls is instantaneously increased, at first the outer surface temperature drops and the inner surface temperature rises, while the interior temperature is still unchanged.
In this situation less heat escapes from the building than is released by the indoor heating system. The imbalance leads to a slow ascent of the interior temperature that continues until the outer surface temperature returns to its original value. The initial cooling of the outer surface temperature is analogous to the quasi-instantaneous cooling that occurs in the upper half of the atmosphere. The cooling is only transient and has no permanent component.
A building with windows and no CO2… Assuming instead that there are parts of the building envelope that are more weakly insulated than the remainder, as is typically the case with thin glass windows. The outer surface temperature in equilibrium is higher at the windows than it is at the walls.
A larger fraction of the total energy escapes via the windows compared to how much they contribute to the total area of the building envelope. The outer surface temperature of the wall is again diminished instantly. But once in the new equilibrium, even more energy escapes through the windows and less through the walls.
The permanent cooling of the outer surface temperature of the walls is analogous to the cooling in the higher atmosphere. An insulated building undergoing heating illustrates the blocking effect of CO2-induced mid to upper atmospheric cooling. The separation between walls and windows physically is analogous to the separation into opaque and transparent radiation bands spectrally, and energy transfer as heat conduction in the walls of a building is analogous to radiation in the atmosphere.
An analogy for the blocking effect from … http: Clive, perhaps you have found another reference to the one you linked to in your Feb 4, explanation of radiative forcing If you cannot find another source with the same equation, and since the one you cited no longer exists, then what basis for the equation you cited can you use to substantiate its validity and foundation? I have thus since then stored on my computer the actual authors, their university or research institutes, dates of information provided and the basis of references the authors use.
Though more time consuming and tedious on my part I at least have my original source to refer to if data or basis is questioned or if I find future reason to question or compare it with other sources I find later. You have a dead link on this page: All of that energy has to escape back out to space. The only place for it to escape is back out through the atmosphere.
Heat flow between the surface of the earth and the top of the atmosphere is related to the temperature difference between those points, and also dependent on the raidative resistance of the air layer between them. The atmosphere has high radiative resistance due to greenhouse gasses. So the temperature inside the lower atmosphere has to rise to keep the heat flowing out through the top at the same rate it is coming in — creating a large temperature drop across the 10 miles of atmosphere.
That results in a lapse rate of temperature, i. Without the atmosphere, the heat would simply escape by raidating directly to space, and the temperature of the surface would be lower.
The outside of a panel of glass of a greenhouse is hot to touch and even hotter on the inside. The atmosphere is not thin and solid like glass. It is thick, compressible and convective like gas. Climate is a long term average of many short term cyclical processes and that makes it hard to assign cause to effect. Doubling CO2 and basic physics — Climate Collections. Is there a source for the length of the free path for other re-radiating gases, for example H2O?
The number 25m is for CO2 near the surface, and is just an average value over the 15 micron emission. The CO2 molecule gets thermally excited into s of quantum vibrational modes. These then decay emitting a photon. Those moving upwards are absorbed by other CO2 molecules and the process is repeated until the air becomes so thin that for a given wavelength the photon escapes into space carrying energy. This is the effective emission height for that wavelength.
I calculated this here in this post: H2O is more complicated and there is a wide band of emission frequencies. It is a much more effective greenhouse gas, but most water vapour is in the lower atmosphere. There is also the complexity of evaporation latent heat , cloud formation etc. Water vapour also changes the lapse rate reducing CO2 greenhouse effect.
The full effects of H2O on the climate are still not fully understood! Hello Clive, thanks for your answer. The following paper finds a free path for a photon before absorption by CO2 at the surface of Because of the high density of water vapor at surface level, the free path for water vapor must be much shorter.
In an absorbance experiment, light is attenuated not only by the solution, but also by the solvent and reflections from every interface in the light path.
In the case of a cuvette-based measurement, the appropriate reference would be the cuvette filled with just the solvent. Ensure that no dust or fingerprints are on the transmitting surfaces, as these will add scatter and absorbance signatures of their own.
If the sample is in a buffer solution, the reference must be the buffer solution with no sample present. In dual beam spectrophotometers, the reference solution would be placed in a reference slot for direct comparison for the duration of the experiment. When using an Ocean Optics spectrometer, you simply store a reference spectrum and then replace the cuvette with the sample to be measured.
The software takes care of subtracting the reference spectrum, as well as applying any other correction factors that are selected. It is a good idea to look at the reference solution periodically as a gauge of system drift. Drift can be caused by lamp intensity variations, changes in temperature, or even changes in the reference solution depending on the chemistry.
It takes very little time to take a new dark and a new reference measurement, so it is good practice to do so frequently while making measurements. Do I need an absorbance standard? Absorbance standards are used to verify the accuracy and consistency of response of an absorbance system relative to NIST-traceable standards.
This is required as part of quality control procedures in biomedical and pharmaceutical industries, as well as the food and beverage, petrochemical, semiconductor, and pulp and paper industries. Neutral density filters can be used for the same purpose, but do not assess factors like staff ability to prepare stock solutions, liquid and cuvette handling procedures, or the quality of cuvettes being used.
They are provided with absorbance charts for each solution, collected using NIST-calibrated instruments. Why is stray light important? Stray light refers to any light that reaches the detector via scattering. This can include light that did not travel through the sample, or photons of the wrong wavelength hitting a pixel. Stray light has many sources, including ambient light that leaks into the instrument, light that bypasses the sample like light that gets wave-guided through a cuvette wall , higher-order diffraction from the grating, and scattering from optical surfaces inside the spectrometer.
Even when a spectrophotometer is designed to minimize stray light effects, there is a physical limit imposed by the zero-order scattering of the grating.
Fortunately the stray light of an instrument can be measured and a correction applied in software. Stray light I s always appears as additional signal in both the sample I and reference I 0 measurement in the absorbance equation:. When the absorbance equals zero, like when the reference solution is inserted as the sample, the stray light terms cancel out.
As absorbance increases, I decreases and stray light begins to affect the absorbance value, reducing it from the true value. At very low light levels, the stray light, I s , approaches or exceeds the transmitted light, I , and becomes the dominant term. At this point, it becomes the limiting factor for the absorbance that can be measured. When the stray light of a system is quantified, it is usually expressed as a percentage of the reference value. Our spectrometer models with the lowest stray light are the Torus 0.
As shown in the figure below, absorbance readings in the 0. Since stray light is a property of both the spectrometer and of the light source used, it must be characterized at the system level. One method is to measure absorbance using a highly concentrated sample. For example, if the concentrated sample is known to have an absorbance near 5, then the light reaching the detector would be reduced by a factor of 10, Any light measured above this level could be considered stray light.
A longpass filter can also be used, as these are designed to block by 5 or more orders of magnitude at the shorter wavelengths. When using an Ocean Optics spectrometer, the stray light value can be entered into the software and then scaled and subtracted from all other readings.
Note that stray light varies with wavelength. Near infrared wavelengths often contribute more than others to stray light, so using a shortpass filter prior to the spectrometer may help to reduce the amount of stray light reaching the spectrometer detector. Reducing stray light can also be as simple as turning off the tungsten halogen light source when working at wavelengths covered by the deuterium portion of the light source, or using a bandpass filter to limit the light source to illumination over only the wavelength range of interest.
How do I use Beer's Law to calculate concentration or extinction coefficient? This can also help to remove errors that are particular to the experiment, the equipment, or the particular set of samples being studied. First, carefully prepare a series of standard solutions for which the concentrations are known, and then measure their absorption as a function of wavelength.
For most compounds, there is typically at least one wavelength where the sample absorption peaks. Choose one of these wavelengths to monitor and create your calibration curve.
As an example, the graph below shows the calibration curve for calcium dipicolinic acid in deionized water. Measurements were taken at nm, the wavelength of maximum absorbance for this sample.
The reference was pure deionized water. Using this graph, the concentrations of unknown samples can easily be calculated using the slope of the line. Similarly, the extinction coefficient can be determined if the other parameters are known. For the most accurate results, it is best to use ten or more data points evenly distributed over the desired interpolation range.
Four points does not a calibration make! Using a calibration curve conveniently eliminates the need to know the extinction coefficient or exact pathlength. This is handy, because very few chemicals come with a molar absorptivity curve for the exact solvent being used. It also allows the use of a sample holder of unknown pathlength, provided it is used consistently.
If the calibration curve turns out to be non-linear, it can still be used by fitting a polynomial function to the data. Interpolations have the potential to be just as accurate as those from a linear calibration curve, as accuracy is dependent on the quality of the curve fit, not the shape of the line.
Deviations from linearity may indicate chemistry that is occurring within the sample, including, but not limited to, other species and changing equilibrium conditions. So before a nonlinear calibration curve is used, it is a good idea to verify the result using a fresh set of standard solutions.
All calibrations will be non-linear if a wide enough range of concentrations are used due to stray light and of limitations in the instrument. The detector measures the numbers of photons striking the detector during the integration time. Those photons arrive randomly, and the random variation in how many photons strike the detector is equal to the square root of the number of photons an effect called shot noise. At high absorbance values, the number of photons reaching the detector is low and the signal-to-noise is relatively poor.
At low absorbance values, there are plenty of photons and higher signal-to-noise. However, the uncertainty in measuring the percent transmission dominates the error in the measured absorbance value. In other words, the spectrometer is not as sensitive to small changes in absorbance concentration when absorbance is already low. The ideal range to work in is from about 0. By adjusting the concentration of the samples through dilution, by choosing cuvettes of different pathlength, or both, the absorbance values measured can be adjusted to be in this range to get the most accurate results.
What's the difference between relative and absolute absorbance? If the illumination is diffuse, there will be a variety of paths taken through the cuvette, resulting in an average pathlength for the combined cuvette and system that differs from the specified length of the cuvette being used. Uncollimated light through a sample. Collimated light through a sample. If diffuse illumination is combined with collimated detection using a lens for light gathering , the result is a relative absorbance measurement.
That is, the absorbance reading for a specific sample will depend on the specific instrument used. Our direct-attach and integrated cuvette holders provide diffuse illumination to the cuvette via light focused directly from a bulb. Transmission dip probes and flow cells are also relative absorbance sampling optics. Collimated illumination combined with collimated detection results in absolute absorbance measurements, which are independent of the instrument used to make the measurement.
Any of our cuvette holders which use a fiber and collimating lens combination provide collimated illumination, as the light exiting the fiber does so with a well-defined range of angles, allowing proper collimation. Be aware, however, that making adjustments to the position of the collimating lens in these cuvette holders will affect collimation of the incident light.
Relative absorbance systems work very well for determining concentration when used with a calibration curve. They are not suitable, however, for determining extinction coefficients, as the exact optical pathlength is not known.
Absolute absorbance sampling optics:. How do I take the best dark measurement? When taking a dark measurement, it is best to block the light at the light source if possible. Turning the light source off and then on again will throw the light source out of thermal equilibrium and require a new reference measurement. Alternatively, many cuvette holders have a filter slot where the light can be blocked.
Paper, even cardboard, can be deceptively transmitting, and it only takes a very low level of light to affect a measurement. How do I take the best reference measurement? To take the best reference measurement, first allow the light source to come to thermal equilibrium this can take up to 30 minutes in some cases.
Ensure that all surfaces of the cuvette are clean and clear of fingerprints, dust, and dirt. Fill the cuvette with the exact solvent or buffer solution to be used for the sample, and check for bubbles. It is especially important to check for bubbles if using a transmission dip probe or flow cell, as they are prone to this source of error, particularly at the shorter path lengths. Keep boxcar width to approximately the same value as the pixel resolution of the spectrometer, otherwise it can affect the spectral resolution.
Once the reference has been acquired, go into transmission mode and take a look at the resulting spectrum. Wavelength regions with more noise indicate the wavelengths at which accuracy will be the least for the sample measurement typically the shortest and longest wavelengths.
How do I make repeatable measurements? In any measurement that is made relative to a reference, the enemy is instability. Temperature changes or heating in the light source can cause the reference or dark measurement to change slightly, affecting all data. How do I measure very low concentrations or low absorbance? At low absorbance values, the uncertainty in measuring the percent transmission may be as large as the attenuation created by the sample.
This makes it very hard to get an accurate absorbance reading for dilute or low attenuation samples. First, ensure that the wavelength of peak attenuation for the sample is being monitored. Then, increase the pathlength of the sample cell until the absorbance readings are in the sweet spot of 0. Alternatively, concentrate the sample prior to measurement or use less solvent for sample preparation.
If the amount of sample available is limited or precious, try using our SpectroPipetter. How do I measure very high concentrations or high absorbance? At high absorbance values, the signal reaching the detector is very low, and signal-to-noise is limited by the shot noise of the detector.
The effect of stray light also increases at higher absorbance values, reducing the perceived absorbance from its true value see section on stray light for more information. Using a spectrometer that has been specifically designed for low stray light can improve the accuracy of high absorbance measurements considerably.
The stray light of a system is usually expressed as a percentage of the reference value. Stray light is instrument-dependent, so once measured for a specific system, it can be corrected in the software. This also improves the accuracy of high absorbance measurements significantly. Stray light correction is highly recommended for any measurements above 2 absorbance units, and can even improve accuracy for lower measurements. When possible, it is best to reduce the pathlength of the system or dilute the sample to bring measurements into the 0.
We also offer ultrashort path flow cells, including adjustable pathlength micro flow cells for process applications. Is there an easy way to make kinetics measurements in the software?
The strip chart feature allows you to select the spectrometer, spectrum type absorbance vs. This can then be easily imported into Excel for analysis. Should I correct for electrical dark? Think carefully about whether you want to turn on electrical dark correction. Dark current levels tend to vary slightly over time due to temperature variations, and the electrical dark correction option will keep the offset dark levels stable for a longer period of time.
This correction does add noise, however, as it is a subtraction calculation. It would not be advisable for very low absorbance measurements.
So consider your environment, absorbance value and the amount of temperature variation you typically see. Should I use the non-linearity correction? Non-linearity correction improves the accuracy of the spectral shape, but also adds more noise to your original signal.
The error is somewhat subtle and usually smaller than the experimental errors associated with handling liquid reagents.