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Is the CO2 effect saturated?

What the science says...

Select a level... Basic Intermediate Advanced

The notion that the CO2 effect is 'saturated' is based on a misunderstanding of how the greenhouse effect works.

Climate Myth...

CO2 effect is saturated

"Each unit of CO2 you put into the atmosphere has less and less of a warming impact. Once the atmosphere reaches a saturation point, additional input of CO2 will not really have any major impact. It's like putting insulation in your attic. They give a recommended amount and after that you can stack the insulation up to the roof and it's going to have no impact." (Marc Morano, as quoted by Steve Eliot)

At-a-Glance

This myth relies on the use (or in fact misuse) of a particular word – 'saturated'. When someone comes in from a prolonged downpour, they may well exclaim that they are saturated. They cannot imagine being any wetter. That's casual usage, though.

In science, 'saturated' is a strictly-defined term. For example, in a saturated salt solution, no more salt will dissolve, period. But what's that got to do with heat transfer in Earth's atmosphere? Let's take a look.

Heat-trapping by CO2 in the atmosphere happens because it has the ability to absorb and pass on infra-red radiation – it is a 'greenhouse gas'. Infra-red is just one part of the electromagnetic spectrum, divided by physicists into a series of bands. From the low-frequency end of the spectrum upwards, the bands are as follows: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Gamma rays thus have a very high-frequency. They are the highest-energy form of radiation.

As our understanding of the electromagnetic spectrum developed, it was realised that the radiation consists of particles called 'photons', travelling in waves. The term was coined in 1926 by the celebrated physicist Gilbert Lewis (1875-1946). A photon's energy is related to its wavelength. The shorter the wavelength, the higher the energy, so that the very high-energy gamma-rays have the shortest wavelength of the lot.

Sunshine consists mostly of ultraviolet, visible light and infra-red photons. Objects warmed by the sun then re-emit energy photons at infra-red wavelengths. Like other greenhouse gases, CO2 has the ability to absorb infra-red photons. But CO2 is unlike a mop, which has to be wrung out regularly in order for it to continue working. CO2 molecules do not get filled up with infra-red photons. Not only do they emit their own infra-red photons, but also they are constantly colliding with neighbouring molecules in the air. The constant collisions are important. Every time they happen, energy is shared out between the colliding molecules.

Through those emissions and collisions, CO2 molecules constantly warm their surroundings. This goes on all the time and at all levels in the atmosphere. You cannot say, “CO2 is saturated because the surface-emitted IR is rapidly absorbed”, because you need to take into account the whole atmosphere and its constant, ongoing energy-exchange processes. That means taking into account all absorption, all re-emission, all collisions, all heating and cooling and all eventual loss to space, at all levels.

If the amount of radiation lost to space is equal to the amount coming in from the Sun, Earth is said to be in energy balance. But if the strength of the greenhouse effect is increased, the amount of energy escaping falls behind the amount that is incoming. Earth is then said to be in an energy imbalance and the climate heats up. Double the CO2 concentration and you get a few degrees of warming: double it again and you get a few more and on and on it goes. There is no room for complacency here. By the time just one doubling has occurred, the planet would already be unrecognisable. The insulation analogy in the myth is misleading because it over-simplifies what happens in the atmosphere.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Further details

This myth relies on the use of a word – saturated. When we think of saturated in everyday use, the term 'soggy' comes to mind. This is a good example of a word that has one meaning in common parlance but another very specific one when thinking about atmospheric physics. Other such words come to mind too. Absorb and emit are two good examples relevant to this topic and we’ll discuss how they relate to atmospheric processes below.

First things first. The effect of CO2 in the atmosphere is due to its influence on the transport of 'electromagnetic radiation' (EMR). EMR is energy that is moving as x-rays, ultraviolet (UV) light, visible light, infrared (IR) radiation and so on (fig. 1). Radiation is unusual in the sense that it contains energy but it is also always moving, at the speed of light, so it is also a form of transport. Radiation is also unusual in that it has properties of particles but also travels with the properties of waves, so we talk about its wavelength.

The particles making up radiation are known as photons. Each photon contains a specific amount of energy, and that is related to its wavelength. High energy photons have short wavelengths, and low energy photons have longer wavelengths. In climate, we are interested in two main radiation categories - firstly the visible light plus UV and minor IR that together make up sunshine, and secondly the IR from the earth-atmosphere system.

The Electromagnetic Spectrum

Fig. 1: diagram showing the full electromagnetic spectrum and its properties of the different bands. Image: CC BY-SA 3.0 from Wikimedia.

CO2 has the ability to absorb IR photons – it is a 'greenhouse gas'.So what does “absorb” mean, when talking about radiation? We are all familiar with using a sponge to mop up a water spill. The sponge will only absorb so much and will not absorb any more unless it's wrung out. In everyday language it may be described, without measurements, as 'saturated'. In this household example, 'absorb' basically means 'soak up' and 'saturated' simply means 'full to capacity'. Scientific terms are, in contrast, strictly defined.

Now let's look at the atmosphere. The greenhouse effect works like this: energy arrives from the sun in the form of visible light and ultraviolet radiation. A proportion reaches and warms Earth's surface. Earth then emits the energy in the form of photons of IR radiation.

Greenhouse gases in the atmosphere, such as CO2 molecules, absorb some of this IR radiation, then re-emit it in all directions - including back to Earth's surface. The CO2 molecule does not fill up with IR photons, running out of space for any more. Instead, the CO2 molecule absorbs the energy from the IR photon and the photon ceases to be. The CO2 molecule now contains more energy, but that is transient since the molecule emits its own IR photons. Not only that: it's constantly colliding with other molecules such as N2 and O2 in the surrounding air. In those collisions, that excess energy is shared with them. This energy-sharing causes the nearby air to heat up (fig. 2).

CO2 heat transfer

Fig. 2: The greenhouse effect in action, showing the interactions between molecules. The interactions happen at all levels of the atmosphere and are constantly ongoing. Graphic: jg.

The capacity for CO2 to absorb photons is almost limitless. The CO2 molecule can also receive energy from collisions with other molecules, and it can lose energy by emitting IR radiation. When a photon is emitted, we’re not bringing a photon out of storage - we are bringing energy out of storage and turning it into a photon, travelling away at the speed of light. So CO2 is constantly absorbing IR radiation, constantly emitting IR radiation and constantly sharing energy with the surrounding air molecules. To understand the role of CO2, we need to consider all these forms of energy storage and transport.

So, where does 'saturation' get used in climate change contrarianism? The most common way they try to frame things is to claim that IR emitted from the surface, in the wavelengths where CO2 absorbs, is all absorbed fairly close to the surface. Therefore, the story continues, adding more CO2 can’t make any more difference. This is inaccurate through omission, because either innocently or deliberately, it ignores the rest of the picture, where energy is constantly being exchanged with other molecules by collisions and CO2 is constantly emitting IR radiation. This means that there is always IR radiation being emitted upwards by CO2 at all levels in the atmosphere. It might not have originated from the surface, but IR radiation is still present in the wavelengths that CO2 absorbs and emits. When emitted in the upper atmosphere, it can and will be lost to space.

When you include all the energy transfers related to the CO2 absorption of IR radiation – the transfer to other molecules, the emission, and both the upward and downward energy fluxes at all altitudes - then we find that adding CO2 to our current atmosphere acts to inhibit the transfer of radiative energy throughout that atmosphere and, ultimately, into space. This will lead to additional warming until the amount of energy being lost to space matches what is being received. This is precisely what is happening.

The myth reproduced at the top – incorrectly stating an analogy with roof insulation in that each unit has less of an effect - is misleading. Doubling CO2 from 280 ppm to 560 ppm will cause a few degrees of warming. Doubling again (560 to 1130 ppm) will cause a similar amount of additional warming, and so on. Many doublings later there may be a point where adding more CO2 has little effect, but recent work has cast serious doubt on that (He et al. 2023). But we are a long, long way from reaching that point and in any case we do not want to go anywhere near it! One doubling will be serious enough.

Finally, directly observing the specific, global radiative forcing caused by well-mixed greenhouse gases has - to date - proven elusive. This is because of irregular, uncalibrated or limited areal measurements. But very recently, results have been published regarding the deep reinterrogation of years of data (2003-2021) from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua Satellite (Raghuraman et al. 2023). The work may well have finally cracked the long-standing issue of how to make finely detailed, consistent wavelength-specific measurements of outgoing long-wave radiation from Earth into space. As such, it has opened the way to direct monitoring of the radiative impact (i.e. forcing + feedback) of greenhouse gas concentration changes, thereby complimenting the Keeling Curve - the longstanding dataset of measured CO2 concentrations, down at the planet's surface.

Note: Several people in addition to John Mason were involved with updating this basic level rebuttal, namely Bob LoblawKen Rice and John Garrett (jg).

Last updated on 31 December 2023 by John Mason. View Archives

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Further reading

V. Ramanthan has written a comprehensive article Trace-Gas Greenhouse Effect and Global Warming.

Further viewing

Video by Rosh Salgado on his "All about Climate" YouTube channel in which he debunks Will Happer's claim that the CO2 effect is saturated in the atmosphere:

Comments

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Comments 76 to 100 out of 712:

  1. Thank you Daniel Bailey, it certainly helps my understanding. If no more warming was available with increased CO2, it is hard to see how Snowball Earth could have ended where my reading is that a trigger was reached sending earth into a transient super-greenhouse.
  2. I know I am coming to this discussion late, but I wanted to discuss the statement from the advanced tab that states: "We can see that although the absorption dip cannot fall below the 220 K curve, it becomes wider and the absorbed energy increases accordingly." I have an alternate/additional hypothesis that I am trying to explore: * Raising the CO2 concentration should raise the effective altitude of the "last layer", since you need to go higher to get to a place where CO2 is thin enough to "let the IR escape". * Raising the altitude of the new "last layer" take us to a layer with a lower average temperature. * That cooler layer will radiate less energy. * To return to equilibrium, that new "last layer" must warm up, which will in turn warm all the layers below it. This mechanism is in addition to the effects of line broadening that have already been discussed. This fall apart a bit if that "last layer" is already at or above the tropopause. The temperatures in the model suggest that the "last layer" is still a little below the tropopause. Does any one here 1) have any links to the level of the effective "last layer"? 2) comments or corrections to what I am hypothesizing?
  3. tjfolkerts, you are correct. In that same Advanced tabbed page, look for the paragraph "There's one more subtle effect related to increased absorption. Upon increasing CO2 concentration, the layer at which the absorption coefficient at each wavelength is low enough to let the IR light escape will be found higher in the atmosphere. The emitting layer will then have a lower temperature, at least until the tropopause is reached, and hence a lower emitting power." A good source of more info are the RealClimate posts A Saturated Gassy Argument and the followup Part II: What Angstrom Didn't Know.
  4. Tom, Thanks for the info and the link to the other discussions - they were quite informative. I should have guessed that if a relative novice like me can think of it, then others would have already explored the idea in more depth. :-)
  5. tjfolkerts, regarding lapse rate, you'll be interested to read Eli Rabbett's post about a skeptic named Hermann Harde, who used a climate model so simple that it had only two layers of atmosphere--too few layers to adequately represent the strength of the effect of higher layers being cooler.
  6. My take on the science is this: 1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere. 2. The increased absorption of sunlight by the upper atmosphere means a drop in insolation at the Surface of about 1W/m^2. The increased back radiation due to the decreased average altitude of the CO2 surface-bound emissions is about 0.5W/m^2, so the NET direct effect of doubled CO2 on the Surface is a cooling forcing of 0.5W/m^2. 3. At the other boundary, it is clear from the outgoing spectra that CO2 is responsible for between 15 and 18W/m^2 of the emissions to space. It is also very clear that the emissions at the stronger wavenumber 670 are stronger than the rest of the CO2 band. Because emissions to space have to get through the overlying gas, it is also clear that the more strongly absorbed wavenumber 670 emissions are coming from higher in the atmosphere than say the wavenumber 650 emissions. So in this case, Higher = hotter, ie the wavenumber 670 emissions are definitely coming from the stratosphere. 4. All very well, but what about the rest of the CO2 band? At STP 50% of wavenumber 650 emissions are absorbed in the first 25m of atmosphere. At say 17km the same number of CO2 molecules occupy about 250m. The pressure decrease over these 250m means only a small narrowing of the emission/absorption lines, so absorption rate will not be greatly affected: at 17km just under half the wavenumber 650 photons are absorbed within 250m. 5. I calculate that the published absorption data for CO2 means that the great majority of emissions from CO2 must be coming from above the Tropopause. 6. If so, then we would expect a doubling of CO2 to have a COOLING effect on the planet.
  7. novandilcosid takes on basic physics on the CO2 lag thread. He writes:
    "1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere."
    novan calculates this by calculating the change in brightness temperature of the back radiation assuming the atmospheric temperature profile remains constant, and that the increased CO2 concentration reduces the average altitude from which the back radiation is emitted. The problem with this is not that it is in error, but what it ignores. Specifically, what heats the surface is not the back radiation but the sun. The way the back radiation effects the surface temperature is only by modulating the rate at which heat escapes, but it is a minor player in that role. Far more important is convection, which carries heat rapidly to the upper atmosphere. In the event that the upper troposphere warms, as for example, because of reduced IR radiation because of increased CO2 concentrations, that will slow the rate of convective heat transfer, and because heat is being carried away from the surface slower, the surface will warm until equilibrium is reestablished. This will result in an increase in back radiation, but because the lower atmosphere has warmed, not because of the lower effective altitude of emission of back radiation.
    "4. All very well, but what about the rest of the CO2 band? At STP 50% of wavenumber 650 emissions are absorbed in the first 25m of atmosphere. At say 17km the same number of CO2 molecules occupy about 250m. The pressure decrease over these 250m means only a small narrowing of the emission/absorption lines, so absorption rate will not be greatly affected: at 17km just under half the wavenumber 650 photons are absorbed within 250m. 5. I calculate that the published absorption data for CO2 means that the great majority of emissions from CO2 must be coming from above the Tropopause."
    It is odd that novan concentrates his discussion on the 650 wave number. It is well known that at that wave number, CO2 absorption is at its peak, and that as a result the majority of CO2 emissions to space at that wavenumber come from the stratosphere. However, the CO2 absorption band in the atmosphere is approximately 350 cm^-1 wide, with most of that band being much weaker absorption than at 650^-1. Science of Doom has calculated the change in transmission at the troposphere for a doubling of CO2: This is total change in transmittance, and does not take into account the emissions by the CO2, but the effect of the stratosphere and above on transmittance or emissions in the wings (<625cm^-1, >715cm^-1) is negligible. The consequence of including all the line numbers in your calculations (rather than just one, and done by novan) is to show that increasing CO2 concentrations reduces total emissions to space from the upper troposphere, requiring a compensating warming of the surface to restore the energy balance.
    Response: [DB] Closed blockquote tag.
  8. Tom Curtis wrote: "novandilcosid takes on basic physics on the CO2 lag thread. He writes: "1. The undisputed absorption figures for CO2 mean that an increase in concentration cannot directly greatly (I mean by more than 0.5W/m^2) increase the absorption of surface energy by the atmosphere." novan calculates this by calculating the change in brightness temperature of the back radiation assuming the atmospheric temperature profile remains constant, and that the increased CO2 concentration reduces the average altitude from which the back radiation is emitted. The problem with this is not that it is in error, but what it ignores. Specifically, what heats the surface is not the back radiation but the sun. The way the back radiation effects the surface temperature is only by modulating the rate at which heat escapes, but it is a minor player in that role. Far more important is convection, which carries heat rapidly to the upper atmosphere. In the event that the upper troposphere warms, as for example, because of reduced IR radiation because of increased CO2 concentrations, that will slow the rate of convective heat transfer, and because heat is being carried away from the surface slower, the surface will warm until equilibrium is reestablished. This will result in an increase in back radiation, but because the lower atmosphere has warmed, not because of the lower effective altitude of emission of back radiation." For a system in equilibrium (ie for the planet integrated over the surface and over a year) the Surface Energy Flow Balance is: Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water + Conduction For doubled CO2, the Absorbed Sunlight is less by 1W/M^2 because of increased absorption in the upper atmosphere. The Back Radiation is about 0.5W/m^2 more, due to a drop in the average height of CO2 radiation (lower is hotter). So the LHS (the forcing side) is less, and unless there are any other influences the Surface will cool slightly, resulting in slightly less Surface Radiation, and slightly less evaporated water. Note there is no mechanism to change the energy balance at the surface other than by varying the absorbed sunlight or the back radiation. The Surface couldn't give two hoots about what is happening in the thin cold and radiatively isolated upper atmosphere. It can only change temperature if the LHS of the equation changes. The absorbed sunlight will change if the albedo (clouds, ice) changes, the sun changes or as in this case, the absorption into the atmosphere changes. The back radiation will change if the atmospheric window closes, or if the Greenhouse gases heat up. So I disagree with Tom in one important detail. He suggests the surface heats up because of slowed atmospheric convection, then back radiation increases because of a heated atmosphere. That's not the case. The surface temperature can only increase if the atmosphere heats up first. And I'm not sure that it does. [There are some other interesting aspects: The atmospheric window is almost constant, the conduction is almost constant, so the heat transport from the surface into the atmosphere is almost a constant whatever the surface temperature. What happens as the temperature rises is that the Net radiation (surface radiation less radiation through the window less back radiation) DECREASES and this balances the increase in water vapour condensation. It is also of interest, as Tom points out, that the surface heat transport into the atmosphere is one fifth Net radiation, one fifth conduction, and three fifths condensation of water vapour.]
    Response: [DB] Please do not quote more than a sentence at a time from someone else's comment. A link to their comment plus the specific point you wish to quote will be sufficient. Thanks!
  9. Tom went on to claim that the 15um CO2 band is very wide. But examination of outgoing spectra suggests that the major CO2 effect is confined to the wavenumber 625-700 region, as does a plot of the absorption lines. In this region, the outgoing spectrum is about 15-18W/m^2. Of that around 12-15W/m^2 is being emitted above the tropopause. And that number goes up as the concentration of CO2 goes up, as the emissions come from higher in the Stratosphere (higher = warmer = stronger emission). I don't know how much emission is coming from CO2 molecules emitting the very weak lines outside this region, but not very much. I think it may be time to reveal how much energy is believed to be radiated from these weak lines, and what the exact effect of a doubling of CO2 is thought to be. [I distrust "Transmittance". How is it defined? There needs to be a distance and a concentration specified to make sense of the number. It is far more instructive and useful to use absorption tables, where the percentage remaining after passage through a specified amount of gas is defined. "Change in Transmittance" is even worse!]
  10. novandilcosid @83 (A) claims the surface energy balance is given by: Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water + Conduction Clearly in doing so he is talking about the actual surface - ie the top 1 mm of dirt of water that covers the planets surface. Oddly enough, there are very few thermometers stuck into that top 2 mm, with most thermometers being stuck in the atmosphere 2 meters above that surface. The "Global Mean Surface Temperature" is actually the temperature of the lowest surface layer of the atmosphere, so the proper energy balance equation is: Absorbed Sunlight + Back-Radiation = Surface Radiation + Evaporated water (including water from transpiration in plants) + Convection Although nonstandard, we can still work with novan's actual surface. (B) Novan also claims the only way the temperature can change is if the Left Hand Side of the surface balance equation changes. This is patently false, and refuted by everyday experience. It is standard procedure in cooking to alter the heat flow or temperature of water on the stove by adjusting evaporative heat loss rather than the heating element or flame. I come from Mount Isa where it is standard practice to cool homes by using evaporative air conditioners. Further, in Australia drinking water in the outback is typically stored in canvas bags rather than Jerry Cans so that evaporation will cool the water. If, at the surface, conductive heat flow was restricted, say, by raising the temperature of the layer immediately above the surface, and the inputs were left unchanged, the surface temperature would increase. The surface air layer could be warmed by a reduction in convection (and hence also latent heat transfer) by the warming of the air layer above that, and so on till you reach the upper troposphere where the air will be warmed by a reduction in the net outgoing IR radiation from that level by an increase in CO2 levels. C) Novan purports to have proved from first principles or empirical research or to just know a priori (I'm not sure which) that conduction between the surface and atmosphere is near constant, which is false. He also claims that the change of evaporative heat loss from a surface will automatically match in magnitude, but with opposite sign the change in radiative loss of heat to the atmosphere. This principle apparently holds true whether the surface in question is rocky desert or ocean, and also to hold independently of wind speed over the surface. That is an astonishing result, and I cannot wait to see the proof. I expect to be disappointed, however, for it sounds more like magical thinking than science.
  11. novandilcosid @84 as the situation stands, a large number of scientists using different programs on different computers have calculated the absorption, emission and transmittance for each wave number across the entire IR spectrum for the surface, plus each of 33 or more layers of atmosphere using observationally based information on temperature levels, and trace gas concentrations. In doing so they have produced spectra that almost exactly match those actually observed from space. Using these diverse models, if they increase the amount of CO2 by a factor of two, they reduce the outgoing IR radiation by approximately 3.7 Watts/meter squared. Those scientists and others, using still other computers have used equivalent techniques, but in which they allow the temperature and humidity at each layer to be set by the program based on energy balance equations and produced almost identical results. Deniers almost always ridicule these results as being "only based on models". But you want me to believe your claims about the effects of increasing CO2 based on the fact that you have calculated for just two wave numbers and just two poorly defined levels of the atmosphere. How about you program your line by line model and see if your results actually hold when you consider the whole atmosphere and all of the radiation. In the mean time, if you click on the picture below, you might get a clue: (Atmospheric absorption for 280 and 560 ppm CO2 as calculated by DeWitt Payne using Spectralcalc; difference between values shown in 82 above.)
  12. Tom Curtis @ #85 has fallen into a trap. His claims are all correct. So are mine. It will be noted that I prefaced my analysis with the following words: "For a system in equilibrium (ie for the planet integrated over the surface and over a year)" Essentially this is what is claimed when the IPCC states there is 3.7W/m^2 of Radiative Forcing if CO2 is doubled. Or when a 3 DegC temperature rise is claimed. It is not for a specific location but is an average for the whole planet integrated over a year. Consider a planet 3 degrees hotter (in the above sense). The likelihood is that the relationship between the Surface and Air is the same (this is implicit in the claim of a constant lapse rate) ie the average temperature difference between the air and surface is THE SAME. So the Conductive term, which is solely driven by temperature difference will be the same. We know that a doubling of CO2 has little DIRECT effect on the absorption of surface heat - maybe about 0.5W/m^2 of increase. ie the Window to space only closes fractionally. So both these terms are nearly zero change. The equation for surface heat absorbed into the atmosphere is: Surface Heat Absorbed into the Atmosphere = Surface radiation - the portion escaping through the Window - Back Radiation + Conduction + Evaporated water We also know from the surface energy balance that, providing Conduction and absorbed solar don't change, Change in Back Radiation = Change in Surface radiation + Change in Evaporation, or Change in surface radiation - change in backe radiation = -change in Evaporation or, if radiation through the window is cobstant, Change in NET radiation from the surface into the atmosphere = - Change in Evaporation Putting this in words, any increase in evaporation is balanced by an equal and opposite reduction in Net radiation from the surface. Hope this helps.
  13. Actually, it isn't just anthropogenic global warming... based on his statements, novandilcosid appears to deny the carbon dioxide greenhouse effect entirely. Though how he then explains why the Earth isn't a giant ball of ice, glaciation cycles, the data measuring this 'non-existent' effect in the article above, the disagreement of thousands of scientists (including all the major AGW 'skeptics'), et cetera remains unexplained.
  14. CBDunkerson @88, in fact he goes further. From his 81:
    "6. If so, then we would expect a doubling of CO2 to have a COOLING effect on the planet.
    My emphasis. So not only does he need to explain why the Earth isn't a cozy 255K, he needs to explain why it isn't 250K or less. It is however already apparent that he will not mere observation kill his beautiful theories.
  15. novan >Surface Heat Absorbed into the Atmosphere = Surface radiation - the portion escaping through the Window - Back Radiation + Conduction + Evaporated water "Portion escaping through the window" should not be part of the equation. It is an output from the surface and so must be included in any energy balance equation for the surface. It's quite simple: take all the inputs on one side and all the outputs on the other. So the real total energy balance equation from the surface would be: Absorbed Solar + Back Radiation = Surface radiation + Convection + Evaporated water (latent heat). If we take your assumption that convection and absorbed solar didn't change, then that gives us: Back Radiation = Surface Radiation + Evaporation. or Evaporation = Back Radiation - Surface Radiation So an increase in evaporation may be balanced out by either decrease in surface radiation or an increase in back radiation. It does not hold (even with your assumptions) that increased evaporation must be balanced by decreased surface radiation. Also note that evaporation and surface radiation are tightly related to temperature. It would not make physical sense to have increased evaporation with less surface radiation, as that would imply increased evaporation with lower temperatures.
  16. e's claims at #90 above are erroneous. His second equation should read: Change in Back Radiation = Change in Surface Radiation + Change in Evaporation. The Surface Balance equation can be rewritten: Absorbed Solar = Net Surface radiation into the atmosphere + Net Surface Radiation through the window to space + Convection + Evaporated water (latent heat). Writing this in terms of change, and making the (only slightly wrong) assumptions that changes to Absorbed Solar, Conduction and Net Surface Radiation through the window to space are zero, then yes indeed Net Surface radiation into the atmosphere = -Evaporated water (latent heat). This is another way of saying two things: 1. The energy transported from the surface always equals the insolation. Unless the solar constant or the albedo change, the energy from the surface is a constant. 2. As the Greenhouse tightens we expect the back-radiation to increase at a greater rate than the surface radiation: the radiative balance between the atmosphere and the surface narrows. At a perfect greenhouse, the retransmission of energy from the GHGs would be from the first layer of molecules - no temperature difference, perfect black body so total balance. The relative increase in back radiation allows the surface temperature to rise. This rise increases the evaporation rate in such a way that the relative increase in back radiation balances the increased evaporation. Note that the heat transport into the atmosphere from the surface is approximately Conduction one fifth Net Radiation one fifth Evaporation three fifths If the temperature increases, evaporation goes up and net radiation goes down. The rate at which evaporation increases with temperature is in dispute - essentially it is unkown. Measurement suggests 5% per DegC. The modellers use 2.5% or less. Additionally relative humidity is often taken to be constant. Measurement suggests that this may be abrave assumption.
  17. Tom Curtis wrote at #82: "It is odd that novan concentrates his discussion on the 650 wave number. It is well known that at that wave number, CO2 absorption is at its peak, and that as a result the majority of CO2 emissions to space at that wavenumber come from the stratosphere." Actually my calculations were not for the Wavenumber 670 region (indisputably stratospheric) but used the table values for wavenumber 650. [There are two ways to interpret this table, as it lists absorption rates through different gas depths at 50 wavenumber intervals. So either the table value is a spot measurement, or it is an average across the 50 wavenumber band centred on the tabled value. Either way it does not invalidate the conclusions.] I took a standard line and decremented it iteratively using the amplitude at each frequency as an attenuation factor, checking at each iteration for the total remaining power. In this way I was able to replicate the table absorptions at STP. I then had the number of iterations per atmcm of CO2. I then repeated the exercise at altitude, altering the shape of the absorption line (it gets peakier but narrower with altitude) to see what happens. I found that at wavenumber 650 (not 670) the emissions to space are mostly from the stratosphere. Emissions from the troposphere are not totally extinct but are only a small fraction of the spacebound photons in that band. We should not lose sight of the fact that over 10% of the atmosphere lies ABOVE the Tropopause (8% in the region 35N to 35S, 20% at higher latitudes). In the strong emission/absorption CO2 band from wavenumbers 625 to 725 most emissions are coming from above the Tropopause.
  18. novan, I believe I misread your original energy balance comment so you can disregard my subsequent post. I'm not sure what point you're trying to make with post 87 though. I would rather suggest you stick to the topic at hand (CO2 effect saturation and GHG physics) in order to keep your argument clear.
  19. novandilcosid @92, I will not dispute the claim that the majority of emissions to space in the range 630 to 710 cm^-1 come from the stratosphere. (I am not agreeing, I am just not disputing.) Certainly it comes from high enough that, as shown in 82 and 86 above, that increasing CO2 concentrations make no difference to the amount of radiation escaping from the troposphere at those wave numbers, which is all that is relevant to this discussion. But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1. While you ignore that substantial reduction, your theories are irrelevant. Therefore you need to either accept the values indicated above, in which case we can proceed, or you need to calculate the change in tropospheric radiation at those wave numbers for yourself and show the basis of your dispute with the scientists.
    Response: [DB] Fixed missing bold closing tag.
  20. My apologies to the moderators - I really am giving you a lot of trouble of late.
    Response: [DB] I've been given worse.
  21. DB, if you have been given worse in that sense, I am truly mortified.
    Response:

    [DB] Some days you're the windshield, some days you're the bug. But you can always do this afterwards:

  22. novandilcosid @87, the claim I was responding to is quite specific:
    "There are some other interesting aspects: The atmospheric window is almost constant, the conduction is almost constant, so the heat transport from the surface into the atmosphere is almost a constant whatever the surface temperature. What happens as the temperature rises is that the Net radiation (surface radiation less radiation through the window less back radiation) DECREASES and this balances the increase in water vapour condensation."
    So according to you for any two temperatures T1 and T2, e1sT14-W-Rback1+E1+C1=e2sT24-W-Rback2+E2+C2, where T stands for temperature, W for energy escaping through the atmospheric window, R for back radiation, E for evaporative energy transport (latent heat), C for conduction, e for the emissivity, and s for the Stefan-Boltzman constant. I can allow (as indicated in the notation) that energy escaping the atmospheric window is near constant for small changes in temperature with no changes in GHG concentrations. However, all other factors are variable with temperature. Specifically, you insist that an increase in temperature will result in an increase evaporation. But increased evaporation reduces soil moisture content, thus reducing the emissivity of the soil (factor 1). It also increases the emissivity of the lowest portion of the atmosphere, thus reducing the altitude of emission (factor 2), and at the same time reduces the lapse rate which increases the temperature at any given altitude (factor 3). Factor's (2) and (3) combine to increase back radiation. (The increased humidity will also decreases the size of the atmospheric window, but we will neglect that.) Increasing temperatures also increases wind speed globally, thus increasing conductive heat transfer by increasing the rate of turn over of the layer of atmosphere in immediate contact with the surface (factor 4). Increased humidity will also increase conductive transfer because of the high heat capacity of water vapour. So, you have at least four hetergenious factors you need to juggle to gain your equality, and only one term (W) which can be eliminated from the equation. The proof that change in net surface radiation equals the negative change in net evaporative transfer, therefore does not follow, and is highly implausible.
  23. Tom Curtis @#94 wrote: "the range 630 to 710 cm^-1 come from the stratosphere. (I am not agreeing, I am just not disputing.) Certainly it comes from high enough that, as shown in 82 and 86 above, that increasing CO2 concentrations make no difference to the amount of radiation escaping from the troposphere at those wave numbers, which is all that is relevant to this discussion. But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1. 1. I dispute that there is no change in energy radiated from the troposphere. I think the figures in #82,86 are NOT sufficient to estimate what happens: they are disclosing the opacity of the atmosphere as seen from the ground. This is not helpful when trying to determine what the effects are in the region which is already 100% opaque. It seems obvious that for the level in the atmosphere at which 20% of the photons make it through the CO2 fog to outer space, a doubling of the thickness of the fog will move the 20% emission layer higher. 2. The $64 question is where are the photons coming from in the very active 625-700 region with CO2 at 380ppm? My calculations suggest only 10% are coming from below the Tropopause, the remainder from above. If that is the case, then for this band a doubling of CO2 will mean emissions from higher in the stratosphere. The net effect in this band will therefore be an INCREASE in power radiated to space.
  24. Tom Curtis @ #94 wrote: " But those same figures above clearly show that there is a substantial reduction in radiation to leaving the troposphere outside those that range, but between 500 and 850 cm^-1. " The most active region is the band between 625 and 725. (See http://spectralcalc.com/spectral_browser/db_intensity.php) The lines here are around two orders of magnitude greater intensity than the lines in the rest of the band. 1. The question relevant to saturation is how much additional surface energy is absorbed outside the saturated 625-725 band, ie by how much does the window close, in W/m^2? I have always assumed that this is small - not more than 0.5W/m^2 for a doubling of CO2. 2. At the top of the atmosphere, what is the emission strength from CO2 in these weak parts of the band? The 625-725 region is emitting about 15-18W/m^2 (see plots of outgoing radiation measured in space eg http://acmg.seas.harvard.edu/people/faculty/djj/book/bookhwk7-1.gif http://www.mathstat.dal.ca/~folkins/Cloud-LWspectrum.jpg . http://climateaudit.org/2008/01/08/sir-john-houghton-on-the-enhanced-greenhouse-effect/ ). The much weaker lines outside this region won't be emitting much. So I guess I'd like to see some calculation of both these effects in the weak band to see if it is relevant. If the powers are small then this part of the band can be ignored, even though the majority of the emissions from them are plainly from below the Tropopause.
  25. Tom Curtis responded in #97 to my statement that surface energy into the atmosphere is essentially constant. "Specifically, you insist that an increase in temperature will result in an increase evaporation" Too right! We recall that the statement is only true when the energy flows are integrated over the entire surface over an entire year, then averaged. A second stipulation is that the system is in equilibrium - there are no net inflows or outflows. This is essentially what Kiehl & Trenberth say in their 1997 diagram, and is also implied by any statement that "the average temperature of the planet will increase by X degrees." While the statement will not be true at specific locations, it is true for the planet as a whole (remembering that 70% is water). [Off topic: The amount of increase in evaporation per DegC is disputed (see for example Schneider, Gorman and Levine, 2009, http://arxiv.org/abs/0908.4410 ). It is also unknown if relative humidity changes. The modellers assume constant RH (no better estimate), Clausius-Clapeyron water vapour increase (6.5%/DegC) and around 2.5%/DegC for evaporation. Actual measurements suggest that RH has decreased with increasing temperature, and that the rate of evaporation increase is 5%/DegC. Essentially the water properties of the atmosphere are unsettled science. Many climate scientists disagree with the assumptions in the models.]

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