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Climate change: Water vapor makes for a wet argument

Posted on 2 September 2010 by James Frank

When skeptics use the argument 'Water vapor is the most powerful greenhouse gas', they are trying to imply that an increase in CO2 isn't a major problem. If CO2 isn't as powerful as water vapor, which there's already a lot of, adding a little more CO2 couldn't be that bad, right? What this argument misses is the fact that water vapor creates what scientists call a 'positive feedback loop' in the atmosphere — making any temperature changes larger than they would be otherwise.

How does this work? The amount of water vapor in the atmosphere exists in direct relation to the temperature. If you increase the temperature, more water evaporates and becomes vapor, and vice versa. So when something else causes a temperature increase (such as extra CO2 from fossil fuels), more water evaporates. Then, since water vapor is a greenhouse gas, this additional water vapor causes the temperature to go up even further—a positive feedback.

How much does water vapor amplify CO2 warming? Studies show that water vapor feedback roughly doubles the amount of warming caused by CO2. So if there is a 1°C change caused by CO2, the water vapor will cause the temperature to go up another 1°C. When other feedback loops are included, the total warming from a potential 1°C change caused by CO2 is, in reality, as much as 3°C.

The other factor to consider is that water is evaporated from the land and sea and falls as rain or snow all the time. Thus the amount held in the atmosphere as water vapour varies greatly in just hours and days as result of the prevailing weather in any location. So even though water vapour is the greatest greenhouse gas, it is relatively short-lived. On the other hand, CO2 is removed from the air by natural geological-scale processes and these take a long time to work. Consequently CO2 stays in our atmosphere for years and even centuries. A small additional amount has a much more long-term effect.

So skeptics are right in saying that water vapor is the dominant greenhouse gas. What they don't mention is that the water vapor feedback loop actually makes temperature changes caused by CO2 even bigger.

This post is the Basic version (written by James Frank with a contribution from John Russell) of the skeptic argument "Water vapor is the most powerful greenhouse gas".

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Comments 51 to 100 out of 144:

  1. Johnd, If you don't read what the experts explain you don't understand the basics. The chart shows all the energy comes from the sun. Other sources of energy like volcanos and waste heat are negligable. The outgoing radiation equals the incoming radiation as required by conservation of energy. The increase in greenhouse gasses increases the back radiation. Increased back radiation increases surface temperature. Increased temperatures increases evaporation of water. When CO2 was lower the back radiation was lower and surface temperatures were lower. As temperature increases, humidity increases. This is a positive feedback, since water is a greenhouse gas. When do you expect solar radiation to cease? At night energy dissipates to space, during the day it accumulates. The chart shows the average for the whole day.
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  2. michael sweet at 21:47 PM, it appears that some of your points are being made without reference to the chart. On the point of back radiation, the chart clearly shows that the back radiation value is 324 whilst the value of energy radiated off is 390, a deficit of 66. Any nett loss of energy is a cooling effect not a warming, it is dissipating into the atmosphere through radiation a portion of the energy transferred to the surface by solar radiation. Now remembering that thermal radiation is a transfer of heat energy, in this situation, if it is being lost from the surface through thermal radiation, then it is simply not available to be lost to the surface through evaporation. The processes in practice are vastly more complex than the chart indicates, however the energy cannot be assigned to two different processes simultaneously or accounted for twice when compiling the budget, which is what seems to be suggested.
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  3. Johnd, It is you who cannot read the chart. Incoming radiation from the sun=342 reflected (sun) radiation=107 outgoing longwave=235 reflected + outgoing longwave=incoming as required by physics. The energy radiated from the surface is a combination of energy from the sun and backradiation so it is larger than either. The chart is an accurate summary of the energy balance, if you know how to read it. No energy is counted twice. Some energy is lost from the surface by evaporation and convection. Read the chart more carefully before you try to explain it to others.
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  4. michael sweet at 04:37 AM, I think it was clear that the discussion was focused on back radiation and the evaporation process, not the whole energy budget. Perhaps read back through the thread and pick up on that particular theme again instead of diverting away from it. In the meantime, regarding how the energy radiated from the surface can be larger than the energy from the sun alone, in forming a budget it is the nett result that determines a surplus or a deficit. Clearly the combination of radiation and back radiation shows a nett deficit, which is a cooling process, not warming. If that process is unable to sustain itself, losing energy, how is it able to give up energy to drive evaporation? If it hasn't been given up to evaporation when the water releases it as thermal radiation, a lesser amount of returning thermal radiation is not going to provide extra energy to drive a process that required more energy than was available originally. Evaporation releases excess energy over and above what is being lost by thermal radiation.
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  5. Johnd- as we continue to tell you - the surface is radiated by both the sun AND the back radiation. Once you get this, then you really understand the greenhouse gas effect. While you continue to misunderstand this, then you continue to talk nonsense. Take a while to understand that whole chart. Read the paper.
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  6. scaddenp at 07:04 AM, you are also avoiding the original point. That was where energy required for evaporation originates from, and thus how this affects the amount of water vapour that enters the atmosphere driven by factors that are not driven by the temperature, but instead are the primary drivers. All you have shown so far is that of the solar energy that has been absorbed by water as thermal energy in the case of evaporation, some of it is transferred into water vapour by the evaporation process which requires an energy input, and some is radiated off into the atmosphere, two completely different processes. It should be obvious that if thermal energy is being radiated off, it is not being utilised for evaporation, nor is it adding to the heat content of the water, it cannot be assumed to be in different places at the one time, or being used by concurrent processes. Radiation only occurs when an actual transfer of energy occurs, which in the case of water, any energy content of the water will be reduced by an amount that is the difference between outgoing and incoming thermal radiation as shown on the budget chart. It is already clear that what is radiated off is energy that is not being used in the evaporation process so why would the evaporation process then be able to utilise the lesser back radiation when part of the solar radiation is required to add additional energy to the outgoing radiation leaving even less energy available to drive evaporation. Varying cloud cover has an direct effect on evaporation, and even in an environment of above average air temperatures, evaporation will fall below average levels as cloud cover increases above average levels, not just at any particular point of time, but as a general response over a period of time.
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  7. Johnd: Carefully read the chart and the paper. Do not try to explain to me something you do not understand. The chart clearly shows that 168 w/m2 arrives at the surface from the sun. 324 w/m2 arrives at the surface from back radiation. The surface radiates 390 w/m2 as IR. 78 w/m2 is removed from the surface by evapotransportation (evaporation of surface water and the subsequent release of energy in clouds when the water changes back to liquid). 24 w/m2 is removed from the surface by thermal transportation. Total arriving = 168+ 324 = 492/m2 Total leaving = 390 + 78 + 24 = 492 w/m2 The energy to evaporate the water comes from the sun and the backradiation. What is so hard to understand?? The amount of water evaporated is determined by the temperature. The temperature is a function of the backradiation, caused by greenhouse gasses. The energy balance in this example is closed. There is no imbalance in the radiation budget as you suggest. The amount of energy radiated greatly exceeds the amount transported by evaporation and thermal transfer, although those processes are important. As greenhouse gasses increase, the backradiation increases and that heats the surface. Cloud cover has been considered in making the chart.
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  8. I make no bones about where the energy for evaporation comes from - solar radiation but largely by atmospheric radiation (back radiation). BOTH heat the water - the water molecules dont care which is which. At the fundamental level, evaporation depends on a/ partial pressure water in atmosphere, and b/ temperature difference. Evaporation takes energy away, cooling the water - but not much. The water must radiate according to its temperature (much of which comes back as back-radiation). Radiation and evaporation are both temperature-dependent phenomena and its best to think of them in those terms. Consider what happens when you reduce GHG. Less back-radiation so temperature drops, so it radiates less till new equilibrium found. Cloud cover etc are dealt with in diagram in terms of average global cover.
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  9. scaddenp (#12), you stated: "TOP - the point about water vapour is that it is a feedback not a forcing." Though we often disagree, you generally make sense. However, I am scratching my head over this one. Both CO2 and water vapor absorb Infra-Red radiation.
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  10. GC: Both CO2 and H2O absorb IR and are greenhouse gasses. Because of its short 1/2 life in the atmosphere, H2O responds to other forcings. When CO2 causes the temperature to rise, H2O responds by increasing (it is a feedback). If the Milankovich cycles caused temperatures to decrease H2O would decrease. H2O does not force (cause) the initial change in temperature, it responds to changes caused by other forces. Because humans adding CO2 to the atmosphere, CO2 is forcing (causing) the temperature to increase. In natural cycles, CO2 responds to other forcings (it is a feedback). In the current, human caused change, CO2 is a forcing, not a feedback. It is a little confusing because CO2 can be both a forcing or a feedback.
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  11. michael sweet at 10:42 AM, Phil, you are getting it all back to front. I am trying to explain to you something that you don't understand. Or perhaps you do, as rather than concede it you skirt around it by not actually referring to the specific point. that being what a nett loss of heat, in this case 66, really means in terms of heating and cooling. Thermal energy, heat, is radiated of from the water and thermal energy, heat, is radiated back to the water by the atmosphere, the amount radiated off dependent on each of their relative heat contents, or temperatures. As the diagram shows the heat radiated off 390, is greater than the heat radiated back, 324, from the atmosphere. Thus due to the absorption of solar energy, converted to thermal energy, the water is warmer than the atmosphere to the extent that the difference, 66, is a nett loss of heat from the water to the atmosphere. That is clearly a transfer of energy that cools the water. It is simply is not logical to claim such loss of heat is a warming effect on the body losing the heat. Perhaps you are confusing the rate of heat loss with direction??
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  12. Galloping Camel, water vapor's level in the Earth's atmosphere is limited by temperature. Putting more into the air merely causes an equivalent amount of water vapor to precipitate out. Removing more merely causes an equivalent amount to evaporate in. So the temperature cannot be "forced" higher or lower by using addition or subtraction of water vapor as the primary forcer. As Michael Sweet wrote, the water vapor level reacts to an increase in air temperature that itself has any cause. An example of such a cause is forcing of temperature to be higher by humanity's injection of CO2. Water vapor level increases as a feedback from the increased CO2 level, through the intermediary of increased air temperature. But you are correct insofar as the additional water vapor due to the increased temperature does in turn increase the temperature, because water vapor is a greenhouse gas. But that increase of temperature is strictly limited; it does not run away. And the initial temperature increase that started this chain of events cannot be due to water vapor, as I explained in my first paragraph. That's why water vapor is not a "forcing," but only a "feedback" from some other forcing.
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  13. michael sweet at 01:41 AM, neither CO2 nor water vapour can have any effect whatsoever without the thermal energy each absorbs. Without absorbing sufficient thermal energy CO2 would not even be able to be present in the atmosphere, so it is no different to water vapour in that respect. So can you explain why by adding sufficient thermal energy to CO2 by whatever means to enable it to enter the atmosphere, it is considered a forcing, whereas by adding sufficient thermal energy to H2O by whatever means it is considered a feedback. Thermal energy must be available from other sources before either can become part of the atmosphere, thus both are solely in the atmosphere as feedbacks before any follow on effects can be determined.
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  14. johnd, the energy needed to convert CO2 and H2O from liquid or solid to gas is not relevant to the greenhouse gas feedback versus forcing topic. What is relevant is that in the conditions present on Earth (versus, say, Mars), there are vast pools of liquid water ready to go into the air as soon as the air's temperature is high enough to hold more water as vapor. And there are vast numbers of particles in the air, ready to be nuclei of water vapor precipitation. In fact, both mechanisms operate continuously even while the air's temperature and therefore water vapor capacity are constant, because individual molecules of water continuously swap positions with other molecules among liquid and gas communities. What stays constant with a constant air temperature is the overall average water vapor concentration. In contrast, there are no pools of liquid or solid CO2. And the Earth's air temperatures are far too hot for CO2 to precipitate. Low air temperature is not a limiting factor on CO2 concentration in the air.
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  15. Johnd: As I pointed out at post 56 the amount of energy reaching the surface and leaving the surface are EXACTLY the same. This is required by the second law of thermodynamics. There is no "net loss of heat", you are completely wrong. You are ignoring the input energy from the sun. The energy to evaporate the water comes from the combination of energy from the sun and backradiation. You cannot separate the two as you are trying to do. You have to add them together. The energy budget is closed, there is no loss or gain in the illustration. I am not confused about energy loss, you do not understand the illustration. Perhaps if you read some of the background material we contiously post you would begin to understand the basics. You do not understand the greenhouse effects of CO2 and H2O either. I do not have the time to explain it to you now. In any case, you do not listen to what is explained to you and it would waste my time. I continue posting so that if anyone lurking is reading the exchange and wants an answer they can see what is wrong with your arguments. I am growing tired of having to constantly repeat my previous posts. You are apparently unable to understand the basics of energy exchange in the atmosphere. In addition, you do not understand the simple chart that scaddenp posted. I do not want this to become another "waste heat" discussion so I am not going to post any more about this subject. Your basic understanding of energy exchange is so flawed that it appears to be impossible to convey to you even the most simple facts. I suggest you review the post scaddenp made and his references and see what you can make of it. If you think that professional scientists have left out a large factor that means that you do not understand the paper. You would make a better impression if you said: "I do not understand what this illustration means" rather than "these scientists are wrong". The scientists are right. You do not understand the basic physics.
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  16. Johnd - I am not skirting anything. I am trying to put my finger on which part of fundamental physics you do not understand. I am really struggling to make your sense of comments at all. eg you claim surface losses 390 but only gains 324 so a net loss of 66 which must cool the surface. Huh??? LOOK at the diagram. The surface gains: 168(solar) + 324 (backradiation) = 492 It losses: 390(radiation) + 24 (thermal) + 78 (evaporation) = 492! They balance as they must. I am at loss as to how you could interpret the diagram the way you have.
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  17. JohnD So can you explain why by adding sufficient thermal energy to CO2 by whatever means to enable it to enter the atmosphere, it is considered a forcing, whereas by adding sufficient thermal energy to H2O by whatever means it is considered a feedback. You do not need to add thermal energy to CO2 to make it enter the atmosphere, unless your planet is below -78C (~200K). This is a sublimation point of CO2 (when solid turns to gas). You do need to add energy to H2O because it is a liquid (or solid) at normal earth temperatures. Liquids, such as H2O, (but not CO2 which is a gas) do have a vapour pressure which, as several people have tried to explain to you, is dependent only on temperature. This is why it is a feedback; if the temperature of the atmosphere increases (by whatever means) then the vapour pressure of water increases too. More water vapour in the atmosphere means more IR absorption which means that the heat that will escape into space is retained in the atmosphere for longer, and so the planet heats up. You are still confused about rates of evaporation, seeming to think that this affects the amount of water vapour the atmosphere can hold. This is simply wrong. If the rate of evaporation slows (without the temperature changing) then so does the rate of condensation - so no change in the overall amount.
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  18. GC - Feedback is context of current discussion is something that changes in response to temperature. Water and CO2 in atmosphere are dependent on temperature so both are feedbacks. Forcings are changes that are independent of temperature. Emitting millions of year accumulation of CO2 into the atmosphere is a forcing. It will cause CO2 feedbacks as well. In contrast, you cant change the H2O in the atmosphere independent of temperature, so it cant be a forcing. John Cook - how about a simple spreadsheet on the site (illustrative purposes only) to show how feedbacks work? eg T = k1 * solar + k2*GHG + c1 GHG = f1 * T + c2 Then iterate through time.
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  19. Johnd - looking further at all your comments, you seem to making inappropriate divisions. That evaporation energy only comes from the solar input; that surface radiation is only tied to backradiation etc. The surface would radiate from the solar input alone if there was no atmosphere - you cant make that separation. What warms the water? ALL the incoming energy. What causes the surface radiation? The energy from ALL incoming radiation. What causes backradiation? All the energy in the atmosphere whatever the origin.
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  20. michael sweet at 05:31 AM, there is no dispute as to whether overall the energy budget is balanced or not, or that the energy received at the surface and leaving the surface is the same. That is what compiling an energy budget is all about, so I am bewildered how you can confuse quantifying the nett contribution each process makes to that balance with the combined nett result. Is this a case of not being able to see the forest for the trees, I doubt it. It appears that the point of there being a nett loss of heat from the surface when back radiation is offset against heat radiated off is being avoided simply because the maths of -390 plus 324 = -66 is not compatible with a notion that would be satisfied if it was a positive value instead of the negative one it is. If it was a positive value, then the overall balance would still be maintained by additional energy being input into the evaporation process or thermals and transferred from the surface to the atmosphere by those means. If we were to look at it the other way, the heat energy that is lost through evaporation is in part being driven by the heat energy contained in the rain that returns to earth, and a portion of that energy then becomes part of the energy that increases the heat that is being radiated off. The most basic law of physics confirms that energy cannot be created or destroyed, it can only be changed from one form to another. The argument that you are making is that even though energy is being utilised in one process, it is still available to be used in another process concurrently. That often is demonstrated by accountants as being possible, and widely believed by the masses to be true, but at the end of the day it is simply a matter that someone couldn't tell the difference that a negative value makes to the balance sheet as opposed to a positive value. A deficit is not a surplus, nor a debt an asset, but there are many who will claim otherwise. Is it that when the house purchased for $390,000 is sold for $324,000, that $66,000 then becomes available to renovate the house just sold? That is the argument being put.
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  21. johnd, the conversion of latent heat to sensible heat by the condensation of water vapor does not happen at the surface. It happens in the atmosphere. Thermals transfer energy only from the surface up, not down. Hot air rises, it does not sink. Those two heat "sources" (note the quote marks) heat the atmosphere. Then the atmosphere radiates up and down.
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  22. Scadenp, #65: the way this argument drags out shows the weakness of using that diagram. Indeed: some years ago, I remember being told that one of the famous French math journals, I forget which, had banned articles including proofs which were in turn based on diagrams. Their attitude was that if you need a diagram, then you had not worked out your proof in sufficient detail and rigor. I suspect the same thing is going on here. I have yet to see a good diagram on this issue, Trenberth's is copied over and over -- and is misinterpreted over and over. Yet somehow all these people copying his diagram seem to have forgotten the old saying: the definition of insanity is repeating the same failed operation over and over and expecting a different result. The biggest failing I see in Trenberth's diagram is that although sure, the energies add up as you say, the huge value of energy in backradiation is never explained, and seems to even violate conservation of energy when compared to the energy irradiated at top of atmosphere -- wherever that really is. Then more confusion is added by using yearly average figures, where the energies are averaged over day and night, even though the picture of the energy flows (in particular, their directions) is so very different.
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  23. Well the diagram seems crystal-clear to me - a brilliant depiction of the energy flows. However, it isnt going to make sense if you dont understand the individual processes, especially black-body and greenhouse which I guess is the source of confusion. Since it is a pciture of global heat flows, I cant see what you could gain by day/night - its day somewhere, night somewhere.
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  24. I also think the diagram is crystal clear. That is not the problem. We spent over 300 posts on the waste heat and related threads trying to explain the exchange of heat in the atmosphere to Johnd and RSVP and at the end they still did not understand. Since my last post scaddenp, Tom Dayton and Phil have all tried to help. I doubt that they will succeed.
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  25. MattJ @71 -"The biggest failing I see in Trenberth's diagram is that although sure, the energies add up as you say, the huge value of energy in backradiation is never explained" scaddenp @72 - "Since it is a pciture of global heat flows, I cant see what you could gain by day/night - its day somewhere, night somewhere." The diagram is clear to me as well, but how many laypeople overlook the contribution of incoming solar radiation? i.e. it only occurs to the side of the Earth facing the sun, whereas back radiation occurs day & night all over the planet?, I'd guess quite a few.
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  26. JohnD, Here is a scenario that might help you understand the energy budget diagram. You and your wife wish to buy presents for your three children; You put in $324, your wife puts in $168. Your baby gets a $24 rattle, your young son gets computer games worth $78 and your recently graduated daughter gets clothes worth $390. (The numbers have, of course, been chosen to match the heat budget ones in Trenberths diagram) Three questions: 1. How much money is left ? 2. How much did you (as opposed to your wife) contribute to each present (3 answers) ? 3. How important is it that your daughter got a present $66 more than you contributed ?
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  27. johnd - "-390 plus 324 = -66 " WHY are you only using two numbers and concluding there is a deficit? Why do you think you can do maths on only those two? If we can get to bottom of your thinking on that we might finally make some sense.
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  28. Johnd- on more try. The surface process. Surface is heated by solar (168) and atmosphere (324). As a result of the heating, it losses some energy to convection (24) and evaporation (78). For the energy to balance however, the surface temperature must rise till it radiates the balance of the energy (390). Note that surface radiation is inputs minus non-radiative losses. It is DEPENDENT on the other processes. The amount of energy that can be lost due to convection and evaporation are physically limited so radiation must do what they cannot.
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  29. MattJ at 08:37 AM, I agree entirely with you. The diagram is a rather simplistic depiction of the energy budget, and as with all budgets has to be twigged to balance. What is doesn't do is represent the order of the processes and which processes may have priority over others. That is if heat is being transferred, which process facilitates a slow transfer and which may ramp up as the rate increases and are able to handle excess amounts of energy. Which may ramp up as others are ramping down, still maintaining the nett balance. Earlier on I asked for what I termed a critical path chart. That was using terminology from another discipline and I'm not sure whether such a depiction even exists for this subject of heat transfer given it was only the energy budget diagram that was presented. When solar energy is absorbed by water, I believe that evaporation occurs first and only any excess energy is absorbed by the body of water, thus the evaporation process is primarily a function of direct solar radiation and secondarily of the thermal energy that is stored in the body of water. This can be readily observed in practice where water that is open to the atmosphere AND in direct contact with solar radiation evaporates at a far greater rate than water that is also open to the atmosphere but shaded from direct solar energy. In the case of water being heated by any form of heat, even a immersion heater, as the temperature of the water rises, evaporation and the radiation off of heat both occur, however as the water reaches boiling point it becomes clear that the ultimate determinate of how much heat the water is able to absorb is not the radiating off of heat, but the evaporation process. When the day comes that an equivalent to a solar hot water heater has been developed that works by passively absorbing back radiation, then perhaps we can revisit the topic again from a new perspective.
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  30. Phil at 23:33 PM, you've got it all back to front. You being the bread winner puts in $168, as this is where all the money consequently saved or squandered originates from. The question then becomes do you first pay out on priorities such as utilities, $78 and food, $24, which ultimately are all forms of heat energy, leaving you to find $390 to pay your credit card bill, usually done by drawing a cash advance of $324 to make up the difference. As to who contributes how much for the presents, you would have to examine your credit card statement to find out that given $40 went as interest, you are left with nothing for presents. There must be some interesting discussions at your house each pay day. ;-)
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  31. johnd - You have cause and effect reversed here. Solar energy is absorbed by the water, warming it, and then the warmer water increases it's evaporation rate, providing a negative feedback (limiting response) on the temperature rise of that water. You had that order backwards. And that water also emits IR (water being close to a black body spectrum emitter). Both the IR and latent heat in the evaporated water warm the air over the water, which emits IR in response - providing backradiation (positive feedback) to the water and limiting it's cooling via IR and evaporation. On the other hand, I completely agree that the changes in rates of various energy exchanges is of definite interest. We're an awfully long way away from boiling any oceans, though. Nobody is predicting that.
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  32. KR at 08:33 AM, I'm not sure that I do have cause and effect reversed. Even though all processes occur at the very molecular surface of the water, the solar energy is of far greater magnitude than any back radiation, so the water would be responding immediately by evaporating and only any energy unused by that process then being absorbed by the body of water that then radiates at a rate depending on it's temperature. Evaporation however is dependent on more factors than merely solar radiation or ambient temperatures. It is highly dependent on wind. Whilst there may be limited information that has been collected from the surfaces of the oceans, very detailed information has been collected on land regarding evaporation, and evaporation rates that allows examination of exactly what order of influence each factor occupies, and ambient air temperature, or soil temperatures are not what evaporation responds most immediately to. The information on this link, http://www.bom.gov.au/products/IDV65176.shtml#notes, if followed over a period of time may allow greater understanding of where evaporation falls within the cycle of all events that attempt to achieve equilibrium in the global heat budget.
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  33. Johnd - you do have it backwards. The solar radiation is 168 and the backradation is 324 - more than twice solar. I defy you to come up with some physics that can cause a molecule to move from liquid to gas without heating the liquid. Evaporation is physically limited and wind doesnt vary enough to change that. For global average, wind doesnt change much so evaporation losses are almost entirely tied to temperature. In terms of FORCINGS, wind etc is irrelevant. Change solar or change backradiation (put in more GHG) and evaporation will increase, but you cant change evaporation independently.
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  34. scaddenp at 09:50 AM, one of the features of climate science is that ultimately the results of all the hypothesis and theories must manifest themselves in the physical world in a manner that is not only readily observable, but measurable also. Thus perhaps given the magnitude of the back radiation as opposed to direct solar radiation, in order to better illustrate your explanation can you show where the back radiation exhibits itself, and the magnitude as measured in the table of data that is compiled daily by BOM specifically measuring evaporation rates and all the factors that drive such evaporation. Note that these tables are updated daily so you will need to save each days data if intending to refer to readings that appear on any one day.
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  35. As far as I can see, they arent measuring radiation from the atmosphere. It is manifest in ground temperature - that would be very different without it, especially at night. I also find this emphasis on land evaporation (an extremely minor source of water vapour) rather strange as it has complicating factors not relevant to warm sea water. As for direct observation, well Philipona 2004 is one source while you may prefer Spencer's backyard experiment For systematic measurement network, see GEBA station network. As is often the case, Science of doom also has good discussion about the measurement.
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  36. scaddenp at 14:07 PM, why wouldn't they measure radiation from the atmosphere, that seems strange. Given it is supposed to be twice the magnitude of direct solar radiation it would then be the single largest input into the process. It doesn't make sense that you now claim that back radiation is manifest in the ground temperature. Ground temperature is very stable, it varies only slowly, especially if any moisture is present as the evaporation of moisture actually is a cooling process removing heat from the surface, and as can be seen, other factors have far greater influence in varying the rate. Ground temperatures do respond more rapidly once surface moisture has been removed through evaporation. These measurements are not strange or far removed from the conditions at sea. The actual measurement of evaporation is taken from water in a standard evaporation pan, the same as what would be used to measure evaporation rates in a marine environment.
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  37. johnd - well ask them but they take measurements for a purpose and I suspect backradiation isnt that important for investigation CHANGES in evaporation on land. I do not think that seawater is like evaporation pans. What do you think would the liquid temperatures would be like at night in seawater compared to a pan? I would also guess that on land most evaporation happens in day time with little at night. Evaporation continues at night over sea because surface sea temperature dont fall much. By "Ground" temperature, I meant surface temperature. No backradiation and temperatures would plummet at night. The direct solar is stronger while its shining but backradiation continues at night. You seem to disbelieve backradiation because BOM doesnt it at their evaporation pan sites. How do you account for the measurements at the 1600 sites where it is measured then?
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  38. Johnd - the backradiation from the atmosphere is driven entirely by the temperature (and humidity, to provide water vapor levels) of said atmosphere. Your table of data implicitly includes the backradiation, as anyone familiar with the subject understands that warm humid air keeps the ground warm, while cool dry air speeds temperature drops. That's basic knowledge in agriculture! You're asking for duplicate data. Scaddenp - The various soil temperatures are important for agriculture and crop growth; the purpose of these "Agricultural Observations" tables. Johnd - Trying to claim that backradiation isn't important simply because it's not listed on a table created for another purpose entirely is a very poor argument.
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  39. JohnD @79 OK, I think I understand your problem with the diagram. The figure of 324 backradiation comes from heat accumulated in the atmosphere over time. The figures of 168 and 324 imply to me that solar irradiation takes, on average, twice as long to leave the atmosphere as enter it. This is, of course, the essence of the greenhouse effect; heat is trapped for a period of time in the atmosphere, and the more greenhouse gases, the longer that period of time. I think you are trying to read the diagram as if it applied "from day 1" as it were; I don't it does. Make sense ?
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  40. Doh: I don't think it does.
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  41. Phil at 03:56 AM, Phil, no I am reading it on the basis that the diagram is merely a budget, and just like a household budget it identifies the inputs and allocations but says nothing about any underlying wealth that is generally represented by accumulated assets those being a combination of both fixed and liquid assets. In this case the accumulated assets are the heat contents of the land and oceans, and that of the atmosphere which most obviously represents the liquid assets, those being the assets that are readily drawn upon to cover any short term variations within the overall budget. For a budget to balance, once an amount has been allocated to one outgoing it is simply not available to another outgoing. In the diagram it is clear that 390 is allocated to the liquid assets. This obviously is excess to that allocated to evaporation and convection which are also allocated to the liquid assets. However 324 is also available from the liquid assets as part of the process attempting to maintain budget integrity by balancing out, or seeking equilibrium. Thus as the 390 was outside that required for the other allocations of 78 and 24, the lesser amount drawn upon,324, cannot logically be available either as it is already utilised to makeup the balance of the 390. If on the other hand the budget showed that the flows were reversed with only 324 allocated to the liquid assets whilst 390 could be drawn upon, then obviously the excess, 66 would be available for the other processes, and the allocations of 78 and 24 would be accordingly higher in order for the budget to balance. In either case, nothing changes with what is available from the liquid assets. But that is NOT the case in the diagram, therefore there is nothing to support the assertion that the back radiation has energy available to input into the evaporation process. I understand that the diagram is a rather simplistic depiction, noting it says nothing about contained energy within the system, nor anything about what drives the processes, it merely attempts to depict the flow from where the energy originates to where it is dissipated, just as a household budget does.
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  42. johnd - No, we're not talking about investments. We're talking about energy, and energy exchanges. 'Liquid assets' lead to inappropriate conclusions, a false analogy issue. The Earth (ground/water) radiate at a spatially averaged 396 W/m^2 rate. The air, heated by conduction, convection, latent heat, and primarily IR, radiates at a rate of 324 W/m^2, based entirely on it's temperature and the thermal spectra of the gases involved. That reduces the ability of the ground to radiate heat, otherwise it would reach (rough) equilibrium at a lower temperature than we currently have, rather lower than the ~15C we currently have. Your "accumulated assets" are temperature (the joules required to set a particular ground/water/air to a particular temperature), while the exchanges are the energy transfers available to each portion of this system based upon their characteristics. Investment banking as an analogy, on the other hand, will lead you to false conclusions. This is not an uncommon error - false analogies. But you have to remember that an analogy, while useful for explaining some subset of characteristics of an unfamiliar system to another person, is not where you can draw conclusions about the original, complex system that you have an analogy to! That's just not sensible. Please, oh please - draw your conclusions in the original system, and limit your analogies to explaining subsets of those systems to others. That will avoid incorrect statements such you present here.
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  43. Johnd - the energy diagram is paradoxally "instantaneous" energy flow - the values of annual averages. We tried to explain the causative relationships, but there are interdependences and a very large internal flow thanks to GHG effect that doesnt yield to some "critical path analysis". I'll try again... Solar is obviously dependent on solar output and orbital factors. Backradiation has a dependency on solar (well the ULR), but the independent knob is GHG concentration. This and surface radiation make up the large internal energy flow. These heat the surface. Evaporation and convection are largely dependent on temperature of surface - feedbacks with no way in independently change them on a global, long term scale. Surface radiation is proximately dependent on temperature but temperature will rise or drop to whatever the necessary to conserve energy. Surely that is clear? The really key point is that evaporation cannot be a forcing.
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  44. KR at 12:18 PM, obviously we are not talking about investments, it is about budgets, but it should be obvious that the terms borrowed are appropriate. The heat content of the land and oceans is fixed in that it only changes slowly over time, and if the theories of deep ocean currents are correct some of that heat has been accumulating over very long periods of time. On the other hand the heat content of the atmosphere is readily accessible and responds rapidly both to release and re-absorb heat. The BOM chart I linked to earlier that compiles data relating to measuring evaporation shows this in the soil temperatures that remain very stable, only changing slowly as seasons progress. However the air temperatures show wide variations daily as indicated by the maximum and minimum temperatures recorded at each station. In your last post you referred to the idea that back radiation reduces the ability of the ground to radiate heat. If we refer to the BOM data table again it shows however that the "Terr min", Terrestrial minimum temperature, being the lowest overnight temperature measured at ground level, is always lower, often considerably lower than the minimum air temperature, whilst always considerably higher than the soil temperature immediately below the surface. Can you explain how back radiation allows this to occur in light of your explanation.
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  45. scaddenp at 14:44 PM, re "Solar is obviously dependent on solar output and orbital factors". That may well be the case, but clouds are a major factor given they provide coverage to about 2/3 of the earth's surface. In fact they would have to be the single biggest factor in determining the amount of solar radiation that arrives at the earths surface.
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  46. johnd - I don't know how your BOM table is generated, but looking at the notes for it against your issues, differences between min (air) temp and 'Terr min', I see: # Maximum and minimum temperatures, rainfall, evaporation and wind run are for the period to 9 am on the day of reporting. # Soil temperatures and Delta-T are current at the time of observation. ... # 'Terr min' is Terrestrial minimum temperature. It is the lowest overnight temperature measured at ground level. So - 'Terr min' (which is not a soil temperature, contrary to your statements) is from overnight temps, while the min temp is from 9AM? I would suggest you not base your arguments on a chart unless you understand it. Quite frankly, I'm a bit appalled at the argument you just presented. And again - arguing that back radiation isn't important because it's not on a chart made for other purposes is just silly, back radiation is both easily measured and physically derivable as the IR from atmospheric gases at their current temperature, and water doesn't change it's partial pressure (evaporation) until it's temperature changes. For the last, I would suggest looking at a CRC Handbook for some data.
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  47. KR at 12:14 PM, the BOM table is generated from measurements taken by means that conform to world standards, so there should not be any mystery there as to how it is compiled. Apart from not understanding how BOM compile standard data sets, you also are not comprehending what I have written. NOWHERE have I claimed that the Terrestrial minimum temperature is the soil temperature, in fact if you read carefully the distinction between air temperatures, soil temperatures and terrestrial temperatures is made quite clear,so please, instead of being appalled at perceived inadequacies of others, address your own. What you fail to grasp is that even though back radiation is not recorded as such, how it manifests itself is. Hence the request that you explain why the terrestrial temperatures fall lower than both the air temperatures, and the soil temperature if back radiation drives the terrestrial temperatures in the manner you have indicated given back radiation is considered most relevant when direct solar radiation is not present.
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  48. Johnd - the question you need to ask is how fast would temperatures have dropped if there was NOT backradiation. Perhaps look at what happens on moon - okay not that fast because there is some heat capacity in the atmosphere. How about noting that temperature drop slower on a cloudy night? Now why is that? Instead of constantly referring to BOM stations with measurements in service of agriculture, why dont you look at a station where backradiation IS measured and you can see it. (eg Alice Springs). As to clouds, well dont forget clouds are both positive and negative feedbacks. In a stable climate, clouds are about the same. The question on actual interest is, as the earth warms from GHG increase, will clouds be a net positive or negative feedback and if so, by how much? While I am aware that there are speculative papers pushing for large negative feedback, this is incompatible with empirical measures of climate sensitivity. However, this is changing the goalposts - are you satisfied with the existence and effect of DLR (backradiation) yet?
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  49. johnd - to quote you: "...the "Terr min", Terrestrial minimum temperature, being the lowest overnight temperature measured at ground level, is always lower, often considerably lower than the minimum air temperature, whilst always considerably higher than the soil temperature immediately below the surface. Can you explain how back radiation allows this to occur in light of your explanation." However, the table you point to, the BOM data, clearly indicates that the 'minimum air temperature' and the 'Terr min' are measured at different times - at 9AM and at the coldest portion of the night. They are not comparable, although you seem to indicate they are - at least, that's how the question read to me. The ground temps will not cycle as fast as air temps, so I fail to see any issues with this data in regards to the physics of back radiation.
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  50. Note to johnd - according to the chart you pointed to, the 'Terr min' is the temperature at ground level, not the ground (soil) temperature.
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