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What is the net feedback from clouds?

What the science says...

Select a level... Basic Intermediate

Evidence is building that net cloud feedback is likely positive and unlikely to be strongly negative.

Climate Myth...

Clouds provide negative feedback

"Climate models used by the International Panel on Climate Change (IPCC) assume that clouds provide a large positive feedback, greatly amplifying the small warming effect of increasing CO2 content in air. Clouds have made fools of climate modelers. A detailed analysis of cloud behavior from satellite data by Dr. Roy Spencer of the University of Alabama in Huntsville shows that clouds actually provide a strong negative feedback, the opposite of that assumed by the climate modelers. The modelers confused cause and effect, thereby getting the feedback in the wrong direction." (Ken Gregory)

The effect of clouds in a warming world is complicated. One challenge is that clouds cause both warming and cooling. Low-level clouds tend to cool by reflecting sunlight. High-level clouds tend to warm by trapping heat.

clouds

As the planet warms, clouds have a cooling effect if there are more low-level clouds or less high-level clouds.  Clouds would cause more warming if the opposite is true.  To work out the overall effect, scientists need to know which types of clouds are increasing or decreasing. 

Some climate scientists, such as Richard Lindzen and Roy Spencer, are skeptical that greenhouse gas emissions will cause dangerous warming. Their skepticism is based mainly on uncertainty related to clouds.  They believe that when it warms, low-level cloud cover increases. This would mean the Earth's overall reflectiveness would increase. This causes cooling, which would cancel out some of the warming from an increased greenhouse effect. 

However, recent evidence indicates this is not the case. Two separate studies have looked at cloud changes in the tropics and subtropics using a combination of ship-based cloud observations, satellite observations and climate models. Both found that cloud feedback in this region appears to be positive, meaning more warming.

Another study used satellite measurements of cloud cover over the entire planet to measure cloud feedback.  Although a very small negative feedback (cooling) could not be ruled out, the overall short-term global cloud feedback was probably positive (warming).  It is very unlikely that the cloud feedback will cause enough cooling to offset much of human-caused global warming.

Other studies have found that the climate models that best simulate cloud changes are the ones that find it to be a positive feedback, and thus have higher climate sensitivities.  Steven Sherwood explains one such study:

While clouds remain an uncertainty, the evidence is building that clouds will probably cause the planet to warm even further, and are very unlikely to cancel out much of human-caused global warming.  It's also important to remember that there many other feedbacks besides clouds. There is a large amount of evidence that the net feedback is positive and will amplify global warming.

Basic rebuttal written by dana1981


Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 25 July 2017 by skeptickev. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Comments

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Comments 151 to 200 out of 256:

  1. RW1#149: "net effect of clouds at night is to warm (or slow heat loss)... Again, this is not in dispute, nor does it conflict with net negative feedback for clouds." Oh, that makes it all perfectly clear. A mechanism of warming, 'not in dispute,' doesn't conflict with net negative feedback? Do you have any evidence to support this astounding statement? Or does your model simply require that you assume a net negative feedback and thus do not need to bother with any evidence?
  2. 150, RW1, What else does Dessler say in his paper? Let me give you a hint... your logic that if the effect of clouds is a net negative in the current climate, then a changed climate must have more clouds with the same net negative effect, only more so, is simplistic. It matters what types of clouds form, where they form, and when they form. More clouds in northern latitudes in winter will not nave a net cooling effect. High clouds made of ice crystals that are transparent to visible light will not have a net cooling effect. Clouds that build beyond a certain critical depth will not have a net cooling effect. It's more complicated than your simplistic logic makes it sound.
  3. muoncounter (RE: 151), "Oh, that makes it all perfectly clear. A mechanism of warming, 'not in dispute,' doesn't conflict with net negative feedback? Do you have any evidence to support this astounding statement?" I'm not sure I understand your objection. The net effect of clouds, globally averaged (night and day combined), is to cool. The fact that clouds are much better at trapping outgoing surface emitted radiation than the clear sky, which makes their net effect at night to retain more energy than the clear sky, would only be significant it was more than the energy the clouds reflected away during the day.
  4. Sphaerica (RE: 15), "your logic that if the effect of clouds is a net negative in the current climate, then a changed climate must have more clouds with the same net negative effect, only more so, is simplistic." No, not really. My point is there is really no physical or logical reason why the net cloud feedback would suddenly switch from negative (cooling) to positive (warming) on the next few watts incident on the surface, especially to cause a net warming effect so much greater than the response of the system to the original 98+% (239 W/m^2) incident on the surface from the Sun.
  5. Sphaerica (RE: 152), "It matters what types of clouds form, where they form, and when they form. More clouds in northern latitudes in winter will not nave a net cooling effect. High clouds made of ice crystals that are transparent to visible light will not have a net cooling effect. Clouds that build beyond a certain critical depth will not have a net cooling effect. OK, explain specifically how all the various cloud types will respond in a way that results in a net warming effect on the next few watts at the surface and specifically why all different cloud types don't respond this way to the original 239 W/m^2 incident on the surface from the Sun. "It's more complicated than your simplistic logic makes it sound." I know the balance is complicated. It doesn't change the fundamentals. Besides, Dessler doesn't get into different types of clouds in his analysis.
  6. 154, RW1,
    ...there is really no physical or logical reason why the net cloud feedback would suddenly switch...
    But there is. You're just denying that it exists. Hint: Go to the top of this web page and actually read the post.
  7. Sphaerica (RE: 156), "But there is. You're just denying that it exists. Hint: Go to the top of this web page and actually read the post." I have read the post. I do not see where the issues I've raised has been addressed or answered.
  8. RW1 My point is there is really no physical or logical reason why the net cloud feedback would suddenly switch from negative (cooling) to positive (warming) on the next few watts incident on the surface It doesn't need to switch to a net positive effect in order to be a positive feedback. If the total effect is currently negative, and a warmer climate causes structural changes in cloud cover that makes the total effect less negative, then that will result in additional warming beyond the original forcing. In other words less cooling is equivalent to warming.
  9. 157, RW1,
    I do not see where the issues I've raised has been addressed or answered.
    That's because you ignore the statements that do address them. 1. Your theory is inconsistent with all of the lines of evidence which point to a climate sensitivity of 3˚C or greater. You have seen this presented to you now at least 6 times, and you keep dodging it. How does your theory account for this? Until you answer that question, your theory fails. 2. Your theory is inconsistent with the observational evidence (Dessler 2010) that demonstrates a positive, not negative, feedback in response to short-term warming. While this cannot necessarily directly support a long-term positive effect, it directly refutes your "was negative before, so must be negative in the future" theory. 3. Your argument that models "assume" and require a positive cloud feedback is wrong. While clouds do represent a large area of uncertainty in the models, it is incorrect to think that the scientists who have done the modeling have not thought things through a little more carefully, and in more detail, than you have. You cast aspersions by generalizing their work into the word "assume," and yet provide no direct evidence (other than the general positive/negative thing) that their work is not well considered. 4. Your argument that current warming "depends" on the positive cloud feedback is exaggerated, as has been demonstrated. It reduces potential warming from 3˚C to 2.5˚C or 2˚C, which while helpful is not an inconsequential amount of warming. Like many deniers, you exaggerate one point to try to make it the single, decisive, "AGW killing" argument. 5. Your argument that cloud effect is negative and would not "switch" to positive is at its root flawed and too simplistic. It's rather like saying that May was warmer than April, and June was warmer than May, so every month from now on will get warmer and warmer forever. It takes a too simple premise, and draws an invalid conclusion, because it avoids the complexities of the system. Instead of Occam' razor, your theory uses Occam's guillotine. It is based on a very broad, general, simplistic approach to the problem. It does not consider any details in the issue, such as why the current effect would be negative, or how clouds might or will change. It assumes that all effects are linear and additive. It simply takes the childishly simple view that if current net effect is negative, then a warmer climate must mean more clouds, which must mean more negative. You may feel that this logic is persuasive, and for simple minded people who like to stop thinking as soon as they see an argument that supports their predetermined beliefs, this might well be persuasive. But it doesn't persuade me in the slightest. It matters very, very much where additional clouds form in a warming world (high latitudes, or near the equator), when they exist (during daylight, summer hours, or nighttime or winter hours), and what kind of clouds form (i.e. low, reflective clouds or high, heat trapping clouds).
  10. Sphaerica (RE: 159) "1. Your theory is inconsistent with all of the lines of evidence which point to a climate sensitivity of 3˚C or greater. You have seen this presented to you now at least 6 times, and you keep dodging it. How does your theory account for this? Until you answer that question, your theory fails." I addressed this already HERE. To delve into all those things here would be off topic. Moreover, it is absurd to think that I (or anyone else) is obligated to explain each line of evidence they present in the context of every other line of evidence in the whole subject of climate science.
  11. 106, RW1,
    I addressed this already HERE.
    Really? You call that "addressed?" This was what you said:
    Look, I can only deal with one thing at a time.
    So, for the sixth time you've dodged the question, as well as my other points. You made the following statement:
    I do not see where the issues I've raised has been addressed or answered.
    I pointed out:
    That's because you ignore the statements that do address them.
    I then proceeded to itemize where and how the issues you've raised have been addressed and answered, and I took you to task to yourself address the discrepancies. And you ignored them. Instead your response now is basically that you already have addressed them (you haven't), and that you don't have to... because justifying your personal theories about net cloud feedbacks would be off topic on a thread about cloud feedbacks (although that didn't stop 50 meandering posts about Trenberth's energy budget diagram when you thought that in some way buttressed your personal theories).
  12. Sphaerica (RE: 161), "So, for the sixth time you've dodged the question, as well as my other points." That's what you think. "You made the following statement: 'I do not see where the issues I've raised has been addressed or answered.' I pointed out: That's because you ignore the statements that do address them. I then proceeded to itemize where and how the issues you've raised have been addressed and answered, and I took you to task to yourself address the discrepancies. And you ignored them." No, I've largely ignored your declarations that the issues I've raised are incorrect. Declarations are not scientific discussion.
    Response: [DB] Actually, hand-waving aside, it is indeed pretty clear you've been dodging questions. And not just Sphaerica's.
  13. DB, Which specific questions have I been 'dodging'?
    Response: [DB] Start with Sphaerica's.
  14. Sphaerica (RE: 159), "2. Your theory is inconsistent with the observational evidence (Dessler 2010) that demonstrates a positive, not negative, feedback in response to short-term warming. While this cannot necessarily directly support a long-term positive effect, it directly refutes your "was negative before, so must be negative in the future" theory." Dessler 2010 is primarily just looking at TOA net fluxes and temperatures – he’s made little (if any) attempt to carefully discern cause and effect, and has not come up with any physical reasons or mechanisms behind his interpretation of the data. He admits in the paper at the beginning that the net effect of clouds in the current climate is to cool by about 20 W/m^2, yet doesn’t seem to ascribe much significance to this or express any curiosity as to why this is the case when clearly it needs to be explained. Furthermore, I notice that the SW component is also positive, which seems to be consistent with decreasing clouds causing the warming rather than warming causing decreasing clouds. Even if the claim is warming causes decreasing clouds for positive feedback, how is this consistent with increasing water vapor from warming? Does increasing water vapor from warming cause decreasing clouds? That doesn’t make any sense since water vapor concentration drives cloud formation. It seems to me that unless Dessler can explain all of this and corroborate it with all the other data and system behavior, he really doesn’t have a case.
  15. Sphaerica (RE: 159), "3. Your argument that models "assume" and require a positive cloud feedback is wrong." It's not really "my argument". The IPCC report specifically says this in the fine print, which I have posted here. "While clouds do represent a large area of uncertainty in the models, it is incorrect to think that the scientists who have done the modeling have not thought things through a little more carefully, and in more detail, than you have. You cast aspersions by generalizing their work into the word "assume," and yet provide no direct evidence (other than the general positive/negative thing) that their work is not well considered." No, I have not seen the evidence their work on the cloud feedback has been carefully considered at all, especially because it seems to ignore the basic physics of water vapor and clouds.
  16. RW1 - You might be interested in Wylie 2005. They looked at various satellite measures of cloud cover over the last 20 years. The High Resolution Infrared Radiometer Sounder (HIRS) found no significant cloud trend, while the International Satellite Cloud Climatology Project (ISCCP), with slightly different instruments, found a slight decrease in cloudiness over that period. Keep in mind that while specific humidity (total amount of H2O) in the atmosphere may be rising with temperature, relative humidity (relative to the total amount air can hold at any temperature) may remain steady or even decrease. So - steady or decreasing clouds with rising temperatures, neutral or positive feedback to warming.
    Response:

    [DB] Fixed Link.

  17. RW1,
    Even if the claim is warming causes decreasing clouds for positive feedback, how is this consistent with increasing water vapor from warming? Does increasing water vapor from warming cause decreasing clouds? That doesn’t make any sense since water vapor concentration drives cloud formation.
    Your overly simplistic model of the system completely fails. It doesn't properly consider how clouds form, it doesn't understand that clouds do not need to decrease to provide a positive feedback, it doesn't account for the many varieties, locations (in space, meaning 3 dimensions, and time) of clouds, it fails on many, many other levels. At the same time, your interpretation of Dessler 2010 is flawed. You should probably read the paper several more times before commenting on it again. My advice would be to read more on the subject, and post less. Kitchen table science may make perfect sense to a lot of people, but it's still wrong, and your analysis is kitchen table science.
  18. Sphaerica (RE: 167), "Your overly simplistic model of the system completely fails. It doesn't properly consider how clouds form, it doesn't understand that clouds do not need to decrease to provide a positive feedback, it doesn't account for the many varieties, locations (in space, meaning 3 dimensions, and time) of clouds, it fails on many, many other levels. At the same time, your interpretation of Dessler 2010 is flawed. You should probably read the paper several more times before commenting on it again." I have read the paper multiple times. I even emailed Dessler for clarification on a few things. He admits outright that his analysis doesn't analyze any mechanisms, just data. That the net effect of clouds is to cool by 20 W/m^2 would have to be explained. Just claiming the derivative to changes in surface temperature is positive, as Dessler does, even though the net entire effect is to cool is not good enough.
  19. KR (RE: 166), "Keep in mind that while specific humidity (total amount of H2O) in the atmosphere may be rising with temperature, relative humidity (relative to the total amount air can hold at any temperature) may remain steady or even decrease. So - steady or decreasing clouds with rising temperatures, neutral or positive feedback to warming." This really doesn't make sense. The fundamental problem is that clouds are controlling the water vapor concentration in a highly dynamic manner. The evaporated water vapor condenses in the atmosphere to form clouds, and then the formed clouds precipitate out the water from the atmosphere. As the clouds form and remain in the atmosphere, they reflect more solar energy away because the clouds are more reflective than the surface beneath them. This is why the net measured effect of clouds is to cool rather than to warm. Dessler's analysis is essentially claiming that all of the sudden the incremental effect of clouds on the next little bit of warming will be the warm rather than cool.
  20. 168, RW1, No single paper needs to cover everything, all at once, to completely define something. He doesn't "admit" (and yes, I noticed your cleverly pejorative word choice) that he doesn't cover mechanisms, he simply "tells" you as much. You shouldn't have needed to bother him and ask such an obvious thing, which you would certainly have clearly known if you comprehended the paper. That said, I don't care how many times you've read the paper, you don't seem to be able to comprehend it or, rather, you don't seem to be able to separate what you believe (without adequate logic or evidence) from what current science says. The mechanisms have been explained to you several times. Clouds are not a uniform, one dimensional entity for which more clouds = more of the same. A large number of factors come in to play.
    • Are there more clouds at night, where their albedo is irrelevant?
    • Are there more clouds at the poles or northern hemisphere in winter, where they merely shield reflective snow and ice, and so the difference in albedo is nil, while their radiative warming effects are increased?
    • Are the clouds that form high altitude clouds of ice, that are pretty much transparent to visible light, but still have a strong GHG effect?
    • Do the excess clouds form over or under existing cloud layers, again having little net effect on albedo, but definitely adding their radiative effects?
    Your simplistic view that net cloud impact on temperatures is normally mildly negative, and therefore any increase in clouds due to warming must be comparably more negative, is inadequate. I think you'd be well served to study the topic more before commenting further. I also think you'd be better served by demonstrating some respect (not merely in the words you post, but in your attitude) to the men and women that are actively engaged in studying the science. Believing that you can out-think them when you can't even get a decent grasp on Trenberth's energy budget diagram is just a little bit of a Dunning-Kruger.
  21. Sphaerica (RE: 170), "The mechanisms have been explained to you several times. Clouds are not a uniform, one dimensional entity for which more clouds = more of the same. A large number of factors come in to play." I've never claimed clouds are uniform or a one dimensional entity. "Your simplistic view that net cloud impact on temperatures is normally mildly negative, and therefore any increase in clouds due to warming must be comparably more negative, is inadequate." A -20 W/m^2 net effect is not "mildy negative" - it is very strongly negative (or strongly cooling). In the absence of specifically identified and corroborated physical mechanisms to the contrary, this is an extraordinary claim requiring extraordinary proof. Ultimately, Dessler doesn't have it.
  22. Sphaerica (RE: 170) "Believing that you can out-think them when you can't even get a decent grasp on Trenberth's energy budget diagram..." Find the appropriate thread and I'll be happy to discuss/debate Trenberth's energy budget with you or anyone. Every time I've tried, my posts seem to end up getting deleted for being off topic. Moderators, is there a thread where we can discuss this? If not, can you start one?
  23. 171, RW1, Look. Your comments contain nothing of substance other than to deride Dessler without foundation. He did a study and found that the net change in cloud feedback was positive, which supports the contention of many, many current climate scientists. Make a point and support it, or stop commenting. If you have a valid mechanism by which this may not be so, submit it and support it. If you have data that refutes Dessler's claim, submit it and support it. If all you have to say is "Negative could feedback! Negative cloud feedback! Dessler must be wrong!" then you're wasting everyone's time.
    Response:

    [DB] Agreed.  No one wishes to waste their time by dialoguing with RW1 due to his unwillingness to learn and to properly support a position.

  24. Interesting thread. Is it still active? On mechanisms: Svensmark, Shaviv, J Kirkby et al all suggest a mechanism for cloud nucleation (and thus possibly formation) independent of temperature. I was surprised not to see this mentioned. Other possible mechanisms have been proposed, such as micro organisms prompting nucleation. http://www.wired.com/wiredscience/2011/05/microbes-make-rain/ So while RW1 has not proposed a mechanism, others appear to have. No hard evidence for those mechanisms, but they should perhaps be considered when assessing the evidence for other mechanisms such as co2 forcing.
    Response:

    [DB] "Interesting thread. Is it still active?"

    All threads here at SkS (all 4,000+) are active.  Many are temporarily dormant but any are free to be reawakened at any time.  Regular participants here follow the Recent Comments thread, so they will see any new comment made regardless of the thread it is posted on.

  25. lancelot#174: "Svensmark, Shaviv, J Kirkby et al all suggest a mechanism" Those gentlemen are all part of the 'it's cosmic rays' camp. There are a number of threads addressing their data here at SkS (search: cosmic rays), as well as this excellent RealClimate piece exploding their suggested mechanism.
  26. 174, lancelot,
    So while RW1 has not proposed a mechanism, others appear to have.
    I'm afraid I don't see that. Can you be more specific? The question at hand is: "Given warming that results from anthropogenic CO2, what will be the resulting cloud feedback?" While the work you discuss is interesting, it does not in any way affect the topic at hand -- which is the direction and degree of feedback from clouds in response to warming. That cloud formation is impacted by many factors is obvious. That temperatures are impacted by unexpected but measurable factors such as cosmic rays, through cloud formation, is what is under debate in current science (and on other threads here at SkS) but at the current time is not in any way supported by the evidence available. But in any event, it is not relevant to this thread, which discusses cloud feedbacks, not clouds as a primary forcing.
  27. lancelot, So while RW1 has not proposed a mechanism," The mechanism is the whole of the atmospheric water cycle (ground state water -> evaporation -> water vapor -> clouds -> precipitation -> ground state water), which is the primary way the planet's energy balance and ultimately the globally averaged surface temperature is maintained despite such a large degree of local, regional, seasonal hemispheric and even sometimes globally averaged variability. In general, mechanistically, when clouds are increasing the climate is too warm and trying to cool (more or denser clouds are exposed to space, reflecting more of the Sun's energy) and when clouds are decreasing the climate is too cool and trying to warm (fewer clouds lets in more of the Sun's energy). If water vapor is the primary amplifier of warming, as claimed, what then is the controller? If not clouds via there ability to reflect incoming solar energy and precipitate out the water from the atmosphere, then what? Does anyone think it's just a coincidence that energy from the Sun drives evaporation of water? Is it just coincidence that evaporated water removes heat from the surface, condenses to form clouds and the clouds reflect the sun’s energy? Is it just a coincidence that the water precipitated out of the atmosphere emanates from clouds?
  28. That's a rather medieval style of argumentation RW1 - leading questions and anthropomorphism! So no, the climate isn't "trying" to do anything. It responds to forcings according to the laws of physics. Likewise the answer to your repeated "is it just coincidence?" is, in each case, "no, it's physics". RW1, the "controller" is very well understood. It's temperature. The water vapour content of the atmosphere rises as the atmospheric temperature rises. That is very well understood physics, and has been measured repeatedly in the real world. No leading questions about "coincidences" required! Your "mechanism" lacks both physics and evidence. One really needs to consider the response of the atmosphere in terms of humidity. I'm sure you agree that the absolute humidity of the atmosphere has risen as a result of greenhoue-induced warming. That's uncontestable - we can measure this. How about "relative humidity"? There is some evidence that the water vapour content of the atmosphere might maintain approximately constant relative humidity in a warming world. In such a situation there's no reason to expect the levels of clouds to increase since the atmosphere can maintain increased water vapour without enhanced condensation into clouds. If the water vapour content of the atmosphere rises (i.e. the observed increase in absolute humidity) at a level that is somewhat lower than required to maintain constant relative humidity, then the formation of clouds is more likely to be suppressed. That's consistent with the so far rather limited real world evidence. There's zero real world evidence that clouds increase in a warming world. On the contrary, the limited evidence supports a small positive cloud feedback in a warming world (see the top article of this thread).
  29. 177, RW1, Your "intelligent design" approach which requires that the earth's climate system be constructed and constrained like an electrical engineering project imposes any number of requirements (such as the idea that there be a single controller) which are quite simply fabricated. Your "coincidences" are mere observations of known physics. You imply that because they exist, they must be primary factors in the system, but you provide no evidence of such. You imply that because you haven't bothered to list any other mechanisms here, they cannot exist or must be inconsequential. Your position amounts to argument from ignorance. Your argument boils down to "I can only envision things happening this one way, so how can it be anything else?" Your position amounts to recognizing that you cannot touch the sun but it moves through the sky, therefore it must be the flaming wheel of the sky god's chariot. How could it be anything else?
  30. The climate system's energy balance is extremely dynamic. It's constantly changing spatially and in time - all the time, yet long-term averaged it's very tightly constrained. The global temperature anomaly barely moves by more than a couple tenths of a degree per year despite such variability. This is hardly consistent with net positive feedback on imbalances, let alone net positive feedback of 300%. Water vapor and clouds are also not a homogeneous distribution - they are by far most dynamic component of the entire atmosphere. The notion that the feedbacks of water vapor and clouds are both strong net positive cannot be reconciled with physical process and feedbacks that so tightly constrain planet's energy balance as a whole.
    Response:

    [DB] Fixed text.

  31. RW1 given an incoming heat flux, it is the emission of radiation that mainly constrains temperature. Why on earth the Stefan-Boltzman law, the most important negative feedback, is so often forgotten?
  32. Riccardo, I assume you're talking about the so-called 'Planck' response of about 3.3 W/m^2 per 1 degree of warming?
  33. RW1 wrote: "The global temperature anomaly barely moves by more than a couple tenths of a degree per year..." Which, is a massive amount of heat. You dismiss the idea of positive feedbacks (which BTW are estimated at a 200% increase on the forcings - 300% would be the combined total) because the average annual temperature anomaly is so 'constrained', but that is a completely groundless argument. I could just as easily claim that the massive average annual temperature anomaly shows how large the positive feedbacks must be. In reality, there is no direct connection between the two and thus the argument is meaningless. We know feedbacks are positive because every past and current warming forcing which we can estimate with any degree of accuracy has been enhanced by positive feedback effects. Frankly, it is ridiculous to claim that feedback effects will not be positive given that measurements of forcing and feedbacks from every El Nino, every Summer, and indeed every sunrise prove otherwise. The sun comes up, temperatures rise, dew evaporates, atmospheric humidity increases, that water vapor causes further warming... positive feedback. Happens all the time and not remotely controversial. The idea that this would suddenly just 'stop' happening if the warming comes from increasing atmospheric CO2 levels is without any justification at all.
  34. RW1 the so-called Plank sensitivity or response is derived from the Stefan-Bolzman law.
  35. CBDunkerson, Are you aware that the system is almost always in a state of energy imbalance to some degree? Have you noticed that even when the system as whole warms to a significant degree like during an El Nino event, it always seems to revert to its pre-equilibrium state fairly quickly afterward? This is hardly consistent with net positive feedback acting on perturbations. Also, the temperature rising as the Sun comes up each day is not the result of net positive feedback acting on the increased incident energy. You seem to be confusing a causative positive response to an increase in 'forcing' with positive feedback in response to the causative change. They are two different things. No one disputes that increased energy from GHGs or the Sun will cause warming.
  36. Riccardo (RE: 185), "the so-called Plank sensitivity or response is derived from the Stefan-Bolzman law." OK, explain to me how it's derived? Why the 'Planck sensitivity' 3.3 W/m^2 per 1 degree of warming?
    Response:

    [DB] "OK, explain to me how it's derived?"

    Try here:

    http://scienceofdoom.com/2010/10/24/planck-stefan-boltzmann-kirchhoff-and-lte/

  37. RW1 try here, but let's not go offtopic here and choose a more appropiate place to discuss sensitivity.
  38. Riccardo (RE: 187), What I'm asking is why specifically is it 3.3 W/m^2 per 1 degree of warming? Why not 0.33 W/m^2 or 33 W/m^2 (some other number), for example?
  39. 188 RW1 The earth radiates energy as E=epsilon*sigma*T^4, where epsilon is the emissivity (0.61) and sigma is the Stefan-Boltzman constant. If you increase the average earth surface temperature (287K) by one degrees you'll increase E by 3.3 W/m^2
  40. RW1 - "What I'm asking is why specifically is it 3.3 W/m^2 per 1 degree of warming? Why not 0.33 W/m^2 or 33 W/m^2 (some other number), for example?" I'm more than a bit appalled by this question. You look at the physics, you run the numbers, and you get a result. The only reason the number would be different is if the physics were somehow different, RW1. But reality is a harsh critic.
  41. RW1, You have now demonstrated extreme ignorance on climate science (a complete failure to understand Stefan-Boltzmann, the Planck response as a feedback, and the way that we know that this response is 3.3 W/m2 per degree K). At this point, you must recognize the need to study and learn a whole lot more before you "authoritatively" comment any further on things that you clearly do not grasp.
  42. RW1 wrote: "Have you noticed that even when the system as whole warms to a significant degree like during an El Nino event, it always seems to revert to its pre-equilibrium state fairly quickly afterward? This is hardly consistent with net positive feedback acting on perturbations." So... because the daily cycle of temperature fluxes due to sunrise and sunset returns to its 'equilibrium' state in short order this is evidence against Summer temperatures being warmer than Winter temperatures? That is essentially the 'logic' you are presenting... 'if A shows steady fluctuations around a flat baseline then B cannot possibly show long term increases'. "Also, the temperature rising as the Sun comes up each day is not the result of net positive feedback acting on the increased incident energy." In part, yes... it is. Most of the temperature increase is due to the increased radiation. However, water vapor feedback also plays a part... as anyone who has lived in a very humid area would be able to tell you. A climate 'forcing' is just a change from a baseline. Most often we choose baselines from on yearly averages. However, it is perfectly valid to look at the incoming solar radiation over the course of a day with the daily average as the baseline. In such case, sunrise would represent a massive warming forcing. We can then look at feedback responses to this forcing... specifically, that warming forcing from sunlight will cause water to evaporate. Water vapor is a greenhouse gas. Ergo, this will create a positive feedback. Further, it is a positive feedback that we have known about and studied for centuries. We use the term 'relative humidity' because the amount of water vapor the atmosphere can hold increases as the temperature does... so the relative humidity is the percentage of the possible maximum water vapor content of the atmosphere for the current temperature. If the temperature goes up the amount of water vapor the atmosphere can hold increases as well. A long understood and thoroughly measured phenomenon. Now, if the temperature of the entire planet goes up... why wouldn't the same feedback apply? If the planet's atmosphere is warmer it will hold more water vapor. That water vapor will produce more greenhouse warming. You argue that 'the notion' of positive feedback from water vapor cannot be reconciled with 'tightly constrained' temperature variations in various other cycles (e.g. ENSO, seasons, day/night, 11 years solar cycle, et cetera). I am saying that there is no logical way to conclude that water vapor will not be a positive feedback, because it is always a positive feedback to warming.
  43. lanC (RE: #189), "The earth radiates energy as E=epsilon*sigma*T^4, where epsilon is the emissivity (0.61) and sigma is the Stefan-Boltzman constant. If you increase the average earth surface temperature (287K) by one degrees you'll increase E by 3.3 W/m^2" Correct. Now, why specifically is the emissivity 0.61?
  44. CBDunkerson (RE: #192), "You argue that 'the notion' of positive feedback from water vapor cannot be reconciled with 'tightly constrained' temperature variations in various other cycles (e.g. ENSO, seasons, day/night, 11 years solar cycle, et cetera)." No, I'm arguing that positive water vapor feedback in conjunction with positive cloud feedback cannot be reconciled with how the planet's energy balance is so tightly - but dynamically, maintained.
    Response:

    [DB] "I'm arguing that positive water vapor feedback in conjunction with positive cloud feedback cannot be reconciled with how the planet's energy balance is so tightly - but dynamically, maintained."

    The casual reader will note that, in the absence of doing the physics and showing your work, your statement is devoid of substance and amounts to empty assertion without merit.

  45. DB, Is net negative feedback required for basic stability and maintenance of the current energy balance or not?
    Response:

    [DB] Your question presumes that there is a current energy balance at the TOA; the best understanding of the science indicates otherwise. 

    Energy in ≠ energy out (energy in exceeds energy out).

    You also do not define what physical process you refer to that is providing the "net negative feedback required for basic stability and maintenance".  Energy balance is the sum of physical processes, not hypothetical ones.

  46. DB, "Your question presumes that there is a current energy balance at the TOA; the best understanding of the science indicates otherwise." No, my question presumes the opposite - that there is virtually always an energy imbalance of some degree, especially over the more shorter time scales that the dynamic physical processes of water vapor and clouds operate. The imbalance is either energy in > energy out or energy in < energy out. You are aware that the system is almost never in perfect equilibrium at any given time or over any given time period, right? "You also do not define what physical process you refer to that is providing the "net negative feedback required for basic stability and maintenance". Energy balance is the sum of physical processes, not hypothetical ones." Yes, the planet's energy balance is the net result of all the physical processes (and feedbacks) in the system. Do you agree the net feedback that operates on all the physical processes in the system - whatever they actually are, is negative?
    Response:

    [DB] With all due respect, the last time we discussed this several threads ago, you first need to learn more about the physics of climate science before trying to bend them to your will.  To that end I also recommend Raymond Pierrehumbert's textbook "Principles of Planetary Climate".

    In any event, given the nature of your questions here, it is evident that you have not yet pursued that option.  That is your choice.  But that leaves you on your pre-existent orbit of asking the same questions repeatedly in the hopes that one day you might find an answer more to your liking.  All in all a non-effective path to greater understanding and a waste of other's time.  And indicative of your earlier statement that you were "not here to learn anything"

  47. RW1, you seem rather desperate to demonstrate a net negative feedback for the whole climate system, not just clouds, yet how do you explain palaeoclimatic variations with a net negative feedback? Leprechauns? Positive feedback need not equal runaway feedback.
  48. DB, I already have Ray's book and have read a lot of it. I guess you're not interested in answering my questions?
    Response:

    [DB] If full understanding of the text was not achieved then perhaps you should place those questions over at RC where Ray has a presence.

  49. RW1, Net positive feedback does not lead to runaway warming (Venus result) anymore than net negative feedback leads to Snowball Earth. So, the answer to your question is no. If you do not understand why, you did not understand what you read.
  50. Bibliovermis, I know net positive feedback does not lead to runaway warming. "So, the answer to your question is no." Which question?

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