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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.

Dessler (2010) 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

This rebuttal was updated by Kyle Pressler in September 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 25 July 2017 by skeptickev. View Archives

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Comments 126 to 150 out of 261:

  1. Sphaerica (RE: 116), "115, RW1, The surface cannot be "getting" 517 watts in, as it's only emitting 396 W/m^2. You are ignoring the 23 reflected, 17 transported through thermals and 80 transported through evapotranspiration (396 + 23 + 17 + 80 = 516)." No, I'm not ignoring them. The 23 reflected is part of the albedo and not included in the 239 W/m^2 coming in. Latent heat and thermals are kinetic and not radiative, so the net effect they have on the radiative budget is zero. All the energy entering and leaving the system is radiative. This seems to be a major source of confusion on a multitude of issues. The surface is not getting 516 watts in, as if it was, the surface would be radiating 516 instead of 396. "The 239 comes from ignoring the reflected incoming radiation, which for all intents and purposes never affects the system. So 341 in - 102 reflected = 239. Similarly, 341 out - 102 reflected = 239. Everything balances." Where is the surface emitted of 396 W/m^2 in your numbers? You have to show how the surface is receiving this many watts with 239 entering and 239 leaving. All the energy has to be accounted for, and you can't simply create an additional 120 watts out of nothing (516 - 396 = 120).
  2. Sphaerica (RE: 115), "113, RW1, 'From the ISCCP data, which says that clouds cover 2/3rds of the surface. This means 1/3rd of the surface is clear sky (i.e. cloudless).' No. The ability of clouds to absorb IR is different from "clear sky" (i.e. the atmosphere)." I know - that's the whole point of separating the clear from the cloudy sky, as I did. "One cannot simply take a percentage. It's a meaningless estimation." Relative to the whole of the energy flow from the surface to space, the percentage of clear vs. cloudy sky is what matters. " If my calculations are in error, why do they accurately predict the correct brightness temperature of 255K? Where do you do that, and how?" At the end of my post #2.
    Response: [mc] Fixed closing italics tag.
  3. 126, RW1,
    All the energy entering and leaving the system is radiative. This seems to be a major source of confusion on a multitude of issues.
    All of the energy entering/leaving from space is radiative. That does not allow you to ignore other energy transfers between the surface and atmosphere. Those are not inconsequential. It's an "energy budget," not a "radiation budget." The diagram covers the movement of energy in a three layer model (surface, atmosphere, space). The only way for energy to get in from and out to space is radiative, but that does not apply to transfers between the surface and atmosphere. All energy transfers must be accounted for. You can't simply choose to ignore some numbers. Why do you think things add up properly when they are included, and don't when they are excluded?
    Where is the surface emitted of 396 W/m^2 in your numbers?
    I gave this in post 110, but to repeat and clarify... If you want to consider the atmosphere in total, it gets 79 in from space which is reflected back (a wash). 23 are reflected through from the surface and can also be ignored (a wash), as does the 40 that passes through radiated from the surface. That leaves us with, coming from the surface, 17 from thermals, 80 from evapotranspiration/latent heat, and 356 absorbed through radiation (we've already recognize the 40 that passes through, so we don't work with the whole 396, just the remaining 356), for a total coming into the atmosphere from the surface of 17 + 80 + 356 = 453. Another 78 are absorbed from inbound sunlight, from space, giving a total absorbed by the atmosphere of 531. The atmosphere emits 333 down to the surface as radiation, and 199 (169 from the atmosphere, 30 from clouds) up into space, for a total of 532. So the atmosphere gets 531(532) from above and below, and sends out 532(531) up and down, but not in equal measure (if it did the surface of the planet would be 255˚K, and we'd all be dead, or else we'd be ice-loving lifeforms huddling around geothermal vents in the deep ocean). We can't keep going around and around with this. It's a simple diagram. Sit down with a piece of paper and add the numbers up. It's really not that hard.
  4. Sphaerica (RE: 117), "2) Do you have any response to the question that I've posed 3 times (posts 27, 71, 90) and KR once (post 94)? For the fifth time, do you have any response to the fact that multiple studies, using a wide variety of methods, all point to a climate sensitivity of 3 or greater, and so the chance of cloud feedbacks being negative or neutral is slim to none?" Look, I can only deal with one thing at a time. There are many facets to this whole thing - each of which involve a significant degree of complexity. I can eventually address those things in their appropriate threads.
  5. 126, RW1,
    At the end of my post #2.
    As before, I cannot make heads or tails of those numbers. I can see, though, that you are trying to distinguish clear and cloudy sky in your numbers, and since we have already established that that information is not available in Trenberth's diagram, I can dismiss it as inaccurate. If you'd still like to explain that set of numbers, you can try, but please be clear. What you have now is not. But to give you a generic answer to your "why do they accurately predict" query, if your numbers come to 239 at TOA (no matter how you got there) you are going to get 255K. If they come to 390-396 from the surface, you're going to get 288K-289K. That running your calculations in reverse brought you back to these numbers is no big surprise, but doesn't validate the logic behind the calculations.
  6. 126, RW1,
    Look, I can only deal with one thing at a time.
    Apologies, but you cannot one the one hand claim that there is other evidence for negative cloud feedbacks (without producing it), and on the other ignore the contrary evidence (neatly summarized and cited by SS) provided as rebuttal. But I will agree, we should continue to focus on your numbers, and your interpretation of Trenberth's diagram, as I believe that is where you will get the greatest insight into where you are mistaken. Once we get past that, we can revisit your position on the issue by considering other factors.
  7. Quick correction. At the end of post 128, I incorrectly said the temp would be 255˚K if the atmosphere radiated heat equally in both directions. The actual temperature would be 262˚K. We'd still be ice-loving creatures living in the ocean depths near geothermal vents, but we wouldn't be quite as ice-loving as I implied.
  8. RW1 - "Look, I can only deal with one thing at a time. ... I can eventually address those things in their appropriate threads. " I would like to point out that this is the "What is the net feedback from clouds" thread - that in fact is the appropriate topic here, not various interpretations of the Trenberth energy budget. Looking up the dynamic feedback numbers in the Trenberth diagram, let's see... Look! Nothing! There is no dynamic information, nothing about net feedbacks, nothing about how various elements change with temperature, in the Trenberth diagram!
  9. Sphaerica (RE: 130), "All of the energy entering/leaving from space is radiative. That does not allow you to ignore other energy transfers between the surface and atmosphere. Those are not inconsequential. It's an "energy budget," not a "radiation budget." The diagram covers the movement of energy in a three layer model (surface, atmosphere, space). The only way for energy to get in from and out to space is radiative, but that does not apply to transfers between the surface and atmosphere. All energy transfers must be accounted for. You can't simply choose to ignore some numbers." I'm not ignoring anything. Nor am I claiming the kinetic energy flows of latent heat and thermals from the surface to the atmosphere aren't part of the whole thing. They are. The problem lies in that Trenberth returns the energy from latent heat and thermals to the surface as 'back radiation' when in reality most of it returns in kinetic form through precipitation. The bottom line is it's returned to the surface in equal and opposite amounts, so relative to the radiative budget and COE, its net effect is zero. If any of the kinetic energy moved from the surface into the atmosphere gets radiated into the atmosphere and ultimately radiated out to space, the amount returned to the surface will be less than the amount that left the surface. This will cool the surface and reduce surface emitted radiation by and equal and opposite amount. Again, this seems to be a major source of confusion. In Trenberth's diagram, the latent heat and thermals of 97 are returned to the surface as 'back radiation'. The incoming solar energy of 78 'absorbed by the atmosphere' is also brought to the surface as 'back radiation'. But it's not really 'back radiation' - it's 'forward radiation' yet to reach the surface that last originated from the Sun. The point is 239 W/m^2 from the Sun gets to the surface and becomes 396 through 157 of back radiation from the atmosphere. 333 - 97 - 78 = 158 coming back from the surface emitted of 396. 239 arriving at the surface from the Sun + 157 arriving at the surface from back radiation from the atmosphere = 396 emitted at the surface. From the surface, 70 passes through the atmosphere unabsorbed out to space and 169 is emitted by the atmosphere up out to space. 70 + 169 = 239 leaving at the TOA.
  10. Sphaerica (RE: 128), "Another 78 are absorbed from inbound sunlight, from space, giving a total absorbed by the atmosphere of 531." The atmosphere cannot create any energy of its own. COE dictates this. You can't have 531 absorbed by the atmosphere when only 239 W/m^2 are coming in and the surface is only emitting 396 W/m^2.
  11. 134, RW1,
    ...when in reality most of it returns in kinetic form through precipitation...
    No, this is wrong. The kinetic energy isn't part of the equation. You're right, it's lifted up, and then falls down. What is being transported is the heat. Thermals are bodies of air that are heated by the surface, and rise. The heat doesn't fall back down through the pull of gravity. It stays in the atmosphere until it is radiated away. Evapotranspiration puts the energy into vaporizing the water. When the water condenses in the atmosphere, that energy is released -- to the surrounding atmosphere -- as latent heat. When the rain falls, it's a cool rain, having left its heat behind in the atmosphere.
    In Trenberth's diagram, the latent heat and thermals of 97 are returned to the surface as 'back radiation'.
    Okay, so if you got this, what was the "kinetic energy" bit about? But you are wrong in saying it is returned to the surface. The same goes for the energy absorbed by the atmosphere from the sun. You can't say where it goes versus other energy. The atmosphere is a big pot, and all of the energy is part of the stew. Once it's been added, you can't say "this part of the broth came from here and has to go there."
    239 arriving at the surface from the Sun + 157 arriving at the surface
    I have told you repeatedly. You are making the 157 number up. You cannot extract that with the information given. We need to stop discussing this. If you can't interpret the diagram properly, you certainly can't out think all of the climate scientists. Sit down and work this stuff out. Don't start by assuming you're smarter than everyone. Start by assuming you are the student, and there is something here you don't get. Stop trying to second guess it. Work through the numbers. Understand the diagram. If you can do that, and we can move beyond this, we can discuss negative cloud feedbacks. We've already overloaded this threat with analyzing Trenberth's diagram (for the sake of analyzing your numbers on negative cloud feedbacks) and we're getting nowhere.
  12. (RE: my 134), I wrote: The point is 239 W/m^2 from the Sun gets to the surface and becomes 396 through 157 of back radiation from the atmosphere. 333 - 97 - 78 = 158 coming back from the surface emitted of 396. This should say: The point is 239 W/m^2 from the Sun gets to the surface and becomes 396 through 157 of back radiation from the atmosphere. 333 - 97 - 78 = 158 coming back to the surface for a total of 396 (239 + 158 = 396) (Trenberth purposefully has an extra watt in there).
  13. Sphaerica (RE: my 136), "[The kinetic energy isn't part of the equation]. You're right, it's lifted up, and then falls down. What is being transported is the heat. Thermals are bodies of air that are heated by the surface, and rise. The heat doesn't fall back down through the pull of gravity. It stays in the atmosphere until it is radiated away. Evapotranspiration puts the energy into vaporizing the water. When the water condenses in the atmosphere, that energy is released -- to the surrounding atmosphere -- as latent heat. When the rain falls, it's a cool rain, having left its heat behind in the atmosphere." Thermals and latent heat are in the form of kinetic energy. They are totally separate from and in addition to the 396 emitted radiatively by the surface. I do not dispute that some of the kinetic energy moved from the surface to the atmosphere is radiated into the atmosphere and finds its way radiated out to space. Regardless of whether it's most or only a small amount (Trenberth has all of it being returned), it's net effect is still zero on the radiative budget. I think you may not understand that the surface is emitting 396 solely due to its temperature and nothing else. As a result, it cannot be receiving more energy than this.
  14. @Sphaerica RW1 has made 52 comments to this post, so far. Virtually none of that deserves a reply. He or she went on commenting virtually because you continue to reply to him/her. In my opinion it is most of all off-topic because all those additions and subtractions don't make to "feedback". I don't want to point nothing specifically because I didn't read -nor did nor will, most of the visitors- that ping-pong of some 100 of comment. I'm saying I don't want to point, but I suspect that somebody might try to get some 70W/m2 reflected upwards and some whatever, say, 40W/m2 downwards and "declare" a negative feedback from that when the feedback resides in the change of cloudiness, the type of clouds and the altitude of the clouds so those 70/40 would change maybe to 71/42 or maybe to 72/38 what provides the feedback and its sign. I'm not sure what are you two discussing, but I don't see in Trenberth's figure nor in those finger calculations the feedback that may confirm or falsify the myth subject of this post. If you stop replying I think RW1 messages will end the same way foam vanishes once shaking ceases.
    Response: [muoncounter] This is deja vu all over again; by the standards of the Lindzen and Choi thread, its just getting warmed up.
  15. Sphaerica (RE: my 136), "But you are wrong in saying it is returned to the surface. The same goes for the energy absorbed by the atmosphere from the sun. You can't say where it goes versus other energy. The atmosphere is a big pot, and all of the energy is part of the stew. Once it's been added, you can't say "this part of the broth came from here and has to go there." You can derive them with the constraints COE puts on the system. There is only one source of energy - the Sun. You can't count energy twice, which is what Trenberth does in the diagram by designating 78 being absorbed by the atmosphere and also having it part of the 333 of back radiation to the surface. The atmosphere cannot create any energy of its own - the energy either last originated from the Sun or surface emitted.
  16. Sphaerica (RE: 130), "As before, I cannot make heads or tails of those numbers. I can see, though, that you are trying to distinguish clear and cloudy sky in your numbers, and since we have already established that that information is not available in Trenberth's diagram, I can dismiss it as inaccurate." Only the cloudy vs. clear sky percentages don't come directly from Trenberth's diagram. Everything else is taken directly from the diagram, as I've explained (or tried to at least). "That running your calculations in reverse brought you back to these numbers is no big surprise, but doesn't validate the logic behind the calculations. That's true, but the point is all the calculations work out with the all 'logic' I've used, and the criticisms of the 'logic' don't work out, as I've shown. For example, it was claimed the 169 designated as being 'emitted by the atmosphere' was for the clear sky, but that doesn't work because only 131 W/m^2 is actually emitted to the clear sky. Can you find a better way to quantify the relationships in a way that results in the appropriate output power and brightness temperature of 255K?
  17. @muoncounter response to #139 Oh! I see (my Goodness). So, why not a Yogi Berra section? For instance, one of the last comments telling something like "a body that emits energy solely due to its temperature cannot be receiving more energy than that" or "if the square doesn't fit the circular hole then take a drop hammer and, smash it!".
  18. RW1, We're done. As muoncounter and Alec have pointed out, I've shown way too much patience, and you quite simply don't get it... seemingly because you refuse to. I can't help you with that. The diagram is very, very simple. It's really not all that hard to understand, and that you ever thought you had the genius to prove all of climate science wrong through your clever re-interpretation of it just astounds me. You should put less time into your clever numbers, and more time into reading up on the physics behind climate science. It would help you tremendously, and the number of misconceptions and misunderstandings you hold now seem enormous -- they're holding you back. Really, the mods should go back and delete every single post, because almost none of them relate in any way to cloud feedback, and where they do, they're tainted by your misinterpretation of Trenberth's simple energy budget diagram. Conversation ends.
  19. Sphaerica (RE: 143), "We're done. As muoncounter and Alec have pointed out, I've shown way too much patience, and you quite simply don't get it... seemingly because you refuse to. I can't help you with that. Conversation ends." Suit yourself. "Really, the mods should go back and delete every single post, because almost none of them relate in any way to cloud feedback, and where they do, they're tainted by your misinterpretation of Trenberth's simple energy budget diagram." All of the my posts are directly or indirectly related specifically to the cloud feedback issue. If anything, I was the one frequently pushing to keep the discussion on topic, while others digressed.
  20. Documentary evidence that cloud feedback is positive, courtesy of the good folks at the North Pole webcam site: Spring conditions can be cloudy at the North Pole. Clouds are produced when the North Pole experiences Spring warming and the beginning of Summer melting. Water is evaporated from the melting snow surface, forming the fog and low clouds that are seen in Spring/Summer pictures from the North Pole, such as the one on the right from June 2002. In the left image, from 5/1/02 19:06 UTC, the surface is covered by fog and low clouds. Radiation energy is trapped near the surface and thus the temperatures have increased to a very warm 27 F. -- emphasis added [source] Temperature inset at lower left shows 27F as stated.
  21. muoncounter (RE: 145), "Documentary evidence that cloud feedback is positive, courtesy of the good folks at the North Pole webcam site: Spring conditions can be cloudy at the North Pole. Clouds are produced when the North Pole experiences Spring warming and the beginning of Summer melting. Water is evaporated from the melting snow surface, forming the fog and low clouds that are seen in Spring/Summer pictures from the North Pole, such as the one on the right from June 2002. In the left image, from 5/1/02 19:06 UTC, the surface is covered by fog and low clouds. Radiation energy is trapped near the surface and thus the temperatures have increased to a very warm 27 F. -- emphasis added" It's not disputed that the cloud feedback is positive in areas that are permanently snow and ice covered, such as the North Pole. This is because the albedo of clouds is roughly the same as snow and ice, so the net effect of clouds is to warm by 'trapping' additional surface emitted energy. However, the vast majority of the Earth is not snow or ice covered, which is consistent with net negative feedback for clouds, globally. Also, when ice or snow melts from warming (CO2 induced or otherwise), the primary mechanisms that drive negative cloud feedback reassert themselves - specifically the latent heat of evaporation, which has a strong cooling effect on the surface, and the clouds above become more reflective than the surface, which also has a strong cooling effect.
  22. RW1#146: "the vast majority of the Earth is not snow or ice covered, which is consistent with net negative feedback for clouds" I don't know where you live, but in my neck of the woods, nights don't get cool when there's high humidity (which is almost always) or high clouds. But here's how an actual weatherperson puts it: Clouds are regions of a high density of saturated air, (which form cloud droplets). Clouds (especially low thick clouds) have a high ability to absorb and re-emit longwave radiation. Thus, on cloudy nights much less longwave radiation is able to escape to space. Holding in heat at night is a fingerprint of the enhanced greenhouse effect. So your thesis that clouds will always be negative feedbacks doesn't hold water.
  23. 146, RW1,
    However, the vast majority of the Earth is not snow or ice covered, which is consistent with net negative feedback for clouds, globally.
    So you say, but you offer no (substantive) support that actually proves this. You keep saying there's a net negative cloud effect, but (1) you don't prove it, and (2) as several people have pointed out, the important factor isn't the net current effect, it's the net change as a result of warming. Similarly, your logic is only so much "thought experiment" with no substantive calculations. It's easy to say things like "strong cooling effect" without backing such statements with actual numbers.
  24. muoncounter (RE: 47), "I don't know where you live, but in my neck of the woods, nights don't get cool when there's high humidity (which is almost always) or high clouds. But here's how an actual weatherperson puts it: Clouds are regions of a high density of saturated air, (which form cloud droplets). Clouds (especially low thick clouds) have a high ability to absorb and re-emit longwave radiation. Thus, on cloudy nights much less longwave radiation is able to escape to space. Holding in heat at night is a fingerprint of the enhanced greenhouse effect. So your thesis that clouds will always be negative feedbacks doesn't hold water." Yes, net effect of clouds at night is to warm (or slow heat loss). This is because clouds are better at 'trapping' outgoing surface energy than the clear sky is. Again, this is not in dispute, nor does it conflict with net negative feedback for clouds. Globally averaged data automatically includes the effects of night and day.
  25. Sphaerica (RE: 148), "You keep saying there's a net negative cloud effect, but (1) you don't prove it," I've provided much evidence and logic for net negative cloud feedback. Even Dessler says in his paper the net effect of clouds is to cool by 20 W/m^2. "(2) as several people have pointed out, the important factor isn't the net current effect, it's the net change as a result of warming." I'm aware of this, but I'm not the one making the claim that the net effect of clouds is suddenly going to switch from cooling to warming on the next few watts incident on the surface.

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