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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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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Argument Feedback

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Comments 201 to 225 out of 261:

  1. No, net feedback in the climate system is not required to be negative.
  2. Bibliovermis (RE: 201), "No, net feedback in the climate system is not required to be negative." Then can you explain how the current energy balance is maintained despite such significant amount of shorter-term, local, regional, seasonal hemispheric and even sometimes globally averaged variability?
  3. 202, RW1, Can you explain how such variability could exist with a net negative feedback damping the system?
  4. Sphaerica (RE: 203), "Can you explain how such variability could exist with a net negative feedback damping the system?" It's a highly dynamic and chaotic system with large changes in incident energy flux. Changes from day to night, changes in atmospheric circulation patterns, etc., etc. It's constantly changing everywhere all the time.
  5. Sphaerica (RE: 203), Feedback, by definition, is the response to the changes in energy flux from all the chaos that results in the constant variation.
  6. 204, RW1, Yes, we all know that. It doesn't answer the question.
  7. 205, RW1, Yes, we all know that. It doesn't answer the question. Except for the "from all the chaos that results in the constant variation" part. You added that just to make it look like it fits well with your own hypothesis, but you just made it up. Feedback is the response to the inputs. Period.
  8. 204, RW1, 205, RW1, In case I'm being too subtle, what I mean by that is stop playing games and answer the question.
  9. Sphaerica, Feedback is the response to changes in energy flux. I'm not sure I understand the question. Yes, the constant change and chaos fits well with what I'm saying. That's largely my point.
  10. RW1, I must have missed your answer to my question - how do you explain palaeoclimate variations (glacial-interglacial cycles and so on) with a net negative feedback? Maybe you can provide an answer where Pielke, Spencer and Lindzen have not (to my knowledge)?
  11. The question, rephrased so that you can understand it, is: If you have a net negative feedback, why does the system succeed in fluctuating so greatly? Why does the negative feedback not keep the system stable and within very narrow confines? And separately there is no requirement that the inputs be the "constant change and chaos." Yes, I understand that it fits with what you are trying to arbitrarily impose on the system, but it is too narrow a definition. The feedback is a response to any input, whether that input is part of constant change and chaos, or a new, steady input. Any attempt to frame the definitions and system only within the narrow confines of a predetermined conclusion will confuse the issue. Please stick with proper, true definitions, rather than reframing things in order to score points or twist the argument in a certain direction.
  12. RW1, Your current question to me (#202) is effectively "How can 2 + (2 * 1.5) = 5?" In the context of your question, positive feedback is simple math.
  13. Sphaerica (RE: 211), "The question, rephrased so that you can understand it, is: If you have a net negative feedback, why does the system succeed in fluctuating so greatly? Why does the negative feedback not keep the system stable and within very narrow confines?" Because the feedbacks take time and the system is largely chaotic. Over time, the net negative feedback does keep the system tightly constrained, which is why longer-term globally averaged there is generally very little change relative to the much larger more local and regional short-term change.
  14. Sphaerica (RE: 211), "The feedback is a response to any input, whether that input is part of constant change and chaos, or a new, steady input." Yes. It's interesting that you would mention this because it leads into my next point, and that is the physical processes and feedbacks that maintain the planet's energy balance cannot be separated from those that will act on additional 'forcings', such as GHGs.
  15. Feedbacks need not be instantaneous. For instance, when wolves were shot in the early 20th century in order to increase the deer populations, herds increased immediately. However, the increase in the herds exceeded the carrying capacity of the environment, and the herds decreased over the next several years due to the lack of food supply. The herds varied widely initially, but were eventually constrained by the food feedback to a population which was not all that different from the original.
  16. 213, RW1, Your original question was:
    Then can you explain how the current energy balance is maintained despite such significant amount of shorter-term, local, regional, seasonal hemispheric and even sometimes globally averaged variability?
    My leading question was:
    If you have a net negative feedback, why does the system succeed in fluctuating so greatly? Why does the negative feedback not keep the system stable and within very narrow confines?
    Your answer for my question was:
    Because the feedbacks take time and the system is largely chaotic.
    My answer to your original question is:
    Because the feedbacks take time and the system is largely chaotic.
  17. 214, RW1,
    Yes. It's interesting that you would mention this because it leads into my next point, and that is the physical processes and feedbacks that maintain the planet's energy balance cannot be separated from those that will act on additional 'forcings', such as GHGs.
    Good for you. You are beginning to demonstrate some grasp of how the system operates. Now your questions have been answered. You need to answer some of the questions that have been posed to you, specifically: With a net negative feedback, how do you account for the broad fluctuations in climate that have been identified throughout recorded history (through proxy studies)? And With a net negative feedback, how do you account for the dramatic and historically unique warming of the past 30 years? Why has your powerful net negative feedback not succeeded in constraining temperatures for the past thirty years? If it has not done so in that time frame, how can you imagine that it will do so in the future, as we continue to raise CO2 levels to dramatic extremes?
  18. RW1 - "Then can you explain how the current energy balance is maintained despite such significant amount of shorter-term, local, regional, seasonal hemispheric and even sometimes globally averaged variability?" Conservation of energy, RW1. Internal variation produces lots of fluctuations, but such excursions up and down are limited by the incoming/outgoing energy levels, and will cycle around those energies. And of course, if the amount of energy in the climate changes due to (for example) increased GHG's, the climate will shift it's average behavior accordingly. As to feedbacks, as long as the gain < 1, the system is stable, as per the Does positive feedback necessarily mean runaway warming thread. Net positive feedback means a greater shift in climate state for input/output energy changes - not instability. And positive feedback is observed from the ratio of paleo changes in climate to reasonably well known energy changes, QED. --- RW1 - This has all been discussed with you before, in excruciating detail, on the Lindzen-Choi threads. Your continuing intransigence indicates (IMO) that your opinions and preconceptions are apparently more important to you than the facts.
  19. Sphaerica (RE: 217), I don't think you understand what net negative feedback means. It does not mean that no long-term change can occur (or even short-term change). It means the response to changes in 'forcing' or energy imbalance will be to oppose or diminish those changes rather than re-enforce or amplify them.
    Response:

    [DB] Sphaerica quite well understands both positive and negative feedbacks, including those "net" ones.

  20. RW1, I see you continue to ignore my question to you, put in #197 and #210. How do you explain palaeoclimate variations with a net negative feedback? The initial orbital forcings were much smaller than the resulting climate changes. Palaeoclimate variations, being real-world climate changes with real causes and real effects, already include the cloud feedbacks. I take your non-answer to mean that you, like Lindzen, Spencer and Pielke, do not have an answer to that question...
  21. 219, RW1, I don't think you understand what positive feedback means. It does not mean that only long-term changes can occur. It means the response to changes in 'forcing' or energy imbalance will be in the same direction or enhance those changes rather than reduce or negate them. Now that we're done with the absolute silliness, it had been left that you had your question answered quite clearly and succinctly. Indeed, I allowed you to provide the answer to the question yourself. Now you need, in order to carry the conversation forward, to answer the questions that have been asked of you, without evasion. These questions have now been asked multiple times and you have failed to provide answers. The discerning viewer will begin to come to the conclusion that you either do not have the answers, or you are chagrined at where those answers logically lead. The questions you must answer are: With a net negative feedback, how do you account for the broad fluctuations in climate that have been identified throughout recorded history (through proxy studies)? With a net negative feedback, how do you account for the dramatic and historically unique warming of the past 30 years? Why has your powerful net negative feedback not succeeded in constraining temperatures for the past thirty years? If it has not done so in that time frame, how can you imagine that it will do so in the future, as we continue to raise CO2 levels to dramatic extremes?
  22. sky#220: Not to worry; we're coming up on the one year anniversary of the net negative feedback gambit.
  23. It's like Groundhog Day...all over again.
  24. skywatcher (RE: 220), I can answer those questions, but they are off topic and not really relevant to what's being discussed at present. I'm primarily talking about the planet's current energy balance and whether or not net negative feedback is required to maintain this balance. The claim here seems to be that net negative feedback is not required, though I don't see this could be the case.
    Response:

    [DB] Actually, skywatcher's questions to you are both germane and on-topic.  You are clearly being evasive and avoiding answering questions for which you have no substantive answer.

  25. Sphaerica (RE: 221), "The questions you must answer are: With a net negative feedback, how do you account for the broad fluctuations in climate that have been identified throughout recorded history (through proxy studies)? With a net negative feedback, how do you account for the dramatic and historically unique warming of the past 30 years? Why has your powerful net negative feedback not succeeded in constraining temperatures for the past thirty years?" I'm sorry, but I still don't think you understand entirely what is meant by net negative feedback. The warming we've experienced in the last 30 years is entirely possible with net negative feedback operating on the system. I'm not sure what else to say in regards to this. As to the more 'broad fluctuations' in the climate that have occurred (whatever that means exactly), no doubt there are numerous reasons why. The main ones appear to be changes in energy distribution within the system (from Milankovitch orbital cycles) and the positive feedback effect of melting surface ice (like from glacial to interglacial) or growing surface ice (like from interglacial to glacial).

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