Initial Comments on New Positive Cloud Feedback Paper in Nature

January 1st, 2014 by Roy W. Spencer, Ph. D.

I’ve received several emails asking about the new Nature paper, Spread in Model Climate Sensitivity Traced to Atmospheric Convective Mixing, by Sherwood et al.

So far I’ve only read the abstract and looked at the figures…I’ll either need to find a copy of the paper or buy it to dig into the details.

It looks like a serious attempt to understand the spread in climate model sensitivities, which the authors appear to contend is due more to low cloud feedback (whether low clouds increase or decrease with warming) than any other single mechanism. They are trying to understand what physical processes in the models lead to the spread in cloud feedback across the models, and that understanding would be a good thing.

It appears they go a step further, though…claiming that the models with more realistic convective mixing in the tropical lower troposphere exhibit stronger positive cloud feedback. Their conclusion is that it’s actually the models producing the most warming that should be believed the most.

First, let’s examine the scenario wherein they are right. Since observed tropical warming has been arguably less than ALL models have forecast, there must be some natural cooling mechanism the models do not contain which will magically go away at some point.

When that happens, warming will return with a vengeance. So, when is that going to happen? Of course, no one knows. But the longer it takes, the more dramatic the warming will be, because it eventually has to “catch up” to the forecasts of the models which produce the most warming…those models which Sherwood et al. are now on record as claiming to be the best prognosticators of future doom.

Well, this certainly makes the debate more interesting. It feels like a poker game where you keep drawing crappy cards, but you keep raising your opponents.

I will be very interested to see the details in this paper. Cloud formation is a complex subject…there are many, many variables involved. For now, I at least applaud the authors for trying.

41 Responses to “Initial Comments on New Positive Cloud Feedback Paper in Nature”

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  1. Stevek says:

    If they are correct then the missing heat must be somewhere. Some say deep in oceans.

  2. numberer says:

    “I, at least, applaud the authors for trying”.


    Good intentions butter no parsnips.

    • I’m trying to be more positive for the New Year. I suspect it won’t last long, though.

      • numberer says:

        The shortest-lasting New Year’s Resolution, ever, was mentioned in a letter to the Daily Telegraph of London.

        “My wife resolved to swear less at our boisterous black labrador. Four seconds after midnight on New Year’s Eve he launched an assault on her while she was singing ‘Auld Lang Syne’…”

  3. dave says:

    I love buttered parsnips.

    If I have been promised buttered parsnips merely as a joke, I will be v.v. annoyed and probably recommend loss of grant, loss of tenure, and generally horrible consequences.

  4. Beta Blocker says:

    Dr. Spencer, to your knowledge, is there a cogently written explanation available somewhere on the Internet which describes the water vapor feedback theory of AGW in terms that a layman can understand?

    What I am asking for here is a layman’s description of the feedback mechanism through which the basic 1C to 1.5C warming per doubling of atmospheric CO2 concentration becomes amplified into a 3C-4C temperature rise as concentrations of water vapor increase in response to a warming atmosphere.

    My question arises from a second and larger question, which happens to be this — if an increasing concentration of CO2 can heat the atmosphere sufficiently enough to cause a water vapor feedback mechanism to kick in, why couldn’t some other kind of process (or agent) which traps excess heat in the atmosphere also cause a similar feedback mechanism to kick in?

    An alternative way of phrasing that second question is to ask, are carbon-based GHG’s unique in their ability to trigger a positive water vapor feedback mechanism, one which can amplify the basic temperature response of the initiating agent by two to three times relative to what might otherwise be expected with no amplification?

    • Terry says:

      Beta Blocker. The simple answer is that any agent whether it be GHG’s, solar variation, variation in the earth’s orbit or any so far unknown agent will cause it.

      The fundamental reason is this. If you have an atmosphere that has say a temperature of say 18C, then there will be a given amount of water vapour present (actually about 0.009 kg per kg of air). There will therefore be a fixed amount of cloud in the atmosphere. Now if you increase the temperature to 20C(by whatever means you choose) then the amount of water vapour will increase to 0.01 kg per kg of air, which will “in theory” mean more cloud. That is a very simplistic analysis but actually about the same level of detail that the current models used by IPCC have.

      • numberer says:

        “…more cloud…”

        Which means a greater albedo.

        • Terry says:

          Yes, but the real question is whether or not the albedo is greater than the longwave trapping that also occurs. I have often said that it is very diffuclt to get the “right answer” because it is the difference between two large numbers and small errors result in major changes to the predicted feedback. I think it will take a really clever new way of looking at it to get the bottom of it. The new paper by Sherwood appears to be a start, but Dr Roy’s work is in my opinion quite exciting because it looks at more “real time” effects rather than long term averages. Interesting times

          • numberer says:

            “…albedo is greater than the longwave trapping…”

            No. A change in the albedo is the only thing which will change the temperature of the earth, based on what Mother Nature has decreed for our present physical arrangements.

            The Sun sends us on average through the year at a power of 122 Peta-Watts (net of the albedo effect) which the earth re-radiates to space. The re-radiation is almost exact, because it reaches a dynamic equilibrium by small changes in temperatures (small, because of the 4th- Power radiation Law)

            The most enlightening “consolidation accounting” analysis* of the 122 Peta-Watts is that:

            (1) the surface of the earth receives a net 10 Peta-Watts which it re-radiates directly to space through “radiation windows”.

            (2) the earth system as a whole receives 112 Peta-Watts which is radiated to space by the atmosphere.

            Now; Unless the Albedo changes:

            The atmosphere can’t warm up on its own because it would necessarily radiate more than 112 Peta-Watts to space and the earth as a whole would cool and this would pull the atmosphere back to the temperature at which it radiates exactly 112 Peta-Watts to space.

            The surface of the earth (including the top of the oceans)can’t warm up on its own because it would necessarily increase its present radiation to the atmosphere of 138 Peta-Watts and it would also increase its present non-radiative transfer of 52 Peta-Watts to the atmosphere. And this would increase the temperature of the atmosphere, which is an impossibility on anything except a very short time-scale,as already discussed.

            Conversely, neither the atmosphere nor the surface can cool significantly.

            In other words THE SYSTEM IS STABLE to an extraordinary degree. The reason for this stability is that the greenhouse gas effect is SATURATED in the sense that it is operating at full throttle. The 138 Peta-Watts which the surface is sending by radiation to the atmosphere and which is being absorbed by the atmosphere is the full “effort” of the surface to divest itself of energy in this way. Right now, the atmosphere could absorb almost any amount of extra net longwave radiation the earth might throw at it, in a heartbeat. And throw it away into space in a matter of days.

            *tracing back from the TWO WAYS in which the energy is LOST to space

  5. Steve says:

    I think the graph Steven Goddard has on his post about the Sherwood paper sums it up pretty well:

  6. Josh Cryer says:

    Roy, before delving deeper you probably want to look at “The Role of Subtropical Subsidence in Climate Sensitivity” too, as it also backs up the claim that clouds are a positive feedback (the first paper critical of models in that vein as far as I know). John Fasullo has it posted on his site (he was kind enough to email me it when it originally came out).

    As of note, Steven C. Sherwood also appears to post his papers to his site. So don’t pay for it. At minimum wait for the embargo to be over (it’s slated for Jan 2. Nature publication) or ask Steven for a copy via email. Don’t feed the paywalls, it’s science.

    Happy New Year. :)

  7. numberer says:

    “…greenhouse gas effect is saturated…”

    To clarify, “saturated” in the sense that there is more than enough greenhouse gasses to stop all outgoing longwave radiation which can be stopped. Not in the sense that the atmosphere is incapable of increasing its radiation back to earth. That would certainly happen if there were generally higher temperatures because of a change in solar irradiance or in the albedo.

  8. numberer says:

    “…stop all outgoing longwave radiation…”

    from the surface of the earth heading towards space.

  9. dave says:


    If there were some positive feedback this would apply with even greater force to water vapour ITSELF. Then the multi-year “excursions” of the satellite figures for temperature should should be much greater than they have been, in view of the considerable variability that is there month to month

  10. More of the same. They are trying so hard to come up with reasons why the models which are wrong, are right.

    I think actual temperature declines will be the only way to silence them, and even then they may come up with global warming being the cause for that.

  11. Andrew says:

    This was my reaction, posted elsewhere:

    “So basically, *in models*, this particular effect is very important. We therefore assume it is equally important *in reality*, and furthermore we assume that setting this one parameterization closer to a realistic value necessarily makes what that *causes* in models more realistic. Finally, we assume that, since models agree much better with one another on most other parameterizations, those will not bias estimates of sensitivity, since, agreeing with each other, they must be right.”

    To my way of thinking, this is an absolute absurdity.

  12. numberer says:

    “…actual temperature declines will be the only way to silence them…”

    The present pause has been accompanied by an increase in the proportion of the population in Western countries who believe in the reality of global warming. Older, sceptical, people shuffle off into powerless retirement, while their grandkids are imbibing the new religion with their mother’s milk.

    It was much the same with the growth of Nationalism in 19th Century Europe. At first, the idea of a mystical Germany or England or what have you was merely the creation of a few sentimental University professors of culture. They managed to persuade some of their students, who formed the next generation of High School teachers, who in their turn indoctrinated the next generation of Elementary-School teachers. By the end, tens of millions went joyfully off to die a glorious death for something or other.

  13. bernie says:

    “I do not know who fought who – or why,
    But ’twas a lie that sent them out to die.”

  14. RW says:

    No one (including Roy) seems to see that the entire way the cloud feedback issue is framed is hugely flawed. The issue is indirectly or’hiddenly’ framed as though clouds are static variable in the system whose change upon a change in the energy balance, like from 2xCO2, is unknown or big mystery.

    Clouds and water vapor are by far the two most dynamic and continuously varying components of the whole atmosphere. Each are the main driving components of the net feedback mechanism that maintains the planet’s energy balance from the forcing of the Sun. Note that there must an acting net feedback mechanism, otherwise how is the energy balance maintained – let alone so tightly maintained given all the chaos and complexity? Basic control system theory – not to mention elementary physical logic, says this acting feedback must be net negative.

    Now, the 1.1C of so-called ‘zero-feedback’ is derived from the absolute response of the system to solar forcing, which is about a 1.6 to 1 power densities ratio (390/240 = 1.6). This just means that is takes about 1.6 W/m^2 of net surface power gain to allow 1 W/m^2 to leave at the TOA, offsetting each 1 W/m^2 entering the system from the Sun. 3.7*(390/240) and you get about 6 W/m^2 or +1.1C.

    The 1.6 to 1 (i.e. surface to TOA) ratio is already giving a rough measure of the net effect of all the physical processes and feedbacks operating in the system, including especially water vapor and clouds, as two are by far the most dynamic components of the whole atmosphere.

    Put very simply, one cannot arbitrarily separate the net effect the two most dynamic components of the whole atmosphere (water vapor and clouds) have in the current energy balance from the forcing of the Sun, from the net effect they will have on additional ‘forcings’ or imbalances, such as doubled CO2. The physical processes and feedback mechanisms themselves (from water vapor and clouds) would have absolutely no way of distinguishing such an imbalance from any other imbalance imposed as a result of the regularly occurring dynamic chaos in the system.

  15. I see cloud albedo feedback to greenhouse gas change as slightly positive. Warmer surface and cooler upper troposphere from increase of greenhouse gases will increase convection. Also, generally warmer troposphere means more water vapor, at least in the updrafts.

    The result I see: Updrafts becoming much more efficient at moving heat when greenhouse gases increase. Updrafts gain efficiency at moving heat more than downdrafts, so a smaller percentage of the world’s area is covered by updrafts, and a larger percentage of the world’s area is covered by downdrafts. Since updrafts tend to be cloudier than downdrafts, this situation would make the sky less cloudy. The clouds will have more or (more likely) larger water particles, and will be more efficient at producing precipitation, while covering less of the sky.

    Although I see the cloud albedo feedback as positive, I think it’s a fraction as positive as IPCC likes to see it. A related thing: Decreasing the updraft/downdraft ratio of area coverage would reduce the relative humidity of the troposphere. There is some indication (but short of clear-and-convincing-evidence) that this is occurring. This would make the water vapor feedback less than what it would be with constant relative humidity. IPCC seems to me to favor values of water vapor feedback typical of constant relative humidity.

    I suspect the sum of water vapor and cloud albedo feedbacks is close to what the water vapor feedback alone would be with constant relative humidity.

  16. Vilnius says:

    Re numberer January 2, 2014 at 7:22 AM

    Stable, saturated greenhouse effect? What do you mean? I have seen only one such a theory so far, that of Ferenc Miskolczi.

  17. Jack says:

    Dr. Roy,

    Much convection is “sub-grid scale” and parameterized in the models.

    Are there any estimates of global convective heat flux that you believe are reliable?

  18. Beta Blocker says:

    In the few days that have passed since my original questions concerning the fundamental nature of the postulated water vapor feedback mechanism were asked, several opinions have been offered as to how the water vapor feedback mechanism does, or does not, operate within the earth’s climate system.

    As I understand the situation, the Sherwood et al paper looks at the various climate models now operating on computers as being alternative descriptions of the climate system’s physical reality — descriptions which have many important similarities but also some important differences.

    But what about the “real” climate system, the one that operates up there in the atmosphere; down there in the oceans; and out there in space — not the various representations of the earth’s climatic system that operate inside of computers?

    And so another question might be asked, what kinds of experiments and data collection activities should be conducted within the real earth climate system — the one that operates up there in the atmosphere; down there in the oceans; and out there in space — which can answer the fundamental questions as to how the water vapor feedback mechanism actually operates, if in fact it does actually exist?

    • Steve says:

      You might be interested in this post:

      The seasonal response is certainly consistent with positive water vapor feedback.

      But of course, consistency & hobgoblins and all.

      • Beta Blocker says:

        Steve, your analysis of seasonal radiative response concludes that the existence of a positive water vapor feedback mechanism is consistent with observational data taken directly from the operative real-world climate system.

        But does your analysis demonstrate the existence of such a feedback process to some reasonable degree of certainty?

        If your analysis as it stands today doesn’t quite get there — let us presume that it is in the ballpark, but not as close as one would like it to be in its ability to resolve some number of reasonably expressed doubts — what more could be done to shore up the analysis in terms of pursuing an improved approach to data acquisition and interpretation?

        If we are to demonstrate the existence of a positive water vapor feedback mechanism to some reasonable degree of certainty, what kinds of information do we need to start collecting from the real-world climate system that we aren’t collecting today?

  19. numberer says:


    “Stable” is a theory. I will not explain that again.



    Earth surface (incl. sea) radiates 350 W/M^2 power
    upwards in wavelengths amenable to trapping;

    Atmosphere absorbs whole of said 350 W/M^2.

    That is just a fact. Go to NASA website for averaged earth heat budget, if you do not want to believe me. 40 W/M^2 extra goes from surface direct to space through “radiation windows” i.e. not amenable to trapping (a little may be, widening of absorption shoulders, that sort of thing).

    C’est tout.

    • Vilnius says:


      All right, I see, you’re talking here about the everyday, radiative, or spectral saturation. That’s not true either. You think of the atmosphere as a real wall, with zero transparency, and a window in it, with zero opacity. But that’s not the case. The atmosphere is transparent a bit as well, and the “window” is dim a bit. Adding more h2o or co2, in principle, could make the absorption higher and the window tighter. In this sense the atmosphere is not yet IR-saturated. If your stability-theory rests on this, it will wobble.

      Merci bien.

      • numberer says:

        I STATED that some of the escaping 40 W/M^2 is still amenable to trapping – although truly very litle extra by molecules of carbon dioxide. Of course extra trapping should mean more of the incoming longwave radiation from the sun being trapped, high above our heads.

        Detailed calculations of what it might mean, have to take account of the fact that 4/5ths of the net energy transfer from the surface to the atmosphere is by physical means (conduction/evaporation/condensation/convection) and only 1/5th by radiative imbalance.

        • bernie says:


          I am sure that if the proportion of IR radiation escaping through “the window” ever drops significantly as measured over the long run by satellites*, we will hear about it.

          I have looked at various “official” sites such as NASA, quite regularly for many years, for updates on the Heat Budget. Sometimes they change the gross flows for no obvious reason. But the proportions betwen them? No, they do not change.

          Meanwhile, I just look at the numbers here and at Remote Sensing Systems, and note that they are all within the range made in the 1990s.

          Until something happens, please do not wake me up. I am geting old and like to nap.

          *Say, 10% to 9%, and it is not just a change in the measuring process or a temporary El-Nino thing.

          • Vilnius says:

            Bernie, “proportions”

            The numbers in these budgets are calculated and adjusted from various sources, measurements, reanalyses etc. They all have much higher uncertainties (~10, 20 W/m2) than any expected change caused by human emissions (2-3 W/m2). So do not wait any dramatic effect.

            If numberer wants a firm underpinning of his saturation theory, he should find theoretical reasons for that given flux proportions. That’s what Miskolczi has tried to do for his own, but failed, as Roy himself pointed out here some years ago.

  20. aaron says:

    Is there a way to maybe observe the formation/disipaton of clouds by the light emitted/absorbed when water condenses/evaoprates? Or is the light changed to frequently throughout the atmosphere?

  21. davey says:

    “…only 1/5th by radiative imbalance.”

    Cuts down “the multiplier”, as they say in Economics.

    In Economics they also say, “Other things being equal”!

  22. numberer says:

    “…they also say…”

    and they also say,



    “Investments can go down in value as well as up”

    and, best of all,

    “The results are from a computer simulation and may not correspond with your actual trading experience!”

  23. numberer says:

    “…it will wobble…”

    A little wobble is good for you. Makes things dynamically stable. When your heatbeat becomes absolutely regular, and loses its chaotic signature, it is going to stop.When the wings on your aeroplane stop flexing, they are about to break.
    When the Universe stops twitching, it will be finished.

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  25. Susie says:

    Paper can be downloaded for free here:

    Doesn’t look very robust to me but then again I’m only a chemist.

  26. bernie says:

    Vilnius avers:

    “The numbers in these [heat] budgets…all [sic] have uncertainties [of] ~10,20 W/m2.”

    These are the numbers that go into the computer models as parameters!

    No need to say more.

  27. numberer says:

    There are certain arguments that, when deployed and fired, tend to make the cannon rebound and mash one’s foot!

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