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Climate Hustle

An Even Cloudier Outlook for Low Climate Sensitivity

Posted on 12 December 2010 by dana1981

Research has given us good confidence that if CO2 doubles in the atmosphere then there will be 1.2°C of directly CO2-caused global warming, and a combination of melting snow/ice and increased evaporation of water will act as positive feedbacks to increase this warming by approximately 1 to 2°C.

This climate sensitivity of an additional 1 to 2°C warming would mean most recent global warming was human-caused and more is in the pipeline; but some scientists believe that changes in clouds will cool us down, though the most public paper to claim this (Lindzen and Choi 2009) has been heavily criticized for using a method that can be fiddled to give any desired result and ignores much of the planet.

The strength of the cloud feedback is commonly calculated by determining the change in cloud-caused heat flow for a change in temperature:

F = ΔRcloud /ΔTs

Where "F" is cloud feedback, ΔRcloud is the change in the top of the atmosphere (TOA) flux caused by cloud changes, and ΔTs is the global-average and monthly mean surface temperature anomaly.

Roy Spencer believes these calculations are invalid because we can’t tell whether the warming is changing the clouds or the clouds cause the warming through his hypothesized ‘internal radiative forcing’. If the change in temperature is caused by the clouds in the first place, then we could calculate a positive feedback even if it is actually negative!

A new paper by Dessler (2010) attempts to get around this and calculate the quick cloud feedback using measurements by the Clouds and the Earth’s Radiant Energy System (CERES) instruments from March 2000 to February 2010. The satellite measures how much heat is coming from the Earth at TOA, and Dessler accounts for greenhouse gases, humidity, El Niño Southern Osciallation (ENSO), etc. to determine how much of the heat flow is from clouds. He then looks at how far above or below the average it is for its month, and plots this against temperature.

If the temperature is related to clouds, then you expect a slope in the graph thanks to the above formula. Figure 1 displays the results, and Dessler finds that the short term feedback is 0.54 ± 0.74 (2σ) W m-2 K-1, i.e. far more likely to be positive than negative, although negative values can’t be ruled out based on this data.  However, a small negative feedback is insufficient to support the theory that clouds will prevent significant future warming.


Figure 1: (A) Scatter plot of monthly average values of ΔRcloud vs. ΔTsusing CERES and ECMWF interim data. (B) Scatter plot of monthly averages of the same quantities from 100 years of a control run of the ECHAM/MPIOM model. In all plots, the solid line is a linear least-squares fit and the dotted lines are the 2σ confidence interval of the fit. 

A key point in the paper is that most of these short-term temperature changes are caused by ENSO.  If the temperature change is being caused by ENSO, then it’s likely not being caused by clouds, and Spencer’s hypothesis is potentially sidestepped.  Spencer has countered this by arguing that ENSO changes are caused by clouds, and thus the response of clouds to surface temperature changes cannot be inferred.  Dessler argues that Spencer's hypothesis that ENSO is caused by clouds is new and untested, and the burden of proof falls on Spencer to demonstrate that his hypothesis is correct.

Dessler (2010) adds confidence that the cloud feedback is not significantly negative, and various climate models are largely in agreement with the CERES observations., as illustrated in Table 1.

Table 1: Cloud feedback values. All uncertainties are 2σ.  Feedbacks are calculated from a 100-year  segment of a control run, except for CCSM3, which is based on 80 years.

 

Dessler is careful to point out that there are differences between short-term and long-term cloud feedbacks in models, which suggests that these observations might not be a good guide for the future.  However, although long-term climate sensitivity cannot be determined from 10 years worth of data, the global climate models did pass this test, and the evidence against a strong negative cloud-climate feedback continues to mount.

The paper also comes on the heels of Lauer et al. (2010), which examined and provided support for the high end of current estimates of global climate sensitivity due to a positive cloud-climate feedback.

This guest post was written by Mark Richardson (MarkR) and Dana Nuccitelli (dana1981)

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Comments 101 to 124 out of 124:

  1. 88 Albatross and Riccardo

    It looks like in Spencer's Fig1 that he actually takes Dessler's approach to calculating radiative forcing. He uses different data sets but the methodology is the same. In that figure he seems to show that depending on exactly which data set you use (HADCRUT or satellite for temp) and how you handle the data (different averaging periods) you can get very big differences in the radiative forcing estimate (0-2.5 W m-2 K-1).

    I guess Dessler would counter that he shows robustness by using two data sets of his own and getting similar results.

    Any greater merit in either authors approach?

    Maybe this is not actually getting to the point of disagreement between Spencer and Dessler anyway. The curious thing is using Desslers method Spencer actually gets very similar results to Dessler only with much greater range (Spencer 0 - 2.5 and Dessler -0.2 - 1.3). The point both you (and Dessler) seem to want to emphasise could still be made with Spencer's result, that is using this method there is no evidence of large negative feedback.

    From what I can see though Spencer's issue isn't just about the robustness of the method but whether Dessler's method is valid at all. Even for Spencer that is not answered by the confidence in the stats but by using a different method, phase space plots. I guess what we should be focussing on is whether phase space plots are giving us the added information that shows that Dessler (and others) method for estimating feedback is invalid.
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  2. HR:

    "These are Spencer's words, not Dessler's interpretation of Spencer's words. "

    Uh, his e-mail messages are his words, too, and Dessler presents them verbatim so we can interpret them ourselves. It is clear that Spencer's claiming that scientists have the arrow backwards regarding clouds and ENSO. He says so directly.
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  3. 97 Albatross

    I'm not questioning the sincerity of Dessler, I'm not trying to look for angels and devils in the process. I think the reader at RC is lead down that particular path by the paragraphs following the "ENSO are caused by clouds" statement, I'm not suggesting that Dessler is consciously trying to lead us there but that is what is happening. It's difficult to know where to take this particular arguement when Spencer has explicitly stated on his blog that he does not support the idea that ENSO are caused by clouds.

    Albatross this is again getting away from the science, I should have ignored NewYorkJ and dhogaza's lead. There is actually lots of science in both authors papers that is being ignored by this narrow focus. Hopefully you'll ignore this post and focus on what I raised earlier.
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  4. 100 e

    I agree with you Spencer is saying (some) temperature change is initiated by clouds not that ENSO is initiated by clouds.

    102 dhogaza

    I read the email exchange, I don't see where he says or infers "ENSO are caused by clouds". Please reproduce the quote here so I can find it in the emails.

    96 Stephen Baines

    Stephen you fail to mention deltaT here and it seems to be the relationship between clouds and deltaT that Spencer is arguing over not ENSO. I think when it comes to "initiators" and "feedback" it's the relationship to deltaT that Spencer is concerned about.

    Anybody want to move on from this and talk about phase space plots?
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  5. "It's difficult to know where to take this particular arguement when Spencer has explicitly stated on his blog that he does not support the idea that ENSO are caused by clouds."

    Yet he explicitly states the opposite in his e-mails to Dessler.

    And he says things in his blog that are explicitly incorrect and misleading:

    "Dessler’s claim (and the IPCC party line) is that cloud changes are caused by temperature changes, and not the other way around. Causation only occurs in one direction, not the other."

    No, Dessler says no such thing. Dessler (and everyone except Spencer) is saying that ENSO causes temperature changes which lead to cloud changes which lead to feedback. Not *all* cloud changes, as Spencer is implying. He then measures that feedback. Spencer says no, this is wrong, the arrow of causation is backwards. He is more explicit in his reference to ENSO in his e-mail.

    "But what if the warming was caused by fewer clouds, rather than the fewer clouds being caused by warming? In other words, what if previous researchers have simply mixed up cause and effect when estimating cloud feedback?"

    Remember, we're speaking of ENSO. This is why Dessler asked Spencer explicitly about it. Spencer's answer is there for all to see.

    "What we demonstrated in our JGR paper earlier this year is that when cloud changes cause temperature changes, it gives the illusion of positive cloud feedback – even if strongly negative cloud feedback is really operating!"

    This can not be relevant to Dessler's measuring of cloud changes and feedback during ENSO *unless* Spencer believes that cloud changes are causing ENSO.

    Again, he's been asked explicitly by Dessler, and he has answered explicitly.

    "It doesn’t mean that “clouds cause El Nino”, as Dessler suggests we are claiming, which would be too simplistic..."

    "too simplistic" doesn't mean "wrong", HR. Spencer does some handwaving to try to convince people he's not saying something quite as stupid as "cloud changes cause ENSO", but remove the handwaving, and that's all he's got. As his e-mails to Dessler make clear.

    HR:

    "Albatross this is again getting away from the science, I should have ignored NewYorkJ and dhogaza's lead. There is actually lots of science in both authors papers that is being ignored by this narrow focus. Hopefully you'll ignore this post and focus on what I raised earlier."

    Sorry. ENSO-is-forced-by-cloud-changes is an epic fail too great to be ignored. Spencer's claim has to be true, because if not, then the "illusion of positive cloud feedback" is false and his argument implodes.

    In the physical world, you can't ignore the arrow of causality, and as Dessler makes clear, no one other than Spencer believes that ENSO is caused by cloud changes. Flip the arrow of causality in the direction that every other than Spencer accepts, then his "negative feedbacks replace the illusion of positive feedbacks" goes away.

    "There is actually lots of science in both authors papers..."

    And Dessler acknowledges this, and makes clear that Spencer's done some interesting things, if you ignore his claims regarding what causes ENSO.

    And Spencer? Does he acknowledge that there's lots of science in both papers, i.e. in Dessler's?

    No, he calls a press conference to claim that it's bogus and writes a blog post claiming it's a "step back for science".

    Actually, that negative step is really an illusion and in reality it's a step forward ...
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  6. I don't think HR's bothered to read the Dessler/Spencer exchange. Dessler's last post points out the logical flaw in Spencer's reasoning ...
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  7. dhogaza


    I don't see the necessary logical jump that says because Spencer is talking about the relationship between deltaT and clouds, and the potential for cause and effect to be reversed here, that he's talking about the relationship between ENSO and clouds. The reversal Spencer mentions I think is this

    ENSO>clouds>temperature (internal forcing)
    ENSO>temperature>clouds (feedback)

    that seems to be the content of his publication anyway. As Spencer says there is no need to put clouds before ENSO.

    I actually think in the email exchange that in large parts they talking at odds to each other which as our discussion suggests is more likely to generate heat than light. It wouldn't be surprising given that both believe the other is missing the important point.

    But let's agree there is greater precision in the language used in the peer-reviewed papers and focus on what they say. Phase space plots anybody?
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  8. From Spencer 2010

    "Evidence for this process was shown by Spencer et al. [2007] in their analysis of a composite of 15 strong tropical intraseasonal oscillations, where strong warming events in the tropical troposphere [el Nino] were accompanied by weak SST cooling. This process was driven by stronger surface winds temporarily enhancing the heat flux from the ocean to the atmosphere."

    Clouds cause ENSO???? It's far easier to see what these scientists think when you read their science.
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  9. HR,

    Pardon the pun, but we are arguing in circles here. I really do not know about this stuff to pass judgement on Spencer's or Dessler's method. Murphy and Forster were less than kind in their critique of SB08, so that doesn't instill much confidence in me that Spencer has gotten this right. The phase space plots are new to me. Maybe someone else here is more familiar with them.

    Let us not focus too much on the cause of the warming or on ENSO for now-- the question is, regardless of the initial cause, do cloud behave in a way which acts to enhance the initial warming or offset it? Dessler has made a very compelling case that the clouds very likely enhance that warming slightly. And let us not forget that even if negative feedback is operating, it is only very small, and certainly not sufficient to argue that climate sensitivity is low.

    Why has no-one applied a Granger causality test to these data? I think BPL over at RC has offered, I hope that Dessler takes him up on the offer and that they publish the results.
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  10. "I don't see the necessary logical jump that says because Spencer is talking about the relationship between deltaT and clouds, and the potential for cause and effect to be reversed here, that he's talking about the relationship between ENSO and clouds. The reversal Spencer mentions I think is this"

    He could have, of course, refuted this strongly in his e-mail exchange with Dessler.

    He chose not to. Rather, he disambiguated his position in a way not congruent with your interpertation.

    I appreciate why you want to be his water-carrier here ... but I won't say why, because Cook will delete my post if I do.

    Oh, BTW, if "Humanity Rules", why are you so dogged in your refutation of the ability of humanity to alter climate? Maybe it's because we don't insist that humanity rules climate, but only affects it ...
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  11. "I don't see the necessary logical jump that says because Spencer is talking about the relationship between deltaT and clouds, and the potential for cause and effect to be reversed here, that he's talking about the relationship between ENSO and clouds"

    As Dessler points out, essentially Spencer rejects the standard explanation of ENSO by simply leaving it out of his lead-lag analysis.

    He presumes his conclusion, in simple terms.
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  12. Albatross:

    "Why has no-one applied a Granger causality test to these data?"

    Because no one serious disputes the broad outlines of the current understanding of ENSO? Dessler hints that Spencer's explanation is unphysical because of the vast amount of energy that must be transferred to the oceans to make Spencer's claims true. The standard explanation ... well, it falls within understood science.

    Like so many denialist arguments, if Spencer is right, a WHOLE LOT of science must be overturned that's essentially unrelated to climate science.
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  13. HR:

    "I don't see the necessary logical jump that says because Spencer is talking about the relationship between deltaT and clouds, and the potential for cause and effect to be reversed here, that he's talking about the relationship between ENSO and cloud"

    edited:

    "Spencer is talking about the relationship between deltaT and clouds, and the potential for cause and effect to be reversed here"

    So reversing the causality arrow between deltaT and clouds when analyzing ENSO data means what, then?

    Look up "reverse" and "causality" in the dictionary.

    You essentially saying "just because Spencer claims that clouds cause deltaT (previously thought to be due to ENSO) doesn't mean that Spencer is saying that this causes ENSO". So, then, in what direction does Spencer say the arrow points? Obviously, not from ENSO to temps/clouds ... reversing means that clouds/temps => ENSO.
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  14. Yes...that's the problem. How to move that much heat by some extrinsically driven cloud forcing for long enough to generate the massive heat imbalance one gets with ENSO. Maybe if there was some positive feedback, but that would of course be a feedback and Dessler would still be right. I think he's in a corner.
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  15. #105 dhogaza, "Dessler (and everyone except Spencer) is saying that ENSO causes
    temperature changes which lead to cloud changes which lead to feedback. Not *all* cloud changes,
    as Spencer is implying..."

    Dessler says average cloud changes cause positive feedback. He doesn't know which, so it could be "all" cloud changes although that is unlikely. Some cloud changes also cause SST gradients which cause wind which will enhance or detract from El Nino or La Nina. That effect may be minor and it is likely not to be a "cause" in the most basic sense since no research I have seen shows that any particular patterns of clouds precede El Nino. For La Nina, there are the clouds, rain, pressure gradient and other effects of El Nino that play a role. Saying clouds cause La Nina and ignoring the rest is not supported. Here's a paper http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.144.83&rep=rep1&type=pdf that states:

    "The explanation for El Nino and La Nina involves a circular argument. Changes in sea surface temperature are both the cause and consequence of wind fluctuations."
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  16. "The explanation for El Nino and La Nina involves a circular argument. Changes in sea surface temperature are both the cause and consequence of wind fluctuations."

    I don't like that phrasing. It's not really a circular "argument" (which implies logical fallacy), but an argument for reinforcing system of mechanisms. Those reinforcing mechanisms form feedbacks, which are what gives the system enough momentum to create the large shift in heat distribution, winds and ocean currents observed during El Nino and La Nina.
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  17. Dessler seems to be claiming that clouds are trapping more energy as the surface warms.

    He writes on page 3 of his paper:

    "Because I have defined downward flux as positive, the positive slope here means that, as the surface warms, clouds trap additional energy; in other words, the
    cloud feedback here is positive."

    Is he claiming that clouds are changing in a way that results in them trapping more surface energy? If yes, how has he rectified this with all the data (i.e. how has he shown that the additional energy the clouds trap is greater than the additional energy they reflect away)???
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  18. Can someone help me out here? In figure 1 A and 1 B of Dessler's paper, are the y-axis fluxes LW or SW?

    Thank You.
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  19. RW1 - Looks like both SW and LW; see the bottom of column 1, page 1524, where Dessler 2010 discusses combining the uncertainties of SW and LW measurements to determine total uncertainties.
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  20. KR,

    "RW1 - Looks like both SW and LW; see the bottom of column 1, page 1524, where Dessler 2010 discusses combining the uncertainties of SW and LW measurements to determine total uncertainties."

    Yes, I know about that. That would seem to indicate it is the net SW and LW flux, but I should probably clarify this with Dessler himself just to be sure.
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  21. I've confirmed with Dessler. It's the net flux.
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  22. Dessler is primarily just looking at TOA net fluxes and temperatures – he’s made little (if any) attempt to carefully discern cause and effect or come up with any physical mechanisms or reasons behind his interpretation of the data. He admits in the paper at the beginning that the net effect of clouds at the current operating point in the climate is to cool by about 20 W/m^2, yet doesn’t seem to ascribe any significance to this or express any curiosity about it at all.

    Furthermore, I notice that the SW component is also positive, which would seem 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 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.
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  23. 122, RW1,

    You are grossly misrepresenting the paper, and drawing your own conclusions based on a childishly limited approach to the system in question.

    I strongly suggest that if anyone thinks what you are saying may be true, they download and read the paper themselves. It's quite accessible and easy to read.

    I also suggest that they study a lot more about humidity, water vapor, clouds and all other background information required to even begin to understand the subject. Doing as RW1 is doing, and using "common sense" and everyman's views of humidity, clouds, and the system as a whole, is a trap for the unwary to fall into.
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  24. It's pretty clear from Figure 1A that there is an inferred linear feedback relationship from rising temperature to TOA radiation, or positive cloud feedback. That the support is weak is obvious from the diagram, but that weak support collapses into nothing as soon as one considers the internal forcing of ENSO on clouds. One mechanism, suggested by "Chief Hydrologist" at Judy Curry's site was sulfides. A quick look shows that to be a forcing but both anthropogenic and natural. The natural papers seem to be old. The anthro papers seem to be modern such as "Nonlinear Aspects of the Climate Response to Greenhouse Gas and Aerosol Forcing" by Feichter and Roeckner. Regardless of origin, they are both forcings that at the very least add noise to that scatterplot if not some sort of bias. The paper also points out that the aerosol-temperature feedback is very nonlinear.

    There appear to be papers that simultaneously support and counter Dessler's conclusions, such as ftp://eos.atmos.washington.edu/pub/breth/papers/2007/Zhu-etal-LowCldClimSens-JGR-2007.pdf That paper shows a negative correlation of clouds to SST (bottom of Fig 1), but also shows that other ENSO effects such as changes in circulation patterns have an even bigger effect on clouds than SST ((see top row in Fig 12).
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