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Christy Crock #3: Internal Variability

Posted on 14 April 2011 by dana1981, Albatross

Christy Crocks (200 x 70 pixels)In the recent U.S. House of Representatives Committee on Science Space and Technology climate hearing, Dr. John Christy was the main witness presenting the opinions of the global warming "skeptics."   As we previously noted, the quality of Dr. Christy's testimony was extremely disappointing, as he frequently repeated and affirmed climate myths.  Among them, Dr. Christy touted the myth that internal variability could be the cause of the current global warming:

"When you look at the possibility of natural unforced variability, you see that can cause excursions that we've seen recently"

As we will see here, this statement is simply false.  Natural variability cannot account for the large and rapid warming we've observed over the past century, and particularly the past 40 years.

Swanson and Tsonis

One of the most widely-circulated papers on the impact of natural variability on global temperatures is Swanson et al. (2009) which John has previously discussed. 

Although Swanson 2009 was widely discussed throughout the blogosphere and mainstream media, the widespread beliefs that the study attributed global warming to natural variability and/or predicted global cooling were based on misunderstandings of the paper, as Dr. Swanson noted:

"What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf. Nature (with hopefully some constructive input from humans) will decide the global warming question based upon climate sensitivity, net radiative forcing, and oceanic storage of heat, not on the type of multi-decadal time scale variability we are discussing here. However, this apparent impulsive behavior explicitly highlights the fact that humanity is poking a complex, nonlinear system with GHG forcing – and that there are no guarantees to how the climate may respond."

In their paper, Swanson et al. use climate models to hash out the role internal variability has played in average global temperature changes over the past century (Figure 1). 

Swanson Tsonis variability

Figure 1: Estimation of the observed signature of internal variability in the observed 20th century global mean temperature in climate model simulations

As you can see, over periods of a few decades, modeled internal variability does not cause surface temperatures to change by more than 0.3°C, and over longer periods, such as the entire 20th Century, its transient warming and cooling influences tend to average out, and internal variability does not cause long-term temperature trends.

Additional Studies

A number of other scientific studies have also examined the impact of internal variability on global temperatures, and arrived at a very similar conclusion to Swanson et al.  For example, here are the findings of DelSole et al. (2011)(emphasis added):

"The amplitude and time scale of the IMP [internal multidecadal pattern] are such that its contribution to the trend dominates that of the forced component on time scales shorter than 16 yr, implying that the lack of warming trend during the past 10 yr is not statistically significant...While the IMP can contribute significantly to trends for periods of 30 yr or shorter, it cannot account for the 0.8°C warming that has been observed in the twentieth-century spatially averaged SST."

This conclusion directly contradicts Christy's statement that natural variability can account for all of the recent warming.  This is not a new finding, as it is consistent for example with Stouffer et al. (1994):

"throughout the simulated time series no temperature change as large as 0.5°C per century is sustained for more than a few decades. Assuming that the model is realistic, these results suggest that the observed trend is not a natural feature of the interaction between the atmosphere and oceans."

and with Wigley and Raper (1990):

"Simulations with a simple climate model are used to determine the main controls on internally generated low-frequency variability, and show that natural trends of up to 0.3°C may occur over intervals of up to 100 years. Although the magnitude of such trends is unexpectedly large, it is insufficient to explain the observed global warming during the twentieth century."

These studies are also consistent with Bertrand and van Ypersele (2002), Rybski et al. (2006), and Zorita et al. (2008), among others.  There is a strong consensus that natural variability cannot account for the observed global warming trend, which raises the question: on what is Christy basing his unsubstantiated claims to the contrary?  Although he does not provide any supporting evidence in his congressional testimony, Christy is likely relying on the work of his University of Alabama at Huntsville (UAH) colleague and fellow "skeptic," Roy Spencer.

Spencer's Hypothesis

Dr. Roy Spencer has proposed a hypothesis whereby some unknown internal mechanism causes cloud cover to change, which in turn changes the reflectivity (albedo) of the planet, thus causing warming or cooling.  Spencer also attributes most of the global warming over the past century to this "internal radiative forcing."  There are some significant flaws in this hypothesis.  For one thing, it fails to explain many of the observed "fingerprints" of human-caused global warming, such as the cooling upper atmosphere (stratosphere and above) and the higher rate of warming at night than during the day.

In order for internal variability to account for the global warming over the past century (especially over the past 40 years), it requires that the large greenhouse gas radiative forcing can't have much effect on global temperatures.  For this to be true, climate sensitivity must be low.  But as discussed in Swanson et al. (2009), if climate is more sensitive to internal variability than currently thought, this would also mean climate is more sensitive to external forcings, including CO2.  This is a Catch-22 for Spencer's hypothesis; it effectively requires that climate sensitivity is simultaneously both low and high.

Dr. Andrew Dessler published a study (Dessler 2010) which casts further doubt on Spencer's hypothesis, as detailed in an email exchange between the two scientists.  In short, Dessler argues that cloud cover change is a feedback to a radiative forcing, for example increasing greenhouse gases, while Spencer argues that clouds are changing due to some other, unknown cause, and acting as a forcing themselves.  Unlike Spencer, Dessler explains the mechanism and supporting evidence behind his cloud feedback research:

"My cloud feedback calculation is supported by a firm causal link: ENSO causes surface temperature variations which causes cloud changes. This is supported by the iron triangle of observations, theory, and climate models."

El Niño Southern Oscillation (ENSO)

Although he is very coy about the physical mechanisms behind his hypothesis, Spencer does seem to believe that his hypothesized internal radiative forcing will cause "ENSO-type behavior," such as warming surface air temperatures.  However, Trenberth et al. (2002) examined the role ENSO has played in the global warming over the past half-century, and their conclusions do not bode well for Spencer's hypothesis:

"For 1950–1998, ENSO linearly accounts for 0.06°C of global surface temperature increase."

This 0.06°C accounts for approximately 12% of the warming trend over the timeframe in question.  Foster et al. (2010) also examined the effects of ENSO on global temperature and arrived at the same conclusion.

"It has been well known for many years that ENSO is associated with significant variability in global mean temperatures on interannual timescales. However, this relationship (which, contrary to the claim of MFC09, is simulated by global climate models, e.g. Santer et al. [2001]) cannot explain temperature trends on decadal and longer time scales."

Foster et al. examine a number of previous studies which assessed and removed the effects of ENSO on the global surface temperature (emphasis added):

"In all of these previous analyses, ENSO has been found to describe between 15 and 30% of the interseasonal and longer-term variability in surface and/or lower tropospheric temperature, but little of the global mean warming trend of the past half century."

Pacific Decadal Oscillation (PDO)

ENSO is part of the PDO, which Spencer has also tried to blame for the current global warming.  In a post on his blog following up on Spencer and Braswell (2008), Spencer claims:

"The evidence presented here suggests that most of that warming might well have been caused by cloud changes associated with a natural mode of climate variability: the Pacific Decadal Oscillation."

However, as detailed here by Dr. Barry Bickmore in a three part series, and by Dr. Ray Pierrehumbert at RealClimate, Spencer's attribution of the recent global warming to PDO is no more than an example of how to cook a graph.  As Dr. Bickmore put it,

"Spencer's curve-fitting enterprise could (and did!) give him essentially any answer he wanted, as long as he didn't mind using parameters that don't make any physical sense."

Further, as we have previously discussed, like ENSO, PDO physically cannot cause a long-term global warming trend.  It is an oscillation which simply moves heat from oceans to air and vice-versa, so even if there were a period of predominantly positive PDO over the long-term, the oceans would cool as a consequence of the transfer of heat to the overlying air.  That is not the case: the oceans are warming as well.

It's not Internal Variability

In conclusion, there is simply no supporting evidence or physics behind Christy's unsubstantiated claim that the global warming over the past century could simply be attributed to internal variability.  Studies on the subject consistently show that internal variability does not account for more than ~0.3°C warming of global surface air temperatures over periods of several decades.  Internal variability also tends to average out over longer periods of time, as has been the case over the past century, and cannot account for more than a small fraction of the observed warming over that period.  Spencer's hypothesis cannot account for numerous observed changes in the global climate (which are consistent with an increased greenhouse effect), does not have a known physical mechanism, and there are simply better explanations for interactions between global temperature and cloud cover.

Dr. Christy was simply wrong to tell our policymakers that natural variability can account for all of the observed global warming over the past century, and particularly the past several decades.   One can't help but suspect that Christy was simply telling the Republican policymakers what they wanted to hear.  What is more, he knows the state of the science on this issue, and cannot plead ignorance.  As such, his false statement was disingenuous and the very antithesis of good science.

NOTE: this post has also been adapted into the Intermediate rebuttal to "it's internal variability"

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Comments 1 to 50 out of 104:

  1. Christy dismisses all the evidence supporting AGW as insufficient, perhaps. I would guess that his own theory has a much more compelling set of evidences. But it fails to answer a lot of questions: - Why did DLR increase and OLR decrease over the last decades? - Why did this measured trapped IR energy NOT increase the temperature? What has happened to it? - Where’s the very compelling evidence that global temperatures vary as wildly as the last decades (some 0.6ºC in 40 years). Why did all those clouds decide to warm the planet now, if they don’t usually do it? - Where’s the evidence that cloud cover has varied as much as to justify the observed warming over these decades? I’m a layman, so I’d be pleased if someone more knowledgeble explained to me why my questions are for some reason irrelevant. Or not?
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  2. Both wrong- its external variability- cosmic rays (and the sun) explain the cloud cover. There is low CO2 temperature climate sensitivity- the reaction of the temperatures to major volcanic eruptions shows that.
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    Response: Problem with the "cosmic rays are driving global warming by changing cloud cover" argument is cosmic radiation and climate went in opposite directions in the latter 20th Century - if anything cosmic rays and the sun should be having a cooling effect.


    Reconstructed cosmic radiation (solid line before 1952) and directly observed cosmic radiation (solid line after 1952) compared to global temperature (dotted line). (Krivova 2003)
  3. cloa513... Citations please. Posting wishful thinking is not good science.
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  4. "There is low CO2 temperature climate sensitivity- the reaction of the temperatures to major volcanic eruptions shows that." Major volcanic eruptions have a tiny impact on the amount of CO2 in the atmosphere. Pinatubo for instance released about 1/30 as much CO2 as we did that year. There was never any reason to think that it would increase temperatures. There was plenty of reason to think it would temporarily lower temps because of the ejection of aerosols into the stratosphere; this was predicted before hand and the models showed excellent agreement with the subsequent cooling.
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  5. Alexandre - those are all valid questions. It gets to the point we made in the post that there are a number of 'fingerprints' which AGW can explain but which internal variability cannot. As John sometimes says, they have to explain why the increased greenhouse effect isn't warming the planet significantly, and why their alternative is warming the planet exactly how we expect GHGs to warm it. cloa 513 - please see "it's cosmic rays" and "climate sensitivity is low" where we show both your comments are incorrect.
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    Response: [John] Actually I haven't published that article yet, it's due out on April 28 :-)
  6. "There was never any reason to think that it would increase temperatures." Not only that, but volcanoes also put up far, far more aerosols-into the stratosphere-than they do CO2, so leading to an overall *cooling* effect in the troposphere (but a warming of the stratosphere).
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  7. John C. and Dana, "As John sometimes says, they have to explain why the increased greenhouse effect isn't warming the planet significantly, and why their alternative is warming the planet exactly how we expect GHGs to warm it. " That quote is a great assessment. A keeper for sure.
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  8. Albatross - John's got a good 'if it walks like a duck' analogy. Even better than what I said :-)
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  9. The point would be that internal variability doesn't have to account for all the recent warming just some of it in some of the recent phases to start to upset the understanding. dana has recently done several post attributing different aspects of 20th century warming to different forcings. I don't remember there being any scope for internal variability to contribute to any of these espisodes of warming or 'cooling' by upto 0.3oC. In fact these would seem like an anathema to both dana and the IPCC's approach which seems to only recognize forcings as drivers of the climate. For example the mid-20th century 'cooling' phase is generally put down to aerosols. This paper suggests natural variability might have played a role in that, that could be as high as 50%. The most recent warming episode (post 1970) might have internal variability contributing 30-40%. Where does the IPCC (or dana) take this into account? The simple fact is if you allow natural variability to add to or subtract from global temperatures then you change the calculations. The convenient just so story has to be rewritten. I don't see that being acknowledged either on this website or within the climate science establishment.
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  10. I found this quote from Tsonis, it sounds a little more skeptical or at least lukewarmish "a measure of additional ‘background’ warming due to human activity and greenhouse gases that runs across the MDO cycles....I do not believe in catastrophe theories. Man-made warming is balanced by the natural cycles, and I do not trust the computer models which state that if CO2 reaches a particular level then temperatures and sea levels will rise by a given amount."
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  11. Leaving all else aside, on the "natural variability" theory, what are the chances/odds that the uptick* in temperatures of the last 3 or 4 decades, say, just happens to coincide, precisely, with the uptick in CO2 production of those same 3 or 4 decades? And what are the chances that the combined uptick of the two just happens to coincide with an uptick in denier frenzy on blogs and in the media generally, supported, in large measure, by the corporations responsible for the uptick in CO2 production? *uptick isn't quite right, I seek another metaphor. What is it they play ice hockey with in the northern hemisphere?
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  12. Humanity Rules, have a look at Figure 1 in the article above. Yes, that's right, it's the internal variability as incorporated into the climate models. The "climate science establishment" is well aware of internal variability. They account for it in their models. It doesn't change their conclusions.
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  13. I'd like again stress that it is a generic feature that computer models are generally very bad and unreliable to describe properly internal variability There are numerous examples of that , and very good physical reasons to explain it . Examples include for instance the ENSO oscillation which is not predicted quantitatively by models, and neither all kinds of multidecadal oscillations. The 11 years solar cycle is *not* reproduced by solar models either. The good reason is that these kind of oscillations are not the result of variations of forcings (by definition), but are spontaneous limit -cycles which depend on very sensitive non-linear parameters and cannot be derived from simple conservation laws (that are the only thing giving "robust" results). I give you a comparison : suppose that an extra-terrestrian intelligent being catch a human being and try to "model" it physically. It would be rather easy for him to understand that it is powered by the internal combustion of food and find a rather precise estimate of how much fuel (around 2000 kcal/d) he needs. But it would be very difficult to predict the circadian cycles and why he has spontaneous cycles about 24 hours, just by a physical modeling. So the conclusion is : any argument on unforced variability based on computer simulations is generally speaking unreliable and meaningless. Of course computer models do have their own variability and non linear behaviors, and do exhibit their own internal variability - but it is not justified to use the physical characteristics of this variability as a reliable estimator of the natural ones - no computer model has ever proved to be reliable for that. Of course from time to time, by playing with parameters, you will find similar things - but this is by no ways a robust prediction and cannot be used to predict unknown behaviors. And for instance, we speak of multidecadal oscillations because they have been detected over a century time-scale - but we don't have any precise idea about possible multi-centennal oscillations - that are by no ways excluded by physical arguments.
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  14. "Leaving all else aside, on the "natural variability" theory, what are the chances/odds that the uptick* in temperatures of the last 3 or 4 decades, say, just happens to coincide, precisely, with the uptick in CO2 production of those same 3 or 4 decades? " David , the answer is : 100 %. Because the CO2 has increased exponentially and thus has always the same characteristic timescale - it has not increased just for 30 years but for hundred years. So *any* multidecadal oscillation will coincide , during its rising part, with a CO2 increase - and with all others anthropogenic variations, such as urban heat for instance; it is a very weak criterion.
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  15. Giles You have just demonstrated that you don't understand how climate models operate. The projections of the models do not rely on the ability to reproduce internal variability faithfully. The purpose of the ensemble methods (and Monte Carlo simulations generally) is to average out the effects of different realisations of the stochastic effects of internal variability, leaving the signal of interest, which is the forced component of climate change. The real indication that you don't know what you are talking about is the line "The 11 year solar cycle is *not* reproduced by models either". Well of course it isn't, it is an external forcing! Monte Carlo simulation of chaotic physical systems like the atmosphere has a long history, stretching back to the Manhattan project, and have proven very effective in many branches of physics and statistics. As you have not only just demonstrated that you don't understand how the models work, but that you don't even know the difference between internal variability and external forcing, your assertion about whether the models are reliable or meaningful doesn't carry much weight.
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  16. DM : "The 11 year solar cycle is *not* reproduced by models either". Well of course it isn't, it is an external forcing!" Unfortunately , you didn't understand my point : I wasn't speaking of the influence of the 11 years cycle on the Earth (it is a forcing for the Earth), I was speaking of physics of the sun, of solar physics - not of climate models. The "forcing" for the Solar activity is merely the internal fusion processes that occur in the core and produce heat that is transferred towards the surface. It doesn't change at all on a 11 years basis (actually it doesn't change on a million years basis , which is the typical escape time for a photon). The input of heat from below is strictly constant - however the output is modulated, not by a change of forcing , but by internal variability which stores part of this energy in magnetic fields and releases it periodically through activity cycles. What I said is that the precise characteristics of this variability (amplitude and frequency) are *not* reproduced by models. This is pretty much the same for "climate" internal cycles like ENSO or multidecadal oscillations. Now concerning the climate models, a simple question : any numerical model requires initial conditions. Obviously the state of the Earth in 1880 isn't very well known. So how is it chosen in simulations ? Note that this problem is somewhat hidden when the results are expressed as "anomalies" - you don't know the absolute value of average temperature. So how are these conditions adjusted, following you ?
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  17. Giles It would be better if you could just admit when you were wrong. The 11 year solar cycle is an external forcing to the models, not part of the models (it has very little effect on the climate anyway). I note you dodge the more substantive issue though, the model projections do not depend on any of the model runs predicting the effects of internal variability accurately. Like other Monte Carlo methods, they don't even attempt to predict internal variability. The whole point of the ensemble is to find out what the climate is doing after internal variability is excluded. If you understood climate modelling, you would know that. Again you last comment demonstrates you don't understand what climate models do. Weather is chaotic, it can't be predicted because we don't have accurate initial conditions (one of the founding fathers of chaos theory, Edward Lorenz, was a meteorologist, chaos theory has its origins in weather modelling, so of course climate modellers are perfectly aware of this). However, just because weather is chaotic, that doesn't mean climate (long term statistical behaviour of the weather) is also chaotic. So rather than predict the chaotic weather, the models simulate weather with the same statistical properties as the real weather and take averages to get information about climate. A large number of model runs are used, all with different random initialisations. After a while, the behaviour of the model is statistically independent of the intialisation (In Monte Carlo simulation, this is called "burn in"). You need initial conditions for weather prediction, which is why weather forecasts are useless beyond five days or so; you don't need them for climate modelling. The reason for choosing 1880 has to do with the availability of reasonably reliable instrumental data (hint, when does GISTEMP start?). I would have thought that was obvious. What is the point of generating hindcasts if you don't have something to use as ground truth? BTW climate models are often used for paleoclimate studies, so it isn't even true that they necessarily start at 1880. I suggest that rather than demonstrate your ignorance of climate modelling and Monte Carlo methods any further, you do some reading and fill in the gaps in your knowledge.
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    Moderator Response: [Dikran Marsupial] This discussion of modelling is heading a bit off-topic. I suggest if you want to discuss what models can and can't do, we continue on climate models are unreliable, although I suggest you read the article and the posts on that thread first. You may also find this post informative, where I use a simpler chaotic system to explain the basic aim of climate modelling and how it works (and why initial conditions are not important).
  18. DM : sorry for repeating : I wasn't wrong, I wasn't speaking of the climate of the Earth but of stellar physics". Replace the sun by a variable star without planets , if you prefer ! I just gave this example of another natural limit cycle which is not due to a variation of forcing. "The whole point of the ensemble is to find out what the climate is doing after internal variability is excluded. " My point is : they're not reliable to estimate the precise amount of internal variability. So they adjust their results to match observations without being certain that the relative proportion of internal variability and sensitivity to forcings is the right one. And the fact that the simulations do not show a long term trend doesn't prove anything. " A large number of model runs are used, all with different random initialisations." There is nothing like "random numbers" in an unrestricted interval. There *must* be a range in which you draw your parameters. Again : how is this range chosen following you ?
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    Moderator Response: [Dikran Marsupial] tags fixed (hopefully the way you wanted them)
  19. Gilles Given that the only way to estimate the amount of internal variability is from a climate model (as we have only one realisation of the signal that we have actually observed), it is impossible to say whether the models estimate it "accurately". The error bars on the model projections (which show how much variability is possible) include the observations, which is all that can be expected of the models even if the physics of the model is exactly correct. The climate modellers know this already. Why do you keep on about the models proving anything? They don't and nobody is claiming they do. Models show you the (testable) consequences of a set of assumptions about climate physics. They tell us what we can expect to see based on our best understanding of the climate. Nothing more. As for random initialisations, initialising the initial conditions with the observations for a randomly chosen day would be a random initialisation, and would be a physically realistic initialisation, by definition. As I said, it would be better for you to stop posting on this topic until you have done some background work, you are still just demonstrating your ignorance.
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  20. A lighthearted take on this issue: Harry Potter lost at sea. If a boat has both an engine running and a sail, it makes no sense to claim that the engine has no effect on the boat's movement.
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  21. enough with strawman arguments, please. I never stated that the influence of forcings was zero. I just reminded that it was very difficult-and almost impossible - to quantify precisely the amount of internal variability by computer models - you just get the amount of variability in your model, that's all. for instance in the "solar hockey stick" post, you find this kind of curve do you believe we have good models to explain the variation of solar activity over thousands of years ? (again I'm not speaking of the influence on the Earth, just of the origin of solar variations). No - absolutely not - not the slightest idea of where they come from. We have models of the sun - but nothing like explanations of that. So if you rely on models to know if these variations could be "natural" or "anthropogenic", would you conclude that they cannot be natural since the models do not show them, and thus must be anthropogenic ? of course this would be totally absurd. So - we can't rely on models to exclude natural cycles. And yes - natural cycles on timescales of 1000 years can exist, of course. Our modern measurements are much too recent to see them at the required accuracy. Again I am *not* stating that the influence of CO2 is zero. Just that having a very clear separation between it and natural variations is extremely difficult in my opinion, thus reinforcing the uncertainty on the climate sensitivity - and that the outputs of computer simulations are not really useful to fix this issue.
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  22. So you got yourself an unfalsifiable hypothesis there Gilles ... useful.
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  23. Gilles wrote: "I just reminded that it was very difficult-and almost impossible - to quantify precisely the amount of internal variability by computer models " However, as I pointed out, it is the only way to estimate the internal variability of the climate - you can't measure it directly as we have only one realisation that we can observe. That means you can't separate the signal from the noise without making assumptions about both the signal (the forced response) and the noise (the internal variability or unforced response); as soon as you make a meaningful attempt to do that you end up with somthing very like a climate model. That means you can't argue that the models don't accurately quantify the amount of internal variability as you have no ground truth with which to make such a comparison. Continuing to do so just illustrates your ignorance of the subject. Giles also wrote: "you just get the amount of variability in your model, that's all.". Well duh! Of course, but as the models encode our best understanding of climate physics, the amount of the variability in the model is the amount of plausible variation in climate according to our best understanding of the climate. Given that we can't directy or indirectly measure climate variability (for the reason I have already given), how could climatologists possibly do any better than that. Note the climatologists know this perfectly well, and Gilles could do with resolving his Dunning-Kruger by reading up on climate models and what the modellers claim they can and can't do.
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  24. By the way, Christy says "When you look at the possibility of natural unforced variability, you see that can cause excursions that we've seen recently", then if he means the excursions we have seen over the last couple of decades, then he is right and the climate models predict that this sort of thing will happen, see the paper by Easterling and Wehner: David R. Easterling and Michael F. Wehner, "Is the climate warming or cooling?", GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L08706, 3 PP., 2009 (www) This paper shows that the kinds of "excursions" we have seen over the last two decades is expected to happen due to unforced variability (although they can't predict the timing as it is a chaotic weather thing rather than a climate thing), even in the presence of a long term warming trend due to e.g. CO2 radiative forcing. Of course the longer the "excursion" the less plausible the obsertvations become assuming the model assumptions are correct (which is why the models are still falsifiable - the do make falsifiable predictions). Easterling and Wehner is also a good answer to Gilles canard about the models ability to quantify the variability of the climate.
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  25. DM : "That means you can't separate the signal from the noise without making assumptions about both the signal (the forced response) and the noise (the internal variability or unforced response)" I disagree with the assertion that only computer can answer the quesion. In principle, we could, since precise measurements of the variability, and of the natural changes of forcings in the past , could give a good estimate of it. After all, what's the use of paleoclimatic studies and past millenary reconstructions, if not ascertaining the natural variability ? but here we face another problem - the lack of accuracy of these measurements. This is not a *fundamental* problem, it is a *practical* one. If modern thermometers, satellites, and meteorological stations would have existed everywhere in the world for thousands of years, we would probably have much better estimates of the past variability. "the amount of the variability in the model is the amount of plausible variation in climate according to our best understanding of the climate. " Yes, but the "best understanding" can be bad - this has to be kept in mind. There is a number of things in the world we don't clearly understand - and I wouldn't put climate variability in the group of what we DO clearly understand.
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  26. "Easterling and Wehner is also a good answer to Gilles canard about the models ability to quantify the variability of the climate." I don't think so.
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    Moderator Response: [DB] Cease with the trolling.
  27. "So you got yourself an unfalsifiable hypothesis there Gilles ... useful" Of course it is falsifiable , in the way I said - we COULD find good and accurate proxies of the natural variability and of astronomical changes, TSI, volcanoes, and so on - actually this is the quest of many people in the world. The fact that we don't have them is not due to some "metaphysical" or non scientific character of the question - just to the lack of current good way of measuring it , but it is of course, in principle, measurable.
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  28. Giles: Now you are just being silly. You can't measure climate variability from one realisation of a stochastic process if the underlying system (e.g. the forcings) is time varying. It simply can't be done without making assumptions about the nature of the noise and of the signal. This is true regardless of how much data you have, or how accurate it is. Secondly, do we have accurate measurements of past climate (beyond a century or so)? No. Are we ever going to get them? No, not unless we discover time travel. The point of paleoclimate studies is to help us understand past climate. The interest is largely in the forcings, not the variability as the variability is essentially paleoweather not paleoclimate. Of course we know that our understanding of the climate is incomplete and the model predictions may not be accurate. It would be idiotic not to realise that, and the climatologists are not idiots. Understanding climate variability does not imply an ability to predict climate variability. I understand the variability of a double pendulum, it is a very simple chaotic system, but that doesn't mean I can't predict it. The whole point of climate projections is to see what is left after excluding the effects of variability. The climate projections shown only the "forced response" of the climate. The spread of the model runs is an indication of what our understanding suggests is plausible given the unpredictable unforced response. The fact you keep harping on about the variability is merely reinforcing the impression that you don't understand how the models work, or what they tell us. Did you read the Easterling and Wehner paper? If not I suggest you do.
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  29. Gilles wrote "I don't think so" Well that settles it then! LOL
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  30. Or, and I realise this is just one of those off-the-planet crazy ideas, we could work out the physics of CO2 in the atmosphere, and then relate the observed temperature changes (and all the associated rapid changes in this little biosphere we call home) to that, see if, by come wild chance, they happen to match. Then we could use computer modelling to work out how that might develop in future, just on the crazy off-chance that the physics and observations and knowledge of past climate shifts are correct. And then, if it looked like the planet was going to be in deep doo doo, what with acidifying oceans, increasing droughts and other severe weather events, rising oceans, melting ice caps, species extinctions, failing agriculture, why, then we could convince the world's governments that there needed to be a quick response in reducing CO2 output. Yeah, that should work I think, not as if there are going to be people trying to stop governments responding to the clear and present danger, are there?
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  31. " The point of paleoclimate studies is to help us understand past climate. The interest is largely in the forcings, not the variability as the variability is essentially paleoweather not paleoclimate." I think I see your epistemological problem - you *postulate* that the climate cannot change spontaneously over centuries without change of forcings - and you *deduce* that the changes can only be due to forcings. Do you understand that my own point is that we have neither experimental evidence, nor theoretical proof (even with computer simulations) that your first hypothesis is true ? and so that your way of reasoning is totally circular ?
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  32. Giles: I postulated no such thing, it is purely your own invention. A chaotic system can have more than one attractor, nowhere did I suggest that is not the case of the weather (which means that is is possible natural variability could result in long term changes - e.g. snowball Earth). The primary interest though is in the responses to forcings. If all of the model runs agree on the long term hindcast, that is reasonable grounds to think it is probably forcings, if some fall into one cluster and others fall into another, that would suggest more than one "attractor" (not sure that actually happens though), that would be an indication that it was not only forcings. In both cases, we don't know anything for certain, we just know the consequences of what out current knowledge of suggests is plausible, nothing more. As I have repeatedly said, (paleo)climatologists know that perfectly well. You will notice I used a lot of probabilistic qualifiers in that paragraph, there is a good reason for that, which is that any knowledge we gain from any observation is necessarily uncertain. I can't believe you are still going on about proving a hypothesis to be true. This shows a complete lack of understanding of the philosophy of science, an hypothesis regarding objective reality can never be proven, only disproved. This is central to the writings of Karl Popper, which IIRC you claimed you understood. My reasoning is not circular, the models are used to determine the consequences of a set of assumptions, nothing more. Nobody assumes the models are correct (in fact as GEP Box suggests, we know they are not correct, but that doesn't mean they are not useful).
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  33. Internal variability ... - let's look into the paper 2010 UKCP09. : „Uncertainties remain in estimates of natural internal climate. Internal variability is difficult to estimate from available observational records since these are influenced by external forcing, and because records are not long enough in the case of instrumental data, or precise enough in the case of proxy reconstructions, to provide complete descriptions of variability on decadal and longer time scales.” Of course you can cite the paper: A Significant Component of Unforced Multidecadal Variability in the Recent Acceleration of Global Warming, DelSole, Tippett and Shukla, 2010. : “While the IMP can contribute significantly to trends for periods of 30 years or less, it cannot account for the 0.8 o C warming trend that has been observed in the twentieth century spatially averaged SST.” However, I would recommend NIPCC comment to this paper: “In considering the latter portion of the record (1946-2008), results indicated that the internal variability component of climate change (the IMP) operated in a cooling mode between 1946 and 1977, but switched to a warming mode thereafter (between 1977 and 2008), suggesting that the IMP is strong enough to overwhelm any anthropogenic signal.” Does the past - the Holocene - we had a strong global changes, that are difficult to explain simply the influence of external factors? Mid-Holocene regional reorganization of climate variability, Wirtz et al. 2009. : “We integrate 130 globally distributed proxy time series to refine the understanding of climate variability during the Holocene.” “Secondly, at most sites, irreversible change occured in the Mid-Holocene. We suggest that altered ocean circulation together with slightly modified coupling intensity between regional climate subsystems around the 5.5 kyr BP event (termination of the African Humid Period) were responsible for the shift.” “It seems likely [comparison n 250, 550, 900 and 1450 yr cycles] that altered ocean circulation together with slightly modified coupling intensity between subsystems (regional interplay of ice, ocean, atmosphere and vegetation) after the 5.5 kyr BP event made these subsystems either more or less prone to oscillations. The discussion of possible mechanisms behind changed climate variability, however, has to be substantiated by future modelling studies.” The same we can said of the MCA - LIA. Medieval Climate Anomaly to Little Ice Age transition as simulated by current climate models, González-Rouco et al., 2011.: “Most models have used relatively high TSI variations from the MCA to the LIA and their pattern of response is typically a uniform warming in the earlier period. In spite of this, there are considerable differences among the simulations that highlight a feasible influence of initial conditions and internal variability. Furthermore, if reduced levels of past TSI are given more credit, as in the MPI-ESM-E1 ensemble, the temperature response for the MCA–LIA is less uniform in sign and visibly more influenced by internal variability. Therefore, under both high and low TSI change scenarios, it is possible that the MCA–LIA reconstructed anomalies would have been largely influenced by INTERNAL VARIABILITY. [...]”
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  34. Impossible to post on most other threads. e.g. models are unreliable thread does not accept posts.
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    Moderator Response: The climate models thread absolutely accepts posts, as does every thread on this site. If you would like to discuss climate model reliability in general, you are encouraged to take your discussion there.
  35. Yet according to IPCC models that tiny addition from volcanoes (Kroatoa particularly) should have caused a massive temperature change- the temperature change is barely noticeable.
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  36. HR @10, I would take everything Davis rose writes on climate with a pinch of salt, even the stuff he places in quotation marks. Do you honestly believe that a reputable scientists and modeller like Tsonis does not understand the difference between modelling weather and modelling climate as the article alleges he believes? And since when did it become fashionable to cite the Daily Mail as a reliable source of scientific information? It has not, at least in the realm of real and reliable and reputable science. And for the record, I have vehemently defended the distortion of Latif's remarks (made in late 2009) made by the media. You are trying to detract from the words that Tsonis published at RealClimate on this matter. it is not going to work.
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  37. All, Please note. Christy attributed all the observed recent warming to natural variability. All of it-- even Pat Michaels does not go that far. The scientific literature does not support Christy's unsubstantiated assertion, in fact it is a demonstrably false statement as shown in this post. It is unbelievable that people here would defend Christy misleading congress. And that was not the only demonstrably false statement that he made to congress as shown here at SkS.....there is more to come. Dana have more papers that demonstrate that Christy is wrong in his beliefs on this, including some from Zorita.
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  38. http://www.2gb.com/index2.php?option=com_newsmanager&task=view&id=8613 World renowned scientist not in favour of reducing carbon emmissions
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    Moderator Response: This comment has nothing to do with the topic of this thread or the discussion at hand. Note per the Comment Policy, off-topic posts are not permitted. Please use the search dialog in the upper left to find the appropriate thread for your comment. Future off-topic comments will be deleted.
  39. Cloa513, Great, first david rose, and now a Australian talk show. Your link is irrelevant to the topic at hand. Also, he contradicts Christy, saying that recent changes are small-- Christy suggests that the changes (from a natural climate variability) are quite large quite large-- almost 0.9 C. Dana I see a Lindzen crock in your future-- Lindzen repeats his favourite trick, and the interview was made on 6 April 2011 .
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  40. Arkadiusz @33, Thanks, climate scientists know very well that there exists such a thing as natural or internal climate variability. But you are missing the point in your post. The papers that you cite speak to a period earlier in the Holocene before anthropogenic GHG forcing. Christy was specifically referring to "recent" warming when anthropogenic forcing has played a notable/significant role in modulating global temperature trends. So I am afraid that your papers are irrelevant to this discussion. Additionally,The NIPCC is not a credible source of scientific information. It is propaganda and nothing more than a elaborate misinformation document.
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  41. re cloa513 I think I've read this somewhere: "Skeptics vigorously criticise any evidence that supports man-made global warming and yet uncritically embrace any argument, op-ed piece, blog or study that refutes global warming."
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  42. I suspect that if the models supported Gilles' preconceived notions, he'd have absolutely no problem with them. Or rather, no need to invent problems with them.
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  43. I think I can summarize the arguments used by Gille: We do not know everything; therefore, we know nothing. A is true, but the premise that A->B is false.
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  44. Chris G@43 That may not be what Gilles intends to convey, but it seems a reasonable interpretation of what he actually writes on most of the threads to which he has contributed. Second language issue perhaps?
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  45. DM :concerning " If all of the model runs agree on the long term hindcast, that is reasonable grounds to think it is probably forcings," - It's slightly OT in my sense, but it is an important point. It is not because all models agree together that they're proved to be true, especially if they share systematic errors or weaknesses. Taking again solar models, they all agree that an 11 -years activity cycle doesn't exist ! but in this respect, they're just all wrong. Now as you say, models can be disproved. In that sense, observation that surface oceans are *not* warming for 6 years disproves "something" (hence the reaction of Dr Trenberth) : it disproves the idea that there is a 0.9 W/m2 imbalance that is stored in upper layers of oceans. So actually it's kind of good news to be able to make this observation, because we can try to improve the model. Now I'm simply reminding that an open possibility is that the missing heat is stored in deep ocean, and another open possibility is that the 0.9 W/m2 is wrong - which wouldn't be possible if we had an independent , reliable measurement of TSI and TOA budget, showing that this 0.9 W/m2 is certain. My impression is that by reading the OP, one could have the impression that the second possibility is excluded because we would know for sure that the 0.9 W/m2 imbalance exists - however, as Dr Trenberth himself reminds us, this is not the case - we don't have any reliable , independent measurement of this 0.9 W/m2 imbalance. Chris G. #43 : you simply misunderstood what I'm saying - read again carefully, I'm just trying to remind carefully what we know and what we don't know for sure.
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  46. sorry I mixed up with the other topics on Trenberth's sentence :)
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  47. "As we will see here, this statement is simply false. Natural variability cannot account for the large and rapid warming we've observed over the past century, and particularly the past 40 years." Natural variability can easily account for recent warming because it has been much warmer in the past. I would also argue the warming we have seen is small and has not been rapid. Could someone please provide the change in GAT from 1850-present?
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    Response:

    [DB] You can find answers to your questions by looking at the Skeptics arguments by Taxonomy.  These specifically might be of use:

    Climate's changed before

    It warmed just as fast in 1860-1880 and 1910-1940

     

    Data source for GAT (land is shown but you can re-run with both; data only since 1880):

    http://data.giss.nasa.gov/gistemp/maps/

  48. Gilles@45 "It is not because all models agree together that they're proved to be true" There you go waffling on about proof again, it is almost as if you are deliberately ignoring my repeated statements that nothing can ever be proven, only disproven! No, of course the models agreeing doesn't prove anything, but the logical conclusion is that the projection is most likely to be due to the forcings rather than variability given our current understanding of climate physics as encoded into the model. The final caveat applies to all models, we all know it, it isn't news. The output of any model is contingent on its modelling assumptions. Gilles wrote "I'm just trying to remind carefully what we know and what we don't know for sure." we don't know anything for sure, and we never will. This goes back to Hume, who proved that you can never obtain certain knowledge of causal relationships by purely empirical means (i.e. you have to make some assumptions or have some hypothesis). We all know this, and it is the height of arrogance for you to keep "reminding" us of something we all know already, and indeed have told you so repeatedly. In that context it becomes "trolling". Bon appetit, I assume you are now replete.
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  49. @ Cadbury...you are confusing natural variability in forcing and natural variation due to internal non-linear dynamics. The former are the cause of the paleo climate changes and are consistent with GHE and AGW, the latter are the subject of this article. This seems to be a common confusion here. I don't think Christy is subject to it, but those listening to him clearly are.
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  50. Jay@47, if natural variability means that any climate within the bounds that the Earth has ever seen can be attributed to "natural variability", then it is an unfalsifiable theory, as nothing we could possible observe would disprove it. That means it isn't a scientific theory (Popper), a scientific theory must make restrictions on what we could observe, otherwise it is no different to astrology. That doesn't mean it might not be true, just that it isn't science.
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