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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 51 to 100 out of 113:

  1. On line with DKs very proper epistemological stance, I should have said past variations in climate are "consistent" with natural variability in GHE forcings given our understanding of the associated physics.
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  2. Cadbury... "It's been warmer in the past..." Can you provide some context? Are you talking century, millennial or millions of years ago? You ask about 1850-present. On that time scale we are clearly warmer today than at any period in that time frame. Easy one, right? So, what we're discussing here is whether internal variability can account for that warming. The research is very very clear on this. Internal variability can NOT account for the current century scale warming we see. This is pretty much undisputed science except for a very small number of climate scientists (Christy being one of them).
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  3. Well here is how I am thinking in my head. "How can the recent temperature increases be attributed to human activity when it has risen naturally before?" Ultimately, I think that the truth of our climate will be a combination between what both sides think. I think that carbon dioxide will cause warming but I think it will only be dangerous at levels in the thousands of parts per million, probably 3,000ppm. Also, I looked at wikipedia and it states "The data from these stations show an average surface temperature increase of about 0.74 °C during the last 100 years." So if you average that out, it comes out to 0.01 per year. This makes it seem as though the warming is minor but I feel like my discovery is a misleading number?
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  4. Jay@53 Try a more specific case, "how can a forest fire be attributed to a carelessly discarded cigarettes when it has been cause by lightning before". That is an argument of exactly the same form, but in this case the answer is pretty obvious. It is almost (but not quite) as obvious for temperature as well. If you think CO2 will only be dangerous at levels in the thousands of parts per million, perhaps you would like to explain the evidence and theory that justify that position.
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  5. @Rob I just want to make sure I understand what you are saying. From 1850-present, you're saying that the temperature has been warmer in the more recent years of 1850-present. The context I was speaking of was the GAT of the last 600 million years. Honestly, I am a history major so with pretty much every subject I go back as far as I can into history. So I've seen that temperatures and atmospheric co2 levels have been much higher so I automatically assume that the earth can sustain itself at those levels again. Now, this could be a very bad way of forming my conclusion. For example, I know that humans were not around for much of that time so we don't know how the higher GATs would affect us. So I am pretty happy to be able to ask these questions here because I think the moderators are very fair and try hard to answer the questions.
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  6. DM : it seems that you also persistently miss my point. As you said (and I agree) models can only be disproved. But the important thing is that sometimes, alternative hypothesis are *indeed* disproved; classical mechanics is disproved by the motion of Mercury,by the relativistic phenomena that occur routinely in particle accelerators, or by all types of quantum effects that are in fact necessary to explain all the usual features of our world (starting with very simple observations as the color of objects, the finite size of matter, the existence of chemical reactions). So they are plenty of situations were theories have indeed been disproved. All the game here is whether alternatives have been really disproved or not. It is not epistemologically correct to say it is impossible ! It *is* without doubt possible - the only question is if it has really been done ! In my opinion, the answer is *no* in a significative number of issues - including the possible existence of long term oscillations, the possibility of unindentified back-reactions, etc.. It is not unusual in science that several hypothesis are still debatable - what is unusual - and disingenuous - is to pretend that it is not the case, when it is the case.
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  7. Jay... The problem with that thinking is that we fully understand the radiative forcing of CO2 in the atmosphere. It's one of the well understood aspects of the climate change issue. The uncertainties in the climate's response to increased concentrations of CO2 (climate sensitivity) are less certain and a very hot topic of research these days. But we have many studies that look to find out what the climate responses have been in the past. That's where the IPCC comes up with the 1.5C to 4.5C with 3C being a best fit for a doubling of CO2. If you are looking back in history to when concentrations were 3000 ppm you're also looking at a vastly different planet than today. Life evolved during that period and was adapted to that global climate. Pushing our current climate up to 3000 ppm would quite literally be end of game for live that has evolved and is adapted to our current climate. I'm not making stuff up here. This, as I understand it, is the consensus of the broader scientific community.
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  8. "So if you average that out, it comes out to 0.01 per year. This makes it seem as though the warming is minor but I feel like my discovery is a misleading number? " No it's the correct order of magnitude. Your life is threatened by an average 0.015 *C/yr, despite the natural "weather" variability of the local temperature of where you're living, even averaged on one year, is probably one hundred times this value or so. Welcome to climate science :).
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  9. Jay @ 55... Yes. Absolutely. Life can exist, and has existed, in much warmer climates than today. Everyone understands that. But go back and look at the Siberian Traps. Rapid changes in global climate have disastrous results on the existing life of that time. I always like to say: You know, the planet is going to be just fine. It's going to still be here in a million years, and in a billion years, and several billion years beyond that. Survival of the human species has nothing to do with survival of the planet.
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  10. Gilles @ 58... Yes. That is correct. Welcome to the science of climate, as opposed to weather.
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  11. Thanks for the explanation Rob.
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  12. I'm curious, Gilles and Cadbury, do you stand by Christy's demonstrably false statement?
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  13. Tsonis loses quite a bit of credibility with (as noted in #10): "Man-made warming is balanced by the natural cycles" How does something that persistently leads to warming get "balanced" by a cycle, which has no inherent trend? In searching for that quote from Tsonis, I also found: "These models cannot be trusted to predict the weather for a week, yet they are running them to give readings for 100 years" Readers of SkepticalScience know the fallacy behind that statement. Hard to believe serious scientists would engage in this sort of rhetoric.
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  14. Giles: If you agree with me that you can only disprove, not prove, it is hardly surprising that I misunderstand you if you keep going on about proving stuff! "All the game here is whether alternatives have been really disproved or not." That is part of it; however two (or more) competing hypotheses are not equally plausible just because neither has been disproven. The "game" of climatology is primarily about relative plausibility as short term natural variability is greater in magnitude than the long term trend, which makes it difficult to definitively disprove either theory. Shame you dismissed the Easterling and Wehner paper, if you grasped that, you would have a much better idea of the issues. "It is not epistemologically correct to say it is impossible ! It *is* without doubt possible - the only question is if it has really been done !" Nobody is saying it is impossible, in fact I have been asserting the exact opposite, namely that it is all that is possible (in terms of certain knowledge). It is proving that is impossible, not disproving, sadly you can't prove a hypothesis by disproving all of the alternatives for the simple reason there may be alternative hypotheses that you haven't thought of. Nobody is ruling out natural variation as impossible (certain knowledge), just implausible (uncertain knowledge). There is a difference. The observations and theory are stacked against "natural variability" - for a start nobody has a causal mechanism for this "natural variability". Ask Spencer what causes cloud cover to change for his hypothesis and whether there is any unambiguous experimental or observational support for it.
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  15. NewYork @63, I agree, but only if that is what Tsonis actually said. Remember, this is an article in a British media outlet with a less than credible history on this file, not to mention it is written by a discredited "journalist" (Davis Rose) who has recently been shown to do an awfully good job of mangling the science and misrepresenting scientists. Anyhow, let us not get distracted what is circulating on contrarian blogs. I am far more concerned about the likes of Christy knowingly misleading congress and the general public. Really, Christy's actions border on scientific misconduct. Sadly contrarians and "skeptics" seem to be uncritically accepting his misinformation.
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  16. Gilles#58: "Your life is threatened by an average 0.015 *C/yr," Try again. Global average 0.14 deg C/decade; but northern hemisphere (Europe) closer to 0.3, Canada 0.5, Arctic >0.6. There are threads here that substantiate all that, but you're hardly impressed by actual data.
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  17. DM : I think neither you nor anybody answered my question here: how is determined the range of random initial conditions used by numerical GCM computations, such as those used in the Easterling and Wehner paper (that I indeed read) ?
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    Moderator Response: [DB] Fixed html.
  18. Gilles: Yes I did answer that question, in the post immediately following the one in which you posed it! Using the observations for a randomly chosen day would be one method, but as it happens, after the "burn in" phase, the model is statistically independent (i.e. in terms of long term trends and averages) of the intialisation, so it is pretty irrelevant. The initialisation gives rise to the difference between the model runss, but the variabilty of the model runs (i.e. the spread) is essentially independent of the initialisation. Those long term averages and trends are what we call "climate". I pointed out the statistical independence in the post immediately preceding the one in which you posed the question! This suggests you should spend less time posting and more time reading on these threads. The initialisation is important for weather forecasting, not climate modelling. If you understood climate modelling, you would understand why that is the case.
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  19. Dikran @68, "The initialisation is important for weather forecasting, not climate modelling" You are right. Modelling climate is not an initial value problem (numerical weather prediction though is), climate modelling is a boundary problem. This is pretty basic knowledge.
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  20. Albatross (#65), You're absolutely right. We shouldn't take anything a tabloid-quality source prints at face value (even a direct quotation) and I haven't a seen a reliable source report on it. The first quote is clearly at odds with his published work, and is rather silly. Contacting Tsonis would be the only way to confirm it. If he's been misquoted, I would think a lawsuit would be in order.
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  21. I'm sorry but you have to start from an initial condition anyway, and you cannot choose an initial condition in 1880 with a day randomly chosen in 2010, since the state is of the Earth is supposed to have changed (you think it has changed don't you ?) - you seem to answer as if you know GCM computations, but it's obviously not the case- so why don't you say simply "I don't know "?
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  22. Gilles @71, I'm sorry, but you are talking though your hat. Actually scientists and modellers do know what they are doing.....I'm looking for a suitable book to refer you to read on the subject. But modelling weather versus modelling climate is not the subject of this thread. Christy's misinformation and deception is. Did you see my question to you and others here?
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  23. Gilles@71 Yes, you do have to start from an initial condition, however, as I pointed out they don't affect the output if left to "burn in". If you doubt the truth of that, download the source code for, say GISS Model E, and try it for yourself. Reproducing Easterling and Wehner would be a good experiment, see if the initialisation makes a significant difference to the result. As long as the initialisations are plausible, I predict that it won't. There you are, a Popperian falsifiable prediction, go for it, prove me wrong. The comment about me not knowing about GCM computations gave me a good laugh. Lets leave it at that shall we? ;o) Albatross, I have had a look though this book on climate modelling in my local bookshop, looks nice, I have been tempted to buy it on more than one occasion, but have not done so yet.
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  24. Dikran @74, Re the book Ann Henderson-Sellers knows her stuff. I have not read the book, but the authors have an excellent track record, so you probably will not be disappointed.
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  25. OK, I believe you know GCM computations :) . So explain me how you find that "the initializations are plausible...." ? (and what is a "implausible" initialization ?) a related question is : what is the characteristic relaxation timescale for an "implausible" initialization to reach quasi-steady state ?
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    Moderator Response: [DB] Feel free to respond if you wish, Dikran, but it is obvious that you are being trolled here. [Dikran Marsupial] No problem I spotted it, as noted in my reply.
  26. Gilles, stop arguing strawmen and quote mining stolen emails and trolling and making sweeping generalizations. Feel free to believe that all climate modellers are inept. That is just pure folly, but you are of entitled to you beliefs, no matter how misguided or incorrect. i'm sure those 'skeptical' scientists who do modelling are perfectly credible in Gilles' eyes, oh wait...and oh dear, and oh my. Now you still have not answered my question @62, electing instead to float red herrings ;) Why do 'skeptics' have such an awful time of it staying on topic?
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  27. Gilles@76 The method I have already suggested (using the observations for a randomly chosen day) is guaranteed to give plausible initial conditions. We know they are plausible because the actually happened. You only need to know what "implausible" means for the meaning of an implausible initial condition to be obvious - a set of initial conditions that are impossible or extremely unlikely. Who cares about the "characteristic relaxation timescale for an "implausible" initialization to reach quasi-steady state?"? There is no reason a climate modeller would want to initialise a model in an implausible state. The question is nonsense and frankly just blatant trolling, you know it, I know it and everybody else knows it.
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  28. 77 - but weren't 2010 conditions "implausible" in 1880, since conditions of 2010 were never met 100 years ago ? "Who cares about the "characteristic relaxation timescale for an "implausible" initialization to reach quasi-steady state?"?" I care, and I think you should. This is not trolling : its give an indication of the maximum period of variability that the model is able to simulate. 76 - Albatross : if the relevant citation is ""When you look at the possibility of natural unforced variability, you see that can cause excursions that we've seen recently", I think it's perfectly true in computer simulations since some runs show sometimes variations of 0.6 °C in three decades - but anyway as I said it not really a proof of anything.
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    Moderator Response: [Dikran Marsupial] Sorry I am not going to respond to your trolling anymore. If you think there is a problem with the initialisation of the models, download some code and see if you can demonstrate it. Report back here when you are done. I suggest others do likewise and DNFTT.
  29. @Albatross “So I am afraid that your papers are irrelevant to this discussion.” Nothing could be further from the truth. The changes described in the cited papers that I was rapidly and quickly - today are identical. External factors described for the past - are discussed, eg a direct effect of the TSI and volcanoes - not to prove. If past IMP was able to cause rapidly and quickly changes, perhaps eg as stochastic remainder D.-O. ... Abrupt glacial climate changes due to stochastic resonance, Ganopolski and Rahmstorf 2002., Centennial-to-millennial-scale Holocene climate variability in the North Atlantic region induced by noise, Prange, Jongma and Schulz, 2010., Holocene temperature records show millennial-scale periodicity, Loehle &Singer, 2010. Sure you can say that so much the worse for current warming - a small impulse - RF CO2 - a powerful change ... Therefore, you can also say, however, and that a further increase p.CO2 in the atmosphere is insignificant when all process of feedback has been running ... “The NIPCC is not a credible source of scientific information. It is propaganda and nothing more than a elaborate misinformation document.” 1. Please prove it on the example cited by me - instead of using "ad hominem” and invective. 2. NIPCC says the same about the IPCC. Christy is an eminent scientist - to discredit him, have done better. @Stephen Baines “... paleo climate changes and are consistent with GHE and AGW ...” - with very, very large range of possible error - yes. I think we detailed "to discuss” the Holocene Optimum and its abrupt end - in a separate post.
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  30. Let me add a quote from this website: “Ultimately, breakthroughs in our understanding of Earth's climate evolution will come from close interactions between paleoproxy experts, paleoclimate modelers, and climate dynamicists. It is time to train a new generation of scientists familiar with all these fields.
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  31. @Albatross I stand by Christy's statement because he used the word "possibility". I think it is possible that natural, internal variations could have caused the rise in temperature. So it may not be likely but not impossible.
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  32. Arkadiusz @79 and 80, "Christy is an eminent scientist - to discredit him, have done better." That is your opinion. I for one am not trying to discredit Christy (he is doing a fine job of that by his own actions), I am taking issue with him making misleading and factually incorrect statements. "you can also say, however, and that a further increase p.CO2 in the atmosphere is insignificant when all process of feedback has been running.." This is not about "what ifs" or wishful thinking (i.e., some mystical natural negative feedback or non-transient internal climate mode is going to offset the strong radiative forcing from doubling or trebling GHGs) Arkadiusz, it is about facts and a very clear statement made by Christy. "The changes described in the cited papers that I was rapidly and quickly - today are identical.", The changes may or may not be very similar, but were the forcing mechanisms the same? But this is all besides the point. Again, let me remind you what we took issue with here, because you seem to be having issues comprehending what this at issue-- the fact that Christy stated as fact that the recent warming could be explained by natural variability alone. Unlike we have done here, he did not support his assertion with science. Moreover, the science and observations does not support his position. You showing that natural variability produced similar excursions in the past is a red herring and strawman and not relevant to the current situation, and I suspect that you fully know that. One does not need to invoke natural variability to explain all the recent warming, but one does need to invoke it to explain the inter-annual and inter-deccadal variability (i.e., the noise) in the global surface air temperature record. Christy's statement is simply false, unless he (or you) can present a model which has been published in the literature (and stood the test of time) that includes only natural unforced variability (and a physical mechanism) to account for all the observed recent warming, while at the same time accounting for the many fingerprints being attributed to anthropogenic warming. You are making strawman arguments Arkadiusz. I do not disagree with Timmerman that you linked us to at Colose's web site, and I am sure neither does, for example, James Hansen who has spent much time looking at mechanisms of previous climate change. PS: I am not going to debate the merits (or not) of the NIPCC or play tit for tat with you-- perhaps the "credibility" of the NIPPC can be the topic of a future post here.
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    Moderator Response: [Dikran Marsupial] Tags (hopefully) fixed
  33. Jay @81, Christy said "When you look at the possibility of natural unforced variability, you see that can cause excursions that we've seen recently, you see that can cause excursions that we've seen recently". That second part of the sentence is pretty definitive. And as I and others have pointed out, Occam's razor applies here-- there is no need to do mental gymnastics to try and invent hypotheticals as Spencer is trying to do to explain the recent warming. Christy is apparently telling you what you want to hear, and you are uncritically buying into it-- people are also very good at rationalizinfg their poor decisions (i.e., but he said "possibly"). I would like nothing more than the theory of AGW to be untrue, but alas, I'm afraid that the physics and science say otherwise, and I cannot deny that, no matter how inconvenient. PS: Thanks Dikran! Feel free to delete my post #83.
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    Moderator Response:

    [Dikran Marsupial] No problem, it is probably the most useful thing I've done today!

    [DB] Albatross, check your email for a message from me.

  34. @Albatross Well would you agree that it is harder to measure natural variations in the environment as compared to measuring co2 emissions and therefore it is harder to distinguish between a natural forcing and a manmade one?
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  35. Jay... I think the variation is actually quite easy to measure (if I get your meaning). The challenge is to extract the various signals from the noise. When people like Christy say it's natural variability they are having to turn a blind eye to the elephant in the room, which they all tacitly admit is real. The radiative forcing of CO2. We've clearly added a significant forcing to the climate system. If what we are experiencing is natural variability then where is the radiative forcing from CO2 going?
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  36. @ Arkadiusz "Nothing could be further from the truth." Sorry, but given your tendency to believe complete rubbish, in complete contradiction of scientific fact-not just in relation to global warming, but into the cancer causing effects of dioxins & DDT-based simply on the *opinion* of a single individual, you'll excuse me if I take your claims regarding "truth" with a fairly substantial amount of salt.
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  37. DM#78 : So I will help you a little bit to answer. May be you know that GCM models are commonly prone to systematic drifts that can reach 1°C/century, and have been carefully worked out throughout the history of computation to avoid these drifts , and to use "plausible" initial conditions that match just as closely as possible the steady state ? because of course we can't know what 1880 initial conditions can be ! and to conclude after that there wasn't any possibility of long term natural variations in the models ?- the main reason being that they have been carefully excluded ?
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    Moderator Response: [Dikran Marsupial] I didn't say I couldn't answer, but that I wouldn't, on the ground that you are trolling. You still are. If you think you have a point, download some GCM code, do some experiments, publish a paper. That would be constructive, trolling here pretending you know what you are talking about (but not providing any verifiable references of course), following multiple posts where you have repeatedly demonstrated your ignorance, just to get a bit of attention isn't.


  38. "When you look at the possibility of natural unforced variability, you see that can cause excursions that we've seen recently" And here you keep citing several studies which conclude that natural variability cannot account for the LONG term trend. Christy used the word "recently". He most likely ment the satellite era which is the last 30 years. But of course you like to misinterpret and then fight against strawmen, again. And last 30 years is claimed 100% anthropogenic by the IPCC by using the GCM:s. That is false, even your own references conclude (DelSole) that internal patterns explain 0.08K/decade for the 30 year trend. Of course you failed to cite this important phrase from the paper. And only this finding alone, makes the IPCC house of cards to collapse. AND because there were similar warm periods like MWP and RWP in the past, which yet remain completely unexplained, it might mean the ocean circulation patterns and internal variability could operate in not just multidecadal but also multicentennial timescales. And we do not have the sufficient OHC data to verify anything about this.
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    Moderator Response: [DB] "And last 30 years is claimed 100% anthropogenic by the IPCC by using the GCM:s." Strawman. Please support this statement with a link to the specific IPCC chapter where this quote is supposedly taken. Otherwise, your house of cards strawman comment invalidates itself and will be deleted as a trolling comment.
  39. protestant#88: "... similar warm periods like MWP and RWP in the past, ... might mean the ocean circulation patterns and internal variability could operate in not just multidecadal but also multicentennial timescales." 'It might mean' a vast number of things. 'It might mean' is hardly a scientific statement. What you lack is a credible theory, consistent with existing data and the fact that these multidecadals and their hypothetical multicentennials must be driven by something. 'It might mean' AGW. 'It might mean' Spencer's magic clouds. 'It might mean' LGM. Science has standards other than forming a list of possibles; it is a process of eliminating the improbables from consideration.
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  40. DM : are you arguing that it's wrong to say that GCM models were easily prone to secular drifts, or did I misunderstand you ? Mucounter :"< it is a process of eliminating the improbables from consideration." Precisely - that's why you have to demonstrate carefully that the other alternatives are improbable, and that we're totally entitled to ask you the justification - do we agree that saying "I can reproduce what I see with my hypothesis" , and even "I cannot reproduce what I see with my computer simulation" is far from being sufficient to say that ?
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    Moderator Response: [Dikran Marsupial] I intended to suggest you should provide evidence to back up your assertion if you want to discuss that.
  41. Re : the NIPCC. It was set up by Fred Singer and his SEPP organisation (who also dismiss the risks of smoking and ozone delpetion), and backed by the Heartland Institute. Biased, much ? Appeals to those of a certain political persuasion, perhaps ? Trustworthy ? (The answer to the last is 'NO')
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  42. DM#90 well for instance, look at this page and please explain me how you understand the experiment#2 "present-day control experiment" "for most models this experiment is not needed, but for some it is the control for experiments 8-9. There will be no natural forcing and anthropogenic influences will be set at present-day level. The control experiment should be long enough to extend to the furthest point in time reached by the end of the perturbation experiments (which branch from it). Thus the control should allow us to subtract any residual, unforced drift from the perturbation simulations." substract any residual, unforced drift ?
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  43. Giles@92 That doesn't say there is unforced drift, just that for some models there may be a unforced drift that may be corrected using the control run. It does not say that this was was actually done. This is seems to me just an example of scientists taking a "belt and braces" approach and check these things to be sure. What you are doing is quote mining, not science. Go find a paper or source that shows this drift is actually a problem. IMHO trying to make something of an experiment having a control is a bit of an odd scientific attitude!
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  44. sorry but what you say is quite unclear : what does "may be corrected" mean ? - when do we need to correct them ? note that a drift cannot be indefinite since it would lead eventually to unreasonable high temperatures - so it can only be a part of a very long oscillation - much longer than the duration of the run. It is a "drift" just because our capabilities of computation do not allow to compute a long enough time to see the oscillation - do you agree with that ?
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  45. "Many of the non-flux adjusted models suffered from unrealistic climate drift up to about 1°C/century in global mean surface temperature." so my question is : when you use "flux adjusted" models, what do you adjust and how ?
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  46. other example : clearly enough, drift has always been a problem and models have evolved to avoid the drifts meaning that there has been a selection bias leading computer scientist to favor models with low drifts as the "best ones". I don't think you can reasonably deny that.
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    Moderator Response: [muoncounter] Please do not use search text in place of actual citation.
  47. Giles@94 Blatant trolling again, if you knew what you were talking about you would know when they needed to correct them. You have no evidence that any of the models actually were corrected, just that there was a suggestion from the organisers of the project that a control run were made for those models where it was thought it might be necessary so that any drift could be corrected if required, and you are presenting it as if that implied that the models actually did exhibit a drift. I was merely applying the same sort of pedantry to your arguments that you have used on virtually every thread to which you have "contributed". Now, if you have a reliable source e.g. a peer-reviewed paper that shows that these drifts are actually a problem, then lets see it. It is time to "Put up, or shut up".
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  48. Giles@95 Modern GCMs, have not included flux adjustments for a very long time. If you read the Wikipedia article rather than quote mining, you will see that they are talking about the 2001 TAR, which means they are talking about models in use over a decade ago. Things have moved on significantly from there. The really funny thing though, is that if you actually read the page in the report you linked to in message 96, you will find that it says (bear in mind it was published in 2005, so they are talking about models of late 1990 to early 2000 vintage): "Until recently [DM emphasis mine], it has been necessary to used so-called flux adjustments (or "flux corrections", Sausen et al 1987) to prevent drift in the climate of the coupled system that arises from the inadequacies in the component modules and in the simulated fluxes at their interfaces" You do know what "Until recently" means don't you Gilles? Also if you read the rest of that paragraph, you will find that were the flux adjustments were still being used in the early 2000s, the corrections had been getting smaller as the models improved, and that the IPCC had found no systematic bias in the climate variability between models where the flux adjustments were used and where they were not and that both types of models are useful for attribution studies. Your own source suggests that drifts are correctable and do not pose a problem. You have made a fool out of yourself by your quote mining. Next time see if the material is (i) up to date and (ii) actually does support your assertions.
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  49. DM : you don't understand what I'm saying. I'm not saying that all models present a significative drift. I said that many models have presented such drifts, that this has always been considered as a problem when it happened, so that models have evolved to avoid these drifts. You are saying that "models improved" - I'm just saying that the "improvement" has been quantified by an absence of drifts - and that the goal has been to AVOID them or correct them when they happen. don't you understand that this is quite like a darwinian selection, insuring that models converge towards an absence of drift ? and allowing to say at the end, triumphally : "look, we don't have any long term drift anymore without anthropogenic forcing" ?
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  50. Giles@99 If you point is that models used to have drifts because of their limitations, but now they have improved so that they don't, then that is an entirely vacuous point. You have provided no evidence whatsoever that the drift are problematic, just assertion. The models were not randomly evolved to reduce the drift, it is nothing like Darwinian evolution. The drift was eliminated as a consequence improving the physics on which the models are based and their resolution. It was an indicator of a shortcoming of the models, but only one of many that are discussed in the literature. GCMs are physics based models, not statistical ones, the drift was corrected by better physics/resolution, not tuning. Your argument is a bit like saying the laws of planetary motion were the result of Darwinian evolution where Kepler's model eliminated the drifts from the earlier Copernican system, allowing him at the end to say triumphantly "look we don't have a long term drift in the predicted orbits of the planets anymore". Well duh, that is the way science progresses! Old models (heliocentric, Copernican) are replaced by better, more accurate ones (Kepler, relativistic corrections etc.).
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