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How reliable are climate models?

What the science says...

Select a level... Basic Intermediate

Models successfully reproduce temperatures since 1900 globally, by land, in the air and the ocean.

Climate Myth...

Models are unreliable

"[Models] are full of fudge factors that are fitted to the existing climate, so the models more or less agree with the observed data. But there is no reason to believe that the same fudge factors would give the right behaviour in a world with different chemistry, for example in a world with increased CO2 in the atmosphere."  (Freeman Dyson)

Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice – and the sun. This is clearly a very complex task, so models are built to estimate trends rather than events. For example, a climate model can tell you it will be cold in winter, but it can’t tell you what the temperature will be on a specific day – that’s weather forecasting. Climate trends are weather, averaged out over time - usually 30 years. Trends are important because they eliminate - or "smooth out" - single events that may be extreme, but quite rare.

Climate models have to be tested to find out if they work. We can’t wait for 30 years to see if a model is any good or not; models are tested against the past, against what we know happened. If a model can correctly predict trends from a starting point somewhere in the past, we could expect it to predict with reasonable certainty what might happen in the future.

So all models are first tested in a process called Hindcasting. The models used to predict future global warming can accurately map past climate changes. If they get the past right, there is no reason to think their predictions would be wrong. Testing models against the existing instrumental record suggested CO2 must cause global warming, because the models could not simulate what had already happened unless the extra CO2 was added to the model. All other known forcings are adequate in explaining temperature variations prior to the rise in temperature over the last thirty years, while none of them are capable of explaining the rise in the past thirty years.  CO2 does explain that rise, and explains it completely without any need for additional, as yet unknown forcings.

Where models have been running for sufficient time, they have also been proved to make accurate predictions. For example, the eruption of Mt. Pinatubo allowed modellers to test the accuracy of models by feeding in the data about the eruption. The models successfully predicted the climatic response after the eruption. Models also correctly predicted other effects subsequently confirmed by observation, including greater warming in the Arctic and over land, greater warming at night, and stratospheric cooling.

The climate models, far from being melodramatic, may be conservative in the predictions they produce. For example, here’s a graph of sea level rise:

Observed sea level rise since 1970 from tide gauge data (red) and satellite measurements (blue) compared to model projections for 1990-2010 from the IPCC Third Assessment Report (grey band).  (Source: The Copenhagen Diagnosis, 2009)

Here, the models have understated the problem. In reality, observed sea level is tracking at the upper range of the model projections. There are other examples of models being too conservative, rather than alarmist as some portray them. All models have limits - uncertainties - for they are modelling complex systems. However, all models improve over time, and with increasing sources of real-world information such as satellites, the output of climate models can be constantly refined to increase their power and usefulness.

Climate models have already predicted many of the phenomena for which we now have empirical evidence. Climate models form a reliable guide to potential climate change.

Mainstream climate models have also accurately projected global surface temperature changes.  Climate contrarians have not.

Various global temperature projections by mainstream climate scientists and models, and by climate contrarians, compared to observations by NASA GISS. Created by Dana Nuccitelli.

A 2019 study led by Zeke Hausfather evaluated 17 global surface temperature projections from climate models in studies published between 1970 and 2007.  The authors found "14 out of the 17 model projections indistinguishable from what actually occurred."

There's one chart often used to argue to the contrary, but it's got some serious problems, and ignores most of the data.

Christy Chart

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Dana Nuccitelli: Principles that models are built on.

Last updated on 9 September 2019 by pattimer. View Archives

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Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

Carbon Brief on Models

In January 2018, CarbonBrief published a series about climate models which includes the following articles:

Q&A: How do climate models work?
This indepth article explains in detail how scientists use computers to understand our changing climate.

Timeline: The history of climate modelling
Scroll through 50 key moments in the development of climate models over the last almost 100 years.

In-depth: Scientists discuss how to improve climate models
Carbon Brief asked a range of climate scientists what they think the main priorities are for improving climate models over the coming decade.

Guest post: Why clouds hold the key to better climate models
The never-ending and continuous changing nature of clouds has given rise to beautiful poetry, hours of cloud-spotting fun and decades of challenges to climate modellers as Prof Ellie Highwood explains in this article.

Explainer: What climate models tell us about future rainfall
Much of the public discussion around climate change has focused on how much the Earth will warm over the coming century. But climate change is not limited just to temperature; how precipitation – both rain and snow – changes will also have an impact on the global population.


On 21 January 2012, 'the skeptic argument' was revised to correct for some small formatting errors.


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Comments 201 to 250 out of 1297:

  1. Actually, ref, comment #195, please don’t make assumptions about my motives. You are completely wrong about me wanting to delay things. What I’m wanting to do, as hopefully most sceptics do, is my best to ensure that the climate change medicine dispensed by the politicians is not more damaging to humans than any natural or unnatural changes to the global climates. Until I am convinced that the medicine will not make things worse I will continue searching for a better understanding. At least there are some people here who are trying to help me get that better understanding, but you are not one of them. Tom (Dayton) ref. comment #207: I do read Realclimate articles and comments but always in a very sceptical manner because of the pedigree of the main contributors. I do like that quotation you gave - "I use the term validating not in the sense of ‘proving true’ (an impossibility), but in the sense of ‘being good enough to be useful’)” but the question is good enough to be useful for what? For me the validation of computer systems starts with the user requirements. Policy-makers (including politicians) are among the primary users of those climate models. There are others like environmentalists. I leave it to you to work out what “good enough to be useful” means. Must dash, as the boss is calling. Best regards, Pete Ridley
  2. I am having a good chuckle at the discussion about "being good enough to be useful" The parliamentary inquiry last year into the long term weather forecasting capabilities of BOM and the CSIRO received a submission from the federal Department of Agriculture describing the current forecasts as too inaccurate for farmers to use, whilst the submission from the South Australian Farmers Federation described them more to the point as "less then useful". This confirmed that nothing has changed since a University of Melbourne study 5 years ago found the same situation then. However the good news was that if the government could provide "significant further investment" in super computers, reliable usable predictions may be available in at least 3 years, but possibly as far away as 7 seven years.
  3. johnd, I believe you are mixing up your climate forecast models and your weather forecast models. SAFF weren't impressed with the seasonal forecasts they are given, especially as they are not yet detailed enough to give localised information. Weather, not climate.
  4. JMurphy at 02:56 AM , I think it is quite clear that I was referring to "long term weather forecasting capabilities". It is not so much about insufficient localised information, but about forecasts that are so vague that they are meaningless (a 50% chance of above average rains and a 50% chance of below average rains is a common forecast) and despite the vagueness they still have a poor strike rate. In contrast, private forecasters are able to demonstrate an overall much higher degree of accuracy plus provide detailed local information to satisfy their customers requirements. In the meantime as long as the government injects sufficient funds to upgrade to super computers, we still have to wait perhaps 3 to 7 years before we get forecasts that are "good enough to be useful".
  5. Jmurphy, ref. comment #210, I suspect that you aren’t aware of a relevant statement by a senior executive of the Met. Office during the first of the UK’s whitewash enquiries into the Climategate scandal. The question put by a member of the Science and Technology Select Committee was “Is there a problem with scientific software? We have had emails from Professor Darrel Ince and from Professor Les Hatton saying that there are severe problems with scientific software. Do you think that is a general problem in UK or world science?”. Met Office Chief Scientist Professor Julia Slingo (Note 1) said “At least for the UK the codes that underpin our climate change projections are the same codes that we use to make our daily weather forecasts, so we test those codes twice a day for robustness”(Note 2). So the “codes” used for UK weather forecasting are the same as those used for global climate projections - shortly after that that the Met. Office discontinued its long-range forecasts because they were so useless. (The rest of that testimony is worth reading.) It is worthwhile listening to what Professor John Beddington had to say in January (Note 3), which included the gross understatement “..that scientists had perhaps not been as good at communicating the value of uncertainty to the general public .. ”. Professor Barry Brook of Adelaide University and scientific advisor to the Australian Government on climate change was less reticent when saying over a year ago (Note 4) “There are a lot of uncertainties in science, and it is indeed likely that the current consensus on some points of climate science is wrong, or at least sufficiently uncertain that we don’t know anything much useful about processes or drivers”. Brook is a staunch supporter of The (significant human-made global climate change) Hypothesis so then goes on to try to imply that 95% of the science is understood. As Boddington said in January (Note 5) “I don’t think it’s healthy to dismiss proper scepticism. Science grows and improves in the light of criticism. There is a fundamental uncertainty about climate change prediction that can’t be changed”. Phil (Scadden), ref. comment #212, I am not enquiring here into the validity the design of the software or the validity of the underlying science of those climate models. What I am questioning is the extent to which the models have been validated and their starting parameters are “tweaked” and “re-tweaked” before a run produces an output that resembles reality. I do not have enormous confidence that those with a vested interest in convincing others that their research findings or software development skills produce useful models will present an unbiased opinion on the validity of any model forecasts. There are plenty examples in areas where the underlying sciences are much better understood than are those involved in unravelling the complexities of global climate processes and drivers where vested interest has resulted in false claims. There is no good reason to think that things are different for climate forecasting. Let’s not overlook the fact that scientists and software engineers not saints but humans with human failings. As the late Stephen Schneider said Your opinion of me is irrelevant and is bound to differ from mine. You are a staunch supporter of The (significant human-made global climate change) Hypothesis whereas I am a sceptic. Ref. comments #41/48 & 50 on the “Rebutting skeptic arguments in a single line” thread, you (and others here) ought to be aware by now that the IPCC shares Dr. Gray’s opinion that those models do not provide predictions of future global climates, merely projections (based upon that unsound science). If the global mean temperature estimates produced by the Hadley Centre etc. are to be trusted (“lies, damned lies and statistics”) we may have already had over 10 years of “flat or negative temperatures while GHGs rise” so may not have much longer to wait in order to “clearly invalidate AGW”. In your humble opinion “Hansen 1988 did very well for a model so primitive.”. In mine he hit lucky to get closeish with one of his scenarios for 10 years then failed miserably after that. actually (thoughtfull?). does that answer your questions in comment #195? NOTES: 1) see 2) see 3) see 4) see 5) see That’s enough for now. I’ll respond to others soon. Best regards, Pete Ridley
  6. Pete Ridley, if you wish to believe that the 'Climategate' enquiries are all "whitewashes", and that the "scandal" still remains (albeit only in the minds of those who don't wish to face up to the facts), then I cannot write anything that will get through to you : you only see what you want to see. I will, though, disagree with you with regard to the Met Office's Seasonal Forecasts - they had obviously already decided to scrap them before announcing so on March 5, so I doubt whether the House of Commons enquiry had anything to do with it. You, no doubt, would disagree, but, again, you must believe what you want to believe. In the same way, you believe those Seasonal Forecasts were "useless", so, again, nothing I write would be able to change your mind. To end, code written to represent the Physical qualities of the make-up of potential weather would, I would imagine, be useful not only for short-term forecasts but also as a basis for long-term climate forecasts.
  7. Jmurphy, you do what supporters of The (significant human-made global climate change) Hypothesis often do, distort what is said. What I said about the first UK whitewash hearing into Climategate and the Met. Office’s decision to stop its long-rage forecasts was “ .. shortly after that that the Met. Office discontinued its long-range forecasts because they were so useless .. ”. That is not the same thing as saying that the decision by the Met Office was a consequence of what was said at the hearing. That should remove one area of assumed disagreement between us. Others, such as the whitewashes, the validity of The Hypothesis and your belief that “code written to represent the Physical qualities of the make-up of potential weather would .. be useful not only for short-term forecasts but also as a basis for long-term climate forecasts”, will be much more difficult to clear up. Best regards, Pete Ridley
  8. Steady on, Pete. You claim there are inconsistencies and inadequacies in the models and argument of "proponents" of AGW. I'd suggest that if you want to maintain consistency with your claim to be a "sceptic" that you avoid expressions like - 'the first UK whitewash hearing'. That seriously undercuts the position you claim to advance.
  9. Pete Ridley, I am not a "supporter of The (significant human-made global climate change) Hypothesis" (although I don't know how to react to that rather convoluted and bizarre term - doesn't Anthropogenic Global Warming [AGW] do it for you ?) : I am an accepter of the scientific facts behind AGW. Until I see such facts over-turned, or a better theory come along, I will stick with the AGW one.
  10. Pete Ridley - I'm still interested in your response to my question on evaluating Hansen 1988 as a scientific model. I believe this is critical to the thread and the discussion.
  11. Peter Hogarth, ref. #204, I think that Physicist Luboš Motl’s blog thread “John Cook: Skeptical Science” (Note 1) Item 4 should help you. Motl says “It's cooling: Again, Cook's graphs and statements are obsolete and a few years from the moment he wrote the page were enough to falsify his new predictions about the accumulating heat. The reality is that between 1998 or 2001 or other years on one side and 2009 on the other side, the global mean temperature dropped. Sometimes it's cooling, sometimes it's warming. The year 2010 is likely to be much warmer than 2009, approaching the temperatures of 1998, but when the El Nino fully switches to a La Nina, things can be very different. The fact that there's been no significant warming for 15 years has been accepted by both sides of this debate. And since 1998, it's just cooling. Cook has no counter-arguments. He just says that the heat flows influence the temperature and I agree with that. Except that he doesn't show in which way the flows are going to go e.g. in the next 10 years”. Motl also comments at Item 5 about this thread with “Models are unreliable: Cook says that models have made predictions that were successfully compared to observations. Except that this is not enough for the models to be reliable. For them to be reliable, it would have to be the case that the models have produced no predictions that were inconsistent with the observations - because one wrong prediction is enough to falsify a model. Clearly, such falsification has taken place with all of them. In particular, all IPCC-endorsed models predicted a warming since 1998 that didn't occur. They're gone. Again, both sides agree that we can't rely on them. Kevin Trenberth agrees that the disagreement of the models and the data is a travesty. There are hundreds of recent examples showing how deeply flawed the existing IPCC-endorsed models are”. KR, Here are Motl’s comments about those global temperature measurements you were on about in #203 “Temp record is unrealiable: In his counter-point, Cook talks about the urban heat island effects that are "negligible". Well, they're surely not negligible because the estimated urban warming in typical large cities exceeds the whole assumed warming caused by CO2 - something like 0.6 °C. So it matters a lot whether the urban effects are isolated. But the urban effects are far from being the only problem with the surface temperature record. The number of recently found dramatic problems with the surface record is so huge that I can't even enumerate them here”. The rest of Motl’s thread is worth reading too – enjoy. NOTE 1) see Best regards, Pete Ridley
  12. Pete Ridley writes: And since 1998, it's just cooling. I am not aware of any global temperature index that shows a cooling trend since 1998. From Jan 1998 through last month, both satellite series (UAH and RSS) and all three of the major surface series (GISTEMP, HADCRUT, and NCDC) have a positive slope. This is pretty remarkable considering that you've cherry-picked an interval with the largest El Nino on record at the start, and a substantial La Nina near the end. FYI, here's a graph of RSS (satellite) temperatures that I posted in another thread recently: You will note that most of the past decade has been above the 1979-2000 trend line. The apparent "flattening" you refer to is just an artifact of the more-rapid jump of temperatures at the start of this past decade (2000-2002).
  13. Pete Ridley writes: In his counter-point, Cook talks about the urban heat island effects that are "negligible". Well, they're surely not negligible because the estimated urban warming in typical large cities exceeds the whole assumed warming caused by CO2 - something like 0.6 °C. So it matters a lot whether the urban effects are isolated. But the urban effects are far from being the only problem with the surface temperature record. The number of recently found dramatic problems with the surface record is so huge that I can't even enumerate them here”. Comparing the elevated temperature in urban areas to the magnitude of the global increase in temperatures is misleading since urban areas constitute a tiny fraction of the surface area of the earth. The greatest warming is occurring at high latitudes where there are no large urban areas. We have a thread here that addresses many of the alleged problems with the surface temperature record. In my experience, most of the "skeptical" claims about that record have turned out to be groundless once people started looking into them quantitatively.
  14. Pete Ridley - you claim no warming since 1998. That's a frequent, and incorrect skeptic argument addressed here, in "Did global warming stop in 1998?", which you might want to take a look at. You claim no warming since 1998; But there's huge warming since 1997, and huge warming since 1999 - 2 out of 3 wins? Cherry picking your start date, as you do with 1998, to a 2 sigma noise spike can give you any answer you like, but the statistics clearly show continuing warming. As to the accuracy of the surface temperature reconstructions, there are at least four independent data sets producing the same answers, with all variations of UHI and calibration adjustments by any analyst producing answers between 0.15 and 0.175 oC/decade, the two satellite estimates at 0.13 and 0.15. Multiple independent data sets, all adjustment variations, and they come to about the same answer. That's pretty much the definition of reliable measurements. And hence the decent models (including Hansen 1988) actually do match the data, indicating some degree of accuracy in the models. Unless you have a different definition of a scientific model?
  15. Ned, ref. #220, I’m sure you wouldn’t wish to mislead anyone with your “Pete Ridley writes: And since 1998, it's just cooling”. More correctly, Pete Ridley quotes Physicist Luboš Motl who writes: … What I said on the subject (see #213) was:- If the global mean temperature estimates produced by the Hadley Centre etc. are to be trusted (“lies, damned lies and statistics”) we may have already had over 10 years of “flat or negative temperatures while GHGs rise” so may not have much longer to wait in order to “clearly invalidate AGW”. The Hadley Centre “Global average temperature 1850-2009” graph (Note 1) tells me that since 2000 the anomaly (wrt 61-90) has changed by under 0.05C. That’s near enough flat in my book. Correct me if I am mistaken but if the 21-year smoothing is removed then the last decade, according to those same statistics, has experienced virtually no change in mean global temperature The Met. Office commented on this (Note 2) with “ .. Recent Met Office research investigated how often decades with a stable or even negative warming trend appeared in computer-modelled climate change simulations. Jeff Knight, lead author on the research, says: “We found one in every eight decades has near-zero or negative global temperature trends in simulations. Given that we have seen fairly consistent warming since the 1970s, the odds of one in eight suggest the observed slowdown was due to happen.” Our decadal forecast predicts an end to this period of relative stability after 2010. We project at least half of the years after 2009 will be warmer than the 1998 record. Climate researchers are, therefore, reinforcing the message that the case for tackling global warming remains strong. Commenting on the new study, Vicky Pope, Head of Climate Change Advice at the Met Office, said: “Decades like 1999–2008 occur quite frequently in our climate change simulations, but the underlying trend of increasing temperature remains .. ”. Also, “Warming On 11 Year Hiatus” (Note 3) presents a graph on this. You say in #221 that “ .. urban areas constitute a tiny fraction of the surface area of the earth ...”. Equally, the temperature measurements, which are subjected to significant statistical manipulation before being considered suitable for presenting a picture which supporters of The (significant human-made global climate change) Hypothesis through our use of fossil fuels, only take place at a tiny fraction of the surface area of the earth. NOTES: 1) see 2) see 3) see Best regards, Pete Ridley
  16. Pete, I've given my opinion about the perceived "slowdown" or "flattening" over in the thread about surface temperature reconstructions, particularly this comment. Regarding the last paragraph of your comment, you've created a false parallel. Urban areas are where they are; no extrapolation is needed or appropriate. We don't suspect that there might be a hitherto unknown city in the middle of the North Atlantic, based on interpolation between Boston and London. In contrast, we use a very small subset of the entire surface of the Earth (weather stations) to calculate the broad-scale mean climate. In fact, as mentioned in the other thread this can be done to some degree using as few as 61 stations. At the same time, we can test our temperature reconstructions by comparison to spatially more-extensive measurements from satellite. Finally, you might want to consider toning down the writing style a bit. Sentences like "[...] the temperature measurements, which are subjected to significant statistical manipulation before being considered suitable for presenting a picture which supporters of The (significant human-made global climate change) Hypothesis through our use of fossil fuels [...]" may seem like an amusing way to slip in lots of little digs at climate scientists, but all they really do is lead to turgid prose and a disinclination on the reader's part to keep reading.
  17. I did post a longer comment prior to my #219 but it looks as though admin removed it. I’ll E-mail it to Phil instead, meanwhile this bit may be allowed. Phil, ref. #206, You ask “Where have the models failed?” and I can do no better than quote Vincent Gray “they have failed to predict the temperature in the Lower Troposphere and any future climate event .. “ and “ .. climate models have never been validated in the manner I have stated ..”. Jmurphy. in #217 you ask of my use of The (..) Hypothesis" “.. doesn't Anthropogenic Global Warming [AGW] do it for you ? .. ”. Like you, I and many other sceptics accept “ .. the scientific facts behind AGW ..” but what we don’t accept are the assumptions made about its significance or other assumptions made in the face of the enormous uncertainties about the processes and drivers of global climates. I use my alternative “ .. .. rather convoluted and bizarre term -.. “ to highlight the distinction between “DAGWers” and “Deniers” – that word “significant”. KR, ref. #203/205/218, using your criteria in #203: a) Ability to match previous observations (historic data) b) Ability to predict future observations c) Ability to estimate different future states based on different inputs (Given 'A', predict 'B') d) Match of model internal relationships to known physical phenomena e) Simplicity (no nested 'crystal spheres' for epicycles) my understanding is that because no independent validation has ever been undertaken there is no evidence to refute the argument that: a) can only be achieved through making adjustments to parameters until the desired result is achieved (as you acknowledge “The actual pattern of temperature rise that you get in the model depends on how the model is initialised.”), b) no dependable predictions have ever been made, c) estimates are not dependable predictions, d) it is the significant unknowns that make the models incapable of making dependable predictions, e) it is their simplicity which renders them little more reliable than crystal balls. If you have evidence to the contrary then it would help if you provided a link to it. Regarding the attempt to estimate mean global temperature, your “ .. argument really doesn't hold water .. ”. Reading “The Elusive Absolute Surface Air Temperature” (Note 7) and “NASA GISS Inaccurate Press Release On The Surface Temperature Trend Data” (Note 8) may be of assistance to you. NOTES: 1) see 2) see Best regards, Pete Ridley
  18. That's a very tired list, Pete. Before various people here drag themselves through the effort of once again providing some corrections, have you by any chance already discussed this elsewhere? If so, could you quickly list what rebuttals you encountered? That would be most helpful in saving everybody some time and wasted effort.
  19. Pete Ridley - Regarding the model value as discussed here, I would have to disagree with your statements. The Hansen model (and others) map physical phenomena into the computer model (white box modeling) and attempt to replicate previous system behavior. Adjustments to match historic results are certainly made - and if the modelers are doing their job right, this is part of an investigation to understand critical parameters such as feedback levels, time constants, and the like (black box modeling). Both white box (all known, first principles) and black box (estimations of unknowns) are core techniques for modeling. The critical power of a model really lies in estimating future states, the "Given 'A', predict 'B'". The Hansen model did this quite well - Scenario B, which Hansen considered most likely, was actually close to the economic and industrial conditions that have prevailed over the last 22 years, and the predictions made by Hansen were correspondingly close to what has actually happened. When fed the actual industrial numbers (a matter of economics and political decisions, rather than purely physics interactions) it's accurate to well within the weather noise level. See this link for an overview, and quite frankly the Hansen 2006 document describes this most clearly. That's an excellent model - it makes useful predictions that have been shown to be accurate. It certainly doesn't capture every element of chaotic weather overlaid on climate, cannot predict the frequency of volcanic eruptions, and doesn't model down to the cubic millimeter - but the predictions and the interaction estimates certainly hold up. Demanding 100% accuracy means that you will never accept a model. That's certainly your choice, but I believe that will leave you with quite a few tools missing from the toolbox. If you feel that a model, one which given actual industrial activity levels closely predicts temperatures 22 years into the future, and which allows exploring different outcomes based upon our actions, is not worthwhile, well, then I'll have to continue to disagree. As an aside, I must note that I don't consider Luboš Motl a reliable source - he's obviously an expert in string theory, but has no climate background and seems unfamiliar with logarithmic responses to GHG's. He also posts from a clear ideological framework rather than a scientific one in the climate arena. I prefer numbers, myself...
  20. " than quote Vincent Gray “they have failed to predict the temperature in the Lower Troposphere and any future climate event .. “ and “ .. climate models have never been validated in the manner I have stated ..”." I can only assume you mean the denialist canard about tropospheric hot spot because models predict lower tropospheric temperatures very well. For some real information, try tropospheric hot spot As to Gray's validation. Since you apparently understand what he means, can you enlighten the rest of us? And can you please read the Hansen 2006 paper that has been repeatedly pointed out to you. "a) can only be achieved through making adjustments to parameters until the desired result is achieved (as you acknowledge “The actual pattern of temperature rise that you get in the model depends on how the model is initialised.”)," No - you are completely misunderstanding what is meant by 'initialisation of models'. How can you be so critical of models when it appears you know so little about them? This is discussed in depth in IPCC WG1 and in the text of the Keelyside et al paper has more. This Keenlyside paper is criticized and the matter discussed further here You also seem to stubbornly refuse to accept that predictions, accurate to level within the prediction, have been made. Any prediction of any scientific value has error limits associated with it. Demanding a prediction be better than those internal limits is pointless.
  21. There follow a couple of comments that I posted originally on 28th at #226 but was removed by admin, perhaps because I had inadvertently carried over some links from a previous comment. I’ll post it now in two parts in case there was something else that was not found to be acceptable.
  22. PART 1 KR, ref. #222, I know that it is not uncommon for politicians to distort the facts but please don’t misrepresent what I post about The (significant human-made global climate change) Hypthesis. I am not aware that I “ .. claim no warming since 1998 ..”, was “Cherry picking (a) start date, .. 1998” or claiming anything about 1998. If I did then please point me to where and I’ll retract. If you can’t find anything of the sort then try reading my posts again and you may spot where you may have misinterpreted what I actually said. Regarding those attempts to measure global temperatures, perhaps you’d like to help me out and identify those “ .. four independent data sets .. ” but please make sure that they are indeed independent of each other, starting with the raw data then progressing through the statistical manipulations.
  23. PART 2 Ned, ref. #224, perhaps you’d like to advise the extent of the uncertainty of estimating global mean temperature anomaly “.. using as few as 61 stations.” but would you be good enough to provide it in Centigrade degrees. If the attempts at estimation by The Hadley Centre are to be believed, we’ve only had about 1C in 100 years – nothing to get excited about really. I’m not sure that you would agree with KR about four independent data sets but perhaps you do. I don’t get that impression from your article. Vincent Gray has drafted a paper which inlcudes commentary on those temperature measurements so I’ve sent him a link to the “Assessing global surface temperature reconstructions” thread. You might like to try reading “The Elusive Absolute Surface Air Temperature” (Note 1) and “NASA GISS Inaccurate Press Release On The Surface Temperature Trend Data” (Note 2) that I mentioned in #225. As for toning down my writing style, thank you for the advice but I’ll leave it to the blog administrator to decide if my tone is unacceptable. Best regards, Pete Ridley
  24. Pete Ridley writes: Ned, ref. #224, perhaps you’d like to advise the extent of the uncertainty of estimating global mean temperature anomaly “.. using as few as 61 stations.” but would you be good enough to provide it in Centigrade degrees. You're referring to the work of Nick Stokes as described here. Specific questions about his reconstructions should probably be addressed to him. That said, comparing the standard errors listed for the 61-station reconstruction to the full land/ocean reconstruction using all stations (here) suggests that there's about twice as much uncertainty in the reduced set (for which the trends are 0.0855 +- 0.00835 C/decade in 1901-2009, and 0.282 +- 0.0393 C/decade in 1979-2009). It does not seem particularly surprising that the standard error would double when using a much smaller number of stations. PR continues: If the attempts at estimation by The Hadley Centre are to be believed, we’ve only had about 1C in 100 years – nothing to get excited about really. Globally it's a bit less than that, perhaps an 0.75 C increase over the past century. It's important to understand that number in context, however -- a global temperature increase of 0.75 C is actually quite large given the very short time frame involved. (It's roughly 10% of the change in temperature since the last glacial maximum, a time when the location of my house was buried under a couple km of ice). In addition, the real concern is not the impact of the 0.75 C rise from 1900-2010, but of the probable 2-4 C rise from 2010 to 2100. Both the climate and our technological infrastructure have a great deal of inertia, so it is important to figure out what needs to be done and start working on it ASAP. Had we done so 20 years ago, we would have much more flexibility. If we wait another 20 years, we will have much less.
  25. Pete Ridley, perhaps you'd like to dismiss the Japanese Meteorological Agency's temperature figures too. Maybe, because they were under American occupation for so long after the last war, they have been inducted into that great big conspiracy that the rest of us (whoops, have I given the game away ?) are involved in ?
  26. Pete Ridley - Regarding temperature data, I must apologize; apparently there are three independent data sets, not four. The two satellite sets are derived from the same sensors, albeit with very different data processing. So, the independent data sets are: satellite data (two major statistical analyses), the GHCN database data (currently 1500-2000 stations, many many analyses), and the Global Summary of the Day (GSOD) database (9000 stations, fewer analyses). You can add to that the increasing Ocean Heat Content, sea level rises, longer growing seasons, and a ton of other data, as per the recent NOAA State of the Climate 2009 All raw data indicates rising temperatures, including the last 10 years. All analyses except short term runs with start dates chosen to be 2-sigma events like the 1998 spike indicate rising temperatures, including the last 10 years. I will stand by my statements on the surface temps, and the lack of a decline in recent years.
  27. I can recommend Paul N. Edwards (2010) "A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming". I'm just starting on the final chapter and its by far the best text on the origins and applications of modeling in climate science. Highly recommended!
  28. Mats (Frick), thanks for advising about "A Vast Machine: Computer Models, Climate Data, and the Politics of Global Warming". I responded on 31st July and 1st August but my comment was removed so I’ve modified it a little and hope it is now acceptable to the moderator. I note that Professor Edwards is not a scientists involved in any of the numerous disciplines contributing to improving our poor understanding of global climate processes and drivers, so I wonder what has convinced him that “I think climate change is real, and I think it is the biggest threat the world faces now and will face for generations to come. ... Climate change is not a matter of opinion, belief, or ideology. This book is about how we came to know what we know about climate — how we make climate knowledge” (Intro xiv). It’s that “climate change is .. the biggest threat the world faces .. “ bit that I disagree with. He makes no mention of “uncertainty” anywhere in that introduction, which makes me suspicious about the extent of his understanding of those processes and drivers and of his environmental activism. I will be getting a copy but as you’ve read most of the book can you tell me if he touches on any of that or the subject of validation. The manner in which Edwards presents what Professor Freeman Dyson said about the reliance on models gives a somewhat different impression to how I interpret them. I’m think that Dyson was referring specifically to computer models rather than models in general. Chapter 13 is the one that I’m most interested in reading – any comments on that, taking into consideration my previous comment here? I’ll have a more careful read after my holiday and get back to you. Best regards, Pete Ridley.
  29. Jo Nova’s blog has an interesting new article “The models are wrong (but only by 400%) ” (Note 1) which you should have a look at, along with the comments. It covers the recent paper “Panel and Multivariate Methods for Tests of Trend Equivalence in Climate Data Series” (Note 2) co-authored by those well-known and respected expert statisticians, McIntyre and McKitrick, along with Chad Herman. David Stockwell sums up the importance of this new paper with “This represents a basic validation test of climate models over a 30 year period, a validation test which SHOULD be fundamental to any belief in the models, and their usefulness for projections of global warming in the future”. David provides a more detailed comment on his Niche Modeling blog “How Bad are Climate Models? Temperature” thread (Note 3) in which he concludes “But you can rest assured. The models, in important ways that were once claimed to be proof of “… a discernible human influence on global climate”, are now shown to be FUBAR. Wouldn’t it have been better if they had just done the validation tests and rejected the models before trying to rule the world with them?”. Come on you model worshipers, let’s have your refutation of the McIntyre et al. paper. NOTES: 1) see 2) see 3) see Best regards, Pete Ridley
  30. James Annan comments on M&M's comment as published in ASL: A commenter pointed me towards this which has apparently been accepted for publication in ASL. It's the same sorry old tale of someone comparing an ensemble of models to data, but doing so by checking whether the observations match the ensemble mean. Well, duh. Of course the obs don't match the ensemble mean. Even the models don't match the ensemble mean - and this difference will frequently be statistically significant (depending on how much data you use). Is anyone seriously going to argue on the basis of this that the models don't predict their own behaviour? If not, why on Earth should it be considered a meaningful test of how well the models simulate reality? Of course the IPCC Experts did effectively endorse this type of analysis in their recent "expert guidance" note, where they remark (entirely uncritically) that statistical methods may assume that "each ensemble member is sampled from a distribution centered around the truth". But it's utterly bogus nevertheless, as there is no plausible situation in which that can occur, for any ensemble prediction system, ever. Having said that, IMO a correct comparison of the models with these obs does show the consistency to be somewhat tenuous, as we demonstrated in that (in)famous Heartland presentation. It is quite possible that they will diverge more conclusively in the future. Or they may not. They haven't yet. Annan Should be quite a stir out of this, papers of this sort being few and far between. Worth noting that Annan is an unflinching critic of whatever he sees wrong w/IPCC, etc. Probably a useful snapshot metric of the significance of M&M's output here.
  31. I might add as a gratuitous fling, the amount of back-slapping and rejoicing around M&M's first accepted comment in years is indicative of the general poverty of their camp. Looking at the comment threads erupting around this I'm reminded of meat being thrown into a kennel full of emaciated dogs. Folks outside the kennel have more to eat than they care to look at, frankly, are amply fed with dismal facts. Less gratuitously, this publication immediately moves me to point out that not everybody can feed from the meal on offer. Those who've committed themselves to trying to show the temperature observations under discussion are meaningless will have to go hungry unless they disagree w/M&M. Those saying there's no trend will also have to continue listening to their stomachs rumbling, because again M&M's results depend on observing a trend.
  32. Pete, worth noting also that you won't find a refutation to M&M 2010 coming from here, you'll find it reported if and when such a refutation appears. The sites you mention are in full celebration but of course they're not adding any information of their own, the actual information is all in the paper itself. Hopefully for M&M the air the party won't be over before their work actually appears in print. :-)
  33. Pete Ridley at 07:12 AM on 11 August, 2010 I'm guessing you read the comments and not the details of the paper? The paper itself is interesting, as M,M&H confirm that tropical Lower Troposhere temperature trends from 1979 to end of 2009 are significantly positive, and to an extent reflect the earlier views in Santer 2008. See my comment on tropospheric hot-spot for some background on this. At the time of writing that comment I suggested that the inclusion of the 2010 data would allow the trends to more closely approach statistical “robustness”, so confirmation is a useful step. They also confirm the known issues with the earlier models used by Santer, and also confirm that the differences between the UAH and RSS MSU datasets are now statistically significant. For the Tropical Lower Troposphere temperature data they quote “In this case the 1979-2009 interval is a 31-year span during which the upward trend in surface data strongly suggests a climate-scale warming process”. That the original model was flawed in this case is old news, and this has been discussed here previously. I note once again some of your sources (and the comments on this new paper) lack context and scientific objectivity.
  34. There is a trade off betweeen concern for the most vulnerable and mistrust of governments. I am not a confirmed beleiver in the network of socialists doctoring results for their trotskyite masters. That said inevitably there will be incidences where the responsability of stewardship weighs heavy on scientific rigour. The code should be available so we can move on. We all agree models will be better in the future. Not to heed what they are currently delivering is an imprudency beyond recall.
  35. Fun! Schmidt and Knappenberger are found at Annan's blog, discussing M&M 2010. Minor celebrities For extra credits in "Climate Science Arcana" coursework, follow the "old dark smear" links at the top of Annan's post. Those have a bit of useful background material to the M&M 2010 treatment of Santer 2008, to do with RPjr. If you have a clue what that's all about, you spend too much time on climate blogs.
  36. Do any climate models have substantial agreement with the last century of precipitation data?
  37. rcglinski. Not precipitation and not a century, but this item gives a really neat alignment of humidity over the last 40 years. I've not followed the references through, but you might find some leads to what you're after if you do.
  38. Well that comment of mine on 11th August @ 07:12 did elicit some interesting responses but, as Doug acknowledged @ 08:03 “you won't find a refutation to M&M 2010 coming from here”. I think that Doug’s contribution @ 14:10 offered the best read, at friend James’s blog (Note 1). There are lots of interesting comments there, the one that I found most appropriate being from Ron Cram on 12th August @ 01:10 QUOTE: Gavin writes "It is also perhaps time for people to stop trying to reject 'models' in general, and instead try and be specific." People are not trying to reject models in general. It has already been done. Generally speaking commenters are bringing up points already published in Orrin Pilkey's book "Useless Arithmetic: Why Environmental Scientists Can't Predict the Future." Nature is simply too chaotic to be predicted by mathematical formulas, no matter how sophisticated the software or powerful the hardware. None of the models relied on by the IPCC have been validated. It is fair to say the models are non-validated, non-physical and non-sensical. Perhaps it is time to quit pretending otherwise UNQUOTE. NOTE: 1) see Best regards, Pete Ridley
  39. Pete, regarding validation you ought to take a look at Hargreaves' remarks here. Concerning that item, be sure also to read Annan's remarks here where as you can see he leads us to the conclusion that making broad condemnatory statements about purported lack of model utility is not circumspect.
  40. Doug, thanks for that link to Julia Hargreaves’s paper. I wholeheartedly agree with her conclusion that “Uncertainty analysis is a powerful, and under utilized, tool which can place bounds on the state of current knowledge and point the way for future research, but it is only by better understanding the processes and inclusion of these processes in the models that the best models can provide predictions that are both more credible and closer to the truth”. There’s a lot more research to be done into obtaining a proper understanding of those horrendously complicated and poorly understood global climate processes and drivers before any reliable models can be constructed and used for predictions. Best regards, Pete Ridley
  41. Yeah, Pete: circumspect, conservative. Hargreaves notes that Hansen's 1988 model passes the "null hypothesis" test but does not leap to any conclusions about "all the models are really great."
  42. KR, on 30th July at 02:41 (#228) you said that “Regarding temperature data .. there are three independent data sets .. ”. NASA appears to think otherwise according to its 3rd August draft of paper "Global surface temperature change". It says “Analyses of global surface temperature change are routinely carried out by several groups, including the NASA Goddard Institute for Space Studies, the NOAA National Climatic Data Center (NCDC), and a joint effort of the UK Met Office Hadley Centre and the University of East Anglia Climatic Research Unit (HadCRUT). These analyses are not independent, as they must use much the same input observations.” (See Any comment? Best regards, Pete Ridley
  43. Pete Ridley - I believe that those various analyses you list are based on the GHCN database, which as I had noted has had a lot of analysis applied to it. The independent GSOD and satellite data sets match trends with the GHCN database (in pretty much any analysis whatsoever). This is shown in the Assessing global surface temperature reconstructions thread. That's an excellent support for the data, and indicates (in the absence of any contradictory data) that these trends are real. The lowest estimate on warming is from the UAH analysis of satellite data (~0.13 C/decade?), which has had some known issues. Averaging the various estimates of land/sea increase gives a number closer to ~0.16 C/decade.
  44. New (model) model comes online: BOULDER—Scientists can now study climate change in far more detail with powerful new computer software released by the National Center for Atmospheric Research (NCAR). ... The CESM builds on the Community Climate System Model, which NCAR scientists and collaborators have regularly updated since first developing it more than a decade ago. The new model enables scientists to gain a broader picture of Earth’s climate system by incorporating more influences. Using the CESM, researchers can now simulate the interaction of marine ecosystems with greenhouse gases; the climatic influence of ozone, dust, and other atmospheric chemicals; the cycling of carbon through the atmosphere, oceans, and land surfaces; and the influence of greenhouse gases on the upper atmosphere. In addition, an entirely new representation of atmospheric processes in the CESM will allow researchers to pursue a much wider variety of applications, including studies of air quality and biogeochemical feedback mechanisms. Press release Release includes this remarkable picture (click for full resolution): "Modeling climate’s complexity. This image, taken from a larger simulation of 20th century climate, depicts several aspects of Earth’s climate system. Sea surface temperatures and sea ice concentrations are shown by the two color scales. The figure also captures sea level pressure and low-level winds, including warmer air moving north on the eastern side of low-pressure regions and colder air moving south on the western side of the lows."
  45. A good, short, essay on the role of computer models in science is in the journal Communications of the ACM, the September 2010 issue, page 5. I can see it on line for free, but I don't know if that's because I'm an ACM member: Science Has Only Two Legs.
  46. Tom, thanks, and that link does appear to work for us in the Great Unwashed Masses. Vardi makes an excellent point.
  47. johnd wrote (on another thread) : "With regards to the previous original reference to the JAMSTEC discussion, I provided the full link so that anyone interested could have full access to the entire discussion, as you so obviously had done, I therefore could not have been accused of being selective or cherry picking parts of the discussion to suit." Unless the particular comment of yours, to which you are referring, has been deleted, I cannot see where you have provided that link. All I can see from you is this from your post which contained the actual quote : His details are at As far as I am aware, the link to the actual email discussion was provided by doug_bostrom. That is why I replied in the ways (here and here) I did.
  48. Continuing from here. "The algebra of probabilistic distributions is extremely complex ... Extrapolating complex environmental data described by complex statistical relationships into the future is indeed a difficult process" What you've described (in the linked comment) sounds like a fairly routine problem in particle physics. And yet we build devices that rely on the motion of electrons through semiconductors; we manage to collide protons and anti-protons with statistical certainty (and avoid hysterical claims that we'd be creating mini black-holes in the process). We can even make sense of the results and produce a very competent model of the sub-atomic world. Your argument suggests that if a problem is too complex, we can't put any faith in a model solution. The implication is that it's a waste of time and money to begin that process. Yet that is a challenge that has been met successfully in other disciplines. Some of the comments above suggest that it can work here as well.
  49. Also, there a some things we can say with a lot of certainty. - CO2 is increasing (want to guess the uncertainty there?) - CO2 increase is anthropogenic. - CO2 is a greenhouse gas. The major uncertainty to quantify then is sensitivity. Models estimate it but I agree there are issues but its not the only way to estimate sensitivity.
  50. Suppose they took the world's best computers, and the best modellers, and worked on the last twenty years Kentucky Derby results and form. Eventually they produce a model that predicted them all. Would you sell your house, and put the money on the same model's prediction for the next Kentucky Derby?

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