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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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

Printable Version  |  Offline PDF Version  |  Link to this page

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.

Update

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

Comments

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Comments 1251 to 1291 out of 1291:

  1. "What makes you think I haven't looked at those sources ..."

    If you had looked at them properly and with an open mind then you would have formed more specific and meaningful questions. That is why I think you have not looked at them. 

    The "control knob is easily debunked" is not a statement that is easy to engage with. 

  2. John Seers @1251

    I only asked how the current climate models show that humans are causing global warming — nothing more, nothing less.  How much more "specific" am I supposed to be?  It is these "sources" that are vague and not answering my question.  Frankly, I am very much disturbed by the fact that the climate science "experts" are using every scare tactic available to get nations to drastically cut CO2 emissions at a great economic sacrifice, yet none can give a straight answer as to how they used their models to conclude there is global warming and that humans are causing it.  Making your studies clear and traceable is an important part of doing good science, and it is not happening in the AGW community.

    Response:

    [TD] At the top of the home page there is a big image labeled "Newcomers, start here." In the resulting "Welcome to Skeptical Science" page, look for the section "Good starting points for newbies." Click the links in that section.

  3. ClimateDemon @1252,

    Are you familiar with the United Nations Intergovernmental Panel on Climate Change? I ask because your comment @1252 only makes sense if you are not familiar with this organisation and its work. I would draw your attention to IPCC AR5 WG1 which reviews the science showing both that "there is global warming" and that "humans are causing it." I would draw your attention to Chapter 10 'Detection and Attribution of Climate Change:from Global to Regional' and, as you have show interest specifically in the role of CO2 in the global warming, also Chapter 5 'Information from Paleoclimate

  4. ClimateDemon - here is a challenge for you: register for our MOOC "Denial101x - Making sense of climate science denial" and work through the six weeks worth of lectures. You'll get a good understanding of the basics of climate science - including about models - and how/why these basics get regularly distorted. Once done, come back to the comment threads here with any clarifying questions you might still have.  But frankly, there shouldn't really be (m)any as what you keep asking here has been answered more than enough already - it's up to you to put in the effort to learn and understand.

    Here is the link to the MOOC: https://sks.to/denial101x

  5. Climate Demon @ 1252

    For you to say you have asked a question and "nothing more, nothing less" is disingenuous. Comments like "the control knob is easy to debunk" say a whole lot more. 

    Others more knowledgeable than me have attempted to signpost you to more enlightening information but you think you are too informed to be bothered with that.

    I will give a partial answer to your no more, no less question. The question iteself shows you are not really clued up enough. Climate models do not provide proof humans are causing global warming. Climate models are a consequence of the scientists testing their theories against the data and evidence. They prove nothing in themselves. They are confirmation of what we think we know and help us feel we are on the right track. If we trust them enough we can use them for projections. Our trust grows over time as they are developed and used. (And as our computers get faster!)

    Models are one piece of evidence (not proof) of the consilience of evidences that add up to proof of AGW. That is evidence from many sources and lines of enquiry all point in the direction of AGW. 

    So, how much more specific can you be? A suggestion is you look through the references supplied (I recommend the Richard Alley lectures and his course) and then, (as you can simply debunk them Ha Ha), form a very specific question and work through it with the refutations you will get. You might learn something if you do it diligently.

     

  6. I'm trying to make sense of Climate Demon post at 1252 and it's difficult.

    This "they used their models to conclude there is global warming" is rather strange. The real situation is: the models suggest that global temperatures would rise under an increase in non-precipitable GHG scenario, accompanied by other phenomena like some decrease in stratospheric temp and changes in tropopause height, etc. Independently of models, multiple observations (tropospheric temps, sea surface temps, stratospheric temps, sea level, species movement upward and poleward, Arctic sea ice loss, etc) show without a doubt that there is global warming. These observations are what leads to the conclusion that there is global warming, not the models. They are, however, consistent with the expectations obtained from models when increased forcing from non-precipitable GHG are introduced. All this is in the original post.

  7. BaerbelW @1254

    I have seen some of the videos and other materials used in this course, and I highly doubt that you and the other faculty/staff members would want me in it.

  8. Well, I must thank you all for sending me such an impressive stack of references covering various aspects of arguing for AGW, most of which I have never heard about, and I will agree that as scientists, we must consider all available evidence on any issue before coming to a conclusion. I must also point out, however, that a chain is only as strong as its weakest link, and with AGW, the CO2 “control knob” is absolutely essential, yet it has never been proven. Without such a control knob, H2O vapor becomes the controlling as well as the strongest GHG, and in this case human contributions to temperature changes would be insignificant.


    In most of the peer-reviewed literature on climate change, existence of the control knob is simply assumed without references or supporting arguments. If references are given, I find they don’t explain the justification for the control knob either. The only paper I have found that even pretends to address this issue is the Lacis et. al. 2010 paper that I cited in a few earlier postings, although I have heard that other authors have made similar arguments. The problem, however, is that they make two false assumptions in setting up their model. First, they use a zero-dimensional model which assumes a single-temperature earth whereas temperatures on the real earth can vary by 50-60 degrees C over the surface. Second, they apply the Clausius Clapeyron equation to obtain the water vapor concentration. This equation assumes constant thermal equilibrium when in fact the earth is never in thermal equilibrium. Thus, there is no valid proof of the CO2 control knob effect.


    Unfortunately, since we cannot establish the existence of a CO2 control knob, all of those references you sent me are rendered meaningless.

    Response:

    [DB]  Continuing to make things up is unhelpful.  Sloganeering snipped.

  9. ClimateDemon @1258,

    It appears you require your feed of information served up to you in the most readily consumable form.

    Lacis et al 2010 use a model. You say that model is "a zero-dimensional model which assumes a single-temperature earth."

    The model used was GISS ModelE. This model is a full-blown GCM. What you say about GISS ModelE is complete and utter nonsense.

  10. " Without the radiative forcing supplied by CO2 and the other noncondensing greenhouse gases, the terrestrial greenhouse would collapse, plunging the global climate into an icebound Earth state."

    Link to publication

    Response:

    (BW) re-formatted the link

  11. ClimateDemon @1257

    Well, judging from your comments here, you'd provide ample examples for the students in our MOOC of how science denial can look like! Your contributions in the forum might therefore end up as actual case studies for them of what they'll encounter in real life! And who knows, you might still learn something - at least if you are prepared to really engage with the material and watch the expert interviews included in the course.

  12. Climate Demon @1258

    You have gone from "the control knob is easily debunked" to "absolutely essential" (for AGW) to "never been proven" to "simply assumed" to some waffle about zero-dimensional models to some mumbo-jumbo about Claudius Clapeyron to there is "no valid proof".

    You finish with a flourish. Everything is "rendered meaningless"

    It's a bit of a cop-out on your part, isn't it? Just make a list of random assertions, assert it is all meaningless and pat yourself on the back. 

    Sorry, you have to put more effort into it than that.

  13. Yes, Baerbel, ClimateDemon is a good example of denial because he's such a bad example. Even in his most recent post:

    • "...most of which I have never heard about..."

    ...but he still knows

    • "In most of the peer-reviewed literature on climate change, existence of the control knob is simply assumed ..."

    ...and he concludes

    • "...all of those references you sent me are rendered meaningless."

    So, he isn't aware of of much of what we pointed to, but knows that the entire field of climatology assumes things that they don't, and dismisses an entire field of science as "meaningless" even though he isn't aware of what it contains. Rinse, Repeat.

    It doesn't matter what is presented to him - without reading it, he knows it is all wrong.

    The Morton's Demon is strong in ClimateDemon.

  14. BaerbelW, I rather think that Climatedemon is like our old friend cosmowarrior/coolearth et al.  He/she struggles to comprehend information that is at odds with prior beliefs so would struggle in the course.

  15. MA Rodger @1259


    In Lacis et. al. (2010) the authors state:


    A clear demonstration is needed to show that water vapor and clouds do indeed behave as fast feedback processes and that their atmospheric distributions are regulated by the sustained radiative forcing due to the noncondensing GHGs. To this end, we performed a simple climate experiment with the GISS 2° × 2.5° AR5 version of ModelE, using the Q-flux ocean with a mixed-layer depth of 250 m, zeroing out all the noncondensing GHGs and aerosols.


    Now, the authors did not provide the input data they used, but they did say they performed a simple demonstration. Of course, I don’t know their definition of “simple”, but I believe it most likely would include a uniform temperature and zero fluid velocity and pressure gradients. Also, examining Figure 2, I see that one of the results of their ModelE runs is a single-value global temperature for each time point, which we already know is unrealistic. Although I am not familiar with ModelE, I do know a few things about GCMs in general, including the fact that the results of any such number crunching is highly dependent upon the initial conditions, many of which are unknown. This is what makes these models “tweakable” for purposes of hindcasting, but even that process is far from perfect. Although the ModelE demonstrations may well have produced valid results for the particular set of initial conditions chosen, they should not be regarded as “typical” output from the model.


    Therefore, my claim that the CO2 “control knob” has not been proven still stands.

  16. I would like to post this fun question to all of you AGW folks and anyone else interested in participating.  And who knows?  It may just resolve some confusion about the concept of thermal equilibrium.

    Suppose we have a planet similar to Earth, except that the temperature is everywhere uniform.  But like Earth, much of the surface is covered with water and the terrain outside of the water has varying elevations.  At the lower elevations the air is generally moist and there are lots of lakes and rivers, and at the higher elevations, the air is much dryer and the climate is much more desert-like.

    Question:  Is this planet in global thermal equilibrium?

  17. ClimateDemon @1266 , your question must necessarily include a pre-condition ~ How long can this planet maintain equilibrium?

    You propose an interesting hypothetical planet.  To have a uniform surface temperature, that would require it be evenly surrounded by a sphere of identical suns numbering 40 (better, 100 or more).  Unfortunately, the planet's central location would not be gravitically stable, and the planet would drift into one of the suns.  So the planet's evenly-distributed temperature would persist until shortly before impact.

    The unpleasant scenario would have to include the 40 (or 100) suns gravitically attracting each other, and converging to the original central location including the planet (unless the planet had moved some distance ~ owing to the chaotic & nonlinear wing-flapping of an especially powerful gravitic butterfly).

    The Clausius-Clapeyron Equation indicates that the planet's beautiful lakes rivers & oceans would rapidly enter a state of very low relative humidity . . . until reaching the plasma state [a state not describe by the C-C Equation, if I understand your earlier comments].

    (Moderators may care to remove this slightly Off-Topic post. )

  18. ClimateDemon @1265,
    Bar moderator intervention, you are of course at liberty to parade your ignorance here.

    What do you not understand about "GISS 2° × 2.5° AR5 version of ModelE"? Presumably all of it. (You might find this CarbonBrief article on GCMs useful in raising your understanding of GCMs to a less embarassing level.) And why would the values presented in the paper's Fig 2 throw any light on the complexity of the model used to generate them when, as the Fig 2 clearly states, they present "Global Annual Mean" data? Without there being more than one "globe", such a graph will only have "a single-value global temperature for each time point".

    As for your little speech about "inital conditions", perhaps you can give an example of which of these "inital conditions" could be "tweeked" to alter the fundamental finding of Lacis et (2010). (Remember this simple experiment is removing some 30Wm^-2 of greenhouse effect. Such a climate forcing, even without feedbacks, is enough to drop global average temperatures by far more that the last ice age achieved.)

    ClimateDemon @1266,
    I assume your cunningly crafted question is intended to show that a model of an Earth-like planet's climate in which "the temperature is everywhere uniform" would not capture the topological complexity of such a planet. As Lacis et al did not use such a model, your question is entirely misplaced.

  19. ClimateDemon:

    Since you seen keen on the concept, why don't you explain, in complete and unambigous terms, just exactly what you think you mean by "global thermal equlibrium".

    Unless you have a working definition of that phrase, you're just playing games, not doing science.

  20. MA Rodger @1268

    All right, so scrap the entire 1265 posting.  I never was very good at guessing games anyway.  If you go to the paragraph that starts near the top of the third column on page 357, however, you will see that the authors of the Lacis et. al. (2010) paper do in fact use that zero dimensional model with a single temperature earth to make some prediction on the sustainable amount of atmospheric water vapor in the example they were showing.  Their ModelE runs were for something else.

  21. ClimateDemon @1270:

    You mean where Lacis et al use the phrase "If the global atmospheric temperatures were to fall as low as TS=TE..."

    Clearly, you have no idea what Lacis et al are saying when they use the symbols TS and TE, even though they explain it in the second paragraph of the paper: "...mean surface temperature (TS = 288 K) and the global mean effective temperature (TE = 255 K)...

    That they describe a three-dimensional system by using mean values does not indicate they used a zero-dimensional model.

    Frankly, you have absolutely no idea what you are talking about.

  22. ClimateDemon, I will simplify Bob Loblaw's response to you. Here is a set of numbers: 8, 15, 3, 9, 4. Here is a "descriptive statistic" that summarizes the central tendency of that set of numbers, thereby making the set as a whole easier to understand for some purposes, by subsuming its details: The mean of that set is 7.8.

    Now look at my second sentence written above. Those five numbers still are there. They did not magically disappear merely because I typed their mean as "7.8." That ability is called "object permanence."

    Response:

    [DB] The user in question has recused themselves from further participation in this venue.

  23. SpaceMan @1273,

    Your presence here may be limited (as the moderator response @1272 implies) but while you are here, the speculation set out by Lacis et al (2010) which talks of "TS=TE" and "the Clausius-Clapeyron relation" is part of an illustrative introduction to their employment of a full General Circulation model, such models being stacked full of 'dimentional' stuff. Are you with me so far? If so, that would be good, as that puts an end to your nonsense about them using zero-dimension climate models.

    Response:

    [TD] Indeed, they are a sock puppet and have been removed.

  24. I have a few comments:

    1. These so called models, many of them, were made with public money.  Why has the public no access to play with the models?  For example, enter inputs (CO2 concentrations), and see what the predicted outputs (e.g.  temperature) are.   

    2. Where are these models, who programmed them, who owns them, who controls them, who maintains them, who checks them?

    3. From the best public models, what are the predictions the models are making?  Are these predictions published?  Can we compare future outcomes vs model predictions?  Do these models predict based on scenarios?   What percent of previous models been correct in their predictions?    Which accessible model is the best one, based on past predictions/forecasts vs. actual empirical data.  What are the current predictions of this model ?  Are these predictions contingent on certain scenarios, conditions and assumptions?  What are these?  Have these been documented, published and made public?  

    “What can be asserted without evidence can also be dismissed without evidence.”

    Response:

    [DB] Sloganeering snipped.

  25. gzzm2013:

    1. The General Circulation Models (GCMs) can run only on supercomputers. (Well, they can run on lesser hardware in principle, but you'd need to wait years, decades, or centuries for results.) There are numerous dramatically simpler models used for teaching the principles, such as this one by Tim Osborn that you can play with as you requested. Tamino described a model you can play with, without needing a computer at all. Other evidence not involving computer models is abundant on this SkepticalScience site, and in a huge number of other sources, including a video by investigative journalist Potholer54.
  26. gzzm2013:

    2. Numerous groups of researchers all over the world create and run climate models, which intentionally differ from each other to provide consilience in the evidence. Scroll down in this page in the RealClimate site for a list of links to just a few of the model's web sites, where you will find the information you asked for. The most prominent, though certainly not only, organized effort to create and compare multiple models is CMIP--Coupled Model Intercomparison Project. The most recently completed version of that multimodel project is CMIP5. CMIP6 is in progress. There is a summary of the degree of independence of the most prominent models, in this RealClimate post. More fundamentally, you need to learn better what "model" means in this context; Steve Easterbrook's post is a good summary. Getting at the root of your questions, watch Steve's TEDx talk.

  27. gzzm2013:

    3. I'm not going to waste my time answering these questions, when you have not bothered to read the post on which you are commenting. I suspect your questions are merely rhetorical--actually, that's dignifying them too much. I suspect you are just drive-by ranting. Please do prove me wrong, by posting more specific questions that reveal you have done at least basic reading already.

  28. RealClimate has posted its 2021 comparison of models to observations.

  29. Recommended supplemental reading:

    If scientists can create a new way to predict climate change – making it as accurate as, say, forecasting the weather – it would help people make everyday decisions: how high to build a sea wall or what crops to plant.

    Meet the team shaking up climate models by Doug Struck, Environment, The Christian Science Monitor, Jan 22, 2021

    Note: This is a very well-researched and well-written indepth article.  

  30. Eclectic:

    In his Politics, Aristotle believed man was a "political animal" because he is a social creature with the power of speech and moral reasoning: Hence it is evident that the state is a creation of nature, and that man is by nature a political animal.

    To think that the IPCC is not political is naive at best.  The United Nations Security council is formed by the victors of WW2, nations that have been colonial empires and empires.  They are great exporters of weapons and they have financed the United Nations.  

    You cannot analyze the science of climate change without questioning its funding, motives, mechanisms, governance and who is not sitting at the table, and who is not represented. 

    Response:

    [DB] Off-topic snipped.

  31. Dayton

    1. So you are saying that because those models are to be run on expensive computers they cannot be accessed by the general public.  Why can't the public enter the input to the model, send it to the operators, then get the output of the model?  Is the public not paying for the models?   Every model has inputs and outputs.  Its that simple.  Can you list what are the input parameters of the best model?  And what are its output parameters?   Are the models too busy with experts entering inputs on them all the time that there is no time for the public to use what they paid for?   Can things not be explained in plain English?  Someone very smart said that if you can't explain it to a 6 year old you don't understand it yourself.   

  32. Dayton

    2 and 3. So let's put it this simply, let us draw an analogy.  Many so called sciences like economics claim that they have economic "models" , which model complex systems, but the fact remains that the economics science is not able to predict the next global financial crisis in magnitude or timing or nature.   

     

    Yet people are claiming that the climatic models are reliable and can actually predict future climate (but long term trends only).   I would like to hear from the best model, you chose it, name it, locate it, say who programmed it, who maintains it, who financed it (the onus is on the claimant, not me) and say what is the sea level (however they define it) in year 2025, 2030, 2035, 2040, and so on until year 5000.  Also change in global temperature (however they define it, give the formal unchanging definition).   We of course don't know what the sun is going to do, or volcanoes.   So the prediction is contigent of factors that are unforeseable, so the predictions are a function of different combinations and series and progressions of multivariable values.   I want to see the data.  Should not be hard for a proven theory, right? 

      4.  New topic.  Where is the proof that CO2 is driving the climate and not a third exogenous variable, like solar energy.   Please post the evidence that proofs undeniably this supposed fact.  Remember that correlation does not mean causation. 

    Response:

    [TD] Regarding your new question #4, see the post “CO2 is main driver of climate.” Post any comments on that topic, in the thread off of that post. Your comments about that topic are off topic in this thread, and further off topic comments will be deleted.

  33. gzzm2013: Your two responses to me show that you have not bothered to read any of the material I linked for you. That behavior of refusing to engage in actual back and forth conversation is called "sloganeering" and is prohibited by the policies of this site, which you need to read. 

  34. Dayton

    Your argument is a red herring to distract from the fact that you won't answer my questions.  The material you offer does not address directly the questions.  The onus is on the claimant to produce the evidence.  I don't have to produce anything. I am simply questioning the claims. 

    Response:

    [BL] "Just asking questions" as a rhetorical ploy does not cut it here. You must be willing to learn - and willing to put an effort into learning.

    There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions.  That's why we recommend that Newcomers, Start Here and then learn The Big Picture.

    I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history.

    Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (odds are, there is).  If you still have questions, use the Search function located in the upper left of every page here at Skeptical Science and post your question on the most pertinent thread.

    All pages are live at SkS; many may be currently inactive, however.  Posting a question or comment on any will not be missed as regulars here follow the Recent Comments threads, which allows them to see every new comment that gets posted here.

    Comments primarily dealing with ideologies are frowned upon here.  SkS is on online climate science Forum in which participants can freely discuss the science of climate change and the myths promulgated by those seeking to dissemble.  All science is presented in context with links to primary sources so that the active, engaging mind can review any claims made.

    Remember to frame your questions in compliance with the Comments Policy and lastly, to use the Preview function below the comment box to ensure that any html tags you're using work properly.

  35. Gzzm @1282 ,

    thank you for replying to Tom Dayton, who, I gather, was inclined to bet that you yourself were simply one of those "timid-but-angry" commenters who make a drive-by comment . . . and are never seen again here, owing to their strange psychological make-up.

    Gzzm, clearly you are made of sterner stuff and wish to add some rational intelligent points to the online discourse.  And it's never too late to begin in earnest !

    In reply to your point /4.   [in brief because off-topic]  :-

         4.  Where is the proof ... CO2  ... variable like solar energy ...

    Alas, Gzzm, this is "off-topic" here at this thread.  You will find the evidence you ask for, at the Top Left of this page, via  MOST USED Climate Myths number 2  "it's the sun"  . . . or the other thread recommended by the Moderator.    Indeed, your education would be greatly enhanced by you reading through at least the first half-dozen Myths in their Original Post form [basic thru advanced ] .   And as has already been suggested, please read the OP of this thread here (which you appear to have omitted from your things-to-do-first  list.)

    Back on topic, Gzzm, with the models are unreliable  ~ I can recommend some later reading for you, for the counter-arguments which can be found on the WattsUpWithThat  blogsite.   At WUWT  the view is that all the scientists' models have subsequently proven to be completely wrong . . . and therefore all climate science is wrong.

    Gzzm, you may not have heard of WUWT  , or perhaps you have been warned to avoid it because of its strong tendency to promote half-baked science (or disproven science) and even more to repeatedly  promote rubbish which is "Not Even Wrong".   But fear not, Gzzm ~ among the pig-swill there, you may occasionally find a pearl or two from genuine scientists like Nick Stokes.   Alas, Stokes does not appear there often . . . likewise there are a few other scientific minds to be found in the WUWT  comments columns, but few and rare, because they generally get driven out of WUWT  by the editors/censors.  (Or perhaps these scientific minds get tired of the incessant torrents of mindless vitriol they receive at WUWT  .)

    Nevertheless, Gzzm, the WUWT  blogsite is a fascinating exhibition of logical fallacies and intellectual insanity.  An excellent guide to What Not To Do  with one's brain.   Most interesting of all, is the huge amount of anger  there, underlying the flakey thinking and political extremism and lack of human compassion.

    Gzzm, I have the strong impression that you yourself may be able to enlighten me about the deepest psychiatric basis of the sheer anger in these disparate "contrarian" minds.  Some of it may be a genetic personality-type anger in all or most of the denialists, but there may well be one or more other factors.   Your own insight would be welcome !  (But please reply on a more appropriate thread.)

    Response:

    [BL] Please leave moderation to the moderators.

    Discussing the character of people's behaviour at other blog sites is not helping this discussion.

     

  36. Eclectic

    Your reply at "Eclectic at 16:08 PM on 24 January 2021"

    Constitutes a series of ad-hominem attack fallacies... no substance.

    Waiting to hear direct responses to the questions I have raised from others as I am not going to bite on these attacks. 

    Response:

    [BL] You are continuing to refuse to engage in honest discussion.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

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  37. [deleted]

    Response:

    [BL] Moderation complaints deleted.

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  38. Any model that requires calibration is wrong; there are an infinite number of models for a system with more than 6 or 7 in interdependant variables can be backtested with 100% coorelation yet differ in future predictions.   So, all the models show is the bias of the modeler.  It's non-sense to claim any model of the climate is accurate.    Basically, the model must work without any calibration or the results simply reflect the bias of the modeler.   Humanity may have increased the amount of CO2 in the atmoshere; but, humanity has simply no idea what the impact will be. 

    https://www.scientificamerican.com/article/finance-why-economic-models-are-always-wrong/

    Response:

    [BL] Link activated.

    The web software here does not automatically create links. You can do this when posting a comment by selecting the "insert" tab, selecting the text you want to use for the link, and clicking on the icon that looks like a chain link. Add the URL in the dialog box.

  39. robnyc987:

    You have made several empty assertions without evidence.

    All models require some level examination between model outputs and observations, and all models undergo modification to improve their ability to match observations. That is good science.

    You will need to provide some sort of definition for what you call "calibration" before anyone will take your criticism seriously.

    Where do you get "6 or 7" from, and what is the basis for your claim that 6 or 7 variables is enough for "100% correlation"? It sounds like you think all models are purely statistical fits to data. If this is what you think, you are wrong. If you think that hind-casting models can be 100% accurate with only a few variables, you are wrong.

    Your assertions of nonsense, working without calbration, bias and "no idea" are all just rhetorical waffling.

    Of what relevance is a link to economic models  to a discussion about climate models? The link refers to one case of a geophysical oil field model. Over-fitting a model - even one that is physically-based - is poor science, but that does not mean that every model is over-fitted and suffers the same problems. You will need to come up with an example of a climate model that is over-fitted if you want to be taken seriously.

    If you do not understand the difference between statistical models and physically-based models, then you are woefully uninformed.

    By the way, we know all models are "wrong" in that they are incomplete - but they can be useful.

    You may have no idea, but the science of climatology does. Try reading and learning. Start with the blog post you are supposedly commenting on. If you continue to comment, I suggest that you actually respond to specifics in the blog post at hand. Comments need to be on topic, not just meaningless rants.

  40. Bob Loblaw @1289,

    The paper that fuelled the 2011 Scientific American item linked @1288 is presumably Carter et al (2005) 'Our calibrated model has poor predictive value: An example from the petroleum industry' [ABSTRACT] which may provide the argument for "6 or 7 in interdependant variables" preventing model calibration although likely this is no more than a different version of the famous Fermi quote:-

    “I remember my friend Johnny von Neumann used to say, with four parameters I can fit an elephant, and with five I can make him wiggle his trunk.”

    However, this Fermi quote concerns "arbitrary parameters" and what Carter had in mind when he says "As far as I can tell, you'd have exactly the same situation with any model that has to be calibrated," isn't defined. But this 2011 Scientific American quote of Carter (I don't see an earlier statement of it) has occasionally been used by denialists to suggest the same calibration situation affects climate models. Of course GCMs do have a big challenge with calibration but I don't think it is down to the number of independent variables. There are many physical measures that can be used to callibrate the processes within GCMs, which is probably why they can (collectively) demonstrate useful predictive qualities. (The graphic is from this 2021 RealClimate post.)

    RealClimate GCM performance 2020

  41. MAR:

    This all hinges on what is meant by "calibration", and whether or not the parameters in a model are arbitrary.

    Wiktionary defines "calibrate" as "To check or adjust by comparison with a standard." When discussing climate models, this implies that there is some adjustable parameter (or seven) or input that can be varied at will to create a desired output.

    There are many problems with this argument [that climate models are "calibrated" to create a result]:

    • What are we calibrating for? A global 3-d climate model has thousands (if not millions) of outputs. Global mean surface temperature is one simple statistical summary of model output, but the model has temperatures that vary spatially (in 3-d) and temporally. It also has precipitation, humidity, wind speed, pressure, cloud cover, surface evaporation rates, etc. There are seasonal patterns, and patterns over longer periods of time such as El Nino. All of these are inter-related, and they cannot be "calibrated" independently. Analyzing the output of a GCM is as complex as analyzing weather observations to determine climate.
    • How many input parameters are devoid of physical meaning and can be changed arbitrariiy? The more physcially-based the model is, the fewer arbitrary parameters there are. You can't simply decide that fresh snow will have an albedo of 0.4, or open water will evaporate at 30% of the potential evapotranspiration rate, just because it makes one output look better. So much of the input information is highly constrained by the need to use realistic values. All these have uncertainties, and part of the modelling process is to look at the effect of those uncertainties, but the value to use can be determined independently through measurement. It is not a case of choosing whatever you want.

    So, robnyc987's claim that you can achieve 100% accuracy by "calibrating" a small set of parameters is bunkum. If climate models are so easy to "calibrate", then why do they show variations depending on who's model it is? Or depending on what the initial conditions are? That variability amongst models and model runs indicates uncertainty in the parameters, physics, and independent measurements of input variables - not "calibration".

    Perhaps robnyc987 will return to provide more explanation of his claim, but I somehow doubt it.

  42. Back to basics, concerning Christy's popular graph:

    He states that the data is of the bulk atmosphere.

    Are 102 model runs also for the bulk atmosphere, or are they for the surface?

  43. sailingfree @1292,

    The GCM models cover the entire climate system so it is up to the analyst creating a graph what part of the modelled climate system he takes data from for his comparison.

    The problem with Christy is that he is rather too enthusiastic about demonstrating his denialism and so makes a very poor job of his comparisons.

    RealClimate provide comparisons of model output with temperature data including global & tropical TMT data and have also provided a critique of Christy's efforts.

  44. MA,Thanks.

    I'll look at RealClimate.   So did Christy use model predictions for the "bulk atmosphere?

  45. sailingfree:

    To add to what MA Rodger said about climate models, analyzing the output from a three-dimensional general circulation model is about as complex as analyzing climate observations - maybe even more so.

    Think about the number of locations world-wide where we have measurements of surface temperature, humidity, wind speed, precipitation, radiation, etc. Then add in upper air, oceanic, ground temperature opservations, etc.

    Then think about how sparse some of those observations are - how much of the globe is not well-measured.

    Then think about things that are not routinely measured - vertical motions, cloud water content, spectral (wavelength-dependent) radiation. The list goes on.

    ...and then realize that a 3-d climate model is calculating all those things on an ongoing basis (minute by minute, hour by hour), at a 3-d set of points covering the entire globe.

    Comparing the model to observations can be done where the two types of data match, and commonly involves some sort of statistical summary (of both the model output and the real-world measurements).

    I don't know what Christy means by "bulk atmosphere". My guess would be that he is averaging over the entire vertical profile, but I consider Christy to be such an unrelaible source that I don't want to spend valuable time trying to figure out what he means.

  46. sailingfree @1294,

    You ask "Did Christy use model predictions for the bulk atmosphere?"

    He says he does.

    It is not easy to be sure what Christy "uses" as he is not a reliable researcher. In specific cases it would/should be possible to see what he says he is "using" and then compare the numbers he "used" with what he says. But this is not always a trivial task and Christy's public statements are not considered of the slightest scientific importance by those best positioned for this task. So they mainly ignore them. But note the issue of modelled tropical tropospheric temperatures (which is real) is being addressed with, for example Vergados et al (2021) or Po-Chedley et al (2021).

    You mention @1292 the "102 model runs", so a specific case of data use (although Christy happily reuses his grand finding oblivious to any errors it contains). The prime-time appearance of "102 model runs" was presumably Christy's testimony to the U.S. House Committee on Science, Space & Technology 2 Feb 2016 and in this case Christy's use of data has been questioned more than once but this is technical enough for even climatologists to trip over this task (as the correction within yet another RealClimate posting illustrates). What is perhaps most telling in this situation is the silence of John H Christy who thus acts more like a troll than a proper scientist who would be expected to defend his position by resolving any doubt on the matter.

    Christy's misleading graphs

    So on these graphics we see John Christy saying he uses "Global Bulk Atmospheric Temperature, Surface to 50,000ft" and also 'Global' and 'Tropical' "TMT Temperature Variations"  (which actually go a bit higher than 50,000ft). The TMT satellite data is a statistical sample of emissions from a great swathe of altitudes, even up into the stratosphere where it is cooling due to AGW.

    MSU weighting functions The RSS browser tool with the correct choice of 'Channel' and 'Region' shows a TMT Tropical trend of +0.145ºC/decade. This compares with the UAH TMT Tropical trend of +0.09ºC/decade. Christy's assessment of model data puts the comparable model trend at +0.214ºC/decade although the model assessment presented by the RealClimate critique linked above gives a model trend of +0.19ºC/decade.

    This +0.214ºC/+0.19ºC isn't a massive difference but this and the visual trickery employed by Christy has resulted in a film (actually a 7 minute YouTube video).

    Christy latest wheeze is to brandish yet another fun-with-figures graphic (below) which compares TMT data (measured from surface up to 70,000ft with differing strength) with a small layer of the modelled atmosphere (roughly from 30,000ft to 40,000 ft). Presumably this is because the denialists require redder meat with the passing years.

    Chrisiy's latest nonsense.

  47. To follow-up again on MA Rodger's excellent description, two things to note:

    1. Satellite data are not a measurement of atmospheric temperature. Satellites measure radiation. To transform the radiation data into an estimate of temperature requires some sort of model. A detailed atmospheric radiation transfer model. To call the results "observations" is playing loose with the term, although it is a common use of the term.
    2. In the last diagram that MA Rodger provides, note the expression "the models and observations are not from the same physical system". As MAR notes, the results from the climate models are an average of the entire atmosphere from the surface to 70,000 feet (>20km). The "observations" (Christy's model conversion of the satellite data) cover the pressure range from 300 to 200 hPa, which is roughly from 30-40,000 feet (9km to 12 km). That the two are "not from the same physcial system" is known prior to doing any statistical analysis.

    Christy's "analysis" takes two things that are known to be different, and tries to make it look like the difference disproves some aspect of climate theory.

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