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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)

At a glance

So, what are computer models? Computer modelling is the simulation and study of complex physical systems using mathematics and computer science. Models can be used to explore the effects of changes to any or all of the system components. Such techniques have a wide range of applications. For example, engineering makes a lot of use of computer models, from aircraft design to dam construction and everything in between. Many aspects of our modern lives depend, one way and another, on computer modelling. If you don't trust computer models but like flying, you might want to think about that.

Computer models can be as simple or as complicated as required. It depends on what part of a system you're looking at and its complexity. A simple model might consist of a few equations on a spreadsheet. Complex models, on the other hand, can run to millions of lines of code. Designing them involves intensive collaboration between multiple specialist scientists, mathematicians and top-end coders working as a team.

Modelling of the planet's climate system dates back to the late 1960s. Climate modelling involves incorporating all the equations that describe the interactions between all the components of our climate system. Climate modelling is especially maths-heavy, requiring phenomenal computer power to run vast numbers of equations at the same time.

Climate models are designed to estimate trends rather than events. For example, a fairly simple climate model can readily tell you it will be colder in winter. However, it can’t tell you what the temperature will be on a specific day – that’s weather forecasting. Weather forecast-models rarely extend to even a fortnight ahead. Big difference. Climate trends deal with things such as temperature or sea-level changes, over multiple decades. Trends are important because they eliminate or 'smooth out' single events that may be extreme but uncommon. In other words, trends tell you which way the system's heading.

All climate models must be tested to find out if they work before they are deployed. That can be done by using the past. We know what happened back then either because we made observations or since evidence is preserved in the geological record. If a model can correctly simulate trends from a starting point somewhere in the past through to the present day, it has passed that test. We can therefore expect it to simulate what might happen in the future. And that's exactly what has happened. From early on, climate models predicted future global warming. Multiple lines of hard physical evidence now confirm the prediction was correct.

Finally, all models, weather or climate, have uncertainties associated with them. This doesn't mean scientists don't know anything - far from it. If you work in science, uncertainty is an everyday word and is to be expected. Sources of uncertainty can be identified, isolated and worked upon. As a consequence, a model's performance improves. In this way, science is a self-correcting process over time. This is quite different from climate science denial, whose practitioners speak confidently and with certainty about something they do not work on day in and day out. They don't need to fully understand the topic, since spreading confusion and doubt is their task.

Climate models are not perfect. Nothing is. But they are phenomenally useful.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Further details

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 shown 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. Sea level rise is a good example (fig. 1).

Fig. 1: 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. A 2019 study led by Zeke Hausfather (Hausfather et al. 2019) 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."

Talking of empirical evidence, you may be surprised to know that huge fossil fuels corporation Exxon's own scientists knew all about climate change, all along. A recent study of their own modelling (Supran et al. 2023 - open access) found it to be just as skillful as that developed within academia (fig. 2). We had a blog-post about this important study around the time of its publication. However, the way the corporate world's PR machine subsequently handled this information left a great deal to be desired, to put it mildly. The paper's damning final paragraph is worthy of part-quotation:

"Here, it has enabled us to conclude with precision that, decades ago, ExxonMobil understood as much about climate change as did academic and government scientists. Our analysis shows that, in private and academic circles since the late 1970s and early 1980s, ExxonMobil scientists:

(i) accurately projected and skillfully modelled global warming due to fossil fuel burning;

(ii) correctly dismissed the possibility of a coming ice age;

(iii) accurately predicted when human-caused global warming would first be detected;

(iv) reasonably estimated how much CO2 would lead to dangerous warming.

Yet, whereas academic and government scientists worked to communicate what they knew to the public, ExxonMobil worked to deny it."


Exxon climate graphics from Supran et al 2023

Fig. 2: Historically observed temperature change (red) and atmospheric carbon dioxide concentration (blue) over time, compared against global warming projections reported by ExxonMobil scientists. (A) “Proprietary” 1982 Exxon-modeled projections. (B) Summary of projections in seven internal company memos and five peer-reviewed publications between 1977 and 2003 (gray lines). (C) A 1977 internally reported graph of the global warming “effect of CO2 on an interglacial scale.” (A) and (B) display averaged historical temperature observations, whereas the historical temperature record in (C) is a smoothed Earth system model simulation of the last 150,000 years. From Supran et al. 2023.

 Updated 30th May 2024 to include Supran et al extract.

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

Last updated on 30 May 2024 by John Mason. 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.

Denial101x videos

Here are related lecture-videos from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Dana Nuccitelli: Principles that models are built on.

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Model

Please check the related blog post for background information about this graphics resource.

Comments

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Comments 1201 to 1225 out of 1291:

  1. Deplore_This , yes everyone with reasonable climate knowledge has heard of Dr Judith Curry ( and I myself visit her blog several times a month . . . it's a sort of upmarket version of WUWT  blog ).   Dr Curry's commentary is an excellent object lesson for those who wish to exercise their critical thinking!    She is one of the very very  few climate-contrarian scientists (a dying breed, it appears).

    Now, I notice your rapid-fire uploading of long posts at 1:23 AM and 1:24 AM and 1:25 AM.    Clearly these were pre-selected & prepared to go, and were not really a response to Scaddenp.

    And as you say: "... I've read criticism of the validity of ..."    And there is the nub of your problem, Deplore_This.

    The internal evidence of your many posts, is that you have not bothered to learn the fundamental science of climate yet.  Once you have done so, then you will be able to (A) make an informed decision whether or not to attempt the various complexities of climate modeling (with or without access to a supercomputer)

    . . . and (B) see right through the ludicrous nonsense of "the 500" scientists you mentioned

    . . . and (C) see right through Dr Curry's vague obfuscatory sophistry.

    It is a red-flag sign, that you have allowed yourself to be taken in by the simply unscientific propaganda exhibited by "the 500".    But Dr Curry's propaganda is a different matter ~ she uses a more subtle approach (analogous to what the hypnotherapists call "the Indirect method" ).   If you yourself are strongly motivated to believe her - which indeed you are - then she seems to make sense.   That is, she seems to make sense until you educate yourself past the "veneer" level of climate science.  And then, using skepticism and critical thinking, you will see the fatal flaws in her presentations.

    #  My apologies for sounding patronizing ~ but you really do need to learn the climate science first.   Don't be an Ivar Giaever, who succumbed to Motivated Reasoning, and reckoned that half a day or so on the internet sufficed for him to lecture the climate experts on their multitude of errors.   ( Yes, there are many humorous events to be found in the sphere of climate science ! )

    Response:

    [TD] I deleted Deplore_This's lengthy cut and paste about Curry, because only a tiny fraction of it was directly relevant to the Models topic of this thread. Despite the baiting that Deplore_This is doing, please let's try to stick to the thread topic. Thanks.

  2. Deplore_This:

    You have now reached the point where moderators are starting to cut stuff.

    You posted a long story from E&E. You are hitting all the main climate denier sites. Well done. You are selecting to quote places that confirm your bias.

    https://www.desmogblog.com/energy-and-environment

    FYI, I started learning about this stuff in the 1970s. I read a lot of the primary literature long before there was an IPCC. I can tell when someone is trying to fool me.

  3. My opinion is that the lady that protest too much might be Curry.

    From the WIKI page on GCMs: "Versions designed for decade to century time scale climate applications were originally created by Syukuro Manabe and Kirk Bryan at the Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, New Jersey.[1]"

    Further:"In 1956, Norman Phillips developed a mathematical model that could realistically depict monthly and seasonal patterns in the troposphere. It became the first successful climate model.[2][3] Following Phillips's work, several groups began working to create GCMs.[4] The first to combine both oceanic and atmospheric processes was developed in the late 1960s at the NOAA Geophysical Fluid Dynamics Laboratory.[1]"

    It is obvious that Fluid Dynamics are at the foundation of all the current coupled atmosphere-ocean GCMs. I find that the dissatisfied search for a specific university course on such models is perhaps disingeneous. They are an area of research, very much at the edge of knowledge. People who participate in them have already obtained graduate degrees in fluid dynamics, applied mathematics and a variety of other fields. I doubt that there are university courses on specific protein folding methods, short of outlining the basic principles and current state og knowledge. However, those who want to orient themselves in that field will easily come across the areas of knwoledge they should master first. Then they can try to go hack it at the cutting edge.

    Curry does a favorite trick of hers by exploiting the fact that GCMs are not very good at delivering regional results, something well known in the modeling community, to suggest that they have no usefulness. In any case, the claim that fluid dynamics expertise is absent in the modeling community has no merit.

  4. Yes, the "search" for a class on "Make your own GCM" is certainly odd.

    I'll bet if I did a search through university catalogues for courses on "How to program a Word Processor", I would not find much at all. To use that as evidence that word processing software is not useful - hey, I"m a word processing skeptic! - would not be an effective argument.

    I could then switch to listing people that have found bugs in word processing programs as evidence that "word processing is not settled", or that "you can't trust word processors".

    Yet somehow, each day people use word processing softare to create all sorts of useful texts. (They seem to create some awful ones, too, but that is another story...)

  5. Bob Loblaw @1204 ,

    The "search" for a course on DIY  GCM's is not just certainly odd  ~ it is positively hilarious.

    But maybe technology is moving faster than I thought.  And I had better check Amazon for stocks of those long-promised pocket-size quantum supercomputers (powered by cold fusion, I hope).   Doubtless these miniaturized marvels would be quite expensive at first ~ but perhaps early adopters will be issued with a bonus App for a GCM or two.

    Our moderator seemed to think that the good Deplore_This  was doing some "baiting" ( aka "trolling" ? ).    Never in a million years would I have thought such a thing . . . but it might explain the underlying motivation of this recent "encounter" at SkS, and it would explain the confused rambling denialism that he/she is throwing up.  And explain the DK-like complacency.

    Phillipe C @ 1203 ,

    your suggestion that the Lady in Question might be the good Dr Curry, is, surely, a tad ungentlemanly?   After all, the literary style is somewhat different ~ though I suppose I could be wrong on that (or the style might have had an extensive makeover per Grammarly or similar App).

    Still, it will be interesting if there are more developments.  I always hope there will be something new to learn, from every "challenge" to mainstream climate science.   Admittedly, my hopes have always been dashed ~ but some day there may be a grain of wisdom to be found among the bucketloads of BS.

  6. Deplore_me. Hmm, some disappointing stuff there - it is very disappointing when the best predictor of person's beliefs on a purely scientific question is which side of the US cultural wars they on - but if you are prepared to invest in courses to get answers, then that is great and makes me hopeful. While I am tempted to respond to your answers, I doubt that would either productive or on topic, so sticking to topic.

    Assuming you get a model by some means and figure out the workings, it would be interesting to know how you would use it. In particular,  what kinds of answers could you imagine your investigations producing that would change your mind. It would be good to be thinking about this and getting the necessary domain knowledge so that you are not misled. Many "skeptics" go after straw-men - trying to take apart claims that modellers and scientists never made. (eg modellers claim no skill in decadal level of prediction). EdGCM would be a good starting point.

    Oh and I am in NZ, working in more or less the equivalent of the USGS though our science structures are very different to US.

  7. @ Eclectic, @Bob Lowlaw, @Philippe Chantreau, The moderator

    Your sophomoric comments memorialize your lack of credibility and reflect poorly on all of the proponents of this website and to some extent to the entire climate science profession. Your adolescent giddiness that you can slander me and the moderator will strike my response that challenges your opinion demonstrates that in your little sandbox here you are not practicing science. If Judith Curry was your Professor I’m sure she’d be embarrassed at your unprofessional and juvenile behavior.

    From my perspective your behavior here demonstrates that she is right “We've lost a generation of climate dynamicists. These are the people who develop theories and dig into data on the system and really try to find out how the system works. We've ceded all that to climate models, and the climate models are nowhere near good enough. The climate models were designed to test sensitivity to CO2. They don't even do a very good job at that…we've lost a generation of climate dynamists, and that's what worries me greatly.”
    web.archive.org/web/20170105183617/www.eenews.net/stories/1060047798

    And in the end, you’ve all failed to answer my question so what is your reason for being here.

    Good day.

  8. @scaddenp 1206

    Thank you for your response. Candidly a reason for your disappointment evades me. As I stated in my post 1195 to you I’m trying to evaluate the validity of the GCMs referenced by the IPCC against the criticism of scientists like those posted in 1193 and 1194. All I find from the climate science community are responses like those above who merely state your sources aren’t credible, read this and you’ll understand what we do and if you don’t agree with us you’re a flat earther.

    I’m not looking to create a GCM but to understand what they are, their structure, their fidelity and the assumptions that go into the GCMs used by the IPCC. To state it simply I am questioning the validity of the IPCC’s consensus opinion and am trying to find a way to evaluate it myself. I thought that I would take it to the next level and look at the underlying models themselves. I’m not on a career track in the climate science profession I’m merely looking to satisfy my personal curiosity. I thought I would take a university course that climate scientists use to learn the development and use of GCMs and posted here for recommendations. No one here has recommended one yet so I think my only recourse is to contact Penn State and see if course material is available from their last course on GCM.

    BTW I’m in the US retired from the wireless equipment manufacturing business. I visited NZ 20 years ago for a broadband wireless system we supplied. The landscape is remarkable; the emerald green of Ireland painted over the rock of Gibraltar and I found the people friendly (that is once I realized that wearing the shirt of the national rugby team of Scotland was a big mistake).

    Thanks again for your response.

  9. Philippe C , I may have to back-pedal on my skepticism about your Questionable Lady hypothesis.  There does indeed seem to be a Curry worship of almost Sub-Continental dimension.  Perhaps the good Doctor has a Mrs Hyde facet to her personality?

    Deplore_This , your truculence & tone-policing are a red flag.   So much so, that your "search for a GCM course" seems merely a pretext for your postings.

    Yet if you do have a genuine concern about the value of climate models, then please express those concerns in your own words.  Without doing a "cut and paste" from the typically vague and non-substantive rhetoric which is the standard output of Dr Curry.

    You seem not to be aware that the GCM's are not the basis of climate science nor are they the basis of expectations of continued global warming & the consequential major problems.   The basic physics / paleo climate evidence / and the past 150 years of empirical evidence of climate response to rising atmospheric CO2 . . . all combine to give adequate grounds for policymakers to take urgent action to reduce CO2 emissions.

    Climate models can sometimes be used as a test bed for certain sub-components of climate or energy fluxes.  And they can (famously) produce a large range of interesting projections.  But their pragmatic usefulness for projections, is low for the present & near future.

    And that should be very obvious to you, when you take note of the wide range of Equilibrium Climate Sensitivity which is generated by the typical models.   In other words, Deplore_This , you will largely be wasting your time if you pursue "a course in GCM's" .   You really really  do need to study the basic science of climate.

  10. @ Eclectic

    You obviously don't realize that you've just proven the point that I made in my post at 1207.

  11. D_P @1210 ,  alas you are too non-specfic in your reference.

    If you meant "The climate models ... don't even do a good job"  ~ then that is stating the obvious.

  12. 1176 Deplore_This


    You seem to be hitting on the same frustrations I am in regard to getting straight information about the climate models and how they are used. It turns out that you can do a free download of many of the codes used in implementing the climate models, and with the make utilities of most Unix systems (including Linux), actually compile and run them. Don't hold your breath, however, in understanding the "nuts and bolts" of the programs or even how to set up and submit a job on those systems. The only people who get that kind of help are the techie types recently hired by a government contractor specifically to do such number-crunching. 


    Anyway, I will answer your questions as best I can, realizing that I may not know much more about the AGW community than you do. First, I believe that the development and testing of today’s climate models is generally legitimate and done to meet the needs of climate and environmental researchers. Of course, these models were not done single-handedly, but with a team consisting of individuals with several different areas of expertise. Over the decades, they have worked out quite well, and I believe that the statements made by the SkS staff at the top of the page are generally correct.


    However, I believe there is something important concerning these models that the AGW community in general is not telling us. I would like to tell you more, but would rather not do so in this forum. If you are interested please send a message to the (temporary) email address x7evz2yg@protonmail.com and I will send you a return message from the more “permanent” email account I would like to use.

  13. Eclectic @1174

    Please explain what you mean by the bigger context, and paleological evidence.  Also, please explain how your CO2 "control knob" is supposed to work.

    Response:

    [TD] Among a huge number of other resources, there is the wonderful and easily understandable 2009 AGU talk by Richard Alley, The Biggest Control Knob: Carbon Dioxide in Earth's Climate History. Steve Easterbrook wrote a good summary, but you really should watch Alley's one hour video. Then read Lacis et al. (2010), Atmospheric CO2: Principal control knob governing Earth's temperature. Alley gave (yet another!) excellent talk six years later, this time just half an hour and to the NAS, 4.6 Billion Years of Earth’s Climate History: The Role of CO2. Among several relevant posts here at SkS is How Do We Know More CO2 Is Causing Warming? Please post your comments in an appropriate thread.

  14. "Candidly a reason for your disappointment evades me." Well the right wing dog whistles and then repeating the GWPF nonsense with claims you should have been able to refute unaided given your IPCC reading had you looked at it critically. 

    I repeat that it is great idea to understand the models, but only if you are going into without the biases of trying to find something which would aid your disbelief and with no clear idea as to what might change your mind. 

    If your preference for Curry is because she expresses similar political belief to yourself and not her publishing record in climate models, then I dont think we have much to discuss, and certainly not on this thread.

  15. It is an interesting thought that somebody who uncritically references both a GWPF publication (ie Briefing Paper No 24) that attempts to trivialise the usefulness of climate models (as @1193) and the 2019 Dutch denialist petition to the UN that attempts to reverse the global consensus on AGW  (as @1194) would somehow obtain a deep enough understanding of the limitations of GCMs to form a useful judgement on ECS from a rather basic course on the subject, especially given that such a judgement could be gained more simply by other means.

    The CLINTEL petiton (CLINTEL is basically an attempt to create a Dutch version of GWPF, the latter having been quite successful in masquerading as an educational charity and finding fertile ground within influential parts of right-wing UK politics) and the GWPF publication both contain the same bold assertion which is fundamental to their denialist argument that GCMs cannot be relied upon.

    "The world has warmed at less than half the originally-predicted rate, and at less than half the rate to be expected on the basis of net anthropogenic forcing and radiative imbalance. It tells us that we are far from understanding climate change." CLINTEL petition.

    "There is growing evidence that climate models are running too hot and that climatesensitivity to carbon dioxide is at the lower end of the range provided by the IPCC." GWPF Briefing Paper No24.

    I would suggest the commenter first considers whether it is correct and proper to present such argument rather than attempting to "get under the hood and see how the models work for myself and to evaluate the predictive sensitivity of these models."

    Operations Research (Operational Research my side of the pond) is only narrowly about the mathematics so I am intrigued that somebody with an "extensive background in operations research" (as per described @1162) would consider 'getting under the hood' as the first response to  having "read criticism of the validity of the climate temperature models referenced by the IPCC."

  16. ClimateDemon @1213 , the bigger context is the paleo evidence ( you can start reading at (SkS) Climate Myths 12 and 13 , and expand out from there.

    The modern empirical evidence ~ a temperature rise of 1 - 1.2 degreesC since industrialization 1850-ish,  all with a 1.4x rise in air CO2 . . . and your own back-of-envelope logarithmic calc extrapolates that to around 2.0 - 2.4 as TCS and hence ECS around 30-40% higher again.   IOW, an ECS of around (roughly) 2.5 -3.5 C.   [Which is way higher than the deluded Lord Moncton "calculates".]    And which also fits with the paleo estimates.

    That all connects well with the "CO2 control knob" (remember to adjust for solar brightening/dimming over time).  Find the right thread, if you wish to comment.

  17. Recommended supplemental reading directly related to the current discussion initiated by Climate Demon...

    Explainer: How the rise and fall of CO2 levels influenced the ice ages by Zeke Hausfather, Carbon Brief, July 2, 2020

    From the article...

    In this explainer, Carbon Brief explores how the last ice age provides strong evidence of the role CO2 plays as a “control knob” for the Earth’s climate. It also acts as a cautionary tale of how the climate can experience large changes from relatively small outside “forcings”.

  18. Steve Easterbrook has written multiple blog posts describing how computerized climate models are designed, built, tested, maintained, and used. I eagerly await his "forthcoming" book, but in the meantime I suggest everyone interested in that topic peruse his blog posts. For example, there is is his post When is a Model Not a Model?

  19. It is important to understand that GCMs are only a small subset of "climate models," and therefore the evidence that "climate models" provide is far broader and deeper than the evidence that GCMs provide. I highly recommend Naomi Oreskes's book Why Should We Trust Science?, for the broad background on those topics beyond climate science, though she does use some examples from climate science.

  20. I take issue with DeploreThis characterization of my post. I re-read it and I find nothing deserving to be called "sophomoric", "adolescent giddiness" and whatever else was in that flurry of name calling. I was not the one referring Shakespeare in the first place.

    A quote from Curry was provided that laments the lack of fluid dynamic expertise in the modeling community. I pointed to the fact, verifiable, that GCMs have originated and are constantly refined in the top fluid dynamic labs of the country. DeploreThis then repeated the same quote without specifying how merely repeating it made any difference. I will add that Curry's characterization is not accurate, as there is plenty of hard physical science contribution to climate science now, and plenty of data crunching people, data papers, etc. Does she provide a breakdown of papers according to "types" of work that she finds less "dynamicist"? All she has is a vague and general statement designed to create a negative perception without, ironically, real world data, to back it up.

    Further I noted that it is disingeneous to ask for a university course on how to makle a GCM because of the nature of the enterprise. I completely stand by that statement. Nobody is going to go to a business school and ask for for a course in "how to make an Amazon-like mega company." That would be the same type of enquiry in a different domain. I am not surprised that it can't be found. Passed all the name calling, hand-waving, self-rightneousness and indignation, I do not see any cogent argument from DeploreThis as to why that would be a valid enquiry.

  21. There may be some interesting points in this paleo evidence and the “bigger context” described by Eclectic, but it’s not really the issue I am trying to address. What I am trying to address are the current arguments for CO2 being the “control-knob” GHG (despite the fact that H2O vapor is the stronger GHG) which subsequently leads to the claim that humans are overheating the earth with their CO2 emissions, and that our very survival depends on government intervention. Now, in every reference I can find, including the Lacis et. al. 2010 paper and this website, the reason given for CO2 being the controlling GHG is that H2O vapor is condensable whereas CO2 is not. Furthermore, it is asserted without clear grounds that the H2O vapor concentration is given by the Clausius-Clapeyron equation at the current temperature, or IOW at 100% relative humidity. With this constraint on the H2O vapor concentration, it can then be only a feedback to temperature changes. CO2, however, has no such constraint and can actually cause temperature changes simply by adding more of it. This is the argument by which CO2 becomes the controlling GHG even though it is the weaker GHG. Note that without somehow constraining H2O vapor to being a feedback only to temperature change, then the entire basis of AGW collapses since H2O would then be the controlling as well as the stronger GHG. Humans may have some control over the amount of atmospheric CO2, but not H2O vapor since over 70% of the earth’s surface is covered with H2O liquid.

    Therefore, we see that the AGW theory stands or falls on whether or not CO2 is the controlling GHG, and I believe I pointed out (in 1173) some serious problems with the arguments in favor of the CO2 “control knob”. If these problems are not adequately resolved, it would be a real “show-stopper” for the AGW theory.

  22. ClimateDemon, your objections at 1173 were not convincing. When one attempts to overturn a large area of scientific knowledge, they should have extraordinary evidence.

    It seems you are making the argument that water vapor can be injected into the atmosphere and serve as a forcing instead of feedback. If that was the case, it would not get us off the hook with fossil fuels since the problem resides with the general relation:

    CH+O2 ==> CO2+H2O

    Combining hydrogen from the crust with atmospheric oxygen to create additional water hardly seems like a good idea under your scenario.

  23. @Philippe Chantreau 1220

    Talk about self-righteousness indignation.

    Actually there is a university course on GCM.
    www.met.psu.edu/intranet/course-syllabi-repository/2020-spring-syllabi/meteo-523

    And MBA programs use case studies extensively. I earned mine before Amazon but I suspect Amazon is a case study(s) in most current MBA programs.

  24. ClimateDemon, your claim in comment 1173 that "The only model that predicts AGW and the CO2 control knob is the one used by Lacis et. al. 2010" is incorrect. The Lacis model and paper describing experiments with it are merely the most explicit and easily understood (at the time) explanations of specifically that particular point. Please see also, just for example, a video of an NAS lecture by Richard Alley, or of his longer AGU lecture.

  25. Deplore_This: How is it that you cannot see the contradiction of you simultaneously complaining that there are no university courses on climate modeling, and pointing to exactly such available courses? Everybody knows there are courses on climate modeling. What people have been telling you, over and over, is that the vast majority of university teaching of climate modeling is done in courses that are not explicitly and specifically titled "climate modeling."

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