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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

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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.

Update

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

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 1076 to 1100 out of 1291:

  1. michael sweet @ 1075

    "We are in deeper doo-doo than we thought."

    On this point, the Economist article on "negative emissions" did not provide any "percentage" measurement as to how much reliance the climate models have placed upon the withdrawal of CO2 from the air compared to reductions in present emissions.  Are we talking 20% for the assumed contribution from "negative emissions" or more than that?  Can someone point me to where this has been discussed? 

    It clearly was not it in the Chapter 9 of the Fifth Assessment. 

    I have to admit that after reading Chapter 9 in its entirety and the admitted problems discussed in that chapter associated with the uncertainties caused by trying to simulate cloud processes and their feedbacks in the models that I have personally decided to focus my climate education on actual observations of temperature increases and sea level changes (including the impact of melting ice in Greenland and the Antarctic) representing the two of the most significant effects of AGW. 

  2. NorrisM @1076,

    You ask "Are we talking 20% for the assumed contribution from "negative emissions" or more than that?"

    I ask "20% of what?"

  3. Norrism:

    Since I currently live in Florida and come from California I will suggest you add stronger storms (especially higher precipitation and hurricanes) and a longer fire season with bigger fires to your list of significant effects of AGW. 

    A drought linked to AGW was one of the prime causes of the Syrian civil war.  The fall of the Egyptian government was partially due to increased bread prices due to drought in Russia that caused their harvest to fail.  That drought was AGW linked.

    The widespread failure of farming is probably more significant in your lifetime than sea level rise (and my lifetime although I have friends  in Tuvalu and own land in Florida).

  4. MA Rodger @ 1077

    I admit that my question was not well-posed.  I went back to the Economist article and realized that I had missed their more detailed discussion of negative emissions at page 20.  What I was trying to get a sense of is how significant is the problem of not having proven negative emission technologies (NETs) in place.

    I appreciate that measuring this as a percentage is difficult in that we are really looking at what carbon budget we have left if we wanted to stay below 2C and what amount of CO2 has to be sucked out of the atmosphere.  But the numbers are significant.  My understanding is that we are presently pumping about 40 bn tonnes of CO2 into the atmoshere and that, according to this Economist article, we need to take out 810 bn tonnes by 2100 to have a reasonable chance of staying at 2C by 2100.

    But if CarbonBrief.org is correct, we can only pump into the atmosphere another 800 bn tonnes of CO2 if we want a 66% chance of staying under 2C by 2100.  On their website they correctly show that at the present rate we run out of our remaining "carbon budget" in 20 years.

    So I agree that my question was confusing.  But this is an astounding amount.  The negative emissions required by 2100 represents 100% of our remaining carbon budget we have if we want to have a 66% chance of staying below 2C.

    Based upon the chart on page 21 of the Economist, by 2100, the negative emissions have to represent approximately 20 bn tonnes per year to match the 20 bn tonnes per year of remaining CO2 and other emissions to arrive at a net zero emission level.

    I think I have this right.  I am sure you will correct me if I am wrong.

  5. michael sweet @ 1078

    I hear what you are saying but I do not want to get into issues such as whether AGW is causing more intense hurricanes (what happened between Katrina in 2005 and Irma et al in  2017?).  Clearly the IPCC states that we will have more droughts and more precipitation.  I fully accept that.

    As for residents of Florida and California, there is a certain amount of "caveat emptor".  You do not buy land near an airport and then complain about the noise of jetliners.  Everyone who can afford expensive real estate in Florida and California can afford insurance to protect them from these risks.  No question there are other areas of the world where this is not the case but again, this is an issue that Bob Loblaw and I discussed at length (on some other thread) and I personally do not want to revisit it.  We have both stated our differing positions. 

    But even at this last meeting in Bonn we have seen what has happened to the climate fund for developing countries.  Politicians are good at talking but when it actually comes to coming up with cash out of their national budgets it is a different thing.   We even now see China and India coming back to the table with the old theme of saying that a disproportionate share should be contributed to this fund by the developed countries because of past CO2 contributions.   Back to the drawing board it seems.

    Moderator.  I appreciate this is getting off topic.  Just wanted to reply to michael sweet on his additions.

  6. NorrisM @1079.

    WIthout checking the figures you quote, do be aware that it is not CarbonBrief who set out the carbon budget you quote; it is IPCC AR5 simply with the used emissions budget being subtracted.

    And perhaps to give some indication of the sort of figures your comment seems to be aiming at, the figure from Anderson & Peters (2016) here suggests a value of  perhaps 600Gt(CO2) by 2100.

    And do note this comment is verging on being off-topic.

  7. I hold that it is a mistake to call the effects of fossil CO2 emissions "Climate Change". For a start, it is too mild. The effects could be Catastrophic Climate Change.
    But my point, with respect to models, is that climate modelling is far more difficult than the simple thermodynamic equation that was contained in the warning of Svante Arrhenius, about a century ago.
    For several millennia, except for the occasional huge volcanic eruption, the temperatures on Earth, or as we might more usefully call it "within the biosphere" remained within a range to which the living organisms had evolved to accustom themselves.
    Arrhenius showed that the thermodynamic balance between radiation received and radiation emitted depends upon the temperatures of terran surfaces being such as to emit radiation, mostly infrared, that balances what has to escape plus that which is recaptured by gases that turn it into their own kinetic energy, and share that.
    Arrhenius showed that carbon dioxide was indeed remarkably capable of capturing infrared radiation of exactly the range that comfortably warm and not-too-cold surfaces emit.
    It is a simple step from there to conclude that a rise in proportion of CO2 from 280 ppm to 400 ppm, which is today well documented, will cause the biosphere to accumulate heat annually at some rate that eventually gets it "warm" enough to emit more energetic infrared.

    The danger is that since the cause of the problem is that accumulation, but the rate of its manifestation is the rate at which snows and ice can melt, and entire oceans can warm, lots of people and even governments may fail to be convinced, until it's too late.

  8. michael sweet

    Here is my comment which was snipped for being off-topic.  

    I think the real difference between what I will call the "warmists" versus the "luke warmers" is not really a difference on the science. Both sides accept that the planet is getting warmer and CO2 emissions constitute at least 50% of the warming (with the difference largely related to whether there are 60 year oscillations of the AMO). The real difference between the warmists and the luke warmers is a disagreement on the ability of the models to accurately predict what will happen after 2050. 

    But is that not what this all comes down to? We cannot agree on: 1. whether the temperature increases in RCP 8.5 are realistic based upon the limited ability of the models to replicate the climate 50 years into the future; and 2. whether the assumptions of fossil fuel use in RCP 8.5 are realistic. As well, all the "scary stuff" in the models seems to take place from 2050 onwards so we really cannot even point to any spectactular  failure of the models today. The models are not falsifiable because we have to wait 30-50 years.

    It is true that Einstein's theory of relativity was only "proven" many years later (I cannot remember the comet's path which seemed to prove it correct) but in that case the world was not asked to change its source of energy over a relatively short time period given that presently approximately 85% of our energy needs are provided by fossil fuels and less than 5% by wind and solar power.

    Response:

    [DB] Sloganeering and blatant handwaving snipped.  Either bring actual credible evidence to support your contentions or acknowledge that these assertions by you are simply your uninformed opinions.  A number of posts at SkS already detail the accuracy of model projections vs actual performance (like herehere and here).  Indeed, there is a plethora of posts examining just how well models as far back as even the 1980s and 1970s have performed.

    Models and observations

    BEST Model performance

    CMIP3 models are spot-on

    CMIP5 models are spot-on

    You are welcome to make your case using actual evidence.  You are not welcome to spread misinformation or to represent your opinions as anything other than that (opinions); without credible evidence to support them, they will be disregarded and dismissed if they differ from established science and scientific research.  I'm not going to bother to warn you further as the fact is: you've been given ample warnings and simply ignored them.

  9. Your "luke warmers" used to argue that there was no warming.  They changed their hats when it became impossible to continue with their past lies.  They continue to lie to the public about the changes expected from warming.  Look at the briefs submitted to the court by deniers in the case of young people suing the government.  You cannot concede the possibility of sea level rise contained in the US Climate Change report which is described by its author as "very conservative".

    The real difference between warmists and luke warmers is that the luke warmers are deliberately lying to the public about the dangers we face.

    The models can be falsified in myriad ways.  You are just making excuses.  The problem is that you are listening to oil company lobbyists and not scientists.  There is much more than temperature modeled.  We can compare the models to ocean heat, atmospheric humidity, rainfall patterns, drought predictions, extreme storm predictions, floods, temperature changes in different areas, river flow, and many more.  All these data points give us evidence of the accuracy of the models. 

    We already see the stronger storms, drought, flooding and sea level rise.  You want to wait and see if it really gets as much worse as scientists have projected?  You realize the it will continue to get worse after 2100 in any case?  You want to wait until civilization collapses before you take any action?

    The fact that Arhennius in 1896 made projections that are still in the range of what is expected tells us that scientists are close to the mark.  How long do you need to wait?  It has already been 120 years, why would we need to wait another 30?  James Hansen testified to congfress in 1989, 30 years ago.   Fossil fuel intrests used exactly your argument 30 years ago.  Now that the future has realized we see that Hansens projections were very accurate and you say we need another 50 years to wait?  Does that make sense?

    You are making excuses so that you can make money while everyone younger than you will suffer.  10 years ago scientists did not use the term carastrophic global warming and the deniers (luke warmers do not exist) used that term to insult scientists.  Today scientists warn of catastrophic damages and deniers say it will not be too bad.  The consequences have gotton so much worse in the past ten years that it is no longer extreme for scientists to warn of castrophe.

    Scientists work for 150 years to develop the knowledge to project the future climate.  You do not like the projections because it means you will make less money.  You say we will just have to wait and see if it is really that bad.  There is a consensus that warming over 2C could threaten the collapse of civilization and you say we should wait and see what happens at 4C?  That is insane.

    You produce no peer reviewed papers to support you absurd claims.  You dismiss Stern, Hansen and Jacobson with a handwave.  You have only the opinion of a lawyer who invests heavily in fossil fuels.  You ignore the evidence you are presented.  Why do you waste our time here when you do not care about the evidence?

    Arguing that  you do not understand the consequences of material that you refuse to read is not rational.  

    Please do not insult us here again with your comparisons of "luke warmers" and scientists.

  10. michael sweet @ 1084

    Given the moderator's comments, my plan is to largely sit back and read rather than comment on this website.  In fact in a number of instances I have taken this approach rather than "dive in".

    I actually find this site very valuable and it has clearly focussed my views on climate change perhaps more so than the "other site" that I tend to also read.  I have contributed to this site and plan to do so in the future assuming that I do not get blacklisted.

    But before I sign off for a period of time, I have to respond to what I find troubling about your attitude compared to all of the other regular contributors to this website.

    In many respects, you try to "dehumanize" me.  Like you, I am most interested in the welfare of this world.  No, I am not a selfish capitalist involved in oil and gas matters.  I clearly disclosed my financial interest in the oil and gas business so that everyone could judge my views knowing where I was coming from.  Not everyone on this website has done so.

    But I am 71 years old with my children in no way dependent on the oil and gas industry.  One lives in New York and the other in Vancouver.  Over the next 10-20 years, I highly doubt that that portion of my investments involved in oil and gas interest will be really impacted by this debate.  I am not so stupid as to have most of my "chips" on the oil and gas square. 

    I have zero interest in anything other than what is in the best interests of this world.  And I do mean the whole world and not just Europe and North America.  I am trying to rationalize the massive increases in CO2 emissions and the dangers this creates with still keeping the incredible advances we have made in this world since we leveraged our energy requirements using fossil fuels.  Honest people can have honest disagreements on what to do.

    What I find in your remarks is a reluctance to accept that anyone with a brain could possibly disagree with your views.  Rather than reply to some of my remarks with rational responses you would rather demonize me by suggesting that I have ulterior motives and therefore can be dismissed.  

    But I thought the purpose of this website was to educate.  The moderator has replied to me on my issue regarding the models and I appreciate his information.  I plan to read what he has provided to see if what he has provided to me on the climate models can counter my views.  I thought this was the purpose of this website.  I do not think that every person who provides a comment on this website has to have read every blog on this website before providing a comment.  Certainly by me raising a question about whether we can trust the models to predict temperatures in 50 years this is an opportunity of this website to provide references to evidence to support why we should be able to do so, or reasons why we should do so in spite of the difficulty.

    But you would prefer to attack me as having ulterior motives.  I appreciate that at any time I could be "deleted" from this website, but is that a victory?  I think not.  I think providing information that contradicts my general perception is what rational human beings should do.

     So rather than say that I am a "money grubbing" conservative, I would rather hear from you on my question regarding the models.  The moderator has done so, why not you?

    Response:

    [DB] Off-topic and moderation complaints snipped.

  11. NorrisM @1085 , the primary purpose of SkepticalScience website is educational, through the daily articles and multiple links.   The listed Climate Myths provide a strongly educational underpinning, and indeed there is much to be learnt from the comments columns (where an informal panel of well-educated scientific thinkers provides further explication).

    NorrisM, the SkS website could delete all your comments (and all my  comments, too) and be none the lesser for it.   SkS is far bigger than any individual commenter.   While you and I might aspire to contribute praiseworthy eclat or scintillating enlightenment for the benefit of readers, it is nevertheless true that we have (thus far) fallen completely short of that target.

    Michael Sweet @1084 , your comment is relevant and well-phrased.   If I could expand on it, I would say that the human population [re climate] forms a bimodal distribution.   One peak represents the scientific-thinking people, and the other peak represents the science-denying people.

    Interestingly, there is almost no shoulder region between these two mountain peaks — certainly I myself have never heard of or met someone who truly occupies that "intermediate shoulder" between peaks.

    The mainstream "scientist" group vary only slightly in the degree of expression of alarm about the the speed & consequences of AGW.    ~OTOH the denialist group occupy a wider spectrum, ranging from highly-extreme craziness of denial of reality . . . through to low-extreme craziness of so-called lukewarm positions (positions which still amount to "let's ignore the problem and do little or nothing to tackle it effectively").

  12. Norrism:

    I noticed at the top of this page a reply to one of your posts that is almost a year old.  After a year posting at SkS you still have to be constantly reminded to post on topic.

    I have provided you copius references to peer reviewed papers in that year.  You frequently dismiss these with a wave of your hand.  Recently you stated effectively that nothing James Hansen said was worth discussing. 

    You dismiss the US Climate Change report as not the IPCC and cite a paper that claims minimum sea level rise is much less that the IPCC reports.  Hansen's  paper has 200 citations since 2016 while your citation has only 20 since 2014. That means that scientists think Hansen's paper was important while your paper was not.  You will not listen to what Hansen has to say.  Your position is contrary to science.

    This repeats through the entire year you have posted.  You invariably support "lukewarm" positions at the extreme lowest amount (or below) of possible damage and say all decisions should be based on that possibility.  You do not even consider consensus reports like the US Climate Change report.  You never consider the posibilities of severe effects which scientists fear are possible.  

    That dismissal of severe effects is contrary to all known proper risk management.  If it turns out that the fears of Rignot and Hansen that sea level rises several meters the world will be screwed by 2100.   If it turns out that Curry is correct than sea level rise will be slower and the world will not be screwed untill 2200, but it will still be screwed.  The USA is only 250 years old and sea level rise alone will cause immense damage in less than 250 years.  And you do not care.

    There is no down side to switching to renewable energy.  In 100 years oil will run out and the switch will have to be made anyway.  Why delay the switch untill we have permanently screwed future generations?

    The war in Syria was caused partly by a drought that was the biggest in history (over 2000 years).  AGW predicts drought in that region.  The refugee crisis (millions of people) of the past few years was a direct result of drought predicted in advance as caused by AGW.

    I will not go into more detail about hurricanes destroying cities, wildfires consuming greater and greater parts of the globe, ocean currents slowing, floods, glaciers and ice sheets melting, and other disasters caused by AGW already.  It is too depressing and you do not care.

    You rely on your opinion and refuse to even read articles that describe facts you do not like.  After a year I have lost my patience with you.   As I recall, for the first month or so that you posted I was helpful and tried to give you information.  As it became clear that you did not really want information but just wanted to lecture us on your beliefs (without any evidence to support those beliefs) I have gotten much shorter and shorter with you.  I note that over the past year at least 5 other posters (including the moderator) have lost patience with you and will no longer engage with you.

    This is a scientific board.  You must post data to support your wild claims.  You have consistently refused to support your claims and dismiss data presented to you with a hand wave.  That is the problem.

    Response:

    [DB] The participant to whom you responded has recused themselves from further participation here.

  13. How do you explain the fact that the average of climate models is so far off of what has really happened in the last 30 years?

    https://ktwop.files.wordpress.com/2013/10/73-climate-models_reality.gif

    https://ktwop.files.wordpress.com/2013/10/73-climate-models_reality.gif

    Response:

    [PS] Annual comparisons of models and temperate can be found here. But please look at the post the DK indicates below to understand the misinformation that misled you.

  14. ecgberht, see this post about that dodgy graph: Republican's favorite climate chart has some serious problems.

  15. The most reliable climate model of all is the solar cycle.

    It is 93% accurate when past climate data is used to predict present-day climate.

    https://nextgrandminimum.com/2018/11/22/professor-valentina-zharkova-breaks-her-silence-and-confirms-super-grand-solar-minimum/

    No computer model comes close to that.

    Why do climate scientists refuse to acknowledge the solar cycle as a model for climate change?

    Is it because the solar cydle doesn't yield the desired answer?

    Response:

    [DB] Claims made by skeptic blogs are scarcely credible in this venue.  The gold standard is peer-reviewed papers published in credible science journals and primary providers like NOAA or NASA.  When Zharkova publishes her research in a credible science journal, it will be properly examined.  The blog post you cite contains little actual, verifiable details and is this not credible.

    "Why do climate scientists refuse to acknowledge the solar cycle as a model for climate change?"

    Scientists use a metric called Total Solar Irradiance (TSI) to measure the changes in output of the energy the Earth receives from the Sun. And TSI, as one would expect given the meaning behind its acronym, incorporates the 11-year solar cycle AND solar flares/storms.

    The reality is, over the past 5 decades of significant global warming, the net energy forcing the Earth receives from the Sun had been negative. As in, the Earth should be cooling, not warming, if it was the Sun.

    TvsTSI

    It's not the Sun.

    [PS] See also here on effect of grand maximum. Any further discussion should be on this thread. The solar cycle is not a model. If you want to bet on solar, then consider what happened to last solar physicists who were willing to bet (but have refused to pay up).

  16. JoeTP,

    Your reference only discusses solar cycles, it does not mention climate.  It discusses the magnetic cycles of the sun.  It refers to a presentation made at the GWPF, a well known anti-science organization.  Can you cite a peer reviewed report to support your wild claims?

    Scientists generally have trouble predictinig solar cycles.  Claiming to be able to predict solar cycles hundreds of years in the past and future does not seem like a reasonable claim.

  17. As I've stated in other posts, I am a non-scientist layman. I've gone through thousands of comments on this site and several articles on RealClimate. I just got done reading the article and comments over there on "30 years after Hansen’s testimony" here 

    Based on everything I've read so far, this is what I've internalized (please correct me as needed) — all climate models are obviously dependent upon the assumed inputs of both man-driven forcings and natural forcings, which the models use in physics-based simulations of the resulting outputs. Such models do not pretend to have intradecadal accuracy, rather the target is skill in projecting 30 year trends. Hansen was obviously required to guess those forcings, which he incorporated into 3 different scenarios. His man-driven forcings included not only CO2, but also N2O, CH4 and CFC. His CO2 forcings, in retrospect, were "pretty close" for Scenario B but he overshot on the others because humans actually tackled those other emissions. Gavin at RealClimate took a stab at adjusting Hansen's Scenario B and concluded that the adjusted results indicated a quite skillful model.

    So my (perhaps dumb) question is — why not re-run the actual models with the actual man-made forcings that happened in those 3 decades, to see exactly how close the projections got for Scenario B? It seems like they might be "pretty darn close" and bolster the cause?

  18. AFT - based on a comment izen in this discussion,  I believe this has been attempted but it is anything but straightforward because of changes to compilers, hardware and the state of the data files. There is more about the veracity of the model in this article here and perhaps further comments about Hansen 1988 belong there. In short, the model produces a climate sensitivity that is on the high side compared to modern models for a variety of interesting reasons. However, the article also points out a number of ways in which the model has been misrepresented by deniers. Continued work on reproducing the model is unlikely to help with those who determined to deceive. 

  19. The excellent "Science of Doom" has a critique of your debunk. 

    Someone from SKS may wish to engage.   SoD is generally an excellent site for true scepticism. 

    https://scienceofdoom.com/2019/01/06/opinions-and-perspectives-5-climate-models-and-consensus-myths/

  20. I am not sure his series amounts to a "critique". He states "Climate models are the best tools we have for estimating the future climate state."

    and

    "There are lots of papers written by climate scientists on the difficult subject of evaluating climate models. They do some things well. They do some things badly. Different models get different results. Sometimes widely different results."

    No arguments there.

  21. I have a very simple question. Is it possible to predict what the global climate will look like in 5000 years time using the current models?

  22. Bripuk:

    It is impossible to predict how much CO2 humans will eventually release.   Without that information it is hard to be confident in all future projections.

    If it is assumed that humans stop releasing CO2 in 2050 or 2100 a projection can be made but it will have significant possible unknowns.  Long range projections have been made for 5000 years with a variety of different scenarios.  Some look OK and others are scary.

  23. It's been suggested that 'models are unreliable' is a particularly pernicious myth. The models have been useful, and are getting even better, but some make the false claim that models have deviated demonstrably from reality.

    Those who are misinformed or content to be misinformed often make up unsourced past 'predictions', perhaps because they are reacting against journalists' sometimes sensationalist ways of describing individual studies. Eg in the last few days in response to a climate article: "By 2016, New York will be under a foot of flood-water because of all the melting ice caps, melting glaciers and so on", which is clearly not a direct quotation despite being in quotation marks and impossible to trace as a statement.

    If they're schooled in climate confusion, they might refer to Peter Wadhams's projections of sea ice, or the chat with James Hansen; on social media you often find images of local press cuttings, taken out of context and with pink highlighter taken from Tony Heller's blogs. (There's also the argument, which that because models can't reliably predict short-term weather patterns, how can predictions be made for decades in advance, how the range of weather is affected by changes in the Earth's energy balance.)

    This article includes links to CarbonBrief's series on modelling, but I don't see a link to Zeke Haufather's comparison of historical models against later trends:
    LINK

    (The late Wally Broecker's simple 1975 model was nearly spot on. Then there's the 1979 Charney Report.)

    Also, I found this a useful resource:
    LINK

    It's not just that 'Models successfully reproduce temperatures', but also patterns of warming.

    Putting these together in one image (not sure if it will come out):
    Reliability of climate models from CarbonBrief and Barton Paul Leveson

    Response:

    [PS] Fixed image. Please read comment policy for details of image. You must restrict image to max width of 450px using the "appearance" tab of the image inserter.

    [DB] Shortened URLs

  24. Well, I don't have the credentials of many of you, but I do have some understanding of statistics, modeling, and the like.  I also understand that if you take a graph of temps from any small period of time, (remembering that we could be dealing with a couple of billion years, at least, that you can pretty much get any trend you want, if you only look at a few hundred of those years.  I also often hear thing like 'this is the hottest year since e.g.,1898, which leads me to ask the question about how we have suddenly caused a cataclysm, yet the temps were the same or higher in the 19th century (before the proliferation of the internal combustion engine) Lastly, I know that solar panels generate lots of heat, so why does anyone think that having 100x the number (or more) will somehow reduce the average temperature of 'anywhere'.  Somehow, I think that Mother Nature will take care of the planet just fine, while we waste our time trying to justify a few degrees here and there, when I doubt that we could have done anything to prevent (or help) any of the Ice Ages . . . let's think a little more long term, rather than just a few hundred years . . . then maybe wecan accomplish something productive.

    Response:

    [DB] "yet the temps were the same or higher in the 19th century (before the proliferation of the internal combustion engine)"

    There's no evidence of that.  Please use evidence for claims instead of making things up.

    US Government Hockey Stick

  25. "CommonSense" @1099 :

    <Well, I don't have the credentials of many of you ... >

    Actually, the word you meant was credibility.

    Gain some credibility by citing the evidence that "temps were the same or higher in the 19th century".   Your other claims are similarly bizarre, and seem to be based on religion rather than science.  Or you are simply jesting.

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