One analogy too far

Several times in the Cook lecture I couldn’t resist smiling and thinking that he couldn’t believe that himself. Could he? The first time was when Cook said that for complicated issues we rely on the experts and then gave an analogy: bridges. The public is trusting those who build bridges. They trust that bridges are save to cross. The implication seems clear. Why shouldn’t we give the same trust to our climate scientists? Those are the “experts” when it comes to the climate.

I heard that one in several variations and it is rather funny if you think about it.

Sure, I trust that crossing a bridge is save. I realize that bad things can happen (like for example the Tacoma bridge), but this happens rather seldom. It is fair to say that bridge engineers know what they are doing and I have no problem trusting their expertise when walking across a bridge.

Analogies are great, but only go as far as the similarities go. Climate science is a different kind of breed compared to engineering. People build bridges for many thousand years. In engineering the basis is well established, the properties of the materials well known. Feed this into a model and it will work pretty reliable.

Compare that to climate science which is a fairly new science that is studying a very complex matter. Many things are not (well) known, observational data is only available from the end of the 1970s, uncertainties are huge, the science politicized,…

So the comparison is rather flawed. Let’s make the correct comparison.

Suppose you knew that the technology of building bridges was fairly new. Suppose you knew that the technology of bridge building was based on scarce and incomplete observational data. Suppose you knew that only few bridges were build and that most of them collapsed. Suppose you knew that the properties of the materials were hardly known, there were huge uncertainties on how all these things fit together and nobody knew exactly how they would act under a load.

Would you be able to cross that bridge in a relaxed way?


When lookingt at other commentaries they seem to focus more on the question “if 97% say the bridge will collapse and 3% who say the bridge will not collapse, who to believe?”. Maybe I missed something while making notes. For some reason I connected the “expert” statement with the analogy, probably because they followed each other. Have to check with the video how it was actually brought.

Whatever be the case, the analogy will always fail because of the incorrect comparison of bridge engineers (who study a well defined, well understood topic) with climate scientists (who study a complex system with huge uncertainties). Therefor it can easily be reversed. If that 97% agreement is based on incomplete data, processes not yet (well) understood,… then whatever the level of agreement is that the bridge will fail, it will be basically meaningless.

There are also many other possible analogies. See below in the comments for additional thought experiments.


20 thoughts on “One analogy too far

  1. Pingback: My report on the Cook talk in Bristol – attendees are invited to leave their impressions | Watts Up With That?

  2. mrsean2k

    The main fault in self-serving analogies like Cook’s is that they present action (or in this particular analogy, inaction) as having no negative consequences.

    A more honest analogy:

    You are *already* standing in the middle of a bridge.

    97% of engineers believe the bridge is swayed by both external factors – such as the wind, rain and earthquakes – and by your own motion as you walk.

    1.6% of those engineers believe that if you *do* attempt to walk to safety, your motion will be the major factor in causing the bridge to swing so far it will pitch you into the ravine.

    Do you stand absolutely still and hope the external factors don’t perturb the bridge enough to throw you off, or do you decide to walk towards the end?


  3. kaboom1776

    Let’s not forget that if a bridge were to collapse due to bad engineering and injury and damages occur, the engineers go to jail. No climate scientist is under threat of any consequences for their failed predictions or to compensate for the massive amounts of economic damage they have already wrought.


  4. Bobl

    Can I comment on these false analogies. On the surface these analogies make sense except they are misrepresenting the role of the climate scientists. The climate scientists aren’t the engineers, they are the architects. Architects regularly design things that can’t be built.

    97 architectural bridge modellers using an average of 20 models that produce vastly different results to each other and all perform totally unlike real bridges told you that it is 95 percent probable that the bridge they are building with your 800 billion dollars will hold up somewhere between half and twice the load you need it to hold- 3 real engineers told you that the physics of bridges is nothing like the models use, they say that the models are overestimating the load the Bridge will hold and that bridges built like the models design historically fail at less than 1/4 the load that the model mean produces, and they would never in practice ever build bridges like that, they recommend you use the traditional design given by the international standards ( defer to the null hypothesis) do you spend you 800 billion dollars to build that bridge according to the architects models?

    It’s like the cancer analogy, in this case the climate scientists are cancer researchers with a model, a proper analogy goes like this..

    97 cancer statistical modelers took your age, height, blood pressure and skin color, and pronounced that a cohort of these cancer models, that vastly disagree with each other on average predict it is 95% likely you have liver cancer. 3 real doctors look at the evidence, take pathology an MRI, a CT and PET scan and find no evidence of cancer. ?.. Do you have that liver transplant?

    Back to climate.
    97 climate scientists using the average of a cohort of computer models that don’t agree with each other declare it is 95 percent likely temperature in 100 years will be 1.5- 5 degrees hotter and that the earth is gonna die. 3 practitioners ie meteorologists and geologists, and a horticulturalist looked at the actual climate and tell you that the actual climate is nothing like the models, they tell you that climate is chaotic and too complicated for simple computer models. They tell you that in the historical context the 20th century warming is actually cooler than the MWP, Holocene climate optimum and Roman warming and is clearly within the limits of natural variation. They explain that the LIA which was just 0.8 degrees less than today killed half the population of Europe and that it’s therefore much more desirable historically to have a warm climate than a cold one. They explain that CO2 feeds plants and that warmth and increased CO2 increases the food supply allowing the earth’s population to continue to be fed, and that reducing CO2 and temperature would reduce the global food supply. Do you spend that 1/4 of a quadrillion dollars fighting climate change or do you cure cancer instead?


  5. Roger D B Eng PGeol

    Also recognize that bridges are engineered with a “safety factor” which is to say, for ten times expected load in case of pedestrian traffic, five times for auto.
    Also, his analogy is in the negative, as you point out, in that the 97% consensus says the bridge is safe, if you put another ten billion dollars into it…


    1. trustyetverify Post author

      Indeed, looking at other commentaries they focused on the negative analogy (if 97% it will collapse…). For some reason I connected it in my notes with the expert statement that came before the analogy. Will check with the video when it comes online and when having better internet access.

      However, the basis of the story was about the incorrect comparison of the two professions. Whether positive or negative, the analogy will always fail because how both professions do their work is not comparable. This could as well be rewritten for the negative. See the update.

      The last idea is indeed a nice addition to the positive analogy. Wished I had thought about that.


  6. bobl

    Did you get my last comment? I addressed this and provided the correct metaphors, EG Climate scientists are not practitioners of science like engineers, they are researchers, they are closer to Architects than Engineers. Even architect is probably too practical for these guys, they are more like the artistic impressionist that paints the clients idea for the Architect. The Engineers are the ones that have to try and make the childish whims of the artist and architect stand up in a stiff breeze. In climate they are the Meteorologists, Geologists and Engineers the people that really know and do things.

    The Sydney opera house came out of an Architect arranging a pile of orange halves (segments). He had no idea whether it could be built or not. It turned out to be nearly impossible to construct. The building of the opera house was an extraordinary feat of engineering.


    1. trustyetverify Post author

      Thanks for commenting.
      For some reason both of your comments were in the spam folder. I am a bit slow in responding/approving and keeping up with all the reactions because I didn’t see this sudden rush on my normally very quiet blog coming. Was caught by surprise. You may look at my (coming) post of today for some background.


    1. lokenbr

      Yet another humbling demonstration of the complexities of nature. This bridge met all applicable engineering codes and best practice of the time. But – there were very few bridges of that scale and very few engineers designing them. The limits were being pushed. It was a failure of the profession to fully understand wind dynamics.

      This in a field where every effort was made to control & verify material quality, loads, models, workmanship, etc. A factor of safety applied on top of to try and account for uncertainty.

      To think one can make any meaningful prediction of climate 100 years in the future is the height of hubris.



  7. John B

    I didn’t see this sudden rush on my normally very quiet blog coming. Was caught by surprise.

    Blame that Watts guy – Watts Up With That?


  8. Josie360

    There appear to be a limited number of known variables in bridge building, and the properties of materials that might be used are known or well tested.

    Let’s see, how does gravity work? Which is stronger, wood or steel?

    In climate science, they have the luxury of making assumptions for unknowns, like, “let’s assume that the sun is a constant” or “let’s assume that the clouds are a constant.” Once they have done that, they can come up with all kinds of interesting conclusions, whether the assumptions are correct or not.

    In Engineering however, they not only can’t assume away unknowns, they actually have to design around the unknowns. They have to estimate and anticipate where their calculations and assumptions will fail, and then attempt to make corrections to avoid the possible failures.

    The bridge analogy is most inept.


  9. mark b

    99.999% of doctors say that ulcers are caused by stress and diet. Two say it’s bacterial. How much do you spend on Maalox?



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