4 ms·

Models say only what the modeler tells them to say.

nabla9 5y ago
That's not true. Climate models model and simulate physical and chemical condition on Earth. Modellers don't know what they say beforehand. Offhandedly portraying scientists and researchers as dishonest and conspirators in every opportunity possible seems the default here.
- refurb 5y ago
  Models are constantly tweaked to make them more accurate. How do you do that without looking at output and then going back to tweak it?
  - magicalhippo 5y ago
    One way is to verify them. Run multiple variations on data from the 1950's and see how they compare to measured values up to today. Throw away the models that don't fit the measured values. Then you have some confidence that the remaining variations may be representative when run into the future. This is also done in weather forecasting, though maybe they run the model in reverse, I can't recall. Same idea though, verify with existing data before predicting.
    - sanxiyn 5y ago
      Yes this happens, but it is very controversial. To quote from the article I linked above: > The question of whether the twentieth-century warming should be considered a target of model development or an emergent property is polarizing the climate modeling community, with 35% of modelers stating that twentieth-century warming was rated very important to decisive, whereas 30% would not consider it at all during development. Some view the temperature record as an independent evaluation dataset not to be used, while others view it as a valuable observational constraint on the model development. Likewise, opinions diverge as to which measures, either forcing or ECS, are legitimate means for improving the model match to observed warming. The question of developing toward the twentieth-century warming therefore is an area of vigorous debate within the community.
      - refurb 5y ago
        Not going to lie but it sounds like there is significant disagreement among scientists on evaluating climate models? And do I read it right that 35% of scientists deem it important that a model indicates future warming? Science doesn’t work that way, you don’t get to choose a conclusion then model for it.
        sanxiyn 5y ago
        Yes, there is (and continues to be) significant disagreement among scientists on evaluating climate models. This is normal and has always been the case from the very beginning of climate models. No, you read it wrong. 35% thinks it appropriate to fit to past warming. Of course nobody is suggesting to fit to future warming! But past warming is observed. If you are familiar with training/test split in machine learning, some thinks past warming is in training set (and test with things like reproducing ENSO), and some thinks past warming is in test set. I think it boils down to disagreement over how determined was twentieth-century warming.
  - sanxiyn 5y ago
    I will treat this as a genuine question. This is a complex topic. You could start by reading "The Art and Science of Climate Model Tuning". https://journals.ametsoc.org/view/journals/bams/98/3/bams-d-15-00135.1.xml https://journals.ametsoc.org/view/journals/bams/98/3/bams-d-...
  - nabla9 5y ago
    You add more physical parameters. Climate models are not parameter fitting from the past data, they are physical models. Of course you test them with old data too, but they are mainly for verification and controlling for variables that are still missing. They test these models with other planets too. Set in parameters for Mars or Venus and they precinct pretty well how those climates behave.
- chasd00 5y ago
  Upthread there’s a climatologist openly admitting to lying to make their point seem more dire. The whole field has a credibility problem. I don’t blame laypeople for their skepticism.
freen 5y ago
I am 100% sure that the Exxon model from 1982 was not what Exxon wanted. It also has been and continues to be tremendously accurate and predictive. https://xkcd.com/2500 https://xkcd.com/2500
- sampo 5y ago
  > https://xkcd.com/2500 https://xkcd.com/2500 I am unable to find any 1982 Exxon prediction that would meander like the line in that graph. The only plot I was able to find is this [1] from this 1982 Exxon report [2], which is just a slightly curved upward rising sketch, not nearly as detailed as in the xkcd graph. > the Exxon model from 1982 I also failed to find any signs of there having been any "1982 Exxon model". What [2] is, is a 39-page report, a synthesis and review of publicly available climate research. The list of references is quite extensive: 10 pages. [1] https://pbs.twimg.com/media/D6fbaqdWwAEPg5Z.png https://pbs.twimg.com/media/D6fbaqdWwAEPg5Z.png [2] https://www.climatefiles.com/exxonmobil/1982-memo-to-exxon-management-about-co2-greenhouse-effect/ https://www.climatefiles.com/exxonmobil/1982-memo-to-exxon-m...
  - sampo 5y ago
    Oh right, I misinterpreted the xkcd plot. It's only the single (x)-marked dot in the top right of the graph, that is the Exxon prediction. Not the graph itself.
    - freen 5y ago
      Perhaps a bit more epistemically humility is in order. For all of us, myself included. That said, even highly adversarial climate models greated almost half a century ago have tremendous predictive power. Large systems are modelable. Not with any degree of precision, of course, but a high degree of accuracy. Otherwise insurance companies wouldn’t exist.
      - sampo 5y ago
        > That said, even highly adversarial climate models greated almost half a century ago have tremendous predictive power. Yes. About the warming effect of doubling the atmospheric CO2 (Equilibrium Climate Sensitivity): Manabe and Wetherald 1967, said 2.3°C. The Charney Report 1979, said 3.0 ± 1.5°C. IPCC AR6 2021, says 3.0°C (2.5 to 4.0). https://journals.ametsoc.org/view/journals/atsc/24/3/1520-0469_1967_024_0241_teotaw_2_0_co_2.xml https://journals.ametsoc.org/view/journals/atsc/24/3/1520-04... https://www.bnl.gov/envsci/schwartz/charney_report1979.pdf https://www.bnl.gov/envsci/schwartz/charney_report1979.pdf https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_07.pdf#page=118 https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6...
WoahNoun 5y ago
Do you have any evidence for this? Are you implying that climate change isn't happening?
- pmjones 5y ago
  > Do you have any evidence for this? It's the very definition of how computer models work. The modeler writes the program, determines all the inputs, determines how the logic of the program will respond to the inputs, etc. The modeler is in complete control of the model, tells it how to behave, and thus the model says only what the modeler tells it to. > Are you implying that climate change isn't happening? Non sequitur.
alexanderdmitri 5y ago
So in this case the modeler just needs to tell the model to (1) accurately calculate the degree to which the Earth's climate will change in the next few decades and (2) give a comprehensive global forecast of the accompanying extreme weather events.
adamrezich 5y ago
modeling an infinitely fractal set of chaotic systems can only do exactly this

That's not true. Climate models model and simulate physical and chemical condition on Earth. Modellers don't know what they say beforehand. Offhandedly portraying scientists and researchers as dishonest and conspirators in every opportunity possible seems the default here.

refurb 5y ago
Models are constantly tweaked to make them more accurate. How do you do that without looking at output and then going back to tweak it?
- magicalhippo 5y ago
  One way is to verify them. Run multiple variations on data from the 1950's and see how they compare to measured values up to today. Throw away the models that don't fit the measured values. Then you have some confidence that the remaining variations may be representative when run into the future. This is also done in weather forecasting, though maybe they run the model in reverse, I can't recall. Same idea though, verify with existing data before predicting.
  - sanxiyn 5y ago
    Yes this happens, but it is very controversial. To quote from the article I linked above: > The question of whether the twentieth-century warming should be considered a target of model development or an emergent property is polarizing the climate modeling community, with 35% of modelers stating that twentieth-century warming was rated very important to decisive, whereas 30% would not consider it at all during development. Some view the temperature record as an independent evaluation dataset not to be used, while others view it as a valuable observational constraint on the model development. Likewise, opinions diverge as to which measures, either forcing or ECS, are legitimate means for improving the model match to observed warming. The question of developing toward the twentieth-century warming therefore is an area of vigorous debate within the community.
    - refurb 5y ago
      Not going to lie but it sounds like there is significant disagreement among scientists on evaluating climate models? And do I read it right that 35% of scientists deem it important that a model indicates future warming? Science doesn’t work that way, you don’t get to choose a conclusion then model for it.
      - sanxiyn 5y ago
        Yes, there is (and continues to be) significant disagreement among scientists on evaluating climate models. This is normal and has always been the case from the very beginning of climate models. No, you read it wrong. 35% thinks it appropriate to fit to past warming. Of course nobody is suggesting to fit to future warming! But past warming is observed. If you are familiar with training/test split in machine learning, some thinks past warming is in training set (and test with things like reproducing ENSO), and some thinks past warming is in test set. I think it boils down to disagreement over how determined was twentieth-century warming.
- sanxiyn 5y ago
  I will treat this as a genuine question. This is a complex topic. You could start by reading "The Art and Science of Climate Model Tuning". https://journals.ametsoc.org/view/journals/bams/98/3/bams-d-15-00135.1.xml https://journals.ametsoc.org/view/journals/bams/98/3/bams-d-...
- nabla9 5y ago
  You add more physical parameters. Climate models are not parameter fitting from the past data, they are physical models. Of course you test them with old data too, but they are mainly for verification and controlling for variables that are still missing. They test these models with other planets too. Set in parameters for Mars or Venus and they precinct pretty well how those climates behave.
chasd00 5y ago
Upthread there’s a climatologist openly admitting to lying to make their point seem more dire. The whole field has a credibility problem. I don’t blame laypeople for their skepticism.

freen 5y ago

I am 100% sure that the Exxon model from 1982 was not what Exxon wanted. It also has been and continues to be tremendously accurate and predictive. https://xkcd.com/2500 https://xkcd.com/2500

sampo 5y ago
> https://xkcd.com/2500 https://xkcd.com/2500 I am unable to find any 1982 Exxon prediction that would meander like the line in that graph. The only plot I was able to find is this [1] from this 1982 Exxon report [2], which is just a slightly curved upward rising sketch, not nearly as detailed as in the xkcd graph. > the Exxon model from 1982 I also failed to find any signs of there having been any "1982 Exxon model". What [2] is, is a 39-page report, a synthesis and review of publicly available climate research. The list of references is quite extensive: 10 pages. [1] https://pbs.twimg.com/media/D6fbaqdWwAEPg5Z.png https://pbs.twimg.com/media/D6fbaqdWwAEPg5Z.png [2] https://www.climatefiles.com/exxonmobil/1982-memo-to-exxon-management-about-co2-greenhouse-effect/ https://www.climatefiles.com/exxonmobil/1982-memo-to-exxon-m...
- sampo 5y ago
  Oh right, I misinterpreted the xkcd plot. It's only the single (x)-marked dot in the top right of the graph, that is the Exxon prediction. Not the graph itself.
  - freen 5y ago
    Perhaps a bit more epistemically humility is in order. For all of us, myself included. That said, even highly adversarial climate models greated almost half a century ago have tremendous predictive power. Large systems are modelable. Not with any degree of precision, of course, but a high degree of accuracy. Otherwise insurance companies wouldn’t exist.
    - sampo 5y ago
      > That said, even highly adversarial climate models greated almost half a century ago have tremendous predictive power. Yes. About the warming effect of doubling the atmospheric CO2 (Equilibrium Climate Sensitivity): Manabe and Wetherald 1967, said 2.3°C. The Charney Report 1979, said 3.0 ± 1.5°C. IPCC AR6 2021, says 3.0°C (2.5 to 4.0). https://journals.ametsoc.org/view/journals/atsc/24/3/1520-0469_1967_024_0241_teotaw_2_0_co_2.xml https://journals.ametsoc.org/view/journals/atsc/24/3/1520-04... https://www.bnl.gov/envsci/schwartz/charney_report1979.pdf https://www.bnl.gov/envsci/schwartz/charney_report1979.pdf https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_07.pdf#page=118 https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6...

WoahNoun 5y ago

Do you have any evidence for this? Are you implying that climate change isn't happening?

pmjones 5y ago
> Do you have any evidence for this? It's the very definition of how computer models work. The modeler writes the program, determines all the inputs, determines how the logic of the program will respond to the inputs, etc. The modeler is in complete control of the model, tells it how to behave, and thus the model says only what the modeler tells it to. > Are you implying that climate change isn't happening? Non sequitur.

alexanderdmitri 5y ago

So in this case the modeler just needs to tell the model to (1) accurately calculate the degree to which the Earth's climate will change in the next few decades and (2) give a comprehensive global forecast of the accompanying extreme weather events.

adamrezich 5y ago

modeling an infinitely fractal set of chaotic systems can only do exactly this