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Climate Models for the Layman

Jack Hays

Jack Hays

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This is Judith Curry's take on climate models. Not surprisingly she's not impressed. Without the GCM's how much of the AGW message remains?

Climate models for the layman

Posted on 21 Feb 17 by PAUL MATTHEWS • 2 Comments
Judith Curry has written a new paper, Climate models for the layman, published today by the GWPF. She hasn’t done a blog post about it, nor has anyone else as far as I can see, so here’s a venue to discuss it. The aim is “to describe the debate surrounding GCMs to an educated but … Continue reading →

Judith Curry has written a new paper, Climate models for the layman, published today by the GWPF.
She hasn’t done a blog post about it, nor has anyone else as far as I can see, so here’s a venue to discuss it.
The aim is “to describe the debate surrounding GCMs to an educated but nontechnical audience”.
Here are the key points from the summary:

  • GCMs have not been subject to the rigorous verification and validation that is
    the norm for engineering and regulatory science.
  • There are valid concerns about a fundamental lack of predictability in the complex
    nonlinear climate system.
  • There are numerous arguments supporting the conclusion that climate models
    are not fit for the purpose of identifying with high confidence the proportion
    of the 20th century warming that was human-caused as opposed to natural.
  • There is growing evidence that climate models predict too much warming from
    increased atmospheric carbon dioxide.
  • The climate model simulation results for the 21st century reported by the Intergovernmental
    Panel on Climate Change (IPCC) do not include key elements
    of climate variability, and hence are not useful as projections for how the 21st
    century climate will actually evolve. . . .

 
[h=1]Curry: Computer Predictions Of Climate Alarm Are Flawed[/h]New paper explains inherent flaws of computer models predicting future climate change London, 21 February: Claims that the planet is threatened by man-made global warming are based on science that is based on inadequate computer modelling. That is the conclusion of a new briefing paper published today by the Global Warming Policy Foundation (GWPF). The…
Continue reading →
 
Man-made-global-warming-disaster prophets write the computer program that tells them what they want to hear
 
Mac77 said:
Man-made-global-warming-disaster prophets write the computer program that tells them what they want to hear
Click to expand...

Or that pays them best. Got to keep their political paymasters happy doncha know
 
Climate Models / Opinion
[h=1]The Climate ‘Deus ex Machina’ is shown to be a false God[/h]Guest essay by Charles G. Battig, M.D. Some say that “God” might reside in a computer…the Deus ex Machina, literally means “god from the machine”. Amongst those individuals are those divining climate with climate computers in which are embedded general circulation models. This has generated a belief system…belief that all variables which drive global climate at…
 
Global temperature observations have been remarkably consistent with both hindcasting and forecasting based on GCMs.

They're pretty good in other words, but Curry - writing for political advocacy group the Global Warming Policy Foundation - attempts to argue that they're just not good enough: Apparently, that instead of energy policy being based on the best available information about long-term outcomes, it should be based on no information whatsoever.

This does not seem like a rational approach, to my mind.

32331179692_11aa30d8de_h.jpg
 
Mithrae said:
Global temperature observations have been remarkably consistent with both hindcasting and forecasting based on GCMs.

They're pretty good in other words, but Curry - writing for political advocacy group the Global Warming Policy Foundation - attempts to argue that they're just not good enough: Apparently, that instead of energy policy being based on the best available information about long-term outcomes, it should be based on no information whatsoever.

This does not seem like a rational approach, to my mind.
Click to expand...
If you had read any of Judith Curry's peer reviewed publications on climate sensitivity,
you would understand that her scientific findings based on the observable data,
show the climates sensitivity to added CO2 to be at the low end of the IPCC's range.
Most of the studies based on the observable data are at the low end, this is what led the IPCC is AR5
to state,
https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WGIAR5_SPM_brochure_en.pdf
16 No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies
Click to expand...
The models based on open loop feedback (speculating what the sensitivity will be) tend to come in higher than the models based
on how the climate has responded in the past,(observational data).
So what is the best available information about long-term outcomes? The models based on speculation, or the models based on observation?
My experience ,is that the odds favor the observational data!
 
longview said:
If you had read any of Judith Curry's peer reviewed publications on climate sensitivity,
you would understand that her scientific findings based on the observable data,
show the climates sensitivity to added CO2 to be at the low end of the IPCC's range.
Most of the studies based on the observable data are at the low end, this is what led the IPCC is AR5
to state,
https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WGIAR5_SPM_brochure_en.pdf

The models based on open loop feedback (speculating what the sensitivity will be) tend to come in higher than the models based
on how the climate has responded in the past,(observational data).
So what is the best available information about long-term outcomes? The models based on speculation, or the models based on observation?
My experience ,is that the odds favor the observational data!
Click to expand...

You are mistaken: Of the studies examined in AR5 which estimate climate sensitivity based on instrumental observations (Figure 12.2-1), 8 provide a best estimate lower than 2.4 degrees while 11 provide a best estimate of 2.4 or higher (five of them 3 degrees or higher). Of the studies which estimate climate sensitivity based on paleoclimate observations, 4 estimate a sensitivity below 2.4 while 6 provide a higher estimate (five of them above 3 degrees). Of those which use a combination of approaches, only one gives a best estimate below 2.4 while the other 5 have an estimate in the 2.4 to 3.1 range.

Combined with the fact that observations have generally been within the middle third of the IPCC projection envelopes (in fact often the upper third of SAR and TAR projections), there's no reason a lay person should consider AR4's three degree best estimate particularly improbable. ECS may very plausibly be 10 or 20% lower than that of course, but by the same token it's almost as likely to be 10 or 20% higher.

Again, a "close your eyes and hope for the best" approach is not at all rational, in my view. The transition away from oil and coal dependency has always been desirable and inevitable to begin with: Considering whether to implement any policies to hasten that transition, it's hardly sensible to look only the best of all possible hopes and dreams. If anything it'd make more sense to look at the worst plausible scenarios and consider whether it's worth the risk. According to a correspondence you've cited in the past, even a ~4.7 degree climate sensitivity is within a 5-95% confidence interval based on four decades of observation. Using a mere 3 degree estimate for looking at probable consequences was and still remains the simplest and most reasonable baseline to work with.
 
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Jack Hays said:
This is Judith Curry's take on climate models. Not surprisingly she's not impressed. Without the GCM's how much of the AGW message remains?
Click to expand...

All of it.

No models, just data:
CO2-Temp2016.jpg
 
NEW PAPER: COMPUTER PREDICTIONS OF CLIMATE ALARM ARE FLAWED


  • Date: 21/02/17
  • Global Warming Policy Foundation
Claims that the planet is threatened by man-made global warming are based on science that is based on inadequate computer modelling. That is the conclusion of a new briefing paper published today by the Global Warming Policy Foundation (GWPF). The report’s author, eminent American climatologist Professor Judith Curry, explains that climate alarm depends on highly complex computer simulations […]
 
Jack Hays said:
Now you're just being silly.
Click to expand...

You're the one who posted the misleading graph, along with the admission that it was misleading. And I'm being silly?
 
Poor Debater said:
You're the one who posted the misleading graph, along with the admission that it was misleading. And I'm being silly?
Click to expand...

It is an illustration of how easy it is to mislead, and labels itself as such. It was posted in response to your graph.
 
Jack Hays said:
It is an illustration of how easy it is to mislead, and labels itself as such. It was posted in response to your graph.
Click to expand...

Please explain why my graph is misleading, or withdraw your slanderous accusation.
 
Poor Debater said:
Thanks for the admission that you're deliberately misleading.
Click to expand...

Here's a graph from the ever-reliable Wikipedia:

600px-Frequency_distribution_of_climate_sensitivity%2C_based_on_model_simulations_%28NASA%29.png

https://en.wikipedia.org/wiki/Climate_sensitivity

Looks like the IPCC's "ensemble" says CO2's climate sensitivity is around 3.2°C per doubling.
Temperature has trended up about 0.8° since 1850 and CO2 is up a little over 40%.
My simple linear arithmetic says the IPCC overshot reality by about half a degree.

You know, yesterday's record high on Washington's birthday here in Milwaukee was about 70°F
if it weren't for the warming so far it might have been only 68 F. And I'm supposed to change
the way I live because of that. Well you know where you can go and what you can do.
 
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Poor Debater said:
Please explain why my graph is misleading, or withdraw your slanderous accusation.
Click to expand...

Well given your track record how can we know its one you haven't 'doctored' in order to get it to say what you want ?
 
Poor Debater said:
All of it.

No models, just data:
View attachment 67214354
Click to expand...

I believe I've finally got 'round to replicating your results:

https://docs.google.com/spreadsheets/d/1ofbw72DDspPtzXIRoYhasqy6zF_u55NakdvKeI0qtw8/edit?usp=sharing

But assuming I've done it right, I'm not sure how useful this would be in estimating climate sensitivity, because the results seem to depend very heavily on both the temperature data used and the lag estimate applied.

Comparing ln(CO2) against HadCRUT temperatures lagged 2 years, climate sensitivity is estimated at around 2.2 degrees (r^2=0.845)
Comparing ln(CO2) against GISS temperatures lagged 2 years, climate sensitivity is estimated at around 2.6 degrees (r^2=0.886) (second sheet)
Comparing ln(CO2) against HadCRUT temperatures lagged 21 years, climate sensitivity is estimated at around 3.3 degrees (r^2=0.864) (first sheet)
Comparing ln(CO2) against GISS temperatures lagged 21 years, climate sensitivity is estimated at around 3.8 degrees (r^2=0.897)

For comparison - for any others interested - the r-squared value of a trendline from a regular temperature time series is about 0.76 (third sheet). Using a series starting at 290 (same as CO2) but varying randomly by values between -2 and 2, the average r-squared value was 0.307 (from twenty-five trials). Using a series starting at 290 but randomly increasing by 0 to 2 (hence on average ending up around 426 'ppm,' compared to the actual 404ppm), the average r-squared value was 0.8118 from twenty-five trials (the two highest values were 0.841 and 0.837). From a simple linear increase from 290 to 426ppm (+1 each year) the r-squared value would be 0.814. The actual observed CO2 concentrations provide a closer fit because they have increased more rapidly in recent decades (as temperatures in general have tended to).

lnCO2.jpg
 
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Mithrae said:
You are mistaken: Of the studies examined in AR5 which estimate climate sensitivity based on instrumental observations (Figure 12.2-1), 8 provide a best estimate lower than 2.4 degrees while 11 provide a best estimate of 2.4 or higher (five of them 3 degrees or higher). Of the studies which estimate climate sensitivity based on paleoclimate observations, 4 estimate a sensitivity below 2.4 while 6 provide a higher estimate (five of them above 3 degrees). Of those which use a combination of approaches, only one gives a best estimate below 2.4 while the other 5 have an estimate in the 2.4 to 3.1 range.

Combined with the fact that observations have generally been within the middle third of the IPCC projection envelopes (in fact often the upper third of SAR and TAR projections), there's no reason a lay person should consider AR4's three degree best estimate particularly improbable. ECS may very plausibly be 10 or 20% lower than that of course, but by the same token it's almost as likely to be 10 or 20% higher.

Again, a "close your eyes and hope for the best" approach is not at all rational, in my view. The transition away from oil and coal dependency has always been desirable and inevitable to begin with: Considering whether to implement any policies to hasten that transition, it's hardly sensible to look only the best of all possible hopes and dreams. If anything it'd make more sense to look at the worst plausible scenarios and consider whether it's worth the risk. According to a correspondence you've cited in the past, even a ~4.7 degree climate sensitivity is within a 5-95% confidence interval based on four decades of observation. Using a mere 3 degree estimate for looking at probable consequences was and still remains the simplest and most reasonable baseline to work with.
Click to expand...

Considering that there are only 10 instrumental reading on your cited chart, I assume your numbers came from somewhere else.
Also there is a very good reason why ECS would be lower, consider that at the time of the TAR,
the accepted energy imbalance from a doubling of CO2 was 4 Wm-2, with a warming assigned of 1.2 C.
http://www.grida.no/climate/ipcc_tar/wg1/pdf/tar-01.pdf
Since that time the energy imbalance number has been refined down to 3.71 Wm-2,
Since the 1.2 C is the supposed input for the climate amplifier, if the input drops by 7.3%,
so does the output! If the same amplification factor is applied to the input, the output would be 2.75C instead of 3C,
but there is not physical basis for the 3 C to begin with, it is just based on speculation.
 
longview said:
Considering that there are only 10 instrumental reading on your cited chart, I assume your numbers came from somewhere else.
Click to expand...

There are actually twenty shown there, though best estimates are provided for only nineteen of them. The ten for which publication details are actually shown on the chart are the ones which were new since AR4: Out of those, 4 provide an ECS best estimate lower than 2.4 degrees and 5 provide a higher estimate (three of them above 3 degrees by the looks, though I'm just eyeballing it this time), while Scharwtz 2012 is the one for which no best estimate is provided.

Clearly, it is not the case that "most" studies support an estimate on the low end of the IPCC range. On the contrary, most studies support a 'best estimate' around the 3 degree mark +/-20% (with many of them suggesting 5-95% confidence ranges that extend above 4 degrees), and your decision to blindly dismiss this scientific research as "just based on speculation" purely because you have been proven wrong in your assertions is disappointing, to say the least.

As Poor Debater has suggested, even simply comparing ln(CO2) with recorded temperatures implies a climate sensitivity somewhere in the 2.2 to 3.8 degree range (if memory serves in the past he has pegged his personal estimate at 2.7 or 2.8 degrees).
 
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