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Marotzke's circularity

A few days ago I noted a new paper by Marotzke and Forster which claimed to show that the recent divergence of model predictions and observations was all down to natural variability. The paper was getting considerable hype from Marotzke's employers, the Max Planck Institute:

Sceptics who still doubt anthropogenic climate change have now been stripped of one of their last-ditch arguments...the gap between the calculated and measured warming is not due to systematic errors of the models, as the sceptics had suspected, but because there are always random fluctuations in the Earth's climate.

Marotzke was also quoted as saying: "The claim that climate models systematically overestimate global warming caused by rising greenhouse gas concentrations is wrong" and he went on to get quite a lot of media coverage, including the Mail, the Sydney Morning Herald, Deutsche Welle, and the Washington Post

Based on media coverage of the paper's contents, I expressed considerable concern over what the authors had apparently done. It seems, however, that my criticisms at the time were understated. It is in fact "worse than we thought".

These uncomfortable facts are revealed in Nic Lewis's analysis of the paper, which has recently appeared at Climate Audit. Nic, assisted by Gordon Hughes and Roman Mureika, has identified some glaring statistical errors in the paper, but these turn out to be just the tip of the iceberg, as I shall now try to explain.

Marotzke's method involved seeing how far inter-model differences in the temperature trends in a group of climate model runs could be explained by differences between models in changes in forcing and two "structural elements":  the climate feedback parameter and the ocean heat uptake efficiency. However, the time series for the forcing changes and the estimates of the structural elements came from another paper, by Forster et al. (and hence Forster's appearance as a co-author, or at least so one assumes).

Unfortunately, Marotzke seems not to have understood that Forster had calculated the forcing time series using an equation that expressed them as a function of model temperature. This meant that when the figures were plugged back into Marotzke's regression model he effectively had temperature on both sides of the equation: he was regressing temperature on a function of temperature and the logic was circular!

But in fact, even if the work could be redone without the circularity, Nic reckons the general approach is still "doomed". Readers will have gathered from my introduction that the whole study revolves around model output. It's completely divorced from the real world, apart from a brief and somewhat tenuous claim that "the simulated multimodel ensemble spread accurately characterizes internal variability". But unfortunately, even in model-world, the values Marotzke used for the ocean heat uptake efficiency vary wildly from those estimated from the model runs he uses. For example, in some models a degree of surface temperature rise over 1951–2012 produced twice as much inflow of heat into the oceans as that implied by the model ocean heat uptake efficiency value used by Marotzke. In others it produces only half as much. The same problem may well also arise with climate feedback parameter, but Nic tells me the circularity issue means one can't tell. With the diagnostic data being so poor, you are never going to be able to explain the causes of variation in historical temperature changes between models.

Amusingly, Marotzke declared on the paper's release that "The difference in sensitivity explains nothing really...I only believed that after I had very carefully scrutinised the data on which our graphs are based". It appears that his scrutiny was not careful enough.

I think it's fair to say that this is the last we will be hearing of Marotzke and Forster 2015.

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Reader Comments (63)

Mark T --- the way I read the comment I referred to was Mann took 9 years to the actual PhD (ie. not including the bachelor and Masters degrees)

Feb 6, 2015 at 9:12 AM | Unregistered CommenterRoss


Wikipedia give reasonable details of Mann's academic history. He initially started a PhD in physics (semi-conductors), and obtained an MPhil for the work undertaken prior to switching to a geological/geophysical field. His second attempt at a PhD related to determination of natural cycles in climate, and yielded an MPhil. It is not clear why this one was not completed, as the work (on AMO) appears to me to be well up to the standard needed for a PhD - certainly is a lot more significant and substantive than my own PhD research...

The third (successful) attempt was the hockey stick.

Mann graduated with his Batchelors degree in 1989 and with his PhD in 1998, having been in academia continuously for that time. As such, it is reasonable to say his PhD took 9 years, although clearly there are reasons for this.

More interesting to me is that he was given the opportunity to change direction twice. Also, of course that he was promoted to such a highly responsible position in the IPCC authorship so soon after completion of his PhD

Feb 6, 2015 at 10:09 AM | Unregistered CommenterIan Blanchard

Marotzke and pals offer us a sciencey version of the fundamentalist argument about their assertion that the Bible is perfect inerrant word of God.

Feb 6, 2015 at 12:43 PM | Unregistered Commenterhunter

If Christopher Booker was short of copy for this Sunday's column, he need look no further.

Feb 6, 2015 at 1:58 PM | Unregistered Commenterigsy

Ian Blanchard its easy to think of Mann has dum or stupid because of the way he behaves and manner in which he produces such very poor science.
In pratice you do get smart bast**ds, and evil people with PHd's , in this case he looks like his been smart enough to go hunting acedmic areas which offer him opportunities that his talents would in normal world never offer him . And in AGW he struck 'gold ' he feed the IPCC exactly what they needed and they in turn made him a 'hero'
That he still lacks any real skill in his area , and this is why he so often resorts to bullying , has not actually made any difference and its his good luck that the area in general has standards so low that a snake would have trouble getting under them.

Mann is smart in a very special way , his real weakness is his massive ego , something that does seem to be a requirement for prophets of 'the cause' and its that I will bet which will mean that a day will come when his thrown under the bus by 'the Team' in attempt to save themselves, and that day cannot come to soon.

Feb 6, 2015 at 7:38 PM | Unregistered CommenterKnR

A bit OT, but I have just come across this in an article by Bernard Levin from The Times in 1982. I don't for a moment suggest that environmentalists are Nazis, but the sentiments seem worth quoting: "When I was a student of Sir Karl Popper he once faced us with a conundrum. Suppose, he said, that you could prove to a Nazi that Nazism was erroneous and wicked - really prove it, so that he was entirely convinced. Would you wish to do so, and would you think it worthwhile? Yes, we said, of course. "But what" said the sage "if the Nazi replies "I spit on your proof " and shoots you?" We fell silent at the extraordinary paradox of a mind that rejects mind. We would not, I think, find it so extraordinary today."

Feb 7, 2015 at 10:49 AM | Unregistered Commentermike fowle

Marotzke's method involved seeing how far inter-model differences in the temperature trends in a group of climate model runs could be explained by differences between models in changes in forcing and two "structural elements"

So has he run the models with all the SAME "changes in forcing" and two "structural elements" ??

Is all a bit complicated to follow , imho..

These models: they use random input data where the random seed can be set, right.
They can all be run with the same data , or not ??
the data they run on is external (exogenous) influences on earth right ? (solar input, cosmic radiation)

Feb 7, 2015 at 12:55 PM | Unregistered CommenterMars Shmallow

In December 2014, Willis posted GMT series generated by 42 CMIP5 models, along with HADCRUT4 series, all obtained from KNMI.

We were able to analyze the temperature estimates of CMIP5 models and compare them with HADCRUT4 (1850 to 2014), as well as UAH (1979 to 2014). The models estimate monthly global mean temperatures (GMT) backwards from 2005 to 1861 and forwards from 2006 to 2101.

Bottom Line:
In the real world, temperatures go up and down. This is also true of HADCRUT4.
In the world of climate models, temperatures only go up. Some variation in rates of warming, but always warming, nonetheless.

The best of the 42 models according to the tests I applied was Series 31. Here it is compared to HADCRUT4, showing decadal rates in degrees C periods defined by generally accepted change points.
1850-1878 0.035 0.036 0.001
1878-1915 -0.052 -0.011 0.041
1915-1944 0.143 0.099 -0.044
1944-1976 -0.040 0.056 0.096
1976-1998 0.194 0.098 -0.096
1998-2013 0.053 0.125 0.072
1850-2014 0.049 0.052 0.003

In contrast with Series 31, the other 41 models typically match the historical warming rate of 0.05C by accelerating warming from 1976 onward and projecting it into the future.
Over the entire time series, the average model has a warming trend of 1.26C per century. This compares to UAH global trend of 1.38C, measured by satellites since 1979.

However, the average model over the same period as UAH shows a rate of +2.15C/cent. Moreover, for the 30 years from 2006 to 2035, the warming rate is projected at 2.28C. These estimates are in contrast to the 145 years of history in the models, where the trend shows as 0.41C per century.

Clearly, the CMIP5 models are programmed for the future to warm more than 5 times the rate as the past.

Feb 8, 2015 at 2:25 AM | Unregistered CommenterRon C.

"..the recent divergence of model predictions and observations was all down to natural variability"

Am I being unreasonable to expect that an accurate GCM would include simulations of natural variability that would show up in the confidence spread and therefore that spread would include the actuals?

Based on many years in CompSci, including using some fairly complicated simulations, I would have to say that if the simulation output does not agree with the actuals then clearly something is wrong, missing, or both. Even a climate "scientist" should be able to suss out that much - dontcha think? Of course to accurately solve any problem with a computer you must first completely understand the problem and completely specify the solution. So who'll be first to completely understand the World's climate?

Feb 8, 2015 at 4:42 PM | Unregistered Commenterchris moffatt

Please note that Marotzke & Forster have published a response to Nic Lewis' criticisms:


Feb 8, 2015 at 6:23 PM | Unregistered CommenterEd Hawkins

it's getting colder but because Marotke have run their computer models, it is actually not true what the thermometers tell us, and it is actually getting warmer?

Have I understood it all now ??

Feb 8, 2015 at 6:35 PM | Unregistered CommenterMars Shmallow

chris moffatt your forgetting the first rule of climate 'science ' which is if the models and reality differ in value its reality which is in error. Hear we are just seeing that rule in application , remember this is 'settled ' unchallengeable 'science' where the only thing a research paper should do is seek to prove how its 'worse then we thought ' and show others the authors are 'true believers' who should keep their seats on the gravy train .

Feb 8, 2015 at 9:20 PM | Unregistered CommenterKnR

The only problem with this posting all all past posting using GISS, Hadcrut ect is that its all fraudelant data, so its basically meaningless including ALL the NATURE ect publications. I think that this is now well established and is going to be more so day by day
There is no pause there never was one because the temperatures before DID NOT RISE except if they were made to rise by fraudelant adjustments. (except RSS and AMSU dat which is only from 1979 and totally irrelevant in climate terms. Unfortunately probably all the work by Mcintyre, Watts, The Global warming swindle ectt is also useless because they all assumed the data to be correct (a rise) and have been had as most "skep[tical" seem to continually quote or use this data to justify a pause. Please wake up you've really been had.

Feb 8, 2015 at 11:02 PM | Unregistered Commentereliza

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