The Hockey Stick and Climate Science

Posted Yesterday to the discussion at Climate Audit on the topic of “The Team Defends Paleo-Phrenology”

It may help …. to understand the nature of the science. It relies on statistical techniques to establish results. These, crucially, depend for their validity on the elimination of bias. If a researcher has faulty data, then the results are undermined. If the researcher is selective in the data, then the results are undermined. It outliers are not eliminated then the results are undermined. This all means that where there is extremely complex data, and problems of measurement, it is extremely difficult to establish conclusions that cannot be overturned. This is both true of economics and of paleoclimate.

I would contend that climate scientists, as a junior scientists, need to learn from other disciplines.
– From accountancy, about sense-checking the data (see link below)
– From research into new drugs, about the necessity for more technicians to collect and collate data, and to experiance dead-ends.
– From law, to distinguish between levels of evidence and distinguish baseless rhetoric from cogent arguement
– Most of all from statistical theory, where you will find you results will have no validity unless you take active steps to eliminate bias. Even then, with complex data, your results may still be later undermined, despite passing a battery of tests.

For all of these reasons, we should accept that the results of research are tentative. We should recognise the limits of our knowledge. In recognising the boundaries, and establishing procedures to quickly identify error, paleoclimate may be able to move forward.

 

The whole hockey stick issue, brought to a head with the Tamino posting, shows the problem of bias. To obtain a temperature reconstruction requires using data that usually gives a very weak signal indeed. Therefore any data needs to be carefully collected and every conceivable bias removed. It is only by eliminating bias that the statistical analysis can begin. In many cases there will be no significant results. Much painstaking work will achieve a dead end. And there is the rub. Careers are not made by failing to get a result. In this arena phenomenal fame and prestige can come to those who produce results that fortify the consensus. And there is plenty of recognition to those with supporting roles as well.

The original MBH98 may never have emerged in a more muted form if an expert reviewer had asked how such a novel result could be reconciled with the existing view that there was a medieval warm period. Hence my point about sense-checking in the previous blog posting. Similarly the comment that the 20th century warming was unprecedented should be answered with how do you know that? Read the Hockey Stick Illusion and you will find that the claim lacks scientific validity.  

If climate science it to mature it needs more painstaking data collection and analysis. As a science, it needs to find the current boundaries and limits of our current knowledge.

For those who believe that the Hockey Stick Team still have something worthwhile to say, should start with Steve McIntyres repost of “Tamino and the Magic Flute“. Compare that with Tamino’s posting “The Montford Delusion”.

Look at

1. Who gives the fullest answers?

2. Which side evades the points, or attempts sleight of hand?

3. How are contrary or neutral points treated. Clue – look at how Judith Curry (who is trying to remain neutral) is treated. Further, look at how contrary opinions are treated.

4. Finally who are the real deniers in all of this?

Tamino v. Montford – A Sense-Check

Clarification – This post is an attempt to say two things – but badly.

First, a simplistic verification of a global temperature reconstruction is to cross-check against local temperature reconstructions from around the world. These, on average, strongly contradict the hockey stick.

Second, Tamino’s claim is essentially McIntyre has just been taking pot-shots at sound science. Instead McIntyre has looked at all the steps in making a reconstruction, and found all wanting.

So what of a neutral lay-person trying to compare the Montford’s Hockey Stick Illusion and Tamino’s debunking? From my accountancy experience, it is normal to try to get a sense-check. What is the expected result? If the actual is different from the expected, then difference needs to be reconciled. The MBH98, MBH99, and the subsequent reconstructions in the book, completely overturned perceived thinking, so there needs to be a sense-check to make sure the results are valid. 

 The sense-check for the global temperature reconstructions can be from localized reconstructions from around the world, to see if the global reconstruction replicates the typical pattern. A website, CO2science.org, documents peer-reviewed articles estimating temperatures in the medieval warm period. For those that have a temperature estimate, those that agree with the hockey stick – that temperatures were lower than today – are out-numbered 5 to 1 by those that say temperatures were higher in the MWP. The raw median, median, and mode values are that temperatures were about 0.75oC warmer than today. The weaker, qualitative, studies have a similar picture. Those that suggest that temperatures in the MWP were similar to or lower than today are outnumbered more than 4 to 1 by those that suggest temperatures were higher. So when the more scientific, global, reconstructions come up with a novel, contrary, result, there needs to a full reconciliation to explain why. Without such an explanation, we just have McIntyre’s multi-layered* findings that the global reconstructions are critically flawed stands.

*McIntyre’s findings are multi-layered, including.

a)      Hockey Stick shapes were given undue weighting by the short-centering of the PC analysis. For instance, McIntyre calculated that Sheep Mountain had 390 times the weighting of Mayberry Slough (p113-114). Of the 112 original proxies in MBH9, just 13 had a hockey stick shape. Tamino does not counter this, only looking at the 22 longer hockey stick series, made up of individual series, such as Gaspe, along with regional combinations such as NOAMERPC1.

b)      Dodgy data and infilling. Looking across the columns of data, McIntyre noticed identical data in adjacent columns, as though infilling had taken place. (p78-81)

c)      Many of these series were based on old data. If Mann had used the most recent data available in 1998, could the final Hockey Stick have been less pronounced? (p83-84)

d)      Some of the most important original proxies were flawed.

  1.  
    1. Gaspé has better data, but was unpublished. (p174) It also had an alternative proxy with better data in Alaska. (More here)
    2. Sheep mountain had updated proxies that fails to show an HS (p 357-361)
    3. The Graybill bristlecone series had a number of flaws (e.g. p121-125 & p353-357)

e)      The failure of alternative reconstructions. (Chapter 10).

f)        There was considerable evidence of biases in the data selection in the proxies (along with small sample sizes); the selection of the proxies in the reconstruction; and the short-centring which gave rise to hockey sticks on random data 99% of the time. Given this, any measure of correlation statistic was rendered largely meaningless. McIntyre did not explore this. However, Montford provides evidence that the verification statistic used was highly irregular in the disciplines outside of climate science. (e.g. p156-164)  Latest – McIntyre shows the evidence that to suggest verification statistic was cherry-picked.

That is, the selection of data in the proxies, the proxy selection, the bias by short-centering, and the selection of verification statistic are all different levels in establishing a reconstruction, and all shown by McIntyre to have failed.

For a different take – which side pursues scientific understanding, see the follow-up https://manicbeancounter.wordpress.com/2010/07/27/the-hockey-stick-and-climate-science/

Tamino v Montford on the Gaspé series

Have just finished reading A.W. Montford’s (alias Bishop Hill) The Hockey Stick Illusion. Although I thought it excellent, and agree with the reviews (e.g. Air Vent), I thought I would look for contrary opinions, to allow me to compare and contrast the different sides. It just so happens that Tamino has posted a critical review at Real Climate blog on July 22nd. Bishop Hill has responded.

In the spirit of allowing you to make up your own mind, let me present one aspect, which does not need a scientific background to evaluate.

Tamino claims that McIntyre rejects Gaspé because

 “This particular series doesn’t extend all the way back to the year 1400, it doesn’t start until 1404, so MBH98 had extended the series back four years by persistence — taking the earliest value and repeating it for the preceding four years. This is not at all an unusual practice, and — let’s face facts folks — extending 4 years out of a nearly 600-year record on one out of 22 proxies isn’t going to change things much.”

 

I would agree with Tamino, if that was the only problem with Gaspé. But other problems Montford recounts.

  1. It had the biggest hockey stick of any of the 112 series. 1975 was 3.05 standard deviations from the series mean. Only 12 others had any sort of hockey stick shape. (p.75)
  2. It was included twice in the proxies – once as part of the North American PC series and once on its own. (p.140).
  3. It did start in 1404, but until 1421 relied on a single tree, and two up to 1447. The original authors “had not used the early portion of the series at all in their own reconstruction”, but Mann had. (p165.)
  4. Mann’s own claim for its’ inclusion was that the study represented the northern treeline. But Gaspé was well south of the treeline. As a sensitivity analysis, McIntyre replaced Gaspé with the Sheenjek River Series in Mid-Alaska. It was further north and had more trees. When this was replaced, the medieval warm period re-appeared. (p.166).*
  5. McIntyre showed “that you could only get rid of the Medieval Warm Period by using the Gaspé series twice and by including the unreliable early portion, and by extending this highly dubious data back to the start of the fifteenth century.”
  6. An updated study was done taking the data to 1991, instead of 1982. There was nothing like the same growth spurt in recent times. The data went unpublished, and the author claiming to have lost the location. So the results could not be independently replicated. (p.174).
  7. Montford says in reply to Tamino

“The observation that “McIntyre argued that the entire Gaspe series should be eliminated because it didn’t extend all the way back to 1400” is wrong. MBH had its steps starting at 50-year intervals. Gaspe should therefore have been in the 1450 step not the 1400 one.”

 

From my simple view, the criticism of the Gaspé proxy series is multilayered. It was used inappropriately; there was a better proxy available (or an update); it was clearly an outlier; and was used twice.

Finally, Steve McIntyre has already criticised Tamino on Gaspé here. McIntyre makes the additional point

“The Gaspé series is a cedar chronology. There is no botanical evidence that cedars respond linearly to warmer temperatures. World experts on cedar are located at the University of Guelph, Ross McKitrick’s university. Ross and I had lengthy discussions with these cedar experts about this chronology – they said that cedars like cool and moist climate.”

 

* Gaspé is around 49o North (same as Paris), Sheenjek River 65o North. (same as Iceland).