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Hockey Stick Groundhog Day

August 1, 2019

By Paul Homewood



Paul Matthews has more analysis on the latest studies, which purportedly claim that “current warming is unparalleled in the last 2000 years”:



Some ancient history

Fifteen to twenty years ago, Michael Mann and colleagues wrote a few papers claiming that current warming was unprecedented over the last 600 to 2000 years.  Other climate scientists described Mann’s work variously as crap, pathetic, sloppy, and crap.  These papers caught the interest of Stephen McIntyre and this led to the creation of his Climate Audit blog and the publication of papers pointing out the flaws in these hockey stick reconstructions. In particular, Mcintyre and his co-author Ross McKitrick showed that the method used by Mann and colleagues shifted the data in such a way that any data sets that showed an upward trend in the 20th century would receive a stronger weighting in the final reconstruction.  With this method, generation of a hockey-stick shape in the temperature reconstruction was virtually guaranteed, which M&M demonstrated by feeding in random numbers to the method.

As climate scientist Rob Wilson put it in an email,

The whole Macintyre [sic] issue got me thinking about over-fitting and the potential bias of screening against the target climate parameter… I first generated 1000 random time-series in Excel…   The reconstructions clearly show a ‘hockey-stick’ trend. I guess this is precisely the phenomenon that Macintyre has been going on about.

But the climate science community admitted nothing in public. One climate scientist wrote one of the most revealing emails:

-How should we deal with flaws inside the climate community? I think, that “our” reaction on the errors found in Mike Mann’s work were not especially honest.


This is all ancient history, and the issue is discussed in detail in Andrew Montford’s book, The Hockey Stick Illusion.

Two new papers

So, I felt a strange sense of deja vu or Groundhog Day when I heard from the BBC that ‘new’ research had found that current warming was unparalleled in 2,000 years. The two papers are written by the PAGES2k team, headed by Raphael Neukom. They are Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era and No evidence for globally coherent warm and cold periods over the preindustrial Common Era (both paywalled). They use data from a 2017 paper by themselves, A global multiproxy database for temperature reconstructions of the Common Era.

The PAGES2k data has come in for a lot of criticism at Climate Audit. There are numerous problems, such as inconvenient data being deleted or used upside-down, or the use of ‘stripbark’ data, against the recommendation of an NAS panel.

 Read Paul’s full account here.


Steve McIntyre is already on the case, and one of the major problems with this new study is its use of “screening”.

Paul neatly summarises the problem here:


The screening fallacy

The problems with proxy screening were very widely discussed a few years ago at several climate blogs, including Lucia’s Blackboard, Jeff’s Air Vent, and Climate Audit. But some of you may have forgotten, and some of you may be too new to the game, so here’s a refresher. I’ll try to explain it as simply as possible, so that even a BBC environment correspondent could understand it.

Suppose that you have a number of time series, covering the last 2000 years, coming from annual tree ring measurements or anything else. You think that they might be related to temperature, that is, be a ‘proxy’ for temperature. Or at least some of them might be. How can you check? Well, you have a reasonable idea of the temperature rise over the last 100 years from thermometer measurements, so you can compare each series against that, to check if it matches. Then you might discard those that don’t fit well (screening) or assign a weighting to each one according to how good the match is.

This sounds at first glance like a good idea. But there’s a problem. It’s actually a lousy idea. With this method, your data sets could be just random noise, and you’d still get a hockey stick result! A picture is worth a thousand words here. This one was posted by commenter “Jeez” at Climate Audit in 2012 (in the case discussed there, the paper, Gergis et al, was withdrawn after claims that they had avoided the screening fallacy were shown to be false).

Suppose that you have six time series, as shown in the first six diagrams. The first four go down-up, up-down, down-down, up-up, and the next two are flat. You carry out your screening test, and you find two of them that match fairly well with the 20th century temperature record – that’s the two with the red circles. Then you average those two, and you get the bottom picture – the hockey stick that you wanted! The two oppositely directed parts at the left-hand end (grey lines) average out to the flat (dotted) line. You can add in the two flat ones as well if you like, they won’t make any difference to the picture. In climate-science-speak, your reconstruction is “robust”!




I would thoroughly recommend Andrew Montford’s book, The Hockey Stick Illusion, for anyone who has not read it.

It explains in simple layman’s terms all of the statistical jiggery pokery behind Michael Mann’s hockey stick, along with the unreliability of many of the proxies.

Above it all, it exposes all of the political shenanigans going on in the background, in Mann’s attempts to stop Steve McIntyre and Ross McKittrick from first getting access to the data, and secondly from getting their findings published.

  1. Sheri permalink
    August 1, 2019 11:13 am

    If you want to illustrate clearly why proxies are not at all scientific and accurate, build a new apartment building using people’s feet as the proxy for a tape measure for long distances and their hands as proxies for the shorter distances (window inserts, etc). The measurements will be “pretty close” and I’m sure the building will be a construction masterpiece.

    • Adrian permalink
      August 1, 2019 11:24 am

      Is this why the pyramids are all ‘pointy’? I always wondered.

    • Gerry, England permalink
      August 1, 2019 2:03 pm

      I had a lining contractor that measured out parking bays with his. All went well until he did a whole parking zone wearing the wrong boots….

  2. August 1, 2019 11:36 am

    I read Andrew Montford’s book, ‘The Hockey Stick Illusion’ at least twice (482 pages, including contents and references etc). I would highly recommend it and it is more gripping than most works of fiction.

    • rms permalink
      August 1, 2019 12:07 pm

      Here! Here! Agree! Andrew’s book is a masterpiece. Pn par with other great writers of similar genre, e.g John McPhee writing on geology, and another special book on Mississippi river “Control of Nature”. Read that one to better understand what happens when we try to do a number on Mother Nature. Relevant to “combatting climate change” saga.

    • August 1, 2019 12:20 pm

      Along with that book (which I have), I would recommend “A Disgrace to the Profession””the World’s Scientists in their own words on Michael E. Mann, His Hockey Stock, and Their Damage to Science, compiled and edited by Mary Steyn (2015, Stockdale Publishing, LLC). It is a compendium of comments from many scientists on the “work” of Mann and serious refutations. Some of these folks are believers in man-caused climate change, but highly critical of Mann’s methods and conclusions.

      I have filled my copy with underlines, stars in the margins, highlights, paperclips and pages noted inside the covers.

      It was a valuable resource due to the number of scientists quoted for a talk I gave in 2016: “Science Gets a Slap-Shot from Michael Man’s Hockey Stick.”

      • August 1, 2019 12:23 pm

        Let us try a corrected version:
        Along with that book (which I have), I would recommend “A Disgrace to the Profession” the World’s Scientists in their own words on Michael E. Mann, His Hockey Stick, and Their Damage to Science, compiled and edited by Mark Steyn (2015, Stockdale Publishing, LLC). It is a compendium of comments from many scientists on the “work” of Mann and serious refutations. Some of these folks are believers in man-caused climate change, but highly critical of Mann’s methods and conclusions.

        I have filled my copy with underlines, stars in the margins, highlights, paperclips and pages noted inside the covers.

        It was a valuable resource due to the number of scientists quoted for a talk I gave in 2016: “Science Gets a Slap-Shot from Michael Man’s Hockey Stick.”

  3. jack broughton permalink
    August 1, 2019 12:11 pm

    The fake news is intensifying. Last night News at 10 on ITV spent at least 10 minutes howling about the coming armageddon: heavy rain and flooding and high temperatures all because of global warming: unprecedented weather events, etc. Not a mention of the fact that the UK is a miniscule player in this field nor a balancing viewpoint on the “proven science”. How low can the depths of junk-journalism go?

    Fortunately, I was enjoying a nice glass of wine, so the TV survived.

  4. Jackington permalink
    August 1, 2019 12:26 pm

    The hockey stick is like the Brexit backstop – indestructible; will we ever be rid of them? Too many supporters I guess, BBC, Guardian, channel 4 and all academe.

    • Sheri permalink
      August 1, 2019 6:36 pm

      Any rational, well-trained scientist would immediately question their results if they got a “hockey stick”. Such graphs don’t occur in the science world often. In fact, in college, presenting a graph like the hockey stick without pages of justifications and calculations would get one flunked. It’s an extraordinary claim with virtually no evidence.

  5. JimW permalink
    August 1, 2019 12:29 pm

    I wonder what will happen if Trump gets re-elected? ‘They’ have been following the ‘green’ path a long time to capture total power, I doubt ‘they’ will give up easily.

    • Gerry, England permalink
      August 1, 2019 2:05 pm

      If the logic follows from Canada and Australia, going on the save the planet at vast cost ticket is a surefire loser.

  6. August 1, 2019 12:49 pm

    Lipstick on the pig time again. Still a pig though.

  7. Jack Minnock permalink
    August 1, 2019 1:04 pm

    When I worked and came across computers, I asked the designer on how the data was collated and how could you confirm if the result was was right or not. He replied with the acronym, SISO, explained its, S*** in, S*** out, never trusted a program after that.

  8. August 1, 2019 1:20 pm

    In an Editorial – “The great climate conundrum”

    The ‘hockey stick’ is dismissed –

    ‘Climate variability during the past two millennia — the Common Era — has been a subject of intense debate for more than two decades. The early notion of a hockey-stick-shaped temperature record, with little variability and cool temperatures in the early part of the record (the ‘handle’), followed by a steep rise in temperature over the final 150 years or so, has long been replaced by a much more nuanced view’

    There was a sharp increase in global temperature between about 1980 and 2000 –

    ‘The 20th century, not unexpectedly, is unique: it has the largest global-mean warming trends over periods of at least 20 years.’

    Little or no real progress has been made to explain what happened –

    ‘It is clear that the late 20th century stands out in the context of the Common Era. Disentangling exactly where we should set the boundary between natural, pre-industrial climate and the period of substantial human influence is likely to remain challenging for some time to come’

    This also means the exponential plethora of ‘grants’ and research papers will continue.

    The fossil ‘fuel’ resources are vital to civilisation as we know it, and It therefore makes sense make use of renewables where reasonable and for the right reasons.

    I’m not convinced that the connection with climate change and CO2 is as simple as it is made out, but if one assumes that it is part of a real or imagined problem then the focus should be as much on tackling de-forestation.

    National Grid have produced a document titled, ‘Future Energy Scenarios’ –

    This is in my opinion an effort to deflect blame when people realise that they don’t have a secure electricity supply. It is clear though that some of the envisaged changes in the use and management of energy will have profound consequences.

    The BBC is perhaps even more irresponsible than it is biased.

  9. August 1, 2019 1:37 pm

    Just realised –

    ‘Climate variability during the past two millennia — the Common Era — has been a subject of intense debate for more than two decades’

    Try telling that to our national broacaster

  10. August 1, 2019 1:42 pm

    Another flaw in the hype around these papers is the claim that Medieval warming was regional and not synchronized, while warming today is global and happening everywhere. Neither part of that is true.

    Kevin Anchukaitis, a paleoclimatologist at the University of Arizona not involved in the research, says the idea that the Medieval period and Little Ice Age weren’t eras of truly global change has been discussed in previous studies, and the authors’ recent conclusions support that earlier work. “They were broad warm and cold periods, within which different regions of the globe had their coldest or warmest periods at different times. For the Little Ice Age, we know this is linked to volcanism,” Anchukaitis says.

    Despite the fact that more data is available to paleoclimatologists than ever before, Anchukaitis believes that significantly more work needs to be done if scientists are to gather a truly global picture of past climate. “To make progress in understanding the climate of the [past 2,000 years], we should move beyond applying a smorgasbord of different statistical methods,” he says via email. Instead, scientists need a renewed effort to gather paleoclimate records from places and times that are underrepresented in compilations like PAGES 2k.

    “The proxy network is largely Northern Hemisphere tree-rings, tropical records (corals) decline rapidly by 1600, and there are relatively few Southern Hemisphere records outside of the Antarctic ice cores,” Anchukaitis says. “So claims about global spatial patterns prior to about 1600, particularly for the tropics and southern hemisphere, must be viewed cautiously.”

    As for present day, the diversity of climate patterns and trends over the global land surface is evident in the Koppen climate zones.

  11. Don B permalink
    August 1, 2019 4:34 pm

    Alaska’s Mendenhall Glacier is melting and retreating, exposing the trunks of ancient trees. Carbon dating has revealed that some trees were growing about 1,000 years ago, and others more than 2,000 years ago. In other words, the Medieval Warm Period and the Roman Warm Period were both warmer than our Modern Warm Period, and were warm long enough for forests to flourish where the Mendenhall glacier has recently been. That earlier warmth was natural, with no human emissions.

  12. I_am_not_a_robot permalink
    August 1, 2019 10:04 pm

    A question remains whether Mann et al. adopted the fallacious screening procedure — viz. the absurd assumption that some individual trees were reliable temperature proxies during their entire long life and others weren’t simply based on an approximate correlation or not with the supposed past 100 years thermometer record — through ignorance or malfeasance.
    It is debatable which would be worse.

    • I_am_not_a_robot permalink
      August 1, 2019 11:26 pm

      … as if some trees are honest as the day is long and other trees are inveterate liars.

  13. Coeur de Lion permalink
    August 2, 2019 2:32 pm

    I do so agree about “The Hockey Stick Illusion” and “A Disgrace To The Profession”. Recently the BBC screened a TV programme called “Climate Change – The Facts” which soon became known as “Climate, Change the Facts” as every postulate was shown to be in error and loveable David Attenborough was made to look an idiot. But Michael Mann was prominent. I complained to the BBC and asked could they parade “the most discredited and dishonest scientist on the planet” and asked whether they remembered Climategate at all? In my view spitting in the face of the British public. Got the usual boilerplate reply with a list of Mann’s propositions ‘which are widely agreed’. One was that ‘climate change is happening far faster than we imagined’.
    I smell a conspiracy here. Probably controlled by conspirator Horrorbin (see Montford ‘The Propaganda Bureau’) who is smarting from the results of the BBC’s exculpating of Climategate actors and has a long term plan to engineer justification. “They were right all along – look, Hockey Sticks”

  14. August 2, 2019 4:08 pm

    Reblogged this on Climate- Science.

  15. swan101 permalink
    August 2, 2019 9:19 pm

    Reblogged this on ECO-ENERGY DATABASE and commented:
    Can’t bury the truth for ever….thank goodness. More such revelations will be welcome for those who prefer their facts untarnished.

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