The Curious Case of the Hockey Stick that Didn’t Disappear. Part 1: The Police Lineup

But who killed the Medieval Warm Period?

Before we begin the investigation into the usual suspects, some background for people who those who don’t follow climate science closely, which certainly includes most of the disinformers and  apparently at least two statisticians.

  1. There is a high probability that the recent warming is unprecedented for 1000 years and probably much longer (see “Sorry disinformers, hockey stick gets longer, stronger: Earth hotter now than in past 2,000 years” and here and here).
  2. This conclusion is based on an analysis of multiple proxies for temperature, which individually engender much uncertainty and collectively still engender a fair amount.  It is a canard of Curry-esque proportions to assert that scientists have not clearly explained the nature and extent of these uncertainties. They have bent over backwards to do so.
  3. The temperature trend in the past millennium prior to about 1850 is well explained in the scientific literature as primarily due to changes in the solar forcing along with the effect of volcanoes, whereas the recent rise in temperature has been driven primarily — if not almost entirely — by human activity (see Scientist: “Our conclusions were misinterpreted” by Inhofe, CO2 — but not the sun — “is significantly correlated” with temperature since 1850 and Part 3 [to come]).
  4. Absent human emissions, we’d probably be in a slow long-term cooling trend due primarily by changes in the Earth’s orbit — see Human-caused Arctic warming overtakes 2,000 years of natural cooling, “seminal” study finds.
  5. Thus, the rate of human-driven warming in the last century has exceeded the rate of the underlying natural trend by more than a factor of 10, possibly much more.  And warming this century on our current path of unrestricted greenhouse gas emissions is projected to cause a rate of warming that is another factor of 5 or more greater than that of the last century.  We are punching the climate beast — and she ain’t happy about it!

Back to the investigation of attempted murder — and the ‘innocent victim’ who may have been killed in the attempt.  The folks who don’t follow climate science closely have been trumpeting a new paper “A Statistical Analysis of Multiple Temperature Proxies: Are Reconstructions of Surface Temperatures Over the Last 1000 Years Reliable?” by McShane and Wyner about to be published in Annals of Applied Statistics.   Supposedly it is fatal to the Hockey Stick.

Here is the police lineup.  Take a look at three independent reconstructions of the past one to two  millennia and the new one by the statisticians — and see if you can pick out which one allegedly killed the others (with apologies to Deltoid):

mann1.jpgLake Tanganyika lake surface temperature



Did you figure out who the alleged killer was?  Yes it is the final reconstruction (of Northern Hemisphere temperatures) that is supposedly our Keyser Söze.  The helpful graphic overlay is by Deltoid from his post, “A new Hockey Stick: McShane and Wyner 2010” [the comments contain many gems].

While WattsUpWithThat thinks this paper is so important that he has been running a post on it at the top of his blog for days, he conveniently omits this rather remarkable statement from the authors:

Using our model, we calculate that there is a 36% posterior probability that 1998 was the warmest year over the past thousand. If we consider rolling decades, 1997-2006 is the warmest on record; our model gives an 80% chance that it was the warmest in the past thousand years.


The judge has no choice but to dismiss the primary murder charge because the Hockey Stick still lives.

But there appears to have been some collateral damage.  The new model seems to have done away with that favorite of the anti-science crowd, the Medieval Warm Period, which I suppose could be accidental homicide, except that would have required the victim to have existed in the first place, which is at best an open question.

Indeed, this new reconstruction shares a similar form to the one immediately above it, of the Arctic, from the 2009 Science paper, “Recent Warming Reverses Long-Term Arctic Cooling.”  So let me excerpt some of the  analysis and commentary surrounding that paper:

Arctic temperatures in the 1990s reached their warmest level of any decade in at least 2,000 years, new research indicates. The study, which incorporates geologic records and computer simulations, provides new evidence that the Arctic would be cooling if not for greenhouse gas emissions that are overpowering natural climate patterns.

So reports the National Center for Atmospheric Research (NCAR), which coauthored the study.  The Washington Post story notes:

The analysis, based on more than a dozen lake sediment cores as well as glacier ice and tree ring records from the Arctic, provides one of the broadest pictures to date of how industrial emissions have shifted the Arctic’s long-standing natural climate patterns….

It’s basically saying the greenhouse gas emissions are overwhelming the system,” said David Schneider, a visiting scientist at the National Center for Atmospheric Research and one of the Science article’s co-authors.

The same could be said about the entire planetary ecosystem “” on our current path, we’re going to overwhelm the whole system (see “Intro to global warming impacts: Hell and High Water“).  Indeed, in some sense we already have, as a number of climate scientists have pointed out.  The NYT‘s Andy Revkin interviewed Thomas Crowley, a climate specialist at the University of Edinburgh:

“I would say that this is another piece of evidence that strengthens the argument that humans are now capable of preventing the onset of a future ice age,” he told me. Another scientist holding this view is James E. Hansen of NASA, whom I interviewed about the timing of the next ice age in 2003.

The Arctic study suggests (again) that the Medieval warm period was limited to only a part of the Northern Hemisphere, and that recent human-caused warming is quite outside the boundary of the last two millennia:

Darrell Kaufman of Northern Arizona University, the lead author and head of the synthesis project, says the results indicate that recent warming is more anomalous than previously documented.

“Scientists have known for a while that the current period of warming was preceded by a long-term cooling trend,” says Kaufman. “But our reconstruction quantifies the cooling with greater certainty than before.”

Some of our leading climate scientists say this Arctic reconstruction is an especially important paper, as the WP piece notes:

Mark Serreze, director of the National Snow and Ice Data Center at the University of Colorado at Boulder, said the study was significant because it helps confirm scientists’ current understanding of how the earth’s climate has changed over millennia.

“It’s not that we don’t know how the climate works, it just we didn’t have anyone at that time measuring the climate forcing then,” referring to 2,000 years ago. “Climate doesn’t change all by itself for no good reason. Something has to force it.”

Precisely.  I will return to this point in Part 3.

Robert Correll, who chairs the Arctic Climate Impact Assessment, said the paper in Science will likely “in the long haul become a seminal piece in the scientific literature” because it allows other climate researchers “to set their work in a long time scale.”

And Revkin’s print piece underscores the danger:

Jonathan T. Overpeck, a study author and climate specialist at the University of Arizona, said the rising concentration of long-lived greenhouse gases guaranteed warming at a pace that could stress ecosystems and cause rapid melting of Greenland’s great ice sheet.

The fast rate of recent warming is the scary part,” Dr. Overpeck said. “It means that major impacts on Arctic ecosystems and global sea level might not be that far off unless we act fast to slow global warming.”

Bottom line:  It appears to remain the case that, with the appropriate caveats, there is a high probability the recent warming is unprecedented for 1000 years and probably much longer — and that the current rate of warming is unprecedented in the recent paleoclimate record.

In Part 2,  I am planning to reprint a forthcoming forensic debunking of statisticians’ paper.  Feel free to post any critiques you have in the comments section.  It does not look like a terribly strong paper given how much it cites Wegman and McIntyre (talk about your ‘usual suspects’) — and the fact that it cites Al Gore’s movie  and three Wall Street Journal pieces,  which must be a first for that journal (and probably any other publishing pieces on paleoclimate reconstructions)!


45 Responses to The Curious Case of the Hockey Stick that Didn’t Disappear. Part 1: The Police Lineup

  1. Lamont says:

    The other alarming thing about that picture is that even if we hold CO2 constant at 380-400 ppm there’s another ~1C or so of warming “in the pipeline”, so we’re on a heading for the very upper right corner of that graph if we just hold CO2 level.

  2. DeNihilist says:

    Dr. Romm, interesting post and paper. Too early to really comment on it yet, but if nothing else, it is kinda nice to see PhD statisticians getting involved, as per Oxenburgh and Wegman, among others, suggestion. Thanx for the heads up.

  3. Vorlath says:

    The reconstruction was done to show how it should have been done. But it states quite clearly that it can’t be used for anything. Random data performs better than that graph for correlating to instrumental temperatures.

    Keep showing the graph if you must, but skeptics will just laugh at this post hysterically.

    [JR: Best. Comment. Ever! Yes, skeptics are hysterical. Seriously, Watts showed the graph! And bragged on it! Anyway, I don’t write this blog for the anti-science disinformers. They laugh at those who devote their lives trying to explain science and prevent the needless and preventable suffering of billions. They are indeed hysterical, but not because of this graph.

    The paper itself will be shown to be risible. But the notion that people would write a paper and publish a graph that they don’t want people to reprint is risible in itself.]

  4. homunq says:

    Vorlath, you are wrong. There are giant error bars quite visible on that graph. Within those error bars, it is pretty reliable. That means that anybody who says that the last decade was not the warmest in a thousand years, or that the last century doesn’t show the fastest change in either direstion in that same period, is lying.

    The correlation of random data with anything is 0. Instrumental temperature and that graph have both gone up in the past century, so their correlation is above 0. You may be right about the hysterics of septics, but you are simply wrong about that graph.

  5. riverat says:

    Joe, I looked at the lineup in the top picture and thought to myself there should have been a 7 footer on then end. It would look more like a hockey stick then. :)

  6. johna says:

    Ötzi the Iceman would have something to say on this, if he could talk. Yet
    his remains tell a story despite his silence. He was buried in an Alps snowbank
    for 5,300 years. In all that time it never thawed, until he melted free in 1991.

  7. Lamont says:

    Rabett makes this point:

    “Since the proxies are affected by the local temperatures (and precipitation and some other things that are all local) and the local temperatures varied much more strongly than the global in most cases, and surely for those cases where the proxies vary strongly, this is kindergarten work.”

  8. Nick says:

    Good point,Johna. Ignore your paleo proxies if you want,and look at Otzi,and Grosjean et al 2007 as well.

    “The preservation of Neolithic leather indicates permanent ice cover at [the Schnidejoch] site from ca.4900 calendar years BP until AD2003,implying that ice-cover was smaller in 2003 than at any time during the last 5000 years.”

    Premature,ignorant triumphalism, and not a word on methodolgical flaws,Vorlath?

  9. wag says:

    The key to the hockey stick debate is that it doesn’t matter. We care about the future increase in temperature, not the 1 degree “blade” on any existing hockey stick that we’ve already experienced. I’ve drawn a rough new graph showing what a hockey stick would look like with a modest 3.75 degree C increase over the 21st century (it’s pretty terrifying):

  10. sod says:

    Using our model, we calculate that there is a 36% posterior probability that 1998 was the warmest year over the past thousand. If we consider rolling decades, 1997-2006 is the warmest on record; our model gives an 80% chance that it was the warmest in the past thousand years.

    let us al watch how “sceptics” wil completely ignore this phrase in their discussion of the paper.

    and it is already funny to watch the “random data is better” claim, over and over again. (remember, random data has a 50% chance of bending DOWN DOWN DOWN at the end!)

    ps: and what are you actually doing here Joe? you are supposed to delete all comments on this subject, not write a post on it! at least that is what the conspiracy theory says (including of course Judith Curry…)

  11. Lamont says:

    DC has some thoughts in one comment about the issues:

    Unfortunately, it takes about 30 seconds for Watts to take a pile of quotes out of context and declare victory, while it takes many hours of work for any kind of serious commentary on the paper to get produced.

  12. Doug Bostrom says:

    According to JC M&W looks like “the real thing,” McShane and Wyner are two “leading statisticians.” Pom-poms, much?

    Measure the emotional importance of McShane & Wyner item by how many aggrieved contrarians show up here to tout its importance and squeal if it is criticized.

  13. John Mason says:

    Copy of my post over at Tamino’s blog:

    I did try posting on WUWT last night, not something I do often, suggesting that people waited until the paper was published and other specialists in the relevant field had formally responded before arriving at a considered opinion – as per standard academic procedure.

    It didn’t make me that popular, although some of the membership did seem to broadly agree.

    I feel that this practice of circulating a draft MS around the blogosphere prior to publication – for any reason – is an unwelcome development in this or any other scientific discipline. It encourages the exact opposite to objectivity.

    Cheers – John

  14. John Mason says:

    Re – objectivity BTW – I was responding to some WUWT members who – in less time than it would take to read the abstract – were already doing high-fives!

    I see Deepclimate is going to post a review of the M&W MS later today as well…

    Cheers – John

  15. Prokaryotes says:

    Just came across this book:

    Belief, being a lively conception, can never be entire, where it is not founded on something natural and easy.

    This I take to be the true state of the question, and cannot approve of that expeditious way, which some take with the sceptics, to reject at once all their arguments without enquiry or examination. If the sceptical reasonings be strong, say they, it is a proof, that reason may have some force and authority: if weak, they can never be sufficient to invalidate all the conclusions of our understanding. This argument is not just; because the sceptical reasonings, were it possible for them to exist, and were they not destroyed by their subtility, would be successively both strong and weak, according to the successive dispositions of the mind. Reason first appears in possession of the throne, prescribing laws, and imposing maxims, with an absolute sway and authority. Her enemy, therefore, is obliged to take shelter under her protection, and by making use of rational arguments to prove the fallaciousness and imbecility of reason, produces, in a manner, a patent under her band and seal. This patent has at first an authority, proportioned to the present and immediate authority of reason, from which it is derived. But as it is supposed to be contradictory to reason, it gradually diminishes the force of that governing power and its own at the same time; till at last they both vanish away into nothing, by a regulax and just diminution. The sceptical and dogmatical reasons are of the same kind, though contrary in their operation and tendency; so that where the latter is strong, it has an enemy of equal force in the former to encounter; and as their forces were at first equal, they still continue so, as long as either of them subsists; nor does one of them lose any force in the contest, without taking as much from its antagonist. It is happy, therefore, that nature breaks the force of all sceptical arguments in time, and keeps them from having any considerable influence on the understanding. Were we to trust entirely to their self-destruction, that can never take place, until they have first subverted all conviction, and have totally destroyed human reason.

  16. Raul M. says:

    Once read a book by a noble prize winner who
    described the travels of an oriental monk who
    went on a journey following the invasion of
    his religion. He traveled during the story
    through India in the late 1800’s.
    His training gave him the ability to do a
    circular drawing of the ways of the world.
    And as he traveled he added a sketch of the
    main way of the area and the space between
    the sketches showed distance traveled.
    Sort of an art to form what could have been
    called the circle of life.

  17. Eli Rabett says:

    Martin Vermeer put it simply for Eli

    My explanation at link for why the M&W reconstruction is erroneous, was a little too simple. It’s the Wabett who gets it completely right: the fundamental error is calibration only against a hemispheric average, when local data — the 5×5 degree grid cells of instrumental data as used by Mann et al. — provide a so much richer source of variability — i.e., signal — to calibrate against.

  18. Raul M. says:

    I’ve no real training in drawing the circle of life,
    but I think that the artist could place size to the
    individual sketches and show their position in relation
    to the other sketches in a overall circular pattern
    to show significant or the most dominant feature of
    a given area.
    In that no roads are depicted in the drawing would
    show the transitory nature of such.
    That the natural features of the environment would
    contribute to or encompass the central feature of
    the location or the ability for society to survive
    could be said to be the deciding feature of the
    direction and essence of the sketch.
    For the nature would have to be there for feature
    to exist and all would know of the direction to
    It is said that it takes great time to make a comparable
    circle of life drawing.

  19. Raul M. says:

    Back in the 60’s travel groups did something
    like the circle of life overlayed onto the
    map of Florida. But if the landscape changes to
    fast for the city to be known for some tourist
    attraction, some could say it is in bad taste
    to mention the change and to just leave it off
    of the map. But, still revisionist history going
    all the way to the old tourist maps?

  20. Raul M. says:

    Possibly a circle of life drawing of a person
    could show the most important aspects of the
    person’s existence as the person would see it.
    Say a great person with the major changes the
    person has led into being sketched in a circular
    pattern around the person.
    Some people are so influential that the changes
    could be shown with multiple landscape photos.
    Alternate photos could depict the leavings
    that the changes entailed.

  21. Raul M. says:

    Or a biologist could do a circle of life drawing
    about a product. Showing the various disturbances
    to life (disease of death) following the life
    cycle of the product (product production and
    the trashing of the product.)

  22. Mike says:

    @ John Mason says:
    August 17, 2010 at 4:37 am

    “I feel that this practice of circulating a draft MS around the blogosphere prior to publication – for any reason – is an unwelcome development in this or any other scientific discipline. It encourages the exact opposite to objectivity.”


    In many academic fields it is common practice to post papers prior to publication. In math, preprints were sent out by surface mail to interested parties before they were even accepted. Now they are posted on preprint servers. It can take years before a paper finally appears in press. The M&W paper has been accepted and the link is to the journal’s site. BTW, M&W do not work in a “scientific discipline.” They are statisticians at businesses schools (Kellogg at NU and Warthon at UPenn, resp.). The paper should be judged on its merits, which of course is not possible at WUWT.

  23. mike roddy says:

    Wag, #9, good one, thanks, especially the chart. I agree- most of us who are concerned or borderline obsessed with where we are headed are reacting to what even IPCC says about likely conditions in 2100. Not to mention MIT and others, or course.

    The problem appears to be people’s lack of imagination, in addition to fossil fuel disinformation. The future is by definition unknown and abstract. Yet many of those who don’t seem to care about 2100 believe that their future is in Heaven anyway. Go figure.

    Joe, thanks for doing this hard work for the record, and for putting Watts etc in their places once and for all. I hope this blog’s records will be preserved, because it will provide a fascinating and informative history for a long time.

  24. Marco says:

    DeNihilist: that has been done before: Li, Nychka, and Ammann. Major difference with this paper is that the latter two actually know stuff about paleoclimatology.

    Expect the fall-out from this new paper to be that statisticians should involve people who know about the subject the statisticians are investigating…

  25. BillD says:

    I occasionally counsult with statisticians about the analysis of my scientific data and the collaboration can be quite helpful. However, based on my experience, statisticians analyzing scientific data without the help of a scientist would be more likely to make mistakes than scientists who analyze their own data without the assistance of a professional statistician. I get help from statisticians from departments of mathematics and statistics who have experience with scientific projects. I have not tried working with statisticians, such as M & W, who work primarily (I assume) with economic and business data. Even though the M & W paper was submitted to a statistics journal, the review process should include some scientific input.

  26. Jeffrey Davis says:

    There’s a paper working its way that posits that we can learn nothing about climate from temperature proxies.

    Stay tuned for the double-think that imagines that MWP doesn’t depend upon proxies.

  27. Guy says:

    Seems like Otzi was travelling in the Alps at a time when it was as warm or warmer than today; a little over 5,000 years ago, during the Holocene Optimum. Check out JoNova for information on numerous studies that show that the MWP was a global phenomenum.

  28. stroller says:

    Didn’t the two statisticians restrict themselves to working with Mann’s own datasets?

    The datasets the Wegman report so roundly criticised?

  29. Skip Smith says:

    I love how people on both sides of this debate pretend they could understand that paper.

    Blog science. LOL.

  30. Vorlath says:

    @JR: “Seriously, Watts showed the graph! And bragged on it!”

    I never said they would laugh at the graph. I said they would laugh at your post because your interpretation of it is laughable.

    It’s bad enough that the data is being twisted. Now you’re twisting my words.

  31. Prokaryotes says:

    #29, he is called “Ötzi the Iceman” for a reason.
    #30 If you have trouble understanding that there is no debate, try the picture.

  32. #31. Vorlath

    We know what you said. We are laughing at Watts and his fan club — yourself evidently included — for their galactically obtuse inability to read and understand simple text, or simply look at the graphs that they themselves are posting.

  33. Mike says:

    I read this in some blog but don’t remember where, so I may have this wrong: The article will appear in a special issue along with rebuttals.
    The journal is new (four years) and it is a tough market for journals now. So, maybe the editors want to have a “controversial” special issue to drive up sales. Top climate guys would have to submit papers to defend their field which would increase citations. Of course this is speculation. Maybe I’m being too ‘conspiracy theory’ minded.

  34. DeNihilist says:

    Marco, yes!

  35. Nick says:

    GailC, humankind IS currently producing close to as much CO2 as possible,whatever campaigns you or anyone else wants to stimulate. Given ongoing feedbacks,some of which are quite slow,our current anthropogenic CO2 dump will keep us well out of the next global ice age for thousands of years,given the time it takes natural processes to re-sequester fossil carbon.

    There’s plenty of regional evidence from separate studies that we are regionally warmer now than we have been for from 1400 to 5000 years,so we’re winding temperatures back towards the mid-Holocene Optimum very smartly indeed. The big difference for us between then and now is close to seven billion humans,and the severely modified and degraded ecosystems on which they depend,which is a great challenge even in the absence of GW or GC. Burning fossil fuels as fast as possible in order to head in the opposite direction to an ice age cannot be regarded as unambiguously positive policy. Burning fossil fuel as fast as possible in an ad hoc short-termist free market frenzy may be a colossal mis-direction of finite resources,given the energy required to retool to a low carbon future.

  36. Charlie says:

    Keep up the good work!
    But how can we win the general public?
    We have to react to that overabundant amount of untruth about climate change published on YouTube et al.

  37. Doug Bostrom says:

    Guy says: August 17, 2010 at 6:09 pm

    Check out JoNova for information on numerous studies that show that the MWP was a global phenomenum.

    Yeah, but wear your rain gear, she splutters a lot.

    After you’re dry again:

    How Jo Nova doesn’t get past climate change

    Skeptical Science also has a corrective pill for those suffering Nova Pamphlet Syndrome:

    A Scientific Guide to the ‘Skeptics Handbook’

  38. dramcam says:

    You forgot IPCC 1995 that shows the Medieval Warm Period being warmer than currently … but who in their right might would believe a political body like the IPCC ?

  39. Lars Karlsson says:

    The MWP in IPCC 1990 (actually) was based on reconstructions by Hubert Lamb of Central England temperatures.

  40. richard verney says:

    Wag (post 9) raises an interesting point, namely that we are only concerned with the blade not the handle.
    I agree that it is the blade which suggests that temperatures are increasing (during the past 50 years or so) and there are seperate studies that suggest that there may be future problems should the temperature continue to so increase. However, if the handle of the stick suggests that in the past 1000 years temperatures were similar or exceeded those of today, given that in the past CO2 could not explain those high temperatures, it follows that there would be strong evidence to suggest that CO2 is not the villain that it is thought to be(ie., not the cause of the high temperatures).

    [JR: Uhh, not actually true, as I’ve said. What warmth there was 1000 years ago was also forced, just not by human emissions of CO2.]

    Thus if the hockey stick was tilted with the handle being at a temperature similar or above those of today, there would be strong case suggesting that money should not be spent on decarbonising the world (since the evidence would suggest that CO2 is probably not a villain and decarbonising will not in fact restrict the increase in temperature and therefore this would be a futile and wasted exercise) but rather that money should be spent on dealing with the effects of the increase in temperature should the effect of this increase actually cause a real problem.

    [JR: Again, untrue.]

  41. Susan Anderson says:

    Thanks VERY much for this article, particularly its title.

    Wag, that’s terrific, picture being worth millions of words.

  42. Dana says:

    For the record, McShane – who Curry calls “a leading statistician” – just got his PhD a couple months ago.

    Pretty impressive that he’s already made the list of Judith Curry’s Leading Statisticians!

  43. jobnls says:

    For all of you having a hard time interpreting the new M&W paper see this nice walk through.

    [JR: Uhh, there is no walk through there, just a repetition without analysis of a few of the points. But he has one big whopper, which is to fail to see the sharply reduced uncertainty in the past several decades of the temperature record. The response from the real experts is coming.]