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What evidence is there for the hockey stick?

What the science says...

Since the hockey stick paper in 1998, there have been a number of proxy studies analysing a variety of different sources including corals, stalagmites, tree rings, boreholes and ice cores. They all confirm the original hockey stick conclusion: the 20th century is the warmest in the last 1000 years and that warming was most dramatic after 1920.

Climate Myth...

Hockey stick is broken

“In 2003 Professor McKitrick teamed with a Canadian engineer, Steve McIntyre, in attempting to replicate the chart and finally debunked it as statistical nonsense.  They revealed how the chart was derived from "collation errors, unjustified truncation or extrapolation of source data, obsolete data, incorrect principal component calculations, geographical mislocations and other serious defects" -- substantially affecting the temperature index.” (John McLaughlin)

The "hockey stick" describes a reconstruction of past temperature over the past 1000 to 2000 years using tree-rings, ice cores, coral and other records that act as proxies for temperature (Mann et al. 1999). The reconstruction found that global temperature gradually cooled over the last 1000 years with a sharp upturn in the 20th Century. The principal result from the hockey stick is that global temperatures over the last few decades are the warmest in the last 1000 years.

Figure 1: Northern Hemisphere temperature changes estimated from various proxy records shown in blue (Mann et al. 1999). Instrumental data shown in red. Note the large uncertainty (grey area) as you go further back in time.

A critique of the hockey stick was published in 2004 (McIntyre & McKitrick 2005), claiming the hockey stick shape was the inevitable result of the statistical method used (principal components analysis). They also claimed temperatures over the 15th Century were derived from one bristlecone pine proxy record. They concluded that the hockey stick shape was not statistically significant.

An independent assessment of Mann's hockey stick was conducted by the National Center for Atmospheric Research (Wahl & Ammann 2007). They reconstructed temperatures employing a variety of statistical techniques (with and without principal components analysis). Their results found slightly different temperatures in the early 15th Century. However, they confirmed the principal results of the original hockey stick - that the warming trend and temperatures over the last few decades are unprecedented over at least the last 600 years.

Figure 2: Original hockey stick graph (blue - MBH1998) compared to Wahl & Ammann reconstruction (red). Instrumental record in black (Wahl & Ammann 2007).

While many continue to fixate on Mann's early work on proxy records, the science of paleoclimatology has moved on. Since 1999, there have been many independent reconstructions of past temperatures, using a variety of proxy data and a number of different methodologies. All find the same result - that the last few decades are the hottest in the last 500 to 2000 years (depending on how far back the reconstruction goes). What are some of the proxies that are used to determine past temperature?

Changes in surface temperature send thermal waves underground, cooling or warming the subterranean rock.  To track these changes, underground temperature measurements were examined from over 350 bore holes in North America, Europe, Southern Africa and Australia (Huang et al. 2000). Borehole reconstructions aren't able to give short term variation, yielding only century-scale trends. What they find is that the 20th century is the warmest of the past five centuries with the strongest warming trend in 500 years.

Figure 3: Global surface temperature change over the last five centuries from boreholes (thick red line). Shading represents uncertainty. Blue line is a five year running average of HadCRUT global surface air temperature (Huang et al. 2000).

Stalagmites (or speleothems) are formed from groundwater within underground caverns. As they're annually banded, the thickness of the layers can be used as climate proxies. A reconstruction of Northern Hemisphere temperature from stalagmites shows that while the uncertainty range (grey area) is significant, the temperature in the latter 20th Century exceeds the maximum estimate over the past 500 years (Smith et al. 2006).

Figure 4: Northern Hemisphere annual temperature reconstruction from speleothem reconstructions shown with 2 standard error (shaded area) (Smith et al. 2006).

Historical records of glacier length can be used as a proxy for temperature. As the number of monitored glaciers diminishes in the past, the uncertainty grows accordingly. Nevertheless, temperatures in recent decades exceed the uncertainty range over the past 400 years (Oerlemans 2005).

Figure 5: Global mean temperature calculated form glaciers. The red vertical lines indicate uncertainty.

Of course, these examples only go back around 500 years - this doesn't even cover the Medieval Warm Period. When you combine all the various proxies, including ice cores, coral, lake sediments, glaciers, boreholes & stalagmites, it's possible to reconstruct Northern Hemisphere temperatures without tree-ring proxies going back 1,300 years (Mann et al. 2008). The result is that temperatures in recent decades exceed the maximum proxy estimate (including uncertainty range) for the past 1,300 years. When you include tree-ring data, the same result holds for the past 1,700 years.

Figure 6: Composite Northern Hemisphere land and land plus ocean temperature reconstructions and estimated 95% confidence intervals. Shown for comparison are published Northern Hemisphere reconstructions (Mann et al. 2008).

Paleoclimatology draws upon a range of proxies and methodologies to calculate past temperatures. This allows independent confirmation of the basic hockey stick result: that the past few decades are the hottest in the past 1,300 years.

Intermediate rebuttal written by John Cook

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Additional video from the MOOC

Interviews with  various experts


Last updated on 12 October 2016 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

The National Academy of Science's summation of the various temperature proxies are available online at Surface Temperature Reconstructions for the Last 2,000 Years.

Tamino has an interesting blog post Not Alike where he compares the Moberg temperature reconstruction (one of the least hockey stick like reconstructions with a distinct Medieval Warm Period and Little Ice Age) to modern temperature trends. He finds modern temperatures are 0.53 deg.C hotter than medieval times and the modern warming rate is 64% greater than the fastest rate in medieval times.

The NOAA Paleoclimatology Reconstructions Network has made available paleo data for download including 92 high-resolution temperature records over the past 2+ millennia.


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Comments 26 to 50 out of 167:

  1. Regarding the supposed debunking of the hockey stick by McShane and Wyner, "A new Hockey Stick: McShane and Wyner August 16, 2010, by Tim Lambert
  2. McShane and Wyner is apparently yet another smoking "gub," looks like. Nailed by their lack of expertise? The tasty nugget at the center of the paper, for skeptics: In other words, our model performs better when using highly autocorrelated noise rather than proxies to predict temperature. The real proxies are less predictive than our "fake" data. It appears M&W compared the performance of proxies sensitive to regional changes against the global NH temperature record. Naturally, the thermometer on your porch (for instance) will turn out to be a poor proxy for global NH temperature if you're trying to tease out changes on the order of a couple of degrees. Even I should have been able to see that. Rats. Noted in various places.
  3. Re: Comparing proxies against global NH (i.e. EIV) versus regional temperature records (i.e. CPS). The two methodologies are compared in Mann 08 and are also compared in the new paper (see sections 3.2 and 3.6 in Doug's link in post 26)
  4. And that makes this time period......the 26th warmest period in the Holocene era. Big deal.
    Response: See the Argument "It's Not Bad," also titled "Positives and Negatives of Global Warming."
  5. Deep Climate has done a detailed analysis of the McShane and Wyner paper.
  6. McShane and Wyner's paper was tossed into the ring of public contention prior to being graced with the full benefit of review. Presumably this was voluntary on the authors' part, or let's hope so. DeepClimate has a lengthy post delving into various features of M&W, and as well there's a robust discussion in the comments there for folks who'd like to get caught up one way or another. DC is not the only outfit to notice the strangely situated political freight loaded onto the M&W train of thought.
  7. Regarding McShane and Wyner: Is being reviewed. We will wait with baited breath. I guess I missed the "political freight" when I read it today. DC seemed to be going for the ad hominem argument in that regard. I would have preferred that DC skip over the jibes at political incorrectness and spent that time delving into the paper itself. There was a lot going on in those 45 pages. McShane and Wyner take their own shot at the climatological world for being statistically challenged as well. Data is data after all and that is the world of statisticians. One of the conclusions: ...we conclude unequivocally that the evidence for a ”long-handled” hockey stick (where the shaft of the hockey stick extends to the year 1000 AD) is lacking in the data. In other words, there might have been other sharp run-ups in temperature, but the proxies show them. The hockey stick handle may be crooked, but the proxies can't show it one way or the other. Note that McShane and Wyner don't necessarily think the historical record is all wrong, but rather that the anomaly signal that the global warming crowd is using is not necessarily detectable the data.
  8. TOP if M&W choose to include a narrative of the political history of paleoclimate studies in what is advertised as a technical critique and improvement of statistics employed in proxy temperature reconstructions, it's not an ad hominem attack when readers are arrested by this unusual feature and begin to speculate on why the extra material is included. The authors themselves after all have chosen to include this distraction; presumably they wished to call attention to their paper in this way. They've succeeded. To wit, this example paragraph, which you apparently did not notice when reading the paper: Quotations like the above and graphs like those in Figures 1, 2, and 3 are featured prominently not only in official documents like the IPCC report but also in widely viewed television programs (BBC, September 14, 2008), in film (Gore, 2006), and in museum expositions (Rothstein, October 17, 2008), alarming both the populace and policy makers. Al Gore? Alarming? Really? Can you spot the statistics in that? I can't, but I do read what many would term as "dog whistle" political words. Now do you notice how the choice to include political fluff makes it more difficult to discuss their work? Why do I have to ask, because I made M&W mention Al Gore, or because M&W chose to write about Al Gore instead of statistics?
  9. TOP - where is the ad hominem in DC's article? Ie the attempt to discredit the argument by an attack on the persons of M&W, rather than on the argument that they present? DC helpfully makes it possible to check M&W version of history is correct or not, but the teeth of article deals with the technical argument.
  10. It is easy to see why M & W was not submitted to a climate journal. First question they'd be asked is why they used local proxies to correlate to global temperatures and then criticized those same proxies for not being predictive of global temperatures. If they had any sense they would of compared them to the LOCAL temperatures that the proxies actually respond to...
  11. Moderator: The link to Tamino's post "Not Alike" in the Further Reading section is broken. The actual link to where it can be accessed is: Courtesy of the Internet Archive Wayback Machine". Tamino's posts older than March of 2010 are gone, and pre-existing links to them are probably broken. Posts older than August 22 of 2008 can be found at the archive search link provided. Anyone have any ideas for missing posts between those dates? The Yooper
  12. As far as I know Tamino has written a book, and that may be a reason why he deleted the older post.
  13. Re: Bodo (38) AFAIK, the missing posts are a result of a dispute between Wordpress and Tamino over content. At one point, one of the two parties pulled all past content. All posts prior to March or so of this year are gone from Tamino's Wordpress blog. Some of the missing content is still accessible, as I note. The Yooper
  14. GC - you claim Tamino supports papers that deny the historical record. I assume this has something to do with MBH? Can you be more specific please? I assume you think MBH denies history. Do you also assume that all those other papers in Paleoclimate chapter of AR4 using different methods and proxies, published since M&M are also "denying the historical record"?
  15. scaddenp, (From "Lies, Damn Lies & the IPCC) My problem with MBH 08 & 09 plus the hundreds of subsequent papers and commentaries including those by my ex-colleagues such as Gabby Hegerl or distinguished statisticians such as Tamino is their ignorance of the historical record. The first test of any paleo-climate reconstruction should be whether it portrays past climate in a plausible way. Any set of proxies that disagrees with history should immediately be discarded. Specifically, I mean that at least the following warm periods should be seen: Minoan, Roman (2), Medieval and Modern. Cold periods should include: Dark Ages and Little Ice Age. For proxies that go back into pre-history, one would expect to see the Younger Dryas. While we don't have a true historic record of this there is a good archaeological record of the Clovis people. You should be honest enough to recognize that MBH et seq. fail this test in dismal fashion, yet there are some proxies that portray the historical and even pre-historical (Younger Dryas) temperatures quite well. You don't have to believe they are correct but at least admit that they pass the initial acid test of being consistent with history and archeology. The proxies I find credible are ice cores. As the historical record in the southern hemisphere is thin, one can only check a tiny part of the Antarctic ice core record against history. It is quite a different story in the northern hemisphere where we have the Greenland ice cores. Here is a "ftp" link to Richard Alley's (2000) ice core data for central Greenland: I downloaded this file and prepared a number of plots over different time periods. This is quite time consuming so you can get the same information from the following site and learn about the Eisenhower administration at the same time: Your comments will be appreciated as I plan to visit NOAA in Asheville, North Carolina in mid October to discuss this and related issues.
    Response: [RH] Embedded link.
  16. Quite why *should* an hemispheric or a global temperature record detail all known regional or local climate variations? Ignorance of the historical record is a significant accusation, I wonder if you can back that up with any more than the suggestion that global temperature series should record local fluctuations? Historical observations of Medieval or Roman (clue in the name) warmth come from small portions of the world (dominantly Europe). If most of the rest of the world showed little temperature change or a change of opposite sign, then the impact of even large local changes recorded in the historical record will be outweighed by the record (not stored in written history, but faithfully recorded by proxies) from the rest of the world. Or are you assuming, incorrectly, that all climate fluctuations must always occur worldwide and be globally synchronous?
  17. Not to mention Mann et al. (2008) do use ice cores. If ice cores perform so much better (different) than other proxies, I would assume they would mention it. Also, link dump! Gavin's response to MW2010. Martin Tingley's response to MW2010. McIntyre's response to Mann2008. Reply to McIntyre by Mann
  18. GC - your initial accusation is that MBH and later reconstructions supported by Tamino etc do not honour the historical record so for starters that should limit you to the considerations of the last 1000 years, NH only, as earlier climate events are outside the scope of the papers supposed ignorance of history. Fig 6.10 in AR4 WG1 has summary figure of the various reconstruction, and Box 6.4, Fig 1 shows the individual temperature proxies for different parts of NH. And what do these show? Well for starters, where is the mismatch with history? The proxy records for sites in the area of historical records match what you can infer about temperatures in the pre-thermometer age. That things like the "medieval warm period" occurred at different times in different places is established from the historical records for Greenland, Europe, Russia and China. The NH reconstruction do indeed show a LIA which may be global (you would expect it to be from what we know of forcing at the time). I find no evidence of a problem here though I do certainly accept that MBH, being the first attempt at a multi-proxy reconstruction, needed improved methodologically and has been. I dont think its substantial conclusions has changed much with later reconstructions. Perhaps you could also point out which defense of a paper by Tamino you find so objectionable. Looking back further for evidence that climate science and history are in opposition also produces a blank. Was it warm in the Bronze age? Almost certainly warmer than now is what the climate science says (see WGA for papers). Solar production proxies globally and orbital forcing for NH point to an expectation of warmer temperatures which is borne out in historical and paleoclimatic record. There is evidence of warming similar to now in SH as well. Just as well we dont have that solar forcing now on top of our CO2 concentrations. Younger Dryas - I am not sure why you brought this up as for life of me I can see why you think there is a conflict with "historical record" - perhaps you could explain? I cant see that archeological record is much easier to interpret than the paleoclimate one and boy does it have fun with YD. Be aware that YD is area where techniques are being refined, better time calibration is coming and so watch for new papers in next couple of years. Also note that events like YD are features of glacial terminations and thankfully we lack evidence that interglacial periods are prone to such rapid climate shifts. Time for a quick reset of the respect-o-meter perhaps in face of all that data?
  19. scaddenp (#44), Starting at the end, the Younger Dryas is relevant because it is another example of Alley's ice cores being in synch with history/archeology. You are selling history short if you think it only goes back 1,000 years. There is no merit in multi-proxy studies if most of the proxies are junk science. Mann's tree rings should have been thrown out the minute they failed to model the warm and cold periods over the last 1,000 years.
  20. apeescape (#43), What is this "link dump" thing? Scaddenp asked for data so I sent a NOAA ftp link. Then I try to help by sending a reference that has pre-digested the data into a series of charts. I will read your links; perhaps you will be kind enough to read mine unless you are afraid of being confused by facts.
  21. skywatcher (#42), You are right to be wary about applying measurements from a small area to the entire globe, so get your blinkers off and acknowledge that is exactly what Mann tried to do. He took measurements on spruce trees from a few sites all in high latitudes and tried to draw conclusions relating to the entire planet. Take a look at the Yamal peninsula studies that came down to a few carefully selected trees. I won't send you the links as that might offend "apeescape".
  22. GC - This thread started elsewhere with the claim you didnt like Tamino because he supported papers that were in conflict with the historical record. The papers you objected to only cover the last 1000 years. I am not selling history short (as rest of comment indicates), only that objections to those particular papers are for events of last 1000 years. If you have other papers that you think imply conflict with the historical record, then name them. Your comments so far ignore my objection to this. Further you claim that Mann inferred global climate from only Yamal tree rings. Also not true - the paper used a variety of proxies from many location; that was what was new. The first multi-proxy reconstruction. I am not clear whether you are agreeing that climate science view of YD in concordance with history (no problem then) or not.
  23. I am also still interested what paper you think Tamino mounted an inappropriate defense.
  24. gallopingcamel writes: What is this "link dump" thing? I think apeescape was referring to the bunch of links that she/he included immediately below that line. It wasn't a remark about your own comment.
  25. apeescape (#43), It seems I misinterpreted your "link Dump". Please accept my apologies. Thank you Ned, once again. Scaddenp, it seems we are having communications difficulties. I will try to rephrase my arguments more clearly tomorrow when there is no Monday night football. While I am doing that, what is your opinion on Alley's temperature reconstructions for central Greenland? Plausible or not?

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