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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 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 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 2004), 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 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 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 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 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 2006).

Figure 4: Northern Hemisphere annual temperature reconstruction from speleothem reconstructions shown with 2 standard error (shaded area) (Smith 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 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 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 51 to 100 out of 167:

  1. GC - perhaps indeed. To clarify. You made this statement. "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." The implication was that the papers you listed did indeed disagree with history. I pointed you to data, relevant to those papers which show you are wrong. The proxy record is consistent with history. Feel free to point to other papers and the historical records that invalidate them. I have no reason to think Alley's temp reconstruction for central greenland is substantially flawed. I am intrigued to know what historical records you have for central greenland to compare it with.
  2. I second that, scaddenp, I'd also like to know what historical variations in climate Mann's (or any of the many other multi-proxy reconstructions) disagree with. So far as I'm aware, most areas in which events such as the MWP or LIA are recorded historically, show these events in their proxy records. It is areas elsewhere in the world (actually, by far most of the rest of the world), which don't necessarily show the same variations. Are you the blinkered one, not grasping the implications of that, GC? Do you believe that all climate variations are spatially and temporally uniform? I'd like to see you support the accusation of Mann using only a few Yamal trees with some evidence, givent he latest paper used over a thousand proxies from a worldwide network, from many different kinds of proxies. Such accusations of cherry-picking have been debunked over and over again, not least by the multiple independent studies with different methodologies showing largely the same results.
  3. scaddenp & Co., With regard to Tamino, I have nothing to contribute to the discussion other than to say that I find "Climate Audit" more plausible than "Open Mind". The Tamino/McIntyre spat has turned into a cottage industry and good luck to both of them. Statisticians are like economists; if you put them all "End-to-End" they still won't reach agreement. The point I am trying to make is that if studies defy the historical record it is the studies that must be thrown out. Mann and his myriad supporters still insist that history be ignored but it is a battle they must ultimately lose. They should be ashamed for defending the indefensible. The post above and recent events support me. Take a look at Figure 1 that started it all. About 850 years with tiny variations and a very gentle decline followed by a rapid temperature rise. No sign of the MWP or LIA. Move on to Figure 2 that is almost identical to Figure 1. Shame on Wahl-Ammann! Still no sign of the MWP or LIA. The tiny variations are totally implausible when you consider the extreme weather events that occurred during the last 1,000 years such as the hot, dry summers around 1540 that caused major rivers in Europe to dry up. On the other extreme, the river Thames in London froze over on 24 occasions from 1408 to 1814. If you have not seen the following link before, enjoy! Recently, the "Climate Science" community has begun to realize that their credibility has been ruined by historians so growing number of paleo-climate reconstructions show historical events as in Figure 6 (Mann 2008). Here, the MWP and LIA can be seen as minor excursions. What would happen if one left out the tree ring data? Here is a paper by Loehle with the answer: This 2000 year reconstruction shows temperature excursions greater than 1 degree Kelvin and Medieval temperatures higher than 2010. Loehle has been demonized by establishment scientists such as Schmidt and Mann; nevertheless there are still folks like Ljungqvist who can produce similar results even with tree ring proxies included: Climate science needs to stop muddying the waters by creating multi-proxy analyses that include even one proxy that fails the acid test of being consistent with history/archeology. Few if any tree ring proxies would survive and some other proxies might fail the cut too. The Ljungqvist paper covers 2000 years with decadal resolution using proxies located from 30N to 81N. It therefore covers the non-tropical northern hemisphere over recent historical times. The amplitude of temperature variations is 0.9 degrees compared to 3.3 degrees in Richard Alley's ice cores. However, global warming (or global cooling) should be much more pronounced at high latitudes (the central Greenland site was at 73N). When one overlays the temperature variations in Loehle 2007, Ljungqvist 2010 and Alley 2000 the historical features such as "Dark ages", MWP and LIA all show up in the right places so these analyses have some credibility, unlike MBH 98 et seq. apeescape, I read all those links (@43). Methinks they protest too much. Gavin in particular is beginning to sound a little desperate. He is paid to do what he does but he is not winning hearts or minds.
  4. GC, it sounds as though you're in tacit agreement that recent observations of Arctic ice extent, loss of terrestrial ice mass in both hemispheres, globally shrinking diurnal temperature variations, lopsided extreme heat statistics, an upward trend in ocean heat content, increasing signs of intensified convection plus a lengthy list of other consistent indicators with which you are probably painfully familiar all point to a modern change in climate? These are after all recorded in superior cultural records to the instrumentally void and comparatively sparse narratives you consider to obviate proxy temperature data. Looking at your opinion from a different perspective, I'd say your endorsement of historical records bolsters the case for new and startling history being made today. Meanwhile, a differently advanced cultural heritage provides us with a plausible explanation for our present observations. The past is not necessarily prologue; we'll need to look farther back in time to seek an offset of sufficient span and power to be capable of nullifying the secular trend we appear to have started. Once we dip farther back in chronology than historical time, your faith will have to be fully invested in proxies, if you're to seek solace in anachronism.
  5. GC - I asked for specific instance of Tamino criticism for a very good reason - I wanted evidence that Tamino was defending the indefensible as your accusation implied. Which paper do you think is the definitive account of the historical record that you think so reliable? (and the answer had better not be Lamb). I'll stand by my statement that individual proxies reflect local historical record while acknowledging that combining them into a multiproxy record is difficult. Loehle is hardly criticised for excluding tree proxies - other papers have done the same - but for numerous other errors. If he had published in something other than E&E then he might got some quality feedback for improvement instead of having to publish corrections later. The problem with leaving tree proxies out is that is all you have for too periods of too many regions. Undoubted more data will help improve this situation. I would also note very small difference between Mann 2009 and latest from Ljungqvist. Is Mann still "denying" history, but Ljungqvist isnt? McIntyre would have some credibility if he actually published instead of just misleading statements and innuendo from the sidelines.
  6. gallopingcamel has kindly moved the discussion of Loehle and Ljungqvist over to the new thread, but I just want to make sure this doesn't remain here un-amended: gallopingcamel wrote This 2000 year reconstruction (Loehle 2008) shows temperature excursions greater than 1 degree Kelvin and Medieval temperatures higher than 2010. It does show a >1K temperature difference between the peak of the MWP and the bottom of the LIA. It does not, however, show Medieval temperatures higher than 2010. In fact, the warmest decades in Loehle's MWP are 0.5K cooler than 2010. Loehle's reconstruction is centered on its own 2000-year mean, and the final datum is from around 1930. In order to compare Loehle's MWP to current temperatures, it is necessary to re-center Loehle's reconstruction to match some other temperature series (e.g., the instrumental record) that actually shows the current temperature. An example of this is included in the update to this post.
  7. GC, as you're still ignoring the point and restating your incorrect assertions, I can only presume you can't actually answer my question: Why would you assume that every local temperature variation is recorded in full in a global dataset? And can you point to detailed examples of where the regional reconstruction fails to pick out regional climatic variations recorded in local history, and show how that has fed into and distorted the meta-analyses? I doubt you can. The climate science community's credibility has certainly not been affected in the slightest by the historical record.
  8. My comment to part of this article is in relation to the section which says that the McIntyre(2004) publication says that "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." I do not believe this is a correct interpretation of the aricle - i think the article claims that the hockey stick shape was a results of using an incorrect "scaling" of the time series by using only the last part of the entire time series - the 20th century only. He claims this overly weights the data and results in the hockey stick affect and the hockey stick is not actually resident in the data without this scaling (at least not as a PC1 component). In addition I do not think he claims that the data temperatures where from one bristlecone but that the bristlecone data is not necessarily reliable as it exagerates the true temparuture due to the species magnified growth in a higher C02 environment. This is evident in the article written in 2005 by McKitrick to the APEC Study group titled "what is the Hockey Stick Debate about?"
  9. Sadly this debate is the classic example of some people ignoring reality. The Hockey Stick is a misleading graph that has no place anymore in the argument. It was created with some wrong assertions and a lack of accurate data that led to the now infamous graph. I find it incredulous that a so called respected researcher could be fooled by his error so painfully. The Medieval Warm Period and the Little Ice Age are well documented and reported periods of the last 1000 years. To adjust data sets to start just as the climate was cold and then warmed is misleading. There are graphs out there that paint a different picture: This next graph shows the temperature records take from the Vostok Ice Cores and have appeared in numerous publications, including Science, over the last couple of years. The current temperature is 0 on the graph with the variation above and below this as either a positive or negative value. It is for 10,000 years and clearly shows a high degree of variation in average temperature Then we have Ice core data from Greenland's GISP2 Ice Core which clearly shows that our current understanding of how the climate naturally varies over time leaves a lot to be desired. This graph was produced by Climate Change researchers and clearly does not support the anthropogenic argument. When it comes to discussing climate, we should not be looking at trends in data for 10, 30 or even hundred year block of time, but we must study the data for thousands of years worth. The planet does not work on human timescales so our observations must reflect this fact. Bleating about the impact man has or is not having is pointless, we must simply stop polluting our environment and let nature sort the rest out. We need to make significant changes to how we deal with environmental matters, quick fixes are not intelligent or likely to work, only long term, thought out and sustainable changes will achieve any measure of success.
    Response: [muoncounter] Since you didn't bother to read the rules of this road, here's a summary: Stick to the topic. No accusations of deception. No personal attacks (bleating? really?) Cite the sources you use for information (and those should be reputable sources, not dime store blogs). Last warning before deletion.
  10. @Muoncounter: Please explain to me where in my post I have made a personal attack and to whom did I direct it? Regarding information about the graphs...fair point, but if you look at the links, they are hardly dim store blogs (surely is that not a personal attack on the blogger?) One is actually on this site. Bleating is something we all do...the western world is bleating about Climate change and ignoring the bigger picture which is far more important in my opinion. I thought my post made it clear what my position is, I do not agree with AGW, but I do agree with not polluting the environment, so I am not opposed to cleaning things up, just for the right reasons. I have kept the post on topic, it is about the hockey stick is it not? Well to counter one argument you need to justify that stance, I think I did that rather well.
  11. There's a quick discussion of LandyJim's first 'graph' here. There's much more wrong with it than just a dodgy y-axis.
  12. @JMurphy #62 I will concede that the graph could have a better quality about it, however it was used for illustrative purposes. Graph 3 of the Vostok Ice cores comes from a Climate campaigner in New Zealand who is a member of the New Zealand Climate Science Coalition This information originates in a very reputable and peer reviewed article: Petit, J.R., J. Jouzel, D. Raynaud, N.I. Barkov, J.-M. Barnola, I. Basile, M. Benders, J. Chappellaz, M. Davis, G. Delayque, M. Delmotte, V.M. Kotlyakov, M. Legrand, V.Y. Lipenkov, C. Lorius, L. Pépin, C. Ritz, E. Saltzman, and M. Stievenard. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436. If you would like to read more information about the Vostok cores, you can here.. The last graph is a reproduction of one that appeared in a Science Online and Journal Peer reviewed article which is actually pro AGW. There is credit for the article in the image if you look. R. B. Alley1, J. Marotzke2, W. D. Nordhaus3, J. T. Overpeck4, D. M. Peteet5, R. A. Pielke Jr.6, R. T. Pierrehumbert7, P. B. Rhines8,9, T. F. Stocker10, L. D. Talley11 and J. M. Wallace8 And an online link is here If you wish to see other articles written by Richard Alley.. What I am am saying is that we should not dismiss natural variations in the climate, we must not dismiss influences on those variations, only then can the impact that we have be truly assessed and then action taken accordingly. To me that is common sense.
  13. Here is another reputable reference for the GISP2 Ice Core Data sets from Richard Alley And here is the abstract from the top of at work. ABSTRACT: Greenland ice-core records provide an exceptionally clear picture of many aspects of abrupt climate changes, and particularly of those associated with the Younger Dryas event, as reviewed here. Well-preserved annual layers can be counted confidently, with only 1% errors for the age of the end of the Younger Dryas 11,500 years before present. Ice-flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty. Glaciochemical and particulate data record atmospheric-loading changes with little uncertainty introduced by changes in snow accumulation. Confident paleothermometry is provided by site-specific calibrations using ice-isotopic ratios, borehole temperatures, and gas-isotopic ratios. Near-simultaneous changes in ice-core paleoclimatic indicators of local, regional, and more-widespread climate conditions demonstrate that much of the Earth experienced abrupt climate changes synchronous with Greenland within thirty years or less. Post-Younger Dryas changes have not duplicated the size, extent and rapidity of these paleoclimatic changes.
  14. Your second graph, LandyJim, I presume comes from Monckton, or someone similar ? The latest date on it would have to be 1994, I would imagine. How do you think it would look with the temperatures up to 2010 - whatever the temperature scale on that graph actually means and for which location. Do you know ? What do you believe you are trying to show with the Vostock graph - that temperature has varied in the past ? How does that relate to today ? There are more of these you can see here and here, if you like those sort of long-term measurements. As for the fourth one, it isn't from the Abrupt Climate Change paper as you stated; and neither is it from the The Younger Dryas cold interval as viewed from central Greenland" as suggested in your subsequent post. Well, I couldn't find it, anyway, after a quick look, although I did find the data. Perhaps you could point it out more exactly ? You can even see EPICA and VOSTOK compared here, if you would like.
  15. I would like to call your attention to the most recent temperature reconstruction, which was published in Science this month. The paper entitled "2500 Years of European Climate Variability and Human Susceptibility" by Büntgen et al. actually suggests that the current warming has no parallel in the last 2500 years. ABSTRACT Climate variations have influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. Discrimination between environmental and anthropogenic impacts on past civilizations, however, remains difficult because of the paucity of high-resolution palaeoclimatic evidence. Here, we present tree ring–based reconstructions of Central European summer precipitation and temperature variability over the past 2500 years. Recent warming is unprecedented, but modern hydroclimatic variations may have at times been exceeded in magnitude and duration. Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from ~AD 250 to 600 coincided with the demise of the Western Roman Empire and the turmoil of the Migration Period. Historical circumstances may challenge recent political and fiscal reluctance to mitigate projected climate change.
  16. A recent reconstruction of the Indo-Pacific Warm Pool reported by Woods Hole Institute found that for the most important body of water in the Pacific the MWP sea surface temperatures were comparable to today's. Woods Hole Institute's report on the MWP in the Indo-Pacific Warm Pool
  17. Considering all the accusations of fraud and incompetence that have been thrown at Mann for the hockey stick, I find it especially important to point toward what can be uncovered when the skeptics's work is examined with the kind of attention they claim should be applied to scientific work. A major point in the accusations of McIntyre is from McIntyre&McKitrick 05, which expanded on a previous 04 paper. It is there claimed that Mann's statistical methods generate hockey sticks from artificially generated random data that do not contain a signal. Closer examination of the M&M computer code used in this "discovery" shows that the code is designed to sort hockey stick shapes first, then retain only these samples from a much larger number. These are the ones shown by M&M. The rest of M&M's work is riddled with much of what they accuse others to practice. The much touted Wegman report is no better. In addition wegman has been especially reluctant to let others examine his computer code, a behavior that skeptics systematically equate with fraudulent intentions. Thanks must be given to Deep Climate for investigating this in real skeptic fashion: What is most shocking about the whole thing is how little attention has been paid in the mass media, always so quick at picking up climate deniers accusations toward scientists.
  18. This is a response to TTTM @ Muller Misinformation#1 "Adding a warming bias" = "Using modern, accurate records"? You know something? Whenever I have something modern that accurately performs some task, I prefer it. Using a laser level when doing household repairs is a great deal better than the tedious back-and-forthing of earlier techniques. However, we sometimes find ourselves without our modern gadgetry, so we use the best of what we've got. When we get the chance we check with the best modern equipment and information. And that's what the paleo + modern assembly does. It would be really terrific if every single paleo reconstruction were both accurate and adequate for recent, shorter timescales, but some aren't for one reason or another, eg the ones with century averaging periods. We do the best we can with what we've got. And MBH's work has been validated by similar results with other paleo series that don't have such issues. If MBH were being promoted as the "best" despite disagreement with everyone else's work in this field, you might have a point. But there's agreement, so your point fails.
  19. TTTM said... "Take out the smoothing and the uptick at the end of the series in figure three (above) disappears. The temperature proxy should show a decline in temperatures as recorded by the tree rings." The problem there is that there in no decline in the temperature. We have actual recorded data showing what the modern temps are.
  20. Once again we have a science paper indicating warmth of the more distant past clearly exceeded that of the recent past, with the peak temperature of the MWP exceeding that of the current period by about 0.6°C, or about the same temperature increase that is expected by a doubling of CO2 concentration. This indicates there is nothing unusual, unnatural or unprecedented about the earth's current level of warmth in this particular part of the planet. Ran, L., Jiang, H., Knudsen, K.L. and Eiriksson, J. 2011. Diatom-based reconstruction of palaeoceanographic changes on the North Icelandic shelf during the last millennium. Palaeogeography, Palaeoclimatology, Palaeoecology 302: 109-119.
  21. Bud@everywhere See here and here. You are exploring well charted ground without consulting the maps or the natives.
  22. Bud - what do you mean "once again"? There are no millenial reconstructions which show the MWP hotter than present. For this paper, the North Icelandic Shelf does not represent the entire hemisphere or globe. And the study concludes the sea surface on the North Icelandic shelf "was not as warm during the last century as during the Medieval Warm Period." It's not the last century anymore. And finally, the anthropogenic global waming theory is based on physics, not on being "unprecedented". The fact that the planet warmed naturally in the past doesn't change the physics that humans are causing warming now.
  23. Dana, "For this paper, the North Icelandic Shelf does not represent the entire hemisphere or globe." Exactly--"skeptics" cherry picking again. They seem to never learn from their mistakes--i.e., the misrepresentation of the GIPS2 data. Also a recent paper by Thibodeau et al. (2010) shows that: "We conclude that the 20th century warming of the incoming intermediate North Atlantic water has had no equivalent during the last thousand years. " Just saying....
  24. Sorry, I of course meant to say "GISP2", not "GIPS2"
  25. Sigh. I wonder if they read these things before they post.
  26. @dana: In August 1997, Huang, Pollack, and Shen. Geophysical Research Letters. Using the borehole data, they reconstructed the temperature in the last 20,000 years. Their results are three curves based on different degrees of variation. Shown are a warm holocene climate optimum, a warm and pleasant period around 8,000 years ago that lasted for about 3 millenia, a cool period 2000 years ago followed by the medieval warm period 800 years ago which was also warmer than the present. I will respond at length on physics elsewhere, so that perhaps I won't be deleted by the monitor of this blog.

    [DB] Comments that are on-topic and formulated to comply with the Comments Policy receive no moderation.  This, as always, applies to all participants here.

  27. Sorry, I did NOT say Ran, L., Jiang, H., Knudsen, K.L. and Eiriksson was global. No cherry picking by me. Knee jerk reactions by some of you though.
  28. Bud - the study you reference excluded data from the 20th century, aside from other problems. See the Notes section here.

    [DB] Dana, I'm not sure the Notes sections are viewable to the public.  If that is the case, the gist is this:

    Summary and Conclusions [25]

    The 20,000 year reconstructions presented in HPS97 utilized observations contained in a database of terrestrial heat flux measurements.

    Data from the depth range 0– 100 meters, the depth range where most of the information about 20th century climate change resides, were excluded from the reconstruction because of noise considerations.

    Thus the reconstructions derived from that dataset cannot be used to compare the Medieval Warm Period to changes taking place in the 20th century.

  29. Bud #79 - and I quote:
    "Once again we have a science paper indicating warmth of the more distant past clearly exceeded that of the recent past....I did NOT say Ran, L., Jiang, H., Knudsen, K.L. and Eiriksson was global."
    Stop playing games. If you want to argue that the the North Icelandic Shelf was hotter during the MWP than now, then say so. Don't pretend we're misrepresenting you when you talk about "warmth" in a hockey stick (northern hemisphere) temperature discussion.
  30. Bud @77, Huang et. al. have an updated paper here, published in 2008. From the abstract (emphasis mine): "We present a suite of new 20,000 year reconstructions ... all referenced to the 1961–1990 mean of the instrumental record. ... The reconstructions show the temperatures of ... the maximum of the MWP at or slightly below the reference level ... and end-of-20th century temperatures about 0.5 K above the reference level. Note that they found that end-of-20th century temperatures were warmer than the MWP, and keep in mind that the 21st century is known to be warmer still. Also note the discussion of their previous paper: "Below we describe their respective datasets, and show why the results of HPS97 cannot be used for comparing MWP warmth to the 20th century." So Bud, you readily cited the work of these particular scientists when you felt their conclusions agreed with yours. Are you going to stick with them now that their conclusions differ? Are you actually willing to change your point of view given new evidence, or are you just going to cherry pick the versions that you agree with?
  31. Dana. I pretend nothing. These scientists find that Iceland was warmer. "Once again" meant that they are by no means the only scientists to publish of warmer periods. Since you claimed "There are no millenial reconstructions which show the MWP hotter than present" I gave you a reference to the August 1997, Huang, Pollack, and Shen paper in Geophysical Research Letters. Here's another reconstruction. There's a nice graph on this page: Bibliography here:

    [DB] Please see e's pre-emptive reply to you at 80 above.

  32. Bud >These scientists find that Iceland was warmer. So what? The topic of discussion is global warming. Do you have up to date evidence that the globe was warmer that the present (meaning 2000-2010 not the 90's)? More importantly, why would that even be relevant to your argument? The key question is the physics that underly the warming and what that means for future temperature trends.
  33. Dana. This 2002 paper using data from China confirms period AD 200 that is "The peak at about AD 200 represents the warmest stage of the last two millennia, temperature was even higher than during the 20th century." "General characteristics of temperature variation in China during the last two millennia," GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 9, 1324, 10.1029/2001GL014485, 2002 Bao Yang Institute of Cold and Arid Regions Environmental and Engineering, Chinese Academy of Sciences, China Achim Braeuning Institute for Geography, University of Stuttgart, Stuttgart, Germany Kathleen R. Johnson Department of Earth and Planetary Science, University of California, Berkeley, CA, USA Shi Yafeng Institute of Geography and Limnology, Chinese Academy of Sciences, 210008, Nanjing, China,%202002.pdf

    [DB] Please slow down the linear posting of studies until you have properly discussed the ones you have already posted.  For example, e countered your Huang et al 1997 with Huang et al 2008 which effectively overcomes your position altogether.

  34. Bud, This is getting ridiculous. You were asked about global warming, so now you produce a paper about warming in China? What's more, the timeframe referenced for the warm period in that paper is substantially different from the time period in your first paper. The Icelandic warming is timed around 1000 A.D., while the Chinese warming is around 200 A.D. These are different warming events localized to different regions Bud. Please show us some truly global evidence and stop spamming this thread with irrelevant and outdated papers.
  35. To piggyback on the prevailing sentiment, regionalized warming/cooling is that: regional. For your examples given, the warming experienced regionally during the MWP was just that: regional periods of warming interspersed with bouts of regional cooling. So for every "dog" study showing a certain region was "warm at a certain time period therein, another "pony" study showing cooling during the period can be rolled out. As an example, Martín-Chivelet et al 2011, showed that the 20th century was the time with highest surface temperatures in Northern Spain in the last 4000 years (more robust discussion here), which includes the MWP. Whoopee. But where the warming/cooling of the past differs from the warming experienced in the last century & this is two-fold: 1. This warming is truly global 2. It is driven largely (especially since 1975 or so) by us with our GHG emissions. Please take the time to read the literally hundreds of posts at this site going over this in exquisite detail. Whichever sources of information you've been learning from so far have done you a disservice.
  36. All, Bud seems to be cherry-picking papers from the NIPCC's "Prudent Path" misinformation document. If so, he can keep at this for some time.... Also, in the face of evidence to the contrary of his beliefs the "skeptics" just keeps forging ahead, mostly ignoring the inconvenient evidence. At this point one has to wonder whether the person is a "skeptics" or someone in denial about AGW. There are more Hockey Sticks out there than can be used by a NHL team, some generated using independent data not used in the original HS graph. e @85, good catch!

    [dana1981] I suggest we follow Daniel's sage advice.  DNFTT.  Until Bud can address the fact that the lone hemispheric reconstruction he has referenced is flawed and outdated, there's little point in feeding him further.

  37. Hey I'm new to this fourm but Steven McIntyre has got a rebuttal to his rebuttal and a rebuttal to any new hockey sticks. here is a reconstruction showing Briffa's exclusion of data and what it really is supposed to be. From the Keigwin 1996 study. I will debate the Heat Island Effect on the specific section which I challege the graphs provided here.

    [DB] A better thread for the tree ring discussion is probably Climategate: Hiding the Decline?

    As you are new to this forum, you may want to read it before proceeding further.  Respondees to this, please take it up there.

    The hockey stick challenge Roh234 issues is fair game here.

    Take heat island comments to the It's Urban Heat Island effect thread.  Please read both the Basic and Intermediate tabs to prepare yourself.

    For the record, please in the future also indicate the paternity of your sources for furnished graphics.  Ex:

    Graphic 1 above:

    Graphic 2 above:

    Graphic 3 above:

    Graphic 4 above:

    Congratulations, no peer-reviewed primary sources used.

  38. Roh234 - the world has moved on from 1998, but Mc Intyre hasn't. The rebuttal to future hockey sticks remark is amusing, but in all seriousness the evidence is overwhelming that present temperatures surpass that of the Medieval Warm(ish) Period. For starters: 1. Glaciers were advancing in North America during the MWP. See SkS post: Icing the Medieval Warm Period 2. The North American cordillera snowpack was much heavier during the MWP - indicating that it was colder back then. See: The Unusual Nature of Recent Snowpack Declines in the North American Cordillera - Pederson (2011) 3. Atmospheric circulation patterns match the paleoclimate proxies - See SkS post: The Medieval Warm(ish) Period in Pictures 4. Paleoclimate reconstruction below:
  39. It would also by nice if you provided a link back to your sources. You are aware of various non-tree ring proxy reconstructions as well?
  40. Roh234, as others have pointed out, the 'hockey stick' has been confirmed by numerous subsequent studies by different groups of scientists, and even 'skeptics', all over the world using several different data sources. Alot of this is also detailed in the article above. On McIntyre's specific claim about 34 tree ring data sets... have you heard of the divergence problem? Basically, over the past century many trees have shown very low growth even as the temperature has increased. This is believed to be due to environmental toxins and other factors. However, what it means is that the rings on these trees are not accurate proxies for RECENT temperatures. Thus, McIntyre essentially went out and found recent tree rings (from a completely different study BTW) that did not match ACTUAL temperatures and is claiming that Briffa should have factored them in. In short, he is criticizing Briffa for not using INCORRECT data. That McIntyre is wrong should be obvious to any thinking person who looks at the graph. The red and black temperature lines essentially match up until the last 50 years or so. Then the black line plummets downward while the red shoots up. Now let's engage basic reasoning for a moment... What have actual temperatures done over the past 50 years? Has it gotten significantly colder? If not, then the black line is wrong. Ask yourself how 'skeptical' you are being when you blindly accept the validity of a graph which is at odds with observed reality.
  41. On the Briffa-Yamal series being "crack cocaine for paleoclimatologists" (the comment made by McIntyre), there were non-addictive alternatives available: e.g. and versus Briffa: Briffa's response to the impact of his series: McIntyre's response to Briffa's response:
  42. The thread of the argument in the top post is a little disorganised. The skeptical point at the top begins "In 2003 Professor McKitrick teamed with a Canadian engineer, Steve McIntyre, in attempting to replicate the hockey stick and debunked it as statistical nonsense...." M&M03 doesn't get discussed at all in the article proper, which is a bit of an oversight I think. Also, McIntyre 2004 (?) is referenced, but the paper linked is actually McIntyre & McKitrick 2005.
  43. Eric, as I explained in comment #90 above (and as can be clearly seen in Ro234's first graph), McIntyre's 'alternative' tree ring data series diverge from reality over recent decades. So the question is... why should Briffa have sought out and incorporated erroneous data? McIntyre is here not disputing the 'stick' but rather the 'blade'... the recent large upward turn. Yet that is established not only by selection of ACCURATE tree ring proxies, but by numerous other proxies (see the main post above)... and actual surface temperature measurements... and satellite readings... and ice loss... and species migration... and... The planet has NOT experienced a massive drop in temperatures since the 1950s. So McIntyre's argument that Briffa should have shown that it had is pure nonsense. He's accusing Briffa of malfeasance for showing CORRECT results.
  44. Roh234 (@ 87) shows how easy it is for those that wish to misrepresent the science to pick-n-choose stuff that seems to support their misrepresentations. He shows a graph from Keigwin (1996). This data set refers specifically to a location in the Sargasso sea. If one was to address this particular data set scientifically, one would likely conclude that it was consistent with the evidence that the temperature variations during MWP (and to a lesser extent) during the LIA, were significantly related to ocean current and wind transport regime changes (solar driven?) that changed the distribution of global heat, with a large contribution involving “Gulf Stream” heat transport to the high Northern latitudes. It’s not surprising that temperatures in the Sargasso sea are sensitive to these. In support of this interpretation Keigwin and Pickart (1999) have shown that if one samples historical temperatures from cored proxies in the Laurentian Fan area to the NW of the Bermuda Rise, Sargasso Sea data, that sea surface temperatures were apparently much colder during the MWP compared to the LIA, and the temperatures of the Bermuda Rise-Laurentian Fan vary in “antiphase” as current regimes change. So if Roh234 (or the people that construct and disseminate misrepresentations) were to have selected Keigwin and Pickart (1999) rather than Keigwin (1996) he would have come to the opposite conclusion. Interestingly, Monckton uses the Keigwin 1996 graph to pursue exactly the same misrepresentation which is perhaps testament to the inherent laziness of those that consider it useful to attempt to pull the wool over our eyes!
  45. Chris, I think you have highlighted one of the difficulties in using proxy data. Roh234 showed that even recent proxies can result in opposite conclusions. Consequently, some scientific organizations have backed away from claiming that recent temperatures are higher / lower than those during the MWP.

    [DB] "some scientific organizations have backed away from claiming that recent temperatures are higher / lower than those during the MWP"

    Kindly please support that assertion with links; thanks!

  46. Jonathon, the issue Chris discussed was the misuse of a small area proxy to falsely claim a global trend. This does not suggest that proxies are unreliable... just that some people will misrepresent them. That said, the tree ring divergence problem of the past century does show an example of proxy results being unreliable. However, when you get matching temperature proxy results from glaciers, stalagmites, rock boreholes, tree rings, and many other sources it becomes very difficult to argue that they ALL experienced some effect OTHER than temperature which caused matching variations. Which is one of many reasons that the original Mann 1998 finding that the MWP was a localized effect with global temperatures significantly lower then current is now considered far more strongly established than it was then.
  47. CB, By localized, do you mean NH only? Because no significant difference has beenestablished between the NH temperatures then and today. I agree that some proxies have been used to misrepresent the data.
  48. Jonathon wrote: "Because no significant difference has beenestablished between the NH temperatures then and today." That statement is simply false. As extensively documented in the post at the top of the thread.
  49. Jonathan - "Because no significant difference has beenestablished between the NH temperatures then and today." That's not just wrong, that's blatantly wrong, and contradicted by the peer reviewed literature. As CB said, read above! I'm puzzled as to why you would make such an unsupportable statement.
  50. First, with one exception, the graphs show that recent temperatures are the warmest in ~500 years. I have no argument with that statement; and many scientific association seem to agree, as many of their statements claim that recent temperatures are higher than any time in the past four centuries. They have backed away from claims of the past millenium. The following are a few temperature reconstructions in peer reviewed literature that support my earlier statement. Also, see the Greenland ice core data in post #59. You seem to be selectively choosing that data which supports your position, while ignoring that which does not. This is similar to what you are saying about using proxies to misrepresent the data. Recent temperatures may very well be warmer than any tiem in the past millenium. However, there is sufficient data in the literature which shows otherwise.

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