The MWP in the Warm Pool

You may recall Hansen’s strange splice of modern instrumental records with a Mg/Ca SST proxy ending in 4320 BP based on a partially dissolved core.’ A couple of months ago, I mentioned a new paper by Newton et al (including L Stott) with a high Warm Pool MWP and briefly discussed Netwon’s presentation at AGU (which additionally used modern Mg/Ca values from 1990-1994 as reference.)’ Here is an interesting diagram of Warm Pool SSTs from Lowell Stott, a senior researcher in the field. Unfortunately the webpage didn’t specify what core this was from or otherwise specify the calculation.’ However, the diagram does seem somewhat inconsistent with Hansen’s claim about it being the warmest in a milllll-yun years, if it wasn’t even the warmest in a 1000 years. But Hansen’s article was personally reviewed by Ralph Cicerone, President of NAS.

Update: Lowell Stott confirmed that this is MD81, discussed in Stott et al 2004.


  1. tom
    Posted Dec 28, 2006 at 6:30 AM | Permalink

    Does anyone know of a blog that discusses global warming issues in
    nontechnial language that people without scientific backgrounds
    can understand. I always feel that the topics discussed on this
    site are very interesting. But, I need help with the teminology
    and abbriveations. Is there a blog like: “Global Warming Science
    for Idiots.”

    In the PR department, there are many blogs that are Gore-like pro
    global warming. But, I can’t find one that is more balanced.

    Thank you

  2. Paul M
    Posted Dec 28, 2006 at 6:53 AM | Permalink

    You could try There are some non-scientific overviews there but also plent of technical stuff.
    Matter of opinion as to whether it is unbiased but it does try to stick to the science.

    Regards and HNY

    Steve a belated Happy Christmas and Happy New Year and thank you for the excellent work even if like Tom I
    struggle with some of the terminology and science.

  3. Dave Dardinger
    Posted Dec 28, 2006 at 11:01 AM | Permalink

    re: #1

    I’d suggest the following. Open a separate browser window (using a differnt brower perhaps so you don’t lose your place. Whenever you find a term you’d like to know more about then paste it into whatever your favorite search engine is and pick one or more links to find out about it. Then you can go back to where you were at CA and continue on reading. I don’t really think you’re going to find a more (truly) balanced site than here.

  4. Paul Zrimsek
    Posted Dec 28, 2006 at 11:23 AM | Permalink

    I can see where this series poses a challenge to those who are trying to abolish the MWP, but how does it bear on Hansen’s claim about it being the warmest in a millll-yun years, considering that it appears to leave off around AD1825?

  5. Paul Penrose
    Posted Dec 28, 2006 at 12:01 PM | Permalink

    Re: #4
    According to this data modern temps are not warmer than the MWP. Since the MWP is within the claimed million year period you don’t need any earlier data to disprove the claim.

  6. David Smith
    Posted Dec 28, 2006 at 12:21 PM | Permalink

    Re #5 I think Paul Z is noting that the graph appears to end in the nineteenth century.

  7. Ken Fritsch
    Posted Dec 28, 2006 at 12:39 PM | Permalink

    Re #5 I think Paul Z is noting that the graph appears to end in the nineteenth century.

    And you are just the person to provide the missing data — without splicing, of course.

  8. Gil Pearson
    Posted Dec 28, 2006 at 2:27 PM | Permalink

    I thought that it was generally accepted that sea level was about 6 meters higher during the last two inter-glacials. The last two inter-glacials were also shorter than this one, so doesn’t this mean that they must have been warmer than now? Sounds too obvious! Must be missing something! Can anyone clarify?

  9. Steve McIntyre
    Posted Dec 28, 2006 at 3:16 PM | Permalink

    #4. Alicia Newton was confronted on this issue at AGU (in the same session as my presentation) by Michael Mann, who was very supercilious. Newton said that her modern comparandum was sediment trap Mg/Ca values from 1990-1994. So while the coretop was dated to the early 19th century (as you observed), the comparandum wasn’t. In a quite charming southern way, she stuffed Mann.

    She stated categorically that modern SST proxy values were less than MWP values.

  10. Ken Fritsch
    Posted Dec 28, 2006 at 3:51 PM | Permalink

    In a quite charming southern way, she stuffed Mann.

    She stated categorically that modern SST proxy values were less than MWP values.

    Well, I do declare. I would guess as a scientist she would be less concerned with the MWP to modern SSTs comparison than say a policy advocate/scientist like Mann.

  11. Sam
    Posted Dec 28, 2006 at 3:53 PM | Permalink

    Happy New Year to everyone. Great work Steve. Please continue to shine the light. Like Tom in #1, I need a
    great deal of catch up work to become more conversant with the jargon and technical issues. My son bought me
    “Statistics for the Utterly Confused” for Christmas so I am hoping that will increase my acumen. This is one of my
    must read sites that I rely on for information every day. Thanks so much to everyone.

  12. Steve Bloom
    Posted Dec 28, 2006 at 5:21 PM | Permalink

    Re #8: Gil, it’s not that simple. The difficulty is that the glaciations are triggered by combinations of orbital wiggles (Milankovitch cycles) that affect (most significantly northern hemisphere) insolation in somewhat different ways for each cycle. Differences in integlacial sea level are be a function of degree of melt of (mainly) the Greenland and West Antarctic ice sheets. Timing and hemispheric extent of the insolation changes are important because the WAIS is a grounded (below sea level) ice sheet that is capable of melting (taking “melting” to include physical collapse) far more rapidly than Greenland (which is ringed by mountains and has limited outlets to the sea). One of the problems with deconvoluting all of this is that it’s hard to extract the timing of the melts from the geologic record. So, taking the example of the last interglacial, we know that sea level was approximately two meters higher (IIRC) than present, but that does not imply that global temps were warmer (although they may have been). Also, when we say “warmer” we have to define what we mean since apparently the ice sheets can melt subtantially given a relatively short warm spike in the course of an otherwise cool interglacial.

  13. Steve Bloom
    Posted Dec 28, 2006 at 5:23 PM | Permalink

    Re #9: Did she provide data on that comparandum? I have to say that five years sounds a little short for such a purpose.

  14. Steve McIntyre
    Posted Dec 28, 2006 at 5:44 PM | Permalink

    #13. When I emailed her asking for data, she promptly sent me data, unlike – ahem- the Team. I asked Gabi Hegerl whether Tom Crowley’s hard drive had been recovered and still no answer.

  15. TAC
    Posted Dec 28, 2006 at 6:55 PM | Permalink

    #12 SteveB: Can the inter-glacial sea level rise be attributed entirely to ice melt?

  16. Paul Zrimsek
    Posted Dec 28, 2006 at 8:57 PM | Permalink

    #9: It sounds like Newton’s data is what really should have accompanied this particular post, then. Though Stott’s is certainly interesting in its own right: I wouldn’t fancy playing hockey with that, even if extending it to the present were to put a blade on the end of it.

  17. Steve McIntyre
    Posted Dec 28, 2006 at 9:46 PM | Permalink

    #16. Stott was a coauthor of Newton’s. My notes indicate that Newton said that Mg-Ca sediment trap information showed 1990-1994 values about 0.5-1 deg C less than MWP values – which would put them around 29.5 deg C. In Hansen’s PNAS diagram, he shows 2001-2005 Warm Pool SST values at about 29.7-29.8 deg C. Ruber Mg-Ca is reported to run a bit cooler than instrumental SST (perhaps reflecting calcification below surface).

    I agree that this information is necessary to tie this together. To some extent, all I was doing here was documenting this interesting graphic – which, in this case, is not well documented by Stott (who writes interesting articles upon which I plan to do some posts.)

  18. Steve Bloom
    Posted Dec 29, 2006 at 2:05 AM | Permalink

    Re #15: Glacial rebound and thermostearic rise due to the expansion of warmer water are the other significant factors, although far smaller than the contribution from the ice sheets.

    Re #14/7: So you do or don’t have the ’90-’94 data? BTW, although Newton is lead author, she’s Thunnell’s grad student and this is her first real paper AFAICT. Bear in mind regarding the Q+A between her and Mike that it probably would have been bad form for him to be seen to give her a hard time under those circumstances.

  19. Steve Bloom
    Posted Dec 29, 2006 at 2:18 AM | Permalink

    Re #17: If Hansen and Stott are both talking about Warm Pool average values, then how are the Newton results (from a very small area of the Warm Pool) especially comparable? Also, as I think about this more I realize I know absolutely nothing about the meaning to the LIA of a southward shift in the ITCZ at that location. Has a broad ITCZ shift been proposed to be linked to the LIA?

  20. Steve McIntyre
    Posted Dec 29, 2006 at 7:45 AM | Permalink

    #19. I’m all for looking at Warm Pool values as a general index of global temperatures – a point made by Hansen which seems sensible. I get the impression that site information is more likely to have regional significance than – say – a tree ring chronology, where one site means virtually nothing. Hansen presented results from one site, as did Newwron et al. Stott et al 2004 presented 3 sites.

    The ITCZ issue is very interesting. Yes, northward-southward movements of the ITCZ are currently being associated with the MWP-LIA. See Newton et al for a disucssion of tropical proxies in this context. There is literature on this associated with Cariaco as well.

    On an earlier thread, I suggested that Kim Cobb’s “evidence” for a cool medieval PAcific – dO18 levels in some corals – could be economically explained by a slight northward movement of the ITCZ in the MWP. This looks more and more plausible.

  21. TAC
    Posted Dec 29, 2006 at 9:03 AM | Permalink

    #18 SteveB: Thanks.

    A couple of other questions: Would it be correct to conclude that sea level is closely tied to global temperature history? If so, do you have a sense of the magnitude of the time frame over which temperature influences sea level?

  22. bender
    Posted Dec 29, 2006 at 9:39 AM | Permalink

    Re #18(2)

    it probably would have been bad form for him to be seen to give her a hard time under those circumstances

    Under the circumstances (and only under these circumstances!), I would agree. Of course, just because Dr Mann deferred doesn’t mean he was in the right. Forget the personalities and focus on the science; who was right?

  23. Steve McIntyre
    Posted Dec 29, 2006 at 10:31 AM | Permalink

    it probably would have been bad form for him to be seen to give her a hard time under those circumstances

    It’s not that he didn’t try. His question was expressed in a very snotty know-it-all way; it’s just that she was better informed than him and had a good answer. You only get one crack at AGU; there’s no opportunity for follow-up. If you don’t ask the right question the first time, that’s it. But it’s not that he would have had any relevant follow-up anyway.

    As to Mann and Hughes being worried about “bad form”, excuse me. They obviously weren’t worried about “bad form” or else they would have expressed themselves differently when they commented on my presentation. They had no comments that scored any points against me; they were simply rude and embarrassed themselves.

  24. bender
    Posted Dec 29, 2006 at 11:33 AM | Permalink

    Re #23
    So Mann did not defer follow-up, as I assumed in #22; he had no choice. Thanks for the correction.

  25. buck smith
    Posted Dec 29, 2006 at 11:35 AM | Permalink

    This is pretty funny. RealClimate has an end of year post up and one of the items was:

    Boldest impractical policy idea: Geo-engineering.
    I posted this comment which it appears that are not going to publish:

    I agree with Peter Backes about geo-engineering. Also I do not understand the biggest increase in uncertainty as a function of more research would be with aerosols. Hansen himself weights the various forcings and shows that upper atmosphere aerosol have a big influence on climate.

    And the effect of aerosols should known with more precision than any other forcing since it is the only one with periodic negative going spikes. Determining the relative effect among the other forcings must necessarily have a greater range of uncertainly since they all show a simple ramp function during the period we have data.

    I know that the posters on this board pride themselves on being true scientists and having the best understanding of the problems of global warming. But sometimes the best solution to a problem is to let’s the engineers work on it. πŸ˜‰ That’s why it’s called geo-engineering! I think we could harness private enterprise to prototype some solutions with an X-prize style contest, say $10M for a prototype system that could deploy and retrieve particle clouds in the upper atmosphere or in orbit.

  26. Mark H
    Posted Dec 29, 2006 at 1:09 PM | Permalink

    RE 23


    Perhaps I missed it but I have not seen a specific thread on your presentation and the questions. Does one have to buy the proceedings publication? Are the questions/answers of the session included. Love to hear about it.

  27. Steve McIntyre
    Posted Dec 29, 2006 at 3:18 PM | Permalink

    #26. It looks like I didn’t do a specific post – I thought that I’d done one. If you browse through this post , you’ll see some reports of the session, including some from TAC that are almost instantaneous.

  28. Mark H
    Posted Dec 29, 2006 at 5:44 PM | Permalink


    Thanks for the info. Thought someone should note that I was unable to access your power-point presentation – got an “unauthorized” message.

  29. Steve McIntyre
    Posted Jan 8, 2007 at 1:49 PM | Permalink

    I sent an inquiry to Lowell Stott, who promptly confirmed that this was indeed MD81 with a slightly revised age model.

  30. Mr D
    Posted Jan 11, 2007 at 5:45 AM | Permalink

    Hi, this is my first post on here. I’m a teacher (ages 11-16) trying to understand the evidence for and against man-made global warming so I can teach it to my class. (The usual thing seems to be just to tell the students that CO2 emissions are causing global warming and be done with it). I’ve looked at the Ppt presented above and just wondered if anyone could answer what I hope are a few simple questions about it, please?

    1. From slide 5 do I understand that ALL the proxy methods (other than bristlecones) show pretty much random ‘noise’, or just the ones shown?
    2. What, simply, is the problem with using these trees? (I am assuming it is the tree ring sizes that give an estimate of temperature?)
    3. How was the “different spaghetti recipe” graph on slides 4 and 16 constructed? Is it a reconstruction of each of the lines shown on the LHS of slide 4?
    4. Presumably the y-axis of the “different spaghetti recipe” shows temperature in degrees C? What does the “zero” correspond with?
    5. What does the black line (labelled CRU) mean?

    Thank you so much for any help you can give me here.

  31. jae
    Posted Jan 11, 2007 at 12:39 PM | Permalink

    #30: There are many good proxies, but most of the tree ring studies are seriously flawed. Perhaps the best place to go to get the background you need is the “Spot the Hockeystick” article link under “Favorite Posts,” on the left of your screen.

  32. Posted Jan 12, 2007 at 2:53 AM | Permalink

    Mr. D: Steve McIntyre can answer your questions much better than I can, and there are definitely documents/posts explaining these things on this web site, but in the interest of simplicity for your sake I’ll have a go at answering the them:

    1. I don’t know if you can say that all proxies just show random noise other than the bristlecones/foxtails, but put it this way: if you take an average of a random assortment of proxies excluding those two groups (which are related types of trees), you typically don’t get anything very interesting. So, to put it another way, the only really strongly correlated signal evident upon casual analysis tends to be in proxies of those types. Other individual proxies seem to contain signals but they generally don’t agree with each other very well, especially those from locations far apart.

    2. There are several problems with using the trees, but I’ll mention the most important. Firstly the tree ring proxies do not correlate well with modern instrumental temperature records taken at nearby stations. If these proxies are indeed good temperature proxies, you’d expect they would. This is explained away by saying that the proxy is a “teleconnection” – i.e. it’s a proxy for something else which somehow represents temperature elsewhere. I think that violantes Occam’s Razor, personally, and there’s really no good strong evidence for it, other than the fact that global instrumental temperature record seem to be going up in the last 50 years or so, and so do the bristlecone/foxtail ring widths. Correlation is not causation, but this seems to rely on it being the case. Mr. McIntyre calls this type of situation “spurious regression” and he has some strong statistical evidence that this is indeed the case.

    The other problem is that in general, tree rings are proxies for a number of different parameters, such as temperature, rainfall, CO2, snow pack, insect population, etc. What’s worse, trees don’t necessarily respond linearly. A really hot year may actually cause a tree to grow less than normal, not more, just as a cold year might. What’s worse, which factors affect the growth of a particular tree may vary over time. Put this all together, and extracting a good clean temperature signal from ring widths, even from carefully picked trees, is not trivial. Some of the people who sampled the bristlecones and foxtails explicitly stated in their paper(s) that the late 20th century spike in growth can not be explained by temperature. Therefore in my opinion, these proxies should not be used in temperature reconstructions without a very good explanation.

    3. I’m not looking at the document right now but I think that you’re looking at graphs constructed from red noise. In other words, random numbers were generated which look a lot like proxies, but are in fact random. (To make them look similar, they are generated with a similar degree of autocorrelation). These are then fed into the MBH98/99 method and a “hockey stick” pops out. Random numbers going in should not cause a trend to pop out with a proper method of analysis.

    4. It’s probably degrees C delta. 0 would be some kind of baseline temperature, often the average temperature from 1900 to 1980 or something like that. So what you’re seeing is the purported temperature variation from some baseline average.

    5. CRU is, I believe, an instrumental temperature aggregate data set. So chances are, you are looking at the reconstructed temperatures from proxies being laid over with the actual recorded temperature average delta. if the reconstruction is good, you’d expect a high correlation.

  33. MarkR
    Posted Jan 12, 2007 at 6:11 AM | Permalink

    #30 Mr D
    Try this.

  34. Mr D
    Posted Jan 12, 2007 at 12:25 PM | Permalink

    Hi Mark, Nicholas and Jae – thanks for your help. πŸ™‚ I was refering to this ppt
    I’ve found lots of useful info against Mann’s hockey stick now, but am still trying to understand the problem with the other proxies. Have I got this right:

    1. All the graphs from the ‘spaghetti’ share a lot of data
    2. It is only really the bristlecone proxies that show a sustained warming
    3. One reason different studies give different graphs is because of the way the evidence is weighed?

    So if the hockey stick weighed data in a different way it might come out like those spaghetti graphs, and therefore show the MWP (Medieval Warm Period), just like some of the spaghettis do?

  35. Mr D
    Posted Jan 12, 2007 at 12:32 PM | Permalink

    PS I have been trying to wade through the evidence for and against man-made global warming for a long time now and have come up with a way of trying to teach it to the children in my class. The idea is to present several pieces of evidence both for and against, each written on a little piece of card, along with the source of my information so they can think about that. The children discuss which evidence they find most compelling for each side, and which position they believe. Then I’ll give them several other cards, each of which contains information against one of the original cards (to show the interpretation of the evidence is in dispute). The children then have to match these up with the original ones and then discuss which evidence they find most convincing now.

    I tell you this just because I’m interested to have other people’s feedback on what I’ve done – have I made any errors, is there better evidence to present, etc… Would anyone here be interested in looking at them when I’ve finished?

  36. Posted Jan 12, 2007 at 1:11 PM | Permalink

    Mr. D:

    Sorry, only time for a quick response, so I don’t have time to look at the document right now (but I’m sure I’ve read it before). However, I’ll answer quickly as best I can.

    1) Yes, the “spaghetti” graphs are often describe as providing “independent” evidence for unprecedented warming. Mr. McIntyre has shown that they are not what you would normally describe as independent. In many cases they share upwards of 50% of their proxies, and almost all of them have one or two of about three very suspect proxies or proxy groups. The idea of claiming that they’re independent is that if one is found to be wrong, the claim is that it doesn’t matter, because the others show the same thing. However Mr. McIntyre has found problems with most/all of them, in many cases traced back to this small set of questionable proxies.
    2) The bristlecones are the prime suspect. There are a couple of other popular proxies which have an uptick at the end and which show up in many of the “independent” studies, but they are typically just one or two individual proxies, whereas the bristlecones/foxtails are a whole set of proxies, which tends to give them greater influence in the larger multiproxy studies like MBH98 and MBH99.
    3) Yes, the weighting is often very wrong. A straight average of all proxies often shows nothing interesting. Theoretically, the multiproxy studies are supposed to be representative of many places around the world, and well geographically distributed, but in reality something like 75% or more of the variance of the final reconstruction is based on a small area of North America (where the bristlecones/foxtails exist). Mr. McIntyre has shown that if you remove the biased methods which assign these massively distorted weightings, the “hockey stick” tends to vanish in the noise.

    I would call this “evidence against AGW”. I would say that much of the claimed strong evidence of AGW is in fact evidence of nothing. But absence of proof is not proof of absence. The case for AGW is simply nowhere near as strong as many people make it out to be. Not that evidence based upon multiproxy studies, anyway.

    Many of us here seem to think that written human history is a pretty good argument FOR long term climate variability. If nothing else, it tells us that to assume that the climate has been historically stable until industry came along is a dubious prospect. Therefore we should be skeptical of those claiming that climate does not vary outside of anthropogenic forcings. Similarly we should be skeptical when people say that they know what is causing a given fluctuation, because we don’t understand the natural variability well enough to rule it out in many cases. Those are my 2c anyway.

    I’m sure if you post up a link when you’re finished at least some of us will be willing to take a look and comment. I think we’ll be fair about it, for the most part.

  37. Posted Jan 12, 2007 at 1:13 PM | Permalink

    I would not call this “evidence against AGW”. Opps, missed a word, sorry.

  38. jae
    Posted Jan 12, 2007 at 7:05 PM | Permalink

    Mr. D: I think your method of teaching this subject is great. I wish more teachers would teach “both sides” of issues. It teaches the students many things, especially how to think independently. I think Nicholas did a good job explaining the tree proxy issue. As I mentioned, I think there are some really good proxies. Wander around this site, and you will find a lot of very interesting ones, with great comments by Steve M and others. I personally like proxy studies involving sediment cores, stalactites, carbon 14 in tree rings (for solar influences), tree-line studies, some ice cores. One really good way to look at things like the Medieval Warming Period (and perhaps even the Roman Warm Period) is to simply look at the written history. One of the things that bugs me about some of these scientists is that their study results are contrary to actual recorded events.

  39. Mr D
    Posted Jan 16, 2007 at 2:03 PM | Permalink

    Hi guys,

    Thanks so much for all your help and encouragement. I’m pleased to say I’ve pretty much finished the adventure now. πŸ™‚ However I’m afraid to say that I don’t have a website so can’t post a link. If any of you would like to see what I’ve written please e-mail me bartholomew “at” (I’ve written “at” because I heard spammers get your e-mail easier if you type it properly).

    Thanks again!

    PS why are you guys still looking at posts on such an old thread – do you keep looking at all of them? Where does everyone hang out on this message board?

  40. jae
    Posted Jan 16, 2007 at 3:05 PM | Permalink

    Mr. D: you can post your stuff to a free url site, like and then link to it. Most folks hang out at the sites of the most recent postings. You must have got here thru a link of some sort. Just use the main web address:

  41. Dave Dardinger
    Posted Jan 16, 2007 at 3:23 PM | Permalink

    Mr. D,

    Actually I think we regulars normally just look at the recent comments box on the top right. Or we hit the Home spot at the top center and then just check to see if there are not new messages to look at If you want to really follow things closely you could write down the number of comments on each thread and check if it’s changed when you come back. Usually threads go pretty dormant after a couple of weeks.

    Or you can subscribe to get the RSS feed and get the new comments automatically. I haven’t tried that so I don’t know if it’s useful or not.

  42. MarkR
    Posted Jan 16, 2007 at 4:25 PM | Permalink

    Mr D, Aside from the recent comments on specific topics, (top right), one can usually find general chat going on at Unthreaded.

  43. MarkR
    Posted Jan 16, 2007 at 4:28 PM | Permalink

    Oops, that should be More Unthreaded.

  44. SteveSadlov
    Posted Sep 27, 2007 at 3:40 PM | Permalink

    Here’s a good one:

    Where this is heading is “Weakest Walker Circulation in a millllllllyun yearrrrrrrrs!”

    I guess they never heard of PDO. Or want to pull a MWP manoever to make it go away …..

  45. pdm
    Posted Mar 29, 2008 at 11:47 AM | Permalink

    I recall reading, i think in the wegman category, about an email from someone on the Team “…trying to figure out how we can get rid of the MWP…”. Did or does such an email exist or did I read that somewhere else?

  46. Andrew
    Posted Mar 29, 2008 at 12:26 PM | Permalink

    This is what you are looking for:

    Dr. David Deming (University of Oklahoma)
    β€œ Around 1996, I became aware of how corrupt and
    ideologically driven current climate research can be.
    A major researcher working in the area of climate
    change confided in me that the factual record
    needed to be altered so that people would become
    alarmed over global warming. He said, “We have to
    get rid of the Medieval Warm Period.”

    I don’t know if this statement was ever actually made, but Deming is th origin of the claim that someone said it. I’d buy it, personally.

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  1. By The Trouet Ocean Proxies « Climate Audit on Sep 11, 2010 at 10:34 AM

    […] series showing a warm Warm Pool MWP (discussed previously at CA on a number of occasions – here and here ) with related data used in Newton et al. Data is available online, but I haven’t […]

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