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Was there a Medieval Warm Period?

Posted on 28 November 2009 by John Cook

The Medieval Warm Period spanned 950 to 1250 AD and corresponded with warmer temperatures in certain regions. During this time, ice-free seas allowed the Vikings to colonize Greenland. North America experienced prolonged droughts. So just how hot was the Medieval Warm Period? Was it warmer than now? A new paper Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly (Mann et al 2009) (see here for press release) addresses this question, focusing on regional temperature change during the Medieval Warm Period and Little Ice Age.

Prior temperature reconstructions tend to focus on the global average (or sometimes hemisphere averages). In this study, more than 1000 tree-ring, ice core, coral, sediment and other assorted proxy records spanning both hemispheres were used to construct regional temperature change over the past 1500 years. The paper discusses many interesting topics, including some interesting consequences of prolonged La Nina conditions during the Medieval Warm Period. I'm still digesting this info and will return to it in a future post. But the central result of the paper is the regional temperature pattern during the Medieval Warm Period.


Figure 1: Reconstructed surface temperature anomaly for Medieval Warm Period (950 to 1250 A.D.). Temperature anomalies are defined relative to the 1961– 1990 reference period mean. Gray areas indicates regions where adequate temperature data are unavailable.

The Medieval Warm Period found warm conditions over a large part of the North Atlantic, Southern Greenland, the Eurasian Arctic, and parts of North America. In these regions, temperature appears to be warmer than the 1961–1990 baseline. In some areas, temperatures even even as warm as today. However, certain regions, such as central Eurasia, northwestern North America, and the tropical Pacific are substantially cooler.

So the Medieval Warm Period was not a global phenomen. Warmer conditions were concentrated in certain regions. Some regions were even colder than during the Little Ice Age. For this reason, the paper's authors refer to the Medieval Warm Period as the more technical sounding 'Medieval Climate Anomaly' (the MCA in Figure 1). Personally, I don't see the term becoming ubiquitious. 

There is also an examination of temperature patterns during the Little Ice Age. There is pronounced cooling over the Northern Hemisphere continents. However, some regions such as parts of the Middle East, central North Atlantic, isolated parts of the United States and tropical Eurasia displaying warmth comparable to present day.


Figure 2: Reconstructed surface temperature anomaly for Little Ice Age (1400 to 1700 A.D.). Temperature anomalies are defined relative to the 1961– 1990 reference period mean. Gray areas indicates regions where adequate temperature data are unavailable.

What does this all mean? To claim the Medieval Warm Period was warmer than today is to narrowly focus on a few regions that showed unusual warmth. However, when we look at the broader picture, we see that the Medieval Warm Period was a regional phenomenon with other regions showing strong cooling. Globally, temperatures during the Medieval Period were less than today.

UPDATE 29 Nov 2009: NewYorkJ makes the suggestion of comparing the Medieval Warm Period temperature pattern to modern times. Here is the temperature anomaly for the last decade (1999 to 2008). As the color scale from the NASA map covers a broader range from -4C to 4C, I've edited the colours so they more closely match the MWP colour range.


Figure 3: Surface temperature anomaly for period 1999 to 2008. Temperature anomalies are defined relative to the 1961– 1990 reference period mean. Gray areas indicates regions where adequate temperature data are unavailable (NASA GISS)

UPDATE 1 Dec 2009: gp2 has also created a temperature pattern for the last decade using NOAA data. This time, the colour scale matches exactly the colour scale used in the Medieval Warm Period figure.


Figure 4: Surface temperature anomaly for period 1999 to 2008. Temperature anomalies are defined relative to the 1961– 1990 reference period mean. Gray areas indicates regions where adequate temperature data are unavailable (NOAA)

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Comments 1 to 50 out of 69:

  1. Before you consider the MWP read The Great Warming by Brian Fagan, renowned archeologist. <$10 on Amazon.

    What is fascinating about Fagan is that he has fell for the same elixir as so many others drink. In his introduction he talks about how the tree ring data shows the warming, but at the time of his writing he didn't know about the "tricks" used. If the data don't fit, just splice something in that does! No matter what, don't give any cannon fodder to the those who might have inquiring minds.

    How can we trust the tree ring data, when it doesn't fit since 1960??? So the tree ring data fits the MWP when we didn't even have thermometers, but it doesn't fit the era when we had literally thousands of surface based temperature stations throughout the world.

    Corals, sediments, ice cores, proxies...I think in the last week we have only scratched the surface.
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    Response: "How can we trust the tree ring data, when it doesn't fit since 1960?"

    You're talking about the divergence problem. The short answer is that the tree ring proxy record shows good agreement with other proxies in past periods. It is only in recent decades that tree ring proxies diverge from other proxies and the instrumental record. For more details, see the page on the tree-ring divergence problem.
  2. Nofreewind, you don't really understand much about tree rings, do you?

    In fact the divergence problem is only associated with a very small number of trees from one particular place. These are the rings reported by Briffa.

    Since his original papers there has been a recent paper published which explains why these particular trees were abnormal in their temperature response. As originally thought, there were other factors involved at that particular location.

    "Recent unprecedented tree-ring growth in bristlecone
    pine at the highest elevations and possible causes".

    Matthew W. Salzer, Malcolm K. Hughes, Andrew G. Bunn, and Kurt F. Kipfmueller

    http://www.pnas.org/content/early/2009/11/13/0903029106.full.pdf+html
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  3. Actually, Ian, the divergence problem refers to tree ring chronologies, mostly at high latitudes, that show *less* growth than expected in relation to increased temps in the 1960s.

    I think the paper you cite (Salzer et al) shoot down those who claim that recent *accelerated* growth in bristlecone pines at high elevations (but not latitudes) might be due to CO2 fertilization or something else other than a response to temps. It solidifies the bristlecone pine proxy so scathingly dismissed by skeptics (they also saw no significant difference between stripbark trees and those that don't show that growth pattern).

    However ... to nofreewind ... Ian's point still holds partially in that not all high latitude tree ring chronologies suffer from the divergence problem (in particular Briffa's Yamal reconstructions, which is probably why McIntyre is so focused on trying to demolish that particular reconstruction with such vehemence).

    There are three possible likely sources of the divergence problem:

    1. anthropogenic changes (air pollution, for instance)

    2. precip or snowmelt timing changes (causing drought/water stress rather than temp to be the limiting growth factor after temps warm to a certain point)

    3. global dimming (which from my reading is thought to be a stretch, i.e. not likely)

    If #1 is true, then the current divergence has no relevance for reconstructions in the deep past.

    If #2 is true, it's only a problem where temps were warm enough in the past to trigger enough change in precip and/or snow melt timing changes to cause that to become the limiting growth factor. This could lead to an underestimation of the MWP from what I can see, but wouldn't be a factor at other times during the reconstructions. But there are other proxies, including (but not only) tree ring proxies not showing the divergence problem, that show a cooler-than-today MWP for many regions (and at least one northern siberian tree ring chronology showing a warmer regional MWP) that well, you end up with what Mann '09 here says ... some regional warming greater than today, some regional cooling, over all no global warming comparable to today.

    Oh, there are actually two more potential gotchas in the divergence problem:

    4. Use of RCS rather than certain other smoothing techniques causes it to go away to some extent in many of the chronologies, i.e. there are end point problems with some smoothing techniques that contribute to an artificial "tailing off".

    5. The thermometers are typically at lower elevations and some distance away from the various tree sites used by researchers, so there are microclimate differences that would lead one to expect that the temp and proxy results would differ.

    AFAIK, pretty much all of the above are being actively looked into by researchers, judging from a relatively recent review paper I've read (2007).
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  4. Having said all of the above, let me make clear that I'm just a layman with too much time on my hands, interpreting stuff I've read that's written by the experts. I may have, in fact likely have, gotten some of it wrong, so YMMV.
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  5. Good post. For comparison, here's the anomaly map for the last couple of decades, same base period. Different color scale, but we can get the idea.


    It seems a bit unusual for both MWP and LIA to show a warm anomaly in the North Atlantic, until it's noted that the map is an offset from the 1961-1990 average, which showed generally cooler temperatures in that region during that period. Here is the 1961-1990 period in comparison to the 1900-2008 average.

    It would be interesting to see the MWP and LIA in context of the last century average (a more apples to apples comparison in terms of timeframes being compared), and also in comparison with the last 20 years. What's notable is that the anomaly map from the study isn't a comparison with the recent decade or two but with the 1961-1990 average.
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    Response: You know, when I was writing this post, I did think it would be useful to compare current temperature patterns to the MWP pattern. But in my defence, it was approaching midnight when I wrote this post and I had just spent 5 hours that afternoon playing cricket in incredibly hot and humid Queensland conditions. But enough excuses! I've added the temperature pattern of the last decade. Thanks for the comment.
  6. The consensus in Norway seems to be that in the period 500-1500, the temperature in Scandinavia was 0.5-1 oC higher than the 1961-90 mean, which by no means seems to be reflected in fig 1.

    You may download a pdf (in Norwegian) from
    http://nou-klimatilpassing.no

    This is a official report, documenting climate changes and discussing possible changes towards 2100.
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  7. Can anyone who has read the paper please let me know how they can possibly get sufficient proxy data to cover the entire globe? I am particularily curious how they would work out the anomalies for the oceans. Is there some sort of algorithm at work here?

    Cheers, :)
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  8. #3 dhogaza
    Surely that list of caveats also applies to the data that 'fits' the model. I've noticed a trend were data that fits the theory is often simply presented and described while data that goes against the theory is often followed by a list of possible explanations to invalidate it. That's assuming the researchers have the grace to present it in the first place.
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  9. With regard the the Mann paper.
    John it would be useful for you to show the map of proxy locations (i.e. the rest of fig2 from Mann) for those that can't access the paper. Although I think everybody can access the supporting data freely here.

    To describe the spatial data for the MWP as sparse I think is generous. There are 6 proxy data sets for the whole area east of the horn of Africa. I would be interested how you get the large blue (cold) area in central eurasia when there are no proxy records for that area. Although its difficult to overlap the temp and proxy maps it appears that the only proxy points around central eurasia conicide with the couple of hotspots in that region.
    Also there are no proxy data over any ocean regions, most of africa, anywhere in S.America away from the west coast, the whole of malaysia/indonesia/philipines/australia(except tasmania)/pacific Islands, the middle east,Western Europe..... Do you get the point!!
    I really struggle to see he can allocate a colour to most of the globe during the MWP. I'd love to see the reviewers comments.
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  10. #7 Shawnhet you can get the map of the proxy positions from the supplementary data. See link in #12
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  11. Because you are comparing high quality recent observations with past reconstructions, you would expect the past reconstructions to show more regional variation simply as a result of much lower quality data


    Actually, you'd expect random uncertainty in the data set to average out, given a sufficient sample, and a 1000 proxies is a large sample ...
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  12. How does 300years of La Nina conditions work?
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  13. Surely that list of caveats also applies to the data that 'fits' the model.


    Why? Liebig's Law of the Minimum is well-established, has nothing to do with climate science or paleo reconstructions of tree-ring temperature proxies, and is based on sound understanding of plant physiology important to science-based agriculture.

    Essentially you're saying "I don't like what I'm hearing, so I don't accept it".
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  14. nofreewind
    You said
    "So the tree ring data fits the MWP when we didn't even have thermometers, but it doesn't fit the era when we had literally thousands of surface based temperature stations throughout the world."

    I totally agree!

    ---------------------------------
    John,
    In previous articles, in looking for proof for global warming, local Antartic cooling is played down as not counting, whereas in this article, local conditions are interpreted as just a shifting of the Earths energy distribution.
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    Response: The way to approach Antarctic cooling is the same as the approach to the Medieval Warming Period. Rather than focus on a specific region while neglecting the broader picture, look at the global pattern. Figure 3 above demonstrates that while there has been cooling in some Antarctic regions, the full global picture is that of warming. The planet has a net energy imbalance and is accumulating heat. This is in contrast to the global temperature pattern during the Medieval Warming Period which only suffered a mild energy imbalance and consequently showed a mild net warming.
  15. Referring to the last graph. It seems odd that temperature anomalies are seen to affect the northern polar regions more accutely, whereas this region is plunged in darkness almost half the year. This does not seem to play into the idea that CO2 is the main cause of global warming. If this were the case, you would expect a distribution with the largest anomalies in the equatorial regions happening first.

    What the map seems to indicate is direct convective warming of the polar regions from a warmer atmosphere, and if man made, likely due to latent exothermal pollution sources. I am aware that this is not a popular idea, as I've been told that this energy doesnt amount to a hill of beans, but on the other hand, I am also suppose to believe in a environment that is precariuosly sensitive. It is sensitive, but not that sensitive, etc. At any rate, I understand, once you have sipped the Kool-Aid, its too late. There is no going back.
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  16. re13:
    "Actually, you'd expect random uncertainty in the data set to average out, given a sufficient sample, and a 1000 proxies is a large sample ..."

    The variation in spatial data and distribution (ie maps above) would not 'average out' in a large dataset, as they are not 'random uncertainties'; they are in-built weaknesses inherant whenever one uses proxies, which will tend to increase with age in comparison with a standard dataset (eg 1961-1990). (Much the same reason human history becomes more unreliable the further back in time you go-these 'unreliables' dont 'average out', they just get worse). This quite predictably, and expectedly, actually enhances and highlights, rather than 'averages out', the outliers etc of an older dataset, when compared to a modern standard. This is what 'standards' are supposed to do, highlight discrepancies in a non-standard dataset, which ironically, is just what the paper of Mann et al 2009 does. The MWP data is therefore misinterpreted, and which is also the skeptical contention of the hockeystick of Mann et al 1998-that the proxies are not picking up the full range of warmth of the MWP. This new Mann et al paper largely shows this again to be the case.

    The final graph is also a bit misleading, relative to the above discussion. If the proxies do not pick up past warmer periods well, and moreover will always show a greater number of (spatial) outliers and in-built variations and uncertainties, it will be a rather misleading and false comparison if they are then placed against any other warm instrumentally-based data. All that the final map, relative to the above discussion, shows, is show that the older proxies in the MWP are not picking up warmer temperatures the way modern instrumental methods do.
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  17. The variation in spatial data and distribution (ie maps above) would not 'average out' in a large dataset, as they are not 'random uncertainties'; they are in-built weaknesses inherant whenever one uses proxies


    You only need a sample size with sufficient spatial distribution to build a map of a particular resolution. So what you have to do here is to prove that the 1,000 proxies Mann has studied don't support the resolution he's claiming in his analysis.

    Yes, the spatial resolution is not as good as you go further back and have less spatial data. I note that the proxy reconstruction map uses big boxes- relatively poor resolution - while modern temperature maps such as the decadal map John's posted has much higher resolution.

    This quite predictably, and expectedly, actually enhances and highlights, rather than 'averages out', the outliers etc of an older dataset, when compared to a modern standard.


    I see no basis for this claim whatsoever.


    The MWP data is therefore misinterpreted, and which is also the skeptical contention of the hockeystick of Mann et al 1998-that the proxies are not picking up the full range of warmth of the MWP.


    Nor this - not that it matters. A warmer MWP than science actually supports doesn't impact the reality that a warmer tomorrow's going to require extremely expensive mitigation efforts.
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  18. >Nofreewind, you don't really understand much about tree rings, do you?

    you are right! but i have a good head for finding out the truth and 8 yrs of science degrees.

    >In fact the divergence problem is only associated with a very small number of trees from one particular place. These are the rings reported by Briffa.

    You mean there was no divergence in the MBH reconstruction? It is incorrect that much of the Mann 2001 IPCC graph was primarily from a few bristlecone's in Colorado?

    What is "nonsesne" in this paper?
    http://www.climateaudit.org/pdf/ohio.pdf

    Seriously, have all climate scientists taken the time to look at the archeological history. (FAGAN, FAGAN, FAGAN - and he is one of yours!)I think if you did you would agree that the warming from 1976 to 1998 was completely unremarkable, at least the rate of change, even the CET series will tell you that.

    I agree that that 1998 might have been the warmest year for at least 500 years. And the past decade might be the warmest for 500 years or so. If there is even such a things as "global temperature".

    How comes Wikipedia doesn't even mention the word divergence in their Hockey Stick controversy article? Is this divergence something that was somewhat hidden before ClimateGate, or is this something that has been discussed as part of the ClimateAudit work?

    If they can't calibrate their instruments with good recent hopefully 100% accurate temperature data, (???), how do they know there weren't period of hundreds of years in length 200 or so years ago where there was "divergence".
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    Response: The divergence problem was discussed in the peer review literature as early as 1995, suggesting a change in the sensitivity of tree growth to temperature in recent decades  (Jacoby 1995). There have been a number of papers since then examining the problem. For more info, see the page on the tree-ring divergence problem.

    And for the record, if you're talking about global temperature, 1998 is not the hottest year on record. 2005 is.
  19. "How comes Wikipedia doesn't even mention the word divergence in their Hockey Stick controversy article? Is this divergence something that was somewhat hidden before ClimateGate, or is this something that has been discussed as part of the ClimateAudit work?"

    The divergence problem (along with various other uncertainties) was discussed well before Steve McIntyre began his crusade against climate science. See John's post "What do the hacked CRU emails tell us?"
    and note the following article.

    Not sure about the Wikipedia article, but my take is that it covers mostly the political controversy instigated by M&M. It would be nice to update the Wikipedia article to include the fact that relevant issues such as the divergence problem were already documented in the peer-reviewed literature (some people seem to think McIntyre discovered this). Consider also that the original "hockey stick" graph contained a large uncertainty range, something consistent with a more pronounced MWP and LIA.

    See also the latest Mann et al. reconstruction.

    http://www.ncdc.noaa.gov/paleo/pubs/mann2008/mann2008.html

    thingadonta,

    "All that the final map, relative to the above discussion, shows, is show that the older proxies in the MWP are not picking up warmer temperatures the way modern instrumental methods do. "

    Well if one has already concluded that the MWP was warmer than today (based on?), that conclusion might make sense (keep in mind that reconstructions without tree rings reveals a similar pattern). I think there are many who badly want to believe that. Although it has no impact on greenhouse gas physics (although some might argue a more variable climate is a more sensitive one), if skeptics can show the MWP is equal or warmer than today, they think it will help convince folks that modern warming is entirely natural.
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  20. dhogaza, yes I inadvertently referred to the divergence that Briffa discussed in the illegally released e-mails with THE divergence problem which predated Briffa's paper. However, nofreewind was (I think, it is hard to follow most denier's thinking) discussing the Briffa divergence.

    nofreewind, I do not have the time to waste reading what will no doubt turn out to be non-scientific nonsense by SM.
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  21. Ian, I have time to read this site, and I don't consider this site as "nonsense", in fact this seems like quite a scientific place compared to most of what I read. What I like best about McIntyre piece
    http://www.climateaudit.org/pdf/ohio.pdf
    is his describing how hard he tried to get the actual raw data and couldn't. Then he asked for advice to reproduce the data with new samples and was told it was terribly technical to do. After a Starbucks coffee he found the same crooked, erratically growing Bristlecone that were used to take the initial samples. No I don't know much about tree rings, but as layperson I am surprised that the scientists use crooked, erratically growing trees as a proxy for anything whatsoever. But I would appreciate someone pointing me to the nonsense in the paper, I am sure RealClimate has it figured out somewhere. Excuse me, but I don't have formal climate science training and obviously regular common sense fails when analyzing many of these issues. I am willing to learn, but need more than "trust me, I did these complex mathematical calculations/error massaging which you could never understand".
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  22. I know that the suns influence on climate is in dispute, even the skeptics don't seem to be agree on the sun. But could someone tell me if the Warmers accept this solar activity graphs as true. Even if the affect on climate is just a coincidence, because I remember reading that Warmers saying that there is not enough energy in the suns "changes" to add energy to our system.
    http://www.landscheidt.info/images/newc141.jpg
    I find these Fagan books fascinating for many reasons, I just ordered a few more. The Little Ice Age book is so interesting because Fagan goes to great lengths to give all the historical references about the long periods w/o sunspots in the LIA. And what makes these books even better is he is a AGW believer, so we know when he talks history/archeology he is not attacking nything. But I am curious about that graph, were people really measuring sunspots in the MWP? Apprently the telescope wasn't even invented until the 1600's.
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    Response: I've reproduced the JPEG image you linked to. I can't confirm the veracity of the graph as it doesn't cite sources but qualitatively it looks right.



    This graph doesn't come from sunspots - as you say, the reliable sunspot data doesn't go earlier than 1600. But solar activity also has an effect on carbon isotopes so this data would be taken from carbon captured in tree wood.

    Note that this graph ends in the early 20th Century. The rise in solar activity in the early 20th Century coincides with early 20th Century warming. If the graph was extended to present times, you would find that solar activity flattened in the 1950s and has shown no long term trend since then (if anything, a slight cooling trend in recent decades). Since the 1970s, sun and climate have gone in different directions.
  23. What I like best about McIntyre piece
    http://www.climateaudit.org/pdf/ohio.pdf
    is his describing how hard he tried to get the actual raw data and couldn't.


    The 2% of the data that CRU is not, legally, able to hand out freely. The other 98%, of course, which is all that NASA GISS uses, has been available on the internet for years now.

    Same with Briffa ... Briffa said, "go ask the Russians, it's their data", McIntyre got it from the Russians in 2004, and continued to scream "Briffa won't give me the data", and later, when called on it, "oh, I didn't know it was the same data ..."

    Sheesh.

    McIntyre reminds me of a two year old with a migraine.
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  24. I know that the suns influence on climate is in dispute, even the skeptics don't seem to be agree on the sun


    The really great thing about denialist "theories" is that they're so self-contradictory yet many denialists hold them all to be true at once. So you can have Watts screaming "there's no warming, it's just UHI" in the morning, and "it's the sun!" during lunch.
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  25. nofreewind:

    Supposedly, sunspots were observed as far back as 28 B.C.
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  26. nofreewind,
    it's hard to comment on a graph without the figure caption or an explanation. It appears to be a reconstruction of solar activity based on 14C cosmogenic production, not sunspot numbers.

    Anyway, it's related more to solar physics than to climate; in particular, to the possible link between gravitational influence of the planets and the sun activity.
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  27. nofreewind, your graph also stops in 1950 so you can't make any connection between post 1950 warming and solar activity. This was a distortion used by other well known deniers.
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  28. There is a beautiful graphic of the MWP
    here. Looks like your german cousin!!
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  29. NFW>McIntyre piece http://www.climateaudit.org/pdf/ohio.pdf
    is his describing how hard he tried to get the actual raw data and couldn't.

    dhogaza REPLY
    >The 2% of the data that CRU is not, legally, able to hand out freely. The other 98%, of course, which is all that NASA GISS uses, has been available on the internet for years now.

    NFW: I don't understand. I know Mann works at Penn State, news article yesterday. I didn't know that his data is kept at CRU or NASA GISS, aren't they keepers of temperatures, no tree-ring data? The Hockey Stick was pre-2001, yet here I read in the Wegman Report dated 2006
    http://www.climateaudit.org/pdf/others/07142006_Wegman_Report.pdf pages 48-49
    "4. In response to the letter from Chairman Barton and Chairman Whitfield, Dr. Mann did release several websites with extensive materials, including data and
    code. The material is not organized or documented in such a way that makes it practical for an outsider to replicate the MBH98/99 results. For example, the
    directory and file structure Dr. Mann used are embedded in the code. It would take extensive restructuring of the code to make it compatible with a local machine. Moreover, the cryptic nature of some of the MBH98/99 narratives means that outsiders would have to make guesses at the precise nature of the
    procedures being used."

    So this was the 3rd investigation of Mann. The 1st was the NAS report, then the Congressional hearing, which spawned The Wegman Report. So Wegman says in response to the Congressman Mann released the data. Why did he have to release it if it was at CRU or NASA? Also, they basically state they can't reproduce it because it is such a complicated thing to do. Well, we will have a fourth official inquiry into this matter, maybe the science is not settled, Penn State administration thinks something is not settled.

    The NAS found his work "plausible", that is pretty much the entire summation of their findings. I am no grammar expert, but isn't plausible a step below possible? Would you use the word plausible to define something that you have a high level of confidence in?
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  30. NFW: I don't understand. I know Mann works at Penn State, news article yesterday. I didn't know that his data is kept at CRU or NASA GISS, aren't they keepers of temperatures, no tree-ring data?


    Yes, I thought you were talking about McI's whining about 2% of the data used by CRU not some of the tree ring used in Mann's reconstructions.

    The Hockey Stick was pre-2001, yet here I read in the Wegman Report dated 2006
    http://www.climateaudit.org/pdf/others/07142006_Wegman_Report.pdf pages 48-49
    "4. In response to the letter from Chairman Barton and Chairman Whitfield, Dr. Mann did release several websites with extensive materials, including data and
    code.


    "releasing several websites" means "here's the URL to the website ..."

    The material is not organized or documented in such a way that makes it practical for an outsider to replicate the MBH98/99 results. For example, the
    directory and file structure Dr. Mann used are embedded in the code. It would take extensive restructuring of the code to make it compatible with a local machine.


    Oh, gosh, such an insurmountable obstacle, you might have to partition a disk and recreate Mann's directory structure on it, the horror! The unscientificness of it!

    As a software engineer with nearly 40 years experience in my field, this complaint makes me laugh. It might take a day or so to replicate the environment or to change the directory and file structure embedded in the code.

    Big deal. If this counts for quality criticism among denialists (and I know it does), then they're just being pathetic.

    Note the goalpost move, though:

    1. The code is secret, we can't run it!

    2. The code is public, but it's got hardwired directories in it! We can't run it!

    Pffft. Scientists aren't in the job of providing software *products* they're in the job of writing code useful for their own research.

    A ROTFLMAO moment for this highly-qualified software engineer.
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  31. >As a software engineer with nearly 40 years experience in my field, this complaint makes me laugh.

    Neither of us are tree ring experts. But I do know that this stuff is EXTREMELY complicated statistical and mathematical data and corrections have to be made for various reasons. Are you trying to tell me that when you write software, everyone can figure out the steps A & B that may have gotten you to G? Are you telling me that it would be quite easy to find steps C to F. With all due respect to Mann, there are various tricks used to correct data for variables, do you think all of various data tricks and methodology were completely explained in a few data files on a server?

    Do you think the Congressman ordered the Wegman report and the release of data, after the NAS report, because all of this very complex data, with necessary corrections was widely available? That doesn't make "common sense" to this layperson. Didn't you read any of the emails lately which openly discussed not releasing data? The emails may not matter to the science or the reality of climate, but it certainly sheds light on the entire process of how this work is done.
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  32. I apologize for possibly misleading someone who knows even less than me. Because obviously there is plenty of tree ring data on the CRU servers, and much of it is related to Mann. Here is comment regarding Mann data.
    http://www.americanthinker.com/2009/11/crus_source_code_climategate_r.html
    scroll halfway down. I think you will find that this tree ring data, proxies etc. is EXTREMELY complicated to reproduce, even for an expert, I am sure even for a like-minded colleague. Dhogaza - since 11/20/09 the game has completely changed. We are going to now start to play fair. Truth is the child of time......
    ---------------------------------------
    Climate Audit, can be found throughout the source code. So much so that perhaps the most ubiquitous programmer's comment (REM) I ran across warns that the particular module "Uses 'corrected' MXD - but shouldn't usually plot past 1960 because these will be artificially adjusted to look closer to the real temperatures."

    What exactly is meant by "corrected” MXD," you ask? Outstanding question -- and the answer appears amorphous from program to program. Indeed, while some employ one or two of the aforementioned "corrections," others throw everything but the kitchen sink at the raw data prior to output.

    For instance, in the subfolder "osborn-tree6\mann\oldprog," there’s a program (Calibrate_mxd.pro) that calibrates the MXD data against available local instrumental summer (growing season) temperatures between 1911-1990, then merges that data into a new file. That file is then digested and further modified by another program (Pl_calibmxd1.pro), which creates calibration statistics for the MXD against the stored temperature and "estimates" (infills) figures where such temperature readings were not available. The file created by that program is modified once again by Pl_Decline.pro, which "corrects it" – as described by the author -- by "identifying" and "artificially" removing "the decline."

    But oddly enough, the series doesn’t begin its "decline adjustment" in 1960 -- the supposed year of the enigmatic "divergence." In fact, all data between 1930 and 1994 are subject to "correction."

    And such games are by no means unique to the folder attributed to Michael Mann.

    A Clear and Present Rearranger

    In two other programs, briffa_Sep98_d.pro and briffa_Sep98_e.pro, the "correction" is bolder by far. The programmer (Keith Briffa?) entitled the "adjustment" routine “Apply a VERY ARTIFICAL correction for decline!!” And he or she wasn't kidding. Now IDL is not a native language of mine, but its syntax is similar enough to others I'm familiar with, so please bear with me while I get a tad techie on you.

    Here's the "fudge factor" (notice the brash SOB actually called it that in his REM statement):

    yrloc=[1400,findgen(19)*5.+1904]

    valadj=[0.,0.,0.,0.,0.,-0.1,-0.25,-0.3,0.,-0.1,0.3,0.8,1.2,1.7,2.5,2.6,2.6,2.6,2.6,2.6]*0.75 ; fudge factor

    These two lines of code establish a twenty-element array (yrloc) comprising the year 1400 (base year, but not sure why needed here) and nineteen years between 1904 and 1994 in half-decade increments. Then the corresponding "fudge factor" (from the valadj matrix) is applied to each interval. As you can see, not only are temperatures biased to the upside later in the century (though certainly prior to 1960), but a few mid-century intervals are being biased slightly lower. That, coupled with the post-1930 restatement we encountered earlier, would imply that in addition to an embarrassing false decline experienced with their MXD after 1960 (or earlier), CRU's "divergence problem" also includes a minor false incline after 1930.
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  33. I'm not a climatologist or a computer scientist. But at least I know how to search the internet a little bit! RSVP @17 -- you made two highly uneducated and unscientific assertions: one about expectations and the other about kool-aid. Here is the oldest reference I can find to show how wrong you are (I'm quoting a Cecelia Bitz post at Real Climate):

    'Manabe and Stouffer (1980) first popularized the phrase “polar amplification” to describe the amplified rate of surface warming at the poles compared to the rest of the globe in their climate model’s response to increasing GHG levels. Their early climate model had a simple ocean component that only represented the mixed layer of the water. Their model had roughly symmetric poleward amplification in the two hemispheres, except over the Antarctic continent, where they argued the ice is too thick and cold to melt back (see Fig 1). Both poles warmed more at the surface than the midlatitudes or equatorial regions.'

    I wonder if you'll see this confirmation of the model expectations and start to think that the experts actually know something (and knew it a long time ago). It seems popular, in some circles, to say: Notice that they say "climate change" now instead of "global warming"? What happens in minds when people are told that the IPCC (guess what CC stands for!) was formed in 1988. And what happens in those minds when they find out regional differences in warming were expected before then? When the expectations are met or exceeded by the observations, do they acknowledge that the science made good/useful predictions or do they run off to claim "Kool-Aid" about something else?
    0 0
  34. nofreewind, Gavin already explained at RealClimate that you (and others) are wrong about that code.
    0 0
  35. Neither of us are tree ring experts. But I do know that this stuff is EXTREMELY complicated statistical and mathematical data and corrections have to be made for various reasons. Are you trying to tell me that when you write software, everyone can figure out the steps A & B that may have gotten you to G? Are you telling me that it would be quite easy to find steps C to F.


    I would never claim that software engineering is easy, nor understanding other people's code. I don't mind, that's one reason my hourly rate is so high.

    No one has ever said that science is easy, either.

    Why this expectation that "anyone can figure out the steps"? I understand the tree ring stuff in quite a lot of detail because I've invested time into doing a fair amount of reading, but I don't know enough to write my own RCS code to create my own chronologies, and I see no reason to learn.

    But experts in the field can, without doubt (actually I think McI did, but I have no idea if he's done it correctly).
    0 0
  36. We are going to now start to play fair.


    Accusing researchers of scientific fraud based on UNUSED RESULTS found in a program they've toyed around with, when none of that shows up in the published research which is how results are communicated, isn't "playing fair".

    It's participating in McCarthyism.
    0 0
  37. This stuff is fascinating. In the last few days I've been looking at studies that Co2science.org lists that address the MWP. Now, I checked out this website and I understand they are not impartial, so please don't waste time explaining that. The thing is, I looked at several of the actual studies at the source (I have academic access) for different areas of the SH dealing with the MWP and to be honest, from a layman's point of view they look just as plausible as Mann's study. How would you address the seeming difference between Mann's results showing the MWP to be limited geographically and the results from other researchers which show a MWP in the SH?
    0 0
    Response: Mann's study does show regions in the Southern Hemisphere that showed warmth comparable to the latter 20th Century. Eg - the north of South America, mid-Africa, parts of Australia. I would suggest digging through the studies cited at co2science.org, see which regions they focus on and compare those regions to Mann's study. And please report back on what you find.
  38. The data is obviously not there otherwise McI would have taken it and reproduced the experiment. No doubt giving his own slant on the results. In fact if the data was free and easily available I wouldn't be surprised if multiple skilled individuals (from both sides of the debate) attempted the same thing. If I had the skill I'd do it tomorrow.

    The data isn't there in a useable form. I think there is sufficient evidence within the leaked emails to see that is a fact. After all if it's out there why would Jones be threatening to delete stuff so McI can't get his hands on it. Judith Curry's comments on this, while I'd be critical of some points, have at least been an attempt to shed light on the matter.
    0 0
  39. I see what you're saying. I'll take a closer look at Mann's paper next weekend as well as his sources.
    0 0
  40. Standard cherry-picking broght to the extreme consequences. Just a single (and not understood) line of code demonstrates the frode. The magic of out of context claims.

    It's useless keep crying about "the code's not clear enough". Why the hell should it be? The only thing that matter is the output of the code. I read claims by software engineers that the code is not well written. Probably; i also write the code myself and the only thing a care of is if it's correct, if it run smooth and efficiently, not if it's nice or easily readable.

    Forget the code, take the data or collect your own if possible, analyze and compare. This is the standard practice. Everything else is just chattering.
    0 0
  41. To Steve L
    Thank you for educating me on the term. Googling it took me to this:
    http://climateprogress.org/2009/03/12/what-exactly-is-polar-amplification-and-why-does-it-matter/
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  42. Mann 2009 is an interesting paper since it shows characteristic MCA patterns particularly warm north atlantic and cold equatorial pacific,another earlier paper, Trouet 2009 linked the persistent NAO+ pattern to cold pacific ocean.

    I've plotted a map from NOAA dataset with a similar colormap except that i've added two color at the extreme due to some pixel above 1.4°C anomaly in the last decade:
    http://ultraxs.com/image-8871_4B140B80.jpg
    0 0
    Response: Thanks for the very relevant link to Trouet 2009 and the NOAA colourmap which is particularly useful because it uses the same colour scale as Mann 2009. I've added the graphic below:

  43. This is extremely interesting.
    http://icecap.us/index.php/go/political-climate
    Let's look at the "credibility" of the Mann of who is at the heart of this data...
    _______________________________

    In fact, one skeptic raised this very issue about tree-ring data in a comment posted in 2004 on RealClimate, the blog operated by climate scientists. The comment, which questioned the propriety of “grafting the thermometer record onto a proxy temperature record,” immediately drew a sharp retort on the blog from Michael Mann, an expert at Penn State University:

    Mann: “No researchers in this field have ever, to our knowledge, ‘grafted the thermometer record onto’ any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation Web sites) appearing in this forum.”

    Dr. Mann now tells me that he was unaware, when he wrote the response, THAT SUCH GRAFTING HAD BEEN DONE IN THE EARLIER PRIOR COVER CHART, and I take him at his word. But I don’t see why the question was dismissed so readily, with the implication that only a tool of the fossil-fuel industry would raise it.
    Here it is here on RealClimate:
    http://www.realclimate.org/index.php/archives/2004/12/myths-vs-fact-regarding-the-hockey-stick/#comment-380

    Is Mann referring to the 2001 IPCC? Or whatever cover, you mean he didn't know about it????? This was the fault of the fossil-fuel industry, their influence? Sadly, people who don't know how to type to keep a bookmark folder seem to know very little about any of this!
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  44. Seriously, I respect this blog and the blog owner trying to enforce a "code of conduct", but what term could I use but calling Mann a LIAR? in his response to the commenter who asking him about grafting? Please tell me where I am talking nonsense? I have a funny feeling that Mann would come up with a very confident retort as he did in that 2004 RC post. We have to look at credibility, it is vital to science, in fact it is science.
    0 0
  45. Dhogaza, you said in regards to accessing and replicating the data. "Oh, gosh, such an insurmountable obstacle, you might have to partition a disk and recreate Mann's directory structure on it, the horror! The unscientificness of it! As a software engineer with nearly 40 years experience in my field, this complaint makes me laugh. It might take a day or so to replicate the environment or to change the directory and file structure embedded in the code."

    You might want to read the programmers comments embedded in the code(not sure what data he refers to), seems like some pretty precise work that they do to determine the earths temperature from thousands of data points, etc etc etc. all very very precise.

    I Saw Mommy Kissing Santa Claus....
    http://www.torontosun.com/comment/columnists/lorrie_goldstein/2009/11/29/11967916-sun.html

    As you read the programmer's comments below, remember, this is only a fraction of what he says.
    DHogaza, your comments might be convincing to the guy down the street but they aren't going to work with me!

    - "This whole project is SUCH A MESS ..." (266)
    - "But what are all those monthly files? DON'T KNOW, UNDOCUMENTED. Wherever I look, there are data files, no info about what they are other than their names. And that's useless ..." (Page 17)
    - "It's botch after botch after botch." (18)
    - "The biggest immediate problem was the loss of an hour's edits to the program, when the network died ... no explanation from anyone, I hope it's not a return to last year's troubles ... This surely is the worst project I've ever attempted. Eeeek." (31)
    - "Oh, GOD, if I could start this project again and actually argue the case for junking the inherited program suite." (37)
    - "... this should all have been rewritten from scratch a year ago!" (45)
    - "Am I the first person to attempt to get the CRU databases in working order?!!" (47)
    - "As far as I can see, this renders the (weather) station counts totally meaningless." (57)
    - "COBAR AIRPORT AWS (data from an Australian weather station) cannot start in 1962, it didn't open until 1993!" (71)
    - "What the hell is supposed to happen here? Oh yeah -- there is no 'supposed,' I can make it up. So I have : - )" (98)
    - "You can't imagine what this has cost me -- to actually allow the operator to assign false WMO (World Meteorological Organization) codes!! But what else is there in such situations? Especially when dealing with a 'Master' database of dubious provenance ..." (98)
    - "So with a somewhat cynical shrug, I added the nuclear option -- to match every WMO possible, and turn the rest into new stations ... In other words what CRU usually do. It will allow bad databases to pass unnoticed, and good databases to become bad ..." (98-9)
    - "OH F--- THIS. It's Sunday evening, I've worked all weekend, and just when I thought it was done, I'm hitting yet another problem that's based on the hopeless state of our databases." (241).
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  46. nofreewind (#46),

    In your attempt to criticize Dr. Mann with some political commentary, you (or Tierney in this case) selectively quote him from a 2004 blog comment. Yet, left out is the rest of the paragraph:

    "...Most proxy reconstructions end somewhere around 1980, for the reasons discussed above. Often, as in the comparisons we show on this site, the instrumental record (which extends to present) is shown along with the reconstructions, and clearly distinguished from them (e.g. highlighted in red as here). Most studies seek to "validate" a reconstruction by showing that it independently reproduces instrumental estimates (e.g. early temperature data available during the 18th and 19th century) that were not used to 'calibrate' the proxy data. When this is done, it is indeed possible to quantitatively compare the instrumental record of the past few decades with earlier estimates from the proxy reconstruction, within the context of the estimated uncertainties in the reconstructed values (again see the comparisons here, with the instrumental record clearly distinguished in red, the proxy reconstructions indicated by e.g. blue or green, and the uncertainties indicated by shading)"

    This is the sort of thing being done as political goons eagerly parse through personal emails looking for dirt or the appearance of dirt. It certainly says more about Tierney and others doing the spin than it does about Dr. Mann. To borrow a line from you, "your comments might be convincing to the guy down the street but they aren't going to work with me".
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  47. Is if possible that the divergence problem of tree ring anomalous proxies since 1960 is due to global dimming? I believe the earth DID dim during the period 1960-1975 and this shows up in the temperature record as falling temperatures, masking the global warming effect. Tree growth would have been affected by dimming to a degree much greater than just the effect of falling temperatures. Reduced photosynthesis would have led to narrow rings which might have been put down to temperature. Just a thought.
    0 0
    Response: Yes, it certainly is possible global dimming is one of the causes of the divergence problem. A few studies explore this option. However, the issue is complex - there doesn't seem to be one smoking gun to explain the decline in tree ring growth. More onthe tree-ring divergence problem...
  48. Nevermind, just read: dhogaza at 05:51 AM on 29 November, 2009
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  49. Why do you post Mann and not Baliunas and Soon were authors of excellent work confirming the existence of the Medieval Warm Period (MWP) from a multitude of sources?
    0 0
  50. Truthseeker, re #50. You are being sarcastic, right?
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