Trouet et al 2009: “Scuppering the Deniers”

Trouet et al (2009), Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly, published in Reader’s Digest Science a few days ago. Esper the non-Archiver is a co-author. New Scientist breathlessly reported :

Europe basked in unusually warm weather in medieval times, but why has been open to debate. Now the natural climate mechanism that caused the mild spell seems to have been pinpointed.

The finding is significant today because, according to Valerie Trouet at the Swiss Federal Institute for Forest, Snow, and Landscape Research in Birmensdorf, the mechanism that caused the warm spell in Europe – and meant wine could be produced in England as it is now – cannot explain current warming. It means the medieval warm period was mainly a regional phenomenon caused by altered heat distribution rather than a global phenomenon.

The finding scuppers one of the favourite arguments of climate-change deniers. If Europe had temperature increases before we started emitting large amounts of greenhouse gases, their argument goes, then maybe the current global warming isn’t caused by humans, either.

Michael Mann told the New Scientist that the new results may imply that the situation is even worse than we thought.

If one actually reads the article, the word “regional” only occurs once

The North Atlantic Oscillation (NAO) … has a substantial influence on marine and terrestrial ecosystems and regional socio-economic activity

The word “phenomenon” is not used anywhere. Nor are the words “altered” or “heat distribution”. If New Scientist is correctly reporting her statements, I did not locate anything in the article that specifically supports the reported oral summary of the conclusions. Indeed, the following sentence seems to suggest the exact opposite – that the transition from the “MCA” to the Little Ice Age was “globally contemporaneous” and, in language reminiscent of Hubert Lamb, that this was due to “a notable and persistent reorganization of large-scale oceanic and atmospheric circulation patterns”:

The relaxation from this particular ocean-atmosphere state into the LIA appears to be globally contemporaneous and suggests a notable and persistent reorganization of large-scale oceanic and atmospheric circulation patterns.

I take no position in the present post on whether the MCA was or wasn’t global – I’m merely observing that the article itself does not draw the conclusion that was reported in the aftermarket promotion. Penny mining stock press releases are not permitted to go beyond the information in their prospectuses or qualifying reports and it always surprises me to see climate scientists issue press releases that promote well beyond the four corners of what was approved for publication.

In a quick read, I spotted a number of issues that are of interest, not all of which will be covered in today’s note. On another occasion, I’ll try to connect the present analyses of NAO and the Atlantic meridional overturning circulation to what Hubert Lamb and William Gray said on these topics respectively (please save such comments for another day.)

Today I’ll post some notes on the provenance of the data. Their NAO reconstruction is based on a comparison of highly smoothed Scottish speleothem bandwidth data to a Morocco tree ring chronology by Esper the non-Archiver. They also refer to an England-Wales (EW) documentary precipitation reconstruction, which surprisingly proved to be from Lamb (1965) and an Alps temperature reconstruction by Mangini – the one that Gavin Schmidt complained about when Loehle used it. Scottish speleothem data was used in Mann 2008 as a temperature proxy, while an earlier version of the Morocco tree ring chronologies was used in MBH98, MBH99 and Juckes 2007, again as a temperature proxy.

Their Figure S1 illustrating their 4 money proxies is shown below. Given that the article is said to refute MWP concepts in some sense, it’s a little surprising that none of the underlying data in their illustration is particularly HS-shaped; on the contrary, these data sets all seem to have a medieval “anomaly” as pronounced as the modern anomaly.

Trouet Figure S1 Original Caption: Long-term winter proxy records from Europe. Comparison of the tree-ring based Morocco (S2) and speleothem based Scotland (S1) records with a documentary based estimate of September-June England-Wales precipitation (S10) and speleothem based estimate of winter temperature from the central Alps (S13) (A). Time series consist of 25-year averages, standardized over the common period (1075-1925). The Morocco PDSI record was inverted.

Unfortunately, the authors failed to provide any digital data citations (see for example AGU policies on this, though AGU journals don’t require climate scientists – and perhaps others – to comply with these policies), though they provide references to dead tree literature from which the data provenance for 3 of the 4 series can be plausibly surmised. The “tree-based Morocco” data set is from Esper the non-Archiver, previously published in GRL without archiving any data. (Esper the non-Archiver flouted AGU policies requiring use of archived data – not that AGU journals bother enforcing what on paper is an excellent policy.)

The Scotland speleothem series is attributed to Proctor et al 2000, for which data is archived at NCDC. In the right panel below, I show rescaled versions of the archived Proctor precipitaiton reconstruction, including original data raw (blue), 25 year average (red) and 50 year average (navy blue). Although Trouet et al stated that “Time series consist of 25-year averages, standardized over the common period (1075-1925)”, this appears to be untrue as their Figure S1 does not match a 25-year average, but does match a 50-year average. This would obviously reduce the degrees of freedom even further from the already substantial reduction and the effect of this, if any, needs to be checked.


Figre 2. Left – Trouet Figure S1; right – Proctor ppt recon from speleothem: blue – as archived; red – 25 year average; navy blue – 50 year average,

The cyan series September-June England-Wales precipitation in Trouet Figure S1 has a very familiar looking shape. S10 is Lamb 1965; the shape of this figure may remind keen-eyed readers of the famous IPCC temperature curve (derived from Lamb) showing the MWP. See discussion at CA here which has many relevant figures. Here is Lamb 1965 Figure 4 showing the precipitation reconstruction, which is related to the temperature reconstruction (I’ll try to get to this on another occasion. For interested readers, I’ve placed Lamb 1965 online – see below – it has many comments about wind circulation relevant to the present discussion. As discussed on another occasion, IPCC AR4 sneered at Lamb’s work: “Lamb’s analyses also predate any formal statistical calibration of much of the evidence he considered.” I don’t want readers to spend any time debating the merit or lack of merit of the IPCC criticis, (which one disregarded reviewer took some exception to). What’s intriguing in the present context is that Lamb’s reconstruction is used to scale the Scottish speleothem record, perhaps a surprising calibration method under the circumstances.

For the PSR analysis in this work, the Scotland speleothem record was transformed into precipitation (as fraction of modern climatology) using Lamb’s documentary evidence-based estimate of a 13% MCA-to-LIA reduction in September-June England-Wales rainfall (S10).

Lamb 1965 Figure 4 showing rainfall reconstruction. Sept-June precipitation is in the bottom panel.

The green series in Trouet Figure S1 is from Mangini’s temperature reconstruction from speleothems – again this appears to be the 50-year average, rather than the 25-year average as shown below using original data.

Figure 3. Re-scaled Mangini temperature reconstruction.

We’ve discussed this series a couple of times in the past. Gavin Schmidt excoriated Loehle’s use of this data here (See CA discussion here, on the basis that “no validation of this temperature record has been given” and that it had “been given a unique negative correlation to temperature.”

Unfortunately, no validation of this temperature record has been given… However, only one terrestrial d18O record is used by Loehle (#9 Spannagel), and this has been given a unique negative correlation to temperature…

Trouet calibrate the Mangini speleothem against a documentary series (I haven’t looked at this calibration yet) and arrive at the same “unique negative” orientation as the one that Schmidt complained about in Loehle’s usage. The difference in scale noted below would not affect the z-score plot shown here.

For Alps temperature, the smoothed (25-year running mean) Spannagel (S13) record was calibrated using linear regression against smoothed area-average (6-14E, 46-48N) December-February temperature from a documentary evidence-based data set (S14, S15) over the period 1525-1903. The correlation between these records is 0.69, with both time series showing four distinct peaks (see Fig. 4 in (S13)) over the calibration period. No rescaling was applied for this reconstruction. The resulting reconstruction gives an MCA-to-LIA winter temperature decrease in the Alps of approximately 0.4° C.

The article calculates many statistics and I’ll review some of these calculations if and when the relevant data is archived. The data has been hugely smoothed – a practice abhorred by most working statisticians (See Matt Briggs on this)- and I’d be surprised if the significance calculations hold up, but we’ll see.

Trouet, V, Esper J, Graham NE, Baker A, Scourse JD, Frank DC (2009) Persistent positive North Atlantic Oscillation mode dominated the Medieval Climate Anomaly. Science 324, 78-80. (pdf)
Lamb 1965 url


  1. Dave Dardinger
    Posted Apr 4, 2009 at 12:25 AM | Permalink

    one of the favourite arguments of climate-change deniers.

    Does New Scientist give an example of Anyone who denies that climate changes? It’s bad enough that some people think it’s ok to insist on using terminology which insults their opponents. But when their own neutering of a term like “global warming” into “climate change” renders their insult totally irrational, don’t you think they might try coming up with a new insult?

    • Chris Wright
      Posted Apr 4, 2009 at 4:35 AM | Permalink

      Re: Dave Dardinger (#1),

      As a major sceptical argument is that the climate is always changing, that’s completely bizarre. It’s actually New Scientist who are the climate change deniers, as they have tried to whitewash both the MWP and LIA from history. In fact the hockey stick could be described as the icon of climate change denial….

  2. Andrew
    Posted Apr 4, 2009 at 12:42 AM | Permalink

    Oh brother. Hey guys, how do you explain the behavior of the NAO in your models exactly? Oh, that’s right, you don’t. This article that might otherwise have been interesting in good contains a strawman version of claims about the MWP-that the must have the same “cause”-and that if you eliminate that cause as responsible for recent warming, you prove AGW. Non sequitors rule the day yet again. Hey guys, what about all those other unexplained eigenthingys? P”DO”, A”MO”, ENS”O”, etc. your models any good with them yet? Didn’t think so…

  3. Andrew
    Posted Apr 4, 2009 at 12:43 AM | Permalink

    Steve, the link to Lamb’s article doesn’t work.

  4. John Silver
    Posted Apr 4, 2009 at 3:06 AM | Permalink

    “I take no position at present on whether the MCA was or wasn’t global ”

    Define “global”!
    One of he reason the Erikssons settled in North America was winters without snow.
    (Note the UN support)

  5. John Silver
    Posted Apr 4, 2009 at 3:12 AM | Permalink

    “I take no position at present on whether the MCA was or wasn’t global”

    Define “global”
    One of the reasons the Erikssons settled in North America was winters without snow.
    (Note UN support)

  6. Posted Apr 4, 2009 at 4:10 AM | Permalink

    I admit I don’t have access to the actual Science paper so it is entirely possible that there is something there that isn’t mentioned in this post here as CA. However from the CA post what I’m reading is that the researchers took 4 European proxies and from them showed
    1) a Medieval warm period
    2) a connection between that and the NAO
    (though a NAO that lasts for a century or more seems pretty amazing to me and that appears to be implied)

    What seems to be missing would be some proxy or series of proxies from elsewhere that show no warming at the same time (e.g. something in China or South Africa or S America). Without that the whole thesis as reported in New Activist appears to be based on no foundation what so ever. Are we supposed to compare these proxies with someone else’s bristlecones ourselves to see that things were different?

  7. Posted Apr 4, 2009 at 4:47 AM | Permalink

    Steve asks why this work is being cited as evidence for a purely regional MWP.

    If I read Trouet in New Scientist correctly, these workers are claiming that the MWP was mechanistically linked to La Nina conditions in the Pacific. And La Nina, the converse of El Nino, is associated with cooling in the Pacific. So the MWP warming would not be global.

    But then wouldn’t La Nina have to dominate ENSO for centuries, in order to maintain the MWP for centuries? And if La Nina dominated for centuries, wouldn’t this be ample time for La Nina to cool the whole planet, including the MWP region?

  8. Posted Apr 4, 2009 at 5:09 AM | Permalink

    Further to my #10, see Francis T. in #8 which makes essentially the same point. Trouet et al. in New Scientist seem to be saying that the MWP is due to interactions connecting the NAO and La Nina, with the high NAO being the WMP (regional). Francis T. asks if it is credible to have a strong NAO for the centuries-long period of the WMP. I asked if it is credible to have a strong La Nina for the centuries-long period of the MWP. These are complementary aspects of the same question.

  9. Edouard
    Posted Apr 4, 2009 at 5:39 AM | Permalink

    The glacier retreats of the Alps during the MWP show us that the MWP must have been as warm as 2003 and 2006 in Europe. AND we know, that the winters were much colder 1000 years ago than they were during the last 100 years.

    This must be very disturbing for the AGW-crew.

    I have the impression that this is a very funny way to tell us that a MWP, which is scientifically proven from the Alps to Greenland and that Mr Mangini has found in caves all around the world, did only happen in Europe.

    2008 was colder because of La Nina, 1980 to 1998 wasn’t warmer though, because of El Nino ….

    software error, system restarting in 5 seconds, press delete for setup …. beep beep beep ….

  10. Posted Apr 4, 2009 at 5:42 AM | Permalink

    I have an idea as to the reasoning. These “authorities” are in the woolly blanket of academia (vid. year start June & end April). They live in the world of models which are about to have toes amputated to fit the Cinderella’s Shoe of the real evidence. They have renamed the MWP so that they can claim to have discovered this phenomenon, which (because of the persistent references here and elsewhere) can no longer be denied existence. Having “discovered” it, they can say “nyeh, we suspected it all along”. They’ve convinced themselves so thoroughly that the recent warming is due to CO2 that now they don’t need to pay attention to that one. All they need is to “explain” the MWP – er, newly-discovered MCA – which they’re trying to do with ocean currents about which they have yet to lay down the official line. They think they will not be spotted being hauled over the coals re the well-known cyclicity of the ocean currents.
    “Get rid of the MWP” has morphed interestingly.

  11. Malcolm
    Posted Apr 4, 2009 at 6:59 AM | Permalink

    Being Scottish I cannot accept for one moment that Scotland was ever warm.

    As Shir Shean Connery would shay, “Shurely shome mishtake in the schience.”

  12. Boris
    Posted Apr 4, 2009 at 7:41 AM | Permalink

    Can anyone tell me if Esper archives his data? Thanks in advance.

  13. Ryan O
    Posted Apr 4, 2009 at 7:59 AM | Permalink

    Boris is funny. 🙂

  14. Brooks Hurd
    Posted Apr 4, 2009 at 7:59 AM | Permalink

    The New Scientist statement that

    wine could be produced in England as it is now

    assumes that temperature is the only factor involved in wine production and thus current temperatures in England are similar to MWP temperatures.

    This is another straw man argument since wine today is produced in colder climes than was possible in the past because of grape clones which can prosper in temperature regions which would not have been possible in the past. This is thanks to the work of agricultural scientists at universities such as UC Davis.

    One might expect that someone at New Scientist is aware of the positive effects of modern science on the global wine industry.

    • Pompous Git
      Posted Apr 6, 2009 at 3:23 PM | Permalink

      Re: Brooks Hurd (#18), Wine most certainly could not be produced in England as now during the Medieval Warm Period. According to the Wine Standards Board, only one year in ten do British grapes come up to the required sugar level for winemaking. In nine out of ten years, British winemakers are allowed to use vacuum distillation, or add sucrose to the must in order to achieve the required alcohol content.

      Vacuum distillation is a technique not available during the MWP. Nor was sucrose available in anything like the quantities that would be required for a viable wine industry that produced grapes of such poor quality as those produced today. Medieval England was certainly warmer than today.

      While honey can be used to supplement the sugar in grapes, this product was called pyment, not wine.

  15. Craig Loehle
    Posted Apr 4, 2009 at 8:27 AM | Permalink

    It is hilarious that the same people who dismissed my reconstruction as only having 18 proxies are quite happy to make a bold statement about the MWP based on 4. It also stretches my credulity that the NAO was stuck in one mode that long.

  16. bender
    Posted Apr 4, 2009 at 8:51 AM | Permalink

    Steve M, your mastery of the numerous paleoclimatic data series that are out there always astounds me in posts like these. It’s so easy to point to contradictions and double standards when you have that level of command of the data.

  17. Posted Apr 4, 2009 at 9:29 AM | Permalink

    I don’t think the NAO ‘scuppers’ those who point to recent natural climate variability:

    Wang, Swanson and Tsonis, GRL (2009): ‘The pacemaker of major climate shifts.’

    The Abstract states:

    Models and data suggest that the interplay of major climate modes may result in climate shifts [Tsonis et al., 2007]. More specifically it has been shown that when the network of North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), El Nino/Southern Oscillation (ENSO) and North Pacific Index (NPI) synchronizes, an increase in the coupling between these oscillations destroys the synchronous state and leads the climate system to a new state. These shifts are associated with significant changes in global temperature trend and in ENSO variability. Here we probe the details of this network’s dynamics to investigate if a certain oscillation is the culprit in these shifts. From a total of 12 synchronization events observed in three climate simulations and in observations we find that the instigator of these shifts is NAO. Without exception only when NAO’s coupling with the Pacific increases a shift will occur. Our results suggest a dynamical sequence of events in the evolution of climate shifts which is consistent with recent independent empirical and modeling studies.

    The paper concludes:

    Many studies have in the past dealt with the origin and mechanisms of climate oscillations as well as with the consequences of their interactions. Our study with the help of a novel approach identifies for the first time which may be the most significant of these oscillations. In a dynamical scenario where the major modes of variability in the northern hemisphere are synchronized, an increase in the coupling strength destroys the synchronous state and causes climate to shift to a new state. Here we were able to identify that the major participant in this coupling strength increase is NAO, which we found to be behind all climate shifts observed in observations as well as in three climate simulations. Understanding variability of our extremely complex climate system is far from complete as new and often contradicting views are proposed. In this realm we hope that our results will provide some direction and focus to this perpetual quest for understanding climate variability.

    Kyle Swanson and Anastasios Tsonis GRL (2009):‘Has the climate recently shifted?’

    The Abstract states:

    This paper provides an update to an earlier work that showed specific changes in the aggregate time evolution of major Northern Hemispheric atmospheric and oceanic modes of variability serve as a harbinger of climate shifts. Specifically, when the major modes of Northern Hemisphere climate variability are synchronized, or resonate, and the coupling between those modes simultaneously increases, the climate system appears to be thrown into a new state, marked by a break in the global mean temperature trend and in the character of El Ni˜no/Southern Oscillation variability. Here, a new and improved means to quantify the coupling between climate modes confirms that another synchronization of these modes, followed by an increase in coupling occurred in 2001/02. This suggests that a break in the global mean temperature trend from the consistent warming over the 1976/77–2001/02 period may have occurred.

    The paper concludes:

    If as suggested here, a dynamically driven climate shift has occurred, the duration of similar shifts during the 20th century suggests the new global mean temperature trend may persist for several decades. Of course, it is purely speculative to presume that the global mean temperature will remain near current levels for such an extended period of time. Moreover, we caution that the shifts described here are presumably superimposed upon a long term warming trend due to anthropogenic forcing. However, the nature of these past shifts in climate state suggests the possibility of near constant temperature lasting a decade or more into the future must at least be entertained. The apparent lack of a proximate cause behind the halt in warming post 2001/02 challenges our understanding of the climate system, specifically the physical reasoning and causal links between longer time-scale modes of internal climate variability and the impact of such modes upon global temperature. Fortunately, climate science is rapidly developing the tools to meet this challenge, as in the near future it will be possible to attribute cause and effect in decadal scale climate variability within the context of a seamless climate forecast system [Palmer et al. 2008]. Doing so is vital, as the future evolution of the global mean temperature may hold surprises on both the warm and cold ends of the spectrum due entirely to internal variability that lie well outside the envelope of a steadily increasing global mean temperature.

    Tsonis et al, GRL (2007): ‘A new dynamical mechanism for major climate shifts’

    In the mid-1970s, a climate shift cooled sea surface temperatures in the central Pacific Ocean and warmed the coast of western North America, bringing long-range changes to the northern hemisphere. After this climate shift waned, an era of frequent El Ninos and rising global temperatures began.

    Tsonis et al. have investigated the collective behavior of known climate cycles such as the Pacific Decadal Oscillation, the North Atlantic Oscillation, the El Nino/Southern Oscillation, and the North Pacific Oscillation. By studying the last 100 years of these cycles’ patterns, they find that the systems synchronized several times.

    Further, in cases where the synchronous state was followed by an increase in the coupling strength among the cycles, the synchronous state was destroyed. Then. a new climate state emerged, associated with global temperature changes and El Nino/Southern Oscillation variability.

    The authors show that this mechanism explains all global temperature tendency changes and El Nino variability in the 20th century.

    Major climate shifts have occurred or will occur around 1913, 1942, 1978, 2033, and 2072 according to the authors of this recent paper, who also predict a 0.2 Celsius cooling between 2005 and 2020 which should be followed by a 0.3 Celsius warming until 2045 or so – then cooling for the rest of the 21st century.

  18. Bill Illis
    Posted Apr 4, 2009 at 9:34 AM | Permalink

    There are reconstructions of the AMO going back to 1572 by Stephen Gray which shows a really big spike in the AMO at the beginning of the record. (It doesn’t go back far enough for the timelines of this study).

    And Michael Mann also participated in a study which simulated the effects of the AMO on climate over longer timescales (he actually does some good work when he stays away from tree-rings and unproven mathematical techniques).

    Click to access KnightetalGRL05.pdf

    Personally, I don’t recommend using the North Atlantic Oscillation. It is just a measure of pressure (and winds in essence) (for which we really don’t have good historical high resolution data) and it does not produce very good correlations with any temperature records. The AMO is a superior proxy/driver in comparison for both of these issues.

    And I don’t see how pressure differentials in the atmosphere can last for more than a few days (or up to months on occasion) at a time so any time series showing it lasting decades is suspect. The daily NOA index fluctuates rapidly and there are often different pressure differentials at different levels of the atmosphere.

    The ice sheets on Greenland and the north polar vortex provide a blocking mechanism for warmer wind currents and it seems the NAO just represents these climate features. Both of these are affected by the AMO so we are just back to the AMO again.

    Just to reinforce this, here is the monthly NAO index versus the Hadcrut3 global temperature anomaly (with the scale of the NAO reduced to 15% for scale). Not much correlation there or with the Northern Hemisphere Hadcrut3 numbers either.

  19. Steve McIntyre
    Posted Apr 4, 2009 at 12:04 PM | Permalink

    This post is primarily about specific proxies. In the post, I asked people not to discuss the NAO and the Atlantic meridional overturning circulation as follows:

    On another occasion, I’ll try to connect the present analyses of NAO and the Atlantic meridional overturning circulation to what Hubert Lamb and William Gray said on these topics respectively (please save such comments for another day.)

    IS it unreasonable for me to expect readers to observe this request? I don’t think so. Further comments on oscillations on this thread will be moved to an obscure and stale Unthreaded.

    #7 and responses – please assume that I am aware of the available proxy evidence on the MWP. From an editorial point of view, it is far more productive to examine what Trouet and coauthors said in this article than to re-hash things about the Vikings.

  20. Posted Apr 4, 2009 at 12:23 PM | Permalink

    They live in the world of models which are about to have toes amputated to fit the Cinderella’s Shoe of the real evidence.

    An apt metaphor and a reference to a little known detail about the original tale by the brothers Grimm. Well done!

  21. Hank
    Posted Apr 4, 2009 at 12:58 PM | Permalink

    Another great article. Hoist ’em on their own petard! I especially enjoyed it since it works so nicely with Gavin Schmidt’s April 1st lecture at (entitled “Advocacy vs. Science”) on the dangers of seizing on every latest paper as confirmation of one’s own understandings and prejudices. Do you suppose Gavin imagines that his bromides wouldn’t be beneficial to all camps of this debate?

    I apologize if this comment seems if it would be better placed over at realclimate, but all my posts over at the impartial, non-advocacy blog get censored.

  22. stan
    Posted Apr 4, 2009 at 1:11 PM | Permalink

    So we must conclude on the basis of this statistical treatment of four proxies that the MWP has been proven to be only regional in its impact. Wow. I guess I’m not cut out to be a climate scientist.

    When my friend’s daughter was little, she loved to say her ABC’s because mommy and daddy always gave her a cheer when she finished. She looked forward to the cheer so much that she would sometimes go straight from …e,f,g to w,x,y,z! Why bother with all those unneccessary intermediate letters.

    So it seems with climate science. Having begun the process of trying to show A, they immediately proceed to announce the proof of Z (all in the expectation of a great cheer from fellow alarmists).

  23. jeez
    Posted Apr 4, 2009 at 1:24 PM | Permalink

    Steve, when they say 25 year average, they mean 25 years on either side, thus the match to your 50 year average–duh!

    • Andrew
      Posted Apr 4, 2009 at 1:25 PM | Permalink

      Re: jeez (#28), That would be a 51 year average…

  24. Not sure
    Posted Apr 4, 2009 at 2:10 PM | Permalink

    Did you mean William Briggs?

  25. Robert Wood
    Posted Apr 4, 2009 at 2:22 PM | Permalink

    So, the mediaeval Warm Period is now refered to as the Mediaeval Climate Anomoly.

    Are the Mannists now going to refer to the Modern Warm Period as the Modern Climate Anomoly?

    They walked into that one. When does an anomoly become a dangerous trend 🙂

  26. Posted Apr 4, 2009 at 3:34 PM | Permalink

    Re: Proctor’s stalagmite record used in Trouet et al.

    Here’s some context for this record – I hope it is helpful and apologies if this post is rather long! Starting with annual growth rate, or laminae width (akin to tree ring width). The theory behind how fast stalagmites grow has been developed over about 20 yrs by Wolfgang Dreybrodt (Bremen, now retired). His work is based on both the chemistry of stalagmite deposition (e.g. how saturated the water is with carbon dioxide, which has been dissolved from the overlying limestone) and also the physics (how carbon dioxide that is involved in this chemical reaction diffuses from the stalagmite surface to the air and vice versa). Basically, there are many factors that can affect stalagmite growth rate – the important and variable ones are the amount of limestone which has previously been dissolved in the water which has lead to it being saturated with carbon dioxide, the amount of water supply (which determines the amount of this carbon dioxide transported to the stalagmite), the cave temperature (which determines the chemical rate kinetics) and the carbon dioxide concentration of the air in the cave (if this is high, then the water feeding the stalagmite will be, relative to the air, less saturated, and so less stalagmite will be deposited). If you do a sensitivity analysis on these variables, the most important of these are the amount of water supplied (for very slow drips, so that all the dissolved carbon dioxide reacts to form some stalagmite calcite and the stalagmite is essentially ‘waiting’ for the next drip so that it can grow some more) and/or the amount of dissolved carbon dioxide (more carbon dioxide in the drip water = faster stalagmite growth).

    If the carbon dioxide saturation of drip water is important, then of course we need to know what determines that. This carbon dioxide derives from the soil, where carbon dioxide can be orders of magnitude higher than in the atmosphere due to microbial respiration. Crudely, a high soil carbon dioxide concentration will lead to a high drip water carbon dioxide concentration and faster stalagmite growth, and soil carbon dioxide increases with temperature. It might also relate to soil moisture content, especially in waterlogged soils, as waterlogging will decrease aerobic bacterial activity, or very arid soils, where water is limiting. But in most cases, you would expect a warmer climate to yield a higher soil carbon dioxide concentration.

    So, stalagmite growth rate is a mixed proxy, likely to be driven by one or both of temperature and precipitation. Therefore, each cave, and also each stalagmite within the cave, will have a different relationship between climate and growth rate. Especially important here is the hydrological connection between the surface climate, which will differ between stalagmites, so just like other proxies, no two records even within in one cave will be the same. Finally, the groundwater transfer from the surface, via the soil, to the cave, also means that there is an environmental / natural smoothing of any surface climate signal, with a mixing of waters of different residence times. So, stalagmites would be expected to preferentially record low frequency climate variability (e.g. annual to decadal variability) over high frequency variability (sub-annual variability).

    Back to the Proctor et al record. The cave is covered by ‘blanket bog’ (0.5-3m peat) and the soil carbon dioxide in such soils is moisture limited. In dry years, the water table drops and carbon dioxide is produced, in wet years the soil remains saturated and carbon dioxide production is limited. On top of that, the stalagmite studied has very slow drip rates (typically slower than 30 mins per drip – often too slow to measure in a practical fieldwork session). This is an order of magnitude over than the threshold that Dreybrodt’s theory suggests that a drip will have completely used up any dissolved carbon dioxide. So we think that on both counts that this is a rainfall sensitive stalagmite. Of course, it is not so simple – for example, although winter precipitation in the region has a strong correlation with the NAO, warm summers will also decrease the water table in the peat and this might also affect the stalagmite growth rate. So, like all stalagmites, it is a mixed proxy, but one where we think that the sensitivity to rainfall dominates, and that any climate signal will be smoothed /damped by ground water mixing and travel time.

    If anyone is interested in some primary sources for all of that, the following might not be ideal but all are at least public access and you can track back to some key original papers (all three journals have free access to all issues):

    A 2008 Dreybrodt paper on stalagmite growth in Acta Carsologica:

    A 2008 paper on the cave site (the paper is actually about isotopes)

    And if it’s not too cheeky, a 2008 review article about laminated stalagmites:

    • Steve McIntyre
      Posted Apr 4, 2009 at 4:49 PM | Permalink

      Re: Andy Baker (#33),

      Andy, thanks for the note. Do you have digital versions of the Morocco chronology and Trouet’s NAO recon that you could send me? PErhaps you could communicate to Trouet that the archiving and data citations for the article are very unsatisfactory. I haven’t had any luck with Esper in the past other than through a series of journal complaints and it would be nice to avoid this for once.

      Thanks, Steve

    • Jonathan Schafer
      Posted Apr 4, 2009 at 8:16 PM | Permalink

      Re: Andy Baker (#33),

      Thank you for the informative post. It was easy to understand without having to be an expert on speleothems.

  27. Alan Wilkinson
    Posted Apr 4, 2009 at 6:29 PM | Permalink

    snip – please see request in #24

  28. Mike Lorrey
    Posted Apr 4, 2009 at 7:40 PM | Permalink

    a) Mann’s Hockey Stick denies the existence of the LIA and MWP. So why is he commenting on a paper that contradicts his own claims?
    b) Lorrey, et al’s NZ Speleotherm studies demonstrate both LIA and MWP were global, not confined to europe or the north atlantic.

    • Andrew
      Posted Apr 4, 2009 at 7:54 PM | Permalink

      Re: Mike Lorrey (#36), Mann actually claims these were regional events, restricted to the North Atlantic region. So while he does make some dubious claims, the paper doesn’t exactly contradict him. Indeed, there is some serious bending over backwards going on here…

      • Mike Lorrey
        Posted Apr 6, 2009 at 1:35 AM | Permalink

        Re: Andrew (#37), however, my second point, Lorrey et al, clearly smashes Mann’s claims that MWP and LIA were regionally restricted.

        Here’s another issue: so what if MWP was regional? Most warming of the late 20th was restricted to the same regions.

        • Andrew
          Posted Apr 6, 2009 at 3:34 PM | Permalink

          Re: Mike Lorrey (#49),

          Lorrey et al, clearly smashes Mann’s claims that MWP and LIA were regionally restricted.

          No argument here.

          Most warming of the late 20th was restricted to the same regions.

          This, however, I don’t agree with. The warming is fairly widespread:

        • Raven
          Posted Apr 6, 2009 at 4:03 PM | Permalink

          Re: Andrew (#53)
          If you do some visual integration you should see that the trend in the SH is near zero.
          That makes the mordern warming period purely a northern phenomena.
          The claim of a global trend based on 40 years of data is self serving at best.

        • Andrew
          Posted Apr 6, 2009 at 4:50 PM | Permalink

          Re: Raven (#54), Raven, you make some fair points. I am terrible at visually integrating. However, I said “widespread” which is different than “global”. 🙂

        • Tolz
          Posted Apr 6, 2009 at 5:43 PM | Permalink

          Re: Andrew (#55),

          One doesn’t hear the current state of the climate being referred to as “widespread warming”, very often, IMO.

        • Andrew
          Posted Apr 6, 2009 at 5:50 PM | Permalink

          Re: Tolz (#56), So true. Sigh.

  29. AnonyMoose
    Posted Apr 4, 2009 at 8:01 PM | Permalink

    The article being discussed is at:
    Oddly, New Scientist mentioned the DOI but linked to the home page of Science instead of to the article.

  30. mccall
    Posted Apr 4, 2009 at 9:48 PM | Permalink

    No problems with thread or comments, except the “Readers Digest” probably deserves more respect. I’m pretty sure RD does not twist, torture or reverse the conclusions of either a literary piece or factual report.

  31. Mark_T
    Posted Apr 4, 2009 at 9:51 PM | Permalink

    What is MCA? I couldn’t find it in the acronyms section.

  32. John F. Hultquist
    Posted Apr 4, 2009 at 10:32 PM | Permalink

    mcall #41
    In years past the editors of RD “directed” the publication of articles to their liking and then “digested” them in the magazine. Thus, they did not have to manipulate them. So, the reference fits, I think.
    Andrew’s comment : “. . there is some serious bending over backwards going on here…” struck me as real close to the truth.
    Also, it seems everyone is in to the renaming thing. No more “war on terror” and other changes.
    Anyway, good ideas here. Thanks to all.

  33. Posted Apr 4, 2009 at 10:53 PM | Permalink

    “Steve: … these sorts of discussions tend to crop up on every thread if left unchecked and monopolize editorially.”

    Sorry. We do try to follow the rules. Ignorance is no excuse, etc…

  34. Leon Palmer
    Posted Apr 5, 2009 at 10:22 AM | Permalink

    As Steve points out, the author’s graphics show the MCA, but notice that New Scientist chose to use the hockey stick as their graphic with the words “Temperature over the past 1000 years”.

    • Andrew
      Posted Apr 5, 2009 at 1:33 PM | Permalink

      Re: Leon Palmer (#46), Its called “editorial discretion”.

      You know, it seems to me, and I’m sorry if I’m being repetitive, but, shouldn’t the authors be required to explain what actually causes the “NAO” before claim that 1. It cause the (regional) MWP and (especially) 2. The same did not cause the current warm period?

      • bender
        Posted Apr 5, 2009 at 9:00 PM | Permalink

        Re: Andrew (#47), They are claiming that the MWP was caused by an MCA that had a fingerprint somewhat like that of the NAO. What is there to explain? Can the ocean not have some internal and inexplicable behavior? The current warm period is global in extent. Therefore it cannot be “explained” by any one regional circulatory pattern.

        • Andrew
          Posted Apr 6, 2009 at 7:43 AM | Permalink

          Re: bender (#48), Okay, I see, their claims are internally consistent, at least. Thanks for clearing that up.

  35. Pompous Git
    Posted Apr 6, 2009 at 3:28 PM | Permalink

    Why MCA? Village of the Damned Idiot People?

    S(t)inging: I want my MWP…

  36. Henry
    Posted Apr 6, 2009 at 6:07 PM | Permalink

    Isn’t the 25/50-year issue visually obvious from the chart: there seem to be 17/18/19 or so turning points on each line in a 900 year period. Some reviewers might spot this sort of thing without needing to look at the sources.

  37. Heath
    Posted Apr 6, 2009 at 8:16 PM | Permalink

    Very interesting website. I am not a scientist in the academic sense but I work in a lab invironment that deals heavily with statistical data. Years ago when I first encountered the famous “hockey stick” graph ie Mann I was taken aback at the fine resolution of the temperature data when coordinated against the very long time axis. If anyone here is familiar with chromatography then you can understand how questionable it is to find significance when data points of interest are so close to baseline “noise”. Indeed, climate fluctuations are an analog phenom and (I should think) subject to the same 3:1 ratio rule that any statistical dataset is.

    I do believe this warming period is real. I also believe that the science behind it has unfortunately been poisoned by politicians (ie Gorites) and others who have emotional and financial motivations to see this hysteria through.

    I have serious concerns when I see supposed “unbiased peer-reviewed” talking heads claiming the matter is “settled” and practically mocking those who offer counter debate. If I were a research scientist I should think that I would WANT and DESIRE open dialogue, to have my research scrutinized to further bring us to THE TRUTH. Unfortunately the nature of modern science which depends on funding and financial backing from whoever holds a checkbook has placed integrity on the backburner in favor of publication and notoriety.

    I apologize if my sarcasm poisons my POV.

  38. Heath
    Posted Apr 6, 2009 at 8:37 PM | Permalink

    On a sidenote, I also have grave concerns about the mentallity of the masses when it comes to understanding these VERY complex and interracting disciplines. My wife, bless her heart, is convinced the poor polar bears are doomed. Just today I explained (or attempted to) the lagging nature of CO2 vs temperature and she responded with, “well everyone has an opinion”. And that is what this debate IS in the mainstream…a conflict of opinions just like pro life/choice or anything else political. Our media has become so instantaneous that questional reports “du jour” litter our favorite homepage and make headlines on CNN morning shows. They have little factual teeth and lots of entertaining fluff designed for Joe Plumber (sorry Obama). We literally have two, maybe three generations of folks who were indoctrinated into the environmentalist movement as children. When I was in school it was “The ozone layer” and was led to believe that spray-painting a rusty charcoal grill was destroying our world and my sister’s hair-style was the essence of evil. Not to mention the seventies brought is the “global cooling” scare.

    It is difficult to find a clear thinking, logical mind who can purely grasp the irony of it all. It is no wonder the AGW train has picked up so much momentum.

    Apologies to Mr. McIntyre if I have strayed off topic. I probably never really was On topic. I just appreciate the opportunity to voice my dissenting view as an intelligent, reasonably educated man who’ll never be heard above the voices who would squash it.

  39. bender
    Posted Apr 7, 2009 at 11:40 AM | Permalink

    New Scientist blurb on Trouet

    Mann is also concerned that the dominance of medieval La Niña conditions now indicated by Trouet’s work might make it more likely that the current man-made warming could also put the El Niño system back into a La Niña mode

    Wait a sec. I thought they reconstructed NAO, not ENSO. How did ENSO get in here?

    El Niño and the NAO are connected by a process called thermohaline circulation, which drives the “ocean conveyor belt” that shuttles sea water of different density around the world’s oceans.

    Oh. No reason to restrict ourselves to discussing NAO when we can extrapolate by looking on down the teleconnective line. Another pea under thimble game.

    According to Trouet, a Pacific La Niña mode and a positive NAO mode could have reinforced each other in a positive feedback loop – and this could explain the stability of the medieval climate anomaly.

    But did Trouet show this in this paper? Or is she theorizing, extrapolating beyond the data? Or was she misquoted/quoted out of context. Val?

    Mann is also concerned that the dominance of medieval La Niña conditions now indicated by Trouet’s work might make it more likely that the current man-made warming could also put the El Niño system back into a La Niña mode, although most climate models so far had predicted the opposite.

    The perfect rescue device. Models that are sufficiently vague that anything is consistent with them. Newflash: This is not a proof by lack of contradiction, guys. It’s called a poor hypothesis test. There’s a difference.

  40. Corey S.
    Posted Apr 10, 2009 at 12:24 PM | Permalink

    I admit I don’t have access to the actual Science paper

    Trouet, V, Esper J, Graham NE, Baker A, Scourse JD, Frank DC (2009) Persistent positive North Atlantic Oscillation mode dominated the Medieval Climate Anomaly. Science 324, 78-80. (pdf)

    Found here.

    Not sure if this has already been supplied from looking over the thread, but here it is.

  41. john mathon
    Posted Apr 13, 2009 at 11:53 AM | Permalink

    The presumption of the article seems to be that the MWP was mainly a regional phenomenon. Are there other instances of hundred to 2 hundred year periods where “regions” of the world have experienced a large temperature increase or decrease where the rest of the world is unaffected? I find this bizarre that somehow there would be this region that experienced much warmer temperatures and the rest of the world was unchanged or maybe dropped in temperature over a period as large as 1 or 2 hundred years. I am not familiar with any other such phenomenon ever having occurred. Does this strike anyone else as completely bizarre?

  42. Alex Atkinson
    Posted Jul 8, 2010 at 2:58 PM | Permalink

    I’ve been re-working speleothem data from a number of locations and comparing them to solar activity proxies for the past ~2000 years. Spannagel is an *extremely* unusual case and I am unsure as to the quality of this temperature reconstruction. If you re-work their data using the above link, and compare this to solar activity (which is availabe at – pref. use the intcal04 data set), there seems to be a 50 year shift in the solar activity data. For example, if we look at the Dalton Minimum, it appears to occur around ~1750 at Spannagel, whilst in the solar record it’s known to have onset around 1790. The whole tuning of this record is suspect and the original paper poorly explains how this record has been produced.

    If anyone can explain to me why I am getting this, and how they have actually produced the solar/temperature link (with a backward sensitivity at that) i’d be very appreciative.

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  1. […] any data. Discussion began here on April 3 in the comments here and later that day I posted on it here observing: Unfortunately, the authors failed to provide any digital data citations (see for example […]

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