Another paper refutes the Mann made hockey stick – MWP was ≈1°C warmer than current temperatures

This new paper uses a rather unique proxy; high-resolution samples micromilled from archaeological shells of the European limpet, Patella vulgata. Mr. Limpet would be proud.

English:

Now, even less credible than before (Photo credit: Wikipedia)

A paper published this week in the journal Palaeogeography, Palaeoclimatology, Palaeoecology finds that the Medieval Warming Period “was warmer than the late 20th century by ~1°C.” The paper adds to the peer-reviewed publications of over 1000 scientists in the Medieval Warm Period Project showing that the global Medieval Warming Period was warmer than the current warming period.

Highlights:

► We investigated oxygen isotope ratios of Viking Age limpet shells.
► Seasonal SST was reconstructed for the early MCA (10th-12th centuries).
► Early MCA winters were cooler and summers were warmer than late 20th century.
► MCA seasonality was almost twice that of the late 20th century.

The paper is titled:

Marine climatic seasonality during early medieval times (10th to 12th centuries) based on isotopic records in Viking Age shells from Orkney, Scotland

  • Donna Surge, University of North Carolina, Department of Geological Sciences, 104 South Road, CB #3315, Chapel Hill, North Carolina, USA, James H. Barrett, McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, CB2 3ER, UK

Here’s the Abstract: 

Seasonal sea-surface temperature (SST) variability during the Medieval Climate Anomaly (MCA), which corresponds to the height of Viking exploration (800–1200 AD), was estimated using oxygen isotope ratios (δ18O) obtained from high-resolution samples micromilled from archaeological shells of the European limpet,Patella vulgata. Our findings illustrate the advantage of targeting SST archives from fast-growing, short-lived molluscs that capture summer and winter seasons simultaneously. Shells from the 10th to 12th centuries (early MCA) were collected from well-stratified horizons, which accumulated in Viking shell and fish middens at Quoygrew on Westray in the archipelago of Orkney, Scotland. Their ages were constrained based on artifacts and radiocarbon dating of bone, charred cereal grain, and the shells used in this study. We used measured δ18OWATER values taken from nearby Rack Wick Bay (average 0.31 ± 0.17‰ VSMOW, n = 11) to estimate SST from δ18OSHELL values. The standard deviation of δ18OWATER values resulted in an error in SST estimates of ± 0.7 °C. The coldest winter months recorded in the shells averaged 6.0 ± 0.6 °C and the warmest summer months averaged 14.1 ± 0.7 °C. Winter and summer SST during the late 20th century (1961–1990) was 7.77 ± 0.40 °C and 12.42 ± 0.41 °C, respectively. Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season. Higher seasonality and cooler winters during early medieval times may result from a weakened North Atlantic Oscillation index.

h/t to “The Hockey Schtick

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55 thoughts on “Another paper refutes the Mann made hockey stick – MWP was ≈1°C warmer than current temperatures

  1. I just finished reading Peter Boettke’s Living Economics and I kept thinking about how the climate science advocates just want to be free to socially engineer societies via models disconnected to reality like so many economists have been able to do.

    Except in climate science it IS so much easier to reinterject reality via actual temperatures.

    While we are cleaning up the absurdities of the AGW modelling, can we also move on to the absurd economic models?

    We really need to get back to individual freedom and economic freedom. Plus objective reality trumping models and theories made up to gain policy implementation and OPM tax dollars and grant funding.

  2. …resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C.

    Probably 1.4°C warmer bearing in mind the newly covered paper on WUWT.

    Authors Steirou and Koutsoyiannis, after taking homogenization errors into account find global warming over the past century was only about one-half [0.42°C] of that claimed by the IPCC [0.7-0.8°C].
    wattsupwiththat.com/2012/07/17/new-paper-blames-about-half-of-global-warming-on-weather-station-data-homgenization/

  3. Extract from the abstract (not even the paper, the abstract) that you actually linked to:

    Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season.

    In other words, the paper warns us not to conclude what you say it concludes (the actual conclusion is actually in the abstract itself, can you spot it?).

    Additionally, I suppose there’s not much point in mentioning that little distinction between “Global” and “North Atlantic” temperatures? I mean, it’s not like it’s the first time, right?

    Never mind. Carry on.

  4. Still not enough warming to account for how the Vikings managed to farm in Greenland during the MWP. However it is at least a step in the right direction (and back towards reality.)

  5. Well, I don’t have access to Elsevier so I can’t read the paper, but I’m quite curious how they can date these limpet shells. Also, how do they match an isotope ratio to an absolute temperature? I’m sure it’s more feasible to match isotope ratios to a specific temperature than it is to match the width and density of a tree ring, but it still seems shaky to me.

  6. Also, this is an obscure journal (to me anyway), but I noticed that they took care to mention caveats and to express uncertainty in their conclusions. I guess if they had not done these things, they could have published in Nature.

  7. Anthony, the first part of the headline may be OK, but the second part is clearly refuted by the abstract itself. Too bad it was so confusingly stated–sort of like Nixon saying that he could have done thus-and-so, but it would not be right.

    A correct headline would be something like “MWP in high latitudes was as warm as the late 20th century.”

  8. Obviously this is another case of localized warming during the MWP. All studies that indicate the MWP was warmer than the present are just localized warming. All studies that indicate the MWP was colder than the present are evidence of global warming via teleconnection. Warming during the MWP is never teleconnected.

    Just ask Michael Mann and RealClimate

  9. Of course the warmists will say the MWP was a northern hemispheric phenomenon. But there are scientific studies that indicate the MWP was global, One such is:

    .Huang, S., H. N. Pollack, and P. Y. Shen (1997), Late Quaternary temperature changes seen in world‐wide continental heat flow measurements, Geophys. Res. Lett., 24(15), 1947–1950, doi:10.1029/97GL01846.

    Abstract:
    Analysis of more than six thousand continental heat flow measurements as a function of depth has yielded a reconstruction of a global average ground surface temperature history over the last 20,000 years. The early to mid‐Holocene appears as a relatively long warm interval some 0.2–0.6 K above present‐day temperatures, the culmination of the warming that followed the end of the last glaciation. Temperatures were also warmer than present 500–1,000 years ago, but then cooled to a minimum some 0.2–0.7 K below present about 200 years ago. Although temperature variations in this type of reconstruction are highly smoothed, the results clearly resemble the broad outlines of late Quaternary climate changes suggested by proxies.

  10. Anthony,

    No, that’s not what this paper says. What they’ve done is to obtain a seasonal analysis of temperatures. They say that *if* you looked at shell evidence for MWP temperatures *without* doing the seasonal analysis you might get the *incorrect* impression that MWP temperatures were on average around 1C higher than the 1960-1990 period. (If you just took a sample of shells of the right age and analyzed their 18O signal, you’d be getting a biased estimate, because more shell is made by these animals in the summer than in the winter).

    Their seasonal analysis shows that summers were around 2C warmer, and winters around 2C cooler. In other words, although the seasonal range was greater, on average, the MWP was *no warmer* than the 1960-1990 baseline.

    And of course the 2000-2012 period has been substantially above the 1960-1990 baseline.

    So I’m afraid this paper says exactly the opposite of what you were hoping it said.

  11. I think that the claim that the alarmists are the only deniers – denier of the scientific method – appears to be gaining strength with each nail in their coffin.

  12. Nigel Harris – so what caused the increase in variability from increased summer temperatures of 2 degrees C (good for growing crops) and the decreased winter temperatures of 2 degrees C (good for killing pests)? Is Global warming an increase in winter temperatures, an increase in night temperatures, a change in average, a change in mean or is it in fact irrelevant since it is just a measured number, most likely irrelevant to the plants and animals? Just for fun I put sheltered thermometers all around my house and farm. Conclusion: Temperatures are affected by wind, rain, humidity, and a ton of factors I don’t understand and highly variable. I see temperature variations of several degrees from thermometers 25 metres apart, simply due to one being closer to a fish pond than the other. Certain sites show higher highs, some lower night time lows’ some higher summer highs and some lower winter lows. My weather station (Central Alberta, Canada) shows an annual variation over the last 10 years of 92 degrees C (+46 to minus 46C). I have a lot of trouble worrying about a fraction of a degree that I don’t think that will affect my hay crop one iota.

    Very unscientific I know, but interesting from the perspective of an old engineer and rancher.

    But the first sentence is the key. From reading here and elsewhere over the past many years, I read many hypothesis about “climate Change” and the only conclusion I can draw is that we know there are many drivers and we don’t know what they all are or their individual effect.

    What I do know is the hay still grows and my animals still eat it. The rest is just noise. Interesting noise, expensive noise, worthwhile noise, but noise nevertheless.

  13. “This conclusion is broadly true for the summer season, but not true for the winter season.” off Orkney, Scotland

  14. It’s obvious that the authors are saying one could *only* reach the conclusion that the MCA was warmer than the late 20th century by ~ 1 °C if one had examined the shells “without the benefit of seasonal resolution”.

    But *because* they applied this seasonal resolution, the authors were able to show that the MCA in this region was *not* warmer than the 1961-1990 period. It was around -2.0 C colder in winter and around +2.0 C warmer in summer – so the net difference between MCA and 1961-1990 is zero.

    Furthermore, during the period from 1991-present, NH average winter and summer temperatures have both been considerably warmer than the 1961-1990 average (+0.54 in winter; +0.58 in summer, according to NASA). This strongly suggests that the *present* period is actually considerably *warmer* than was the period of the MCA examined by this study.

    The headline of this post should be changed and a correction issued.

  15. Reblogged this on evilincandescentbulb and commented:
    Add yoGlobal warming is nothing but a hoax and a scare tactic. EPA government science authoritarians do not control average global temperatures. But we know what does: nominally, it is the sun, stupid. And, GCM model-makers simply ignore the Sun and clouds in addition to other natural phenomena.

    http://evilincandescentbulb.wordpress.com/2012/04/16/a-holistic-process-of-natural-phenomena-is-climate-change/

  16. The influx of the MWP “Deniers” ;-), suggests that this paper has hit a bit of a hot spot!

  17. DWR54 says:

    It’s obvious that the authors are saying one could *only* reach the conclusion that the MCA was warmer than the late 20th century by ~ 1 °C if one had examined the shells “without the benefit of seasonal resolution”.

    No, they did not say that.

    But *because* they applied this seasonal resolution, the authors were able to show that the MCA in this region was *not* warmer than the 1961-1990 period. It was around -2.0 C colder in winter and around +2.0 C warmer in summer – so the net difference between MCA and 1961-1990 is zero.

    They did not say that, either.

    Furthermore, during the period from 1991-present, NH average winter and summer temperatures have both been considerably warmer than the 1961-1990 average (+0.54 in winter; +0.58 in summer, according to NASA). This strongly suggests that the *present* period is actually considerably *warmer* than was the period of the MCA examined by this study.

    They did not say that either.

    The headline of this post should be changed and a correction issued.

    Probably. You should do the same, with respect to your post. Wonder which will happen first, with the least amount of dispute?

    Judging from the content of the abstract, the paper itself appears to be an interesting example of confirmation bias. The response to it, as typified here, is very much a Rorshcach test for ‘global warming’ warriors.

  18. Adam Gallon says:
    July 17, 2012 at 11:14 am

    The influx of the MWP “Deniers” ;-), suggests that this paper has hit a bit of a hot spot!
    ___________________________________
    Of course it has, we are talking about the fate of the ENTIRE WORLD, not to mention the fate of their pay checks…

    Please note how the warm spike in temperature a couple weeks ago on the USA east coast was “evidence of Global Warming” (while Oregon, Alaska, Australia and the UK are freezing) but warmer summer temperatures from this study is not. (Snicker)

  19. Obviously, there are a couple of ways to read the abstract. Without paying for the entire study, my take from the abstract is that the study found the summers during the Medieval Warm Period were approx. 2C warmer, and winters 2C cooler. Equal weighting of the sample materials winter and summer would therefore indicate no change from the comparison period. However, if the sampling process did not allow for differentiating the seasons (no micro sampling), a composite sample would be weighted toward an average of 1C warmer due to the higher volume of shell built during warmer months. They say their sampling process allowed for more precise seasonal analysis that eliminates the bias that would occur in an amalgamated sample.
    The conclusion is apparently that the MWP was warmer in summer, but colder in winter, than the comparison period, perhaps due to a weakened NAO. This indicates that this climate was perhaps confined to the northern hemisphere. So, does that mean the MWP was 2C warmer than the comparison period or not? Depends on your point of view, but 2C is very significant on the warm side, not quite so much on the cold side. More significant is the length of the seasons. I would also like to hear a comparison of the conclusions that can be reached by this method vs. other methods that don’t, for example, have an accurate winter component in the analysis, like tree rings.
    The wording of the abstract could certainly be better.
    This is just another piece of information in the puzzle of how warm the MWP was and how widespread. Further study and research grants will be needed.

  20. “Seasonal sea-surface temperature (SST) variability during the Medieval Climate Anomaly (MCA), which corresponds to the height of Viking exploration (800–1200 AD)”

    So 400 plus years is an anomaly but any weather event post 1950 is a due to a change in climate (man made of course). By calling a 400 year period an anomaly one has to ask, what are they comparing it to that makes it anomalously?

  21. Can we first agree that there was a WMP? A good start would be for the schoolteachers of climatism to admit MBH98/99/08 is scientific fraud. Just admit it. Instead what we can expect is seeing something similar to the Obamamen trying to walk-back the president’s attacks on small business and the American work ethic which is about like getting caught attacking old fashioned paperboys.

  22. Wayne,

    Good to hear your animals enjoy their hay.

    As for the barrage of questions, all I was trying to do, as several others have, is to point out that in this instance, Anthony’s headline is roughly 180 degrees wrong.

    The paper specifically does not claim that the MWP was 1C warmer than current temperatures. Anthony’s headline picks out and quotes a counterfactual statement made in the paper, which they included to illustrate the mistake that others might make in analysing shell data. And they don’t compare MWP to current temperatures, the compare it to the 1960-90 period, which is below current temperatures. And far from refuting the general hockey stick pattern, this paper supports it. It does so directly with a very localized (so probably meaningless) temperature reconstruction that suggests MWP temperatures were not different on average to 1960-90 (although with different seasonal range. More importantly it also supports the general hockey stick notion through the implication that if OTHER MWP temperature reconstructions have relied on shell data without seasonal analysis, they are likely to have over-estimated the temperature during the MWP because of the larger seasonal range, coupled with the growth habits of marine molluscs.

    I’m not saying I support Mann’s hockey stick. I’m saying that this paper supports Mann’s hockey stick.

    I doubt it’s Anthony’s fault. He’s a busy man and no doubt somebody e-mailed a link to this obscure paper to him, having misinterpreted it themselves, and Anthony took it at face value and posted it. And the author’s haven’t exactly made it easy to understand what they were driving at. They were probably trying to be polite while pointing out subtly that other scientists’ published work in this field may be significantly flawed. But they got a bit too subtle for the general reader, perhaps!

  23. Positing that MWP summer temperatures were actually warmer than currently—something a climatist might wish to dispute—and that WMP winter temperatures were colder than currently—which climatists apparently gleefully accept, by averaging the two seasons to arrive at a conclusion that WMP temperatures arguably were not really warmer than today, AGW True Believers do understand that by making this argument they are admitting there actually was a WMP, right? Even Mann finally admitted that. I think we are making progress when Climatists can agree MBH98 etc. is nothing but an Al Gore wet dream.

  24. These might be silly questions – and you will see I am pretty ignorant where statistics are concerned – so apologies in advance.

    If in the MWP winters were colder and summers hotter are there any studies of this in terms of identifying any trends of increasing or decreasing difference between winter and summer temperatures ? from CET or any other long-running data set. If so are there any cycles evident in this ?

    If temperatures and any changes are shown as based upon a running average over any extended period, then if there are any underlying trends (changes) where winters are becoming colder and summers warmer (or vice versa) would this not have an effect on the running average ?

    If summer temperatures were static or even trending down but winter temperatures were trending towards slightly warmer would a running average not show an increase in average temperature overall ? If it did then presumably that would be taken as global warming even though maximum temps did not increase ?

  25. It does appear to me (non-technical reader here) that the 1C higher temp mentioned for MCA is about the case of “without the benefit of seasonal resolution” — (from abstract, my emphasis):

    “…Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century. Without the benefit of seasonal resolution, SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season. Higher seasonality and cooler winters during early medieval times may result from a weakened North Atlantic Oscillation index.”

    The study could still be fascinating for what is says about the wider seasonal variability but maybe not for the 1C issue.

    I have periodically asked more knowledgeable people to explain why any MWP has to be *warmer* than recent temps to be important for the current debates, i.e., even if medieval temps were at or close to current levels (but perhaps not higher) that would still tend to undermine claims of Mann, Karoly, and “The Team” that it is so obvious that current temps are unprecedented etc. Of course they will then argue that we are on some trajectory to surpass the medieval temps, but I don’t see why any MWP must be *higher* than today to be relevant to the discussions. As this paper’s abstract seems to suggest, a wider seasonal temp fluctuation in the medieval period is also something very interesting and an indication that there may be too much we still don’t know about climate to make grand pronouncements.

  26. Wagathon says:

    AGW True Believers do understand that by making this argument they are admitting there actually was a WMP, right? Even Mann finally admitted that. I think we are making progress when Climatists can agree MBH98 etc. is nothing but an Al Gore wet dream.

    “Even Mann finally admitted that”? Like it is anything new? The first work of Mann’s that went back far enough to detect the MWP was not MBH98 but MBH99. In it, they did not deny the existence of an MWP. Rather, they said (http://www.ltrr.arizona.edu/webhome/aprilc/data/my%20stuff/MBH1999.pdf ) the following:

    Our reconstruction thus supports the notion of relatively warm hemispheric conditions earlier in the millenium, while cooling following the 1th century could be viewed as the initial onset of the Little Ice Age sensu lato. Considerable spatial variability is evident however [see Hughes and Diaz, 1994] and, as in Lamb’s [1965] original concept of the Medieval Warm Epoch, there are episodes of cooler as well as warmer conditions punctuating this period. Even the warmer intervals in our reconstruction pale, however, in comparison with modern (mid-to-late 20th century) temperatures.

    So, yes, they finally admitted it back in 1999 when they wrote their first paper reconstructing temperatures back to 1000 AD.

    It is amusing how skeptics then turned this into a claim that “they made the MWP disappear” and then invented the notion that Mann et al had said that there was no MWP whatsoever.

    And, of course, since the reconstruction in the current paper is for one location and not the entire Northern Hemisphere, it would be expected that whatever warmth occurred during the MWP would show up more dramatically than when one averages over the spatial variability in when the peak warmth occurred to produce a hemispheric reconstruction.

  27. Nigel Harris says:

    No, that’s not what this paper says.

    True. Anthony got it wrong. So did you.

    What they’ve done is to obtain a seasonal analysis of temperatures. They say that *if* you looked at shell evidence for MWP temperatures *without* doing the seasonal analysis you might get the *incorrect* impression that MWP temperatures were on average around 1C higher than the 1960-1990 period.

    They did not say that. That MCA temps were around 1C higher than 1960-1990 is not ruled out by their results (at least as presented in the abstract). *Incorrect* is your characterization, and it is *unsupported*.

    (If you just took a sample of shells of the right age and analyzed their 18O signal, you’d be getting a biased estimate, because more shell is made by these animals in the summer than in the winter).

    Interesting aside: The differential quantity of shell that is made in summer vs winter would appear to be another temperature proxy. Wonder what it it would indicate …

    Their seasonal analysis shows that summers were around 2C warmer, and winters around 2C cooler. In other words, although the seasonal range was greater, on average, the MWP was *no warmer* than the 1960-1990 baseline.

    The ‘other words’ that you use are your own, not those of the folks that wrote this paper. They identify that there is a difference in conclusion between an analyses that looks at the year as a whole, vs one that looks at two seasons of the year independently. You may recall that there are four seasons. Assuming that spring and fall average out to zero for the year is very much like assuming that the year as a whole is representative of summer and winter – the incorrectness of that assumption being the point of this paper. Rather than assuming, where is the analysis that shows the effect on the estimate of the amount of shell laid down in the other two seasons?

    The whole deal smacks of the sort of confirmation bias that is all too typical of ‘climate science’. If the proxy results conform to the narrative, circle the wagons and defend to the death. If they don’t, then assume there must be something wrong with the anaylsis. Search dilligently for the error that, when corrected, will bring the story back in line. And then STOP looking for errors.

    So I’m afraid this paper says exactly the opposite of what you were hoping it said.

    No, it doesnt. It doesn’t say what Anthony wanted it to. It doesn’t say what you want it to, either.

    Inkblots.

  28. Limpets shmimpets. Limpet data can be ‘homogenised’ with something else that shows no warming, or has gaps to reduce the average, and we can create a holy hockeystick again.

  29. Some of the arguments on this thread would suggest that the summer growing season would have no relationship on the winter growing season. Temp dependent organism.

    Would that suggest that the growing season temps would not reflect the winter temps in tree rings? Imagine the implications of something like that. Trees dormant in winter and affected by moisture, temp, and other factors in the summer growing season.

    Short memories make for short arguments.

  30. ThePhysicsGuy says:
    July 17, 2012 at 8:56 am
    Of course the warmists will say the MWP was a northern hemispheric phenomenon. But there are scientific studies that indicate the MWP was global, One such is: …
    =========================================================

    I am not convinced that it is possible to prove beyond a reasonable doubt either existence or non-existence of MWP, LIA etc. . The same goes for the “global warming” of our days. This is much easier to demonstrate, than fight a BS with a counterBS.

  31. Greg House,

    There is ample evidence [far beyond any reasonable doubt] showing that the MWP was global, and warmer than current temperatures. That conflicts with the alarmist crowd’s narrative, because CO2 was much lower then. So they try to downplay the MWP, using fabricated terms like the “MWA”.

    And prior to the MWP there were even warmer episodes during the Holocene. Conclusion: CO2 has a much smaller effect than is claimed, therefore it can be completely disregarded for all practical purposes.

  32. Smokey says:
    July 17, 2012 at 8:08 pm
    There is ample evidence [far beyond any reasonable doubt] showing that the MWP was global, and warmer than current temperatures. That conflicts with the alarmist crowd’s narrative, because CO2 was much lower then. So they try to downplay the MWP, using fabricated terms like the “MWA”.
    ========================================================

    I think you are right about them trying to make the MWP disappear. The notion about MWP is indeed older that the modern AGW concept and is therefore an obstacle for the AGW. At the same time, according to my knowledge about how climate scientists work I do not see those statements about past temperatures proven, nor the statements about modern “warming”. That is the point.

  33. Another nail in the already fully nailed coffin of the hockey stick fabrication. Without the hockey stick, gwarming theory doesn’t have any legs to stand on, because it means that current temperatures are not unusual in any way. That means that there is nothing wrong with the climate. So give it up you leftist climate clowns. Don’t try to fix what isn’t broken by throwing a monkey wrench into industrial civilization.

  34. Eric Simpson says:
    July 17, 2012 at 8:28 pm
    Another nail in the already fully nailed coffin of the hockey stick fabrication. Without the hockey stick, gwarming theory doesn’t have any legs to stand on,
    =======================================================

    And what about the warmists’ narrative about CO2 causing warming? This is one of their legs.

  35. This should cause Mann to fire off another tweet or two–that’s about the entent of his rebuttals nowadays.

  36. Anthony, you really should correct this article. As several commenters have pointed out, the way you are presenting this paper simply does not reflect what the abstract says. You even chop one sentence in half and by so doing invert its sense.

    Without the benefit of seasonal resolution , SST averaged from shell time series would be weighted toward the fast-growing summer season, resulting in the conclusion that the early MCA was warmer than the late 20th century by ~ 1 °C. This conclusion is broadly true for the summer season, but not true for the winter season.

    So what the paper actually says is that temps were about the same a recent warm period. This still refutes Mann’s hockey stick work but the selective editing is more in line with what I would expect from the Guardian than what I’m used to finding here.

    Please correct this before it becomes and example of WUWT doing what it criticises other of doing, that will be magnified to damage the credibility of all the work done here.

  37. “Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century.”

    This is the real result here and it may be relevant to GHG arguments. CO2 could lead to warmer winters but would not cause summers to be cooler. One thing that could cause that kind of change is increased cloud cover. There may be others.

  38. If I were a cabbage and the temperature in winter averaged zero and then averaged minus 2, I would not be concerned as I would not grow in either. However if the spring and summer were +2
    I would be a very happy cabbage. Thus a proliferation of food, a welcome commodity and the main cause of the flowering of the mediaeval period. The coldness of winter is not important it can be cold, bloody cold or bloody colder, it is the growing season that is important to humanity.

  39. Thus, during the 10th to 12th centuries winters were colder and summers were warmer by ~ 2 °C and seasonality was higher relative to the late 20th century.”

    If Viking artifacts are still being dug out of the permafrost in Greenland today and Greenland was 2 degrees cooler in the M.W.P than today, how did they get there, just asking.

  40. Smokey says:
    July 17, 2012 at 8:08 pm

    There is ample evidence [far beyond any reasonable doubt] showing that the MWP was global, and warmer than current temperatures.

    Yet you’ve never been able to provide any, instead posting an interminable number of links to regional reconstructions.

  41. The IPCC reports are famous for claiming things in their summaries that aren’t supported by the actual body of the reports. Do abstracts for papers like this one ever suffer from the same problem? What does the body of the paper actually say, and how does that compare to the abstract?

  42. Nigel Harris says:

    As for the barrage of questions, all I was trying to do, as several others have, is to point out that in this instance, Anthony’s headline is roughly 180 degrees wrong.

    No. Anthony’s interpretation is incorrect, but not as you characterize it.

    The paper specifically does not claim that the MWP was 1C warmer than current temperatures.

    The paper specifically does not claim that the MCA was the same temp as the 1960-1990 period, either.

    And they don’t compare MWP to current temperatures, the compare it to the 1960-90 period, which is below current temperatures.

    They don’t compare it to the 1960-1990 period, either. They compare some ‘seasonal’ subset, and conclude that winters were colder and summers were warmer. They don’t compare full year temps.

    And far from refuting the general hockey stick pattern, this paper supports it.

    No, it doesn’t.

    It does so directly with a very localized (so probably meaningless) temperature reconstruction that suggests MWP temperatures were not different on average to 1960-90 (although with different seasonal range.

    The results do not conclude that MCA temps were not different from 1960-90. The abstract doesn’t even reference an estimate of annual temps, let alone any summation of those annual temps over longer periods. It just reports some seasonal temps, from some portion of half the seasons. It is difficult to determine exactly what they mean when they say things like ‘the coldest of the winter months recorded in the shells’ and the ‘warmest of the summer months’. It would be nice to have the methods, to figure out what they did vs having to make assumptions. At any rate – even if they had concluded that the MCA temps were the not different than 1960-90, it would not support the hokey stick, which reported MCA temps significantly LOWER than 1960-90.

    More importantly it also supports the general hockey stick notion through the implication that if OTHER MWP temperature reconstructions have relied on shell data without seasonal analysis, they are likely to have over-estimated the temperature during the MWP because of the larger seasonal range, coupled with the growth habits of marine molluscs.

    Ah yes. Implication. You are correct that this is probably the intended function of this paper.

    I’m not saying I support Mann’s hockey stick. I’m saying that this paper supports Mann’s hockey stick.

    And you are wrong about that. This paper doesn’t say what you think it says, any more than it says what Anthony thinks it says. And if it did say what you think it says, it still wouldn’t support the hokey stick like you think it does.

  43. It’s nice to see more research regarding the MWP. The more done world-wide the better. But regardless of research findings, the CAGW crowd will believe nothing but Mann’s tree rings. From the written records we have from Europe to Asia, there is absolutely no doubt that there was an MWP. And the records of the crops cultivated then as opposed to the current period leave no doubt that the MWP was warmer. It is unfortunate we don’t have a lot of written records (if any) from the Southern Hemisphere in that time period. We then might have historic records proving the MWP in the Southern Hemisphere.

    Jay Davis

  44. Greg House says: @ July 17, 2012 at 8:24 pm

    I think you are right about them trying to make the MWP disappear. The notion about MWP is indeed older that the modern AGW concept and is therefore an obstacle for the AGW. At the same time, according to my knowledge about how climate scientists work I do not see those statements about past temperatures proven, nor the statements about modern “warming”. That is the point.
    ____________________________
    Actually it is not temperatures but the ability to grow crops that is the pointers to MWP and the LIA. Unlike climate scientists, plants do not lie for their pay check.

    Vikings

    Pini – “Two Specialized Medieval Crops: Grapes and Olives in the Po River Valley”

    Archaeobotanical Analysis of Plant Remains, The Robing Room Bishop’s Palace

    From the point of view of farmers (and civilization) it is whether or not the climate allows you to grow food that is the important matter.

  45. JJ – your understanding of this abstract is based on the assumption that when they say “summer” and “winter” they are referring to two out of four seasonal periods, having divided the year into four, and having commented on summer and winter, but not on spring and fall/autumn.

    My understanding of this abstract is based on the assumption that they divided the year into two periods, summer and winter. I perhaps jumped to this interpretation because (a) it makes sense of what they report, and (b) working in the European natural gas industry, I inhabit a world in which years are habitually divided into 6-month periods called summer and winter.

    I wonder which of us is right?

  46. Nigel,

    Your interpretation would appear to be ruled out by the phrasing “The coldest winter months recorded in the shells …” and “the warmest summer months averaged …” which suggest that, however many months they considered to be in each of those seasons, some of those months were left out of the maths.

    That phrasing is odd, vs what one would expect to see used to describe a comprehensive assessment. That would tend to be phrased as “the winter months average” and “the summer months averaged”. I submit to you that the temperature estimates reported may not even be representative of all winters and summers over the period, let alone of annual temps. As described, they would appear to represent the warmest summer temps and the coldest winter temps over the 400 year Viking Era.

    Figuring out what this paper says requires detailed methodology description. If such exists, it is hidden behind a paywall. Hidden information is not information at all, and I’m not about to pay $40 to reveal it. Until someone does, discussing this paper is an exercise in preconceptions.

  47. Didn’t read all the comments but…

    Caleb says:
    July 17, 2012 at 8:02 am

    Still not enough warming to account for how the Vikings managed to farm in Greenland during the MWP. However it is at least a step in the right direction (and back towards reality.)

    We’re expected to believe that Greenland and Greenland alone warmed enough to farm!

    When did science take over from recorded history? 400 years of warming in Greenland and we’re supposed to believe the rest of the World was cooler to compensate with no movement of that energy? History says no!

    DaveE.

  48. JJ,

    I’ve now read the paper, and you’re right.

    The study specifically resolves only the highest summer temperatures and the lowest winter temperatures. They conclude that early MCA seasonality was almost twice that of late 20th century. Early MCA winters were cooler and summers warmer than the late 20th century.

    So I was wrong to suggest that this paper can be interpreted as giving an average annual temperature in the early MCA very close to that of the 1960-1990 period. However, it does clearly state that to conclude that the early MCA was 1C above 1960-1990 would be biased to the high side. They don’t give any estimate of by how much.

    Because the shells in our study grow fastest during the warm season, the
    delta-18-O time series are weighted toward summer SST. Thus, if we attempt to calculate
    annual SST by averaging the time series, our annual averages would be biased toward
    warm temperatures. We would conclude that the early MCA was ~1°C warmer than the
    late 20th century

    So a correct interpretation of their results would be that (as well as the primary finding about increased peak to trough seasonal range) the early MCA average temperature was somewhat less than 1C above the 1960-1990 period.

    Anthony’s headline of MCA being 1C above current temperatures remains wrong.

    As for refuting Mann’s work, the authors say:

    Our findings are consistent with Mann et al. (2009), although the cool winter conditions are not exactly synchronous with their proxy compilation which covers a much larger
    area.

  49. Kevin MacDonald says:
    July 18, 2012 at 4:05 am
    Smokey says:
    July 17, 2012 at 8:08 pm

    “There is ample evidence [far beyond any reasonable doubt] showing that the MWP was global, and warmer than current temperatures.”

    Yet you’ve never been able to provide any, instead posting an interminable number of links to regional reconstructions.

    What has happened to logic these days? Regional evidence for the MWP from all the earth’s continents = evidence for a global MWP. Hellooo! – anyone at home???

    So I guess you were among the first to criticise the tree-ring hockey-stick of Mann, Briffa et al for also being regional??

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