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.
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:
- 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
- Received 1 March 2012. Revised 2 July 2012. Accepted 8 July 2012. Available online 15 July 2012. http://dx.doi.org/10.1016/j.palaeo.2012.07.003
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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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.
Probably 1.4°C warmer bearing in mind the newly covered paper on WUWT.
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.
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.)
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.
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.
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.”
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
Probaly caused by the extra CO2 from burning all the witches!
I have found evidence that the temperature in London was so hot between Sunday 2 September to Wednesday 5 September 1666 that all the thermometers broke!
http://en.wikipedia.org/wiki/Great_Fire_of_London
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.
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.
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.
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.
“This conclusion is broadly true for the summer season, but not true for the winter season.” off Orkney, Scotland
I have to agree. Anthony, the abstract really does not say what’s claimed in your headline
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.
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/
The influx of the MWP “Deniers” ;-), suggests that this paper has hit a bit of a hot spot!
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.
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)
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.
“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?
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.
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!
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.