Nicola Scafetta sends this along, I found this figure quite interesting, but there are many more in the full PDF available below.
A regional approach to the medieval warm period and the little ice age
Fredrik Charpentier Ljungqvist
Stockholm University
Sweden
1. Introduction
In order to gain knowledge of the temperature variability prior to the establishment of a widespread network of instrumental measurements c. AD 1850, we have to draw information from proxy data sensitive to temperature variations. Such data can be extracted from various natural recorders of climate variability, such as corals, fossil pollen, ice-cores, lake and marine sediments, speleothems, and tree-ring width and density, as well as from historical records (for a review, see IPCC 2007; Jones et al. 2009; NRC 2006). Considerable effort has been made during the last decade to reconstruct global or northern hemispheric temperatures for the past 1000 to 2000 years in order to place the observed 20th century warming in a long-term perspective (e.g., Briffa, 2000; Cook et al., 2004; Crowley and Lowery, 2000; D’Arrigo, 2006; Esper et al., 2002; Hegerl et al., 2007; Jones et al., 1998; Jones and Mann, 2004; Juckes et al., 2007; Ljungqvist, 2010; Loehle, 2007; Mann et al., 1999; Mann et al., 2008; Mann et al., 2009; Mann and Jones, 2003; Moberg et al., 2005; Osborn and Briffa, 2006).
Less effort has been put into investigating the key question of to what extent earlier warm periods have been as homogeneous in timing and amplitude in different geographical regions as the present warming.
It has been suggested that late-Holocene long-term temperature variations, such as the Medieval Warm Period (MWP) and the Little Ice Age (LIA), have been restricted to the circum-North Atlantic region (including Europe) and have not occurred synchronic in time with warm and cold periods respectively in other regions (Hughes and Diaz, 1994; Mann et al., 1999; Mann and Jones, 2003). This view has, however, been increasingly challenged through the ever growing amount of evidence of a global (or at least northern hemispheric) extent of the MWP and the LIA that have become available (see, for example, Esper and Frank, 2009; Ljungqvist, 2009, 2010; Moberg et al., 2005; Wanner et al., 2008).
A main obstacle in large-scale temperature reconstructions continues to be the limited and unevenly distributed number of quantitative palaeotemperature records extending back a millennium or more. The limited number of records have rendered it impossible to be very
selective in the choice of data. Palaeotemperature records used in a large-scale temperature reconstruction should preferably be accurately dated, have a high sample resolution and have a high correlation with the local instrumental temperature record in the calibration period (see the discussion in Jones et al., 2009).
The number of long quantitative palaeotemperature records from across the globe, of which a majority are well suited for being used in large-scale temperature reconstructions, have been rapidly increasing in recent years (Ljungqvist, 2009). Thus, it has now become possible to make regional temperature reconstructions for many regions that can help us to assess the spatio-temporal pattern and the MWP and LIA. Only by a regional approach can we truly gain an understanding of the temperature variability in the past 1–2 millennia and assess the possible occurrence of globally coherent warm and cold periods. Presently, only four regional multi-proxy temperature reconstructions exist: two for eastern Asia (Yang et al., 2002; Ge et al., 2010), one for the Arctic (Kaufman et al., 2009), and one for South America (Neukom et al., 2010). Six new quantitative regional multi-proxy temperature reconstructions will here be presented in order to improve our understanding of the regional patterns of past temperature variability.
…
4. Conclusion
The presently available palaeotemperature proxy data records do not support the
assumption that late 20th century temperatures exceeded those of the MWP in most regions, although it is clear that the temperatures of the last few decades exceed those of any multidecadal period in the last 700–800 years. Previous conclusions (e.g., IPCC, 2007) in the opposite direction have either been based on too few proxy records or been based on instrumental temperatures spliced to the proxy reconstructions. It is also clear that temperature changes, on centennial time-scales, occurred rather coherently in all the investigated regions – Scandinavia, Siberia, Greenland, Central Europe, China, and North
America – with data coverage to enable regional reconstructions. Large-scale patterns as the MWP, the LIA and the 20th century warming occur quite coherently in all the regional reconstructions presented here but both their relative and absolute amplitude are not always the same. Exceptional warming in the 10th century is seen in all six regional reconstructions.
Assumptions that, in particular, the MWP was restricted to the North Atlantic region can be rejected. Generally, temperature changes during the past 12 centuries in the high latitudes are larger than those in the lower latitudes and changes in annual temperatures also seem to be larger than those of warm season temperatures. In order to truly assess the possible global or hemispheric significance of the observed pattern, we need much more data. The
unevenly distributed palaeotemperature data coverage still seriously restricts our possibility to set the observed 20th century warming in a global long-term perspective and investigate the relative importance of natural and anthropogenic forcings behind the modern warming.
Full report here (PDF)
a_regional_approach_to_the_medieval_warm_period_and_the_little_ice_age
vukcevic says:
November 25, 2010 at 10:33 am
Here are two temperature’s reconstructions in more detail
As I said, the fact that you have to reverse the correlation for some of the time is the clearest evidence that the correlation is spurious.
@ur momisugly 899: “To presume one thing of necessity demands that its driver be identified.
It’s not unlike this: The spoon stirred the coffee. A hand caused the spoon to move. The brain of the owner of that hand caused the hand to move and stir the coffee.”
That is nicely put. It reminds me of:
” I call the effects of nature the works of God, whose hand & instrument she only is; and therefore to ascribe his actions unto her, is to devolve the honour of the principal agent, upon the instrument; which if with reason we may do, then let our hammers rise up and boast they have built our houses, and our pens receive the honour of our writings.” (Sir Thomas Browne, Religio Medici, I, 16 (1643)
Leif Svalgaard says:
November 25, 2010 at 12:06 pm
As I said, the fact that you have to reverse the correlation for some of the time is the clearest evidence that the correlation is spurious.
I do not generate or change correlation, it is a natural process, that I have brought to the attention.
I’ve just pointed out elsewhere that in certain cases correlation can flip from positive to negative, even in a case of causation, I am not claiming the causation is case here.
That makes your remark questionable.
Guys, being a “geographer” is not a point which is against someone on this issue. Not long ago every single person who studied climate in academia was in a geography department: climatology was considered a sub-field of geography, because it was thought that it was all about know the relevant climate zones-which were thought of as fixed geographic locations, not unlike the positions of the continents were thought to be. There are few “climate” departments at few universities even today, and many studying climate still work in the geography department. Many still regard climatology as a “geography” thing.
@ur momisugly David Middleton : You are right regarding my comment (in my 2:15 post) on the calibration issue. Thank you for pointing that out.
@ur momisugly tonyb (4:25) : I am not sure what your issue is with my (1:47) post.
The point I was making had nothing to do with finding Ljungqvist’s Pdf.
The point was that Anthony picked ONE regional graph from that pdf, even though that one is not representative for the larger set that Ljungqvist posts in his pdf, and certainly not representative for the entire Ljungqvist 2010 presentation.
Also, the “skepticalscience” post shows very clearly that the Greenland graph that Anthony prominently posts here is not representative for Ljungqvist’ 2010, nor for the Northern Hemisphere as a whole, and that Ljungqvist 2010 overall shows very close resemblance to Mann 2008 and Moberg 2005.
Anthony could at least have mentioned that, since otherwise some readers may misinterpret what Ljungqvist actually found, and start to see ‘opposite’ hockey-sticks (at cherry-picked time points) in a graph that has no association with the overall Northern Hemisphere reconstructions.
There is certainly nothing wrong with being a geographer. Many climate scientists come from a geography background and most glaciologists do…
Anthony;
In regard to “eadler” I am compelled to raise the issue of troll quality with you. Both the quantity and the quality have been in decline of late. Could you perhaps put more effort into recruitment? There was a time on this blog when trolls abounded, could carry on a logical discourse, and sometimes even made valid points. One can hardly learn anything from an argument which rests on the premise that a paper may be questionable because it was not peer reviewed by the scientists who wrote papers that are falsified by it.
Not only is the argument so pathetic that it hardly deserves response, it is in fact so pathetic that one can’t even make fun of it. Its just sad really. If you could put some effort into getting some decent trolls, I’d appreciate it.
Until then I shall content myself with rereading accusations that Tonyb is a paid alarmist. Debunked of course by many long before I had a chance, but at least there were some facts on the table to debate, and a conclusion tabled that was so wrong it was hilarious.
899 and stephen richards:
I drew attention to the latitudinal shifting of the jets aspect because that is what links regional changes in climate to changes in the global pattern of climate distribution. That simple observation makes it highly unlikely that events such as the MWP and LIA could ever be merely local or regional events.
Elsewhere, I have gone to quite some lengths (continuing) to try and account for such shifting.
Uh huh. That’s just about what the literature indicates happened: The LIA and the MWP were pretty much a global thing, as far as the writings exist. It’s been a slow roll down the hill from the Holocene Optimum.
And after the global chill had fled
Inuit, Norse and Polyneians greatly spread
DavidmHoffer
“Not only is the argument so pathetic that it hardly deserves response, it is in fact so pathetic that one can’t even make fun of it. Its just sad really. If you could put some effort into getting some decent trolls, I’d appreciate it.”
Wonderful! A career in satire beckons.
For those that defended me against the charge that I was a paid alarmist thank you. Now, about my Christmas present…
Tonyb
@Rob, November 25, 2010 at 5:33 pm
Mann 2008 and Moberg 2005 are fairly similar. The main difference is that Mann employed a version of Mike’s Nature trick to the last ~40 years of his curve. Moberg did not; nor did Ljungqvist. Moberg and Ljungqvist calibrated their reconstructions to the instrumental data. Mann over-rode his reconstruction with the instrumental data.
The problem with Mann’s methodology lies in the fact that the instrumental data and reconstruction proxies are different things. They have very different sampling rates, resolutions, frequency content and amplitude spectra.
The proper way to merge two signals with such differences is to condition one series to fit the other. In signal analysis, this is usually done by deriving a mathematical operator to transform one series to fit the other. This is similar to the process employed in merging seismic reflection surveys of different vintages, with different recording parameters.
Mike’s Nature Trick basically splices a high frequency, high resolution signal onto the tail-end of a low frequency, low resolution signal. This will almost always create the impression of an anomaly at the tail-end. The same thing happens with the CO2 reconstructions. The Antarctic ice core data are very low frequency, low resolution. MLO is very high frequency, high resolution. The modern CO2 level is far less anomalous when compared to plant stomata reconstructions, because those data are closer to MLO in resolution.
eadler says:
November 24, 2010 at 3:15 pm
I never heard of Fredrik Charpentier Ljungqvist, so I tried to find out using Google. It seems he is a graduate student in the department of history at Stockholm U.
I wonder if any climate scientists peer reviewed it. It will be interested to see it deconstructed.
Nice logic. The paper (or whatever) reviews regional, previously published studies from around the world. Pardon me, but I thought geography relates to location. Why would a person want a climate scientist to review published geographical proxy studies?
Data is data. We don’t need no stinkin’ opinions.
EFS_Junior says:
November 25, 2010 at 12:31 am
So a couple questions come to mind; 1) Why is this book for free and bot [sic] for sale (behind a pay wall), and 2) this is not published in a well respected peer reviewed climate science journal, why is that, and will the author publish this in something mildly resembling a peer reviewed publication of any sort?
Note, his previous paper (2009 paleo-reconstruction) was published in some rather obscure (IMHO) Scandinavian geography journal.
This journal has a long and storied history. It is well respected in knowledgeable science circles. It is peer reviewed. Appeals to authority are ignorantly misplaced in this instance.
http://www.docstoc.com/docs/43740994/Geography-in-Sweden
Rob, the point is that “overall Northern Hemisphere reconstructions” are averaged together. Which means that vital information was kicked out in the search for some odd “Global Temperature”. It would be like sending someone to the doctor for some mysterious illness and when you get there all the doctor can say is that you are sick, because the only thing that matters is your rectal temperature.
Pamela,
Now lets agree that the average temperature of the patient taken over many differents part of the body and different times shows a fever, and most doctors agree that the reason is Antropogenic, just like theory predicted.
Just some people still believe that by looking at checky-picked measurements and cherry-picked areas of the body (and by showing a graph of that area with these measurements on wattsupwiththat) shows that there is nothing unusual going on, and that the patient is somehow immune to the substance that in theory should cause a fever indicative of a desease that can potentially be quite devastating.
Now which “vital information” did I leave out ?
Which “vital information” did you leave out?
You left out your diagnoses of Earth’s identical fevers from 863 AD to 897 AD and 1911 to 1944.
Here are the HadCRUT3 Northern Hemisphere instrumental record, Ljungqvist’s 2010 Nothern Hemisphere reconstruction and Alley’s 2000 Central Greenland reconstruction for Central Greenland… Alley, Ljungqvist, HadCRUT3 – 3.5 kya. I calibrated Alley’s Greenland reconstruction to Ljungqvist. What caused the “fevers” from 1450 BC to 1350 BC and 320 BC to 120 BC?
Here’s the same reconstruction expanded to cover most of the Holocene: Alley, Ljungqvist, HadCRUT3 – 3.5 kya. What caused the “fevers” from 6300 BC to 5900 BC, 5250 BC to 4980 BC, 4300 BC to 3700 BC, 3480 BC to 3250 BC, 2820 BC to 2300 BC and 2000 BC to 1680 BC?
David,
The HADCRUT3 1911-1944 +0.5 C increase started out a whopping 0.4 C below the +0.5 C increase since 1975, and global temperaures thus went up almost a full degree C over the 20th century. That (long-term increase) is the fever that one would expect from antropogenic GHG forcing.
And the graph that you show since the start of the Holocene essentially shows only the GISP2 record. May I remind you that that is a single ice core in one spot in Greenland ? That graph really makes my point that some people cherry-pick ONE location and then feel that it has any meaning for the global temperature record.
At least in the following graph there are 8 proxies combined (from various places on Earth),
http://en.wikipedia.org/wiki/File:Holocene_Temperature_Variations.png
This shows again that Greenland (or any other local record) is not representative for the average of this planet. It also shows (again) that temperatures right now are unprecedented as seen over the entire Holocene record.
Why is this so hard for you (and Anthony) to accept ? Why do you guys keep cherry-picking locations (or time intervals) and pretend that such cerry-picking has any meaning in the global picture ?
Rob,
Your Wikipedia source says that “there is no scientific consensus on how to reconstruct global temperature variations during the Holocene.” If there was such a consensus, it certainly would not be to simply average together 8 global proxies. Most paleo climate reconstructions of the Upper Holocene are limited to the Northern Hemisphere. Antarctic ice cores show very little in the way of stadial/interstadial climatic fluctuations. Greenland ice cores, sediment cores, speleothems, etc show quite a lot of stadial/interstadial climatic fluctuations. Antarctic ice cores are not used for Northern Hemisphere reconstructions. Two of the eight proxies are Antarctic ice cores. Most Northern Hemisphere reconstructions are extra-tropical. Three of the eight proxies are from tropical locations.
So, five of the eight proxies would probably not be used in a Northern Hemisphere reconstruction over the entire Holocene.
Despite the flaws of the Wiki-reconstruction, it basically shows the same pattern as the GISP2 reconstruction. The heavy black curve is the average of the 8 proxies. It shows the modern warming to be comparable to the Medieval Warm Period and the Little Ice Age to be the coldest part of the Holocene. It shows a steadily cooling climate since the Holocene Climatic Optimum with a super-imposed millennial warming and cooling cycle. There is nothing unprecedented about the modern warming on the Wiki-reconstruction.
David,
I posted the wiki reconstruction (with 8 proxies) just as an example of how irrelevant single-location / single-proxy samples are in the global record.
Even with just 8 proxies, the picture (of the previous “unprecedented” warming periods that you mentioned) looks entirely different. Regardless of the weight by which each proxy is measured, a large sample of proxies irons out the extreme (“unprecedented”) random/weather anomalies of single samples, and reveals the low-frequency climate trends that climate science is interested in.
From signal theory, we know that for N channels (each with uncorrelated, “local” noise) signal to noise ratio for common signals is SQRT(N) better than for a single channel. Meanwhile, local temperature extremes are moderated by a factor of N. From that we know that more (and more physically widespread) samples are quantifiably better than small number of samples if we are interested in ‘global’ or ‘common’ trends.
Even with just 8 proxies on this Holocene record, the long, slow term down trend since the Holocene Climatic Optimum becomes apparent (which is very well explained with the Milankovitch cycles) and the global (+0.7 C in 100 years) climate anomaly of the 20th Century starts to come out of the noise as well.
In that light, I find it mystifying why you throw out 5 of the 8 reconstructions (because they are not in the extra-tropic Northern Hemisphere).
As you very well know, that just increases the noise, and makes it more difficult to recognize climate trends.
Ljungqvist already reduced the number of proxies that he considered (by separating regions, and then again even for the individual regions as well). Then Anthony used the local noise in the Greenland record and the noise that Ljungqvist created by reducing proxies to somehow imply that 20th Century warming is not unprecedented.
And now you are doing the same thing with the Holocene record.
I start to see the pattern that Ljungqvist (at least in this non-peer-reviewed pdf story), Anthony and you are using :
Reduce the number of samples (preferably by cherry-picking) to the point where the local weather noise is greater than the 20th century warming (or to sample size 1, whichever comes first), and then use that to claim that “therefore” the 20th Century warming is not unprecedented or AGW is in doubt.
Of course, you are just fooling yourself (and some readers here) with noise that you created yourself.
Question is, again : WHY are you guys doing that ? Why not find MORE proxies and combine them with the 1000+ proxies (dating back to many different past times) that we already have ? Why reduce the set, create noise, and then imply statistically irrelevant conclusions ?
Why ?