Yesterday I highlighted the paper The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability, by B Christiansen of the Danish Meteorological Institute and F C Ljungqvist of Stockholm University which showed that using a multitude of proxy samples in the norther hemisphere, that:
“The level of warmth during the peak of the MWP (Medieval Warm Period) in the second half of the 10th century, equaling or slightly exceeding the mid-20th century warming, is in agreement with the results from other more recent large-scale multi-proxy temperature reconstructions.”
Now another paper, by Esper et al published in the Journal of Global and Planetary Change, shows that not only was the summers of the MWP equal or greater than our current warmth, but that the summers of the Roman Warm Period of 2000 years ago were significantly warmer than today.
Variability and extremes of northern Scandinavian summer temperatures over the past two millennia
Jan Esper, Ulf Büntgen, Mauri Timonen, David C. Frank
Abstract
Palaeoclimatic evidence revealed synchronous temperature variations among Northern Hemisphere regions over the past millennium. The range of these variations (in degrees Celsius) is, however, largely unknown. We here present a 2000-year summer temperature reconstruction from northern Scandinavia and compare this timeseries with existing proxy records to assess the range of reconstructed temperatures at a regional scale. The new reconstruction is based on 578 maximum latewood density profiles from living and sub-fossil Pinus sylvestris samples from northern Sweden and Finland.
The record provides evidence for substantial warmth during Roman and Medieval times, larger in extent and longer in duration than 20th century warmth.
The first century AD was the warmest 100-year period (+0.60 °C on average relative to the 1951–1980 mean) of the Common Era, more than 1 °C warmer than the coldest 14th century AD (−0.51 °C). The warmest and coldest reconstructed 30-year periods (AD 21–50=+1.05 °C, and AD 1451–80=−1.19 °C) differ by more than 2 °C, and the range between the five warmest and coldest reconstructed summers in the context of the past 2000 years is estimated to exceed 5 °C. Comparison of the new timeseries with five existing tree-ring based reconstructions from northern Scandinavia revealed synchronized climate fluctuations but substantially different absolute temperatures. Level offset among the various reconstructions in extremely cold and warm years (up to 3 °C) and cold and warm 30-year periods (up to 1.5 °C) are in the order of the total temperature variance of each individual reconstruction over the past 1500 to 2000 years. These findings demonstrate our poor understanding of the absolute temperature variance in a region where high-resolution proxy coverage is denser than in any other area of the world.
[…]
Discussion and Conclusions
The MXD-based summer temperature reconstruction presented here sets a new standard in high-resolution palaeoclimatology. The record explains about 60% of the variance of regional temperature data, and is based on more high-precision density series than any
other previous reconstruction. Importantly, MXD sample replication prior to the Little Ice Age, during Medieval times and throughout the first millennium AD, is much better than in any other record, and we demonstrated – based on calibration trials using reduced
datasets – that these early sections of the N-Scan record likely still contain useful climate information. This persistent climate signal allowed an estimation of temperature variability throughout the Common Era, revealing warmth during Roman and Medieval times were larger in extent and longer in duration than 20th century conditions.
According to this new record, summer temperatures varied by 1.1 °C among the 14th and 1st centuries, the coldest and warmest 100-year periods of the past two millennia. Temperatures ranged by more than 5 °C among the five coldest and warmest summers of the past 2000 years. These estimates are, however, related to the approach used for proxy transfer, i.e. figures would change, if the calibration method, period, and/or target were modified (Frank et al.,2010b). For example, variance among the 30 coldest and warmest N-Scan summers (Table 3) increases from 3.92 °C to 5.79 °C, if scaling (i.e. adjustment of the mean and variance) instead of OLS regression is used for proxy transfer. These differences between scaling- and regression-based approaches are proportional to the unexplained variance of the calibration model (Esper et al., 2005), and we suggest
smoothing the proxy and instrumental timeseries prior to calibration, as this procedure decreases the unexplained variance in all Scandinavian tree-ring records and thus minimizes the differences between various calibration methods (Cook et al., 2004).
Our results, however, also showed that these methodological uncertainties are dwarfed by the variance among the individual reconstructions.
Differences among six northern Scandinavian tree-ring records are>1.5° in 30-year extreme periods and up to 3 °C in single extreme years, a finding we didn’t expect, as the proxy records: (i) all calibrate well against regional instrumental data, (ii) partly share the same measurement series (or use differing parameters – TRW and MXD – from the same trees), and (iii) originate from a confined region in northern Scandinavia that is characterized by a homogeneous temperature pattern. Since we here calibrated all reconstructions using the same method, between-record differences are likely related to varying data treatment and chronology development methods, measurement techniques, and/or sampling strategies, as well as the remaining uncertainty typical to such proxy data. For example, splicing of MXD data on recent TRW trends as done in Briffa92 might have caused this reconstruction to appear at the lower (colder) end of the ensemble, whereas the combination (and adjustment) of novel digital MXD measurements with traditional X-ray based MXD data as done in Grudd08 might have caused this reconstruction to appear at the upper (warmer) end of the ensemble. Other differences are likely related to the combination of sub-fossil material from trees that grew in wet conditions at the lakeshores with material from living trees growing in dryer ‘inland’ sites. Also varying variance stabilization (Frank et al., 2007) and detrending techniques (Esper et al., 2003) in association with temporally changing sample replications and age distributions of the underlying data (Melvin, 2004) likely impacted the variance structure of the long-term records and consequently the absolute levels of reconstructed temperatures.
Between-reconstruction variance as revealed here represents a pending challenge for the integration of proxy records over larger regions and the development of a single timeseries that represents the Northern Hemisphere (e.g., Mann et al., 2008), for example. The composition of such records commonly relies on the calibration statistics derived from fitting regional proxy records against instrumental data (D’Arrigo et al., 2006). However, the records analyzed here would all easily pass conventional calibration-based screening procedures. Yet our analysis revealed that choosing one Scandinavian record instead of another one can alter reconstructed temperatures by 1.5-3 °C during Medieval times, for example. On the other hand, consideration of all records presented here would likely promote a less variable climate history, as the combination of diverging records tends to reduce variance in the mean timeseries (Frank et al., 2007). If such a mean is then combined with instrumental data covering the past 100–150 years, this approach might facilitate hockey stick-shaped reconstructions (Frank et al., 2010a). This seems to be a tricky situation in which expert teams including the developers of proxy records might need to be involved to help assessing timeseries beyond the typical ranking based on calibration statistics.
Our results showed that introducing an improved temperature reconstruction does not automatically clarify climate history in a given region. In northern Scandinavia, we now arrive at a situation where a number of high-resolution proxy records – all passing classical calibration and verification tests – are available within a confined region that is characterized by homogeneous temperature patterns. These records, however, differ by several degrees Celsius over the past two millennia, which appears huge if compared with the 20th Century warming signal in Scandinavia or elsewhere. We conclude that the temperature history of the last millennium is much less understood than often suggested, and that the regional and particularly the hemispheric scale pre-1400 temperature variance is largely unknown. Expert teams are needed to assess existing records, and to reduce uncertainties associated with millennium-length temperature reconstructions, before we can usefully constrain future climate scenarios.
Full paper here (PDF -link fixed)
h/t to WUWT reader Gordon Pye and Tory Aardvarrk
ericgrimsrud says:
October 21, 2012 at 9:05 pm
=========================
Centuries of data correlating the cock’s crow and sunrise show strong agreement, albeit with a lag of less than an hour. We may safely conclude that one event causes the other, or that a third event causes both. This chart (http://en.wikipedia.org/wiki/File:Vostok_420ky_4curves_insolation.jpg)
compares insolation governed by orbital forcng (Milankovitch Cycles) with T and CO2, and again shows good agreement, especially between T and CO2. Again we can assume either T or CO2 drives the other or that a third function governs both. But we have a third function, insolation, governed by the earth’s orbit, which correlates with the other two, generally leading it by c.5ky. So now we have to ask, is T or CO2 driving insolation, or is insolation running the show? Does the rooster make the sun come up? And the claim that CO2 forces T is every bit as absurd. Insolation causes ice sheet growth or melting, which governs T and CO2. And as I’ve been arguing all along, CO2’s contribution to warming is of 2 orders of magnitude less than insolation and albedo feedback combined. That means insignificant. This year the high southern latitudes will get 30 more watts of January insolation than the opposite northern latitudes will in June:
http://aom.giss.nasa.gov/cgi-bin/srmonlat.cgi
–AGF
ericgrimsrud:
re your post tp me at October 22, 2012 at 7:50 am
I will not lower myself to discuss anything with you unless and until you provide a complete, abject and unequivocal apology for your lies.
Anyway, as this thread demonstrates, it is a laughable idea that you are capable of understanding the paper which you cite.
Richard
To RC, Have a good laugh:
The huge problem with the Lindzen and Choi 2009 paper is that they examine only select tropical data. In their chosen data set, they find that during periods of higher surface temperatures, the IR radiation emitted and solar radiation reflected back into space by the earth goes up as well, thereby cooling the Earth. To show this, they select specific intervals of monthly averaged values and compare fluxes at their endpoints. They don’t even provide a criterion for selecting these endpoints, they simply pick some for analysis.
The result one then obtains in depends entirely on the endpoints chosen. The article by Ttrenberth et al shows that the perceived feedback can be whatever one wishes it to be by choosing different intervals and that the result that obtained by Lindzen and Choi is actually very unlikely.
In sort, much more robust sampling is required.
ANd there is much more — later.
Eric Grimsrud:
I await your apology.
I have no interest in your misunderstandings of a paper which you lack the competence to understand. And I doubt that anybody else is interested, either.
I await your apology.
Richard
RC,
You will have a long wait. I am not inclined to apologize to bullies who hand it out in spades and then turn into crybabies when treated in kind.
I will, however, continue explaining the fatal flaws of the Lindzen and Choi paper in a future post or two.
And why would you claim to know what everyone else is interested ? Do you think you run the place?. You have hung your entire case for low sensitivity above on the Lindzen and Choi paper, even though you can’t explain its contents. .Therefore, I suspect that many others might like to know more about its contents – something you have been unable to provide – other than countless repetitions of its erroneous conclusions.
I understand that you are trying the “head off” this pending discussion of science. Again that is when we generally see only your backside along with a few personal insults. But should you regain your interest in the actual science on which you pontificate, please feel free to point out any errors I might make it representling the scientific content of the two papers in question.
Eric
ericgrimsrud :
re your post at October 23, 2012 at 12:43 pm.
I still await your apology for your lies. A man would have provided it by now.
It is not bullying to object to blatant personal lies from a troll.
I don’t run away from you. Why would I? You have the intellect – but not the work rate – of a fly and you are easier to swat. And, as you have so often demonstrated, you lack competence to discuss science.
Copy as many misleading statements from SkS as you want. It will have no effect. Lindzen&Choi are right and their work is confirmed by the other completely independent studies.
Incidentally, I point out that I have a surprisingly high respect for you in that in terms of respect I rank you only two places below a slime mold.
I await your apology. If it is sufficiently grovelling then it may improve my respect for you.
Richard
To RichardsCourtney and any other parties who are interested in the scientiifc content of Lindzen and Choi 2009 and not simply their conclusions.
Another exceedingly important deficiency in L&C, 09 appears to occur in their calculations of CO2’s Sensitivity. They did not include the effects of black body radiation in their feedback parameter. This omission resulted in a net feedback that was negative thus leading to their prediction of low Sensitivity. Inclusion of the radiation effect leads to a positive feedback parameter and a much greater estimate of Sensitivity.
This deficiency of L&C 2009 and others, such as the other one I described in another recent post above, are described extensively in Trenberth et al 2010.
My main point here is not to be overly critical of the paper by L&C. That paper made suggestions that were novel and perhaps worthy of consideration, but were also contrary to more generally accepted thought. It is not surprising therefore that there will be counter arguments and corrections to their paper. That’s how science works.
But my main point here is: for Richardscourtney or anyone else to embrace the conclusions of L&C before that paper has withstood the test of time is most unwise. It already appears that the conclusions of L&C are very probably not valid after a very short test of time.