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
Icarus62 says:
October 21, 2012 at 12:22 am
ericgrimsrud: Exactly right. A low climate sensitivity is ruled out by the data. That, combined with the fact that the anthropogenic greenhouse gas emissions causing the warming are rising faster than ever, is why it’s now becoming widely accepted that we won’t avoid 2C of global warming above mid-20th Century global temperature – unless someone comes up with some effective geo-engineering solutions.
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What gibberish! In the first place warmer is good. Learn that. In the second place your global figures are meaningless–how many times do I have to repeat it? You continue to ignore the mechanism, following Hansen’s intentional misleading. You suffer from invincible ignorance. Respond to this if you can: Albedo is controled by ice sheet extension. Ice sheets are melted by extra June insolation of about 100W TOA. Not 3W; not 1W; 100W TOA, which transmits to about 70W at the surface, which through the process of disappearing ice (at the edge–not CO2) is amplified by the local albedo decrease (not global–that’s the effect, not the cause). Ice albedo is between .5 and 1. Forest albedo is near zero. Multiply 500W by 10% of the earth’s surface covered by ice, and you don’t get a global albedo change of 3W–more like 50 –can’t you do the math? Hansen sure can’t. CO2 has nothing to do with it. Please address this or shut up. You simply reveal your Hansenian ignorance by spouting of this irrational alarm–it has no science behind it–only incompetence and stupidity. –AGF
agfosterjr:
At October 21, 2012 at 6:03 am you say
And you surely know what rising grain prices due to methanol diversion have have done to 3rd World countires (sic)
Yes. I think you may want to read my paper at
http://scienceandpublicpolicy.org/originals/biofuel_issues.html
Richard
Note RichardsCourtney’s “explanation “ of a CO2 sensitivity below 1.0 C below:
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In this case, I am fortunate in not needing to discuss the matter with you because in this thread I have twice explained and fully justified my correct statement with references and links. You are plain wrong (as usual). See my posts at October 20, 2012 at 11:17 am and October 20, 2012 at 4:49 pm.
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Upon looking up those previous posts all one finds is repetitions of the claim that sensitivity is less than 1.0C and references to a few articles that he claims proves the point. Upon looking up those references, however, no such proof is found. Most importantly, RichardsCourtney cannot tell you what exactly it was in those papers that proved his claim.
Thus, he avoids scientific discussion in this manner. In his case, this is a good strategy because he has repeatedly shown that he cannot carry a scientific argument by himself. Statements of so called “fact” with references he cannot explain are all you will get.
His repeated claim to be supported by “observations” is also bogus and I am sure he would not want to explain all of that either. For example and just for starters, why was the Earth so warm about 50 mYrs ago when the Earth was a “waterworld” and alligators lived in Alaska? The only three possible explanations for such a huge difference from today would be a hotter Sun, a much lower albdedo, or a much stronger GH effect. Does he suppose that those differences are also due to “natural variations” ?
While it would be interesting to hear what RC thinks about that very simple and readily understood question, you can be sure he will ignore it. It is in discussions of the simple and obvious questions that the pseudo scientists get exposed. Just watch. If we get any response to this simple question, it will be goppelygook broken only with personal attack and insults.
To Agfostorjr,
You really seem to have things figured out. Perhaps you could even explain the PETM for us. Those of us with less imagination have the notion that 56 mYs ago a huge carbon burst (CO2 and / or CH4) occurred throughout the globe and this caused T to rise very signiicantly, lasing about 150,000 years.. Perhpas you could help us overcome our incompetance and stupidity on that one. I mean, after all how coulda burst of CO2 possibly cause an incrrease in global temperature. It must have been due to some other “natural variation”, right, that just happened to coincide with that carbon explosion.. Or maybesome ice just happened to dissappearr …….ops, there was no ice anywhere on the planet back .then. Or maybe …….. nope. You can see we need your help on that bit of relatively recent (geologically speaking ) history.
agfoster jr says to grimsrud:
“You suffer from invincible ignorance.”
LOL! A perfect grimsrud description. Could not be more accurate.
Now grimsrud has to go all the way back to the PETM [or “PEMT”, as he kept calling it before I corrected hiim] in order to cherry-pick what he believes explains everything. But in fact, the rise in CO2 followed the PETM as usual. Just like today.
Grimsrud cannot produce a chart showing that rises in CO2 are followed by rises in global temperature. Therefore, all he is engaging in is baseless speculation. As usual.
[snip . . you would need to provide some proof of these assertions rather than just stating them otherwise it is just trolling . . mod]
agfosterjr: The 3.5W/m² of albedo forcing from ice sheet and vegetation changes comes from the findings of Hewitt and Mitchell 1997. If you can cite a paper which gives a much larger figure (and hence a lower climate sensitivity than 0.75°C/W/m² (3°C for a doubling of atmospheric CO₂ from 280 to 560ppm), then by all means do so.
Friends:
ericgrimsrud says in his post at October 21, 2012 at 9:50 am
Firstly, it is a fact and NOT merely a “claim” that – as I said – empirical (n.b. not model-derived) determinations indicate climate sensitivity is less than 1.0deg.C for a doubling of atmospheric CO2 equivalent. This is indicated by the studies of Idso from surface measurements
http://www.warwickhughes.com/papers/Idso_CR_1998.pdf
and Lindzen & Choi from ERBE satelite data
http://www.drroyspencer.com/Lindzen-and-Choi-GRL-2009.pdf
and Gregory from balloon radiosonde data
http://www.friendsofscience.org/assets/documents/OLR&NGF_June2011.pdf
Anybody can click a mouse to check the fact for themselves. Grimsrud’s post merely – again – demonstrates his inability to read or – alternatively – that he is a liar.
Richard
DBoeihm is now rewriting the evidence concerning the PETM – when he says
“But in fact, the rise in CO2 followed the PETM as usual. Just like today”.
I would love to see the charts or graphs he is reading. Since they don’t exist, I’m sure we will not see any such evidence. I suspect that he might need some help reading his charts again, just are he did before – maybe Kadaka could help again..
And concerning his “just like today” comment. Could it possibly be that DBoehm thinks the 40% increase in CO2 we has seen over the last 150 years is due to a the small T increase we have also seen over this period. Kadaka, where are you? Help?
Friends:
Further to my earlier post, I add these extracts. From each of the links.
Idso SB, Climate Research (1998)
(Determinations from surface data)
And in view of the relative weakness of the CO2 greenhouse effect at current atmospheric CO2 partial pressures, as revealed by the natural experiments I have described herein—a likely warming of only 0.4°C for a 300 to 600 ppm doubling of the air’s CO2 content—these CO2-induced cooling forces could potentially negate a large portion (or even all) of the primary warming effect of a rise in atmospheric CO2, leading to little net change in mean global air temperature.
[i.e. a climate sensitivity of ~0.4°C for a doubling of the air’s CO2 content : RSC]
Lindzen RS & Choi L-S , Geophysical Research Letters (2009)
(Determinations from ERBE satellite data)
For sensitivities less than 2°C, the data readily distinguish different sensitivities, and ERBE data appear to demonstrate a climate sensitivity of about 0.5°C which is easily distinguished from sensitivities given by models.
And
Finally, it should be noted that our analysis has only considered the tropics. Following Lindzen et al. [2001], allowing for sharing this tropical feedback with neutral higher latitudes could reduce the negative feedback factor by about a factor of two. This would lead to an equilibrium sensitivity that is 2/3 rather than 1/2 of the non-feedback value. This, of course, is still a small sensitivity.
[i.e. a climate sensitivity of ~0.4°C for a doubling of the air’s CO2 content : RSC]
Gregory K, Friends Of Science (2011)
(Determinations from radiosonde ballloon data)
This analysis shows that there has been no significant increase in the greenhouse effect since 1960. The greenhouse effect as characterized by the normalized greenhouse factor has increased by only 0.19% from 1960 to 2008. The temperature change from 1960 attributable to AGW is less than 0.1 °C. The extrapolated temperature change attributable to AGW at doubled CO2 concentration is 0.26 °C. Delaying the start date of the analysis year by year to 1970 gives calculated climate sensitivities that vary about the 0.4 Celsius value.
[i.e. a climate sensitivity of ~0.4°C for a doubling of the air’s CO2 content : RSC]
n.b. The three studies each determine a climate sensitivity of ~0.4°C for a doubling of the air’s CO2 content.
I remind that I conservatively said these papers report a a climate sensitivity of less than 1.0°C for a doubling of the air’s CO2 content.
But the egregious Eric Grimsrud asserted
The quotations I have here provided demonstrate that both of his assertions are falsehoods.
Richard
ericgrimsrud says:
“I would love to see the charts or graphs he is reading. Since they don’t exist, I’m sure we will not see any such evidence.”
Pure projection. Grimsrud cannot produce the chart I keep asking him for. That is because there is no such chart. ∆CO2 does not cause any measurable ∆T.
Prove me wrong, if you can. Post your non-existent chart.
ericgrimsrud says:
October 21, 2012 at 2:28 pm
“Could it possibly be that DBoehm thinks the 40% increase in CO2 we has seen over the last 150 years is due to a the small T increase we have also seen over this period?”
Eric are you admitting that we have seen only a small T increase over the past 150 years? Careful when you are looking down on your superiors that you don’t make such Freudian slips.
When Richardscourtney uses the word “proof”, to him it means that some scientist somewhere has offered an explanation for their observations that RC likes. His repeated misuse if that word shows that RC is no scientist.
In addition, if he had followed the literature in recent years, he would know that the paper he cites by Lindzen and Chio has been ripped to sheds both because of flawed measurements and the mis interpretation of their data- ever since it’s publication in ’09..
A little lesson here for RC: complex relationships are never “proven” beyond all doubt. Papers appear and they sometimes make claims and deductions. Those experiments and claims are then tested by others. A point is seldom proven but is frequently suppoered in follow up studies. The L and C paper did not even make the latter grade. Yet, because the L and C paper offered the explanation RC wanted, he now thinks he is providing “proof” for something just by pointing to some carefully selected references that have already failed to pass the test of time. .
Gary, So far we have seen about 0.8 C increase in T. Do you also think that caused the 40% increase we have seen in atmosphereic CO2.? You might what to check with your supervisors before agreeing with DBoehm on that one.
ericgrimsrud says:
“When Richardscourtney uses the word ‘proof’, to him it means that some scientist somewhere has offered an explanation for their observations that RC likes. His repeated misuse if that word shows that RC is no scientist.”
Richard Courtney is a published, peer reviewed scientist. And he is someone you have previously been forced to apologize to for your baseless attacks. Obviously, your apology was insincere, since you continue to make the same ad hominem attacks — which reflect badly on your own lack of character.
Since DBoehm thinks that
∆CO2 does not cause any measurable ∆T.”
I wonder why he thinks the world was about 12 C warmer some 50 mYrs ago. . Was the Sun hotter? Was the albedo that much lower even though most of the total albedo is caused be cloulds? Gosh, what else might it have been given “DBoehm’s Law” shown above. It must have been “natural variation” right? Or , maybe the Laws of Nature have changed since then – that was a long time ago,right?
Kadada, maybe you could help DBoeihm with this one also. Its really a tough one to deal with given “DBoehm Law”.
ericgrimsrud:
re your post at October 21, 2012 at 3:29 pm.
YOU LIED.
I showed you lied (yet again). And instead of apologising you provide weasel words and say I used the word “proof”. That is another lie. I only use the word “proof” with regard to mathematics.
“Proof” is a word used by pseudoscientists; e.g. you. It is not used by scientists; e.g. me.
The three papers each analyse different data and they each obtain the same result for climate sensitivity. RC and SkS have attacked one of the papers but have failed to publish a significant flaw in it.
All the evidence for the magnitude of climate sensitivity is – as I said – that climate sensitivity is less than 1.0°C for a doubling of the air’s CO2 content. Your superstitious beliefs do not and cannot change that fact.
APOLOGISE FOR YOUR LIES then crawl back under your bridge.
Richard
ericgrimsrud,
You have provided zero scientific evidence showing that the rise in CO2 has caused any global warming. You base your belief on a short term, coincidental correlation that began breaking down over a decade and a half ago.
But if you have any empirical evidence that the rise in CO2 is the cause of global warming — or even part of the cause — then by all means, post it here and now. Be sure to abide by the scientific method, and remember that models are not evidence. Be prepared to show explicit and verifiable cause-and-effect, or you will be laughed at once again for your invincible ignorance.
One more time: ∆CO2 does not cause any measurable ∆T. Your comments amount to mere hand-waving, because you have produced no scientific evidence to refute natural variability. If it were not for your hand-waving, and cherry-picking of outlandish examples from millions of years in the past, you would not have anything to say. As it is, your baseless comments are pseudo-scientific nonsense, and thus very easy to debunk.
BTW — where is that chart showing that ∆CO2 causes ∆T? Still looking for it? Here’s a hint: it doesn’t exist. You have cause and effect reversed, that’s all.
icarus62 says:
October 21, 2012 at 1:42 pm
agfosterjr: The 3.5W/m² of albedo forcing from ice sheet and vegetation changes comes from the findings of Hewitt and Mitchell 1997. If you can cite a paper which gives a much larger figure (and hence a lower climate sensitivity than 0.75°C/W/m² (3°C for a doubling of atmospheric CO₂ from 280 to 560ppm), then by all means do so.
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In fact the paper you cite gives a figure of 5W due to “Topography and surface albedo” (Table 5) and 50W local forcing (p.827a, top), both averaged out over the year and the 5W averaged out over the globe. To better make my point, assume a planet like ours but latitudinally symetrical. Would it be safe to deduce alternating ice ages in both hemsipheres? Global T and surface albedo would be the same whether you happened to be in or out of an ice age–an ice core would tell us little about climate. Now according to Hansen such a scenario would not work since the symmetry would not allow for GHG asymmetry. That is, our hemispherical asymmetry allows for GHG’s to accumulate very roughly out of phase with receding ice caps, which could not happen if the opposite hemisphere were going into an ice age at the same time.
So if you understand the argument and agree with its presentation you have to ask yourself, which world is realistic: would there be ice ages in a world just like ours except with symmetrically configured continents? Hansen says no. What do you say?
And getting back to the albedo, if we were to assume your paper’s 5W global average, and ignore southern ice formation, that “un-averages” to 10W in the north, and 40W in the northern summer quarter. Your paper’s 50W local average would “un-average” to 200W summer quarter if there were no insolation asymmetry, and of course it is that asymmetry which starts the melting in the first place–and extra 100W/m TOA in June.
Hansen is like a fire chief who disables the alarm system in favor of a thermometer stuck on a station window. –AGF
Ericgrimsrud: not even your people blame the 95% of earth’s warm climate history on CO2. Plate tectonics are usually invoked, altering wind and ocean currents. –AGF
Kadaka, Please explain to DBoehm how silly his comment is:
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“BTW — where is that chart showing that ∆CO2 causes ∆T? Still looking for it? Here’s a hint: it doesn’t exist. You have cause and effect reversed, that’s all.
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He apparently does not know that plots do not necessarily show cause. They might show correlation – if there is cause – but they do not prove cause. Similarly why would DBoehm suggest that that same plot proves cause in the reverse direction?. The notion of a cause is provided only by a theory..
I hope you don’t mind that I have asked you for your help in communicating with DB. You two seem to be on a similar wavelength so I just thought your chances of getting through might be better.
And if you understand why he is asking me for a chart all the time, please let me know.. If it Is just so that he can then tell me that correlation does not prove causes, please help him understand that we all already know that.
Grimsrud,
Begging for someone else to support your nonsense beliefs is über lame.
Post a chart showing that a change in CO2 causes a change in temperature, or you lose the argument. Simple as that.
[snip – reword this, not your blog to make demands on – Anthony]
Anthony:
re your snip of my post at October 21, 2012 at 11:23 pm.
Yes,
it is your blog and you can allow or forbid any post you choose to be posted on it,
I write to make a request.
Following other lies about me on other threads, Grimsrud made a series of lies about me on this thread. Here he made repeated claims that
*a) I asserted a series of papers said other than they do
and
(b) they do not contain specific information that I said they did.
Those assertions were more of his personal attacks and I showed that they were lies. They were posted on this blog in this thread.
I demanded that Geimsrud apologise. He did not but made excuses and I complained.
He still did not apologise and I repeated my demand in strong – but not profane – terms,
You have snipped that saying
“[snip – reword this, not your blog to make demands on – Anthony]”
OK. Then please snip any further lies about me from Grimsrud. There have been too many on too many WUWT threads.
Richard
To RichardsCourtney
Have you seen
“Trenberth et al
Relationships between tropical sea surface temperature and top-of-atmosphere radiation. Geophys. Res. Lett., 2011.
In it, Lindzen and Choi 2009 is shown to be wrong on several fronts. If you don’t actually read papers and cannot figure out where the problems with L and C are, I would be pleased to summarize them for you on a following post.
Hope you are feelling better.
Eric