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« The Signal and the Noise | Main | UEA footdragging - Part 2 »

A warm welcome back to the MWP

A new paper by Thomas Melvin, Hakan Grudd and Keith Briffa revisits the famous (and infamous) Tornetraesk tree ring chronology.

We describe the analysis of existing and new maximum-latewood-density (MXD) and tree-ring width (TRW) data from the Torneträsk region of northern Sweden and the construction of 1500 year chronologies. Some previous work found that MXD and TRW chronologies from Torneträsk were inconsistent over the most recent 200 years, even though they both reflect predominantly summer temperature influences on tree growth. We show that this was partly a result of systematic bias in MXD data measurements and partly a result of inhomogeneous sample selection from living trees (modern sample bias). We use refinements of the simple Regional Curve Standardisation (RCS) method of chronology construction to identify and mitigate these biases. The new MXD and TRW chronologies now present a largely consistent picture of long-timescale changes in past summer temperature in this region over their full length, indicating similar levels of summer warmth in the medieval period (MWP, c. CE 900–1100) and the latter half of the 20th century. Future work involving the updating of MXD chronologies using differently sourced measurements may require similar analysis and appropriate adjustment to that described here to make the data suitable for the production of un-biased RCS chronologies. The use of ‘growth-rate’ based multiple RCS curves is recommended to identify and mitigate the problem of ‘modern sample bias’.

Well, well, well.

In its previous incarnation, without a MWP, the series was used in:

  • MBH98
  • MBH99
  • Rutherford et al 05
  • Jones 98
  • Crowley 00
  • Briffa 00
  • Esper 02
  • Mann, Jones 03
  • Moberg
  • Osborn, Briffa 06
  • D’Arrigo et al 06

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Reader Comments (52)

Oh dear, this won't please a few people!
Any signs of "Divergence"?

Oct 27, 2012 at 9:49 PM | Unregistered CommenterAdam Gallon

My dentist recently told me I had a "hair-line fracture" in one of my molars, which eventually might lead to loss of the tooth. Since I'm assuming the referenced author Keith Briffa is the Keith Briffa of Climategate fame, it sounds to me like the CAGW molar also just might have a "hair-line fracture."

Oct 27, 2012 at 9:56 PM | Unregistered CommenterReed Coray

Will mann sue over the fact that a series he used, actually Shows the existence of the MWP, after everything he did to erase it?

Oct 27, 2012 at 10:06 PM | Unregistered CommenterOtter

The science is unsettled.

Oct 27, 2012 at 10:26 PM | Registered CommenterPharos

Not read the paper yet, but my first guess is it does not emply Mannumathics, rather more mainstream statistical processing.

Oct 27, 2012 at 10:55 PM | Unregistered CommenterDon Keiller

I’ve had the feeling lately that the climate reconstruction gang, minus some key names had finally admitted to themselves that the MWP is now incontrovertible. They must deeply regret that those key names pressed them to join together and deny its existence and/or pretend it was just a phenomenon of a few northern hemisphere locations. I really don’t think they would have gone as far as they did without the pressure they got from you know who.

How fortuitously timed for those who might need to prove a temperature hockey stick was in fact a wooden boomerang ;-)

Oct 27, 2012 at 11:10 PM | Unregistered CommenterTinyCO2


Oct 27, 2012 at 11:37 PM | Unregistered CommenterBruce

With the whole CAGW shebang unravelling as nature does what nature does, with funding now looking as if its on shakier ground politically and with the possibility of a.newer generation of less heavily invested, younger scientists looking to make their mark, wouldn't you want to show that even an old hand up to his armpits in past machinations can still get it right if he's pushed?

Oct 27, 2012 at 11:40 PM | Unregistered Commentermrsean2k

Ah but the truth is so inconveniently irrefutable - is it some sort of trick........................... Mike?

Oct 27, 2012 at 11:45 PM | Unregistered CommenterAthelstan.

I can't wait to see the real numbers they came up with! The disconnect between temperatures and CO2 will be even more obvious as in

At least they are coming clean, and it is refreshing to see a "mea culpa" coming out of the AGW crowd!

Oct 27, 2012 at 11:49 PM | Unregistered Commentertomwys

If the case for Global Warming is so strong, why do its proponents keep lying about the data?

Oct 27, 2012 at 11:51 PM | Unregistered Commenterdearieme

Thanks Bish, going to be interesting watching the "audits" of this one! I wonder if Don knows that CRU having started finding things?

Oct 28, 2012 at 12:08 AM | Registered CommenterGreen Sand

'The truth' is out there , obviously.
and these guys might finally be homing in on it.

But, to be frank, they have caused so much trouble and pain, I just wish they would hand the baton on to a new generation.

Oct 28, 2012 at 12:30 AM | Unregistered CommenterEternalOptimist

Tony CO2 "pressure"" from you know who"? Surely you don't mean.........Voldemann

Oct 28, 2012 at 12:41 AM | Unregistered CommenterNick in Vancouver

Nick - shhhh, mention not the name of He-Who-Must-Not-Be-Named. Who do you think you are Harry Read Me?

On another note - I wonder what the spaghetti graph looks like now? Does that only leaves S. Huang (2004)? Not that it matters, as Huang didn't disagree with a warm MWP because it didn't go back that far. I wonder if Dr Iain Stewart of Climate Wars wants to drive about with a hockey stick on his van now?

Oct 28, 2012 at 1:04 AM | Unregistered CommenterTinyCO2

I have long had a feeling Keith Briffa is FOIA. Something about his reconstruction being cut of in the hockey stick, and he's not been much on the radar even after climategate fame.

Time will tell..

Oct 28, 2012 at 1:22 AM | Unregistered Commenteraquix

Surely the airbrushing from history of the MWP was fundamental to the presentation and hence impact of the Mann Hockey Stick?

The authors of this paper have therefore committed apostasy, and heavy punishment will surely follow.

Oct 28, 2012 at 1:17 AM | Registered Commenterrickbradford

The timing of this paper along with Mann's court case has Climategate 'feel' to it.

Oct 28, 2012 at 1:36 AM | Unregistered CommenterRobin

does that mean the lights can be turned back on?

27 Oct: UK Telegraph: Claire Duffin: Street lights turned off in their thousands to meet carbon emission targets
Huge swathes of Britain are being plunged into darkness as more and more streetlights are switched off by councils and roads authorities.
They are making the move despite concerns from safety campaigners and the police that it would lead to an increase in road accidents and crime.
The full extent of the blackout can be disclosed following an investigation by The Sunday Telegraph – which comes on the day that clocks moved back an hour, making it dark earlier in the evening – and found that:
3,080 miles of motorways and trunk roads in England are now completely unlit;
a further 47 miles of motorway now have no lights between midnight and 5am, including one of Britain’s busiest stretches of the M1, between Luton and Milton Keynes;
out of 134 councils which responded to a survey, 73% said they had switched off or dimmed some lights or were planning to;
all of England’s 27 county councils have turned off or dimmed street lamps in their areas…
Local authorities say the moves helps reduce energy bills, at a time when energy prices are continuing to rise…
However some councils admit they may not see savings for another four or five years because of the cost of installing new lights, dimmer switches and complex control systems.
And some councils – as well as the Highways Agency, responsible for motorways and major A roads – say that the lights are being turned off to meet “green” targets to cut carbon emissions, by reducing electricity use…

Oct 28, 2012 at 3:40 AM | Unregistered Commenterpat

You guys are so funny when you just project your prejudices onto papers you haven't read.

The new chronologies presented here provide mutually consistent evidence, contradicting a previously published conclusion (Grudd, 2008), that medieval summers (between 900 and 1100 ce) were much warmer than those in the 20th century.


These conclusions, and the evidence of comparatively similar warmth in medieval and recent century summers, are in accord with earlier temperature inferences based on RCS processing of these or similar earlier Torneträsk data (Briffa et al., 1992; Grudd et al., 2002). However the new results contradict the evidence presented by Grudd (2008) that northern Fennoscandia ‘may have been considerably warmer than previously recognised’ during medieval times and significantly warmer as compared with the late-twentieth century. That analysis showed (April–August mean) medieval temperatures some 1°C above the late 20th century mean values (Grudd, 2008: figure 11) whereas the
results here imply a level of recent summer temperatures that is equivalent, though not yet as persistent over as long a period, to the warmth in medieval time.

Oct 28, 2012 at 4:19 AM | Unregistered CommenterFrank

Keith Briffa disappoints. - gavin.

Oct 28, 2012 at 6:34 AM | Unregistered CommenterJimmy Haigh


The very fact that the paper states that the Medieval Warm Period is on par with today's temperatures is sufficient for the comments here. That's stated in the Abstract. Your quotes from the rest of the paper are just part of an organised retreat rather than a complete capitulation.

Oct 28, 2012 at 6:36 AM | Unregistered CommenterHuub Bakker

"The Science is unsettled"

@Pharos : brilliant. I think the sceptical movement has reached a tipping point!

Oct 28, 2012 at 8:01 AM | Unregistered CommenterFarleyR

This is indeed progress on the part of Briffa, but let us not forget that the paper is about a chronology from Northern Sweden so it does nothing to promote the idea that the MWP was global. Not that I doubt that from other evidence.

Oct 28, 2012 at 8:31 AM | Unregistered CommenterJohn Peter

I still think Briffa along with Mann, Shmidt, Appel, Jones and the rest should go to prison. They know/knew they were cheating in order to improve their funding streams.

Oct 28, 2012 at 8:37 AM | Unregistered CommenterStephen richards

whereas the
results here imply a level of recent summer temperatures that is equivalent, though not yet as persistent over as long a period, to the warmth in medieval time.

AND Frank ??? I know I spend most of my days speaking French but my english is still not totally gone.

"level .... equivelent ..... not as persisitent as MWP ?????? WUWT

Oct 28, 2012 at 8:41 AM | Unregistered CommenterStephen richards

Dendrochronology is like tea leaves at the bottom of the cup. Interesting, diverting, topical and the attention is flattering. And a good fortune teller has the knack of finding something for you to grasp onto. Doesn't mean I should base my life choices on anything the fortune teller will tell me.

Oct 28, 2012 at 8:43 AM | Unregistered CommenterJiminy Cricket

Not sure if it is significant but it is good to see that they have used the traditional MWP, and not the Mannian MCA.

Oct 28, 2012 at 8:47 AM | Registered Commenterlapogus

One thing though, guys, are trees good thermometers?

I'm not so sure, so this paper could merely be another attempt to have trees accepted as a good proxy for historical temperatures - how long will it take for Mann to spot the "fatal flaw" in this paper?

I'd be really interested to know who reviewed this paper.

Also, this paper doesn't make it into AR5, does it?

Oct 28, 2012 at 8:52 AM | Registered Commentermangochutney

From which we deduce that current energy policy will deliver Medieval Warm Period II.

Oct 28, 2012 at 8:53 AM | Unregistered Commenterssat

Sorry, I can't buy dendro just because it agrees with my prejudices. It's still of limited applicability in determining past clmates, beyond the fact that that variety of tree grew in that location. Tree line data is of course very relevant.

Oct 28, 2012 at 9:18 AM | Unregistered Commenterrhoda

Talking about tree ring chronologies does anyone know if there have been any developments regarding the data collected by Queen's University Belfast? Doug Keenan had been using the FOI Act to get hold of the data which he claimed could be of considerable importance to the study of past climates but the last thing I read on this subject was that despite Keenan's legal victories the data supplied was incomplete and not in a usable form.

Surely if climate change is a major issue then it is very important to publish and analyse any relevant data irrespective of whether one thinks the causes are mainly natural or man-made?

Oct 28, 2012 at 9:23 AM | Unregistered CommenterRoy

The same Thomas M. Melvin contributed to this September 1 2012 paper:

Abstract (my italics)

An ultra-long tree-ring width chronology (9111 years long, 7109 BC to AD 2002) has been established based on the analysis and dating of 1432 subfossil/dry dead wood samples and cores from 335 living trees. The material was collected from treeline or near-treeline sites (c. 2000 to 2400 m a.s.l.) mainly in the Eastern Alps. The availability of preserved samples through time at high altitudinal sites is influenced by Alpine forest history and is partly climatically controlled, as shown by comparisons of the sample depth record of the Eastern Alpine Conifer Chronology (EACC) with the Holocene glacier record. The similarity of variations over time between the sample depth of the chronology and the mid-Holocene GISP2 10Be record suggest a relationship between sample depth and solar activity. The Eastern Alpine Conifer Chronology has already been used as a dating base in environmental studies, eg, on glacier fluctuations, as well as in archaeological studies.

Oct 28, 2012 at 10:25 AM | Unregistered CommenterAntonyIndia

Just curious.

Tree rings are considered by some(many) sceptics to be poor or unusable proxies for temperature. Two questions.
1 Does this mean that if a study like this shows some correlation with other temperature proxies or actual thermometer measurements, it is a coincidence?
2 Why has there been no study where tree rings are actually compared with a reliable alternative record of temperature which should now be possible for the past 50-100 years? Is it because thet dendros know what the answer will be?
Just asking.

Oct 28, 2012 at 11:25 AM | Unregistered CommenterPaul Maynard

Answers to Paul Maynard

1. We don't understand it properly, and should not kid ourselves that we do.

2. It's because you can't publish null or 'wrong' results. This is the decline they talk about.

Oct 28, 2012 at 1:42 PM | Unregistered Commenterrhoda

So the science is "self-correcting" then. Look forward to the revision of all the reconstuctions that used the previous "biased" results. And reconsideration of the conclusions based on them.

Oct 28, 2012 at 1:58 PM | Unregistered CommenterGeoff

Hallelujah, Briffa found the MWP. Fascinating how these obvious charlatans are now back tracking knowing full well their scam has been exposed and they now need to rewrite their misinformation and downright lies. As someone suggested earlier, they need to be held accountable for their fraudulent bastardisation of the science, which has caused more harm than good.

A shame they banned the practises of the Salem Witch Trials, then again, it would probably produce too much CO2.

Oct 28, 2012 at 2:09 PM | Unregistered CommenterChristian J.

Paul Maynard
I think we've established that tree rings cannot be trusted as reliable proxies in isolation.
My understanding is that dendrologists (ie those who study the natural history of trees) believe that while tree rings are pretty good at determining the age of trees they are less sanguine about their ability reliably to determine temperature since there are numerous other factors which affect tree ring growth in any given year.
Dendroclimatologists, on the other hand, have heard that tree rings are wider in warm years than in cold ones and not being very bright have gone off half-cocked without bothering to consult those people who actually understand these things.
One by-product of this obsession (combined with the aforementioned limited reasoning power) is that when there is evidence before their eyes that all of a sudden tree rings are not giving the answer they expect (read "want") they try to hide the fact that that divergence renders their whole research meaningless.
You are right up to a point when you suggest that the correlation was coincidental. In fact there will have been times over the period under examination when the correlation was reliable but there is no way of knowing which they were.
I am with rhoda. I am glad to see the return of the MWP but mainly because "everybody knew" it existed. I am no more convinced of its existence by this paper than I was of its non-existence by the 11 which are cited above.
Nice to see Briffa in the rôle of repentant sinner, though!

Oct 28, 2012 at 2:12 PM | Registered CommenterMike Jackson

That this tree ring reconstruction better matches other reconstructions and the history books doesn't make tree rings reliable but it does strengthen the case for a warm MWP. Where one lot of data disagrees with another, it raises questions. Which data is right and which is wrong; or are they both wrong; or are they both right and warming wasn't global? Like the Albert Einstein quote 'No amount of experimentation can ever prove me right; a single experiment can prove me wrong' in reverse. ie No number of proxies make the MWP true but a single disagreeing proxy casts doubt upon it.

One of the key mistakes climate scientists have made was to hide natural variability from the public. The smoothed proxies hide the huge annual swings so when compared to a tiny portion of thermometer data, the current temperature changes seem alarming. A good example is the graph of the Holocene Temperature Variations, seemingly showing 2004 catastrophically warmer than at any time in the last 10,000 years.

Oct 28, 2012 at 2:18 PM | Unregistered CommenterTinyCO2

They just could not bring themselves to state clearly for all and sundry to understand that the 20th Century warming was not unprecedented.

Oct 28, 2012 at 2:29 PM | Unregistered CommentersHx

Does anyone here doubt that if the tide hadn't turned against Briffa's earlier stance (it certainly never qualified as science), he'd still be hustling and peddling it for all he was worth.

Oct 28, 2012 at 2:49 PM | Unregistered Commenterchip

Chip, I don’t know Briffa well enough to say that, but I can imagine how an honest person might be caught up in the heat of the moment and then regret it afterwards.

Imagine you believed passionately about CAGW. All your colleagues believed it. Other scientists you’d never met believed it. Everyone is saying their work confirms it. It must be true. Then you find new information that seems to boost that story. You run with it. Then you start to have doubts about its quality and you voice your concerns to colleagues but they reassure you. Some strangers start poking into your work and ask difficult questions. People you trust and have worked with, tell you that the strangers are bad people and only out to cause mischief. You are indignant and go into defence mode. You stop second guessing yourself. Time moves on. The strangers get more strident. Good questions are asked but you ignore them because they're the enemy. New data arrives. You start to question yourself again and despite the fact you hate to let the bad guys win, you feel you have to tell the truth.

I can’t say I wouldn't fall into such a trap and I like to think that I’m a good person.

Oct 28, 2012 at 3:55 PM | Unregistered CommenterTinyCO2

In other news the BBC is going to revisit Climategate on Halloween


Oct 28, 2012 at 4:59 PM | Unregistered CommenterDolphinhead

Dolphinhead -

Perhaps amusing, considering the context, are the two links at the bottom of the web page:
'Erased Memories and Spotless Minds'
'Human Kind' with an image of a fistful of dollars.

Maybe even intentionally humourous considering the ambiguity of the final question:
'Chris Vallance investigates, asking if this was it a political crime, and, if so, how effective has it been?'

Oct 28, 2012 at 6:31 PM | Unregistered CommenterDerekP

I doesn't really matter whether this agrees with my prejudices, if trees are good ttermometers/rain guages or that the body of the report contains weasel words about not contradicting previous papers or whatever. What is important is that the summary represents backtracking, and backtracking in a big way. The fact it makes me happy is not relevant.

Oct 28, 2012 at 6:56 PM | Unregistered CommenterSandyS

I'm not greatly surprised to see Briffa's name on this.

Oct 28, 2012 at 7:10 PM | Unregistered Commenterjorgekafkazar

'I have long had a feeling Keith Briffa is FOIA'. aquix Oct 28, 2012 at 1:22 AM

Police rarely announce closure of an investigation unless they have their man.

Oct 28, 2012 at 9:14 PM | Unregistered CommenterPharos

Forget the MWP, the graphs show no unique hockey blade. CO2-CAGW is a busted flush if this paper stands.

Oct 28, 2012 at 9:54 PM | Unregistered Commenterssat

Just to refresh the reader's memory, here is Keith Briffa speaking candidly with his colleagues in one of the more notorious Climategate emails:

"I know there is pressure to present a nice tidy story as regards ‘apparent unprecedented warming in a thousand years or more in the proxy data but in reality the situation is not quite so simple. We don't have a lot of proxies that come right up to date and those that do (at least a significant number of tree proxies) some unexpected changes in response that do not match the recent warming. I do not think it wise that this issue be ignored in the chapter. For the record, I do believe that the proxy data do show unusually warm conditions in recent decades. I am not sure that this unusual warming is so clear in the summer responsive data. I believe that the recent warmth was probably matched about 1000 years ago.

That was 13 years ago. Mustabin a helluva pressure to grow a spine that could lift it.

Oct 29, 2012 at 3:12 AM | Unregistered CommentersHx

Surely the important paper by Esper et al at:

provides some support for the validity of using tree rings as temperature proxies -- since Esper et al do use tree rings and numerous other proxies for gaining insight into past temperatures

Oct 29, 2012 at 5:44 AM | Unregistered CommenterTed Swart

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