A bogging temperature reconstruction

Actually it's not that bad, but the headline was too good to resist. I'm grateful to a reader for sending me a copy of the new temperature reconstruction from Moschen et al, recently published in Climate of the Past. The authors reconstruct temperatures from carbon isotope analysis of Sphagnum moss.

The temperature reconstruction is based on the Sphagnum δ13C cellulose/temperature dependency observed in calibration studies. Reconstructed GST anomalies show considerable centennial and decadal scale variability. A cold and presumably wet phase with below-average temperature is reconstructed between the 4th and 7th century AD which is in accordance with the so called European Migration Period, marking the transition from the Late Roman Period to the Early Middle Ages. At High Medieval Times, the amplitude in the reconstructed temperature  variability is most likely overestimated; nevertheless, above-average temperatures are obvious during this time span, which are followed by a temperature decrease.

I did like the bit about the MWP being overestimated - the journal editor will have breathed a sigh of relief at that comment.

The authors seem keen to downplay the MWP, emphasising the similarities to tree ring studies (they cite a northern hemisphere temperature reconstruction by Büntgen et al., which is the green line in the chart above).

The local [growing season temperature] anomalies show a remarkable agreement to northern hemispheric temperature reconstructions based on tree-ring datasets and are also in accordance with climate  reconstructions on the basis of lake sediments, glacier advances and retreats, and historical datasets. Most notably, e.g., during the Early Middle Ages and at High Medieval Times, temperatures were neither low nor high in general. Rather high frequency temperature variability with multiple narrow intervals of below- and aboveaverage temperatures at maximum lasting a few decades are reconstructed.

I'm not sure about this - that sure looks like a medieval warm period to me. (They find no evidence of the Roman Warm Period and peat cutting has destroyed any record of the Little Ice Age.)

That said, I think I would also need some convincing about the validity of the proxy - some of it sounds a bit iffy to me.

Calibration studies have systematically investigated the relationship between climate parameters and the stable carbon isotope composition of cellulose (δ13C cellulose) from modern Sphagnum plants. Ménot and Burns (2001) found that in addition to atmospheric CO2 partial pressure, temperature and water availability play significant roles for their δ13C cellulose values. Regarding potential relationships between the δ13C  cellulose of Sphagnum plant material and micro-climatological parameters, Skrzypek et al. (2007) report  strong correlations between the δ13C cellulose values of Sphagnum and air temperature during the growing season. The major problem in the application of the Sphagnum δ13C cellulose to peat records in order to derive climatic signals arises from the finding that a significant offset exists between the stable carbon isotope composition of cellulose from different Sphagnum plant components (Loader et al., 2007; Moschen et al., 2009). Thus, physical separation of individual plant parts prior to isotope analyses is a necessity to avoid misinterpretations of stable isotope time series.

And you go on to read things like:

Due to the closed coupling of several environmental factors to air temperature, a (presumably indirect) dependency of the stable carbon isotope composition of Sphagnum cellulose on local air temperature has been assumed. To date there is no laboratory study on this relationship, however, the Sphagnum δ13C cellulose/temperature dependency has been proven in field studies (Ménot and Burns, 2001; Skrzypek et al., 2007).

I assume this means that they found a correlation and are assuming causation.

So, not entirely convinced, but it's interesting nevertheless.

The paper is: R. Moschen, N. Kühl, S. Peters, H. Vos, and A. Lücke. Temperature variability at Dürres Maar, Germany during the Migration Period and at High Medieval Times, inferred from stable carbon isotopes of Sphagnum cellulose, Clim. Past, 7, 1011–1026, 2011

Comments

[Tim Channon]

Prior "discusion" paper
http://www.clim-past-discuss.net/7/535/2011/cpd-7-535-2011.pdf

Final paper
http://www.clim-past.net/7/1011/2011/cp-7-1011-2011.pdf

Where is the data? Not found that yet.

[Mac]

"Sphagnum moss"

Brings back memories of David Bellamy, Tiswas and Lenny Henry.

[BBD]

BH

Interesting stuff - thanks for posting this up.

More evidence for an NH MWP (ca 800 - 1200 CE) that was neither consistently warm nor warmer than the C20th?

[stun]

Is it just me but I am not seeing 'a remarkable agreement' with the reconstruction, either on a decadal or smoothed basis? Like the MWP though. Well warm, wannit?

[Nicholas Hallam]

Had the MWP still been in fashion, I dare say the analysis would with more plausibility have been used to confirm its existence.

As it is, I see no "remarkable agreement with northern hemispheric temperature reconstructions", and the quality of the measure as a plausible temperature proxy appears fatally flawed by its extreme volatility and its very poor correlation with 20th century warming - where the proxy trend is flat to down (at best).

[Don Pablo de la Sierra]

Absolutely amazing that this sort of "science" is published.

Due to the closed coupling of several environmental factors to air temperature, a (presumably indirect) dependency of the stable carbon isotope composition of Sphagnum cellulose on local air temperaturehas been assumed. To date there is no laboratory study on this relationship,

(emphasis added)

At least the fair tales I write are clearly labeled as such.

[TerryS]

It is curious how all these reconstructions claim similarities with each other but never quantify it with, as an example, a coefficient of coherence.

[Don Pablo de la Sierra]

Based upon what appears to me to be Einstein's statements, light has long been assumed to be the fastest thing around -- until the recent laboratory experiments in CERN.

At least Einstein was off by only a few per cent as far as the neutrinos are concerned, so I would have to give that to him. But this?????

[SayNoToFearmongers]

@BBD

More evidence for an NH MWP (ca 800 - 1200 CE) that was neither consistently warm nor warmer than the C20th?

Are we reading the same paper? The reconstruction above clearly shows anomalies way higher than the 1998 peak, and for several decades.

Also, given that it's 2011 material, I wonder what the agenda was in cutting off the graph eleven years ago? Are recent observations unacceptable?

[Paul Deacon]

Perhaps: "A bog standard temperature reconstruction".

[lapogus]

SayNoToFearmongers - careful there. I don't regard BBD as a troll but after our exchanges at the foot of page 5 on the Guilty-Men-Guilty-Woman thread I am now far less likely to respond to his comments. Maybe you can have more success than I did but I fear the only acceptable evidence to BBD that the MWP was warmer than now would be if he could secure a trip in a time machine and travel back to personally witness some Vikings sunbathing on the Jakobshavn Glacier. Even then he would say it was just a freak local warm spell, which could be explained by regional variation.

[SayNoToFearmongers]

lapogus,

Thanks for that - just that with a graph at the top of this article clearly showing that the claimed black is in fact white, then my instincts kick in... No need to go all drawn out here, just the existence of a 200-300 year period when temperatures were around the same level or higher than the ephemeral (certainly in terms of this reconstruction) peak we saw last century. No solace whatsoever there for catastrophists, particularly given that the amplitude of the variations in the reconstruction show that recent alleged temperature changes are very much precedented and moreover occur practically incessantly.

[BBD]

SNTFM

Are we reading the same paper? The reconstruction above clearly shows anomalies way higher than the 1998 peak, and for several decades.

The authors state (emphasis added):

At High Medieval Times, the amplitude in the reconstructed temperature variability is most likely overestimated; nevertheless, above-average temperatures are obvious during this time span, which are followed by a temperature decrease.

[...]

Most notably, e.g., during the Early Middle Ages and at High Medieval Times, temperatures were neither low nor high in general. Rather high frequency temperature variability with multiple narrow intervals of below- and above average temperatures at maximum lasting a few decades are reconstructed.

Hence my comment:

More evidence for an NH MWP (ca 800 - 1200 CE) that was neither consistently warm nor warmer than the C20th?

[Patagon]

It is a sad environment when authors feel that they need to stress the unreliability of results opposing the consensus. Why that particular bit unreliable? If so you may forget the whole study and conclude that it was a waste of time.

But there is so much evidence that it would be quite hard to erase the MWP.

Just to add a bit, from Albertus Magnus De vegetabilibus it is known that fig trees and pome granates were cultivated near Cologne in Germany, from this Pfister and others (1997) deduce that

It is hypothesized that Mediterranean plants such as fig trees and olive trees spread northwards during the warm period from AD 1180 to 1299 and that the distribution of these plants was shifted southwards after 1300 when cold winters became, at the same time, more severe and more frequent. These findings agree with those obtained for China where a northward shift in the distribution of subtropical crops such as citrus fruit is demonstrated for the thirteenth century .This indicates a warm stable winter climate with a mean temperature in January being about 0.6°C and a mean extreme rninimum temperature ,about 3.5°C higher than in 1901-1960 (De'er, 1994).

[Patagon]

the paper:
http://www.wsu.hist.unibe.ch/downloads/winter_air.pdf

[Patagon]

A more recent example from the southern hemisphere, presented at a symposium on:
Interaction of Ice Sheets and Glaciers with the Ocean
La Jolla, California, 5–10 June 2011
paper 60A152

Glaciar Jorge Montt is one of the largest tidewater glaciers of the Southern Patagonia Icefield in Chile. A history of its frontal variations has been compiled since the early 20th century, resulting in a frontal retreat of almost 18 km between 1905 and 2011, the largest recorded glacier retreat in South America. The ice elevation changes measured since 1975 have also shown a very large thinning, with values of -11 m a-1 between 1975 and 2002 and -9 m a-1 between 2002 and 2008, according to airborne laser data. In spite of this large retreat and thinning, semiburied trees destroyed 250-460 years BP (C14 dates) were found at the glacier front.

So we get a forest buried by glaciers in Patagonia that is resurfacing now, which is a clear indication of a recent period much warmer than now. I wonder why that was a natural climatic variation and the current one is a human induced tax-demanding aberration?

[Nic Lewis]

It may be worth asking Paul Dennis for his comments on this - he is an expert on stable isotope proxies. I had a feeling that the temperature resolution obtainable wasn't presently high enought for a reconstruction of the detail shown, but I haven't read the paper and I may be quite wrong about that.

[barn E. rubble]

RE: "That said, I think I would also need some convincing about the validity of the proxy - some of it sounds a bit iffy to me."

The good folks @ the University of Saskachewan have been using O, C, H and N isotope systems from fish bones and shells. They are confident enuff to reconstruct temps down to weekly intervals and perhaps more importantly the regional conditions and effects of those temps.

Some interesting reading here:
http://geochemistry.usask.ca/bill.html

-barn

[MikeN]

For what area is this study? Mann has conceded a Medieval Warm Period for Europe and North America, and interestingly, his rejection of a global medieval warm period not only leads to evidence that natural variability is not the likely cause of modern temperature rise, but also that models overstate warming.

[BBD]

Nic Lewis and barn E

The old proxy tango ;-)

At High Medieval Times, the amplitude in the reconstructed temperature variability is most likely overestimated; nevertheless, above-average temperatures are obvious during this time span, which are followed by a temperature decrease. On the contrary, a pronounced Late Roman Climate Optimum, often described as similarly warm or even warmer as medieval times, could not be detected.

The abrupt loss of resolution prior to ca 400CE is very clear (Fig 5).

Unlike the above-average temperatures at High Medieval Times and slightly before, we do not find evidence for any prior warm phase. Although our reconstruction shows slightly above-average temperatures during the second half of the 1st century AD, a Late Roman Climate Optimum often described as similar warm or even warmer as medieval times could not be detected. This is in accordance with other millennial-scale climate reconstructions based on multiple proxy datasets (e.g., Jones and Mann, 2004; Moberg et al. 2005). In contrast to these reconstructions in favour of the
absence of a pronounced Roman Climate Optimum, there are other proxy records that point to relatively high temperatures during the first two centuries AD. Proxies of glacier retreat and low lake levels indicate warm and/or dry conditions in the Alps (Holzhauser et al., 2005; Joerin, et al., 2006; Giraudi, (2009). On the contrary, a record of reconstructed temperatures derived from a well-dated stalagmite d18OCaCO3 record from the Central Alps shows remarkably low winter temperatures during the first four centuries AD (Mangini et al., 2005). The results of Mangini et al. (2005) suggest that the climate of this period was continental and dry. Thus, the dryness of the climate rather than its warmth would explain the widely accepted glacier recession accompanied by low lake levels in the Alps during the Late Roman Period.

[BBD]

MikeN

Durres Maar is a small peat bog a few 100km due south of Cologne.

[Gixxerboy]

BBD

Are you saying that we should trust the authors' conjecture that the 'reconstructed temperature variability is most likely over-estimated', rather than the reconstruction? If so, why?

[Ian W]

According to viticulture (vines - physical and written evidence from temperature-sensitive plants), the climate was probably warmer in the UK than today 50 million years ago, during each interglacial, in the Neolithic and Roman periods - and the Medieval Warm Period *.

What is causing the fluctuations in temperatures? Do you think the Romans were burning too much peat whilst drinking too much wine? After all they came from a warmer climate themselves.

* paraphrased from Prof. Dick Selley, London Lecture Abstract, PESGB October 2011.

[BBD]

The 'argument' about the MWP misses the point, as ever.

Whatever the temperature was in S Germany or the UK during the hottest decades of the MWP relative to today is irrelevant to modern climate change.

The MWP appears to have been caused by increased TSI and low volcanic activity (reduced sulphate aerosols).

Current warming cannot be explained in these terms, but does fit very closely with the predicted effects of increasing RF from CO2.

So comparisons between modern climate change and the Mediaeval or Late Roman or Minoan Warm Periods are misleading.

>>Gixxer

Are you saying that we should trust the authors' conjecture that the 'reconstructed temperature variability is most likely over-estimated', rather than the reconstruction? If so, why?

Yes, because they calibrated the sphagnum d13C proxy and best understand how much confidence to place in it. Read the paper - it's an interesting proxy study in its own right and not very long.

[Bad Andrew]

"The MWP appears to have been caused by increased TSI and low volcanic activity"

BBD,

It appears as though you are pretending you know what you are talking about.

Andrew

[BBD]

Andrew

If you have nothing to say, do not post comments. I got ticked off by the Bish for calling you lazy, but I'm going to risk doing it again because apart from being offensive (as usual), you do not say why you disagree with what I say. That's lazy. In fact it's trolling.

[Ian W]

BBD, I am fascinated to learn how you know that there was low [global] volcanic activity in the Medieval times? I am also a bit concerned about the use of terms like "irrelevant" in this context. Do we really understand everything so well as to be so dimissive?

PS I am new to this. What is TSI?

[Bad Andrew]

"If you have nothing to say, do not post comments."

BBD,

Obviously, I do have something to say. It's your M.O. to make assertions in quantity. As long as you keep doing that, I'm going to pop in from time to time and point it out. If that makes you mad, that is your problem.

Andrew

[Bishop Hill]

Bad Andrew

If you think BBD doesn't know what he's talking about, please could you avoid saying so, but attempt to demonstrate it by questioning him politely.

[BBD]

Ian W

TSI = total solar irradiance. Measured at the top of the atmosphere (TOA!) not the Earth's surface. Solar energy reaching the surface is termed 'insolation'. I mention this as the two are sometimes confused.

A vast deal of work has been done on volcanism. Eruptions leave dust traces that show up in ice cores and lake bed sediments. These can be traced to specific volcanos (geochemical analysis) and dated by isotopic analysis of organic material associated with the dust layer in the core.

Understanding is good enough now to say that comparison of modern warming with the MWP etc is irrelevant, yes.

[Bad Andrew]

"If you think BBD doesn't know what he's talking about, please could you avoid saying so, but attempt to demonstrate it by questioning him politely."

Yes sir. But if you are now applying standards of politeness, I hope these standards include that frequent and verbose commenters answer the questions they are asked in a straightworward manner. It's impolite to simply propagandize and not engage in honest discussion.

Andrew

[diogenes]

do they give any indications of the possible error bands round these measurements? My first guess is that you cannot draw any conclusions from data this messy.

1. Is it slightly odd that this kind of work so often seems to end up in trying to derive a set of thermometer readings for the distant past?

2. Is there nothing better that can be done with this sort of study? It is not as if the modern instrumental records are free from error - so what use are derived temperatures from imperfectly-understood proxies? And before someone pitches in to say that Hadcrut, Gisstemp, NOOA or whatever are perfect, I am not interested in this ongoing debate - which exists among the authorities eg Phil H thinks his series is better than Giss etc - but rather in what insight we are supposed to gain from mossmometers and treemometers. Surely, there are better ways of passing your life as a researcher?

[BBD]

Andrew

It's impolite to simply propagandize and not engage in honest discussion.

What? I'm having a very hard time believing my eyes here.

I provide logical, supported argument and you call it propaganda and a failure to engage in honest discussion. You have not earned the right to accuse me of either. I suggest you pipe down now.

[BBD]

BA

Your next comment needs to contain a coherent explanation as to why current thinking that the MWP was caused by increased TSI and low volcanism is wrong.

Here' s the classic paper on solar influence (heard of Bond Cycles, have we?): Persistent Solar Influence on North Atlantic Climate During the Holocene, Bond et al. (2001) abstract:

Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's “1500-year” cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.

Full paper (pdf)

Do some reading matey.

[Patagon]

"Understanding is good enough now to say that comparison of modern warming with the MWP etc is irrelevant, yes."

BBD, would you care to provide some proofs, as in references, experiments, etc. Aerosols are very poorly understood and heavily parameterized in climate models. There are some attempts to link aerosols to climate (Briffa et al) but no conclusive proof that its lack was a cause of warming during WWP. The GISP2 shows very similar concentrations for year 1000 and year 1900. And as the CLOUD experiment stressed recently aerosol understanding in climate models is rather poor.

Some interesting historical records:

Stöng: In 1104, there was a large eruption at Mt Hekla and the settlements of Thjorsardalur were buried under tons of debris and volcanic ash. In 1939 scandinavian archaeologists excavated in Stöng stong and discovered a farm that was in the Middle Ages, obtain valuable information on the design and construction of the Viking farms. The rebuilt farm is called Thjodveldisbaer (farm of the Commonwealth), and is perhaps the best representation of the medieval Icelandic housing.

[Bad Andrew]

"I suggest you pipe down now."

This is impolite, BBD.

Andrew

[Patagon]

The paper you link above, bbd, has an interesting conclusion:

The results of this study demonstrate that Earth’s climate system is highly sensitive to extremely weak perturbations in the Sun’s en- ergy output, not just on the decadal scales that have been investigated previously, but also on the centennial to millennial time scales docu- mented here. The apparent solar response was robust in the North Atlantic even as early Ho- locene vestiges of the ice sheets continued to exert a climate influence and as the orbital configuration shifted from that of the Holocene optimum to the quite different regime of the last few thousand years. Our findings support the presumption that solar variability will continue to influence climate in the future, which up to now has been based on extrapolation of evi- dence from only the last 1000 years (25). If forcing of North Atlantic ice drift and surface hydrography is fundamentally linked to the Sun and begins in the stratosphere, then atmospheric dynamics and their link to the ocean’s circula- tion are much more important for interpreting centennial and millennial time scales of climate variability than has been assumed.

Unfortunately it does not seem to say much about the present and introduce a "large 2sigma errors in calibrated ages (typically be- tween ±100 and ±150 years)" It also shows an increase in solar radiation during the 20th Century: http://tinyurl.com/6jczdb8

So, I don't understand how this support your point that current warming is unnatural

[BBD]

Patagon

The parameterisation of volcanic aerosols in GCMs is not arbitrary. See Gao et al. (2008) for mind-numbing detail on how a 1500 year volcanic forcing index was reconstructed from ice-core data.

Even if you aren't comfortable with the aerosol factor, the variation in TSI that seems to drive the Bond Cycles is enough to acount for the MWP (see Bond et al. 2001 - link above).

[Patagon]

I presume you wrote your second paragraph before reading my last post.

[BBD]

Patagon

Bond et al. (2001) doesn't provide an escape hatch for sceptics. The physical properties of CO2 are not modified by reading it.

All it says is that the climate is much more sensitive than Spencer and Lindzen would have us believe, and that TSI drives the 1500yr cycle which now bears Bond's name.

Nobody is saying that recent changes in TSI have been sufficient to account for warming post-1950.

But I knew someone would try to twist the conclusion round to argue this.

[BBD]

Yes - our comments crossed.

Do the sums: 1500-year cycle, last iteration ca 900 - 1200CE. Next iteration starts when?

[Patagon]

"escape hatch" from where?

Totally unrelated to Spencer and Lindzen work which is short term feedbacks and sensitivity of climate system.

Bond et al. themselves show a chart of increasing TSI during the last 100 years: http://tinyurl.com/6jczdb8

What Bond concludes is "then atmospheric dynamics and their link to the ocean’s circula- tion are much more important for interpreting centennial and millennial time scales of climate variability than has been assumed." So a lot of work to do, nothing settled, which is the sceptical position.

[Patagon]

I forgot to add that that chart fits very well with a short readvance of small glaciers in the Alps in the 70's

[Patagon]

"Do the sums: 1500-year cycle, last iteration ca 900 - 1200CE. Next iteration starts when?"

We don't do numerology, we check the causes and very whether the measured effects fits the hypothesis, anyway, the numbers are more like:

"The last drift-ice cycle is broadly correl- ative with the so-called Little Ice Age (LIA) and Medieval Warm Period (MWP) (Fig. 2). Although the regional extent and exact age of those two events are still under debate, our records support previous suggestions that both may have been partly or entirely linked to changes in solar irradiance "

[BBD]

Patagon

Puzzled:

Bond et al. themselves show a chart of increasing TSI during the last 100 years: http://tinyurl.com/6jczdb8

I do not see this figure in Bond et al. (2001).

It looks like an obsolete TSI reconstruction after Hoyt and Schatten (1993), but where did it come from?

Climate sensitivity to changing RF is exactly relevant to both Spencer and Linzen's claims that RF forcing by CO2 will not elevate GAT. RF is RF, be it DSW or DLR.

[BBD]

Patagon

The dates don't match, and you know it.

We don't do numerology, we check the causes and very whether the measured effects fits the hypothesis,

Right. So find me an up-to-date TSI reconstruction for the C20th that shows a sufficient increase to force T as observed 1900 - present.

[Patagon]

It is in the supplementary material, in Sciencemag online.

You are mixing a lot of things that need to be considered carefully.

But let me remind you of my sceptical position: we do not know yet how the climate system works, therefore we are not in a position to do 100 year forecasts. All you references give strength to this position

[Patagon]

"So find me an up-to-date "

find you

sorry mate, do your own homework

[BBD]

Sure

Try this:

www.leif.org/research/TSI%20(Reconstructions).xls

[BBD]

Patagon

You are not in a position to tell me that I'm 'mixing a lot of things that need to be considered carefully'.

Take a good look at the composite TSI reconstructions (a field about which you are clearly not well informed), have a think about transient and equilibrium climate sensitivity (ditto), and consider the likely cause of modern warming in the absence of any apparent increase in TSI.

Have fun.