Dendro audit


In 2002, on the train from Hamburg to Stockholm, I happened to hear a conversation between two German farmers about payoff prices for hogs and the latest TV program they had watched. The program had been about somebody who claimed that 300 years in the early Middle Ages and Charlemagne  never existed.

I had not heard about that before. There had been an article in the daily press about some chronology error in connection with the turn of the millennium, however the topic was never discussed in Sweden. But Internet is fantastic: after one hour's surfing I knew the basics about the people around Heribert Illig and their phantom time hypothesis. Based on lots of indications from written and archaeological sources and architectural considerations they postulate that the time between 614 and 911 was invented for various reasons later in the Middle Ages. In our opinion, a more robust indication for the existence of a phantom time might be their observation, that the Gregorian calendar reform possibly does not account for all the years said to have elapsed since the introduction of the Julian calendar.

But one thing made us concerned: Illig's group definitely rejects all dendrochronological support for the correctness of the Christian era chronology. With that they reject the only existing dating method which can be applied independent of historical prerequisites, and which has a one-year-resolution. Knowing that dendrochronology works well as a method, and having effective tools right at our hands, we thought that it would be a piece of cake to show if there were invented years in our calendar, let say between Roman time and the Renaissance, thus rejecting or confirming the very basis for the phantom time hypothesis.

Soon we learned that there were several long tree-ring chronologies running back from today to prehistoric times and linking to archaeological sequences clearly anchored in Roman times, but all the raw measurement series and in many cases also the mean value (master) curves were unpublished. We also learned that raw measurement series as well as master chronologies were unavailable to us, as our investigation was "meaningless" because our question was "ridiculous".

We started our project anyway with some old published material, and with measurement series we successively got from more open-minded scientists. In 2010 the raw measurement series of the Belfast oak chronology became available after a FOI request conducted by Douglas Keenan. Now we were able to show that one allegedly continuous long tree-ring chronology contained gaps and suspicious links and we then hoped that this would make our question less "ridiculous" and initiate a scientific discussion about the matter. Unfortunately, our results were still not considered worth a discussion, unless we succeeded publishing them in a peer reviewed scientific journal.

Of course, this was not an easy task as we are freelancers and not connected to any scientific institute, and had no experience how to write a "scholarly" article. And it did not either work out, it took three trials and more than two years to get everything rejected and finally give up this strategy. However, while the second peer review still was running, we found a truly continuous long master curve and succeeded to date our internally consistent Roman time sequences against it. This exercise showed that Roman time as a whole most probably is dated more than 200 years too old conventionally, meaning that there are indeed invented years in the Christian era in late antiquity and that there are major errors in virtually all European long oak chronologies.

It should not be a real problem for a discipline with scientific ambitions in the year of the Lord 2015 to discuss such a matter (ref.6). However, if the so far dismissing attitude of the scientific community is due to a total misinterpretation from our side, why not show us alternative proof so that we can close the case? Anyway, we are finished with our dendro-investigation and have consistent results which can and should be scrutinized in some way.

You find our manuscripts and the comments of the referees with some own replies here. We choose to make the result of the peer reviews public because there is no other way for us to present any objections against the referees' judgement after reject.

Why does it matter?

If we are right that the synchronization of our calendar towards the Roman calendar is wrong, most historical dates in antiquity would be nominally wrong as well. This does of course not automatically mean that classic history is wrong internally. However, there will be some problems with "phantom time history" written to connect the floating Roman history with Medieval history, e.g. Roman lists of consuls and emperors, and the list of popes. There will be some turbulence within archaeology of that time as well. But does that matter for us living more than thousand years later? Not really, though some historians and archaeologists with antiquity as specialty will cry out to Heaven. On the other hand, once things have been rearranged on the time line, we believe that the historical model will be better than before.

What really matters are the scientific implications. About thirty years ago, dendrochronology was used to "prove" the length of the Christian era. Since then there has been an uncompromising consensus about this question, a fundamental dogma. This was a given because the new long tree-ring chronologies were immediately used to calibrate other dating methods such as radiocarbon dating (ref.1). And as Roman history was regarded as "confirmed", its dates could be used to calibrate e.g. the chemical volcano markers in the ice cores of the northern hemisphere (refs.2, 5).

Here are the real problems, and they indeed matter for us living today, because now scientists use possibly corrupt dendro-data to make statements about past climate and its significance for good times or bad times (e.g. ref.3). Scientists also speculate about natural catastrophes which struck in the past and which are likely to strike again, but there is risk that they miss any reported evidence because of possible disorder on the historical time line (e.g. ref.4).

This is why we are passionate about this case.


Update 2015-08-02

There is hope.

A recent paper (ref.7) by a large interdisciplinary consortium of scientists headed by Michael Sigl puts an end to the fatal calibration of the Greenland ice core time line with a volcanic marker suggested to be the RomAD 79 Vesuvius eruption. With a new approach to use worldwide observed precise time markers generated by cosmic abrupt enrichment events (14C in tree-rings and 10Be in ice cores), it became obvious that there indeed was a chronological offset by a few years between tree-ring chronologies and ice core chronologies in the first millennium AD. After correction, the "79" volcanic marker is now dated 88 and attributed to a volcanic source from the high latitudes. This means also that there is no volcanic marker dated 79, which is not miraculous if we consider the possibility that the Vesuvius eruption which killed Plinius took place much later, among other theories.

The new approach, to striktly consider only measured data and never historical presumptions, is almost consequently applied throughout the whole article. However, for the time before 536 the observed volcanic markers are compared with "Historical documentary evidence of volcanic dust veils" from Babylonian, Chinese and Mediterranean sources. Fortunately no definitive assignments are made, not even to the prominent dust veil event BC 44 to 42 which former was connected with an Etna eruption in the year Julius Caesar was murdered. The authors suggest a tropical eruption as the cause.

In the WSL announcement of the article (ref.8) however, the connection with Julius Caesar appears again. This is unfortunate because no significant dendrochronological proof for the conventional dating of the oak series which are archaeologically anchored in West-Roman time (up to ca. RomAD 400) has been presented yet.

To accentuate it once again: no European oak chronology has ever been published which can demonstrate a significant bridge between early Medieval time and Roman time. On the contrary, our investigations point at a dendrochronological misdating of Roman time oak series by 218 years. Until this problem is properly attended to, scientists should preferably avoid the synchronization of measured natural markers with Roman (and Greek) historical events, and also the use of oak data belonging to the Roman complex. Fortunately, no oak data has been used for the new article.

Mostly though, the article deals with events on the "safe side" of the Roman gap, i.e. after the fifth century. Especially enjoyable is the analysis of the well-known global climate anomalies in 536 to 550, where the authors pinpoint multiple volcanic eruptions as the elicitor of extraordinary prolonged northern hemisphere cooling which led to severe socio-economic consequences. Read more here.


1. Radiocarbon (1986), Vol.28, No.2A/B. read here
2. Vinther B.M.,Clausen H.B.,JohnsenS.J.,Rasmussen S.O.,Andersen K.K.,Buchardt S.L.,Dahl-Jensen D.,Seierstad I.K.,Siggaard-Andersen M.-L.,Steffensen J.P.,Svensson A.,Olsen J. & Heinemeier J. 2006. A synchronized dating of three Greenland ice cores throughout the Holocene. Journal of Geophysical Research, vol 111, D13102.
3. Büntgen U., Tegel W., Nicolussi K., McCormick M., Frank D., Trouet V., Kaplan J.O., Herzig F., Heussner K.U., Wanner H., Luterbacher J., Esper J. 2500 Years of European Climate Variability and Human Susceptibility, Science Express, 13 January 2011. read here
4. Helama, S., Holopainen, J., Macias-Fauria, M., Timonen, M. & Mielikäinen, K. (2013). A chronology of climatic downturns through the mid- and late- Holocene: tracing the distant effects of explosive eruptions from palaeoclimatic and historical evidence in northern Europe. Polar Research 32, 15866. read here
5. Barbante, C., Kehrwald, N. M., Marianelli, P., Vinther, B. M., Steffensen, J.P., Cozzi, G., Hammer, C.U., H. B., Clausen, H.B. and Siggaard-Andersen, L.
2012. Greenland ice core evidence of the 79 AD Vesuvius eruption. Clim. Past Discuss. 8, 2012, 5429–5454. read here
6. Eckstein D. and Cherubini P. 2012. The “dendrochronological community” at Rovaniemi, Finland, 2010: Lessons learned from the past and perspectives for the future. Dendrochronologia, Volume 30, Issue 2, Pages 195-197. read here
7. M. Sigl, M. Winstrup, J. R. McConnell, K. C. Welten, G. Plunkett, F. Ludlow, U. Büntgen, M. Caffee, N. Chellman, D. Dahl-Jensen, H. Fischer, S. Kipfstuhl, C. Kostick, O. J. Maselli, F. Mekhaldi, R. Mulvaney, R. Muscheler, D. R. Pasteris, J. R. Pilcher, M. Salzer, S. Schüpbach, J. P. Steffensen, B. M. Vinther & T. E. Woodruff 2015. Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523, 543–549. doi:10.1038/nature14565. read here and here
8. WSL News and Media, Volcanic eruptions that shook the world, 8 July 2015. read here