CCNet

Editor: Benny Peiser

Faculty of Science, Liverpool John Moores University Tel:- +44 (0)151 231 4338 b.j.peiser@ljmu.ac.uk

THE AD 536-540 MYSTERY:

GLOBAL CATASTROPHE, REGIONAL EVENT OR MODERN MYTH?

There remain serious problems with the statistics and interpretation of proxy-data that are casting new doubt on the nature, magnitude and chronology of the 6th century mystery cloud. More importantly, it is worth remembering that the written documents from the 6th century seem to contradict sharply with the notion of what has been called the "worst climatic disaster in recorded history."
--Benny Peiser, 24 March 2008

It has been acclaimed as the worst climatic disaster in recorded history. In the most wide-ranging scenarios, the year 536 is seen as a watershed moment between the ancient and modern worlds, bringing about economic decline, population movements, political unrest, and ultimately the collapse of civilizations. I have gone through all the available physical and written evidence for the 536 event. The inevitable conclusion from the ancient literary sources is that the historical impact of the cloud must have been extremely limited.
--Antti Arjava, CCNet, 21 November 2006

The situation does not change much if we accept the evidence from tree rings (not confirmed by any literary source), that the coldest years occurred actually around 540. Nevertheless, it is still possible to state the results of this inquiry with relative certainty. Not only is there nothing in our evidence to suggest that the year 536 was a watershed moment between antiquity and the Middle Ages, a conclusion that must have appeared obvious from the very beginning, but it is also evident that, although the cloud occasioned confusion and crop failure at the time of its appearance, its effects did not last long after it had dissipated. The literary sources that record the darkness of 536/37 all seem to consider it a temporary misfortune. Among the innumerable earthquakes, droughts, plagues, swarms of locusts, and slaughters that are listed by the historians of this time, the dark cloud was not considered a particularly severe catastrophe.
--Antti Arjava: The Mystery Cloud of 536 CE in the Mediterranean Sources, Dumbarton Oaks Papers 59 (2005)

AD 536 EVENT LINKED TO VOLCANIC ERUPTION

National Geographic News, 19 March 2008

NEW ICE CORE EVIDENCE FOR A VOLCANIC CAUSE OF THE A.D. 536 DUST VEIL

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, 29 February 2008

536 AD AND ALL THAT

RealClimate, 2 March 2008

GREENLAND ICE CORE EVIDENCE FOR VOLCANIC ERUPTION ~530 AD

Environmental Catastrophes and Recoveries in the Holocene, September 2002

REASSESSING THE MYSTERY CLOUD OF AD 536

Antti Arjava, Department of Classics, University of Helsinki, CCNet, 21 November 2006

ASTRONOMERS SUGGEST COMET TO BLAME FOR 6TH CENTURY "NUCLEAR WINTER"

Derek Ward-Thompson, Cardiff University

SCIENTISTS: COMET CAUSED DARK AGE FROSTS

The Washington Time, 3 February 2004

COLLISION WITH COMET MAY HAVE HASTENED FIRST PLAGUE EPIDEMIC

The Independent, 4 February 2004

SUPER-VOLCANO MAY HAVE TRIGGERED GLOBAL COOLING IN 536 AD

Los Alamos National Laboratory, 17 December 2000

SUPER-DROUGHT MAY HAVE SET OFF EUROPEAN DARK AGES

University of California, Berkeley, 9 December 1998

ICE CORE EVIDENCE FOR VOLCANIC ERUPTION ~530 AD

Lars Berg Larsen, Department of Geophysics, University of Copenhagen

JUMBLING OLD EVENTS WITH MODERN MYTHS

British Archaeology, November 1999

A COMET IMPACT IN AD 536?

Emma Rigby, Melissa Symonds and Derek Ward-Thompson, Astronomy & Geophysics, Volume 45 Issue 1, February 2004

PLAGUE OUTBREAK BLAMED ON COMET STRIKE

The New Zealand Herald, 5 February 2004

KILLER COMET: 'TINY' SPACE ROCK ALERT

Daily Record, 5 February 2004

RE: DID A COMET IMPACT TRIGGER A "NUCLEAR WINTER" IN 536 AD?

Mark Kidger <mrk@iac.es>

SUPER-VOLCANO, SUPER-COMET, SUPER-DROUGHT AND SUPER-NOVA

James A. Marusek <tunga@custom.net>

RE: COMET IMPACT AND DARK AGES

HASTRO-L@LISTSERV.WVU.EDU

COMET IMPACT IN 536 AD?

Michael Paine <mpaine@tpg.com.au>

COMET IMPACT IN 536 AD?

Mark Kidger <mrk@iac.es>

THE 540 AD EVENT

Joel Keene <JJPerf@aol.com>

COMET IMPACT IN 536 AD? THE DEBATE GOES ON

Michael Paine <mpaine@tpg.com.au>

DAVID KEYS' 536 AD VOLCANIC MEGA-ERUPTION THEORY

George Taylor <taylorgh@comcast.net>

COMET IMPACT OR VOLCANIC ERUPTION: WHAT HAPPENED IN AD 536-540?

Benny Peiser <b.j.peiser@livjm.ac.uk>

REPLY TO AD 540 RAMBLINGS

Mike Baillie <M.Baillie@Queens-Belfast.AC.UK>

RE: DID A COMET AIRBURST TRIGGER GLOBAL COOLING IN 536 AD?

Max Wallis <wallismk@Cardiff.ac.uk>

NUCLEAR WINTER OF THE VI CENTURY

Pravda, 14 February 2004

DAVID KEYS: EVIDENCE FOR THE VOLCANIC ORIGIN OF THE AD 535/36 DUST-VEIL EVENT

WERE THE DARK AGES TRIGGERED BY VOLCANO-RELATED CLIMATE CHANGE IN THE 6TH CENTURY? IF SO, WAS KRALATAU THE CULPRIT?

Ken Wohletz, Los Alamos National Laboratory

NEW ICE CORE EVIDENCE FOR AD 536 EVENT RULE OUT IMPACT

Michael Robert Rampino mrr1@nyu.edu

SIXTH CENTURY DARK AGES? WHAT DARK AGES?

Gunnar Heinsohn gheins@uni-bremen.de

VELA SUPERNOVA AND THE LITTLE ICE AGE

James A. Marusek tunga@custom.net

SOUTHERN OCEAN IMPACT AND THE DARK AGES

Nick Sault nick@e-writers.org

CCNet 42/2008 - 24 March 2008 -- Audiatur et altera pars

NEW DOUBTS ABOUT "THE WORST CLIMATIC DISASTER IN RECORDED HISTORY"

An enormous volcanic eruption in the sixth century seems to have triggered catastrophic global cooling, perhaps precipitating famine, cultural conflict and plague across the planet.
--Philip Ball, Nature, 11 March 2008

A "dry fog" that muted the sun's rays in A.D. 536 and plunged half the world into a famine-inducing chill was triggered by the eruption of a supervolcano, a new study says.
--Ker Than, National Geographic News, 19 March 2008

1500 years ago something extreme happened to the world's climate - something that must have terrified those who witnessed it. The sun began to go dark. Rain poured red, as if tinted by blood. Clouds of dust enveloped the earth. Cold gripped the land for two years. Then came Drought, Famine, Plague, Death. Whole cities were wiped out - civilisations crumbled. There is evidence of a catastrophe - a catastrophe whose consequences affected the entire world-and may have changed the course of human history. The mid 6th century catastrophe was the most important date in the history of the past two thousand years. It really did lay the foundations of the world we live in today.
--PBS Documentary "Catastrophe"

========
AD 536 EVENT LINKED TO VOLCANIC ERUPTION

National Geographic News, 19 March 2008
http://news.nationalgeographic.com/news/pf/57518873.html

Ker Than

A "dry fog" that muted the sun's rays in A.D. 536 and plunged half the world into a famine-inducing chill was triggered by the eruption of a supervolcano, a new study says.

The cause of the sixth-century global dimming has long been a matter of debate, but a team of international researchers recently discovered acidic sulphate molecules, which are signs of an eruption, in Greenland ice.

This is the first physical evidence for the A.D. 536 event, which according to ancient texts from Mesoamerica, Europe, and Asia brought on a cold darkness that withered crops, sparked wars, and helped spread pestilence.

Scientists had suspected the dry fog was caused by a volcanic eruption or a comet strike, but searches had failed to uncover evidence for either catastrophe—until now.

"There is no need at the moment to invoke a large-scale extraterrestrial event as the cause, because the evidence is conclusive enough to say that it is certainly consistent with it being a large volcano," said study team member Keith Briffa of the University of East Anglia in the United Kingdom.

The discovery is detailed in a recent issue of the journal Geophysical Research Letters.

Global Ashfall

Tests show the Greenland sulphate molecules were deposited sometime between A.D. 533 and 536. This date correlates well with a sulphate peak found in an Antarctic ice core.

The team suspects the eruption occurred near the Equator, since its ash fell on both ends of the globe.

The Greenland evidence is also consistent with tree-ring data from around the Northern Hemisphere that show reduced growth rates lasting more than a decade starting in A.D. 536.

Curiously, the eruption's cooling effect did not extend to the southern hemisphere, the scientists say.

Together, the tree-ring and acid evidence suggest the sixth-century eruption was even bigger than Indonesia's Mount Tambora eruption of 1815, which also dimmed the sun.

Not Definitive

Ken Wohletz, a volcanologist at Los Alamos National Laboratory in New Mexico, said that while the new evidence strongly supports a large volcanic eruption, a space impact can't be ruled out yet.

"Over two-thirds of Earth's surface is covered with water, and because erosion so quickly wipes away evidence of impacts, the knowledge of when large-scale impacts have occurred in the past is still very incomplete," said Wohletz, who was not involved in the study.

To cement their case, volcano advocates will need to find ash layers deposited by the blast, Wohletz said.

William Ryan, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory in New York, believes it is only a matter of time until ash layers are found.

"I suspect we haven't searched adequately, but this paper will start a hunt," Ryan said.

Indelible Mark

According to written records, the dry fog lingered for just over a year—leaving an indelible mark on human history.

Chinese historians recorded famine events and summer frosts for years after the event.

It was also around this time that a band of Mongolian nomads called the Avars migrated westward toward Europe, where they would eventually establish an empire.

The group may have left home when grasslands that their horses grazed on withered under the darkened skies, historians say.

More controversially, some historians claim that drought caused by the fog contributed to the decline of the Mesoamerican city of Teotihuacan.

The spread of bubonic plague throughout Europe and the Middle East, the rise of Islam, and even the fall of the Roman Empire have also been controversially tied to the event.

Still Vulnerable

If a similar volcanic eruption were to occur today, the effects could be just as devastating, experts say.

The reduced sunlight and ashfall would affect agriculture worldwide, and the thick veil of dust and ash could cripple transportation and communication systems.

"Most aircraft cannot fly in [volcanic] dust clouds," Los Alamos's Wohletz said.

"And these dust clouds have a large electrostatic potential that disrupts radio communication."

To make matters worse, there is practically nothing humans can do to prevent such a catastrophe from happening again—or to lessen its effect.

"In today's society, we're no less independent of nature than humankind has ever been," Wohletz said.

"In fact, we might even be more dependent on it."

© 1996-2008 National Geographic Society. All rights reserved.

EDITOR'S NOTE: It would appear that the 6th century "mystery cloud" has just become more mysterious still. We now appear to have evidence for two acidity peaks in various ice cores: a strong acidity peak at around AD 529 and a weaker signal around AD 533/534. These sets of ice-core evidence look conspicuous and do not seem to match 6th century tree-ring data. Dendrochronological records do not show any evidence of a significant volcanic event at AD 529. And according to tree-ring data, the coldest year of the 6th century was in AD 540, 5 years after the alleged volcanic eruption. Thus, there remain serious problems with the statistics and interpretation of proxy-data that are casting new doubt on the nature, magnitude and chronology of the 6th century mystery cloud. More importantly, it is worth remembering that the written documents from the 6th century seem to contradict sharply with the notion of what has been called the "worst climatic disaster in recorded history." BJP

===========
NEW ICE CORE EVIDENCE FOR A VOLCANIC CAUSE OF THE A.D. 536 DUST VEIL

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, 29 February 2008
http://www.agu.org/pubs/crossref/2008/2007GL032450.shtml

New ice core evidence for a volcanic cause of the A.D. 536 dust veil

L. B. Larsen, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

B. M. Vinther, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U. K.

K. R. Briffa, Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U. K.

T. M. Melvin, Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U. K.

H. B. Clausen, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

P. D. Jones, Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U. K.

M.-L. Siggaard-Andersen, Earth and Planetary Physics, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

C. U. Hammer, Earth and Planetary Physics, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

M. Eronen, Department of Geology, University of Helsinki, Helsinki, Finland

H. Grudd, Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden

B. E. Gunnarson, Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden

R. M. Hantemirov, Laboratory of Dendrochronology, Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia

M. M. Naurzbaev, Dendroecology Department, Sukachev Institute of Forest, Siberian Branch of Russian Academy of Sciences, Krasnoyarsk, Russia
Siberian Federal University, Krasnoyarsk, Russia

K. Nicolussi, Institute of Geography, University of Innsbruck, Innsbruck, Austria

Abstract
New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree-ring data to have occurred in A.D. 536. Tree-ring data suggest that this was the most severe and protracted short-term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

==========
536 AD AND ALL THAT

RealClimate, 2 March 2008
http://www.realclimate.org/index.php/archives/2008/03/536-ad-and-all-that/

Gavin Schmid

"during this year a most dread portent took place. For the sun gave forth its light without brightness… and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear."

This quote from Procopius of Caesarea is matched by other sources from around the world pointing to something - often described as a 'dry fog' - and accompanied by a cold summer, crop failures and a host of other problems. There's been a TV special, books and much newsprint speculating on its cause - volcanoes, comets and other catastrophes have been suggested. But this week there comes a new paper in GRL (Larsen et al, 2008) which may provide a definitive answer….

It's long been known that tree-rings (such as the one pictured from Arizona) often show an extremely small growth ring for AD 536 (you can count back from the marked AD 550 ring). In fact, if you look at the mean anomaly in a whole range of tree ring constructions, this event stands out along with 1601 and 1815 (known volcanic events) as being exceptional over the last 2000 years.

Average of the high-frequency components of 7 northern European tree ring reconstructions from Larsen et al, 2008. The filtering ensures that uncertainties in long term trends (which are not important in this context) don't confuse the issue

These data match the written sources quite well. However, tying it to a cause has always been plagued with problems of chronology. An initial attempt to tie this event to a volcanic pulse in the Dye3 ice core in Greenland foundered when the chronology was revised to put it 20 years earlier. However, there has recently been a concerted effort to place all the Greenland ice cores on a common timescale based on annual layer counts (Vintner et al, 2006). Because all the cores are being counted together, ambiguities in one can be corrected by reference to the others. Once the dates have been better established, the sulphate records (which generally show the impact of volcanic aerosols) can be examined to see if they line up. And low and behold, they do:

The second peak in the picture is dated at 534 AD which is close enough to 536 AD given the one or two year uncertainty in counting. Note that the 534 AD peak is actually smaller than the one a few years earlier. In assessing the importance of an eruption though, it isn't enough to have just a peak in Greenland. That could simply signify an eruption that was close by. Instead, people look for a matching peak in Antarctica. This signifies that the eruption was likely tropical and the aerosols were carried into both hemispheres by the stratospheric circulation. Here is where previous attempts often faltered. The dating of ice cores in Antarctica is less exact than in Greenland because the accumulation is slower (it doesn't snow as much). However, the relatively new Dronning Maud Land (DML) core has comparable resolution to the Greenland ones, and this one does have a clear sulphate peak at about 542 +/- 17 years. That is good enough to be a match to the 536 AD peak in Greenland. The correction you'd need to make to align them exactly would also fix some other apparent offsets for smaller events in the subsequent 100 years.

So it probably was a volcano, somewhere in the tropics, and it was likely the size of Tambora in 1815. There has been some speculation that it was an earlier eruption of Krakatoa (which went off again in 1883), but that is uncertain, as are the numerous consequences such as the fall of the Rome or the rise of Islam which have been attributed to this event. While not exploring that too deeply, this quote from Michael the Syrian indicates dramatically the potential for climate events like this one to really spoil your day:

"The sun was dark and its darkness lasted for eighteen months; each day it shone for about four hours; and still this light was only a feeble shadow … the fruits did not ripen and the wine tasted like sour grapes."

========
GREENLAND ICE CORE EVIDENCE FOR VOLCANIC ERUPTION ~530 AD

Environmental Catastrophes and Recoveries in the Holocene, September 2002
http://atlas-conferences.com/c/a/i/q/21.htm

Lars Berg Larsen, Department of Geophysics, University of Copenhagen

Coauthors: Marie-Louise Siggaard-Andersen (Alfred-Wegener-Institute for Polar and Marine Research,Bremerhaven) and Henrik B. Clausen (Department of Geophysics, NBIfAFG, University of Copenhagen)

In the beginning of the sixth century, early medieval historical data indicate some events, which is believed to be the aftermath of some sort of global climatic catastrophe. The three-ring and ice core data obtained around the world show a temperature anomaly around this period. In the ice cores drilled in Greenland at the sites NGRIP, GRIP, DYE-3 and the Antarctica sitesBYRD and DOME C we investigated special events and other anomalies in the chemistry, isotope end ECM data. In the ECM record we have the third largest signal found in the ECM record the last to thousand years. A detailed chemical analysis of the ice covering the period was made. From the chemical record we identify a volcanic eruption and we estimate the magnitude of the eruption and a possible location. With the chemistry and the isotope data it is possible to do a very precise dating for the eruption. The volcanic eruption is dated to AD. 527 +/- 1 year. The AD 527 volcanic eruption is the only eruption in the period and the only likely candidate to cause some of the calamities described in the historical data. The dating of this volcanic eruption suggest that the event is not the same one described by other sources.

========
REASSESSING THE MYSTERY CLOUD OF AD 536

CCNet, 21 November 2006
http://www.staff.livjm.ac.uk/spsbpeis/Antti-Arjava.htm

Antti Arjava, Department of Classics, University of Helsinki [antti.arjava@skr.fi]

In 1983 Richard Stothers and Michael Rampino of NASA published a list of all ancient volcanic eruptions known from Mediterranean historical sources. Their list included a persistent dust veil or dry fog which darkened the sky for about a year in AD 536--37, bringing about cold, drought and food shortage in the Mediterranean area or, as it has since been claimed, all over the northern hemisphere. Especially following two popular books devoted to the dust veil by David Keys and Mike Baillie, it has been acclaimed as the worst climatic disaster in recorded history. In the most wide-ranging scenarios, the year 536 is seen as a watershed moment between the ancient and modern worlds, bringing about economic decline, population movements, political unrest, and ultimately the collapse of civilizations.

In a lengthy article written in 2004 and just to be published in the Byzantinist journal Dumbarton Oaks Papers' 2005 issue *), I have gone through all the available physical and written evidence for the 536 event. The inevitable conclusion from the ancient literary sources is that the historical impact of the cloud must have been extremely limited. On the other hand, some assumptions about the cloud's physical nature that have hitherto been taken for granted should be re-examined. In the following, I give a brief summary of my paper.

Physical evidence for the 536 event is derived from two main sources: tree rings and acid layers in Greenland ice. The tree rings show 536 and the following ten years as a period of very slow growth for Scandinavian pines, North European oaks and several North American species. However, the contours of a sudden catastrophe cannot be directly read from the tree ring evidence. In many series, the drop in 536 is followed by a recovery in 537--38 and then again by an even more serious plunge. In most cases, the worst years are around 540, and in Siberia 543. In southern Chile, the trough is in 540, while in Argentina there was dramatic growth reduction only after 540, with a minimum in 548. In Tasmania, the tree growth declined between 546 and 552.

Thus, although the year 536 was certainly a very bad growing season in many parts of the world, it is situated in a decade-long downturn in the climate of the Northern Hemisphere and is separated from the really worst seasons by 3--7 years. Moreover, and perhaps even more seriously, in the Scandinavian pines as in the oaks and North American trees, it is possible to see a long-term growth decline during the early part of the sixth century which is matched by an equally slow rise in the average growth during the second half of the century. This would place the years around 540 as the lowest point in a slow climatic cycle. While it does not disprove a climatic anomaly in 536, all this nevertheless suggests that the link between the dark cloud and tree growth is not as straightforward as might be wished. The dendrochronological maxim "trees do not lie" may be true, but neither do they seem to provide unequivocal answers to the questions which historians would like to pose to them.

Historical eruptions are usually attested as acid layers in Greenland ice. In the previously published studies, all the relevant sections of the Greenland ice cores for the mid-sixth century have been either missing, flawed or poorly dated. Recently, Danish scholars have reported that a major eruption can be dated to the early spring of 528. It is unclear whether it might be possible to redate the whole sequence of ice layers by a few years, matching the new attested eruption with the 536 event. Any conclusions therefore must remain tentative, but so far we have to admit that no acid layer sufficient for a major volcanic eruption has been confirmed around 536. That is why the cloud has been attributed to the impact of a comet. This hypothesis is not confirmed by any direct evidence either.

Archaeological evidence does not help us assess the consequences of possible crop failures around 536. Recent archaeological work serves to stress the need for a regional approach: economic and demographic developments may differ in neighboring regions. The whole western part of the Roman empire was in clear decline already in the fifth century. The Persian devastations in northern Syria, combined with recurrent earthquakes and epidemics, would probably suffice to explain any sixth-century economic decline in the Byzantine Near East.

The results of my inquiry into the written sources are relatively straightforward: although the cloud occasioned confusion and crop failure at the time it was seen, its effects did not last long after it had dissipated. Compared with almost all other contemporary civilizations around the world, the circumstances in the Mediterranean area are extremely well documented. The literary sources which record the darkness of 536/7 all seem to consider it a temporary misfortune. Among the innumerable earthquakes, droughts, plagues, swarms of locusts, and slaughters which are listed by the historians of this time, the dark cloud was not counted as a particular catastrophe. Shortage of food was a recurrent phenomenon in the ancient world, and people were used to it, however intense the short-term suffering might be.

For example, two Italian sources, Cassiodorus and the Liber Pontificalis, attest continuing problems with the harvest in 537, which is not surprising if the fog persisted until the summer. Immediate effects of the event are not reported after that. The historian Procopius for his part does not mention the crop failures of 536/7. He says that outside besieged Rome the Goths were also starving, but he rather seems to give the credit for it to a successful Byzantine naval blockade. In contrast, the historian describes at great length a terrible famine in Italy in 539. However, he is quite explicit that it was due to the fields being left uncultivated because of the war. A little later he returns to the subject of food shortage among the Goths, again insinuating that the lack of supplies was a logistic problem. He does not give a hint that climatic conditions might have been blamed for continual bad harvests.

Though these sources leave no doubt that a mysterious fog was seen in an area which extended at least from Italy to Asia Minor and caused bad harvests there for one or two years, they all seem to treat it as a temporary bad omen, not as the beginning of a long period of unfavorable climatic conditions. Of course, the writers might not have noted a slight drop in average temperatures, and might perhaps not have cared to record a change in prevailing winds or precipitation. However, if the direct consequences of such underlying factors for agriculture had been grave enough to undermine the economic well-being of the empire, we would expect somewhat more attention being paid to them by contemporary writers.

Thus, the combined force of the available evidence irresistibly shows that, whatever happened around 536, its historical implications remained very limited, at least in the Mediterranean area. On the other hand, the sources report interesting, though sometimes conflicting, details of the fog. Although the haze has been called a dry fog or dust veil ever since 1984, a passage from the eyewitness antiquarian writer John Lydus which has hitherto been neglected rather suggests that the fog was damp. This is not decisive because it can reasonably be claimed that Lydus may not have been able to observe its actual composition. However, he also asserts that the fog was seen only in Europe, and it is more difficult to discredit this report out of hand. It would be in clear contrast to the common scholarly assumption that the cloud was a global or at least a hemispherical phenomenon. Remarkably, all the other literary sources mention the fog only for an area around Italy and Asia Minor.

Cold and drought are attested in other parts of the world but not the persistent fog. Chinese sources record that the star Canopus was not seen at the spring and fall equinoxes in 536. Although this might be taken to refer to reduced atmospheric transparency (as many scholars have assumed), it seems a rather understated way to describe a darkness which continued for a year. It is especially odd if it was the factor which caused summer frosts, drought and widespread famine, duly recorded in Chinese historical works between 535 (sic) and 538. At least two possibilities emerge: either the Chinese did not mention the fog because opaque skies are not unusual in northern China due to the frequent desert storms there, or the fog was tropospheric and localized in the Mediterranean area. While zonal winds would have spread a stratospheric fog over the northern latitudes within a few weeks or months, a tropospheric fog (volcanic or not) might very well have attenuated before reaching China. The problem remains that no tropospheric fog of such duration has been observed in historical times.

However, if we accept the possibility that the fog may have been seen in northern China though it was not clearly recorded, it might also be possible to explain Lydus' account in a different way. All those areas for which the fog is securely attested (Italy, Constantinople) lie above 35 degrees of northern latitude, perhaps even above 40 degrees, depending on how we interpret Procopius' report. The same is true of northern Mesopotamia (ca. 37° N). In contrast, those areas further east which Lydus claims did not witness the fog (Persia, India) all lie below 40 or even 35 degrees northern latitude, and this also applies to most of China. Thus, we might actually have a cloud which could be seen only at latitudes north of the Mediterranean and in the very north of China. Such a rather abrupt and globally uniform cutoff latitude falling between 30 and 40 degrees has been observed for stratospheric aerosol veils stemming from large eruptions of northern volcanoes, notably Lakagigar (Iceland, 1783), Ksudach (Kamchatka, 1907) and Katmai (Alaska, 1912). For example, the dust cloud from Katmai was seen and measured at Bassour, Algeria (36° N), at Simla, India (31° N) and at two US observatories (34-36° N), but not at Helwan, Egypt (30° N).

If we interpret Lydus' text in this manner, disregarding his report of the moist fog and assuming that the missing or misdated acid layers in the ice cores can be explained somehow, it would add a new dimension to the volcano hypothesis. It would actually support the suggestion made by Richard Stothers that the mystery cloud derived from a far northern volcano, and not from a tropical one like Rabaul (New Guinea), Krakatau (Indonesia) or El Chichón (Mexico), which have been earlier suspects. The observed decline of tree growth in South America in the 540s might seem to be at odds with this. However, it has not yet been established whether a high-latitude eruption could have global climatic effects. The issue is currently debated.

We cannot check the scientific accuracy of Lydus' reports. They may mislead us, but at the very least they invite us to re-examine the scientific evidence for the event. It remains true that the Greenland ice cores have so far produced little proof of volcanic activity around 536, and that the tree rings are surprisingly ambiguous about climatic variation in different parts of the world between 535--552. Two main alternatives emerge. The dark cloud may have originated from a northern volcano, being visible only at latitudes north of the Mediterranean, or the fog may have been locally more restricted, perhaps damp, originating from a totally unknown source. As a tropospheric fog of such duration would be quite exceptional, the first alternative perhaps seems at present more likely. Further ice cores may prove or disprove it in the future. However, for those who are as of yet not convinced by the volcano hypothesis, the second alternative might appear worth serious consideration.

*) Antti Arjava: The Mystery Cloud of 536 CE in the Mediterranean Sources, Dumbarton Oaks Papers 59 (2005), forthcoming in Dec. 2006.

========
AND FINALLY: JUMBLING OLD EVENTS WITH MODERN MYTHS

British Archaeology, November 1999
http://www.britarch.ac.uk/ba/ba49/ba49book.html

by Ken Dark

CATASTROPHE
David Keys
Century, £16.99
ISBN 1-7126-8069-1 hb

Did a huge volcanic eruption in the early 6th century AD cause profound global political, economic, cultural and religious changes? David Keys, a well-known journalist specializing in archaeological news, argues that it did. Drawing extensively on the work of archaeologists, historians, and scholars in other fields, as he makes clear, Keys suggests that an eruption led to a global environmental `catastrophe'. This, he proposes, brought ruin to the Roman Empire, the Avar kingdom in Central Asia and to Teotihuacan in Mesoamerica, and led to the formation of later England, France, China and Japan.

It is a bold thesis, and one which touches on current fears about environmental problems as a global threat. Moreover, while aspects of the argument are not entirely new (for example, the 6th century environmental crisis is credited to Mike Baillie's work), at first sight Keys offers a lot of supporting evidence for his broader interpretation. However, much of the apparent evidence presented in the book is highly debatable, based on poor sources or simply incorrect.

The chapters on Britain illustrate the limitations of the book as a whole. Sites (such as Mothecombe) are mislocated and archaeological evidence (as at Dinas Emrys) misquoted in detail. Unfounded assertions about population (as at Killibury) and desertion (as at Chun) abound.

Important sites which might cause problems for the argument (for example, Dinas Powys) are absent altogether. As for textual evidence, pseudo-historical and historical material is intermingled, and few specialists will accept that late medieval `Arthurian' literature contains any reliable information about the 6th century, the topic of a whole chapter of this book.

Nonetheless, both the global scope and the emphasis on the 6th century AD as a time of wide-ranging change are commendable, and the book contains some fascinating and obscure information which will be new to many. However, it fails to demonstrate its central thesis and does not offer a convincing explanation for the many changes discussed.

Dr Ken Dark is an early medieval specialist at the University of Reading

----------------
CCNet 17/2004 - 4 February 2004

DID A COMET IMPACT TRIGGER A "NUCLEAR WINTER" IN 536 AD?

ASTRONOMERS SUGGEST COMET TO BLAME FOR 6TH CENTURY "NUCLEAR WINTER"

Ron Baalke <baalke@zagami.jpl.nasa.gov>

Contact: Dr Derek Ward-Thompson

derek.ward-thompson@astro.cf.ac.uk

029-2087-5314

Cardiff University

February 3, 2004

Astronomers unravel a mystery of the Dark Ages

Undergraduates' work blames comet for 6th-century "nuclear winter"

Scientists at Cardiff University, UK, believe they have discovered the cause of crop failures and summer frosts some 1,500 years ago - a comet colliding with Earth.

The team has been studying evidence from tree rings, which suggests that the Earth underwent a series of very cold summers around 536-540 AD, indicating an effect rather like a nuclear winter.

The scientists in the School of Physics and Astronomy believe this was caused by a comet hitting the earth and exploding in the upper atmosphere. The debris from this giant explosion was such that it enveloped the earth in soot and ash, blocking out the sunlight and causing the very cold weather.

This effect is known as a plume and is similar to that which was seen when comet Shoemaker-Levy-9 hit Jupiter in 1995.

Historical references from this period - known as the Dark Ages – are sparse, but what records there are, tell of crop failures and summer frosts.

The work was carried out by two Cardiff undergraduate students, Emma Rigby and Mel Symonds, as part of their student project work under the supervision of Dr Derek Ward-Thompson.

Their findings are reported in the February issue of Astronomy and Geophysics, the in-house magazine of the Royal Astronomical Society.

The surprising result of the new work is just how small a comet is needed to cause such dramatic effects. The scientists calculate that a comet not much more than half a kilometre across could cause a global nuclear winter effect. This is significantly smaller than was previously thought.

Dr. Ward-Thompson said: "One of the exciting aspects of this work is that we have re-classified the size of comet that represents a global threat. This work shows that even a comet of only half a kilometre in size could have global consequences. Previously nothing less than a kilometre across was counted as a global threat. If such an event happened again today, then once again a large fraction of the earth's population could face starvation."

The comet impact caused crop failures and wide-spread starvation among the sixth century population. The timing coincides with the Justinian Plague, widely believed to be the first appearance of the Black Death in Europe. It is possible that the plague was so rampant and took hold so quickly because the population was already weakened by starvation.

================

SCIENTISTS: COMET CAUSED DARK AGE FROSTS

The Washington Time, 3 February 2004

http://www.washtimes.com/upi-breaking/20040203-033138-9377r.htm

CARDIFF, Wales, Feb. 3 (UPI) -- Scientists at Cardiff University in Wales say a "nuclear winter" that caused summer frosts in the sixth century was caused by a comet.

Using evidence from tree rings, the scientists at the School of Physics and Astronomy determined that Earth underwent a series of very cold summers around 536-540 A.D. because a comet hit the planet and exploded in the upper atmosphere.

Comet debris from the explosion enveloped Earth in soot and ash, blocking out the sunlight and causing the cold weather.

This period, known as the Dark Ages, has yielded sparse records but what records do exist tell of crop failures and summer frosts.

An article published in the February issue of Astronomy and Geophysics, the in-house magazine of the Royal Astronomical Society, said that only a relatively small comet was needed to cause such a dramatic effect.

The scientists calculated the comet was not more than a third of mile across -- significantly smaller than previously thought.

=============

COLLISION WITH COMET MAY HAVE HASTENED FIRST PLAGUE EPIDEMIC

The Independent, 4 February 2004

http://news.independent.co.uk/world/science_medical/story.jsp?story=487550

By Steve Connor, Science Editor

A collision between Earth and a passing comet in the 6th century AD may have caused the collapse of agriculture, mass famine and indirectly led to the bubonic plague in Europe, a study has suggested.

Scientists have calculated that a relatively small comet, or fragment of a comet, could have caused huge amounts of dust and debris to be ejected into the atmosphere, blocking the sun for months at a time.

The resulting crop failures and famine would have allowed bubonic plague to spread easily among a physically weakened population.

Studies of tree rings - from preserved oaks retrieved from Irish bogs to ancient American pine trees - have shown that plant growth around the world almost stopped between about 536AD to 545AD. Chinese records from this time refer to a "dust veil" obscuring the skies. Mediterranean historians record a "dry fog" that blocked out much of the sun's heat for more than a year.

Scientists have suggested two causes, both involving the ejection of dust or debris into the atmosphere to block the sun and so prevent photosynthesis.

One idea is that a super-volcano erupted, but neither the volcano nor its acidic deposits have been identified, Derek Ward-Thompson, who carried out the latest study at Cardiff University, said. The other proposal involved a collision with a big asteroid or comet, but there was no direct evidence such as a crater.

However, Dr Ward-Thompson and his colleagues Mel Symonds and Emma Rigby believe a much smaller comet which exploded in the atmosphere could easily have generated the dust and debris in the 6th century catastrophe. "The surprising result of these calculations is just how small a comet fragment we have estimated was needed to cause the observed effects," Dr Ward-Thompson said.

"A comet less than 1km in diameter has not been previously considered to represent a global hazard - as opposed to a local hazard - let alone one 0.5km across," he said.

Using information gathered from the impact of Comet Shoemaker-Levy with Jupiter in 1994, the scientists have produced a model of how comet fragments would behave if they collided with Earth. "The comet plunges into the upper atmosphere leaving an effectively hollow tube behind it, where it has been, and into which the surrounding air has not yet had time to diffuse," the scientists write in the journal Astronomy and Physics.

"This tube then acts rather like a gun barrel, focusing much of the energy of the airburst explosion along the tube and carrying with it much of the comet debris," they write.

As a result, the plume would have spread around the world in a massive fountain of debris. "This period coincides with a mass population decrease in Europe. This is commonly known as the Justinian plague, and is believed to be the first appearance of the Black Death in Europe," the scientists say.

They said that if such an event happened today, a large percentage of the population could face starvation.

=============

SUPER-VOLCANO MAY HAVE TRIGGERED GLOBAL COOLING IN 536 AD

Los Alamos National Laboratory, 17 December 2000

http://www.lanl.gov/worldview/news/releases/archive/00-165.shtml

Contact: John Webster, webster@lanl.gov, (505) 667-5543

LOS ALAMOS, N.M., Dec. 17, 2000 -- The beginning of the Dark Ages may have been literal, as well as figurative, as the result of a massive volcanic eruption in the 6th century, according to a volcanologist at the Department of Energy's Los Alamos National Laboratory.

Ken Wohletz said an eruption in the Indonesian archipelago could have produced a 150-meter-thick cloud layer over the entire Earth, triggering a chain of climatic, agricultural, political and social changes that ushered in the Dark Ages.

Evidence supporting the catastrophe includes tree-ring and ice-core measurements, indications of a huge underwater caldera, and ash and pumice in the same area, said Wohletz, who discusses his work modeling such an eruption today (Dec. 17) at the fall meeting of the American Geophysical Union.

The 6th century was a turbulent, unsettling period in human history. The Roman Empire began to fall; nomads of central Asia migrated to Europe and the Near East; civilizations in Persia, Indonesia and South America collapsed; major religions experienced considerable change as natural events were viewed as omens.

Many of these social transformations resulted from widespread crop failures and the explosion of plague around the globe, which in turn were caused by major climatic changes, Wohletz said. Beginning in about the year 535, according to historical and archeological records, the weather was colder and drier, sunlight diminished, snow fell in summer and regions of persistent drought suffered floods.

Wohletz was a resource for a book postulating that the climate changes resulted from a huge volcanic eruption. The book, "Catastrophe: A Quest for the Origins of the Modern World" by David Keys, was published earlier this year.

Wohletz said he worked with Keys to try to identify a volcano that could produce such dramatic climate change. "We came up with an eruption that would certainly be the largest in recorded history, some four or five times bigger than the (1815) eruption of Tambora, which is usually considered the biggest eruption in the past few millennia," he said.

Such an explosion, he said, would eject some 200 cubic kilometers of material, and one-third to one-half of it would be lofted into the stratosphere, where it would remain suspended for months to years while being carried around the globe.

"It would have produced enough dust and water vapor (in the form of ice crystals) to form a cloud layer 150 meters thick over the entire globe, and that's a conservative estimate," he said, adding that a cloud of particles that thick may have diminished the transmission of sunlight by as much as 50 percent.

Wohletz said tree-ring data collected around the world and ice-core measurements in Greenland and Antarctica support the possibility of a huge eruption in the 6th century. Ocean depth measurements between Sumatra and Java where Krakatoa exploded in a well known 1883 eruption indicate the presence of a caldera up to 50 kilometers in diameter, and a recent survey uncovered evidence of ash and pumice layers formed in the area during the appropriate time frame.

Under a likely scenario, a large volcano, which Wohletz calls proto-Krakatoa, connected the islands of Sumatra and Java. When it erupted and then subsided, it created the Sundra Strait and left a ring of smaller volcanoes, including the present day Krakatoa. The ash, dust and water vapor blown into the stratosphere would disperse across both the Northern and Southern Hemispheres.

"This volcano would have had the potential to be a major player in destabilizing the climate around the world," he said. "An eruption that could produce a caldera 50 kilometers across would have been big enough."

Although definitive evidence for such a catastrophic eruption has not been discovered, the possibility deserves a full-scale field study, Wohletz said, in part because of the potential impact on the world if another such catastrophe happens.

"(Key's book) is the first detailed account of how closely humanity is linked to the natural world," he said. "If the natural world goes through some large upheaval, we'll all be affected."

=============

SUPER-DROUGHT MAY HAVE SET OFF EUROPEAN DARK AGES

University of California, Berkeley, 9 December 1998

http://www.berkeley.edu/news/media/releases/98legacy/12-9-1998a.html

BERKELEY -- A tiny Christian village in ancient Greece and a long-dead river have provided the first clues that a terrible drought may have set off the European Dark Ages, at least in the eastern Mediterranean.

The clues come from the archaeological site of Nemea, Greece, where ancient athletic games were held. Stephen G. Miller, professor of classics at the University of California, Berkeley, announced the results of recent digs near the site in an evening lecture on Tuesday, Dec. 8.

While excavating deep into the bed of the small Nemea River which runs through the site, Miller made an unexpected discovery. He found a much larger, older river bed that had completely run dry during the first half of the 6th century A.D.

At about the same time, said Miller, an agricultural community of early Christians at Nemea became impoverished and short on water. They built new wells but used them for only a short period of time.

The Christian community at Nemea was totally destroyed by invading Slavs in A.D. 585, but Miller said the archaeological evidence clearly indicates the community had already fallen on hard times 50 years earlier.

Miller believes these clues, taken together, provide the first evidence of an extraordinary drought in the eastern Mediterranean that may have laid the groundwork for that region's later devastation by plague and marauding Slavic tribes.

His evidence lends weight to a recent theory that the Dark Ages were brought on by a cataclysmic event, a violent volcanic eruption in 536 A.D. that cloaked the skies in volcanic dust and cast the world into cold darkness for more than a year.

According to popular belief, based on Gibbon's classic "Fall of the Roman Empire," barbarians brought about the fall of classical civilization by sacking Rome in 476 A.D. Byzantine civilization in the eastern Mediterranean, however, collapsed about 100 years later after a bubonic plague swept the region and after invasions by Slavic tribes and Persians.

The evidence of drought at Nemea and its implications for classical civilization represent a new direction for Miller, whose excavations at the Greek site since 1974 have led to the reconstruction of much of the original setting for the Panhellenic Games, including the stadium and track, a bathhouse and a temple to Zeus.

In 1996, Miller led a revival of the ancient games by holding a modern day foot race on the ancient track. Hundreds of participants from around the world, including many celebrities, journeyed to Nemea to take part in the race. The Nemean games will be held again in the year 2000, on June 3 and 4.

In 1997, Miller and his team set out to find the course of the ancient Nemea river in order to divert water there and save artifacts scattered throughout the area.

What he discovered, however, were three older rivers and an excellent stratigraphy with which to decipher changes that had occurred since the early Mycenean era in the 12th century B.C.

"We could see cycles of aridity and dampness for more than 3,000 years," said Miller. "There had been a large river during the early Christian era; then, suddenly, there was no river."

The team confirmed through excavation that the river had not been diverted somewhere else, but had actually stopped flowing in the first half of the 6th century A.D.

That period corresponds with worldwide accounts of a massive climatic change, caused perhaps by a volcanic eruption, perhaps in New Guinea in 536 A.D., according to a theory proposed recently by the astrophysicist R. B. Stothers and others, said Miller.

The strange effects were recorded by observers from Rome to China who noted that the sun went dark for more than a year and all the crops failed.

"The Sun gave forth its light without brightness, like the Moon, during this whole year, and it seemed very much like the Sun in eclipse, for the beams it shed were not clear," wrote Procopius of Greece in 536 A.D.

Said another source, the Roman writer Cassiodorus: "We have had a winter without storms, spring without mildness, summer without heat. Whence can we hope for mild weather, when the months that once ripened the crops have been deadly sick under the northern blasts? ... Out of all the elements, we find these two opposed to us: perpetual frost and unnatural drought."

Miller said that further confirmation of this unnatural climatic period comes from tree-ring data in several parts of the world. Ancient trees such as the 4,000-year-old bristle cone pines in California show that the years around 540 A.D. were those of the least growth in four millennia.

The possibility that massive climatic change caused the fall of the Byzantine Empire was discussed by climatologist William James Burroughs in his 1997 book, "Does the Weather Really Matter?" But he noted that the one piece of evidence missing was a sign of drought in the eastern Mediterranean.

"We now have that evidence," said Miller.

===========

ICE CORE EVIDENCE FOR VOLCANIC ERUPTION ~530 AD

Environmental Catastrophes and Recoveries in the Holocene

http://atlas-conferences.com/c/a/i/q/21.htm

Lars Berg Larsen, Department of Geophysics, University of Copenhagen

Coauthors: Marie-Louise Siggaard-Andersen (Alfred-Wegener-Institute for Polar and Marine Research,Bremerhaven) and Henrik B. Clausen (Department of Geophysics, NBIfAFG, University of Copenhagen)

In the beginning of the sixth century, early medieval historical data indicate some events, which is believed to be the aftermath of some sort of global climatic catastrophe. The three-ring and ice core data obtained around the world show a temperature anomaly around this period. In the ice cores drilled in Greenland at the sites NGRIP, GRIP, DYE-3 and the Antarctica sitesBYRD and DOME C we investigated special events and other anomalies in the chemistry, isotope end ECM data. In the ECM record we have the third largest signal found in the ECM record the last to thousand years. A detailed chemical analysis of the ice covering the period was made. From the chemical record we identify a volcanic eruption and we estimate the magnitude of the eruption and a possible location. With the chemistry and the isotope data it is possible to do a very precise dating for the eruption. The volcanic eruption is dated to AD. 527 +/- 1 year. The AD 527 volcanic eruption is the only eruption in the period and the only likely candidate to cause some of the calamities described in the historical data The dating of this volcanic eruption suggest that the event is not the same one described by other sources.

=============

JUMBLING OLD EVENTS WITH MODERN MYTHS

British Archaeology, November 1999

http://www.britarch.ac.uk/ba/ba49/ba49book.html

by Ken Dark

CATASTROPHE

David Keys

Century, £16.99

ISBN 1-7126-8069-1 hb

Dr Ken Dark is an early medieval specialist at the University of Reading

==============

A COMET IMPACT IN AD 536?

Astronomy & Geophysics, Volume 45 Issue 1, February 2004

Emma Rigby1, Melissa Symonds2 and Derek Ward-Thompson2

1Cardiff University, UK (now at Edinburgh University, UK) 2Cardiff University

Emma Rigby, Melissa Symonds and Derek Ward-Thompson review the evidence for the possibility that a comet may have impacted the Earth in historical times, and discuss the size of the putative comet.

Abstract

A global climatic downturn has previously been observed in tree-ring data associated with the years AD 536-545. We review the evidence for the explanation of this event which involves a comet fragment impacting the Earth and exploding in the upper atmosphere. The explosion would create a plume, such as was seen during the impact of comet Shoemaker-Levy 9 with Jupiter. The resulting debris deposited by the plume on to the top of the atmosphere would increase the opacity and lower the temperature. We calculate the size of the comet required, and find that a relatively small fragment of only about half a kilometre in diameter could be consistent with the data. We conclude that plume formation is a by-product of small comet impacts that must be added to the list of significant global hazards posed by near-Earth objects.

The Earth is bombarded every day by debris from space. The majority of this debris takes the form of very small particles of dust. These objects are known as meteoroids which, as they run into the Earth's atmosphere, produce meteors - also known as shooting stars. Such objects are rarely hazardous. However, there are also much less frequent collisions with larger objects ranging in size from tens of metres to kilometres across, which may be asteroids or comets. Asteroids are primarily rocky or metallic in composition, whereas comets are composed mainly of a variety of ices with some rock. Objects of this size are generally more of a hazard. In fact, the UK government even set up a Near Earth Object Task Force to evaluate the risks of impacts from such objects (Atkinson et al. 2000). Depending on the size and strength of the material of the meteoroid, it may explode in the atmosphere before reaching the ground. Such an event is known as an airburst. An airbursting object releases energy in the form of a shockwave, which can devastate large areas and trigger forest fires. Airbursts can also produce a high-altitude haze of particles, such as was seen in the 1908 Tunguska event.

In AD 536 an event occurred which caused significant climatic change. Dendrochronological (tree-ring) evidence in oak trees salvaged from Irish peat bogs indicates a sequence of colder than average summers at this time (Baillie 1991, 1999). A similar effect is seen in Fennoscandian pine trees (Briffa et al. 1990), and a study of European oak tree data as a whole shows that the event starts in 536 and lasts until 545 (Baillie 1994). Figure 1 shows the typical variation in tree-ring widths.

North American bristle-cone and foxtail pines (La Marche 1974, Scuderi 1990), Mongolian tree rings (D'Arrigo et al. 2001) and Argentinean tree-ring data (Baillie 1999) all show the same effect. The decrease in rate of growth in these years corresponds to a global temperature decrease of up to 3 °C (Briffa et al. 1990, Scuderi 1990). In fact, 536 is noted as one of the coldest two or three years globally in the last 2000 years (Briffa et al. 1990, Scuderi 1993, Baillie 1999). Figure 2 shows the results for the Irish oak trees and the US foxtail pines.

There are also some limited historical records from the same period, which record the presence of a "dust veil". Chinese records refer to obscured skies and summer frosts (Baillie 1999). Mediterranean historians also record a "dry fog" event. Procopius (Dewing 1916) records that:

"the Sun gave forth its light without brightness, like the Moon, during this whole year, and it seemed exceedingly like the Sun in eclipse",

and Michael the Syrian (Chabot 1901) states:

"the Sun was dark and its darkness lasted for eighteen months; each day it shone for about four hours, and still this light was only a feeble shadow".

The sixth-century British monastic writer Gildas talks of large-scale fires and widespread destruction of the landscape at around the same time (Winterbotham 1978). Previously Gildas has been thought to have been talking allegorically, with his many biblical references. However, he may have been describing the actual events taking place at this time.

There have been two theories put forward to account for this cataclysmic climatic event. One idea is that a giant "super-volcano" erupted in 536, causing the effects described above (Stothers 1984, Keys 1999). The alternative scenario invokes an impact by an asteroid or comet (Clube and Napier 1984).

The super-volcano theory has several problems. Firstly, no terrestrial volcano can be satisfactorily identified with this event. Secondly, a super-volcano would be expected to produce significant acidity in the atmosphere. This acidity would be recorded in the polar ice caps. Numerous ice-core studies have been carried out in both Greenland and Antarctica (see, for example, Clausen et al. 1997, Hammer et al. 1997). None of these has found evidence for a significant acid layer around 536 of the sort that would be caused by the eruption of a super-volcano.

There are small acid layers associated with 528 and 533, but they are not sufficiently strong that they can be related to a super-volcano (Clausen et al. 1997). In addition there is an Antarctic ice acid layer dated as 504±40 (Hammer et al. 1997), which has been argued could be related to the 536 event (Keys 1999). However, once again this is not the depth of layer that one would expect of a super-volcano (Baillie 1999). Other measurements have proved inconclusive. For example, in one case an ice core broke up across the crucial period (Zielinski et al. 1994) and in another the exact dating proved controversial (Hammer 1984).

The scenario involving an impact by an asteroid or comet may have seemed far-fetched at one time, but recent scientific evidence indicates that such impacts may be more common than was once believed. The impact of comet Shoemaker-Levy 9 (SL9) with Jupiter in 1994 provided dramatic and direct evidence of the damage that even quite small impacts can generate. Figure 3 shows an example of some images of the SL9 impact event. In addition, the impact of a comet or asteroid is now believed to be responsible for the considerable climatic changes at the end of the Cretaceous period (Alvarez et al. 1980).

No known impact crater can be linked to the 536 event so, if it were due to a comet collision, then the crater may lie unrecognized in a region such as the seabed (unlikely, given that the seabed has now been very well surveyed), or else the comet must have been destroyed in an airburst. If the airburst had sufficient energy to ignite one or more large-scale forest fires (Hills and Goda 1993, Adushkin and Nemchinov 1994), we can calculate whether the soot emissions from these fires were sufficient to cause the observed climatic effects.

During the Cold War much effort went into modelling the secondary effects of a conflict involving nuclear weapons, including large-scale fires and related atmospheric effects, referred to collectively as a nuclear winter (see, for example, Turco et al. 1983, 1990, Crutzen and Birks 1992). The basic hypothesis is that the extensive fires started by nuclear explosions would generate a sufficiently large quantity of soot in the upper atmosphere to affect its radiation balance and cause a change in the Earth's albedo. The net result is reduced solar heating at the Earth's surface and hence a lower temperature. This would produce significantly colder summers and hence reduced tree-ring growth. We can use such models to study fires started by a comet impact, since they provide estimates of the soot yields from appropriate masses of relevant flammable materials. We choose the model of Turco et al. (1990) to make our comparison. This model finds that 1011 kg of soot injected into the troposphere is sufficient to produce the effect known as a nuclear winter.

It has been found that airbursting comets can start fires more easily than asteroids (Hills and Goda 1993). This occurs because comets tend to dissipate their energy higher in the atmosphere, which has two main effects. The high-altitude energy dissipation allows them to illuminate a much larger area of the Earth. Simultaneously the high altitude of the airburst makes it more difficult for the associated atmospheric shockwaves to reach the Earth's surface and blow out the fire. We note that calculations on the size of an impacting comet required to ignite pine forests show that an object radius of more than 100 m is needed for such an ignition, setting an effective lower limit.

Dendrochronological data and historical records indicate that Northern Europe is the most likely geographical location for the impact (Baillie 1999). However, we note that this suggestion is not critical to the model of large-scale fires, and any equivalent land area would suffice, provided that it was appropriately forested. In the sixth century Europe's most flammable species of tree was the pine tree and forests in Northern Europe were largely composed of pine trees (Rackham 1993), so a forest fire there is possible. A study of fire behaviour from large-scale biomass burning (Einfeld et al. 1991) provides the following equation for the amount of smoke injected into the troposphere by large-scale forest fires:

M>X = M>FA>BF>CE>X (1)

where MX is the mass yield of a particular gaseous or particulate species X, MF is the fuel load in terms of mass per unit area, AB is the area burned, FC is the fractional consumption of the total fuel load and EX is the emission factor for the species of interest. We can use this equation to estimate what size of forest fire would have been required to produce the cooling recorded in the dendrochronological data.

To calculate MF we assume one tree per hundred square metres of forest (Rackham 1993), which when combined with a typical tree mass gives a fuel load of M>F ~20 kg m^2.

For EX we take a value of 1% (Turco et al. 1990) and for the fractional consumption FC we assume 10%. Inserting these values into equation 1, we find that we would need a forest fire to cover the whole of Northern Europe (5 1012 m2) to inject into the troposphere the 1011 kg of soot required by the nuclear winter model described above. Such a large conflagration seems somewhat unlikely as there would almost certainly have been some form of historical or archaeological record of such a fire. Furthermore, the climatic effects may not last for the time required by the tree-ring data, since soot in the troposphere has a tendency to precipitate out. Consequently, forest fires may have added to the events of 536, but they cannot explain all of the data.

Atmospheric plumes Go to: Choose Top of page The AD 536 event Forest fires Atmospheric plumes << The size of the comet Conclusions References

When comet SL9 broke up into many pieces and collided with Jupiter in 1994, astronomers had their first opportunity in modern times to study in detail a large comet impact with a planet. Many previously unpredicted effects were seen, including giant plumes above the impact sites and huge scars where each fragment had hit. This led several people to model in detail the effects of such collisions. The similarity was noted between the impact of SL9 with a largely gaseous body such as Jupiter and the airburst of a comet impacting the Earth.

Figure 4 shows some results from a model of a 15 megaton equivalent yield comet airburst over the Earth (Boslough and Crawford 1997). The comet plunges into the upper atmosphere, leaving an effectively hollow tube behind it, where it has been, and into which the surrounding air has not yet had time to diffuse. This tube then acts rather like a gun barrel, focusing much of the energy of the airburst explosion along the tube and carrying with it much of the comet debris. This is what causes the observed plume, as material is fired along the tube by the force of the explosion.

The plume expands once it has exited the top of the atmosphere and the material within it then falls back on to the top of the atmosphere. This is the explanation for the observed scars on Jupiter. However, figure 4 has been used to model the Tunguska comet impact of 1908. This was a much smaller comet than SL9, but the chief effects appear to change only in scale. The sequence of events remains the same: impact; airburst; plume.

An eye-witness drawing of the Tunguska event actually resembles the model plume of figure 4, and many witnesses across northern Russia and Europe noted that the sky was light at night for a few days afterwards. This effect can be explained as noctilucent clouds caused by material from the plume.

There was no significant global cooling in 1908 so any comet required to explain the 536 event must be larger than the comet which exploded in the air over Tunguska. The best estimate for the size of the Tunguska comet is a few tens of metres in diameter. We can use the model illustrated in figure 4, together with an estimate of the optical depth of the 536 dust veil, to calculate the size of comet fragment required to cause the 536 event.

The dry-fog event noted in the Mediterranean area has been estimated from the description of the Sun to correspond to an optical depth of 2.5 (Stothers 1984). However, we would question this estimate. It was based purely on assumptions of what was meant in historical records by "the Sun appearing like the Moon" and hence by how much this implied the Sun had dimmed. We can make alternative estimates based on the tree-ring data, which require a decrease in temperature of only up to 3 °C (Briffa et al. 1990, Scuderi 1990).

The temperature of the Earth's surface,

is proportional to L^¼ I

where LI

is the incident luminosity at the surface of the Earth. If the dust veil had an optical depth of then LI

would be decreased by e

and the temperature at the Earth's surface under the dust veil,

TD is given by: T>E+TEe^t4 (2)

Taking TE 300 K and using the maximum temperature decrease of 3 K, we calculate the maximum value required for is 0.04, which is considerably less than the previous estimate.

We make the assumption that the entire mass of the comet is destroyed in the airburst and ejected via the plume. Thereafter the dust condenses out and is deposited on to the top of the atmosphere as small particles of dusty debris. This debris is then spread around the globe roughly uniformly. The dust-to-gas mass ratio in a comet can range from 0.1 to 10 (see, for instance, Weiler et al. 2003 and references therein), so we take a value of order unity (i.e. Mdust 0.5 Mcomet).

The optical depth is then related to the number of dusty particles Nd by the equation: (3)

where a is the typical radius of a particle and RE is the radius of the Earth. Nd is simply given by the ratio of the dust mass of the comet to the mass of a dusty particle. Hence Nd is given by the ratio of the comet density to the dust particle density (a factor 0.5 - see, for example, Fitzsimmons et al. 1996, and references therein), multiplied by the fraction of the comet's mass that is dust (0.5), multiplied by the ratio of the cube of the comet radius RC to the particle radius a. Thus: (4)

and the comet radius is given by: (5)

We know the radius of the Earth ( 6.4x10^6 m) and we assume a typical particle radius to be similar to that of particles in the interstellar medium of 10^6 m (e.g. Fitzsimmons et al. 1996). Hence we find that a of 0.04 requires a comet radius of only 300 m.

Clearly such calculations contain many approximations and assumptions. Some of the numbers that go into this estimate are rather uncertain. We particularly note that we are relying on atmospheric effects to spread the dust evenly over the top of the atmosphere. Nonetheless, the result is interesting. It puts the comet size as intermediate between the Tunguska comet and SL9 and makes it significantly smaller than the comet thought responsible for the dinosaur extinction.

A comparison between the 536 event and the SL9 impact with Jupiter can provide a useful cross-check to our size calculations. The fragments of SL9 that collided with Jupiter ranged in diameter from 300 m to 2 km. The scars created on Jupiter were typically about the size of the Earth or larger. This appears to corroborate our basic premise that a relatively small fragment could have been responsible for the 536 event. We note that a collision with a comet or asteroid of this size has been predicted to occur on the Earth once in several thousand years (Morrison et al. 1994). Consequently we should not be surprised to find evidence for such an impact within the 7000-year dendrochronological record.

The surprising result of these calculations is just how small a comet fragment we have estimated was needed to cause the observed effects. A comet less than a kilometre in diameter has not been previously considered to represent a global hazard (as opposed to a local hazard), let alone one half a kilometre across. For example, the UK government's Near Earth Object Task Force classified impacts from objects in the size range 300-1500 m to be a "large sub-global hazard" (Atkinson et al. 2000) and only recommended monitoring programmes of near-Earth objects greater than a kilometre in size. Yet our estimates show that if plume formation is a common by-product of cometary airbursts (as is believed to be the case), then a relatively small comet fragment can have a global effect.

A possible origin for this object could be the Taurid meteor stream. This stream is the result of the fragmentation of a much larger comet some 20 000 years ago (Bailey et al. 1990). The Earth passes through the Taurid stream in November and June each year, resulting in regular meteor showers normally consisting of microscopic dust particles. A fragmentation of the stream is thought to have occurred around 500 (Clube and Napier 1984). It is possible that a fragment could then have collided with the Earth as it passed through the beta portion of the stream early in 536, causing the atmospheric dust-veil event.

One other historical aspect of the period around 536 may also be significant. This period coincides with a mass population decrease in Europe. This is commonly known as the Justinian Plague, and is believed to be the first appearance of the Black Death in Europe (Russell 1968). The relevance to our hypothesis is that crop failures for several years in a row while the dust veil was present may have caused widespread starvation, leading to an increased susceptibility to disease among the remaining population. Small comets had previously been thought to be less hazardous than small asteroids, but our estimates show that a small comet fragment can have a global effect.

If such an event happened today, and crops failed over a significant part of the globe for several consecutive years, then once again a large percentage of the world's population would face starvation.

References

Adushkin V V and Nemchinov I V 1994 in Hazards Due to Comets and Asteroids eds T Gehrels et al. Univ. of Arizona Press 721-73.

Atkinson H et al. 2000 Near Earth Object Task Force Report HMSO.

Alvarez L W et al. 1980 Science 208 1095-108.

Bailey M E et al. 1990 The Origin of Comets Pergamon Press.

Baillie M G L 1991 World Archaeology 23 233-43.

Baillie M G L 1994 The Holocene 4 212-17.

Baillie M G L 1999 Exodus to Arthur Batsford.

Boslough M R E and Crawford D A 1997 Ann. New York Acad. Sc. 822 236-82.

Briffa K R et al. 1990 Nature 346 434-39.

Chabot J B 1901 Chronicle Belles-Lettres.

Clausen H B et al. 1997 J. Geophys. Res. 102 707-24.

Clube S V M and Napier W M 1984 MNRAS 211 953-68.

Crutzen P J and Birks J W 1992 Ambio 11 114-25.

D'Arrigo R et al. 2001 Geophys. Res. Lett. 28 543-46.

Dewing B H 1916 History of the Wars Harvard University Press.

Einfeld W et al. 1991 in Global Biomass Burning, Atmospheric, Climatic, and Biospheric Implications ed. J Levine, MIT Press 412-20.

Fitzsimmons A et al. 1996 MNRAS 278 781-86.

Hammer C U 1984 Jokull 34 51-56.

Hammer C U et al. 1997 Climatic Change 35 1-15.

Hills J G and Goda M P 1993 Astron. J. 105 1114-44.

Keys D 1999 Catastrophe: an Investigation into the Origins of the Modern World Century.

La Marche V C 1974 Science 183 1043-48.

Morrison D et al. 1994 in Hazards Due to Comets and Asteroids eds T Gehrels et al. Univ. of Arizona Press 59-91.

Rackham O 1993 Trees and Woodland in the British Landscape Orion Publishing.

Russell J C 1968 Demography 5 174-84.

Scuderi L A 1990 Quaternary Research 34 67-85.

Scuderi L A 1993 Science 259 1433-36.

Stothers R B 1984 Nature 307 344-45.

Turco R P et al. 1983 Science 222 1283-90.

Turco R P et al. 1990 Science 247 166-75.

Weiler M et al. 2003 A&A 403 313-22.

Winterbotham M 1978 Gildas: The Ruin of Britain and Other Works Phillimore.

Zielinski G A et al. 1994 Science 264 948-52.

The authors thank Mike Baillie, Mark Bailey, Martin Johnson, Ted Johnson-South and David Williams for interesting and helpful discussions.

CCNet 18/2004 - 5 February 2004

PLAGUE OUTBREAK BLAMED ON COMET STRIKE

The New Zealand Herald, 5 February 2004

http://www.nzherald.co.nz/storydisplay.cfm?storyID=3547472&thesection=news&thesubsection=world

By STEVE CONNOR IN LONDON

A collision between Earth and a passing comet in the 6th century AD may have caused the collapse of agriculture, mass famine and, indirectly, the emergence of bubonic plague in Europe.

Welsh scientists have calculated that a relatively small comet, or a fragment of one, could have caused huge amounts of dust and debris to be ejected into the atmosphere that would have blocked out the sun for months.

The effect would have been crop failures and mass famine that could have allowed bubonic plague to spread more easily among a physically weakened population.

Studies of tree rings - from preserved oaks retrieved from Irish bogs and ancient American pine trees - have shown that plant growth around the world almost stopped completely between about AD536 and AD545.

Chinese historical records refer to a "dust veil" obscuring the skies and Mediterranean historians record a "dry fog" that blocked out much of the sun's heat for more than a year.

Scientists have suggested two possible causes for this sudden shift to winter-like conditions, both involving the ejection of dust or debris into the atmosphere to block out the sun and so preventing plant photosynthesis.

One idea is that a super-volcano erupted somewhere in the world, but neither the volcano nor its acidic deposits have been identified, says Derek Ward-Thompson, who carried out the latest study at Cardiff University.

The other proposal involves a collision with a passing asteroid or comet big enough to cause the effect, but again Ward-Thompson said there was no direct evidence for this in terms of a suitable impact crater.

However, he and his colleagues Mel Symonds and Emma Rigby believe that a much smaller comet which exploded in the atmosphere above ground without leaving a crater could easily have generated the dust and debris that led to the 6th century catastrophe.

"The surprising result of these calculations is just how small a comet fragment we have estimated was needed to cause the observed effects," Ward-Thompson said.

"A comet less than a kilometre in diameter has not been previously considered to represent a global hazard ... let alone one half a kilometre across."

Using information gathered from the impact of Comet Shoemaker-Levy with the planet Jupiter in 1994, the scientists have produced a new model of how comet fragments would behave if they collided with Earth.

"The comet plunges into the upper atmosphere leaving an effectively hollow tube behind it, where it has been, and into which the surrounding air has not yet had time to diffuse,"the scientists write in the jour-nal Astronomy and Physics.

"This tube then acts rather like a gun barrel, focusing much of the energy of the airburst explosion along the tube and carrying with it much of the comet debris."

As a result, the plume would have escaped the atmosphere completely and spread around the world in a massive fountain of debris that would have blocked out the sun for many months, causing widespread crop failures and famine around AD536.

"This period coincides with a mass population decrease in Europe. This is commonly known as the Justinian plague, and is believed to be the first appearance of the Black Death in Europe."

===========

KILLER COMET: 'TINY' SPACE ROCK ALERT

Daily Record, 5 February 2004

http://www.dailyrecord.co.uk/news/content_objectid=13916499_method=full_siteid=89488_headline=-KILLER%2DCOMET-name_page.html

By Annie Brown

A "TINY" space rock could wipe out millions of people, scientists claim.

Astronomers have been watching for years for huge comets on a collision course with the Earth.

But now they believe a rock less than a third of a mile wide tiny in space terms could create massive devastation.

They say a similar comet could have caused widespread crop failures and summer frosts more than 1500 years ago.

They think it exploded in the upper atmosphere causing a'' nuclear winter'' by blocking out sunlight with its ashand soot.

The Cardiff University team started their study after comet Shoemaker-Levy-9 hit Jupiter in 1995. Derek Ward-Thompson, who supervised the research, said yesterday: "We have reclassified the size of comet that represents a global threat.

"Nothing less than 1 km (0.6 miles) was counted before but after Shoemaker-Levy, we thought they had missed a trick."

The effect which causes the nuclear winter is known as a plume, said Dr Ward-Thompson.

He added: "We believe this happens with every comet which hits the Earth.

"A comet only a few hundred metres across could have a devastating impact. Crops would fail for at least two years. We in Europe would not be able to farm and would struggle to feed ourselves but it is the Third World which would be worst off.

"It would suffer mass starvation on a scale we haven ever experienced."

The Government launched the Near Earth Objective Task Force about two years ago to investigate threats from space.

But Dr Ward-Thompson said it had not taken smaller comets into account and funding was not available to monitor them.

Lib Dem MP Lembit Opik, who has been behind the task force, yesterday called for money for the project.

================

RE: DID A COMET IMPACT TRIGGER A "NUCLEAR WINTER" IN 536 AD?

Mark Kidger <mrk@iac.es>

Benny:

With reference to this item, you carry three notes, one suggesting that a comet impact was responsable, another that it was a supervolcano, and a third that it was drought. The mere fact that three big catastrophies have been suggested makes me wonder how convincing the case for any of them could be!

Certainly, in two of the cases (comet impact and supervolcano) we are talking of events capable of causing at least regional devastation. Where though is the evidence of recent regional devastation that one would associate with either of these events? One would expect to see some kind of geological record such as an ash or dust layer. The note on the Greenland core samples talks of a modest acidity peak from a volcanic eruption, but in low-key terms that do not bring to mind a regional catastrophe. One would expect that a major impact, or a gigantic volcanic eruption should leave an absolutely unarguable geological record.

I suspect that such catastrophes as impacts and, in this case, supervolcanos are being over-used as possible explanations for historical events. If all the putative historical impacts that I have seen described in CCNet are genuine (including one very recent one in the South Pacific), there is something horribly wrong with the current statistics that suggest that the impact danger is rather smaller than previously thought.

Any comments anyone?

Mark Kidger

=========

SUPER-VOLCANO, SUPER-COMET, SUPER-DROUGHT AND SUPER-NOVA

James A. Marusek <tunga@custom.net>

Dear Benny

Several of the articles in CCNet 17/2004 - 4 February 2004 discussed the Dark Ages, which began in 536AD. The articles were centered on two major theories. Either the event was triggered by a comet or by a super-volcanic eruption. But the discussion completely ignored the third major theory, that the Dark Ages resulted from a nearby supernova event.

A supernova will produce a burst of highly energetic charge particles (galactic cosmic rays). When these particles collide with Earth, they will break up oxygen and nitrogen molecules in the stratosphere. Many of these particles will reform into nitric oxide, which is highly reactive and will quickly combine with oxygen to form nitrogen dioxide. Nitrogen dioxide is the brownish constituent of smog. The browning of the stratosphere will initially result in greater solar absorption, but most of this increase will be localized in the stratosphere. The natural heat transport mechanism (cloud formation) that functions in the lower atmosphere is energized by stratospheric heating. This heating produced a conveyor belt that can pulled moisture from the planet’s surface and transport it high into the outer regions of the stratosphere, where it forms microscopic ice particles. These flat hexagon shaped ice particles are referred to as diamond dust. The ice crystals are highly reflective and extremely light. While they remain in the stratosphere, they will dramatically reduce solar heating, which will produce a major decline in global temperatures. This creates the condition where "the Sun gave forth its light without brightness, like the Moon, during this whole year, and it seemed exceedingly like the Sun in eclipse" described by Procopius

The surge of cosmic rays is a short event only lasting several weeks before the intensity tapers off. But the climatic change that it produces can last a decade. Diamond dust is very light and aerodynamically shaped. Stratospheric winds can keep the material aloft for many years before it falls back to Earth.

James A. Marusek

============

RE: COMET IMPACT AND DARK AGES

HASTRO-L@LISTSERV.WVU.EDU

Minor point: we historians do NOT call the 6th century AD 'the Dark Ages.' Depending on your viewpoint, it can be Late Antiquity or the Early Byzantine period or the Early Middle Ages. In China, it's the period of the Northern and Southern dynasties, in Iran, the Sassanid dynasty. Written sources from this time are fairly numerous, just not 'classical,' hence seemed 'Dark' to people like Gibbon.

Lester Ness

CCNet 19/2004 - 6 February 2004

COMET IMPACT IN 536 AD?

Michael Paine <mpaine@tpg.com.au>

Dear Benny

Re the debate about an impact around 600AD, can I remind subscribers that the modelling I conducted using John Lewis's software suggests that only 5% of fatal impact events leave an impact crater on land and most of these craters erode or are covered up after a few thousand years. Also the average fatalities per airburst event are 100,000 (the overall average is 2 million per fatal event - see http://www4.tpg.com.au/users/horsts/sta1046.htm ).

The estimated risk has reduced since the software was written but the above values are unaffected by the actual flux.

The lesson is that we can expect a paucity of physical evidence of impacts that may have had an effect on human society. "Absence of evidence is not evidence of absence".

regards

Michael Paine

MODERATOR'S NOTE: Michael, your point is well taken. I have used the same line of reasoning for many years, stressing that we should not underestimate the potential hazard due to relatively frequent impacts of small NEOs. Your general conclusion, however, is only valid for the population of small, stony objects (up to 100 m or so) that tend to disintegrate in the atmosphere. These localised events do not leave much physical evidence, if any, on the earth’s surface. A 500 m comet, on the other hand, would be expected to penetrate the atmosphere and produce a hypervelocity impact crater on the ground. Nevertheless, even smaller NEOs that detonate in the atmosphere generate fingerprints and can be detected empirically. The Tunguska impactor (~50 m) that exploded over Siberia in 1908 produced a strong signal in Greenland ice cores. Studies have shown a 4- to 20fold increase in the iridium concentration in Greenland ice from 1908. There can be little doubt in my mind that a large-scale disaster triggered by the impact of a 500 m wide comet would inevitably produce an even stronger cosmic signal in ice core records that should be easily identifiable - either in form of increased iridium or, alternatively, in significantly enhanced levels of cosmic dust particles. No such evidence - or indeed any physical evidence – for a major cosmic catastrophe in the 6th century has been detected. Even Key's super-eruption, global catastrophe theory suffers from a lack of compelling evidence. In short, as long as there is no empirical support, the 536 AD impact theory (as well as the contending mega-eruption, mega-drought or super-nova conjectures) should be looked upon as valid yet highly speculative hypotheses that are based on nothing more than circumstantial and anecdotal evidence. BJP.

CCNet 20/2004 - 11 February 2004

COMET IMPACT IN 536 AD?

Mark Kidger <mrk@iac.es>

Benny:

With reference to Michael Paine's clever reply (CCNet 6/02/2004) to my comments, he is quite right that absence of evidence is not equivalent to evidence of absence but, as in the Weapons of Mass Destruction debate, one prefers to have evidence. Similarly, in a court of law, a conviction does require proof and to argue that the fact that even one has no evidence it does not mean that a crime was committed by the man in the dock, is not going to convince many juries.

A serious charge has been brought before the court. Namely that a comet was responsible for an episode of dangerous driving that led to deaths and serious misery for many people. If Michael wishes to obtain a conviction he needs something better than circumstantial evidence, hearsay, and a good lawyer.

Mark Kidger

===========

THE 540 AD EVENT

Joel Keene <JJPerf@aol.com>

Dear Benny:

I am writing about the 540 event. I am a nonprofessional, but would like to mention a couple of coincidental connections between the 540 event discussion and past CCNet items.

1. There was an item awhile back about an asteroid on a "horseshoe orbit" that becomes an Earth moon every so often for about 50 years. The last time was 550 AD. This is awfully close to the 540 event. Coincidence?

2. There was another item awhile back concerning a suspected crater in the jungle of Bolivia. Given the rim still existed within a jungle zone, the assumption was that it couldn't be more than a few thousand years old. Since the hypothesis of the 540 event involves a large forest fire scenario, I was wondering if this crater has been dated. It would need to turn out to be only 1500 years old in order to fit the theory.

I was wondering if any of our learned colleagues could speak to these issues. Thank you for your time and your great list

Best Regards

Joel Keene

MODERATOR'S NOTE: The so-called Araona Structure is a suspected impact crater in northern Bolivia which is thought to have formed in the relatively recent geological past (age estimates range from ~5,000 - 20,000 BP). The round structure has not been confirmed yet as a hypervelocity impact crater, nor has its age been dated by scientific dating methods.

CCNet 21/2004 - 12 February 2004

COMET IMPACT IN 536 AD? THE DEBATE GOES ON

Michael Paine <mpaine@tpg.com.au>

Dear Benny (and Mark)

Just to clarify my position on this issue...

I have not researched the 536AD 'event' other than following the postings on CCNet. Subject to this limitation, it seems to me highly unlikely that there was a comet impact at that time. In any case, there are other plausible explanations for odd climate effects at that time.

Acknowledging Benny's footnote about the discovery of distal signatures of the Tunguska event, my main point is that evidence of impacts that could destroy cities is not going to be easy to find. It can be expected that land craters will rarely be associated with such events. Even larger impacts, that could disrupt agriculture for a few years, might not be readily identified if they impact the deep ocean.

regards

Michael Paine

-------

Benny Peiser <b.j.peiser@livjm.ac.uk>

Hi Michael

Thanks for the clarification. Just one other question: How could a large impact in the ocean trigger a climatic downturn but not be detectable in highly sensitive ice cores? I cannot follow your line of reasoning here. Surely, if significant amounts of debris/dust is thrown into the atmosphere so that climate is perturbed for a prolonged period of time, we should expect some fall-out? In any case, the Cardiff paper suggests an atmospheric impact of a 500m comet.

Regards

Benny

------------

Michael Paine <mpaine@tpg.com.au>

Benny

Again, I am no expert on this but I understand the (temporary) climatic effects of, say, a 1km asteroid or comet hitting the ocean would be severe enough to mildly disrupt global/hemispherical agriculture. Although a comet is largely water and so dust is less of a problem, the impact would propel large quantities of water vapour into the upper atmosphere, producing unwanted effects. The explosion would also produce compounds of nitrogen (from the atmosphere) and chlorine (from sea water) that would circulate in the atmosphere.

I am following with great interest, the search for evidence of a possible recent large ocean impact near New Zealand (Dallas Abbott).

A 500m comet, as mentioned in the Cardiff paper, would be much less dramatic but would still probably cause a climate hiccup - maybe like the Tambora volcanic explosion.

Mike

===========

DAVID KEYS' 536 AD VOLCANIC MEGA-ERUPTION THEORY

George Taylor <taylorgh@comcast.net>

Benny:

I read with interest the speculation on the event that occurred in about 540 AD which caused significant societal upheaval. Recently I read a fascinating book that gave a reasonable explanation for what happened:

Catastrophe: An Investigation into the Origins of the Modern World by David Keys (Ballantine Books; February 1, 2000)

Here's the description of the book from the publisher:

It was a catastrophe without precedent in recorded history: for months on end, starting in A.D. 535, a strange, dusky haze robbed much of the earth of normal sunlight. Crops failed in Asia and the Middle East as global weather patterns radically altered. Bubonic plague, exploding out of Africa, wiped out entire populations in Europe. Flood and drought brought ancient cultures to the brink of collapse. In a matter of decades, the old order died and a new world - essentially the modern world as we know it today - began to emerge.

In this fascinating, groundbreaking, totally accessible book, archaeological journalist David Keys dramatically reconstructs the global chain of revolutions that began in the catastrophe of A.D. 535, then offers a definitive explanation of how and why this cataclysm occurred on that momentous day centuries ago.

The Roman Empire, the greatest power in Europe and the Middle East for centuries, lost half its territory in the century following the catastrophe. During the exact same period, the ancient southern Chinese state, weakened by economic turmoil, succumbed to invaders from the north, and a single unified China was born. Meanwhile, as restless tribes swept down from the central Asian steppes, a new religion known as Islam spread through the Middle East. As Keys demonstrates with compelling originality and authoritative research, these were not isolated upheavals but linked events arising from the same cause and rippling around the world like an enormous tidal wave.

Keys's narrative circles the globe as he identifies the eerie fallout from the months of darkness: unprecedented drought in Central America, a strange yellow dust drifting like snow over eastern Asia, prolonged famine, and the hideous pandemic of the bubonic plague. With a superb command of ancient literatures and historical records, Keys makes hitherto unrecognized connections between the "wasteland" that overspread the British countryside and the fall of the great pyramid-building Teotihuacan civilization in Mexico, between a little-known "Jewish empire" in Eastern Europe and the rise of the Japanese nation-state, between storms in France and pestilence in Ireland.

In the book's final chapters, Keys delves into the mystery at the heart of this global catastrophe: Why did it happen? The answer, at once surprising and definitive, holds chilling implications for our own precarious geopolitical future. Wide-ranging in its scholarship, written with flair and passion, filled with original insights, Catastrophe is a superb synthesis of history, science, and cultural interpretation.

------------

Highly recommended!

George Taylor

-------------------------------------

George H. Taylor, CCM

State Climatologist, Oregon

2795 SW Fairmont Dr.

Corvallis OR 97333

(541) 757-1863

(541) 231-3761 cell

-------------------------------------

CCNet 23/2004 - 16 February 2004

COMET IMPACT OR VOLCANIC ERUPTION: WHAT HAPPENED IN AD 536-540?

Benny Peiser <b.j.peiser@livjm.ac.uk>

According to a widely reported article published in this month's Fortune Magazine (http://www.fortune.com/fortune/technology/articles/0,15114,582584,00.html), Pentagon researchers are said to be seriously concerned about the possibility of global cooling that could result in large-scale famine, social turmoil and worldwide upheaval.

If David Stipp is to be believed, the Pentagon's worries and contingency plans focus on the potential threat to the thermohaline circulation (the so-called oceanic "conveyor belt") that is widely believed to contribute to moderate climates in much of the northern hemisphere. Some climate modellers have speculated that rising temperatures could theoretically lead to catastrophic melting of the ice caps and increased river flows into the oceans which, in turn, could significantly dilute the oceans' salt content which may slow down the thermohaline circulation, which may lead to a fall in northern hemisphere temperatures which may result in the decline in agricultural food production, which may result in economic crisis and turmoil. In short, what we are talking about is a nightmare scenario of a highly improbable chain of events.

According worst case scenarios, the abrupt fall in global temperatures would cause massive droughts and agricultural collapse world-wide, "turning farmland to dust bowls and forests to ashes." Global instability, mass migration by hundreds of millions of refugees and social revolution in many parts of the world are foreseen in the event of such climate disaster. Given the minute probability for such an unlikely event, one starts to wonder whose expertise has gone into such alarmist predictions that are not even shared by most proponents of global warming catastrophism.

The problem with this type of apocalyptic speculation, of course, is that research on the oceanic conveyor belt and its dynamics is in its infancy. The data available is scarce and ambiguous. Conclusions drawn from them regarding its mechanism, duration and possible effects are far from certain. What is more, suspected past shutdowns of the thermohaline circulation have been exclusively associated with ice age conditions. Nevertheless, there are speculations that large-scale climate oscillations such as the Medieval Warm Period or the Little Ice Age could possibly be linked to the oscillations of the oceanic conveyor belt.

For many years, I have emphasised on this and other outlets that the potential risks from large-scale climate change - given past experiences - are basically due to episodes of global cooling. In contrast, periods of global warming have always been beneficial to societal progress and technological advancement. One of the major short-term coolings during the last 2,000 years occurred some 1500 years ago. The debate about the possible causes and effects of the AD 536-540 event has been going on since 1980. Most scientists content that a major volcanic eruption at around that time caused the climatic downturn. A number of British scientists, on the other hand, have raised the specter of a cosmic disaster in AD 536.

The proposition made is that a cometary impact triggering a global climate disaster brought down civilizations and set off a centuries-long Dark Age. This idea has recently been reinforced by Cardiff University’s Emma Rigby, Melissa Symonds and Derek Ward-Thompson (Astronomy & Geophysics, vol 45, Feb 2004; CCNet 4 February 2004).

The idea that a cosmic disaster may have caused global devastation some 1500 years ago is not entirely new. The conjecture was originally conceived in the early 1990s by Victor Clube and Bill Napier and later taken up and bolstered by Mike Baillie. The main evidence supportive of an environmental disaster around that time has been the discovery of narrow tree-rings in dendrochronological records found in numerous regions around the world. In fact, quite a number of “narrow tree-ring events” has been detected that are dated to BC 4370, BC 3195, BC 2350, BC 1628, BC 1159, BC 207, BC 44 and AD 540. The sheer number of such narror tree-ring events suggests that we may be dealing with recurrent abrupt cooling events.

Essentially all of these “events” have also been evidenced in form of major acidity peaks in Greenland and Antarctic ice cores that match the dendrochronological records. As a result, all of the narrow tree-ring events are strongly correlated with volcanic eruptions that are thought to have generated climatic downturns. While there is compelling evidence associated with volcanic activity, it remains contentious whether such eruptions can generate the catastrophic downfall of civilisations.

For many years there seemed to be what Mike Baillie has called an “ice core anomaly” for the AD 536-540 event. In 1980, researchers initially claimed to have found in Greenland ice cores an acidity peak dating to AD 540 +/-10. Four years later, however, this dating was revised to AD 516 +/-4 years. For many years, there seemed to be no evidence of a major volcanic eruption around AD 540.

It was this “anomaly” that used to be the main point of departure for the proposition that a cosmic impact could perhaps be the real trigger of the AD 536-540 narrow tree-ring event. Originally, the idea was based on the assumption that there is simply no evidence whatever for a volcanic eruption around the time in question. In the last five years, however, new ice core evidence has emerged that confirms at least one or two volcanic eruptions at almost exactly the crucial period in question. Thus, the ice-core "anomaly" seems to have been removed - in particular given that there is an inherent error margin of 1%-2% in the calculations of ice-core datings.

Accordingly, Rigby et al. do accept that there is compelling evidence for volcanic eruptions at around AD 536. The Cardiff authors question however whether the discovered acidity layers are good enough to evidence a super-eruption necessary to produce a prolonged global dust veil event. "None of these [ice core studies] has found evidence for a significant acid layer around 536 of the sort that would be caused by the eruption of a super-volcano." And since Rigby et al. doubt that the detected acid peaks are strong enough for a mega-eruption, they propose an alternative scenario - cometary impact.

In today’s CCNet, this debate is picked up by Mike Baillie (Queen’s University Belfast) and Max Wallis (Cardiff University). While Baillie stresses the ambiguity in ice core datings and questions David Keys’ reliance upon such data, Wallis points out that cometary dust particles would have to be part of the equation. After all, the whole theory is lacking scientific coherence as long as it fails to spell out what kind of physical evidence we should expect to find as a result of a global impact disaster in historical times.

For now, I remain sceptical that a 300 m wide comet would - Tunguska-like - disintegrate in the atmosphere. But let us consider, for arguments sake, an atmospheric impact of the proposed magnitude that is large enough that it can pertube the global climate for up to 5 years. It would still have to be detectable in the highly sensitive ice cores. A comet that size would deposit huge amounts of cosmic dust particles in the atmosphere. After a while, these dust particles would come down with the rain and the snow and would be deposited as a strong chemical signature in the world’s ice caps.

There are more questions raised by the Cardiff paper: Rigby et al. estimate that the atmospheric disintegration of a 300m wide comet would be able to produce a global climate disaster similar to the controversial 'nuclear winter' scenario. However, this inference conflicts with calculations that put the size threshold for objects capable of triggering a global disaster in the 1km - 2km bracket. The damage caused by the impact of a 300m wide asteroids, for instance, is generally thought to be regional. The authors also claim that impacts of 300 m NEOs occur on the Earth "once in several thousand years." Recent research by Bland and Artemieva (Nature, 424, 288 - 290, 2003), on the other hand, estimate that objects that size are likely to strike the Earth only once every 170,000 years or so.

Finally, it should be remembered that back in the early 1990s, when the AD 536 impact hypothesis was first developed, some researchers were under the impression that Tunguska-sized impacts occurred on average every 100 years while global impact catastrophes (in the range up to 10,000 megatons) occurred once every 5,000 years or so. Yet, during the last ten years, new observations and research findings have significantly reduced the probability for catastrophic impact disasters.

Everything considered, I conclude that the evidence for a cosmic impact at around AD 540 remains rather weak and circumstantial. The odds of an atmospheric impact happening at exactly the same time of the volcanic eruption that occurred at around AD 540 are minuscule indeed. Yet the question whether the "modest" acidity peak evidenced in the ice cores can also account for a severe climatic downturn that supposedly lasted for up to 5 years remains wide open for now.

Benny Peiser

=================

REPLY TO AD 540 RAMBLINGS

Mike Baillie <M.Baillie@Queens-Belfast.AC.UK>

Benny

I'm sure this 'debate' is stretching the patience/interest of CCNet readers. Take George Taylor's suggestion that David Keys' book Catastrophe that gives "a reasonable explanation for what happened". The simple answer is "no, it doesn't". Keys, a journalist with no primary data whatsoever, postulated that a supervolcano erupted in February AD 535. There is not a shred of evidence for this postulation, which in the accompanying TV film, was exposed as a suggestion that there had been a large eruption somewhere between 6000 BC and AD 1200. There is a chronological distinction between dating to a range of seven millennia and to a calendar month. Keys' abuse of a poorly dated eruption was to serve the purpose of rounding out the story in his book.

Moreover, his search for a volcanic vector to explain the global effects around AD 536-545 was because he had been led to believe that the scale of impactor necessary to cause the global effects was far too large, if my memory serves me correctly it had to be at least several Km in diameter.

Now Ward Thompson et al have shown that a mere half Km comet fragment would be enough to cause the downturn. Put simply, the reality of this debate has moved far beyond the stage when Michael Paine's comment "it seems to me highly unlikely that there was a comet impact at that time" is acceptable. There was a global event, the ice-core workers are at pains to stress there is no evidence in the ice cores for a volcano, thus, something else caused it. It now appears that a comet could do the business without leaving a crater nor indeed much physical evidence of any kind given the idea that the debris is blasted into a low orbit around the earth. Remember Bailey, Clube and Napier back in 1990 proposed that AD 400-600 was a period of risk of bombardment, so there is even a prior hypothesis.

Regards

Mike Baillie

=============

RE: DID A COMET AIRBURST TRIGGER GLOBAL COOLING IN 536 AD?

Max Wallis <wallismk@Cardiff.ac.uk>

Benny

Kjeld Engvild postulated (CCNet-ESSAY, 7 July 1999) that Tunguska-like airbursting comets might cause climatic excursions as evident in the decade long, worldwide narrowing of tree rings (Baillie 1995, 1999). Six episodes are well-dated: 540 AD, 44 BC, 207 BC, 1159 BC, 1628 BC and 2345 BC. Only that of 1628 BC may be explained by volcanism.

So what is new in the claim of Rigby et al. (CCNet 17/2004) for the 536-545 AD episode being caused by such an airburst? They say the tree ring narrowing corresponds to a 4% reduction in insolation decreasing global temperatures by 3 deg C and then make the crude estimate of comet dust input into the stratosphere of 10^11 tonnes. An alternative estimate was first given by Hoyle & Wickramasinghe (1978) that 100 times less dust made up of 10 times smaller particles could trigger global glaciation. The elementary structures of cometary dust aggregates, as identified in stratospheric collections from the 1970s, are around 100 nm, not the 1000 nm that Rigby et al. assume.

The dust is supposed to clear from the stratosphere on the decade timescale, so is the dust detected in the ice cores (~20 mg/sq cm for Rigby et al.)? Mark Kidger (CCNet 18/2004 ) doubts this since only a "modest acidity peak" has been detected. The super-volcano hypothesis of Dec. 2000 had a similar tonnage of debris ejected into the stratosphere so also failed the ice-core test. Is that test sensitive enough for 100 times less in submicron dust?

A veil of grains in the stratosphere does not simply deplete incoming sunlight, it also helps trap outgoing thermal radiation. Which is more important depends on the grain sizes and types - dielectric or absorbent - as recognised in the "nuclear winter" calculations cited in the article. H&W proposed porous dielectric grains of silicate or cellulose, which have low opacity in the infrared (1% of that in the visible). Only that way could the infra-red blanketing be low.

Comets do contain some mineral components, as the Halley spacecraft found, but dust particles were mainly the "CHON" ones composed of light elements. Heavy elements were less, in abundance relative to C as in the Sun. Do the carbonaceous particles survive the airburst blasting them into the stratosphere, or only the small fraction (~10 %) of mineral dust?

Unfortunately, Rigby et al. do not face such questions. They fail to take parameters consistent with current knowledge on cometary dust, so do not significantly advance the airburst hypothesis.

References

Baillie M 1999. Exodus to Arthur. Batsford London

Baillie MGL 1995. A slice through time: Dendrochronology and

precision dating. Batsford, London

Hoyle F & Wickramasinghe N C 1978 Astrophys.Space Sci. 53, 523-526.

-----------------------------------------------------------

Max Wallis wallismk@cf.ac.uk

Cardiff Centre for Astrobiology tel. 029 2087 6436

2 North Road fax 029 2087 6424

Cardiff University CF10 2DY

=============

NUCLEAR WINTER OF THE VI CENTURY

Pravda, 14 February 2004

http://english.pravda.ru/science/19/94/377/12060_earth.html

Scientists of Britain's Cardiff University claim that they discovered reasons of bad harvests and summer frosts approximately 1500 years ago.

Back then, a giant comet had struck the earth.

Researchers conducted a special dendrochronological analysis of those trees which had lived in the epoch of constants frosts in approximately 536-540 AD. The analysis indicated the effect of short-term nuclear winter. The results of the analysis have been published in February's issue of Astronomy and Geophysics.

The effect of nuclear winter has been a temporary one and did not last long. It resembled the effect when the comet Shoemaker-Levi 9 has rammed Jupiter in 1995.

Historic manuscripts of that period are known as "The Dark Century". They contain information about poor harvests and summer frosts.

Modeling showed that the comet which caused such drastic consequences in a form of extreme colds had been no larger than 500 meters in diameter. This is significantly smaller than was previously assumed.

It used to be considered that no celestial body of this size is capable to cause such catastrophic consequences on a global scale. The comet's fall resulted in mass crop failures in Europe and hunger among people of the sixth century. This period coincides with emergence of the so-called "Black Death" in Europe.

In order to prove this version however it is necessary to determine the estimated place of the comet's landing. This is a rather difficult task.

=========

DAVID KEYS: EVIDENCE FOR THE VOLCANIC ORIGIN OF THE AD 535/36 DUST-VEIL EVENT

From: David Keys (1999) Catastrophe: An Investigation into the Origins of the

Modern World. London: Century, pp. 270-272

“But there is another clinching piece of evidence which points away from a cosmic-impact explanation and towards a third option – a volcanic one. Buried up to 1,600 feet below the surface of the Greenland and Antarctic ice caps is a tell-tale layer of volcanic-originating sulphuric acid which was almost certainly associated with the 12-18-months-long sun-dimming event of 535/536 and the subsequent ‘nuclear winter’-style climatic chaos.

Back in 1978, a joint Danish/Swiss/US scientific team landed on the south-Greenland ice cap in several large freight aircraft specially fitted with giant skis. The planes – US military C130 Hercules – carried massive quantities of equipment, including generators, refrigeration unites, prefabricated living quarters – and a huge drill.

This latter piece of hardware was used to extract – in 6 ½ -foot lengths – some 1¼ miles of ice-core! In temperatures of between around 14 degrees Fahrenheit and minus 22 degrees Fahrenheit, engineers and scientists from Copenhagen University worked in three shifts, 24 hours a day, drilling deeper and deeper into the ice cap at roughly 400 feet per week.

Then, early in the second year of the operation, after just a few weeks of drilling, the team extracted some lengths of core covering the second quarter of the sixth century AD. Back in a laboratory at Copenhagen University, chemical analysis of the second-quarter sixth-century ice revealed that there had been two substantial volcanic eruptions. These same eruptions were then detected in a second core drilled in summer 1990 in central Greenland.

Because the dating of Greenland ice-cores at that time depths is only roughly accurate (say within 5-8 years, depending on the core concerned), the two cores each gave slightly different dates for the same sulphuric-acid layer. Dates are determined by simply counting back annual layers of snow – so unusually high precipitation can sometimes appear to add extra years, making an acid layer seem marginally older than it is. (...)

For eruption one, the high-altitude GRIP core gave an apparent date of 527, while the lower-altitude Dye 3 core (300 miles to the south) yielded an apparent date of 530. The volcanic explosion must have been very substantial; as evidence from the GRIP core shows that acidity rich snow was falling at the GRIP site in Greenland for more than two years and at the Dye 3 site for at least a year.

For eruption two, the high-altitude GRIP core provided an apparent date of 532, with acid snow falling on the site for just over a year. For this same eruption, the Dye 3 core yielded an apparent date of 534 and evidence of acid-snow falls of around four months.

The final clinching evidence, however, comes from 10,0000 miles to the south – from deep inside the Antarctic ice cap. For 660 feet below the windswept surface, scientists, again using ice-cores, discovered evidence of a truly massive volcanic eruption. The ice-cores material revealed that acid snow had cascaded down on the Antarctic for at least four years running. From the Antarctic ice-cores at that time depth there are no accurate dates available – only rough, 50-year-long ranges of dates. All that can be said is that the four-year-long acid-snow episode recorded in the core occurred some time between 490 and 540.

But by examining other first-millennium AD acid episodes – that is to say, other first-millennium AD eruptions – it is possible, by process of elimination, to conclude that the four-year acid episode must have been associated with the climatic catastrophe and probably with the 535 eruption itself. This is because the two chronologically adjacent Antarctic acid episodes were, respectively, in the 50-year brackets 231-281 and 614-664 – and because the four-year event which occurred in the 490-540 bracket is by far the biggest event recorded in Antarctica for the whole of the first millennium AD.

It is very likely, therefore, that the four-year acid episode in the Antarctic core and the two-year ‘527/530’ Greenland episode (or, much less likely, the ‘532/534’ Greenland episode) record the same atmospheric-polluting, climate-changing event recorded historically and in

tree-ring terms for 535/36.

Alternatively, though much less likely, the four-year Antarctic event could record a second totally separate (or indeed connected) volcanic eruption destabilizing southern hemisphere climate around 54- - and helping to further destabilize northern hemisphere weather, already thrown into chaos by the 535 event. The second Greenland acid signal 532/534 +/- 5-8 years could conceivably, in this alternative though less likely scenario, have been generated by such a 540 second eruption.

===========

WERE THE DARK AGES TRIGGERED BY VOLCANO-RELATED CLIMATE CHANGE IN THE 6TH CENTURY? IF SO, WAS KRALATAU THE CULPRIT?

Ken Wohletz

http://www.ees1.lanl.gov/Wohletz/Krakatau.htm

Los Alamos National Laboratory

LA-UR 00-4608

Modern history has its origins in the tumultuous 6th and 7th centuries. During this period agricultural failures and the emergence of the plague contributed to: (1) the demise of ancient super cities, old Persia, Indonesian civilizations, the Nasca culture of South America, and southern Arabian civilizations; (2) the schism of the Roman Empire with the conception of many nation states and the re-birth of a united China; and (3) the origin and spread of Islam while Arian Christianity disappeared. In his book, Catastrophe An Investigation into the Origins of the Modern World, author David Keys explores history and archaeology to link all of these human upheavals to climate destabilization brought on by a natural catastrophe, with strong evidence from tree-ring and ice-core data that it occurred in 535 AD.

With no supporting evidence for an impact-related event, I worked with Keys to narrow down the possibilities for a volcanic eruption that could affect both hemispheres and bring about several decades of disrupted climate patterns, most notably colder and drier weather in Europe and Asia, where descriptions of months with diminished sun light, persistent cold, and anomalous summer snow falls are recorded in 6th-century written accounts.

Writings from China and Indonesia describe rare atmospheric phenomena that possibly point to a volcano in the Indonesian arc. Although radiocarbon dating of eruptions in that part of the world are spotty, there is strong bathymetric and volcanic evidence that Krakatau might have experienced a huge caldera eruption. Accordingly, I encouraged a scientific expedition to be led by Haraldur Sigurdsson to the area. The expedition found a thick pyroclastic deposit, bracketed by appropriate radiometric dates, that suggests such a caldera collapse of a “Proto-Krakatau” did occur perhaps in the 6th century.

Bathymetry indicates a caldera some 40 to 60 km in diameter that, with collapse below sea level, could have formed the Sunda Straits, separating Java from Sumatra, as suggested by ancient Javanese historical writings. Such a caldera collapse likely involved eruption of several hundred cubic kilometers of pyroclastic debris, several times larger than the 1815 eruption of Tambora. This hypothetical eruption likely involved magma-seawater interaction, as past eruptions of Krakatau document, but on a tremendous scale. Computer simulations of the eruption indicate that the interaction could have produced a plume from 25 to >50 km high, carrying from 50 to 100 km3 of vaporized seawater into the atmosphere.

Although most of the vapor condenses and falls out from low altitudes, still large quantities are lofted into the stratosphere, forming ice clouds with super fine (<10 mm) hydrovolcanic ash. Discussions with global climate modelers at Los Alamos National Laboratory led me to preliminary calculations that such a plume of ash and ice crystals could form a significant cloud layer over much of the northern and southern hemispheres. Orders of magnitude larger than previously studied volcanic plumes, its dissipation and impact upon global albedo, the tropopause height, and stratospheric ozone are unknown but certainly within possibilities for climate destabilization lasting years or perhaps several decades. If this volcanic hypothesis is correct, the global, domino-like affects upon epidemics, agriculture, politics, economics, and religion are far-reaching, elevating the potential role of volcanism as a major climate control, and demonstrating the intimate link between human affairs and nature.

Wohletz KH, 2000, Were the Dark Ages triggered by volcano-related climate changes in the 6th century? EOS Trans Amer Geophys Union 48(81), F1305.

FULL PAPER at http://www.ees1.lanl.gov/Wohletz/Krakatau.htm

CCNet 18 February 2004

NEW ICE CORE EVIDENCE FOR AD 536 EVENT RULES OUT IMPACT

Michael Robert Rampino mrr1@nyu.edu

Benny:

Claus Hammer and his co-workers have now substantiated and redated the volcanic ice-core peak that Richard Stothers and I believed for many years to be associated with the
dim sun conditions of AD 536.

There is absolutely no physical evidence for a comet impact or airburst at that time, so speculation about this "impact event" should now end.

Mike

Dr. Michael R. Rampino

Associate Professor

Earth & Environmental Science Program

New York University

100 Washington Square East Room 1009

New York, NY 10003

212-998-3743; Fax 212-995-4015

==========
SIXTH CENTURY DARK AGES? WHAT DARK AGES?

Gunnar Heinsohn gheins@uni-bremen.de

Hagia Sophia was built by Isidoros and Anthemios in Byzantium from 532 to 537. In 563 the master piece was struck by an earthquake under which the highest dome fell. It was immediately replaced with a higher profile than the original. Thus, history records, at least locally, some impact in 563. It was not a very big one though and definitively not the onset of a dark age but the occasion for a better building.

Gunnar Heinsohn

===============
VELA SUPERNOVA AND THE LITTLE ICE AGE

James A. Marusek tunga@custom.net

Dear Benny

The articles on CCNet 23/2004 of 16 February 2004 debated whether the triggering agent behind the Dark Ages was either a super-volcano or an atmospheric comet impact. The debate ignored the hypothesis that ice age events are generally caused by nearby supernova events. Probably the clearest evidence of this theory at work can be seen in the Little Ice Age. The Little Ice Age spanned the period ~1350AD or 1450AD (depending on the measurement type) to around 1900AD. This correlates very well with the nearest supernova event experienced during modern times.

Around the year 1320AD a type II supernova occurred 650 light years from Earth. A star exploded in the southern sky in the constellation Vela. It produced light as bright as a full moon and was visible for several months in broad daylight to those who inhabited the Southern Hemisphere. The supernova is referred to as RX J0852.0-4622 (also called GRO J0852-4642). The supernova event produced a surge of cosmic rays. Most galactic cosmic rays have energies in the range of 100 MeV to 10 GeV. The higher energy particles 10 eV began bombarding Earth within 3 years. Those in the 1 GeV range hit within 85 years. What these particles lacked in energy they made up for with quantity. There were 50 times more particles striking Earth during this period. Around 370 years after the event (~1700AD) the lower energy charge particles 100 MeV began striking Earth's atmosphere. The cosmic ray flux rate was modulated by variations in the magnetic field of the Earth and Sun. As the energy range of cosmic rays fell below 100 MeV, magnetic field shielding began to cut off the activity.

Galactic cosmic rays collide with the atmosphere producing nitrogen dioxide. This reddish-brown gas partially block sunlight from reaching the Earth's surface causing a drop in global temperatures.

Sincerely
James A. Marusek

MODERATOR'S NOTE: There is some speculation but no compelling evidence that "nearby" supernovae have ever had any detrimental effect on the terrestrial environment or human evolution. Besides, the dating of the RX J0852.0-4622 event is extremely uncertain and contentious. A number of researchers are suggesting that the initial, tentative date calculated for the event if off by a margin in the order of tens of thousands of years; see

http://xxx.lanl.gov/abs/astro-ph/0011554;
http://xxx.lanl.gov/abs/astro-ph/0010510

==============
SOUTHERN OCEAN IMPACT AND THE DARK AGES

Nick Sault nick@e-writers.org

Hi Benny

At this moment teams of scientists are trudging through the bush in Stewart Island, the wind-swept island just south of New Zealand's main islands. They are there to confirm that within the last millennium, and possibly half-millennium, an asteroid 500m wide hit the southern ocean and its tsunami washed ocean debris onto the high coastal regions of this beautiful island.

If this is confirmed, does it not make nonsense of David Morrison's "one Tunguska every 1000 years"? You yourself said "Yet, during the last ten years, new observations and research findings have significantly reduced the probability for catastrophic impact disasters". I understand that for every increase by 10 in the diameter of an asteroid (hence 1000 times volume), the "rarity factor" increases by 100. If this is the case and this New Zealand impacter is found to be a reality, it will make a mockery of the figures.

Then we would hope that the 560 AD cataclysm was not due to an impact. OK, it was more than 1000 years ago, but again it would have had to have been thousands of times larger than the Tunguska object, thus making even more mockery of Morrison's estimate.

I have been looking closely at Mars photos taken from the orbiters, and note a strange distribution of craters. Has anybody performed a statistical analysis of the spread of craters on Mars. I am talking about the craters in the relatively sparsely cratered areas. It is easy to spot the new craters as the old ones are partially buried. If you look closely at the new, nicely rounded craters, you notice that they seem to be either grouped in a sort of spatter pattern, or there is a train of them. Maybe what I am seeing is a random pattern, and my "intelligent eye" is finding groups, but it does concern me that there seems to be the possibility that some of these bodies travel in close formation or trains.

If this is the case, then Spaceguard's impact guesstimates based on the detection of lone asteroids may be way off. If a blind man throws a handful of darts, he is more likely to hit the bullseye, is he not?

This scenario is of course being considered with the great dinosaur extinction; that there was more than one impactor at that time.

Also, in regard to the likelihood of a volcanic eruption at the same time as an asteroid/comet impact in 560 AD, aren't there some places in the world where the impact of a one kilometer asteroid would set off lava eruptions? I know that recent research has postulated that giant impactors have the potential to break through the crust and create a hotspot, but there are weaker crustal areas. I am thinking again of my own country. In North Island New Zealand, the Taupo/Rotorua region is a bubbling wonderland. You can hear and feel the thermal activity right under your feet. Surely a hit in a region like this, even from a moderate sized asteroid, would release all that energy into the atmosphere?

I am not a geologist, so any geologists out there please shoot me down. But anyway, Benny, you must admit that if the 1500 AD impact down here is confirmed, and worse still if the AD 560 one is also confirmed, the impact statistics are blown to pieces. Let's hope neither or these impacts happened. If they did then we certainly should channel that one trillion dollars for a manned Mars mission into saving humanity from the next big one.

Nick Sault

Technical Writing Specialist

E-Writers NZ Ltd

nick@e-writers.org

MODERATOR'S NOTE: I admit that *if* - or better *IF* both the suggested impact event in AD 540 and the AD 1500 oceanic impact were to be confirmed, we would have to seriously
revise the currently accepted impact rate estimates. However, new ice core records have essentially ruled out the AD 540 impact theory, as Michael Rampino points out in his letter
above. Other researchers have also raised serious doubts and reservations about the suggested AD 1500 impact hypothesis. It will be important to monitor whether the suggested 20km impact
crater and its youngish date can be confirmed by the current expedition. With regards to Mars, there is nothing unusual about the impact cratering record on its surface. Since Mars lacks Earth-like erosion processes, some Mars regions are heavily bombarded. Yet most of these impact craters are extremely old (~4.2-4.0 billion years). Given the age of the younger and lightly bombarded surface of other Mars regions, it is obvious that the impact rate has drastically decreased since the period of early heavy bombardment. BJP.

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