Posted on 03/19/2008 2:36:03 PM PDT by blam
Ancient Global Dimming Linked to Volcanic Eruption
Ker Than
for National Geographic News
March 19, 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.
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 effects.
"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."
Light Pollution Reduction Initiative !
Only a few letter off of what I think of Al Gore and his ilk.
Ping for after choir.
It’s quite intersting how many ways man or nature could conspire to knock 100 - 200 years of technology right out from under us. Or kill off 50% of the human race in a few years.
So where is the caldera? A crater larger than Tambora between 23N and 23S can’t be that hard to find.
Ring around the rosie, pocket full of posies, ashfall, ashfall, we all fall down....
susie
OK, smart guys, WHERE WAS THE VOLCANO?
Something of this magnitude could not have happened without leaving some serious clues as to its origin. Or perhaps it was an undersea eruption, maybe somewhere in the Bering Sea?
Interesting post - thanks!
Wait, I thought that driving around SUVs jacked up the temperature by many degrees. Now they say that there is nothing we can do to prevent the earth from cooling in case of a major volcanic eruption? I'm confused.
What is the expected rate of major volcanic eruptions per century? Is there any chance that we are below that rate which would account for any warming? I think Krakatoa in 1883 was the last one which had a major world wide effect on climate.
The book about this event is “Catastrophe”, written back aways. The author thinks the volcanoe that blew was in the area where Krakatau is now, and argued the eruption severed Java from Sumatra and created the Sunda Straits.
Carrier pigeons darkened the sky and buffalo darkened the prairie and ate all the corn.
Well, the abstract for the paper doesn’t say anything about candidate volcanoes. I’ll have to read the whole thing when I stop by the library.
Krakatau was proposed as a candidate and a PBS documentary made about “Catastrophe” but it’s not generally accepted.
I think there are some other 535 candidates, wikipedia mentions Rabaul caldera in the Solomons as a candidate.
China suffered for about 300 years. Byzentium was down for the count for at least 80 years.
Other areas, e.g. the realm of the Arabs who looked to Mecca for economic direction, didn't notice anything had gone wrong (relative to their earlier condition). They ended up conquering pretty much the rest of remaining civilization.
There were losses beyond imagining ~ for example, Michaelangelo was the first artist in a millenum who could produce sculpture the equal of the best produced by sculptors in Classical Times.
That's how much knowledge of that particular technology (sculpting) that had been lost.
A global catastrophe story that does NOT mention “global warming” ...
Oh. I see.
That's because it shows that climate changed naturally BEFORE us evil American capitalists spoiled the earth and killed all living things.
A global climate story that does NOT mention CO2 levels.
Oh. I see.
That's because it shows more evidence of (short-term) cooling in the Dark Ages, BEFORE the US emitted all those evil pollutants. (Of course, the LONG-TERM role of the varying solar output that actually CAUSED the Dark Ages, Medieval Warm Period, and Little Ice Age ARE NOT mentioned.
Bush’s great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandfather’s fault.
Thanks much for the post. As to where the supervolcano might have been ... the Gulf of Mexico, and in fact the whole of the Caribbean, seems to have a caldera shape. Any geologic studies been done on that, other than the possible meteor strike near the Yucatan peninsula?
I wish them luck, getting really crowded with volcanoes out there, the more we look the more we find.
“...the Bering Sea...”
That’s what I was thinking, somewhere in the northwest portion of North America. A sample of the ash is probably sitting in a storage drawer of some University in either Canada or the U.S.
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