Wednesday, March 19, 2008
Volcanic Eruptions Caused Climate Disruption
We've published several articles about this subject in Random Round-up at Goddesschess. It's a topic I find fascinating, especially through analyzing ice cores. This is from the National Geographic: Ancient Global Dimming Linked to Volcanic Eruption Ker Thanfor 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. 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. (Related story: "New Digs Decoding Mexico's Pyramids of Fire'" [October 21, 2005].) 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." "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."