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The '8.2 kiloyear event' is the term that climatologists have adopted for a sudden decrease in global temperatures that occurred approximately 8200 years before the present, or c. 6200 BCE, and which lasted for the next two to four centuries. Milder than the Younger Dryas cold spell that preceded it, but more severe than the Little Ice Age that would follow, the 8.2 kiloyear cooling was a significant exception to general trends of the Holocene climatic optimum.
The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in Greenland ice cores and in sedimentary and other records of the temporal and tropical North Atlantic. It is less evident in ice cores from Antarctica and in South American indices.^[1] The effects of the cold snap were global, however, most notably in changes in sea level during the relevant era.
The cooling event of 6200 BCE may have been caused by a large meltwater pulse from the shrinking but still massive Laurentide ice sheet of northeastern North America — most likely when the glacial Lake Ojibway suddenly drained into the North Atlantic Ocean.^[2] (The same type of action produced the Missoula floods that created the Channeled scablands of the Columbia River basin.) The meltwater pulse adversely effected the Gulf Stream and the global thermohaline circulation regulating the Earth's climate regime (an instance of warming causing cooling). Cooling occurred to 5-6°C (9-11°F) in the temperate zones, and 3°C (5°F) in the tropics: "cores drilled into an ancient coral reef in Indonesia show an abrupt sea surface cooling of about 3 degrees Centigrade."^[3] Cooler and drier conditions prevailed, again as in the Younger Dryas though less extreme. Yet the changes were severe enough to impact the earliest settled human communities: the first phase of Catal Huyuk ended during the 8.2 kiloyear event. The site was abandoned and not re-occupied until about 5 centuries later, when climate conditions had improved markedly.
Drier conditions were notable in North Africa, while East Africa suffered five centuries of general drought. The initial meltwater pulse raised sea levels by as much as 1.2 meters (4 ft.), but the cooling that followed allowed a glacial advance and consequent marine regression. After 2 centuries, or by 8000 ybp (6000 BCE), global sea level had dropped by 14 meters (40 ft.). After that point, however, milder climate conditions re-asserted themselves; by 7800 ybp (5800 BCE) the global climate returned to the clement conditions that prevailed during the Holocene climatic optimum.
In 2003, the Office of Net Assessment at the U. S. Department of Defense was commissioned to produce a study on the likely and potential effects of a modern climate change. The study, conducted under ONA head Andrew Marshall, modelled its prospective climate change on the 8.2 kiloyear event, precisely because it was the middle alternative between the Younger Dryas and the Little Ice Age. The study caused a controversy when it was made public in 2004.^[4]

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See also

References

See also

★ Sahara pump theory

★ 1500-year climate cycle

★ Antarctic Cold Reversal

★ Little Ice Age

★ Older Peron

★ Piora Oscillation

★ Younger Dryas

References

1. Burroughs, William J., ed. ''Climate: Into the 21st Century.'' Cambridge, Cambridge University Press, 2003.
2. Ehlers, Jūrgen, and Philip L. Gibbard. ''Quarternary Glaciations – Extent and Chronology. Part II: North America.'' Amsterdam, Elsevier, 2004; pp. 257-62.
3. Fagan, Brian. ''The Long Summer: How Climate Changed Civilzation.'' New York, Basic Books, 2004; pp. 107-8.
4. Stipp, David. "The Pentagon's Weather Nightmare". ''Fortune'', February 9, 2004, pp. 100-8.