Piora Oscillation

The Piora Oscillation was an unusually cold and wet period that occurred during the Holocene, between around 3900 BC to 3000 BC. It is named after the Val Piora, in the south of Switerland. It can best be seen in the Alps.Lamb, pp. 124, 128, 143. Glaciers advanced in the Alps, apparently for the first time since the Holocene climatic optimum; the Alpine tree line dropped by 100 meters. In the Middle East, the surface of the Dead Sea rose nearly 100 meters (300 feet), then receded to a more usual level. It also triggered the collapse of the Uruk period, through decreased temperatures and increased rainfall, which were believed to contribute to Babylonian and Hebrew flood myths.Lamb, p. 128.

 Link to horse domestication 
The Piora Oscillation has also been linked to the domestication of the horse. In Central Asia, a colder climate favored the use of horses: "The horse, since it was so adept at foraging with snow on the ground, tended to replace cattle and sheep."Matossian, p. 43. The Piora period seems associated with a period of colder drier air over the Western and Eastern Mediterranean, and may have depressed rainfalls as far afield as the Middle East. It is also associated with a sudden onset of drier weather in the central Sahara.

 Causes 
The cause or causes of the Piora Oscillation are debated. A Greenland ice core, GISP2, shows a sulfate spike and methane trough c. 3250 BCE, suggesting an unusual occurrence — either a volcanic eruption or a meteor or an asteroid impact event. Other authorities associate the Piora Oscillation with other comparable events, like the 8.2 kiloyear event, that recur in climate history, as part of a larger 1500-year climate cycle.

It may also be caused by changes in solar activity and orbital parameters. 

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Category:4th millennium BC