Piora Oscillation
The Piora Oscillation was an abrupt cold and wet period in the climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 history of the Holocene Epoch; it is generally dated to the period of c. 3200 to 2900 BCE. Some researchers associate the Piora Oscillation with the end of the Atlantic climate regime, and the start of the Sub-Boreal, in the Blytt-Sernander
The Blytt-Sernander classification, or sequence, is a series of north European climatic periods or phases based on the study of Danish peat bogs by Axel Blytt and Rutger Sernander...

 sequence of Holocene climates.

The spatial extent of the change is unclear; it does not show up as a major, or even identifial, event in hemispheric temperature reconstructions

The phenomenon is named after the Val Piora or Piora Valley in Switzerland, where it was first detected; some of the most dramatic evidence of the Piora Oscillation comes from the region of the Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

. Glaciers advanced in the Alps, apparently for the first time since the Holocene climatic optimum
Holocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

; the Alpine tree line dropped by 100 meters. Yet the climate change extended far beyond the Alps and Europe. It affected what is now the New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

 region of North America, where hemlock
Tsuga is a genus of conifers in the family Pinaceae. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock....

 and elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...

 trees suffered a dramatic decline. Similar evidence comes from California and elsewhere; some changes in flora proved permanent . In the Middle East, the surface of the Dead Sea
Dead Sea
The Dead Sea , also called the Salt Sea, is a salt lake bordering Jordan to the east and Israel and the West Bank to the west. Its surface and shores are below sea level, the lowest elevation on the Earth's surface. The Dead Sea is deep, the deepest hypersaline lake in the world...

 rose nearly 100 meters (300 feet), then receded to a more usual level. A few commentators have associated the climate changes of this period with the end of the Uruk period
Uruk period
The Uruk period existed from the protohistoric Chalcolithic to Early Bronze Age period in the history of Mesopotamia, following the Ubaid period and succeeded by the Jemdet Nasr period. Named after the Sumerian city of Uruk, this period saw the emergence of urban life in Mesopotamia. It was...

, as a Dark Age associated with the floods of the Gilgamesh
Gilgamesh was the fifth king of Uruk, modern day Iraq , placing his reign ca. 2500 BC. According to the Sumerian king list he reigned for 126 years. In the Tummal Inscription, Gilgamesh, and his son Urlugal, rebuilt the sanctuary of the goddess Ninlil, in Tummal, a sacred quarter in her city of...

 epic and Noah's flood
Noah's Ark
Noah's Ark is a vessel appearing in the Book of Genesis and the Quran . These narratives describe the construction of the ark by Noah at God's command to save himself, his family, and the world's animals from the worldwide deluge of the Great Flood.In the narrative of the ark, God sees the...

 of the Book of Genesis.

The Piora Oscillation has also been linked to the domestication of the horse. In Central Asia
Central Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...

, 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." 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.

The cause or causes of the Piora Oscillation are debated. A Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 ice core
Ice core
An ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...

Greenland Ice Sheet Project
The Greenland Ice Sheet Project was a decade-long project to drill ice cores in Greenland that involved scientists and funding agencies from Denmark, Switzerland and the United States. Besides the U.S. National Science Foundation, funding was provided by the Swiss National Science Foundation and...

, shows a sulfate spike and methane trough c. 3250 BCE, suggesting an unusual occurrence — either a volcanic eruption
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 or a meteor
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

 or an asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

 impact event
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...

. Other authorities associate the Piora Oscillation with other comparable events, like the 8.2 kiloyear event
8.2 kiloyear event
The 8.2 kiloyear event is the term that climatologists have adopted for a sudden decrease in global temperatures that occurred approximately 8,200 years before the present, or c. 6,200 BCE, and which lasted for the next two to four centuries...

, that recur in climate history, as part of a larger 1500-year climate cycle.

See also

  • 1500-year climate cycle
  • 22nd century BC drought
  • Bølling-Allerød
    The Bølling-Allerød interstadial was a warm and moist interstadial period that occurred during the final stages of the last glacial period. This warm period ran from c. 14,700 to 12,700 years before the present...

  • Neolithic Subpluvial
    Neolithic Subpluvial
    The Neolithic Subpluvial — sometimes called the Holocene Wet Phase — was an extended period of wet and rainy conditions in the climate history of northern Africa...

  • Older Peron
    Older Peron
    The Older Peron transgression was a period of unusually warm climate during the Holocene Epoch. It began in the 5000 BCE to 4900 BCE era, and lasted to about 4100 BCE...

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