The Piora Oscillation was an abrupt cold and wet period in the

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...

history of the Holocene Epoch; it is roughly dated to c. 3900-3000 BC. 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 sequence of Holocene climates. The spatial extent of the change is unclear; it does not show up as a major, or even identifiable, event in hemispheric temperature reconstructions.

First detection

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 () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...

. Glaciers advanced in the Alps, apparently for the first time since the

Holocene climatic optimum The Holocene Climate Optimum (HCO) was a warm period that occurred in the interval roughly 9,000 to 5,000 years ago BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimu ...

; the Alpine tree line dropped by 100 meters. In the Middle East, the surface of the

Dead Sea The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Ban ...

rose nearly 100 meters (300 feet), then receded to a more usual level. A few commentators have associated the

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

s of this period with the end of the

Uruk period The Uruk period (ca. 4000 to 3100 BC; also known as Protoliterate period) existed from the protohistoric Chalcolithic to Early Bronze Age period in the history of Mesopotamia, after the Ubaid period and before the Jemdet Nasr period. Named af ...

, as a Dark Age associated with the floods of the

Gilgamesh sux, , label=none , image = Hero lion Dur-Sharrukin Louvre AO19862.jpg , alt = , caption = Possible representation of Gilgamesh as Master of Animals, grasping a lion in his left arm and snake in his right hand, in an Assy ...

epic and

Noah's flood The Genesis flood narrative (chapters 6–9 of the Book of Genesis) is the Hebrew version of the universal flood myth. It tells of God's decision to return the universe to its pre- creation state of watery chaos and remake it through the micro ...

of the

Book of Genesis The Book of Genesis (from Greek ; Hebrew: בְּרֵאשִׁית ''Bəreʾšīt'', "In hebeginning") is the first book of the Hebrew Bible and the Christian Old Testament. Its Hebrew name is the same as its first word, ( "In the beginning" ...

Link to horse domestication

The Piora Oscillation has also been linked to the

domestication of the horse A number of hypotheses exist on many of the key issues regarding the domestication of the horse. Although horses appeared in Paleolithic cave art as early as 30,000 BCE, these were wild horses and were probably hunted for meat. How and when ho ...

. In

Central Asia Central Asia, also known as Middle Asia, is a region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes the fo ...

, 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 Eastern Mediterranean is a loose definition of the eastern approximate half, or third, of the Mediterranean Sea, often defined as the countries around the Levantine Sea. It typically embraces all of that sea's coastal zones, referring to commun ...

, 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 Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ...

GISP2 The Greenland Ice Sheet Project (GISP) 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 (NSF), f ...

, shows a sulfate spike and methane trough c. 3250 BCE, suggesting an unusual occurrence — either a

volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...

or a

meteor A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...

or an

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or ...

. Other authorities associate the Piora Oscillation with other comparable events, like the

8.2 kiloyear event In climatology, the so-called "8.2-kiloyear event" was a sudden decrease in global temperatures that occurred approximately 8,200 years before the present ( BP), that is, 6,251 BC. It defines the start of the Northgrippian age in the Holocen ...

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

Notes

References

* * * * * * *{{cite journal , last=Wick , first=Lucia , author2=Tinner, Willy , year=1997 , title=Vegetation Changes and Timberline Fluctuations in the Central Alps as Indicators of Holocene Climatic Oscillations , journal=Arctic and Alpine Research , volume=29 , issue=4 , pages=445–458 , jstor=1551992, doi=10.2307/1551992 4th millennium BC History of climate variability and change Historical eras Uruk period

First detection

Link to horse domestication

Causes

See also

Notes

References