8.2 kiloyear event
Encyclopedia
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. 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
. During the event, atmospheric methane concentration decreased by 80 ppb or 15% emission reduction by cooling and drying at a hemispheric scale.
A rapid cooling around 6200 BCE was first identified by Swiss
botanist Heinrich Zoller in 1960, who named the event Misox oscillation (for the Val Mesolcina
). It is also known as Finse event in Norway. Bond et al. argued that the origin of the 8.2 kiloyear event is linked to a 1,500-year climate cycle
; it correlates with Bond event
5.
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. The effects of the cold snap were global, however, most notably in changes in sea level
during the relevant era.
The 8.2 Ka cooling event may have been caused by a large meltwater pulse from the final collapse of the Laurentide ice sheet
of northeastern North America—most likely when the glacial lakes Ojibway
and Agassiz
suddenly drained into the North Atlantic Ocean. (The same type of action produced the Missoula floods
that created the Channeled scablands
of the Columbia River
basin.) The meltwater pulse may have affected the North Atlantic thermohaline circulation
, reducing northward heat transport in the Atlantic and causing significant circum-North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but drops of around 1 to 5 °C (1 to 11 °F) have been reported. In Greenland, the event started at 8175 Before Present, and the cooling was 3.3 °C (decadal average) in less than ~20 years, and the coldest period lasted for about 60 years, and the total duration was about 150 years. Further afield, some tropical records report a 3 °C (5 °F) cooling from cores drilled into an ancient coral reef
in Indonesia
.
The event also caused a global CO2 decline of ~ 25 ppm over ~ 300 years. However, the dating and interpretation of this and other tropical sites are more ambiguous than the North Atlantic sites.
Drier conditions were notable in North Africa
, while East Africa
suffered five centuries of general drought
. In West Asia and especially Mesopotamia
, the 8.2ky event was a three-hundred year aridification and cooling episode, which provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life. However multi-centennial changes around the same period are difficult to link specifically to the approximately 100-year abrupt event as recorded most clearly in the Greenland ice cores.
The initial meltwater pulse has caused between 0.5 and 4 meters of sea-level rise. Based on estimates of lake volume and decaying ice cap size, values of 0.4–1.2 meters (1–4 ft) circulate. Based on sea-level data from below modern deltas 2–4 (6–12 ft) meters of near-instantaneous rise is estimated, recorded superimposed on background 'normal' post-glacial sea-level rise. Meltwater pulse sea level rise was experienced fully at great distance from the release area. Gravity and rebound effects associated to the shifting of watermasses mean that the sea-level fingerprint is smaller in areas closer to the Hudson Bay. The Mississippi delta records ~20%, NW Europe records ~70% and Asia records ~105% of the global averaged amount. The cooling of the 8200 event was a temporary feature, the sea-level rise of the meltwater pulse was permanent.
In 2003, the Office of Net Assessment
at the United States 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.
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
have adopted for a sudden decrease in global temperatures that occurred approximately 8,200 years before the present, or c. 6,200 BCE
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
, and which lasted for the next two to four centuries. Milder than the Younger Dryas
Younger Dryas
The Younger Dryas stadial, also referred to as the Big Freeze, was a geologically brief period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP, or 12,800 and 11,500 years before present...
cold spell that preceded it, but more severe than the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...
that would follow, the 8.2 kiloyear cooling was a significant exception to general trends of 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...
. During the event, atmospheric methane concentration decreased by 80 ppb or 15% emission reduction by cooling and drying at a hemispheric scale.
A rapid cooling around 6200 BCE was first identified by Swiss
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
botanist Heinrich Zoller in 1960, who named the event Misox oscillation (for the Val Mesolcina
Val Mesolcina
The Misox is an alpine valley of the Grisons, Switzerland, stretching from the San Bernardino Pass to Grono where it joins the Calanca Valley...
). It is also known as Finse event in Norway. Bond et al. argued that the origin of the 8.2 kiloyear event is linked to a 1,500-year climate cycle
Climate cycle
A climate cycle is a type of recurring climate pattern that involves natural cyclic variations in the Earth's surface temperature, as indicated by temperature proxies found in glacier ice, sea bed sediment, tree ring studies or otherwise....
; it correlates with Bond event
Bond event
Bond events are North Atlantic climate fluctuations occurring every ≈1,470 ± 500 years throughout the Holocene. Eight such events have been identified, primarily from fluctuations in ice-rafted debris. Bond events may be the interglacial relatives of the glacial Dansgaard–Oeschger events, with a...
5.
The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in Greenland
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 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. The effects of the cold snap were global, however, most notably in changes in sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
during the relevant era.
The 8.2 Ka cooling event may have been caused by a large meltwater pulse from the final collapse of the Laurentide ice sheet
Laurentide ice sheet
The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacial epochs. It last covered most of northern North America between c. 95,000 and...
of northeastern North America—most likely when the glacial lakes Ojibway
Glacial Lake Ojibway
Glacial Lake Ojibway was a prehistoric lake in what is now Northern Ontario and Quebec in Canada. Ojibway was the last of the great proglacial lakes of the last ice age. Comparable in size to Lake Agassiz , and north of the Great Lakes, it was at its greatest extent c. 8,500 years BP.Lake Ojibway...
and Agassiz
Lake Agassiz
Lake Agassiz was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined, and it held more water than contained by all lakes in the world today.-Conception:First...
suddenly drained into the North Atlantic Ocean. (The same type of action produced the Missoula floods
Missoula Floods
The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...
that created the Channeled scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...
of the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...
basin.) The meltwater pulse may have affected the North Atlantic thermohaline circulation
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....
, reducing northward heat transport in the Atlantic and causing significant circum-North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but drops of around 1 to 5 °C (1 to 11 °F) have been reported. In Greenland, the event started at 8175 Before Present, and the cooling was 3.3 °C (decadal average) in less than ~20 years, and the coldest period lasted for about 60 years, and the total duration was about 150 years. Further afield, some tropical records report a 3 °C (5 °F) cooling from cores drilled into an ancient coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
in Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
.
The event also caused a global CO2 decline of ~ 25 ppm over ~ 300 years. However, the dating and interpretation of this and other tropical sites are more ambiguous than the North Atlantic sites.
Drier conditions were notable in North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
, while East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
suffered five centuries of general drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
. In West Asia and especially Mesopotamia
Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...
, the 8.2ky event was a three-hundred year aridification and cooling episode, which provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life. However multi-centennial changes around the same period are difficult to link specifically to the approximately 100-year abrupt event as recorded most clearly in the Greenland ice cores.
The initial meltwater pulse has caused between 0.5 and 4 meters of sea-level rise. Based on estimates of lake volume and decaying ice cap size, values of 0.4–1.2 meters (1–4 ft) circulate. Based on sea-level data from below modern deltas 2–4 (6–12 ft) meters of near-instantaneous rise is estimated, recorded superimposed on background 'normal' post-glacial sea-level rise. Meltwater pulse sea level rise was experienced fully at great distance from the release area. Gravity and rebound effects associated to the shifting of watermasses mean that the sea-level fingerprint is smaller in areas closer to the Hudson Bay. The Mississippi delta records ~20%, NW Europe records ~70% and Asia records ~105% of the global averaged amount. The cooling of the 8200 event was a temporary feature, the sea-level rise of the meltwater pulse was permanent.
In 2003, the Office of Net Assessment
Office of Net Assessment
The United States Department of Defense's Office of Net Assessment was created in 1973. The Director of Net Assessment is the principal staff assistant and advisor to the Secretary and Deputy Secretary of Defense on net assessment matters...
at the United States Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...
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
Andrew Marshall (foreign policy strategist)
Andrew W. Marshall is the director of the United States Department of Defense's Office of Net Assessment. Appointed to the position in 1973 by United States President Richard Nixon, Marshall has been re-appointed by every president that followed....
, 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.
See also
- Bond eventBond eventBond events are North Atlantic climate fluctuations occurring every ≈1,470 ± 500 years throughout the Holocene. Eight such events have been identified, primarily from fluctuations in ice-rafted debris. Bond events may be the interglacial relatives of the glacial Dansgaard–Oeschger events, with a...
- Antarctic Cold ReversalAntarctic Cold ReversalThe Antarctic Cold Reversal was an important episode of cooling in the climate history of the Earth, during the deglaciation at the close of the last ice age. It illustrates the complexity of the climate changes at the transition from the Pleistocene to the Holocene Epoch.The Last Glacial Maximum...
- Little Ice AgeLittle Ice AgeThe Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...
- Older PeronOlder PeronThe 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...
- Piora OscillationPiora OscillationThe Piora Oscillation was an abrupt cold and wet period in the climate history of the Holocene Epoch; it is generally dated to the period of c. 3200 to 2900 BCE...
- Sahara pump theorySahara pump theoryThe Sahara pump theory is a hypothesis that explains how flora and fauna migrated between Eurasia and Africa via a Levantine land bridge. The theory observes that extended periods of abundant rainfall lasting many thousands of years in Africa are associated with a "wet Sahara" phase, during which...
- Younger DryasYounger DryasThe Younger Dryas stadial, also referred to as the Big Freeze, was a geologically brief period of cold climatic conditions and drought between approximately 12.8 and 11.5 ka BP, or 12,800 and 11,500 years before present...
- Current sea level riseCurrent sea level riseCurrent sea level rise potentially impacts human populations and the wider natural environment . Global average sea level rose at an average rate of around 1.8 mm per year over 1961 to 2003 and at an average rate of about 3.1 mm per year from 1993 to 2003...
- 5.9 kiloyear event5.9 kiloyear eventThe 5.9 kiloyear event was one of the most intense aridification events during the Holocene. It occurred around 3900 BC, ending the Neolithic Subpluvial and probably initiated the most recent desiccation of the Sahara desert. Thus, it also triggered worldwide migration to river valleys, e.g...
- 4.2 kiloyear event4.2 kiloyear eventThe 4.2 kiloyear BP aridification event was one of the most severe climatic events of the Holocene period in terms of impact on cultural upheaval. Starting in ≈2200 BC, it probably lasted the entire 22nd century BC. It is very likely to have caused the collapse of the Old Kingdom in Egypt as...