In climatology, the 8.2 kiloyear event was a rapid drop in global temperatures that occurred around 8,200 years ago, lasting between two and four centuries. This event marks the beginning of the Northgrippian Age within the Holocene epoch. While this cooling phase was not as intense as the earlier Younger Dryas period that occurred just before the Holocene began, it was still significant. During the 8.2-kiloyear event, atmospheric methane levels dropped by 80 parts per billion, a 15% reduction, suggesting a broad cooling and drying trend across the Northern Hemisphere.
A rapid cooling around 8,200 years ago was first identified by Swiss botanist Heinrich Zoller in 1960, who named the event the Misox oscillation for the Val Mesolcina [2] . It is also known as the Finse event in Norway. [3] Evidence for the 8.2 kiloyear event has been found in speleothem records across Eurasia, the Mediterranean, South America, and southern Africa, indicating the event was globally synchronous. [4] The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in Greenland ice cores, sedimentary records, and other records of the temperate and tropical North Atlantic. [5] [6] [7] There is less evidence in ice cores from Antarctica and South American records. [8] [9] The effects of the sudden temperature decrease were global, most notably sea level change.
The event may have been caused by a large meltwater pulse, [10] which probably resulted from the final collapse of the Laurentide Ice Sheet of northeastern North America, [11] [12] [13] most likely when the glacial lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean. [14] The same type of action produced the Missoula floods which formed the Channeled Scablands of the Columbia River basin. The meltwater pulse may have affected the North Atlantic thermohaline circulation, [15] [16] [17] reducing northward heat transport in the Atlantic and causing significant North Atlantic cooling. [18] The Atlantic meridional overturning circulation (AMOC) weakened by 55% [12] or 62%. [18] Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but decreases of around 1 to 5 °C (1.8 to 9.0 °F) have been reported. In Greenland, the event started at 8175 BP, and the cooling was 3.3°C below the decadal average in less than 20 years. The coldest period lasted for about 60 years, and its total duration was about 150 years. [19] [20] The meltwater causation hypothesis is, however, considered to be speculation[ by whom? ] because of inconsistencies with its onset and an unknown region of impact.[ citation needed ]
Researchers suggest that the discharge was probably superimposed upon a longer episode of cooler climate lasting up to 600 years, and it was merely one contributing factor to the event as a whole. [21]
Further afield from the Laurentide Ice Sheet, some tropical records report a 3 °C (5.4 °F) cooling, based on cores drilled into an ancient coral reef in Indonesia. [22] The event also caused a global CO2 decline of about 25 ppm over about 300 years. [23] However, dating and interpretation of other tropical sites are more ambiguous than the North Atlantic sites. In addition, climate modeling shows that the amount of meltwater and the pathway of meltwater are both important in perturbing the North Atlantic thermohaline circulation. [24]
The initial meltwater pulse caused between 0.5 and 4 m (1 ft 8 in and 13 ft 1 in) of sea-level rise. Based on estimates of lake volume and decaying ice cap size, values of 0.4–1.2 m (1 ft 4 in – 3 ft 11 in) circulate. Based on sea-level data from the Mississippi Delta, the end of the Lake Agassiz–Ojibway (LAO) drainage occurred at 8.31 to 8.18 ka and ranges from 0.8 to 2.2 m. [25] The sea-level data from the Rhine–Meuse Delta indicate a 2–4 m (6 ft 7 in – 13 ft 1 in) of near-instantaneous rise at 8.54 to 8.2 ka, in addition to 'normal' post-glacial sea-level rise. [26] Meltwater pulse sea-level rise was experienced fully at a great distance from the release area. Gravity and rebound effects associated with the shifting of water masses meant that the sea-level rise was smaller in areas closer to the Hudson Bay. The Mississippi Delta records around 20%, Northwestern Europe 70%, and Asia 105% of the globally averaged amount. [27] The cooling of the 8.2-kiloyear event was a temporary feature, but the sea-level rise of the meltwater pulse was permanent.
In 2003, the Office of Net Assessment (ONA) at the United States Department of Defense was commissioned to produce a study on the likely and potential effects of modern climate change. [28] The study, conducted under ONA head Andrew Marshall, modeled its prospective climate change on the 8.2 kiloyear event, precisely because it was the middle alternative between the Younger Dryas and the milder Little Ice Age. [29]
Across much of the world, the 8.2 kiloyear event engendered drier environmental conditions. [30] Northern Hemisphere monsoon precipitation declined by 12.4% for every °C of global mean temperature change, while Southern Hemisphere monsoon precipitation rose by 4.2%/°C. [31] The 8.2 kiloyear event was also associated with an increase in ocean salinity and terrestrial dust flux. [32]
Drier conditions were notable in North Africa; the area around the Charef River in eastern Morocco records an episode of extreme aridity around 8,200 BP. [33] East Africa was significantly affected by five centuries of general drought. In West Asia, especially Mesopotamia, the 8.2-kiloyear event was a 300-year aridification and cooling episode which may have provided the natural force for Mesopotamian irrigation agriculture and surplus production, which were essential for the earliest formation of classes and urban life.[ citation needed ] However, changes taking place over centuries around the period are difficult to link specifically to the approximately 100-year abrupt event, as recorded most clearly in the Greenland ice cores.
In particular, in Tell Sabi Abyad, Syria, significant cultural changes were observed at c. 6200 BC; the settlement was not abandoned at the time. [34]
In northwestern Madagascar, the 8.2 kiloyear event is associated with a negative δ18O excursion and calcite deposition, indicating wet, humid conditions caused by the southward migration of the ITCZ. [35] Summer monsoons in the Southern Hemisphere likely became stronger, contributing to precipitation increases. [36] Humidification was two-phased, with an 8.3 kiloyear sub-event preceding the 8.2 kiloyear sub-event by about 20 years. [37]
The sediment core records of the Fram Strait show a short-lived cooling during the 8.2 kiloyear event superimposed on a broader interval of warm climate. [38] In western Scotland, the 8.2 kiloyear event coincided with a dramatic reduction in the Mesolithic population. [39] In the Iberian Peninsula, the 8.2 kiloyear event is linked to greater summer aridity that caused an increase in the frequency of fires and a consequent expansion of fire-resistant evergreen oak trees. [40]
Lacustrine sediment records show that Western Siberia underwent humidification during the 8.2 kiloyear event. [41]
Carbonates from the Riwasa Palaeolake show a weakening of the Indian Summer Monsoon (ISM) synchronous with the 8.2 kiloyear event. [42] Stalagmites from Kotumsar Cave [43] and from Socotra and Oman further confirm the ISM precipitously diminished in strength. [44]
A sediment core from Lop Nur in the Tarim Basin shows a major dry spell occurred during the 8.2 kiloyear event. [45] The impact of the 8.2 kiloyear event on forests in the Korean Peninsula was severe, shown by a sizeable reduction in pollen production. It took approximately 400 years for forest ecosystems to recover from the event to their state before the climatic perturbation. [46]
Evidence from the Gulf of Thailand reveals that a sea level drop occurred concordantly with the 8.2 kiloyear event. Also detectable from palynological and sedimentological records is an increase in runoff. [47]
In Greenland, the 8.2 kiloyear event is associated with a large negative spike in ice core δ18O values. [48] [49] The waters off Cape Hatteras experienced a major increase in salinity. [50] Bat guano δ13C and δD values in the Grand Canyon declined. [51] Southwestern Mexico became significantly drier, evidenced by the interruption of stalagmite growth. [52] In the Gulf of Mexico, bay-head deltas back stepped as sea levels rose. [53] Mustang Island was breached and ceased to be an effective salinity barrier. [54] Gulf of Mexico δ18Oseawater values dropped by 0.8%. [55]
The South American Summer Monsoon (SASM) drastically intensified during the 8.2 kiloyear event as revealed by sediment records from Juréia Paleolagoon. [56]
The Holocene is the current geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene is an interglacial period within the ongoing glacial cycles of the Quaternary, and is equivalent to Marine Isotope Stage 1.
The Younger Dryas was a period in Earth's geologic history that occurred circa 12,900 to 11,700 years Before Present (BP). It is primarily known for the sudden or "abrupt" cooling in the Northern Hemisphere, when the North Atlantic Ocean cooled and annual air temperatures decreased by ~3 °C (5.4 °F) over North America, 2–6 °C (3.6–10.8 °F) in Europe and up to 10 °C (18 °F) in Greenland, in a few decades. Cooling in Greenland was particularly rapid, taking place over just 3 years or less. At the same time, the Southern Hemisphere experienced warming. This period ended as rapidly as it began, with dramatic warming over ~50 years, which transitioned the Earth from the glacial Pleistocene epoch into the current Holocene.
The Last Interglacial, also known as the Eemian, was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. It was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day. During the Last Interglacial, the proportion of CO2 in the atmosphere was about 280 parts per million. The Last Interglacial was one of the warmest periods of the last 800,000 years, with temperatures comparable to and at times warmer than the contemporary Holocene interglacial, with the maximum sea level being up to 6 to 9 metres higher than at present, with global ice volume likely also being smaller than the Holocene interglacial.
A Dansgaard–Oeschger event, is a rapid climate fluctuation; such events occurred 25 times during the last glacial period. Some scientists say that the events occur quasi-periodically with a recurrence time being a multiple of 1,470 years, but this is debated. The comparable climate cyclicity during the Holocene is referred to as Bond events. Dansgaard–Oeschger refers to palaeoclimatologists Willi Dansgaard and Hans Oeschger.
The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels.
The Black Sea deluge is the best known of three hypothetical flood scenarios proposed for the Late Quaternary history of the Black Sea. One other flood scenario proposes a rapid, even catastrophic, rise in sea level of the Black Sea.
The Holocene Climate Optimum (HCO) was a warm period in the first half of the Holocene epoch, that occurred in the interval roughly 9,500 to 5,500 years BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimum, Holocene Megathermal, Holocene Optimum, Holocene Thermal Maximum, Holocene global thermal maximum, Hypsithermal, and Mid-Holocene Warm Period.
A Heinrich event is a natural phenomenon in which large groups of icebergs break off from the Laurentide ice sheet and traverse the Hudson Strait into the North Atlantic. First described by marine geologist Hartmut Heinrich, they occurred during five of the last seven glacial periods over the past 640,000 years. Heinrich events are particularly well documented for the last glacial period but notably absent from the penultimate glaciation. The icebergs contained rock mass that had been eroded by the glaciers, and as they melted, this material was dropped to the sea floor as ice rafted debris forming deposits called Heinrich layers.
An abrupt climate change occurs when the climate system is forced to transition at a rate that is determined by the climate system energy-balance. The transition rate is more rapid than the rate of change of the external forcing, though it may include sudden forcing events such as meteorite impacts. Abrupt climate change therefore is a variation beyond the variability of a climate. Past events include the end of the Carboniferous Rainforest Collapse, Younger Dryas, Dansgaard–Oeschger events, Heinrich events and possibly also the Paleocene–Eocene Thermal Maximum. The term is also used within the context of climate change to describe sudden climate change that is detectable over the time-scale of a human lifetime. Such a sudden climate change can be the result of feedback loops within the climate system or tipping points in the climate system.
The Holocene glacial retreat is a geographical phenomenon that involved the global retreat of glaciers (deglaciation) that previously had advanced during the Last Glacial Maximum. Ice sheet retreat initiated ca. 19,000 years ago and accelerated after ca. 15,000 years ago. The Holocene, starting with abrupt warming 11,700 years ago, resulted in rapid melting of the remaining ice sheets of North America and Europe.
The 4.2-kiloyear BP aridification event, also known as the 4.2 ka event, was one of the most severe climatic events of the Holocene epoch. It defines the beginning of the current Meghalayan age in the Holocene epoch.
Marine Isotope Stage 11 or MIS 11 is a Marine Isotope Stage in the geologic temperature record, covering the interglacial period between 424,000 and 374,000 years ago. It corresponds to the Hoxnian Stage in Britain.
Bond events are North Atlantic ice rafting events which Gerard Bond sought to link to climate fluctuations in the Holocene. Eight such events have been identified. Bond events were previously believed to exhibit a roughly c. 1,500-year cycle, but the primary period of variability is now put at c. 1,000 years.
Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice sheet or frozen surface layer, and the resulting exposure of the Earth's surface. The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier. After the Last Glacial Maximum, the last deglaciation begun, which lasted until the early Holocene. Around much of Earth, deglaciation during the last 100 years has been accelerating as a result of climate change, partly brought on by anthropogenic changes to greenhouse gases.
Siwan Davies FLSW is a Welsh professor of Physical Geography in the department of science at Swansea University.
The early Holocene sea level rise (EHSLR) was a significant jump in sea level by about 60 m (197 ft) during the early Holocene, between about 12,000 and 7,000 years ago, spanning the Eurasian Mesolithic. The rapid rise in sea level and associated climate change, notably the 8.2 ka cooling event , and the loss of coastal land favoured by early farmers, may have contributed to the spread of the Neolithic Revolution to Europe in its Neolithic period.
The African humid period was a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when northern Africa was wetter than today. The covering of much of the Sahara desert by grasses, trees and lakes was caused by changes in the Earth's axial tilt; changes in vegetation and dust in the Sahara which strengthened the African monsoon; and increased greenhouse gases. During the preceding Last Glacial Maximum, the Sahara contained extensive dune fields and was mostly uninhabited. It was much larger than today, and its lakes and rivers such as Lake Victoria and the White Nile were either dry or at low levels. The humid period began about 14,600–14,500 years ago at the end of Heinrich event 1, simultaneously to the Bølling–Allerød warming. Rivers and lakes such as Lake Chad formed or expanded, glaciers grew on Mount Kilimanjaro and the Sahara retreated. Two major dry fluctuations occurred; during the Younger Dryas and the short 8.2 kiloyear event. The African humid period ended 6,000–5,000 years ago during the Piora Oscillation cold period. While some evidence points to an end 5,500 years ago, in the Sahel, Arabia and East Africa, the end of the period appears to have taken place in several steps, such as the 4.2-kiloyear event.
The Homeric Minimum is a grand solar minimum that started about 2,800 years ago and lasted around 200 years. It appears to coincide with, and have been the cause of, a phase of climate change at that time, which involved a wetter Western Europe and drier eastern Europe. This had far-reaching effects on human civilization, some of which may be recorded in Greek mythology and the Old Testament.
The Medieval Warm Period (MWP), also known as the Medieval Climate Optimum or the Medieval Climatic Anomaly, was a time of warm climate in the North Atlantic region that lasted from about 950 CE to about 1250 CE. Climate proxy records show peak warmth occurred at different times for different regions, which indicate that the MWP was not a globally uniform event. Some refer to the MWP as the Medieval Climatic Anomaly to emphasize that climatic effects other than temperature were also important.
The preboreal oscillation (PBO) was a short cooling period within the preboreal stage of the Holocene epoch.