Holocene climatic optimum

The Holocene Climate Optimum (HCO) was a warm period during roughly the interval 9,000 to 5,000 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, Hypsithermal, and Mid-Holocene Warm Period.

This warm period was followed by a gradual decline until about two millennia ago.

Global effects

Holocene Temperature Variations
Temperature variations during the Holocene from a collection of different reconstructions and their average. The most recent period is on the right, but the recent warming is only seen in the inset.

The Holocene Climate Optimum warm event consisted of increases of up to 4 °C near the North Pole (in one study, winter warming of 3 to 9 °C and summer of 2 to 6 °C in northern central Siberia).[1] Northwestern Europe experienced warming, but there was cooling in Southern Europe.[2] The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. Tropical reefs tend to show temperature increases of less than 1 °C; the tropical ocean surface at the Great Barrier Reef about 5350 years ago was 1 °C warmer and enriched in 18O by 0.5 per mil relative to modern seawater.[3] In terms of the global average, temperatures were probably warmer than now (depending on estimates of latitude dependence and seasonality in response patterns). While temperatures in the Northern Hemisphere were warmer than average during the summers, the Tropics and parts of the Southern Hemisphere were colder than average.[4]

Out of 140 sites across the western Arctic, there is clear evidence for conditions warmer than now at 120 sites. At 16 sites, where quantitative estimates have been obtained, local HTM temperatures were on average 1.6±0.8 °C higher than now. Northwestern North America had peak warmth first, from 11,000 to 9,000 years ago, and the Laurentide ice sheet still chilled the continent. Northeastern North America experienced peak warming 4,000 years later. Along the Arctic Coastal Plain in Alaska, there are indications of summer temperatures 2–3 °C warmer than present.[5] Research indicates that the Arctic had less sea ice than the present.[6]

Current desert regions of Central Asia were extensively forested due to higher rainfall, and the warm temperate forest belts in China and Japan were extended northwards.[7]

West African sediments additionally record the African Humid Period, an interval, between 16,000 and 6,000 years ago, when Africa was much wetter. This was caused by a strengthening of the African monsoon by changes in summer radiation, resulting from long-term variations in the Earth's orbit around the Sun. The "Green Sahara" was dotted with numerous lakes, containing typical African lake crocodile and hippopotamus fauna. A curious discovery from the marine sediments is that the transitions into and out of the wet period occurred within decades, not the previously-thought extended periods.[8] It is hypothesized that humans played a role in altering the vegetation structure of North Africa at some point after 8,000 years ago, when they introduced domesticated animals. This introduction contributed to the rapid transition to the arid conditions found in many locations in the Sahara.[9]

In the far Southern Hemisphere (New Zealand and Antarctica), the warmest period during the Holocene appears to have been roughly 8,000 to 10,500 years ago, immediately following the end of the last ice age.[10][11] By 6,000 years ago, the time normally associated with the Holocene Climatic Optimum in the Northern Hemisphere, they had reached temperatures similar to present ones, and they did not participate in the temperature changes of the north. However, some authors have used the term "Holocene Climatic Optimum" to describe the earlier southern warm period, as well.

Comparison of ice cores

A comparison of the delta profiles at Byrd Station, West Antarctica (2164 m ice core recovered, 1968) and Camp Century, Northwest Greenland, shows the post glacial climatic optimum.[12] Points of correlation indicate that in these two locations the Holocene climatic optimum (post glacial climatic optimum) probably occurred at the same time. A similar comparison is evident between the Dye 3 1979 and Camp Century 1963 cores regarding this period.[12]

The Hans Tausen Iskappe (ice cap) in Peary Land (northern Greenland) was drilled in 1977 with a new deep drill to 325 m. The ice core contained distinct melt layers all the way to bedrock indicating that Hans Tausen Iskappe contains no ice from the last glaciation; i.e., the world’s northernmost ice cap melted away during the post-glacial climatic optimum and was rebuilt when the climate got colder some 4000 years ago.[12]

From the delta-profile, the Renland ice cap in the Scoresby Sound has always been separated from the inland ice, yet all the delta-leaps revealed in the Camp Century 1963 core recurred in the Renland 1985 ice core.[12] The Renland ice core from East Greenland apparently covers a full glacial cycle from the Holocene into the previous Eemian interglacial. The Renland ice core is 325 m long.[13]

Although the depths are different, the GRIP and NGRIP cores also contain this climatic optimum at very similar times.[12]

Milankovitch cycles

Orbital variation
Milankovitch cycles.

The climatic event was probably a result of predictable changes in the Earth's orbit (Milankovitch cycles) and a continuation of changes that caused the end of the last glacial period.

The effect would have had maximum Northern Hemisphere heating 9,000 years ago, when the axial tilt was 24° and the nearest approach to the Sun (perihelion) was during the Northern Hemisphere's summer. The calculated Milankovitch Forcing would have provided 0.2% more solar radiation (+40 W/m2) to the Northern Hemisphere in summer, tending to cause greater heating. There seems to have been the predicted southward shift in the global band of thunderstorms, the Intertropical Convergence Zone.

However, orbital forcing would predict maximum climate response several thousand years earlier than those observed in the Northern Hemisphere. The delay may be a result of the continuing changes in climate as the Earth emerged from the last glacial period and related to ice-albedo feedback. It should also be noted that different sites often show climate changes at somewhat different times and lasting for different durations. At some locations, climate changes may have begun as early as 11,000 years ago or persisted until 4,000 years ago. As noted above, the warmest interval in the far south significantly preceded warming in the north.

Other changes

While significant temperature changes do not appear to have been at most low latitude sites, other climate changes have been reported, such as significantly wetter conditions in Africa, Australia and Japan and desert-like conditions in the Midwestern United States. Areas around the Amazon show temperature increases and drier conditions.[14]

See also

References

  1. ^ Koshkarova, V.L.; Koshkarov, A.D. (2004). "Regional signatures of changing landscape and climate of northern central Siberia in the Holocene". Russian Geology and Geophysics. 45 (6): 672–685.
  2. ^ Davis, B.A.S.; Brewer, S.; Stevenson, A.C.; Guiot, J. (2003). "The temperature of Europe during the Holocene reconstructed from pollen data". Quaternary Science Reviews. 22 (15–17): 1701–16. Bibcode:2003QSRv...22.1701D. CiteSeerX 10.1.1.112.140. doi:10.1016/S0277-3791(03)00173-2.
  3. ^ Gagan, Michael K.; Ayliffe, LK; Hopley, D; Cali, JA; Mortimer, GE; Chappell, J; McCulloch, MT; Head, MJ (1998). "Temperature and Surface-Ocean Water Balance of the Mid-Holocene Tropical Western Pacific". Science. 279 (5353): 1014–8. Bibcode:1998Sci...279.1014G. doi:10.1126/science.279.5353.1014. PMID 9461430.
  4. ^ Kitoh, Akio; Murakami, Shigenori (2002). "Tropical Pacific climate at the mid-Holocene and the Last Glacial Maximum". Paleoceanography. 17 (3): 1047. Bibcode:2002PalOc..17c..19K. doi:10.1029/2001PA000724. Archived from the original on January 19, 2010.
  5. ^ D.S. Kaufman; T.A. Ager; N.J. Anderson; P.M. Anderson; J.T. Andrews; P.J. Bartlein; L.B. Brubaker; L.L. Coats; L.C. Cwynar; M.L. Duvall; A.S. Dyke; M.E. Edwards; W.R. Eisner; K. Gajewski; A. Geirsdottir; F.S. Hu; A.E. Jennings; M.R. Kaplan; M.W. Kerwin; A.V. Lozhkin; G.M. MacDonald; G.H. Miller; C.J. Mock; W.W. Oswald; B.L. Otto-Bliesner; D.F. Porinchu; K. Ruhland; J.P. Smol; E.J. Steig; B.B. Wolfe (2004). "Holocene thermal maximum in the western Arctic (0-180 W)". Quaternary Science Reviews. 23 (5–6): 529–560. Bibcode:2004QSRv...23..529K. doi:10.1016/j.quascirev.2003.09.007.
  6. ^ "NSIDC Arctic Sea Ice News". National Snow and Ice Data Center. Retrieved 15 May 2009.
  7. ^ "Eurasia During the Last 150,000 Years". Archived from the original on 8 June 2012. Retrieved 7 June 2012.
  8. ^ "Abrupt Climate Changes Revisited: How Serious and How Likely?". USGCRP Seminar, 23 February 1998. Retrieved May 18, 2005.
  9. ^ Wright, David K. (26 January 2017). "Humans as Agents in the Termination of the African Humid Period". Frontiers in Earth Science. 5: 4. Bibcode:2017FrEaS...5....4W. doi:10.3389/feart.2017.00004.
  10. ^ Masson, V.; Vimeux, F.; Jouzel, J.; Morgan, V.; Delmotte, M.; Ciais,P.; Hammer, C.; Johnsen, S.; Lipenkov, V.Y.; Mosley-Thompson, E.; Petit, J.-R.; Steig, E.J.; Stievenard, M.; Vaikmae, R. (2000). "Holocene climate variability in Antarctica based on 11 ice-core isotopic records". Quaternary Research. 54 (3): 348–358. Bibcode:2000QuRes..54..348M. doi:10.1006/qres.2000.2172.
  11. ^ P.W. Williams; D.N.T. King; J.-X. Zhao K.D. Collerson (2004). "Speleothem master chronologies: combined Holocene 18O and 13C records from the North Island of New Zealand and their paleoenvironmental interpretation". The Holocene. 14 (2): 194–208. doi:10.1191/0959683604hl676rp.
  12. ^ a b c d e Dansgaard W (2004). Frozen Annals Greenland Ice Sheet Research. Odder, Denmark: Narayana Press. p. 124. ISBN 978-87-990078-0-6.
  13. ^ Hansson M, Holmén K (Nov 2001). "High latitude biospheric activity during the Last Glacial Cycle revealed by ammonium variations in Greenland Ice Cores". Geophys. Res. Lett. 28 (22): 4239–42. Bibcode:2001GeoRL..28.4239H. doi:10.1029/2000GL012317.
  14. ^ Francis E. Mayle, David J. Beerling, William D. Gosling, Mark B. Bush (2004). "Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the Last Glacial Maximum". Philosophical Transactions: Biological Sciences. 359 (1443): 499–514. doi:10.1098/rstb.2003.1434. PMC 1693334. PMID 15212099.CS1 maint: Multiple names: authors list (link)
6th millennium BC

The 6th millennium BC spanned the years 6000 through 5001 BC.

It falls into the Holocene climatic optimum, with rising sea levels.

Culturally, Mesopotamia is in the Pottery Neolithic (Halaf culture), and agriculture spreads to Europe and to Egypt.

World population grows dramatically as a result of the Neolithic Revolution, perhaps quadrupling, from about 10 to 40 million, over the course of the millennium.

8.2 kiloyear event

In climatology, the 8.2-kiloyear event was a sudden decrease in global temperatures that occurred approximately 8,200 years before the present, or c. 6,200 BC, and which lasted for the next two to four centuries. It defines the start of the Northgrippian age in the Holocene epoch. Milder than the Younger Dryas cold spell before it but more severe than the Little Ice Age after it, 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, an emission reduction of 15%, by cooling and drying at a hemispheric scale.

Amery Ice Shelf

The Amery Ice Shelf (69°45′S 71°0′E) is a broad ice shelf in Antarctica at the head of Prydz Bay between the Lars Christensen Coast and Ingrid Christensen Coast. It is part of Mac. Robertson Land. The name "Cape Amery" was applied to a coastal angle mapped on February 11, 1931 by the British Australian New Zealand Antarctic Research Expedition (BANZARE) under Douglas Mawson. He named it for William Bankes Amery, a civil servant who represented the United Kingdom government in Australia (1925–28). The Advisory Committee on Antarctic Names interpreted this feature to be a portion of an ice shelf and, in 1947, applied the name Amery to the whole shelf.

In 2001 two holes were drilled through the ice shelf by scientists from the Australian Antarctic Division and specially designed seabed sampling and photographic equipment was lowered to the underlying seabed. By studying the fossil composition of sediment samples recovered, scientists have inferred that a major retreat of the Amery Ice Shelf to at least 80 km landward of its present location may have occurred during the mid-Holocene climatic optimum (about 5,700 years ago).In December 2006, it was reported by the Australian Broadcasting Corporation that Australian scientists were heading to the Amery Ice Shelf to investigate enormous cracks that had been forming for over a decade at a rate of three to five metres a day. These fractures threaten to break off a 1000 square kilometre piece of the Amery Ice Shelf. Scientists want to discover what is causing the cracks, as there has not been similar activity since the 1960s. However, the head of research believes that it is too early to attribute the cause to Global Warming as there is the possibility of a natural 50-60 year cycle being responsible.Lambert Glacier flows from Lambert Graben into the Amery Ice Shelf on the southwest side of Prydz Bay.

The Amery Basin (68°15′S 74°30′E) is an undersea basin north of the Amery Ice Shelf.

The Chinese Antarctic Zhongshan Station and Russian Progress Station are located near this ice shelf.

The Amery Ice Shelf is the third largest ice shelf in Antarctica, after the Ross Ice Shelf and the Filchner-Ronne Ice Shelf.

Atlantic (period)

The Atlantic in palaeoclimatology was the warmest and moistest Blytt-Sernander period, pollen zone and chronozone of Holocene northern Europe. The climate was generally warmer than today. It was preceded by the Boreal, with a climate similar to today’s, and was followed by the Subboreal, a transition to the modern. Because it was the warmest period of the Holocene, the Atlantic is often referenced more directly as the Holocene climatic optimum, or just climatic optimum.

Branchinecta gaini

Branchinecta gaini is a species of fairy shrimp from Antarctica and Patagonia. It is the largest freshwater invertebrate in Antarctica, at 16 mm (0.63 in) long. It lives on bacteria and other organisms, surviving the winter as resting eggs.

Cave of Beasts

The Cave of the Beasts (also named Foggini-Mestikawi Cave or Foggini Cave or Cave Wadi Sura II) is a huge natural rock shelter in the Western Desert of Egypt featuring Neolithic rock paintings, more than 7,000 years old, with about 5,000 figures.

Donjek Glacier

Donjek Glacier (Southern Tutchone: Dän Zhǘr[1]) is located in Kluane National Park, in Yukon, Canada, on the east side of the St. Elias Mountains. Donjek Glacier is about 35 miles (56 km) long and extends into the Donyek River Valley 3,500 feet (1,100 m) to its terminus. Centuries ago Donjek Glacier formed a dam, creating Donjek Lake which is estimated to have been 230 x 106 m3.In 1970 a study was performed at the terminus of the glacier to determine its position during the Holocene climatic optimum but the study found no evidence in the valley that the glacier had retreated from the Donyek River Valley. However there is evidence that the glacier had retreated before it advanced during the neoglaciation. Near the river bed there is also an area of 4–5 feet (1.2–1.5 m) high mounds whose surfaces have been worn by the river. Inside the mounds there is a large amount of groundmass, which indicates the mounds may have been formed of till originally. This suggests Donjek Glacier was much larger than it is now as the mounds would have gone through much erosion.In 1978 Donjek Glacier went through a minor surge but failed to block the Donjek River. In 1998 a subglacial tunnel in Donjek Glacier collapsed after an outbreak of water flooded the area. The collapse created a 50-metre (160 ft) wide ice canyon.

HCO

HCO may refer to:

Hervey Company (Well control Equipment)

Hans Tausen Ice Cap

Hans Tausen Ice Cap (Danish: Hans Tausens Iskappe) is an ice cap in Peary Land, northern Greenland. Ice cores show it is around 3500–4000 years old. It formed since the Holocene climatic optimum of 6000-8000 BP.

Hardangervidda

Hardangervidda (English: Hardanger Plateau) is a mountain plateau (Norwegian: vidde) in central southern Norway, covering parts of the counties of Buskerud, Hordaland and Telemark. It is the largest plateau of its kind in Europe, with a cold year-round alpine climate, and one of Norway's largest glaciers, Hardangerjøkulen, is situated here. Much of the plateau is protected as part of Hardangervidda National Park. Hardangervidda is a popular tourist and leisure destination, and it is ideal for many outdoor activities.

Hemudu culture

The Hemudu culture (5500 BC to 3300 BC) was a Neolithic culture that flourished just south of the Hangzhou Bay in Jiangnan in modern Yuyao, Zhejiang, China. The culture may be divided into an early and late phases, before and after 4000 BC respectively. The site at Hemudu, 22 km north-west of Ningbo, was discovered in 1973. Hemudu sites were also discovered on the islands of Zhoushan. Hemudu are said to have differed physically from inhabitants of the Yellow River sites to the north. Scholars view the Hemudu Culture as a source of the proto-Austronesian cultures.

Index of climate change articles

This is a list of climate change topics.

Minuma

Minuma (見沼, Minuma) or Minuma Rice Paddies (見沼田んぼ, Minuma Tanbo) is an area of paddy fields and other agricultural fields along the Minuma Irrigational Canal in Saitama Prefecture, Japan. The area encompasses 1260 hectares and straddles across five wards of the city of Saitama (Kita-ku, Ōmiya-ku, Minuma-ku, Urawa-ku, and Midori-ku). Despite its close proximity to major urban areas such as Saitama-Shintoshin Station and Ōmiya Station, idyllic scenery consisting of paddy fields, farmlands, forests and rivers still remains.

Neoglaciation

The neoglaciation ("renewed glaciation") describes the documented cooling trend in the Earth's climate during the Holocene, following the retreat of the Wisconsin glaciation, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate during the current interglacial stage. The neoglaciation has no well-marked universal beginning: local conditions and ecological inertia affected the onset of detectably cooler (and wetter) conditions.

Driven inexorably by the Milankovitch cycle, cooler summers in higher latitudes of North America, which would cease to completely melt the annual snowfall, were masked at first by the presence of the slowly disappearing continental ice sheets, which persisted long after the astronomically calculated moment of maximum summer warmth: "the neoglaciation can be said to have begun when the cooling caught up with the warming", remarked E. C. Pielou. With the close of the "Little Ice Age" (mid-14th to late 19th centuries), neoglaciation appears to have been stalled in the late 20th century, assumed to be caused by anthropogenic global warming. Whether it has been temporarily or semi-permanently stalled, neoglaciation has been marked by a retreat from the warm conditions of the Climatic Optimum and the advance or reformation of glaciers that had not existed since the last ice age. In the mountains of western North America, montane glaciers that had completely melted reformed shortly before 5000 BP. The most severe part of the best documented neoglacial period, especially in Europe and the North Atlantic, is termed the "Little Ice Age".

In North America, neoglaciation had ecological effects in the spread of muskeg on flat, poorly drained land, such as the bed of recently drained Lake Agassiz and in the Hudson Bay lowlands, in the retreat of grassland before an advancing forest border in the Great Plains, and in shifting ranges of forest trees and diagnostic plant species (identified through palynology).

The view that neoglaciation is ending in present times, is assumed by those who identify the most recent climate changes and global warming as the onset of a new period in Earth history, speculatively calling it the "Early anthropocene", as a coming geological age dominated by the effects of Homo sapiens.

Neolithic Expansion

At the beginning of the Holocene, about 10,000 BC, humanity entered a period of increasing technological sophistication, resulting in the Neolithic Revolution.

Breadmaking considerably predates this period, but people in the Middle East now began cultivating wild cereal and pulses. Dogs had been domesticated over thousands of years; nomadic shepherding became possible through domestication of goats, sheep, horses, camels and cattle.About 5000 BC, livestock herding was sufficiently established to allow a widespread abandonment of hunter-gathering in favour of settled lifestyles. Pottery was increasingly useful, and permanent buildings, constructed from mudbrick, appeared. These technologies spread out of the Middle East through the Old World (the Americas developed agriculture independently, with only the llama available for domestication).

The Neolithic spread throughout Europe between about 6200 and 4000 BC.

Piora Oscillation

The 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. 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.

Pre-modern human migration

This article focusses on prehistorical migration since the Neolithic period until AD 1800. See Early human migrations for migration prior to the Neolithic, History of human migration for modern history, and human migration for contemporary migration.Paleolithic migration prior to end of the Last Glacial Maximum

spread anatomically modern humans throughout Afro-Eurasia and to the Americas.

During the Holocene climatic optimum, formerly isolated populations began to move and merge, giving rise to the

pre-modern distribution of the world's major language families.

In the wake of the population movements of the Mesolithic came the Neolithic revolution,

followed by the Indo-European expansion in Eurasia and the Bantu expansion in Africa.

Population movements of the proto-historical or early historical period include the Migration period, followed by (or connected to) the Slavic, Magyar Norse, Turkic and Mongol expansions of the medieval period.

The last world regions to be permanently settled were the Pacific Islands and the Arctic, reached during the 1st millennium AD.

Since the beginning of the Age of Exploration and the beginning of the Early Modern period and its emerging colonial empires, an accelerated pace of migration on the intercontinental scale became possible.

Subboreal

The Subboreal is a climatic period, immediately before the present one, of the Holocene. It lasted from 3710 to 450 BCE.

West Greenland Current

The West Greenland Current is a weak cold water current that flows to the north along the west coast of Greenland. The current results from the movement of water flowing around the southernmost point of Greenland caused by the East Greenland Current.

According to Lloyd et al., 2007, the WGC is a WARM current connected to a broader scale North Atlantic climate via the combined influences of Atlantic water from the Irminger Current (IC) and polar water from the East Greenland Current.Paleoclimatology records derived from foraminifera abundance show that periodic influxes of warm subsurface temperatures and near-bottom temperatures occurred throughout the Late Holocene epoch, particularly during the Holocene climatic optimum. The increased flow from the nearby East Greenland Current was associated with increased glacial iceberg calving from the large Jakobshavn Isbrae glacial outlet within the western Greenland Ice Sheet, causing rapid melting and destabilization events. Following the Neoglaciation, the Jakobshavn outlet formed a floating ice tongue around 2000 years before present.

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