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An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an
ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...
. The current
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
interglacial began at the end of the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
, about 11,700 years ago.


Pleistocene

During the 2.5 million years of the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
, numerous glacials, or significant advances of continental ice sheets, in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
and
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials. During interglacials, such as the present one, the climate warms and the tundra recedes polewards following the ice sheets. Forests return to areas that once supported tundra vegetation. Interglacials are identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a specific age are used to identify particular interglacials. Commonly used are mammalian and molluscan species, pollen and plant macro-remains (seeds and fruits). However, many other fossil remains may be helpful: insects, ostracods, foraminifera, diatoms, etc. Recently, ice cores and ocean sediment cores provide more quantitative and accurately-dated evidence for temperatures and total ice volumes. Interglacials and glacials coincide with cyclic changes in Earth's orbit. Three orbital variations contribute to interglacials. The first is a change in Earth's orbit around the Sun, or eccentricity. The second is a shift in the tilt of Earth's axis, or obliquity. The third is the wobbling motion of Earth's axis, or precession. In the Southern Hemisphere, warmer summers occur when the lower-half of Earth is tilted toward the Sun and the planet is nearest the Sun in its elliptical orbit. Cooler summers occur when Earth is farthest from the Sun during the Southern Hemisphere summer. Such effects are more pronounced when the eccentricity of the orbit is large. When the obliquity is large, seasonal changes are more extreme. Interglacials are a useful tool for geological mapping and for anthropologists, as they can be used as a dating method for
hominid The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ...
fossils. Brief periods of milder climate that occurred during the last glacial are called
interstadial Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate while interstadials are periods of warmer climate. Each Quaternary climate phase is associated with a Ma ...
s. Most, but not all, interstadials are shorter than interglacials. Interstadial climates may have been relatively warm, but not necessarily. Because the colder periods (stadials) have often been very dry, wetter (not necessarily warmer) periods have been registered in the sedimentary record as interstadials as well. The oxygen isotope ratio obtained from seabed sediment core samples, a
proxy Proxy may refer to: * Proxy or agent (law), a substitute authorized to act for another entity or a document which authorizes the agent so to act * Proxy (climate), a measured variable used to infer the value of a variable of interest in climate re ...
for the average global temperature, is an important source of information for changes in Earth's climate. An interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable'
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 ...
and often occurs during the middle of that interglacial. The climatic optimum of an interglacial both follows and is followed by phases within the same interglacial that experienced a less favourable climate (but still a 'better' climate than the one during the preceding or succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.


Specific interglacials

The last six interglacials are: * Marine Isotope Stage 13 (524–474 thousand years ago). * Hoxnian / Holstein / Mindel-Riss / Marine Isotope Stage 11 (424–374 thousand years ago). * Purfleet Interglacial / Holstein / Mindel-Riss /
Marine Isotope Stage 9 Marine Isotope Stage 9 (MIS 9) is a Marine Isotope Stage in the geological record. It is the final period of the Lower Paleolithic, and lasts from 337,000 to 300,000 years ago according to Lisiecki and Raymo's LR04 Benthic Stack, which has been ad ...
(337–300 thousand years ago). * La Bouchet Interglacial / Arousa Interglacial / Aveley Interglacial / Marine Isotope Stage 7e (242–230 thousand years ago). MIS 7a, MIS 7b and MIS 7c may or may not be included. MIS 7d was a cold period dividing the MIS 7 interglacial into two distinct periods. MIS 7e contained the climatic optimum. * Eemian / Marine Isotope Stage 5e (130–115 thousand years ago). The preceding interglacial optimum occurred during the Late Pleistocene Eemian Stage, 131–114 ka. During the Eemian the climatic optimum took place during pollen zone E4 in the type area (city of Amersfoort,
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
). Here this zone is characterized by the expansion of ''
Quercus An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ...
'' (oak), '' Corylus'' (hazel), '' Taxus'' (yew), ''
Ulmus Elms are deciduous and semi-deciduous trees comprising the flowering plant genus ''Ulmus'' in the plant family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North ...
'' (elm), ''
Fraxinus ''Fraxinus'' (), commonly called ash, is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous, though a number of subtropical species are evergr ...
'' (ash), ''
Carpinus Hornbeams are hardwood trees in the flowering plant genus ''Carpinus'' in the birch family Betulaceae. The 30–40 species occur across much of the temperate regions of the Northern Hemisphere. Origin of names The common English name ''hor ...
'' (hornbeam), and '' Picea'' (spruce). During the Eemian Stage (from about 128,000 BCE until 113,000 BCE), sea level was between 5 and 9.4 meters higher than today and the water temperature of the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
was about 2 °C higher than at present. *
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
(12,000 years ago to the present). During the present interglacial, the Holocene, the climatic optimum occurred during the
Subboreal The Subboreal is a climatic period, immediately before the present one, of the Holocene. It lasted from 3710 to 450 BCE. Etymology The composite scientific term ''Subboreal'', meaning "below the Boreal," is derived from the Latin ''sub'' (b ...
(5 to 2.5 ka BP, which corresponds to 3000 BC–500 BC) and Atlanticum (9 to 5 ka, which corresponds to roughly 7000 BC–3000 BC). The current climatic phase following this climatic optimum is still within the same interglacial (the Holocene). That warm period was followed by a gradual decline until about 2000 years ago, with another warm period until the
Little Ice Age The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Ma ...
(1250–1850).


See also

* Greenhouse and icehouse Earth * Milankovitch cycles * Snowball Earth *
Interstadial Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate while interstadials are periods of warmer climate. Each Quaternary climate phase is associated with a Ma ...
periods *
Last glacial maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eu ...
* Timeline of glaciation


References

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