The Late Cenozoic Ice Age,National Academy of Sciences - The National Academies Press - Continental Glaciation through Geologic Times https://www.nap.edu/read/11798/chapter/8#80 or Antarctic Glaciation, began 34 million years ago at the Eocene-Oligocene Boundary and is ongoing. It is Earth's current

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 g ...

or icehouse period. Its beginning is marked by the formation of the Antarctic ice sheets. Six million years after the start of the Late Cenozoic Ice Age, the

East Antarctic Ice Sheet The East Antarctic Ice Sheet (EAIS) lies between 45th meridian west, 45° west and 168th meridian east, 168° east longitudinally. It was first formed around 34 million years ago, and it is the largest ice sheet on the entire planet, with far gre ...

had formed, and 14 million years ago it had reached its current extent. In the last three million years, glaciations have spread to the northern hemisphere. It commenced with

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

becoming increasingly covered by an ice sheet in late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 During the

Pleistocene Epoch The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

(starting 2.58 Ma ago), the

Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial period, glacial and interglacial, interglacial periods during the Quaternary period that began 2.58 Year#SI prefix multipliers, Ma (million ...

developed with decreasing mean temperatures and increasing amplitudes between glacials and interglacials. During the

glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

s of the Pleistocene, large areas of northern

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

and northern

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

have been covered by ice sheets. All_palaeotemps

History of discovery and naming

In 1837, German naturalist Karl Friedrich Schimper coined the term , meaning ''ice age'' (or ''ice time'' for a more literal translation). For a long time, the term referred only to glacial periods. Over time, this developed into the concept that they were all part of a much longer ice age. The concept that the Earth is currently in an ice age that began around 30 million years ago can be dated back to at least 1966.The Stanford Daily - Stanford, California, United States - ''Man's Relation To Nature Topic Of Eiseley's Lecture'' - 1966 October 20. As a geologic time period, the Late Cenozoic Ice Age was used at least as early as 1973.

The climate before the polar ice caps

The last greenhouse period began 260 million years ago during the late

Permian Period The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

at the end of the

Karoo Ice Age The late Paleozoic icehouse, also known as the Late Paleozoic Ice Age (LPIA) and formerly known as the Karoo ice age, was an ice age that began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago (Mya), ...

. It lasted all through the time of the non-avian dinosaurs during the

Mesozoic Era The Mesozoic Era is the era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles such as the dinosaurs, and of gymnosperms s ...

, and ended 33.9 million years ago in the middle of the

Cenozoic Era The Cenozoic Era ( ; ) is Earth's current geological Era (geology), era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, Insect, insects, birds and flowering plant, angiosperms (floweri ...

(the current Era). This greenhouse period lasted 226.1 million years. The hottest part of the last greenhouse earth was the Late Paleocene - Early Eocene. This was a hothouse period that lasted from 65 to 55 million years ago. The hottest part of this torrid age was the

Paleocene–Eocene Thermal Maximum The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a ...

, 55.5 million years ago. Average global temperatures were around . This was only the second time that Earth reached this level of warmth since the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

. The other time was during the

Cambrian Period The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

, which ran from 538.8 million years ago to 485.4 million years ago. During the early

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

were connected to Antarctica. 53 million years ago during the Eocene Epoch, summer high temperatures in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

were around . Temperatures during winter were around . It did not frost during the winter. The climate was so warm that trees grew in Antarctica. ''

Arecaceae The Arecaceae () is a family (biology), family of perennial plant, perennial, flowering plants in the Monocotyledon, monocot order Arecales. Their growth form can be climbing palm, climbers, shrubs, tree-like and stemless plants, all commonly k ...

'' (palm trees) grew on the coastal lowlands, and ''

Fagus Beech (genus ''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to subtropical (accessory forest element) and temperate (as dominant element of Mesophyte, mesophytic forests) Eurasia and North America. There are 14 accepted ...

'' (beech trees) and ''

Pinophyta Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ...

'' (conifers) grew on the hills just inland from the coast. As the global climate became cooler, the planet was seeing a decrease in forests, and an increase in savannas. Animals were evolving to have a larger body size.

Glaciation of the southern hemisphere

Australia drifted away from Antarctica forming the

Tasmanian Passage The Tasmanian Passage, also Tasmanian Gateway or Tasmanian Seaway, is the name of ocean waters between Australia (continent), Australia and Antarctica. It was formed from the separation of the two continental plates of Australia and Antarctica a ...

, and

drifted away from Antarctica forming the

Drake Passage The Drake Passage is the body of water between South America's Cape Horn, Chile, Argentina, and the South Shetland Islands of Antarctica. It connects the southwestern part of the Atlantic Ocean (Scotia Sea) with the southeastern part of the Pa ...

. This caused the formation of the Antarctic Circumpolar Current, a current of cold water surrounding Antarctica. This current still exists today, and is a major reason for why Antarctica has such an exceptionally cold climate. The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. At this point, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, CO₂ levels had dropped to 750 ppm. This was the beginning of the Late Cenozoic Ice Age. This was when the ice sheets reached the ocean, the defining point. At 29.2 million years ago, there were three ice caps in the high elevations of Antarctica. One ice cap formed in the Dronning Maud Land. Another ice cap formed in the Gamburtsev Mountain Range. Another ice cap formed in the

Transantarctic Mountains The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted rock (primarily sedimentary) in Antarctica which extends, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats L ...

. At this point, the ice caps weren't very big yet. Most of Antarctica wasn't covered by ice. By 28.7 million years ago, the Gamburtsev ice cap was now much larger due to the colder climate. CO₂ continued to fall and the climate continued to get colder. At 28.1 million years ago, the Gamburtsev and Transantarctic ice caps merged into a main central ice cap. At this point, ice was now covering a majority of the continent. The Dronning Maud ice cap merged with the main ice cap 27.9 million years ago. This was the formation of the

. Global refrigeration set in 22 million years ago. About 15 million years ago was the warmest part of the Late Cenozoic Ice Age, with average global temperatures around . Atmospheric CO₂ levels were around 700 ppm. This time period was called the Mid-Miocene Climatic Optimum (MMCO). By 14 million years ago, the Antarctic ice sheets were similar in size and volume to present times. Glaciers were starting to form in the mountains of the Northern Hemisphere. Between 3.6 and 3.4 million years ago, there was a sudden but brief warming period.

Glaciation of the northern hemisphere

The glaciation of the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

commenced with Greenland becoming increasingly covered by an ice sheet in late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 The current period is the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

, which started 2.58 million years ago. It is divided into the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

, which ended 11,700 years ago, and the current

Holocene The Holocene () is the current geologic time scale, 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 to ...

. The Quaternary is characterized by alternating

s, during which extensive ice sheets cover large portions of the Earth, and interglacial periods, which are warmer with reduced ice cover. The oscillation between glacial and interglacial periods is due to the

Milankovitch cycles Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after the Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he pr ...

. These are cycles that have to do with Earth's axial tilt and orbital eccentricity. Earth is currently tilted at 23.5 degrees. Over a 41,000 year cycle, the tilt oscillates between 22.1 and 24.5 degrees. When the tilt is greater (high obliquity), the seasons are more extreme. During times when the tilt is less (low obliquity), the seasons are less extreme. Less tilt also means that the polar regions receive less light from the sun. This causes a colder global climate as ice sheets start to build up. The shape of Earth's orbit around the Sun affects the Earth's climate. Over a 100,000 year cycle, Earth oscillates between having a circular orbit to having a more elliptical orbit. From 2.58 million years ago to about 1.73 million ± 50,000 years ago, the degree of axial tilt was the main cause of glacial and interglacial periods. Around 850,000 ± 50,000 years ago, the degree of orbital eccentricity became the main driver of glacial and interglacial periods rather than the degree of tilt, and this pattern continues to present-day.

Last Glacial Period

The Last Glacial Period began 115,000 years ago and ended 11,700 years ago. This time period saw the great advancement of polar ice sheets into the middle latitudes of the Northern Hemisphere. The Toba eruption 75,000 years ago in present-day

Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

has been linked to a bottleneck in the human DNA, although such a causal link remains highly controversial. 50,000 years ago, Homo sapiens migrated out of Africa. They began replacing other Hominins in Asia. They also began replacing Neanderthals in Europe. However, some of the Homo sapiens and Neanderthals interbred. Currently, persons of European descent are two to four percent Neanderthal. With the exception of this small amount of Neanderthal DNA that exists today, Neanderthals became extinct 30,000 years ago. The

Last Glacial Maximum 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 m ...

ran from 26,500 years ago to 20,000 years ago. Although different ice sheets reached maximum extent at somewhat different times, this was the time when ice sheets overall were at maximum extent. According to ''Blue Marble 3000'' (a video by the Zurich University of Applied Sciences), the average global temperature around 19,000 BCE (about 21,000 years ago) was . This is about colder than the 1850-1929 average, and colder than the 2011-2020 average. The figures given by the Intergovernmental Panel On Climate Change (IPCC) estimate a slightly lower global temperature than the figures given by the Zurich University of Applied Sciences. However, these figures are not exact figures and are open more to interpretation. According to the IPCC, average global temperatures increased by 5.5 ± 1.5 °C (9.9 ± 2.7 °F) since the last glacial maximum, and the rate of warming was about 10 times slower than that of the 20th century. It appears that they are defining the present as the early period of instrumental records when temperatures were less affected by human activity, but they do not specify exact years, or give a temperature for the present. Berkeley Earth publishes a list of average global temperatures by year. It shows that temperatures were stable from the beginning of records in 1850 until 1929. The average temperature during these years was . When subtracting 5.5 ± 1.5 °C (9.9 ± 2.7 °F) from the 1850-1929 average, the average temperature for the last glacial maximum comes out to 8.3 ± 1.5 °C (46.9 ± 2.7 °F). This is about 6.7 ± 1.5 °C (12.0 ± 2.7 °F) colder than the 2011-2020 average. This figure is open to interpretation because the IPCC does not specify 1850-1829 as being the present, or give any exact set of years as being the present. It also does not state whether or not they agree with the figures given by Berkeley Earth. According to the United States Geographical Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level was about lower than in present times (2012). The volume of ice on Earth was around , which is about 2.1 times Earth's current volume of ice.

Holocene

Anna_Ancher_-_Harvesters_-_Google_Art_Project

The Earth is currently in an interglacial period called the

epoch. However, there is debate as to whether it is actually a separate epoch or merely an interglacial period within the Pleistocene epoch. Between 9,000 and 5,000 years ago there was a warm period called the

Holocene climatic optimum 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 ...

. Being in an interglacial, there is less ice than there was during the last glacial period. However, the last glacial period was just one part of the ice age that still continues today. Even though Earth is in an interglacial, there is still more ice than times outside of ice ages. There are also currently ice sheets in the

, which means that there is more ice on Earth than there was during the first 31 million years of the Late Cenozoic Ice Age. During that time, only the Antarctic ice sheets existed. Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice according to the USGS. The total volume of ice presently on Earth is about (as of 2004). The current sea level (as of 2009) is lower than it would be without the ice sheets of Antarctica and Greenland. Based on the Milankovitch cycles, the current interglacial period is predicted to be unusually long, continuing for another 25,000 to 50,000 years beyond present times. There are also high concentrations of greenhouse gases in the atmosphere from human activity, and it is almost certain to get higher in the coming decades. This will lead to higher temperatures. In 25,000 to 50,000 years, the climate will begin to cool due to the Milankovich cycles. However, the high levels of greenhouse gases are predicted to keep it from getting cold enough to build up enough ice to meet the criteria of a glacial period. This would effectively extend the current interglacial period an additional 100,000 years placing the next glacial period 125,000 to 150,000 years in the future.

References

External links

Blue Marble 3000
an animation by Zurich University of Applied Sciences showing global ice sheets from 19,000 BCE to 3000 CE {{Greenhouse and Icehouse Earth History of Antarctica Antarctic region Aquitanian (stage) Burdigalian Calabrian (stage) Cenozoic Chattian Gelasian Holocene Ice ages Langhian Late Pleistocene Middle Pleistocene Messinian Miocene Neogene Oligocene Paleogene Phanerozoic Piacenzian Pleistocene Pliocene Quaternary Rupelian Serravallian Tortonian Zanclean