fbpx
Wikipedia

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 greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the ice age called Quaternary glaciation.[1] Individual pulses of cold climate within an ice age are termed glacial periods (or, alternatively, glacials, glaciations, glacial stages, stadials, stades, or colloquially, ice ages), and intermittent warm periods within an ice age are called interglacials or interstadials.[2]

An artist's impression of ice age Earth at Pleistocene glacial maximum

In glaciology, ice age implies the presence of extensive ice sheets in the northern and southern hemispheres.[3] By this definition, Earth is in an interglacial period—the Holocene. The amount of anthropogenic greenhouse gases emitted into Earth's oceans and atmosphere is projected to delay the next glacial period, which otherwise would begin in around 50,000 years, by between 100,000 and 500,000 years.[4][5][6]

History of research

In 1742, Pierre Martel (1706–1767), an engineer and geographer living in Geneva, visited the valley of Chamonix in the Alps of Savoy.[7][8] Two years later he published an account of his journey. He reported that the inhabitants of that valley attributed the dispersal of erratic boulders to the glaciers, saying that they had once extended much farther.[9][10] Later similar explanations were reported from other regions of the Alps. In 1815 the carpenter and chamois hunter Jean-Pierre Perraudin (1767–1858) explained erratic boulders in the Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further.[11] An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss-German geologist Jean de Charpentier (1786–1855) in 1834.[12] Comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland[13] and in Goethe's scientific work.[14] Such explanations could also be found in other parts of the world. When the Bavarian naturalist Ernst von Bibra (1806–1878) visited the Chilean Andes in 1849–1850, the natives attributed fossil moraines to the former action of glaciers.[15]

Meanwhile, European scholars had begun to wonder what had caused the dispersal of erratic material. From the middle of the 18th century, some discussed ice as a means of transport. The Swedish mining expert Daniel Tilas (1712–1772) was, in 1742, the first person to suggest drifting sea ice was a cause of the presence of erratic boulders in the Scandinavian and Baltic regions.[16] In 1795, the Scottish philosopher and gentleman naturalist, James Hutton (1726–1797), explained erratic boulders in the Alps by the action of glaciers.[17] Two decades later, in 1818, the Swedish botanist Göran Wahlenberg (1780–1851) published his theory of a glaciation of the Scandinavian peninsula. He regarded glaciation as a regional phenomenon.[18]

 
Haukalivatnet lake (50 meters above sea level) where Jens Esmark in 1823 discovered similarities to moraines near existing glaciers in the high mountains

Only a few years later, the Danish-Norwegian geologist Jens Esmark (1762–1839) argued for a sequence of worldwide ice ages. In a paper published in 1824, Esmark proposed changes in climate as the cause of those glaciations. He attempted to show that they originated from changes in Earth's orbit.[19] Esmark discovered the similarity between moraines near Haukalivatnet lake near sea level in Rogaland and moraines at branches of Jostedalsbreen. Esmark's discovery were later attributed to or appropriated by Theodor Kjerulf and Louis Agassiz.[20][21][22]

During the following years, Esmark's ideas were discussed and taken over in parts by Swedish, Scottish and German scientists. At the University of Edinburgh Robert Jameson (1774–1854) seemed to be relatively open to Esmark's ideas, as reviewed by Norwegian professor of glaciology Bjørn G. Andersen (1992).[23] Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark.[24] In Germany, Albrecht Reinhard Bernhardi (1797–1849), a geologist and professor of forestry at an academy in Dreissigacker (since incorporated in the southern Thuringian city of Meiningen), adopted Esmark's theory. In a paper published in 1832, Bernhardi speculated about the polar ice caps once reaching as far as the temperate zones of the globe.[25]

In Val de Bagnes, a valley in the Swiss Alps, there was a long-held local belief that the valley had once been covered deep in ice, and in 1815 a local chamois hunter called Jean-Pierre Perraudin attempted to convert the geologist Jean de Charpentier to the idea, pointing to deep striations in the rocks and giant erratic boulders as evidence. Charpentier held the general view that these signs were caused by vast floods, and he rejected Perraudin's theory as absurd. In 1818 the engineer Ignatz Venetz joined Perraudin and Charpentier to examine a proglacial lake above the valley created by an ice dam as a result of the 1815 eruption of Mount Tambora, which threatened to cause a catastrophic flood when the dam broke. Perraudin attempted unsuccessfully to convert his companions to his theory, but when the dam finally broke, there were only minor erratics and no striations, and Venetz concluded that Perraudin was right and that only ice could have caused such major results. In 1821 he read a prize-winning paper on the theory to the Swiss Society, but it was not published until Charpentier, who had also become converted, published it with his own more widely read paper in 1834.[26]

In the meantime, the German botanist Karl Friedrich Schimper (1803–1867) was studying mosses which were growing on erratic boulders in the alpine upland of Bavaria. He began to wonder where such masses of stone had come from. During the summer of 1835 he made some excursions to the Bavarian Alps. Schimper came to the conclusion that ice must have been the means of transport for the boulders in the alpine upland. In the winter of 1835–36 he held some lectures in Munich. Schimper then assumed that there must have been global times of obliteration ("Verödungszeiten") with a cold climate and frozen water.[27] Schimper spent the summer months of 1836 at Devens, near Bex, in the Swiss Alps with his former university friend Louis Agassiz (1801–1873) and Jean de Charpentier. Schimper, Charpentier and possibly Venetz convinced Agassiz that there had been a time of glaciation. During the winter of 1836–37, Agassiz and Schimper developed the theory of a sequence of glaciations. They mainly drew upon the preceding works of Venetz, Charpentier and on their own fieldwork. Agassiz appears to have been already familiar with Bernhardi's paper at that time.[28] At the beginning of 1837, Schimper coined the term "ice age" ("Eiszeit") for the period of the glaciers.[29] In July 1837 Agassiz presented their synthesis before the annual meeting of the Swiss Society for Natural Research at Neuchâtel. The audience was very critical, and some were opposed to the new theory because it contradicted the established opinions on climatic history. Most contemporary scientists thought that Earth had been gradually cooling down since its birth as a molten globe.[30]

In order to persuade the skeptics, Agassiz embarked on geological fieldwork. He published his book Study on Glaciers ("Études sur les glaciers") in 1840.[31] Charpentier was put out by this, as he had also been preparing a book about the glaciation of the Alps. Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in-depth glacial research.[32] As a result of personal quarrels, Agassiz had also omitted any mention of Schimper in his book.[33]

It took several decades before the ice age theory was fully accepted by scientists. This happened on an international scale in the second half of the 1870s, following the work of James Croll, including the publication of Climate and Time, in Their Geological Relations in 1875, which provided a credible explanation for the causes of ice ages.[34]

Evidence

There are three main types of evidence for ice ages: geological, chemical, and paleontological.

Geological evidence for ice ages comes in various forms, including rock scouring and scratching, glacial moraines, drumlins, valley cutting, and the deposition of till or tillites and glacial erratics. Successive glaciations tend to distort and erase the geological evidence for earlier glaciations, making it difficult to interpret. Furthermore, this evidence was difficult to date exactly; early theories assumed that the glacials were short compared to the long interglacials. The advent of sediment and ice cores revealed the true situation: glacials are long, interglacials short. It took some time for the current theory to be worked out.

The chemical evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks and ocean sediment cores. For the most recent glacial periods, ice cores provide climate proxies, both from the ice itself and from atmospheric samples provided by included bubbles of air. Because water containing lighter isotopes has a lower heat of evaporation, its proportion decreases with warmer conditions.[35] This allows a temperature record to be constructed. This evidence can be confounded, however, by other factors recorded by isotope ratios.

The paleontological evidence consists of changes in the geographical distribution of fossils. During a glacial period, cold-adapted organisms spread into lower latitudes, and organisms that prefer warmer conditions become extinct or retreat into lower latitudes. This evidence is also difficult to interpret because it requires:

  1. sequences of sediments covering a long period of time, over a wide range of latitudes and which are easily correlated;
  2. ancient organisms which survive for several million years without change and whose temperature preferences are easily diagnosed; and
  3. the finding of the relevant fossils.

Despite the difficulties, analysis of ice core and ocean sediment cores[36] has provided a credible record of glacials and interglacials over the past few million years. These also confirm the linkage between ice ages and continental crust phenomena such as glacial moraines, drumlins, and glacial erratics. Hence the continental crust phenomena are accepted as good evidence of earlier ice ages when they are found in layers created much earlier than the time range for which ice cores and ocean sediment cores are available.

Major ice ages

 
Timeline of glaciations, shown in blue

There have been at least five major ice ages in Earth's history (the Huronian, Cryogenian, Andean-Saharan, late Paleozoic, and the latest Quaternary Ice Age). Outside these ages, Earth was previously thought to have been ice-free even in high latitudes;[37][38] such periods are known as greenhouse periods.[39] However, other studies dispute this, finding evidence of occasional glaciations at high latitudes even during apparent greenhouse periods.[40][41]

 
Ice age map of northern Germany and its northern neighbours. Red: maximum limit of Weichselian glacial; yellow: Saale glacial at maximum (Drenthe stage); blue: Elster glacial maximum glaciation.

Rocks from the earliest well-established ice age, called the Huronian, have been dated to around 2.4 to 2.1 billion years ago during the early Proterozoic Eon. Several hundreds of kilometers of the Huronian Supergroup are exposed 10 to 100 kilometers (6 to 62 mi) north of the north shore of Lake Huron, extending from near Sault Ste. Marie to Sudbury, northeast of Lake Huron, with giant layers of now-lithified till beds, dropstones, varves, outwash, and scoured basement rocks. Correlative Huronian deposits have been found near Marquette, Michigan, and correlation has been made with Paleoproterozoic glacial deposits from Western Australia. The Huronian ice age was caused by the elimination of atmospheric methane, a greenhouse gas, during the Great Oxygenation Event.[42]

The next well-documented ice age, and probably the most severe of the last billion years, occurred from 720 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which glacial ice sheets reached the equator,[43] possibly being ended by the accumulation of greenhouse gases such as CO2 produced by volcanoes. "The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis, which are the two major sinks for CO2 at present."[44] It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian explosion, though this model is recent and controversial.

The Andean-Saharan occurred from 460 to 420 million years ago, during the Late Ordovician and the Silurian period.

 
Sediment records showing the fluctuating sequences of glacials and interglacials during the last several million years

The evolution of land plants at the onset of the Devonian period caused a long term increase in planetary oxygen levels and reduction of CO2 levels, which resulted in the late Paleozoic icehouse. Its former name, the Karoo glaciation, was named after the glacial tills found in the Karoo region of South Africa. There were extensive polar ice caps at intervals from 360 to 260 million years ago in South Africa during the Carboniferous and early Permian periods. Correlatives are known from Argentina, also in the center of the ancient supercontinent Gondwanaland.

Although the Mesozoic Era retained a greenhouse climate over its timespan and was previously assumed to have been entirely glaciation-free, more recent studies suggest that brief periods of glaciation occurred in both hemispheres during the Early Cretaceous. Geologic and palaeoclimatological records suggest the existence of glacial periods during the Valanginian, Hauterivian, and Aptian stages of the Early Cretaceous. Ice-rafted glacial dropstones indicate that in the Northern Hemisphere, ice sheets may have extended as far south as the Iberian Peninsula during the Hauterivian and Aptian.[45][46][47] Although ice sheets largely disappeared from Earth for the rest of the period (potential reports from the Turonian, otherwise the warmest period of the Phanerozoic, are disputed),[40][41] ice sheets and associated sea ice appear to have briefly returned to Antarctica near the very end of the Maastrichtian just prior to the Cretaceous-Paleogene extinction event.[41][48]

The Quaternary Glaciation / Quaternary Ice Age started about 2.58 million years ago at the beginning of the Quaternary Period when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods, glacials or glacial advances, and interglacial periods, interglacials or glacial retreats. Earth is currently in an interglacial, and the last glacial period ended about 11,700 years ago. All that remains of the continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island.

The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic (Eocene-Oligocene Boundary). The term Late Cenozoic Ice Age is used to include this early phase.[49]

Ice ages can be further divided by location and time; for example, the names Riss (180,000–130,000 years bp) and Würm (70,000–10,000 years bp) refer specifically to glaciation in the Alpine region. The maximum extent of the ice is not maintained for the full interval. The scouring action of each glaciation tends to remove most of the evidence of prior ice sheets almost completely, except in regions where the later sheet does not achieve full coverage.

Glacials and interglacials

 
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials.
Minimum and maximum glaciation
 
Minimum (interglacial, black) and maximum (glacial, grey) glaciation of the northern hemisphere
 
Minimum (interglacial, black) and maximum (glacial, grey) glaciation of the southern hemisphere

Within the current glaciation, more temperate and more severe periods have occurred. The colder periods are called glacial periods, the warmer periods interglacials, such as the Eemian Stage.[1] There is evidence that similar glacial cycles occurred in previous glaciations, including the Andean-Saharan[50] and the late Paleozoic ice house. The glacial cycles of the late Paleozoic ice house are likely responsible for the deposition of cyclothems.[51]

Glacials are characterized by cooler and drier climates over most of Earth and large land and sea ice masses extending outward from the poles. Mountain glaciers in otherwise unglaciated areas extend to lower elevations due to a lower snow line. Sea levels drop due to the removal of large volumes of water above sea level in the icecaps. There is evidence that ocean circulation patterns are disrupted by glaciations. The glacials and interglacials coincide with changes in orbital forcing of climate due to Milankovitch cycles, which are periodic changes in Earth's orbit and the tilt of Earth's rotational axis.

Earth has been in an interglacial period known as the Holocene for around 11,700 years,[52] and an article in Nature in 2004 argues that it might be most analogous to a previous interglacial that lasted 28,000 years.[53] Predicted changes in orbital forcing suggest that the next glacial period would begin at least 50,000 years from now. Moreover, anthropogenic forcing from increased greenhouse gases is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years.[54][5][4]

Feedback processes

Each glacial period is subject to positive feedback which makes it more severe, and negative feedback which mitigates and (in all cases so far) eventually ends it.

Positive

An important form of feedback is provided by Earth's albedo, which is how much of the sun's energy is reflected rather than absorbed by Earth. Ice and snow increase Earth's albedo, while forests reduce its albedo. When the air temperature decreases, ice and snow fields grow, and they reduce forest cover. This continues until competition with a negative feedback mechanism forces the system to an equilibrium.

One theory is that when glaciers form, two things happen: the ice grinds rocks into dust, and the land becomes dry and arid. This allows winds to transport iron rich dust into the open ocean, where it acts as a fertilizer that causes massive algal blooms that pulls large amounts of CO2 out of the atmosphere. This in turn makes it even colder and causes the glaciers to grow more.[55]

In 1956, Ewing and Donn[56] hypothesized that an ice-free Arctic Ocean leads to increased snowfall at high latitudes. When low-temperature ice covers the Arctic Ocean there is little evaporation or sublimation and the polar regions are quite dry in terms of precipitation, comparable to the amount found in mid-latitude deserts. This low precipitation allows high-latitude snowfalls to melt during the summer. An ice-free Arctic Ocean absorbs solar radiation during the long summer days, and evaporates more water into the Arctic atmosphere. With higher precipitation, portions of this snow may not melt during the summer and so glacial ice can form at lower altitudes and more southerly latitudes, reducing the temperatures over land by increased albedo as noted above. Furthermore, under this hypothesis the lack of oceanic pack ice allows increased exchange of waters between the Arctic and the North Atlantic Oceans, warming the Arctic and cooling the North Atlantic. (Current projected consequences of global warming include a brief ice-free Arctic Ocean period by 2050.) Additional fresh water flowing into the North Atlantic during a warming cycle may also reduce the global ocean water circulation. Such a reduction (by reducing the effects of the Gulf Stream) would have a cooling effect on northern Europe, which in turn would lead to increased low-latitude snow retention during the summer.[57][58][59] It has also been suggested[by whom?] that during an extensive glacial, glaciers may move through the Gulf of Saint Lawrence, extending into the North Atlantic Ocean far enough to block the Gulf Stream.

Negative

Ice sheets that form during glaciations erode the land beneath them. This can reduce the land area above sea level and thus diminish the amount of space on which ice sheets can form. This mitigates the albedo feedback, as does the rise in sea level that accompanies the reduced area of ice sheets, since open ocean has a lower albedo than land.[60]

Another negative feedback mechanism is the increased aridity occurring with glacial maxima, which reduces the precipitation available to maintain glaciation. The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances.[61]

According to research published in Nature Geoscience, human emissions of carbon dioxide (CO2) will defer the next glacial period. Researchers used data on Earth's orbit to find the historical warm interglacial period that looks most like the current one and from this have predicted that the next glacial period would usually begin within 1,500 years. They go on to predict that emissions have been so high that it will not.[62]

Causes

The causes of ice ages are not fully understood for either the large-scale ice age periods or the smaller ebb and flow of glacial–interglacial periods within an ice age. The consensus is that several factors are important: atmospheric composition, such as the concentrations of carbon dioxide and methane (the specific levels of the previously mentioned gases are now able to be seen with the new ice core samples from the European Project for Ice Coring in Antarctica (EPICA) Dome C in Antarctica over the past 800,000 years); changes in Earth's orbit around the Sun known as Milankovitch cycles; the motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on Earth's surface, which affect wind and ocean currents; variations in solar output; the orbital dynamics of the Earth–Moon system; the impact of relatively large meteorites and volcanism including eruptions of supervolcanoes.[63][citation needed]

Some of these factors influence each other. For example, changes in Earth's atmospheric composition (especially the concentrations of greenhouse gases) may alter the climate, while climate change itself can change the atmospheric composition (for example by changing the rate at which weathering removes CO2).

Maureen Raymo, William Ruddiman and others propose that the Tibetan and Colorado Plateaus are immense CO2 "scrubbers" with a capacity to remove enough CO2 from the global atmosphere to be a significant causal factor of the 40 million year Cenozoic Cooling trend. They further claim that approximately half of their uplift (and CO2 "scrubbing" capacity) occurred in the past 10 million years.[64][65]

Changes in Earth's atmosphere

There is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets, but it is difficult to establish cause and effect (see the notes above on the role of weathering). Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages, such as the movement of continents and volcanism.

The Snowball Earth hypothesis maintains that the severe freezing in the late Proterozoic was ended by an increase in CO2 levels in the atmosphere, mainly from volcanoes, and some supporters of Snowball Earth argue that it was caused in the first place by a reduction in atmospheric CO2. The hypothesis also warns of future Snowball Earths.

In 2009, further evidence was provided that changes in solar insolation provide the initial trigger for Earth to warm after an Ice Age, with secondary factors like increases in greenhouse gases accounting for the magnitude of the change.[66]

Position of the continents

The geological record appears to show that ice ages start when the continents are in positions which block or reduce the flow of warm water from the equator to the poles and thus allow ice sheets to form. The ice sheets increase Earth's reflectivity and thus reduce the absorption of solar radiation. With less radiation absorbed the atmosphere cools; the cooling allows the ice sheets to grow, which further increases reflectivity in a positive feedback loop. The ice age continues until the reduction in weathering causes an increase in the greenhouse effect.

There are three main contributors from the layout of the continents that obstruct the movement of warm water to the poles:[67]

  • A continent sits on top of a pole, as Antarctica does today.
  • A polar sea is almost land-locked, as the Arctic Ocean is today.
  • A supercontinent covers most of the equator, as Rodinia did during the Cryogenian period.

Since today's Earth has a continent over the South Pole and an almost land-locked ocean over the North Pole, geologists believe that Earth will continue to experience glacial periods in the geologically near future.

Some scientists believe that the Himalayas are a major factor in the current ice age, because these mountains have increased Earth's total rainfall and therefore the rate at which carbon dioxide is washed out of the atmosphere, decreasing the greenhouse effect.[65] The Himalayas' formation started about 70 million years ago when the Indo-Australian Plate collided with the Eurasian Plate, and the Himalayas are still rising by about 5 mm per year because the Indo-Australian plate is still moving at 67 mm/year. The history of the Himalayas broadly fits the long-term decrease in Earth's average temperature since the mid-Eocene, 40 million years ago.

Fluctuations in ocean currents

Another important contribution to ancient climate regimes is the variation of ocean currents, which are modified by continent position, sea levels and salinity, as well as other factors. They have the ability to cool (e.g. aiding the creation of Antarctic ice) and the ability to warm (e.g. giving the British Isles a temperate as opposed to a boreal climate). The closing of the Isthmus of Panama about 3 million years ago may have ushered in the present period of strong glaciation over North America by ending the exchange of water between the tropical Atlantic and Pacific Oceans.[68]

Analyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations. During the last glacial period the sea-level has fluctuated 20–30 m as water was sequestered, primarily in the Northern Hemisphere ice sheets. When ice collected and the sea level dropped sufficiently, flow through the Bering Strait (the narrow strait between Siberia and Alaska is about 50 m deep today) was reduced, resulting in increased flow from the North Atlantic. This realigned the thermohaline circulation in the Atlantic, increasing heat transport into the Arctic, which melted the polar ice accumulation and reduced other continental ice sheets. The release of water raised sea levels again, restoring the ingress of colder water from the Pacific with an accompanying shift to northern hemisphere ice accumulation.[69]

According to a study published in Nature in 2021, all glacial periods of ice ages over the last 1.5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns, leading to more CO2 being pulled out of the atmosphere. The authors suggest that this process may be disrupted in the future as the Southern Ocean will become too warm for the icebergs to travel far enough to trigger these changes.[70][71]

Uplift of the Tibetan plateau

Matthias Kuhle's geological theory of Ice Age development was suggested by the existence of an ice sheet covering the Tibetan Plateau during the Ice Ages (Last Glacial Maximum?). According to Kuhle, the plate-tectonic uplift of Tibet past the snow-line has led to a surface of c. 2,400,000 square kilometres (930,000 sq mi) changing from bare land to ice with a 70% greater albedo. The reflection of energy into space resulted in a global cooling, triggering the Pleistocene Ice Age. Because this highland is at a subtropical latitude, with 4 to 5 times the insolation of high-latitude areas, what would be Earth's strongest heating surface has turned into a cooling surface.

Kuhle explains the interglacial periods by the 100,000-year cycle of radiation changes due to variations in Earth's orbit. This comparatively insignificant warming, when combined with the lowering of the Nordic inland ice areas and Tibet due to the weight of the superimposed ice-load, has led to the repeated complete thawing of the inland ice areas.[72][73][74][75]

Variations in Earth's orbit

The Milankovitch cycles are a set of cyclic variations in characteristics of Earth's orbit around the Sun. Each cycle has a different length, so at some times their effects reinforce each other and at other times they (partially) cancel each other.

 
Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice, at 65 N latitude

There is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. The present ice age is the most studied and best understood, particularly the last 400,000 years, since this is the period covered by ice cores that record atmospheric composition and proxies for temperature and ice volume. Within this period, the match of glacial/interglacial frequencies to the Milanković orbital forcing periods is so close that orbital forcing is generally accepted. The combined effects of the changing distance to the Sun, the precession of Earth's axis, and the changing tilt of Earth's axis redistribute the sunlight received by Earth. Of particular importance are changes in the tilt of Earth's axis, which affect the intensity of seasons. For example, the amount of solar influx in July at 65 degrees north latitude varies by as much as 22% (from 450 W/m2 to 550 W/m2). It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter. Some believe that the strength of the orbital forcing is too small to trigger glaciations, but feedback mechanisms like CO2 may explain this mismatch.

While Milankovitch forcing predicts that cyclic changes in Earth's orbital elements can be expressed in the glaciation record, additional explanations are necessary to explain which cycles are observed to be most important in the timing of glacial–interglacial periods. In particular, during the last 800,000 years, the dominant period of glacial–interglacial oscillation has been 100,000 years, which corresponds to changes in Earth's orbital eccentricity and orbital inclination. Yet this is by far the weakest of the three frequencies predicted by Milankovitch. During the period 3.0–0.8 million years ago, the dominant pattern of glaciation corresponded to the 41,000-year period of changes in Earth's obliquity (tilt of the axis). The reasons for dominance of one frequency versus another are poorly understood and an active area of current research, but the answer probably relates to some form of resonance in Earth's climate system. Recent work suggests that the 100K year cycle dominates due to increased southern-pole sea-ice increasing total solar reflectivity.[76][77]

The "traditional" Milankovitch explanation struggles to explain the dominance of the 100,000-year cycle over the last 8 cycles. Richard A. Muller, Gordon J. F. MacDonald,[78][79][80] and others have pointed out that those calculations are for a two-dimensional orbit of Earth but the three-dimensional orbit also has a 100,000-year cycle of orbital inclination. They proposed that these variations in orbital inclination lead to variations in insolation, as Earth moves in and out of known dust bands in the solar system. Although this is a different mechanism to the traditional view, the "predicted" periods over the last 400,000 years are nearly the same. The Muller and MacDonald theory, in turn, has been challenged by Jose Antonio Rial.[81]

Another worker, William Ruddiman, has suggested a model that explains the 100,000-year cycle by the modulating effect of eccentricity (weak 100,000-year cycle) on precession (26,000-year cycle) combined with greenhouse gas feedbacks in the 41,000- and 26,000-year cycles. Yet another theory has been advanced by Peter Huybers who argued that the 41,000-year cycle has always been dominant, but that Earth has entered a mode of climate behavior where only the second or third cycle triggers an ice age. This would imply that the 100,000-year periodicity is really an illusion created by averaging together cycles lasting 80,000 and 120,000 years.[82] This theory is consistent with a simple empirical multi-state model proposed by Didier Paillard.[83] Paillard suggests that the late Pleistocene glacial cycles can be seen as jumps between three quasi-stable climate states. The jumps are induced by the orbital forcing, while in the early Pleistocene the 41,000-year glacial cycles resulted from jumps between only two climate states. A dynamical model explaining this behavior was proposed by Peter Ditlevsen.[84] This is in support of the suggestion that the late Pleistocene glacial cycles are not due to the weak 100,000-year eccentricity cycle, but a non-linear response to mainly the 41,000-year obliquity cycle.

Variations in the Sun's energy output

There are at least two types of variation in the Sun's energy output:[85]

  • In the very long term, astrophysicists believe that the Sun's output increases by about 7% every one billion years.
  • Shorter-term variations such as sunspot cycles, and longer episodes such as the Maunder Minimum, which occurred during the coldest part of the Little Ice Age.

The long-term increase in the Sun's output cannot be a cause of ice ages.

Volcanism

Volcanic eruptions may have contributed to the inception and/or the end of ice age periods. At times during the paleoclimate, carbon dioxide levels were two or three times greater than today. Volcanoes and movements in continental plates contributed to high amounts of CO2 in the atmosphere. Carbon dioxide from volcanoes probably contributed to periods with highest overall temperatures.[86] One suggested explanation of the Paleocene–Eocene Thermal Maximum is that undersea volcanoes released methane from clathrates and thus caused a large and rapid increase in the greenhouse effect.[87] There appears to be no geological evidence for such eruptions at the right time, but this does not prove they did not happen.

Recent glacial and interglacial phases

 
Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a sea level lowering of about 120 m.

The current geological period, the Quaternary, which began about 2.6 million years ago and extends into the present,[2] is marked by warm and cold episodes, cold phases called glacials (Quaternary ice age) lasting about 100,000 years, and which are then interrupted by the warmer interglacials which lasted about 10,000–15,000 years. The last cold episode of the Last Glacial Period ended about 10,000 years ago.[88] Earth is currently in an interglacial period of the Quaternary, called the Holocene.

Glacial stages in North America

The major glacial stages of the current ice age in North America are the Illinoian, Eemian, and Wisconsin glaciation. The use of the Nebraskan, Afton, Kansan, and Yarmouthian stages to subdivide the ice age in North America has been discontinued by Quaternary geologists and geomorphologists. These stages have all been merged into the Pre-Illinoian in the 1980s.[89][90][91]

During the most recent North American glaciation, during the latter part of the Last Glacial Maximum (26,000 to 13,300 years ago), ice sheets extended to about 45th parallel north. These sheets were 3 to 4 kilometres (1.9 to 2.5 mi) thick.[90]

 
Stages of proglacial lake development in the region of the current North American Great Lakes

This Wisconsin glaciation left widespread impacts on the North American landscape. The Great Lakes and the Finger Lakes were carved by ice deepening old valleys. Most of the lakes in Minnesota and Wisconsin were gouged out by glaciers and later filled with glacial meltwaters. The old Teays River drainage system was radically altered and largely reshaped into the Ohio River drainage system. Other rivers were dammed and diverted to new channels, such as Niagara Falls, which formed a dramatic waterfall and gorge, when the waterflow encountered a limestone escarpment. Another similar waterfall, at the present Clark Reservation State Park near Syracuse, New York, is now dry.

The area from Long Island to Nantucket, Massachusetts was formed from glacial till, and the plethora of lakes on the Canadian Shield in northern Canada can be almost entirely attributed to the action of the ice. As the ice retreated and the rock dust dried, winds carried the material hundreds of miles, forming beds of loess many dozens of feet thick in the Missouri Valley. Post-glacial rebound continues to reshape the Great Lakes and other areas formerly under the weight of the ice sheets.

The Driftless Area, a portion of western and southwestern Wisconsin along with parts of adjacent Minnesota, Iowa, and Illinois, was not covered by glaciers.

Last Glacial Period in the semiarid Andes around Aconcagua and Tupungato

A specially interesting climatic change during glacial times has taken place in the semi-arid Andes. Beside the expected cooling down in comparison with the current climate, a significant precipitation change happened here. So, researches in the presently semiarid subtropic Aconcagua-massif (6,962 m) have shown an unexpectedly extensive glacial glaciation of the type "ice stream network".[92][93][94][95][96] The connected valley glaciers exceeding 100 km in length, flowed down on the East-side of this section of the Andes at 32–34°S and 69–71°W as far as a height of 2,060 m and on the western luff-side still clearly deeper.[96][97] Where current glaciers scarcely reach 10 km in length, the snowline (ELA) runs at a height of 4,600 m and at that time was lowered to 3,200 m asl, i.e. about 1,400 m. From this follows that—beside of an annual depression of temperature about c. 8.4 °C— here was an increase in precipitation. Accordingly, at glacial times the humid climatic belt that today is situated several latitude degrees further to the S, was shifted much further to the N.[95][96]

Effects of glaciation

 
Scandinavia exhibits some of the typical effects of ice age glaciation such as fjords and lakes.

Although the last glacial period ended more than 8,000 years ago, its effects can still be felt today. For example, the moving ice carved out the landscape in Canada (See Canadian Arctic Archipelago), Greenland, northern Eurasia and Antarctica. The erratic boulders, till, drumlins, eskers, fjords, kettle lakes, moraines, cirques, horns, etc., are typical features left behind by the glaciers. The weight of the ice sheets was so great that they deformed Earth's crust and mantle. After the ice sheets melted, the ice-covered land rebounded. Due to the high viscosity of Earth's mantle, the flow of mantle rocks which controls the rebound process is very slow—at a rate of about 1 cm/year near the center of rebound area today.

During glaciation, water was taken from the oceans to form the ice at high latitudes, thus global sea level dropped by about 110 meters, exposing the continental shelves and forming land-bridges between land-masses for animals to migrate. During deglaciation, the melted ice-water returned to the oceans, causing sea level to rise. This process can cause sudden shifts in coastlines and hydration systems resulting in newly submerged lands, emerging lands, collapsed ice dams resulting in salination of lakes, new ice dams creating vast areas of freshwater, and a general alteration in regional weather patterns on a large but temporary scale. It can even cause temporary reglaciation. This type of chaotic pattern of rapidly changing land, ice, saltwater and freshwater has been proposed as the likely model for the Baltic and Scandinavian regions, as well as much of central North America at the end of the last glacial maximum, with the present-day coastlines only being achieved in the last few millennia of prehistory. Also, the effect of elevation on Scandinavia submerged a vast continental plain that had existed under much of what is now the North Sea, connecting the British Isles to Continental Europe.[98]

The redistribution of ice-water on the surface of Earth and the flow of mantle rocks causes changes in the gravitational field as well as changes to the distribution of the moment of inertia of Earth. These changes to the moment of inertia result in a change in the angular velocity, axis, and wobble of Earth's rotation.

The weight of the redistributed surface mass loaded the lithosphere, caused it to flex and also induced stress within Earth. The presence of the glaciers generally suppressed the movement of faults below.[99][100][101] During deglaciation, the faults experience accelerated slip triggering earthquakes. Earthquakes triggered near the ice margin may in turn accelerate ice calving and may account for the Heinrich events.[102] As more ice is removed near the ice margin, more intraplate earthquakes are induced and this positive feedback may explain the fast collapse of ice sheets.

In Europe, glacial erosion and isostatic sinking from weight of ice made the Baltic Sea, which before the Ice Age was all land drained by the Eridanos River.


Future ice ages

A 2015 report by the Past Global Changes Project says simulations show that a new glaciation is unlikely to happen within the next approximately 50,000 years, before the next strong drop in Northern Hemisphere summer insolation occurs "if either atmospheric CO2 concentration remains above 300 ppm or cumulative carbon emissions exceed 1000 Pg C" (i.e. 1,000 gigatonnes carbon). "Only for an atmospheric CO2 content below the preindustrial level may a glaciation occur within the next 10 ka. ... Given the continued anthropogenic CO2 emissions, glacial inception is very unlikely to occur in the next 50 ka, because the timescale for CO2 and temperature reduction toward unperturbed values in the absence of active removal is very long [IPCC, 2013], and only weak precessional forcing occurs in the next two precessional cycles." (A precessional cycle is around 21,000 years, the time it takes for the perihelion to move all the way around the tropical year.)[103]

Ice ages go through cycles of about 100,000 years, but the next one may well be avoided due to our carbon dioxide emissions.[5]

See also

References

  1. ^ a b Ehlers, Jürgen; Gibbard, Philip (2011). "Quaternary Glaciation". Encyclopedia of Snow, Ice and Glaciers. Encyclopedia of Earth Sciences Series. pp. 873–882. doi:10.1007/978-90-481-2642-2_423. ISBN 978-90-481-2641-5.
  2. ^ a b Cohen, K .M.; Finney, S. C.; Gibbard, P. L.; Fan, J.-X. "International Chronostratigraphic Chart 2013" (PDF). stratigraphy.org. ICS. Retrieved 7 January 2019.
  3. ^ Imbrie, J.; Imbrie, K. P. (1979). Ice ages: solving the mystery. Short Hills NJ: Enslow Publishers. ISBN 978-0-89490-015-0.
  4. ^ a b Thomson, Andrea (2007). "Global Warming Good News: No More Ice Ages". LiveScience.
  5. ^ a b c . Potsdam Institute for Climate Impact Research in Germany. 2016. Archived from the original on 2020-08-18. Retrieved 2019-01-07.
  6. ^ Archer, David; Ganopolski, Andrey (May 2005). "A movable trigger: Fossil fuel CO2 and the onset of the next glaciation". Geochemistry, Geophysics, Geosystems. 6 (5). Bibcode:2005GGG.....6.5003A. doi:10.1029/2004GC000891. S2CID 18549459.
  7. ^ Rémy F, Testut L (2006). "Mais comment s'écoule donc un glacier ? Aperçu historique" (PDF). Comptes Rendus Geoscience (in French). 338 (5): 368–385. Bibcode:2006CRGeo.338..368R. doi:10.1016/j.crte.2006.02.004. Note: p. 374
  8. ^ Montgomery 2010
  9. ^ Martel, Pierre (1898). "Appendix: Martel, P. (1744) An account of the glacieres or ice alps in Savoy, in two letters, one from an English gentleman to his friend at Geneva; the other from Pierre Martel, engineer, to the said English gentleman". In Mathews, C.E. (ed.). The annals of Mont Blanc. London: Unwin. p. 327. See (Montgomery 2010) for a full bibliography
  10. ^ Krüger, Tobias (2013). Discovering the Ice Ages. International Reception and Consequences for a Historical Understanding of Climate (German edition: Basel 2008). Leiden. p. 47. ISBN 978-90-04-24169-5.{{cite book}}: CS1 maint: location missing publisher (link)
  11. ^ Krüger 2013, pp. 78–83
  12. ^ Krüger 2013, p. 150
  13. ^ Krüger 2013, pp. 83, 151
  14. ^ Goethe, Johann Wolfgang von: Geologische Probleme und Versuch ihrer Auflösung, Mineralogie und Geologie in Goethes Werke, Weimar 1892, ISBN 3-423-05946-X, book 73 (WA II, 9), pp. 253, 254.
  15. ^ Krüger 2013, p. 83
  16. ^ Krüger 2013, p. 38
  17. ^ Krüger 2013, pp. 61–2
  18. ^ Krüger 2013, pp. 88–90
  19. ^ Krüger 2013, pp. 91–6
  20. ^ Hestmark, Geir (2018). "Jens Esmark's mountain glacier traverse 1823 − the key to his discovery of Ice Ages". Boreas. 47 (1): 1–10. Bibcode:2018Borea..47....1H. doi:10.1111/bor.12260. hdl:10852/67376. ISSN 1502-3885. The discovery of Ice Ages is one of the most revolutionary advances made in the Earth sciences. In 1824 Danish-Norwegian geoscientist Jens Esmark published a paper stating that there was indisputable evidence that Norway and other parts of Europe had previously been covered by enormous glaciers carving out valleys and fjords, in a cold climate caused by changes in the eccentricity of Earth's orbit. Esmark and his travel companion Otto Tank arrived at this insight by analogous reasoning: enigmatic landscape features they observed close to sea level along the Norwegian coast strongly resembled features they observed in the front of a retreating glacier during a mountain traverse in the summer of 1823.
  21. ^ Berg, Bjørn Ivar (2020-02-25), "Jens Esmark", Norsk biografisk leksikon (in Norwegian Bokmål), retrieved 2021-02-28
  22. ^ Hverven, Tom Egil. "Isens spor". Klassekampen. Retrieved 2021-02-28.
  23. ^ Andersen, Bjørn G. (1992). "Jens Esmark—a pioneer in glacial geology". Boreas. 21 (1): 97–102. Bibcode:1992Borea..21...97A. doi:10.1111/j.1502-3885.1992.tb00016.x.
  24. ^ Davies, Gordon L. (1969). The Earth in Decay. A History of British Geomorphology 1578–1878. London: New York, American Elsevier Pub. Co. pp. 267f. ISBN 9780444197016.
    Cunningham, Frank F. (1990). James David Forbes. Pioneer Scottish Glaciologist. Edinburgh: Scottish Academic Press. p. 15. ISBN 978-0-7073-0320-8.
  25. ^ Krüger 2013, pp. 142–47
  26. ^ Wood, Gillen D’Arcy (2014). Tambora, the Eruption that Changed the World. Princeton, NJ: Princeton University Press. pp. 160–167. ISBN 978-0-691-16862-3.
  27. ^ Krüger 2013, pp. 155–59
  28. ^ Krüger 2013, pp. 167–70
  29. ^ Krüger 2013, p. 173
  30. ^ Krüger 2013, pp. 177–78
  31. ^ Agassiz, Louis; Bettannier, Joseph (1840). Études sur les glaciers. Ouvrage accompagné d'un atlas de 32 planches, Neuchâtel. H. Nicolet.
  32. ^ Krüger 2013, pp. 223–4. Charpentier, Jean de: Essais sur les glaciers et sur le terrain erratique du bassin du Rhône, Lausanne 1841.
  33. ^ Krüger 2013, pp. 181–84
  34. ^ Krüger 2013, pp. 458–60
  35. ^ "How are past temperatures determined from an ice core?". Scientific American. 2004-09-20.
  36. ^ Putnam, Aaron E.; Denton, George H.; Schaefer, Joerg M.; Barrell, David J. A.; Andersen, Bjørn G.; Finkel, Robert C.; Schwartz, Roseanne; Doughty, Alice M.; Kaplan, Michael R.; Schlüchter, Christian (2010). "Glacier advance in southern middle-latitudes during the Antarctic Cold Reversal". Nature Geoscience. 3 (10): 700–704. Bibcode:2010NatGe...3..700P. doi:10.1038/ngeo962.
  37. ^ Lockwood, J.G.; Zinderen-Bakker, E. M. van (November 1979). "The Antarctic Ice-Sheet: Regulator of Global Climates?: Review". The Geographical Journal. 145 (3): 469–471. doi:10.2307/633219. JSTOR 633219.
  38. ^ Warren, John K. (2006). Evaporites: sediments, resources and hydrocarbons. Birkhäuser. p. 289. ISBN 978-3-540-26011-0.
  39. ^ Allaby, Michael (January 2013). A Dictionary of Geology and Earth Sciences (Fourth ed.). Oxford University Press. ISBN 9780199653065. Retrieved 17 Sep 2019.[permanent dead link]
  40. ^ a b Bornemann, André; Norris, Richard D.; Friedrich, Oliver; Beckmann, Britta; Schouten, Stefan; Damsté, Jaap S. Sinninghe; Vogel, Jennifer; Hofmann, Peter; Wagner, Thomas (2008-01-11). "Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse". Science. 319 (5860): 189–192. Bibcode:2008Sci...319..189B. doi:10.1126/science.1148777. ISSN 0036-8075. PMID 18187651. S2CID 206509273.
  41. ^ a b c Ladant, Jean-Baptiste; Donnadieu, Yannick (2016-09-21). "Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse". Nature Communications. 7 (1): 12771. Bibcode:2016NatCo...712771L. doi:10.1038/ncomms12771. ISSN 2041-1723. PMC 5036002. PMID 27650167.
  42. ^ Kopp, Robert (14 June 2005). "The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis". PNAS. 102 (32): 11131–6. Bibcode:2005PNAS..10211131K. doi:10.1073/pnas.0504878102. PMC 1183582. PMID 16061801.
  43. ^ Hyde WT, Crowley TJ, Baum SK, Peltier WR (May 2000). "Neoproterozoic 'snowball Earth' simulations with a coupled climate/ice-sheet model" (PDF). Nature. 405 (6785): 425–9. Bibcode:2000Natur.405..425H. doi:10.1038/35013005. PMID 10839531. S2CID 1672712.
  44. ^ Chris Clowes (2003). . Paleos: Life through deep time. Archived from the original on 15 June 2009.
  45. ^ Rodríguez-López, Juan Pedro; Liesa, Carlos L.; Pardo, Gonzalo; Meléndez, Nieves; Soria, Ana R.; Skilling, Ian (2016-06-15). "Glacial dropstones in the western Tethys during the late Aptian–early Albian cold snap: Palaeoclimate and palaeogeographic implications for the mid-Cretaceous". Palaeogeography, Palaeoclimatology, Palaeoecology. 452: 11–27. Bibcode:2016PPP...452...11R. doi:10.1016/j.palaeo.2016.04.004. ISSN 0031-0182.
  46. ^ Rodríguez-López, Juan Pedro; Liesa, Carlos L.; Luzón, Aránzazu; Muñoz, Arsenio; Mayayo, María J.; Murton, Julian B.; Soria, Ana R. (2023-10-10). "Ice-rafted dropstones at midlatitudes in the Cretaceous of continental Iberia". Geology. 52: 33–38. doi:10.1130/g51725.1. ISSN 0091-7613.
  47. ^ Wang, Tianyang; He, Songlin; Zhang, Qinghai; Ding, Lin; Farnsworth, Alex; Cai, Fulong; Wang, Chao; Xie, Jing; Li, Guobiao; Sheng, Jiani; Yue, Yahui (2023-05-26). "Ice Sheet Expansion in the Cretaceous Greenhouse World". Fundamental Research. doi:10.1016/j.fmre.2023.05.005. ISSN 2667-3258.
  48. ^ Bowman, Vanessa C.; Francis, Jane E.; Riding, James B. (December 1, 2013). "Late Cretaceous winter sea ice in Antarctica?". Geology. 41 (12): 1227–1230. Bibcode:2013Geo....41.1227B. doi:10.1130/g34891.1. S2CID 128885087. Retrieved 2023-10-26.
  49. ^ University of Houston-Clear Lake - Disasters Class Notes - Chapter 12: Climate Change sce.uhcl.edu/Pitts/disastersclassnotes/chapter_12_Climate_Change.doc
  50. ^ Ghienne, Jean-François (January 2003). "Late Ordovician sedimentary environments, glacial cycles, and post-glacial transgression in the Taoudeni Basin, West Africa". Palaeogeography, Palaeoclimatology, Palaeoecology. 189 (3–4): 117–145. Bibcode:2003PPP...189..117G. doi:10.1016/S0031-0182(02)00635-1.
  51. ^ Heckel, P.H. (2008). "Pennsylvanian cyclothems in Midcontinent North America as far-field effects of waxing and waning of Gondwana ice sheets". In Fielding, C.R.; Frank, T.D.; Isbell, J.L. (eds.). Resolving the Late Paleozoic Ice Age in Time and Space. pp. 275–290.
  52. ^ Walker, M.; Johnsen, S.; Rasmussen, S. O.; Popp, T.; Steffensen, J.-P.; Gibbard, P.; Hoek, W.; Lowe, J.; Andrews, J.; Bjo; Cwynar, L. C.; Hughen, K.; Kershaw, P.; Kromer, B.; Litt, T.; Lowe, D. J.; Nakagawa, T.; Newnham, R.; Schwander, J. (2009). "Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records" (PDF). J. Quaternary Sci. 24 (1): 3–17. Bibcode:2009JQS....24....3W. doi:10.1002/jqs.1227.
  53. ^ Augustin, L; Barbante, C; Barnes, PRF; Barnola, JM; Bigler, M; Castellano, E; Cattani, O; Chappellaz, J; et al. (2004-06-10). "Eight glacial cycles from an Antarctic ice core". Nature. 429 (6992): 623–8. Bibcode:2004Natur.429..623A. doi:10.1038/nature02599. PMID 15190344. S2CID 4342139.
  54. ^ "Next Ice Age Delayed By Rising Carbon Dioxide Levels". ScienceDaily. 2007. Retrieved 2008-02-28.
  55. ^ The Complicated Role of Iron in Ocean Health and Climate Change
  56. ^ Ewing, M.; Donn, W. L. (1956-06-15). "A Theory of Ice Ages". Science. 123 (3207): 1061–1066. Bibcode:1956Sci...123.1061E. doi:10.1126/science.123.3207.1061. ISSN 0036-8075. PMID 17748617.
  57. ^ Garrison, Tom (2009). Oceanography: An Invitation to Marine Science (7th ed.). Cengage Learning. p. 582. ISBN 9780495391937.
  58. ^ Bryden, H.L.; H.R. Longworth; S.A. Cunningham (2005). "Slowing of the Atlantic meridional overturning circulation at 25° N". Nature. 438 (7068): 655–657. Bibcode:2005Natur.438..655B. doi:10.1038/nature04385. PMID 16319889. S2CID 4429828.
  59. ^ Curry, R.; C. Mauritzen (2005). "Dilution of the northern North Atlantic in recent decades". Science. 308 (5729): 1772–1774. Bibcode:2005Sci...308.1772C. doi:10.1126/science.1109477. PMID 15961666. S2CID 36017668.
  60. ^ Huddart, David; Stott, Tim A. (2013-04-16). Earth Environments: Past, Present and Future. John Wiley & Sons. ISBN 978-1-118-68812-0.
  61. ^ Bennett, Matthew M.; Glasser, Neil F. (2010-03-29). Glacial Geology: Ice Sheets and Landforms. Wiley. ISBN 978-0-470-51690-4. Another factor is the increased aridity occurring with glacial maxima, which reduces the precipitation available to maintain glaciation. The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances.
  62. ^ Black, Richard (9 January 2012). "Carbon emissions 'will defer Ice Age'". BBC News. Retrieved 10 August 2012.
  63. ^ Luthi, Dieter; et al. (2008-03-17). "High-resolution carbon dioxide concentration record 650,000–800,000 years before present" (PDF). Nature. 453 (7193): 379–382. Bibcode:2008Natur.453..379L. doi:10.1038/nature06949. PMID 18480821. S2CID 1382081.
  64. ^ Ruddiman, W.F.; Kutzbach, J.E. (1991). "Plateau Uplift and Climate Change". Scientific American. 264 (3): 66–74. Bibcode:1991SciAm.264c..66R. doi:10.1038/scientificamerican0391-66.
  65. ^ a b Raymo, Maureen E.; Ruddiman, William F.; Froelich, Philip N. (1988-07-01). "Influence of late Cenozoic mountain building on ocean geochemical cycles". Geology. 16 (7): 649–653. Bibcode:1988Geo....16..649R. doi:10.1130/0091-7613(1988)016<0649:IOLCMB>2.3.CO;2. ISSN 0091-7613.
  66. ^ Clark, Peter U.; Dyke, Arthur S.; Shakun, Jeremy D.; Carlson, Anders E.; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X.; Hostetler, Steven W. & McCabe, A. Marshall (2009). "The Last Glacial Maximum". Science. 325 (5941): 710–714. Bibcode:2009Sci...325..710C. doi:10.1126/science.1172873. PMID 19661421. S2CID 1324559.
  67. ^ Lee Hannah, Climate Change Biology, 2nd ed. (Amsterdam: Academic Press, 2014), 23-28. ISBN 012799923X
  68. ^ Svitil, K. A. (April 1996). "We are all Panamanians". Discover.—formation of Isthmus of Panama may have started a series of climatic changes that led to evolution of hominids
  69. ^ Hu, Aixue; Meehl, Gerald A.; Otto-Bliesner, Bette L.; Waelbroeck, Claire; Weiqing Han; Loutre, Marie-France; Lambeck, Kurt; Mitrovica, Jerry X.; Rosenbloom, Nan (2010). (PDF). Nature Geoscience. 3 (2): 118–121. Bibcode:2010NatGe...3..118H. CiteSeerX 10.1.1.391.8727. doi:10.1038/ngeo729. hdl:1885/30691. Archived from the original (PDF) on 2017-08-11. Retrieved 2017-10-24.
  70. ^ "Melting icebergs key to sequence of an ice age, scientists find". phys.org. Retrieved 12 February 2021.
  71. ^ Starr, Aidan; Hall, Ian R.; Barker, Stephen; Rackow, Thomas; Zhang, Xu; Hemming, Sidney R.; Lubbe, H. J. L. van der; Knorr, Gregor; Berke, Melissa A.; Bigg, Grant R.; Cartagena-Sierra, Alejandra; Jiménez-Espejo, Francisco J.; Gong, Xun; Gruetzner, Jens; Lathika, Nambiyathodi; LeVay, Leah J.; Robinson, Rebecca S.; Ziegler, Martin (January 2021). "Antarctic icebergs reorganize ocean circulation during Pleistocene glacials". Nature. 589 (7841): 236–241. Bibcode:2021Natur.589..236S. doi:10.1038/s41586-020-03094-7. hdl:10261/258181. ISSN 1476-4687. PMID 33442043. S2CID 231598435. Retrieved 12 February 2021.
  72. ^ Kuhle, Matthias (December 1988). "The Pleistocene Glaciation of Tibet and the Onset of Ice Ages — An Autocycle Hypothesis". GeoJournal. 17 (4): 581–595. doi:10.1007/BF00209444. JSTOR 41144345. S2CID 189891305.
  73. ^ 2c (Quaternary Glaciation — Extent and Chronology, Part III: South America, Asia, Africa, Australia, AntarcticaKuhle, M. (2004). "The High Glacial (Last Ice Age and LGM) ice cover in High and Central Asia". In Ehlers, J.; Gibbard, P.L. (eds.). Quaternary Glaciations: South America, Asia, Africa, Australasia, Antarctica. Development in Quaternary Science: Quaternary Glaciations: Extent and Chronology Vol. 3. Amsterdam: Elsevier. pp. 175–199. ISBN 978-0-444-51593-3.
  74. ^ Kuhle, M. (1999). "Reconstruction of an approximately complete Quaternary Tibetan inland glaciation between the Mt. Everest- and Cho Oyu Massifs and the Aksai Chin. A new glaciogeomorphological SE–NW diagonal profile through Tibet and its consequences for the glacial isostasy and Ice Age cycle". GeoJournal. 47 (1–2): 3–276. doi:10.1023/A:1007039510460. S2CID 128089823.
  75. ^ Kuhle, M. (2011). "Ice Age Development Theory". In Singh, V.P.; Singh, P.; Haritashya, U.K. (eds.). Encyclopedia of Snow, Ice and Glaciers. Springer. pp. 576–581.
  76. ^ "Earth's orbital variations and sea ice synch glacial periods".
  77. ^ "Ice-Age Explanation - Sciforums". www.sciforums.com.
  78. ^ Muller, R. A.; MacDonald, G. J. (1997-08-05). "Spectrum of 100-kyr glacial cycle: orbital inclination, not eccentricity". Proceedings of the National Academy of Sciences of the United States of America. 94 (16): 8329–8334. Bibcode:1997PNAS...94.8329M. doi:10.1073/pnas.94.16.8329. ISSN 0027-8424. PMC 33747. PMID 11607741.
  79. ^ Richard A. Muller. "A New Theory of Glacial Cycles". Muller.lbl.gov. Retrieved 2012-08-07.
  80. ^ Muller, R. A. (1997-07-11). "Glacial Cycles and Astronomical Forcing". Science. 277 (5323): 215–218. Bibcode:1997Sci...277..215M. doi:10.1126/science.277.5323.215.
  81. ^ Rial, J.A. (July 1999). (PDF). Science. 285 (5427): 564–8. doi:10.1126/science.285.5427.564. PMID 10417382. Archived from the original (PDF) on 2008-10-15.
  82. ^ Huybers, Peter; Wunsch, Carl (2005-03-24). "Obliquity pacing of the late Pleistocene glacial terminations". Nature. 434 (7032): 491–494. Bibcode:2005Natur.434..491H. doi:10.1038/nature03401. ISSN 1476-4687. PMID 15791252. S2CID 2729178.
  83. ^ Paillard, D. (22 January 1998). "The timing of Pleistocene glaciations from a simple multiple-state climate model". Nature. 391 (6665): 378–381. Bibcode:1998Natur.391..378P. doi:10.1038/34891. S2CID 4409193.
  84. ^ Ditlevsen, P.D. (2009). . Paleoceanography. 24 (3): PA3204. arXiv:0902.1641. Bibcode:2009PalOc..24.3204D. doi:10.1029/2008PA001673. Archived from the original on 2012-11-01. Retrieved 2012-06-09. as PDF
  85. ^ Guinan, E.F.; Ribas, I. (2002). "Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate". The Evolving Sun and its Influence on Planetary Environments. Astronomical Society of the Pacific. p. 85. ISBN 1-58381-109-5.
  86. ^ Rieke, George. . Archived from the original on 2 June 2015. Retrieved 25 April 2013.
  87. ^ . www.wunderground.com. Archived from the original on 2016-12-02. Retrieved 2016-12-02.
  88. ^ . National Geographic. 2017-01-06. Archived from the original on March 20, 2017.
  89. ^ Hallberg, G.R. (1986). "Pre-Wisconsin glacial stratigraphy of the Central Plains region in Iowa, Nebraska, Kansas, and Missouri". Quaternary Science Reviews. 5: 11–15. Bibcode:1986QSRv....5...11H. doi:10.1016/0277-3791(86)90169-1.
  90. ^ a b Richmond, G.M.; Fullerton, D.S. (1986). "Summation of Quaternary glaciations in the United States of America". Quaternary Science Reviews. 5: 183–196. Bibcode:1986QSRv....5..183R. doi:10.1016/0277-3791(86)90184-8.
  91. ^ Gibbard, P.L., S. Boreham, K.M. Cohen and A. Moscariello, 2007, Global chronostratigraphical correlation table for the last 2.7 million years v. 2007b., jpg version 844 KB. Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge, Cambridge, England
  92. ^ Kuhle, M. (1984). "Spuren hocheiszeitlicher Gletscherbedeckung in der Aconcagua-Gruppe (32–33° S)". Zentralblatt für Geologie und Paläontologie, Teil I. 11/12: 1635–46. ISSN 0340-5109. Verhandlungsblatt des Südamerika-Symposiums 1984 in Bamberg.
  93. ^ Kuhle, M. (1986). "Die Vergletscherung Tibets und die Entstehung von Eiszeiten". Spektrum der Wissenschaft (9/86): 42–54. ISSN 0170-2971.
  94. ^ Kuhle, Matthias (June 1987). "Subtropical Mountain- and Highland-Glaciation as Ice Age Triggers and the Waning of the Glacial Periods in the Pleistocene". GeoJournal. 14 (4): 393–421. doi:10.1007/BF02602717. JSTOR 41144132. S2CID 129366521.
  95. ^ a b Kuhle, M. (2004). "The Last Glacial Maximum (LGM) glacier cover of the Aconcagua group and adjacent massifs in the Mendoza Andes (South America)". In Ehlers, J.; Gibbard, P.L. (eds.). Quaternary Glaciations: South America, Asia, Africa, Australasia, Antarctica. Development in Quaternary Science. Amsterdam: Elsevier. pp. 75–81. ISBN 978-0-444-51593-3.
  96. ^ a b c Kuhle, M. (2011). "Ch 53: The High-Glacial (Last Glacial Maximum) Glacier Cover of the Aconcagua Group and Adjacent Massifs in the Mendoza Andes (South America) with a Closer Look at Further Empirical Evidence". In Ehlers, J.; Gibbard, P.L.; Hughes, P.D. (eds.). Quaternary Glaciations – Extent and Chronology: A Closer Look. Development in Quaternary Science. Amsterdam: Elsevier. pp. 735–8. ISBN 978-0-444-53447-7.
  97. ^ Brüggen, J. (1929). "Zur Glazialgeologie der chilenischen Anden". Geol. Rundsch. 20 (1): 1–35. Bibcode:1929GeoRu..20....1B. doi:10.1007/BF01805072. S2CID 128436981.
  98. ^ Andersen, Bjørn G.; Borns, Harold W. Jr. (1997). The Ice Age World: an introduction to quaternary history and research with emphasis on North America and Northern Europe during the last 2.5 million years. Oslo: Universitetsforlaget. ISBN 978-82-00-37683-5. Archived from the original on 2013-01-12. Retrieved 2013-10-14.
  99. ^ Johnston, A. (1989). "The effect of large ice sheets on earthquake genesis". In Gregersen, S.; Basham, P. (eds.). Earthquakes at North-Atlantic passive margins: Neotectonics and postglacial rebound. Dordrecht: Kluwer. pp. 581–599. ISBN 978-0-7923-0150-9.
  100. ^ Wu, Patrick; Hasegawa, Henry S. (October 1996). "Induced stresses and fault potential in eastern Canada due to a realistic load: a preliminary analysis". Geophysical Journal International. 127 (1): 215–229. Bibcode:1996GeoJI.127..215W. doi:10.1111/j.1365-246X.1996.tb01546.x.
  101. ^ Turpeinen, H.; Hampel, A.; Karow, T.; Maniatis, G. (2008). "Effect of ice sheet growth and melting on the slip evolution of thrust faults". Earth and Planetary Science Letters. 269 (1–2): 230–241. Bibcode:2008E&PSL.269..230T. doi:10.1016/j.epsl.2008.02.017.
  102. ^ Hunt, A. G.; Malin, P. E. (May 1998). "Possible triggering of Heinrich events by ice-load-induced earthquakes". Nature. 393 (6681): 155–158. Bibcode:1998Natur.393..155H. doi:10.1038/30218. ISSN 0028-0836. S2CID 4393858.
  103. ^ Interglacial Working Group Of PAGES (November 20, 2015). "Interglacials Of The Last 800,000 years" (PDF). Reviews of Geophysics. 54 (1): 162–219. Bibcode:2016RvGeo..54..162P. doi:10.1002/2015RG000482. hdl:2078.1/175429.

Works cited

  • Montgomery, Keith (2010). "Development of the glacial theory, 1800–1870". Historical Simulation

External links

  • Cracking the Ice Age from PBS
  • Rina Torchinsky (9 Aug 2021). "Scientists unveil 'best-preserved Ice Age animal ever found'". AccuWeather.
  • Raymo, M. (July 2011). . Archived from the original on 2008-10-22.
  • Eduard Y. Osipov, Oleg M. Khlystov. Glaciers and meltwater flux to Lake Baikal during the Last Glacial Maximum. 2016-03-12 at the Wayback Machine
  • Black, R. (9 January 2012). "Carbon emissions 'will defer Ice Age'". BBC News: Science and Environment.

this, article, about, glacial, periods, general, specific, recent, glacial, periods, often, referred, last, glacial, period, pleistocene, quaternary, glaciation, other, uses, disambiguation, long, period, reduction, temperature, earth, surface, atmosphere, res. This article is about glacial periods in general For specific recent glacial periods often referred to as the Ice Age see Last Glacial Period Pleistocene and Quaternary glaciation For other uses see Ice age disambiguation 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 greenhouse periods during which there are no glaciers on the planet Earth is currently in the ice age called Quaternary glaciation 1 Individual pulses of cold climate within an ice age are termed glacial periods or alternatively glacials glaciations glacial stages stadials stades or colloquially ice ages and intermittent warm periods within an ice age are called interglacials or interstadials 2 An artist s impression of ice age Earth at Pleistocene glacial maximumIn glaciology ice age implies the presence of extensive ice sheets in the northern and southern hemispheres 3 By this definition Earth is in an interglacial period the Holocene The amount of anthropogenic greenhouse gases emitted into Earth s oceans and atmosphere is projected to delay the next glacial period which otherwise would begin in around 50 000 years by between 100 000 and 500 000 years 4 5 6 Contents 1 History of research 2 Evidence 3 Major ice ages 4 Glacials and interglacials 5 Feedback processes 5 1 Positive 5 2 Negative 6 Causes 6 1 Changes in Earth s atmosphere 6 2 Position of the continents 6 3 Fluctuations in ocean currents 6 4 Uplift of the Tibetan plateau 6 5 Variations in Earth s orbit 6 6 Variations in the Sun s energy output 6 7 Volcanism 7 Recent glacial and interglacial phases 7 1 Glacial stages in North America 7 2 Last Glacial Period in the semiarid Andes around Aconcagua and Tupungato 8 Effects of glaciation 9 Future ice ages 10 See also 11 References 11 1 Works cited 12 External linksHistory of researchSee also History of climate change science In 1742 Pierre Martel 1706 1767 an engineer and geographer living in Geneva visited the valley of Chamonix in the Alps of Savoy 7 8 Two years later he published an account of his journey He reported that the inhabitants of that valley attributed the dispersal of erratic boulders to the glaciers saying that they had once extended much farther 9 10 Later similar explanations were reported from other regions of the Alps In 1815 the carpenter and chamois hunter Jean Pierre Perraudin 1767 1858 explained erratic boulders in the Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further 11 An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss German geologist Jean de Charpentier 1786 1855 in 1834 12 Comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland 13 and in Goethe s scientific work 14 Such explanations could also be found in other parts of the world When the Bavarian naturalist Ernst von Bibra 1806 1878 visited the Chilean Andes in 1849 1850 the natives attributed fossil moraines to the former action of glaciers 15 Meanwhile European scholars had begun to wonder what had caused the dispersal of erratic material From the middle of the 18th century some discussed ice as a means of transport The Swedish mining expert Daniel Tilas 1712 1772 was in 1742 the first person to suggest drifting sea ice was a cause of the presence of erratic boulders in the Scandinavian and Baltic regions 16 In 1795 the Scottish philosopher and gentleman naturalist James Hutton 1726 1797 explained erratic boulders in the Alps by the action of glaciers 17 Two decades later in 1818 the Swedish botanist Goran Wahlenberg 1780 1851 published his theory of a glaciation of the Scandinavian peninsula He regarded glaciation as a regional phenomenon 18 nbsp Haukalivatnet lake 50 meters above sea level where Jens Esmark in 1823 discovered similarities to moraines near existing glaciers in the high mountainsOnly a few years later the Danish Norwegian geologist Jens Esmark 1762 1839 argued for a sequence of worldwide ice ages In a paper published in 1824 Esmark proposed changes in climate as the cause of those glaciations He attempted to show that they originated from changes in Earth s orbit 19 Esmark discovered the similarity between moraines near Haukalivatnet lake near sea level in Rogaland and moraines at branches of Jostedalsbreen Esmark s discovery were later attributed to or appropriated by Theodor Kjerulf and Louis Agassiz 20 21 22 During the following years Esmark s ideas were discussed and taken over in parts by Swedish Scottish and German scientists At the University of Edinburgh Robert Jameson 1774 1854 seemed to be relatively open to Esmark s ideas as reviewed by Norwegian professor of glaciology Bjorn G Andersen 1992 23 Jameson s remarks about ancient glaciers in Scotland were most probably prompted by Esmark 24 In Germany Albrecht Reinhard Bernhardi 1797 1849 a geologist and professor of forestry at an academy in Dreissigacker since incorporated in the southern Thuringian city of Meiningen adopted Esmark s theory In a paper published in 1832 Bernhardi speculated about the polar ice caps once reaching as far as the temperate zones of the globe 25 In Val de Bagnes a valley in the Swiss Alps there was a long held local belief that the valley had once been covered deep in ice and in 1815 a local chamois hunter called Jean Pierre Perraudin attempted to convert the geologist Jean de Charpentier to the idea pointing to deep striations in the rocks and giant erratic boulders as evidence Charpentier held the general view that these signs were caused by vast floods and he rejected Perraudin s theory as absurd In 1818 the engineer Ignatz Venetz joined Perraudin and Charpentier to examine a proglacial lake above the valley created by an ice dam as a result of the 1815 eruption of Mount Tambora which threatened to cause a catastrophic flood when the dam broke Perraudin attempted unsuccessfully to convert his companions to his theory but when the dam finally broke there were only minor erratics and no striations and Venetz concluded that Perraudin was right and that only ice could have caused such major results In 1821 he read a prize winning paper on the theory to the Swiss Society but it was not published until Charpentier who had also become converted published it with his own more widely read paper in 1834 26 In the meantime the German botanist Karl Friedrich Schimper 1803 1867 was studying mosses which were growing on erratic boulders in the alpine upland of Bavaria He began to wonder where such masses of stone had come from During the summer of 1835 he made some excursions to the Bavarian Alps Schimper came to the conclusion that ice must have been the means of transport for the boulders in the alpine upland In the winter of 1835 36 he held some lectures in Munich Schimper then assumed that there must have been global times of obliteration Verodungszeiten with a cold climate and frozen water 27 Schimper spent the summer months of 1836 at Devens near Bex in the Swiss Alps with his former university friend Louis Agassiz 1801 1873 and Jean de Charpentier Schimper Charpentier and possibly Venetz convinced Agassiz that there had been a time of glaciation During the winter of 1836 37 Agassiz and Schimper developed the theory of a sequence of glaciations They mainly drew upon the preceding works of Venetz Charpentier and on their own fieldwork Agassiz appears to have been already familiar with Bernhardi s paper at that time 28 At the beginning of 1837 Schimper coined the term ice age Eiszeit for the period of the glaciers 29 In July 1837 Agassiz presented their synthesis before the annual meeting of the Swiss Society for Natural Research at Neuchatel The audience was very critical and some were opposed to the new theory because it contradicted the established opinions on climatic history Most contemporary scientists thought that Earth had been gradually cooling down since its birth as a molten globe 30 In order to persuade the skeptics Agassiz embarked on geological fieldwork He published his book Study on Glaciers Etudes sur les glaciers in 1840 31 Charpentier was put out by this as he had also been preparing a book about the glaciation of the Alps Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in depth glacial research 32 As a result of personal quarrels Agassiz had also omitted any mention of Schimper in his book 33 It took several decades before the ice age theory was fully accepted by scientists This happened on an international scale in the second half of the 1870s following the work of James Croll including the publication of Climate and Time in Their Geological Relations in 1875 which provided a credible explanation for the causes of ice ages 34 EvidenceThere are three main types of evidence for ice ages geological chemical and paleontological Geological evidence for ice ages comes in various forms including rock scouring and scratching glacial moraines drumlins valley cutting and the deposition of till or tillites and glacial erratics Successive glaciations tend to distort and erase the geological evidence for earlier glaciations making it difficult to interpret Furthermore this evidence was difficult to date exactly early theories assumed that the glacials were short compared to the long interglacials The advent of sediment and ice cores revealed the true situation glacials are long interglacials short It took some time for the current theory to be worked out The chemical evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks and ocean sediment cores For the most recent glacial periods ice cores provide climate proxies both from the ice itself and from atmospheric samples provided by included bubbles of air Because water containing lighter isotopes has a lower heat of evaporation its proportion decreases with warmer conditions 35 This allows a temperature record to be constructed This evidence can be confounded however by other factors recorded by isotope ratios The paleontological evidence consists of changes in the geographical distribution of fossils During a glacial period cold adapted organisms spread into lower latitudes and organisms that prefer warmer conditions become extinct or retreat into lower latitudes This evidence is also difficult to interpret because it requires sequences of sediments covering a long period of time over a wide range of latitudes and which are easily correlated ancient organisms which survive for several million years without change and whose temperature preferences are easily diagnosed and the finding of the relevant fossils Despite the difficulties analysis of ice core and ocean sediment cores 36 has provided a credible record of glacials and interglacials over the past few million years These also confirm the linkage between ice ages and continental crust phenomena such as glacial moraines drumlins and glacial erratics Hence the continental crust phenomena are accepted as good evidence of earlier ice ages when they are found in layers created much earlier than the time range for which ice cores and ocean sediment cores are available Major ice agesFor a chronological guide see Timeline of glaciation nbsp Timeline of glaciations shown in blueThere have been at least five major ice ages in Earth s history the Huronian Cryogenian Andean Saharan late Paleozoic and the latest Quaternary Ice Age Outside these ages Earth was previously thought to have been ice free even in high latitudes 37 38 such periods are known as greenhouse periods 39 However other studies dispute this finding evidence of occasional glaciations at high latitudes even during apparent greenhouse periods 40 41 nbsp Ice age map of northern Germany and its northern neighbours Red maximum limit of Weichselian glacial yellow Saale glacial at maximum Drenthe stage blue Elster glacial maximum glaciation Rocks from the earliest well established ice age called the Huronian have been dated to around 2 4 to 2 1 billion years ago during the early Proterozoic Eon Several hundreds of kilometers of the Huronian Supergroup are exposed 10 to 100 kilometers 6 to 62 mi north of the north shore of Lake Huron extending from near Sault Ste Marie to Sudbury northeast of Lake Huron with giant layers of now lithified till beds dropstones varves outwash and scoured basement rocks Correlative Huronian deposits have been found near Marquette Michigan and correlation has been made with Paleoproterozoic glacial deposits from Western Australia The Huronian ice age was caused by the elimination of atmospheric methane a greenhouse gas during the Great Oxygenation Event 42 The next well documented ice age and probably the most severe of the last billion years occurred from 720 to 630 million years ago the Cryogenian period and may have produced a Snowball Earth in which glacial ice sheets reached the equator 43 possibly being ended by the accumulation of greenhouse gases such as CO2 produced by volcanoes The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis which are the two major sinks for CO2 at present 44 It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian explosion though this model is recent and controversial The Andean Saharan occurred from 460 to 420 million years ago during the Late Ordovician and the Silurian period nbsp Sediment records showing the fluctuating sequences of glacials and interglacials during the last several million yearsThe evolution of land plants at the onset of the Devonian period caused a long term increase in planetary oxygen levels and reduction of CO2 levels which resulted in the late Paleozoic icehouse Its former name the Karoo glaciation was named after the glacial tills found in the Karoo region of South Africa There were extensive polar ice caps at intervals from 360 to 260 million years ago in South Africa during the Carboniferous and early Permian periods Correlatives are known from Argentina also in the center of the ancient supercontinent Gondwanaland Although the Mesozoic Era retained a greenhouse climate over its timespan and was previously assumed to have been entirely glaciation free more recent studies suggest that brief periods of glaciation occurred in both hemispheres during the Early Cretaceous Geologic and palaeoclimatological records suggest the existence of glacial periods during the Valanginian Hauterivian and Aptian stages of the Early Cretaceous Ice rafted glacial dropstones indicate that in the Northern Hemisphere ice sheets may have extended as far south as the Iberian Peninsula during the Hauterivian and Aptian 45 46 47 Although ice sheets largely disappeared from Earth for the rest of the period potential reports from the Turonian otherwise the warmest period of the Phanerozoic are disputed 40 41 ice sheets and associated sea ice appear to have briefly returned to Antarctica near the very end of the Maastrichtian just prior to the Cretaceous Paleogene extinction event 41 48 The Quaternary Glaciation Quaternary Ice Age started about 2 58 million years ago at the beginning of the Quaternary Period when the spread of ice sheets in the Northern Hemisphere began Since then the world has seen cycles of glaciation with ice sheets advancing and retreating on 40 000 and 100 000 year time scales called glacial periods glacials or glacial advances and interglacial periods interglacials or glacial retreats Earth is currently in an interglacial and the last glacial period ended about 11 700 years ago All that remains of the continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island The definition of the Quaternary as beginning 2 58 Ma is based on the formation of the Arctic ice cap The Antarctic ice sheet began to form earlier at about 34 Ma in the mid Cenozoic Eocene Oligocene Boundary The term Late Cenozoic Ice Age is used to include this early phase 49 Ice ages can be further divided by location and time for example the names Riss 180 000 130 000 years bp and Wurm 70 000 10 000 years bp refer specifically to glaciation in the Alpine region The maximum extent of the ice is not maintained for the full interval The scouring action of each glaciation tends to remove most of the evidence of prior ice sheets almost completely except in regions where the later sheet does not achieve full coverage Glacials and interglacialsSee also Glacial period and Interglacial nbsp Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials Minimum and maximum glaciation nbsp Minimum interglacial black and maximum glacial grey glaciation of the northern hemisphere nbsp Minimum interglacial black and maximum glacial grey glaciation of the southern hemisphere Within the current glaciation more temperate and more severe periods have occurred The colder periods are called glacial periods the warmer periods interglacials such as the Eemian Stage 1 There is evidence that similar glacial cycles occurred in previous glaciations including the Andean Saharan 50 and the late Paleozoic ice house The glacial cycles of the late Paleozoic ice house are likely responsible for the deposition of cyclothems 51 Glacials are characterized by cooler and drier climates over most of Earth and large land and sea ice masses extending outward from the poles Mountain glaciers in otherwise unglaciated areas extend to lower elevations due to a lower snow line Sea levels drop due to the removal of large volumes of water above sea level in the icecaps There is evidence that ocean circulation patterns are disrupted by glaciations The glacials and interglacials coincide with changes in orbital forcing of climate due to Milankovitch cycles which are periodic changes in Earth s orbit and the tilt of Earth s rotational axis Earth has been in an interglacial period known as the Holocene for around 11 700 years 52 and an article in Nature in 2004 argues that it might be most analogous to a previous interglacial that lasted 28 000 years 53 Predicted changes in orbital forcing suggest that the next glacial period would begin at least 50 000 years from now Moreover anthropogenic forcing from increased greenhouse gases is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years 54 5 4 Feedback processesEach glacial period is subject to positive feedback which makes it more severe and negative feedback which mitigates and in all cases so far eventually ends it Positive An important form of feedback is provided by Earth s albedo which is how much of the sun s energy is reflected rather than absorbed by Earth Ice and snow increase Earth s albedo while forests reduce its albedo When the air temperature decreases ice and snow fields grow and they reduce forest cover This continues until competition with a negative feedback mechanism forces the system to an equilibrium One theory is that when glaciers form two things happen the ice grinds rocks into dust and the land becomes dry and arid This allows winds to transport iron rich dust into the open ocean where it acts as a fertilizer that causes massive algal blooms that pulls large amounts of CO2 out of the atmosphere This in turn makes it even colder and causes the glaciers to grow more 55 In 1956 Ewing and Donn 56 hypothesized that an ice free Arctic Ocean leads to increased snowfall at high latitudes When low temperature ice covers the Arctic Ocean there is little evaporation or sublimation and the polar regions are quite dry in terms of precipitation comparable to the amount found in mid latitude deserts This low precipitation allows high latitude snowfalls to melt during the summer An ice free Arctic Ocean absorbs solar radiation during the long summer days and evaporates more water into the Arctic atmosphere With higher precipitation portions of this snow may not melt during the summer and so glacial ice can form at lower altitudes and more southerly latitudes reducing the temperatures over land by increased albedo as noted above Furthermore under this hypothesis the lack of oceanic pack ice allows increased exchange of waters between the Arctic and the North Atlantic Oceans warming the Arctic and cooling the North Atlantic Current projected consequences of global warming include a brief ice free Arctic Ocean period by 2050 Additional fresh water flowing into the North Atlantic during a warming cycle may also reduce the global ocean water circulation Such a reduction by reducing the effects of the Gulf Stream would have a cooling effect on northern Europe which in turn would lead to increased low latitude snow retention during the summer 57 58 59 It has also been suggested by whom that during an extensive glacial glaciers may move through the Gulf of Saint Lawrence extending into the North Atlantic Ocean far enough to block the Gulf Stream Negative Ice sheets that form during glaciations erode the land beneath them This can reduce the land area above sea level and thus diminish the amount of space on which ice sheets can form This mitigates the albedo feedback as does the rise in sea level that accompanies the reduced area of ice sheets since open ocean has a lower albedo than land 60 Another negative feedback mechanism is the increased aridity occurring with glacial maxima which reduces the precipitation available to maintain glaciation The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances 61 According to research published in Nature Geoscience human emissions of carbon dioxide CO2 will defer the next glacial period Researchers used data on Earth s orbit to find the historical warm interglacial period that looks most like the current one and from this have predicted that the next glacial period would usually begin within 1 500 years They go on to predict that emissions have been so high that it will not 62 CausesThe causes of ice ages are not fully understood for either the large scale ice age periods or the smaller ebb and flow of glacial interglacial periods within an ice age The consensus is that several factors are important atmospheric composition such as the concentrations of carbon dioxide and methane the specific levels of the previously mentioned gases are now able to be seen with the new ice core samples from the European Project for Ice Coring in Antarctica EPICA Dome C in Antarctica over the past 800 000 years changes in Earth s orbit around the Sun known as Milankovitch cycles the motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on Earth s surface which affect wind and ocean currents variations in solar output the orbital dynamics of the Earth Moon system the impact of relatively large meteorites and volcanism including eruptions of supervolcanoes 63 citation needed Some of these factors influence each other For example changes in Earth s atmospheric composition especially the concentrations of greenhouse gases may alter the climate while climate change itself can change the atmospheric composition for example by changing the rate at which weathering removes CO2 Maureen Raymo William Ruddiman and others propose that the Tibetan and Colorado Plateaus are immense CO2 scrubbers with a capacity to remove enough CO2 from the global atmosphere to be a significant causal factor of the 40 million year Cenozoic Cooling trend They further claim that approximately half of their uplift and CO2 scrubbing capacity occurred in the past 10 million years 64 65 Changes in Earth s atmosphere There is evidence that greenhouse gas levels fell at the start of ice ages and rose during the retreat of the ice sheets but it is difficult to establish cause and effect see the notes above on the role of weathering Greenhouse gas levels may also have been affected by other factors which have been proposed as causes of ice ages such as the movement of continents and volcanism The Snowball Earth hypothesis maintains that the severe freezing in the late Proterozoic was ended by an increase in CO2 levels in the atmosphere mainly from volcanoes and some supporters of Snowball Earth argue that it was caused in the first place by a reduction in atmospheric CO2 The hypothesis also warns of future Snowball Earths In 2009 further evidence was provided that changes in solar insolation provide the initial trigger for Earth to warm after an Ice Age with secondary factors like increases in greenhouse gases accounting for the magnitude of the change 66 Position of the continents The geological record appears to show that ice ages start when the continents are in positions which block or reduce the flow of warm water from the equator to the poles and thus allow ice sheets to form The ice sheets increase Earth s reflectivity and thus reduce the absorption of solar radiation With less radiation absorbed the atmosphere cools the cooling allows the ice sheets to grow which further increases reflectivity in a positive feedback loop The ice age continues until the reduction in weathering causes an increase in the greenhouse effect There are three main contributors from the layout of the continents that obstruct the movement of warm water to the poles 67 A continent sits on top of a pole as Antarctica does today A polar sea is almost land locked as the Arctic Ocean is today A supercontinent covers most of the equator as Rodinia did during the Cryogenian period Since today s Earth has a continent over the South Pole and an almost land locked ocean over the North Pole geologists believe that Earth will continue to experience glacial periods in the geologically near future Some scientists believe that the Himalayas are a major factor in the current ice age because these mountains have increased Earth s total rainfall and therefore the rate at which carbon dioxide is washed out of the atmosphere decreasing the greenhouse effect 65 The Himalayas formation started about 70 million years ago when the Indo Australian Plate collided with the Eurasian Plate and the Himalayas are still rising by about 5 mm per year because the Indo Australian plate is still moving at 67 mm year The history of the Himalayas broadly fits the long term decrease in Earth s average temperature since the mid Eocene 40 million years ago Fluctuations in ocean currents Another important contribution to ancient climate regimes is the variation of ocean currents which are modified by continent position sea levels and salinity as well as other factors They have the ability to cool e g aiding the creation of Antarctic ice and the ability to warm e g giving the British Isles a temperate as opposed to a boreal climate The closing of the Isthmus of Panama about 3 million years ago may have ushered in the present period of strong glaciation over North America by ending the exchange of water between the tropical Atlantic and Pacific Oceans 68 Analyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations During the last glacial period the sea level has fluctuated 20 30 m as water was sequestered primarily in the Northern Hemisphere ice sheets When ice collected and the sea level dropped sufficiently flow through the Bering Strait the narrow strait between Siberia and Alaska is about 50 m deep today was reduced resulting in increased flow from the North Atlantic This realigned the thermohaline circulation in the Atlantic increasing heat transport into the Arctic which melted the polar ice accumulation and reduced other continental ice sheets The release of water raised sea levels again restoring the ingress of colder water from the Pacific with an accompanying shift to northern hemisphere ice accumulation 69 According to a study published in Nature in 2021 all glacial periods of ice ages over the last 1 5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns leading to more CO2 being pulled out of the atmosphere The authors suggest that this process may be disrupted in the future as the Southern Ocean will become too warm for the icebergs to travel far enough to trigger these changes 70 71 Uplift of the Tibetan plateau Matthias Kuhle s geological theory of Ice Age development was suggested by the existence of an ice sheet covering the Tibetan Plateau during the Ice Ages Last Glacial Maximum According to Kuhle the plate tectonic uplift of Tibet past the snow line has led to a surface of c 2 400 000 square kilometres 930 000 sq mi changing from bare land to ice with a 70 greater albedo The reflection of energy into space resulted in a global cooling triggering the Pleistocene Ice Age Because this highland is at a subtropical latitude with 4 to 5 times the insolation of high latitude areas what would be Earth s strongest heating surface has turned into a cooling surface Kuhle explains the interglacial periods by the 100 000 year cycle of radiation changes due to variations in Earth s orbit This comparatively insignificant warming when combined with the lowering of the Nordic inland ice areas and Tibet due to the weight of the superimposed ice load has led to the repeated complete thawing of the inland ice areas 72 73 74 75 Variations in Earth s orbit The Milankovitch cycles are a set of cyclic variations in characteristics of Earth s orbit around the Sun Each cycle has a different length so at some times their effects reinforce each other and at other times they partially cancel each other nbsp Past and future of daily average insolation at top of the atmosphere on the day of the summer solstice at 65 N latitudeThere is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age The present ice age is the most studied and best understood particularly the last 400 000 years since this is the period covered by ice cores that record atmospheric composition and proxies for temperature and ice volume Within this period the match of glacial interglacial frequencies to the Milankovic orbital forcing periods is so close that orbital forcing is generally accepted The combined effects of the changing distance to the Sun the precession of Earth s axis and the changing tilt of Earth s axis redistribute the sunlight received by Earth Of particular importance are changes in the tilt of Earth s axis which affect the intensity of seasons For example the amount of solar influx in July at 65 degrees north latitude varies by as much as 22 from 450 W m2 to 550 W m2 It is widely believed that ice sheets advance when summers become too cool to melt all of the accumulated snowfall from the previous winter Some believe that the strength of the orbital forcing is too small to trigger glaciations but feedback mechanisms like CO2 may explain this mismatch While Milankovitch forcing predicts that cyclic changes in Earth s orbital elements can be expressed in the glaciation record additional explanations are necessary to explain which cycles are observed to be most important in the timing of glacial interglacial periods In particular during the last 800 000 years the dominant period of glacial interglacial oscillation has been 100 000 years which corresponds to changes in Earth s orbital eccentricity and orbital inclination Yet this is by far the weakest of the three frequencies predicted by Milankovitch During the period 3 0 0 8 million years ago the dominant pattern of glaciation corresponded to the 41 000 year period of changes in Earth s obliquity tilt of the axis The reasons for dominance of one frequency versus another are poorly understood and an active area of current research but the answer probably relates to some form of resonance in Earth s climate system Recent work suggests that the 100K year cycle dominates due to increased southern pole sea ice increasing total solar reflectivity 76 77 The traditional Milankovitch explanation struggles to explain the dominance of the 100 000 year cycle over the last 8 cycles Richard A Muller Gordon J F MacDonald 78 79 80 and others have pointed out that those calculations are for a two dimensional orbit of Earth but the three dimensional orbit also has a 100 000 year cycle of orbital inclination They proposed that these variations in orbital inclination lead to variations in insolation as Earth moves in and out of known dust bands in the solar system Although this is a different mechanism to the traditional view the predicted periods over the last 400 000 years are nearly the same The Muller and MacDonald theory in turn has been challenged by Jose Antonio Rial 81 Another worker William Ruddiman has suggested a model that explains the 100 000 year cycle by the modulating effect of eccentricity weak 100 000 year cycle on precession 26 000 year cycle combined with greenhouse gas feedbacks in the 41 000 and 26 000 year cycles Yet another theory has been advanced by Peter Huybers who argued that the 41 000 year cycle has always been dominant but that Earth has entered a mode of climate behavior where only the second or third cycle triggers an ice age This would imply that the 100 000 year periodicity is really an illusion created by averaging together cycles lasting 80 000 and 120 000 years 82 This theory is consistent with a simple empirical multi state model proposed by Didier Paillard 83 Paillard suggests that the late Pleistocene glacial cycles can be seen as jumps between three quasi stable climate states The jumps are induced by the orbital forcing while in the early Pleistocene the 41 000 year glacial cycles resulted from jumps between only two climate states A dynamical model explaining this behavior was proposed by Peter Ditlevsen 84 This is in support of the suggestion that the late Pleistocene glacial cycles are not due to the weak 100 000 year eccentricity cycle but a non linear response to mainly the 41 000 year obliquity cycle Variations in the Sun s energy output There are at least two types of variation in the Sun s energy output 85 In the very long term astrophysicists believe that the Sun s output increases by about 7 every one billion years Shorter term variations such as sunspot cycles and longer episodes such as the Maunder Minimum which occurred during the coldest part of the Little Ice Age The long term increase in the Sun s output cannot be a cause of ice ages Volcanism Volcanic eruptions may have contributed to the inception and or the end of ice age periods At times during the paleoclimate carbon dioxide levels were two or three times greater than today Volcanoes and movements in continental plates contributed to high amounts of CO2 in the atmosphere Carbon dioxide from volcanoes probably contributed to periods with highest overall temperatures 86 One suggested explanation of the Paleocene Eocene Thermal Maximum is that undersea volcanoes released methane from clathrates and thus caused a large and rapid increase in the greenhouse effect 87 There appears to be no geological evidence for such eruptions at the right time but this does not prove they did not happen Recent glacial and interglacial phasesMain article Timeline of glaciation nbsp Northern hemisphere glaciation during the last ice ages The setup of 3 to 4 kilometer thick ice sheets caused a sea level lowering of about 120 m The current geological period the Quaternary which began about 2 6 million years ago and extends into the present 2 is marked by warm and cold episodes cold phases called glacials Quaternary ice age lasting about 100 000 years and which are then interrupted by the warmer interglacials which lasted about 10 000 15 000 years The last cold episode of the Last Glacial Period ended about 10 000 years ago 88 Earth is currently in an interglacial period of the Quaternary called the Holocene Glacial stages in North America The major glacial stages of the current ice age in North America are the Illinoian Eemian and Wisconsin glaciation The use of the Nebraskan Afton Kansan and Yarmouthian stages to subdivide the ice age in North America has been discontinued by Quaternary geologists and geomorphologists These stages have all been merged into the Pre Illinoian in the 1980s 89 90 91 During the most recent North American glaciation during the latter part of the Last Glacial Maximum 26 000 to 13 300 years ago ice sheets extended to about 45th parallel north These sheets were 3 to 4 kilometres 1 9 to 2 5 mi thick 90 nbsp Stages of proglacial lake development in the region of the current North American Great LakesThis Wisconsin glaciation left widespread impacts on the North American landscape The Great Lakes and the Finger Lakes were carved by ice deepening old valleys Most of the lakes in Minnesota and Wisconsin were gouged out by glaciers and later filled with glacial meltwaters The old Teays River drainage system was radically altered and largely reshaped into the Ohio River drainage system Other rivers were dammed and diverted to new channels such as Niagara Falls which formed a dramatic waterfall and gorge when the waterflow encountered a limestone escarpment Another similar waterfall at the present Clark Reservation State Park near Syracuse New York is now dry The area from Long Island to Nantucket Massachusetts was formed from glacial till and the plethora of lakes on the Canadian Shield in northern Canada can be almost entirely attributed to the action of the ice As the ice retreated and the rock dust dried winds carried the material hundreds of miles forming beds of loess many dozens of feet thick in the Missouri Valley Post glacial rebound continues to reshape the Great Lakes and other areas formerly under the weight of the ice sheets The Driftless Area a portion of western and southwestern Wisconsin along with parts of adjacent Minnesota Iowa and Illinois was not covered by glaciers See also Glacial history of Minnesota Last Glacial Period in the semiarid Andes around Aconcagua and Tupungato A specially interesting climatic change during glacial times has taken place in the semi arid Andes Beside the expected cooling down in comparison with the current climate a significant precipitation change happened here So researches in the presently semiarid subtropic Aconcagua massif 6 962 m have shown an unexpectedly extensive glacial glaciation of the type ice stream network 92 93 94 95 96 The connected valley glaciers exceeding 100 km in length flowed down on the East side of this section of the Andes at 32 34 S and 69 71 W as far as a height of 2 060 m and on the western luff side still clearly deeper 96 97 Where current glaciers scarcely reach 10 km in length the snowline ELA runs at a height of 4 600 m and at that time was lowered to 3 200 m asl i e about 1 400 m From this follows that beside of an annual depression of temperature about c 8 4 C here was an increase in precipitation Accordingly at glacial times the humid climatic belt that today is situated several latitude degrees further to the S was shifted much further to the N 95 96 Effects of glaciationSee also Glacial landform nbsp Scandinavia exhibits some of the typical effects of ice age glaciation such as fjords and lakes Although the last glacial period ended more than 8 000 years ago its effects can still be felt today For example the moving ice carved out the landscape in Canada See Canadian Arctic Archipelago Greenland northern Eurasia and Antarctica The erratic boulders till drumlins eskers fjords kettle lakes moraines cirques horns etc are typical features left behind by the glaciers The weight of the ice sheets was so great that they deformed Earth s crust and mantle After the ice sheets melted the ice covered land rebounded Due to the high viscosity of Earth s mantle the flow of mantle rocks which controls the rebound process is very slow at a rate of about 1 cm year near the center of rebound area today During glaciation water was taken from the oceans to form the ice at high latitudes thus global sea level dropped by about 110 meters exposing the continental shelves and forming land bridges between land masses for animals to migrate During deglaciation the melted ice water returned to the oceans causing sea level to rise This process can cause sudden shifts in coastlines and hydration systems resulting in newly submerged lands emerging lands collapsed ice dams resulting in salination of lakes new ice dams creating vast areas of freshwater and a general alteration in regional weather patterns on a large but temporary scale It can even cause temporary reglaciation This type of chaotic pattern of rapidly changing land ice saltwater and freshwater has been proposed as the likely model for the Baltic and Scandinavian regions as well as much of central North America at the end of the last glacial maximum with the present day coastlines only being achieved in the last few millennia of prehistory Also the effect of elevation on Scandinavia submerged a vast continental plain that had existed under much of what is now the North Sea connecting the British Isles to Continental Europe 98 The redistribution of ice water on the surface of Earth and the flow of mantle rocks causes changes in the gravitational field as well as changes to the distribution of the moment of inertia of Earth These changes to the moment of inertia result in a change in the angular velocity axis and wobble of Earth s rotation The weight of the redistributed surface mass loaded the lithosphere caused it to flex and also induced stress within Earth The presence of the glaciers generally suppressed the movement of faults below 99 100 101 During deglaciation the faults experience accelerated slip triggering earthquakes Earthquakes triggered near the ice margin may in turn accelerate ice calving and may account for the Heinrich events 102 As more ice is removed near the ice margin more intraplate earthquakes are induced and this positive feedback may explain the fast collapse of ice sheets In Europe glacial erosion and isostatic sinking from weight of ice made the Baltic Sea which before the Ice Age was all land drained by the Eridanos River Future ice agesMain article Next glacial period A 2015 report by the Past Global Changes Project says simulations show that a new glaciation is unlikely to happen within the next approximately 50 000 years before the next strong drop in Northern Hemisphere summer insolation occurs if either atmospheric CO2 concentration remains above 300 ppm or cumulative carbon emissions exceed 1000 Pg C i e 1 000 gigatonnes carbon Only for an atmospheric CO2 content below the preindustrial level may a glaciation occur within the next 10 ka Given the continued anthropogenic CO2 emissions glacial inception is very unlikely to occur in the next 50 ka because the timescale for CO2 and temperature reduction toward unperturbed values in the absence of active removal is very long IPCC 2013 and only weak precessional forcing occurs in the next two precessional cycles A precessional cycle is around 21 000 years the time it takes for the perihelion to move all the way around the tropical year 103 Ice ages go through cycles of about 100 000 years but the next one may well be avoided due to our carbon dioxide emissions 5 See alsoGlobal cooling Discredited 1970s hypothesis of imminent cooling of the Earth International Union for Quaternary Research International science organisation Irish Sea Glacier Huge glacier during the Pleistocene Ice Age Last Glacial Maximum Most recent time during the Last Glacial Period that ice sheets were at their greatest extent Little Ice Age Climatic cooling after the Medieval Warm Period 16th 19th centuries Post glacial rebound Rise of land masses after glacial period Timeline of glaciation Chronology of the major ice ages of the Earth Geologic temperature record Very long term changes in Earth s temperatureReferences a b Ehlers Jurgen Gibbard Philip 2011 Quaternary Glaciation Encyclopedia of Snow Ice and Glaciers Encyclopedia of Earth Sciences Series pp 873 882 doi 10 1007 978 90 481 2642 2 423 ISBN 978 90 481 2641 5 a b Cohen K M Finney S C Gibbard P L Fan J X International Chronostratigraphic Chart 2013 PDF stratigraphy org ICS Retrieved 7 January 2019 Imbrie J Imbrie K P 1979 Ice ages solving the mystery Short Hills NJ Enslow Publishers ISBN 978 0 89490 015 0 a b Thomson Andrea 2007 Global Warming Good News No More Ice Ages LiveScience a b c Human made climate change suppresses the next ice age Potsdam Institute for Climate Impact Research in Germany 2016 Archived from the original on 2020 08 18 Retrieved 2019 01 07 Archer David Ganopolski Andrey May 2005 A movable trigger Fossil fuel CO2 and the onset of the next glaciation Geochemistry Geophysics Geosystems 6 5 Bibcode 2005GGG 6 5003A doi 10 1029 2004GC000891 S2CID 18549459 Remy F Testut L 2006 Mais comment s ecoule donc un glacier Apercu historique PDF Comptes Rendus Geoscience in French 338 5 368 385 Bibcode 2006CRGeo 338 368R doi 10 1016 j crte 2006 02 004 Note p 374 Montgomery 2010 Martel Pierre 1898 Appendix Martel P 1744 An account of the glacieres or ice alps in Savoy in two letters one from an English gentleman to his friend at Geneva the other from Pierre Martel engineer to the said English gentleman In Mathews C E ed The annals of Mont Blanc London Unwin p 327 See Montgomery 2010 for a full bibliography Kruger Tobias 2013 Discovering the Ice Ages International Reception and Consequences for a Historical Understanding of Climate German edition Basel 2008 Leiden p 47 ISBN 978 90 04 24169 5 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link Kruger 2013 pp 78 83 Kruger 2013 p 150 Kruger 2013 pp 83 151 Goethe Johann Wolfgang von Geologische Probleme und Versuch ihrer Auflosung Mineralogie und Geologie in Goethes Werke Weimar 1892 ISBN 3 423 05946 X book 73 WA II 9 pp 253 254 Kruger 2013 p 83 Kruger 2013 p 38 Kruger 2013 pp 61 2 Kruger 2013 pp 88 90 Kruger 2013 pp 91 6 Hestmark Geir 2018 Jens Esmark s mountain glacier traverse 1823 the key to his discovery of Ice Ages Boreas 47 1 1 10 Bibcode 2018Borea 47 1H doi 10 1111 bor 12260 hdl 10852 67376 ISSN 1502 3885 The discovery of Ice Ages is one of the most revolutionary advances made in the Earth sciences In 1824 Danish Norwegian geoscientist Jens Esmark published a paper stating that there was indisputable evidence that Norway and other parts of Europe had previously been covered by enormous glaciers carving out valleys and fjords in a cold climate caused by changes in the eccentricity of Earth s orbit Esmark and his travel companion Otto Tank arrived at this insight by analogous reasoning enigmatic landscape features they observed close to sea level along the Norwegian coast strongly resembled features they observed in the front of a retreating glacier during a mountain traverse in the summer of 1823 Berg Bjorn Ivar 2020 02 25 Jens Esmark Norsk biografisk leksikon in Norwegian Bokmal retrieved 2021 02 28 Hverven Tom Egil Isens spor Klassekampen Retrieved 2021 02 28 Andersen Bjorn G 1992 Jens Esmark a pioneer in glacial geology Boreas 21 1 97 102 Bibcode 1992Borea 21 97A doi 10 1111 j 1502 3885 1992 tb00016 x Davies Gordon L 1969 The Earth in Decay A History of British Geomorphology 1578 1878 London New York American Elsevier Pub Co pp 267f ISBN 9780444197016 Cunningham Frank F 1990 James David Forbes Pioneer Scottish Glaciologist Edinburgh Scottish Academic Press p 15 ISBN 978 0 7073 0320 8 Kruger 2013 pp 142 47 Wood Gillen D Arcy 2014 Tambora the Eruption that Changed the World Princeton NJ Princeton University Press pp 160 167 ISBN 978 0 691 16862 3 Kruger 2013 pp 155 59 Kruger 2013 pp 167 70 Kruger 2013 p 173 Kruger 2013 pp 177 78 Agassiz Louis Bettannier Joseph 1840 Etudes sur les glaciers Ouvrage accompagne d un atlas de 32 planches Neuchatel H Nicolet Kruger 2013 pp 223 4 Charpentier Jean de Essais sur les glaciers et sur le terrain erratique du bassin du Rhone Lausanne 1841 Kruger 2013 pp 181 84 Kruger 2013 pp 458 60 How are past temperatures determined from an ice core Scientific American 2004 09 20 Putnam Aaron E Denton George H Schaefer Joerg M Barrell David J A Andersen Bjorn G Finkel Robert C Schwartz Roseanne Doughty Alice M Kaplan Michael R Schluchter Christian 2010 Glacier advance in southern middle latitudes during the Antarctic Cold Reversal Nature Geoscience 3 10 700 704 Bibcode 2010NatGe 3 700P doi 10 1038 ngeo962 Lockwood J G Zinderen Bakker E M van November 1979 The Antarctic Ice Sheet Regulator of Global Climates Review The Geographical Journal 145 3 469 471 doi 10 2307 633219 JSTOR 633219 Warren John K 2006 Evaporites sediments resources and hydrocarbons Birkhauser p 289 ISBN 978 3 540 26011 0 Allaby Michael January 2013 A Dictionary of Geology and Earth Sciences Fourth ed Oxford University Press ISBN 9780199653065 Retrieved 17 Sep 2019 permanent dead link a b Bornemann Andre Norris Richard D Friedrich Oliver Beckmann Britta Schouten Stefan Damste Jaap S Sinninghe Vogel Jennifer Hofmann Peter Wagner Thomas 2008 01 11 Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse Science 319 5860 189 192 Bibcode 2008Sci 319 189B doi 10 1126 science 1148777 ISSN 0036 8075 PMID 18187651 S2CID 206509273 a b c Ladant Jean Baptiste Donnadieu Yannick 2016 09 21 Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse Nature Communications 7 1 12771 Bibcode 2016NatCo 712771L doi 10 1038 ncomms12771 ISSN 2041 1723 PMC 5036002 PMID 27650167 Kopp Robert 14 June 2005 The Paleoproterozoic snowball Earth A climate disaster triggered by the evolution of oxygenic photosynthesis PNAS 102 32 11131 6 Bibcode 2005PNAS 10211131K doi 10 1073 pnas 0504878102 PMC 1183582 PMID 16061801 Hyde WT Crowley TJ Baum SK Peltier WR May 2000 Neoproterozoic snowball Earth simulations with a coupled climate ice sheet model PDF Nature 405 6785 425 9 Bibcode 2000Natur 405 425H doi 10 1038 35013005 PMID 10839531 S2CID 1672712 Chris Clowes 2003 Snowball Scenarios of the Cryogenian Paleos Life through deep time Archived from the original on 15 June 2009 Rodriguez Lopez Juan Pedro Liesa Carlos L Pardo Gonzalo Melendez Nieves Soria Ana R Skilling Ian 2016 06 15 Glacial dropstones in the western Tethys during the late Aptian early Albian cold snap Palaeoclimate and palaeogeographic implications for the mid Cretaceous Palaeogeography Palaeoclimatology Palaeoecology 452 11 27 Bibcode 2016PPP 452 11R doi 10 1016 j palaeo 2016 04 004 ISSN 0031 0182 Rodriguez Lopez Juan Pedro Liesa Carlos L Luzon Aranzazu Munoz Arsenio Mayayo Maria J Murton Julian B Soria Ana R 2023 10 10 Ice rafted dropstones at midlatitudes in the Cretaceous of continental Iberia Geology 52 33 38 doi 10 1130 g51725 1 ISSN 0091 7613 Wang Tianyang He Songlin Zhang Qinghai Ding Lin Farnsworth Alex Cai Fulong Wang Chao Xie Jing Li Guobiao Sheng Jiani Yue Yahui 2023 05 26 Ice Sheet Expansion in the Cretaceous Greenhouse World Fundamental Research doi 10 1016 j fmre 2023 05 005 ISSN 2667 3258 Bowman Vanessa C Francis Jane E Riding James B December 1 2013 Late Cretaceous winter sea ice in Antarctica Geology 41 12 1227 1230 Bibcode 2013Geo 41 1227B doi 10 1130 g34891 1 S2CID 128885087 Retrieved 2023 10 26 University of Houston Clear Lake Disasters Class Notes Chapter 12 Climate Change sce uhcl edu Pitts disastersclassnotes chapter 12 Climate Change doc Ghienne Jean Francois January 2003 Late Ordovician sedimentary environments glacial cycles and post glacial transgression in the Taoudeni Basin West Africa Palaeogeography Palaeoclimatology Palaeoecology 189 3 4 117 145 Bibcode 2003PPP 189 117G doi 10 1016 S0031 0182 02 00635 1 Heckel P H 2008 Pennsylvanian cyclothems in Midcontinent North America as far field effects of waxing and waning of Gondwana ice sheets In Fielding C R Frank T D Isbell J L eds Resolving the Late Paleozoic Ice Age in Time and Space pp 275 290 Walker M Johnsen S Rasmussen S O Popp T Steffensen J P Gibbard P Hoek W Lowe J Andrews J Bjo Cwynar L C Hughen K Kershaw P Kromer B Litt T Lowe D J Nakagawa T Newnham R Schwander J 2009 Formal definition and dating of the GSSP Global Stratotype Section and Point for the base of the Holocene using the Greenland NGRIP ice core and selected auxiliary records PDF J Quaternary Sci 24 1 3 17 Bibcode 2009JQS 24 3W doi 10 1002 jqs 1227 Augustin L Barbante C Barnes PRF Barnola JM Bigler M Castellano E Cattani O Chappellaz J et al 2004 06 10 Eight glacial cycles from an Antarctic ice core Nature 429 6992 623 8 Bibcode 2004Natur 429 623A doi 10 1038 nature02599 PMID 15190344 S2CID 4342139 Next Ice Age Delayed By Rising Carbon Dioxide Levels ScienceDaily 2007 Retrieved 2008 02 28 The Complicated Role of Iron in Ocean Health and Climate Change Ewing M Donn W L 1956 06 15 A Theory of Ice Ages Science 123 3207 1061 1066 Bibcode 1956Sci 123 1061E doi 10 1126 science 123 3207 1061 ISSN 0036 8075 PMID 17748617 Garrison Tom 2009 Oceanography An Invitation to Marine Science 7th ed Cengage Learning p 582 ISBN 9780495391937 Bryden H L H R Longworth S A Cunningham 2005 Slowing of the Atlantic meridional overturning circulation at 25 N Nature 438 7068 655 657 Bibcode 2005Natur 438 655B doi 10 1038 nature04385 PMID 16319889 S2CID 4429828 Curry R C Mauritzen 2005 Dilution of the northern North Atlantic in recent decades Science 308 5729 1772 1774 Bibcode 2005Sci 308 1772C doi 10 1126 science 1109477 PMID 15961666 S2CID 36017668 Huddart David Stott Tim A 2013 04 16 Earth Environments Past Present and Future John Wiley amp Sons ISBN 978 1 118 68812 0 Bennett Matthew M Glasser Neil F 2010 03 29 Glacial Geology Ice Sheets and Landforms Wiley ISBN 978 0 470 51690 4 Another factor is the increased aridity occurring with glacial maxima which reduces the precipitation available to maintain glaciation The glacial retreat induced by this or any other process can be amplified by similar inverse positive feedbacks as for glacial advances Black Richard 9 January 2012 Carbon emissions will defer Ice Age BBC News Retrieved 10 August 2012 Luthi Dieter et al 2008 03 17 High resolution carbon dioxide concentration record 650 000 800 000 years before present PDF Nature 453 7193 379 382 Bibcode 2008Natur 453 379L doi 10 1038 nature06949 PMID 18480821 S2CID 1382081 Ruddiman W F Kutzbach J E 1991 Plateau Uplift and Climate Change Scientific American 264 3 66 74 Bibcode 1991SciAm 264c 66R doi 10 1038 scientificamerican0391 66 a b Raymo Maureen E Ruddiman William F Froelich Philip N 1988 07 01 Influence of late Cenozoic mountain building on ocean geochemical cycles Geology 16 7 649 653 Bibcode 1988Geo 16 649R doi 10 1130 0091 7613 1988 016 lt 0649 IOLCMB gt 2 3 CO 2 ISSN 0091 7613 Clark Peter U Dyke Arthur S Shakun Jeremy D Carlson Anders E Clark Jorie Wohlfarth Barbara Mitrovica Jerry X Hostetler Steven W amp McCabe A Marshall 2009 The Last Glacial Maximum Science 325 5941 710 714 Bibcode 2009Sci 325 710C doi 10 1126 science 1172873 PMID 19661421 S2CID 1324559 Lee Hannah Climate Change Biology 2nd ed Amsterdam Academic Press 2014 23 28 ISBN 012799923X Svitil K A April 1996 We are all Panamanians Discover formation of Isthmus of Panama may have started a series of climatic changes that led to evolution of hominids Hu Aixue Meehl Gerald A Otto Bliesner Bette L Waelbroeck Claire Weiqing Han Loutre Marie France Lambeck Kurt Mitrovica Jerry X Rosenbloom Nan 2010 Influence of Bering Strait flow and North Atlantic circulation on glacial sea level changes PDF Nature Geoscience 3 2 118 121 Bibcode 2010NatGe 3 118H CiteSeerX 10 1 1 391 8727 doi 10 1038 ngeo729 hdl 1885 30691 Archived from the original PDF on 2017 08 11 Retrieved 2017 10 24 Melting icebergs key to sequence of an ice age scientists find phys org Retrieved 12 February 2021 Starr Aidan Hall Ian R Barker Stephen Rackow Thomas Zhang Xu Hemming Sidney R Lubbe H J L van der Knorr Gregor Berke Melissa A Bigg Grant R Cartagena Sierra Alejandra Jimenez Espejo Francisco J Gong Xun Gruetzner Jens Lathika Nambiyathodi LeVay Leah J Robinson Rebecca S Ziegler Martin January 2021 Antarctic icebergs reorganize ocean circulation during Pleistocene glacials Nature 589 7841 236 241 Bibcode 2021Natur 589 236S doi 10 1038 s41586 020 03094 7 hdl 10261 258181 ISSN 1476 4687 PMID 33442043 S2CID 231598435 Retrieved 12 February 2021 Kuhle Matthias December 1988 The Pleistocene Glaciation of Tibet and the Onset of Ice Ages An Autocycle Hypothesis GeoJournal 17 4 581 595 doi 10 1007 BF00209444 JSTOR 41144345 S2CID 189891305 2c Quaternary Glaciation Extent and Chronology Part III South America Asia Africa Australia AntarcticaKuhle M 2004 The High Glacial Last Ice Age and LGM ice cover in High and Central Asia In Ehlers J Gibbard P L eds Quaternary Glaciations South America Asia Africa Australasia Antarctica Development in Quaternary Science Quaternary Glaciations Extent and Chronology Vol 3 Amsterdam Elsevier pp 175 199 ISBN 978 0 444 51593 3 Kuhle M 1999 Reconstruction of an approximately complete Quaternary Tibetan inland glaciation between the Mt Everest and Cho Oyu Massifs and the Aksai Chin A new glaciogeomorphological SE NW diagonal profile through Tibet and its consequences for the glacial isostasy and Ice Age cycle GeoJournal 47 1 2 3 276 doi 10 1023 A 1007039510460 S2CID 128089823 Kuhle M 2011 Ice Age Development Theory In Singh V P Singh P Haritashya U K eds Encyclopedia of Snow Ice and Glaciers Springer pp 576 581 Earth s orbital variations and sea ice synch glacial periods Ice Age Explanation Sciforums www sciforums com Muller R A MacDonald G J 1997 08 05 Spectrum of 100 kyr glacial cycle orbital inclination not eccentricity Proceedings of the National Academy of Sciences of the United States of America 94 16 8329 8334 Bibcode 1997PNAS 94 8329M doi 10 1073 pnas 94 16 8329 ISSN 0027 8424 PMC 33747 PMID 11607741 Richard A Muller A New Theory of Glacial Cycles Muller lbl gov Retrieved 2012 08 07 Muller R A 1997 07 11 Glacial Cycles and Astronomical Forcing Science 277 5323 215 218 Bibcode 1997Sci 277 215M doi 10 1126 science 277 5323 215 Rial J A July 1999 Pacemaking the ice ages by frequency modulation of Earth s orbital eccentricity PDF Science 285 5427 564 8 doi 10 1126 science 285 5427 564 PMID 10417382 Archived from the original PDF on 2008 10 15 Huybers Peter Wunsch Carl 2005 03 24 Obliquity pacing of the late Pleistocene glacial terminations Nature 434 7032 491 494 Bibcode 2005Natur 434 491H doi 10 1038 nature03401 ISSN 1476 4687 PMID 15791252 S2CID 2729178 Paillard D 22 January 1998 The timing of Pleistocene glaciations from a simple multiple state climate model Nature 391 6665 378 381 Bibcode 1998Natur 391 378P doi 10 1038 34891 S2CID 4409193 Ditlevsen P D 2009 Bifurcation structure and noise assisted transitions in the Pleistocene glacial cycles Paleoceanography 24 3 PA3204 arXiv 0902 1641 Bibcode 2009PalOc 24 3204D doi 10 1029 2008PA001673 Archived from the original on 2012 11 01 Retrieved 2012 06 09 as PDF Guinan E F Ribas I 2002 Our Changing Sun The Role of Solar Nuclear Evolution and Magnetic Activity on Earth s Atmosphere and Climate The Evolving Sun and its Influence on Planetary Environments Astronomical Society of the Pacific p 85 ISBN 1 58381 109 5 Rieke George Long Term Climate Archived from the original on 2 June 2015 Retrieved 25 April 2013 PETM Global Warming Naturally Weather Underground www wunderground com Archived from the original on 2016 12 02 Retrieved 2016 12 02 Quaternary Period National Geographic 2017 01 06 Archived from the original on March 20 2017 Hallberg G R 1986 Pre Wisconsin glacial stratigraphy of the Central Plains region in Iowa Nebraska Kansas and Missouri Quaternary Science Reviews 5 11 15 Bibcode 1986QSRv 5 11H doi 10 1016 0277 3791 86 90169 1 a b Richmond G M Fullerton D S 1986 Summation of Quaternary glaciations in the United States of America Quaternary Science Reviews 5 183 196 Bibcode 1986QSRv 5 183R doi 10 1016 0277 3791 86 90184 8 Gibbard P L S Boreham K M Cohen and A Moscariello 2007 Global chronostratigraphical correlation table for the last 2 7 million years v 2007b jpg version 844 KB Subcommission on Quaternary Stratigraphy Department of Geography University of Cambridge Cambridge England Kuhle M 1984 Spuren hocheiszeitlicher Gletscherbedeckung in der Aconcagua Gruppe 32 33 S Zentralblatt fur Geologie und Palaontologie Teil I 11 12 1635 46 ISSN 0340 5109 Verhandlungsblatt des Sudamerika Symposiums 1984 in Bamberg Kuhle M 1986 Die Vergletscherung Tibets und die Entstehung von Eiszeiten Spektrum der Wissenschaft 9 86 42 54 ISSN 0170 2971 Kuhle Matthias June 1987 Subtropical Mountain and Highland Glaciation as Ice Age Triggers and the Waning of the Glacial Periods in the Pleistocene GeoJournal 14 4 393 421 doi 10 1007 BF02602717 JSTOR 41144132 S2CID 129366521 a b Kuhle M 2004 The Last Glacial Maximum LGM glacier cover of the Aconcagua group and adjacent massifs in the Mendoza Andes South America In Ehlers J Gibbard P L eds Quaternary Glaciations South America Asia Africa Australasia Antarctica Development in Quaternary Science Amsterdam Elsevier pp 75 81 ISBN 978 0 444 51593 3 a b c Kuhle M 2011 Ch 53 The High Glacial Last Glacial Maximum Glacier Cover of the Aconcagua Group and Adjacent Massifs in the Mendoza Andes South America with a Closer Look at Further Empirical Evidence In Ehlers J Gibbard P L Hughes P D eds Quaternary Glaciations Extent and Chronology A Closer Look Development in Quaternary Science Amsterdam Elsevier pp 735 8 ISBN 978 0 444 53447 7 Bruggen J 1929 Zur Glazialgeologie der chilenischen Anden Geol Rundsch 20 1 1 35 Bibcode 1929GeoRu 20 1B doi 10 1007 BF01805072 S2CID 128436981 Andersen Bjorn G Borns Harold W Jr 1997 The Ice Age World an introduction to quaternary history and research with emphasis on North America and Northern Europe during the last 2 5 million years Oslo Universitetsforlaget ISBN 978 82 00 37683 5 Archived from the original on 2013 01 12 Retrieved 2013 10 14 Johnston A 1989 The effect of large ice sheets on earthquake genesis In Gregersen S Basham P eds Earthquakes at North Atlantic passive margins Neotectonics and postglacial rebound Dordrecht Kluwer pp 581 599 ISBN 978 0 7923 0150 9 Wu Patrick Hasegawa Henry S October 1996 Induced stresses and fault potential in eastern Canada due to a realistic load a preliminary analysis Geophysical Journal International 127 1 215 229 Bibcode 1996GeoJI 127 215W doi 10 1111 j 1365 246X 1996 tb01546 x Turpeinen H Hampel A Karow T Maniatis G 2008 Effect of ice sheet growth and melting on the slip evolution of thrust faults Earth and Planetary Science Letters 269 1 2 230 241 Bibcode 2008E amp PSL 269 230T doi 10 1016 j epsl 2008 02 017 Hunt A G Malin P E May 1998 Possible triggering of Heinrich events by ice load induced earthquakes Nature 393 6681 155 158 Bibcode 1998Natur 393 155H doi 10 1038 30218 ISSN 0028 0836 S2CID 4393858 Interglacial Working Group Of PAGES November 20 2015 Interglacials Of The Last 800 000 years PDF Reviews of Geophysics 54 1 162 219 Bibcode 2016RvGeo 54 162P doi 10 1002 2015RG000482 hdl 2078 1 175429 Works cited Montgomery Keith 2010 Development of the glacial theory 1800 1870 Historical SimulationExternal links nbsp The Wikibook Historical Geology has a page on the topic of Ice ages nbsp Wikimedia Commons has media related to Ice ages nbsp Wikisource has the text of The New Student s Reference Work article about Ice age Cracking the Ice Age from PBS Rina Torchinsky 9 Aug 2021 Scientists unveil best preserved Ice Age animal ever found AccuWeather Raymo M July 2011 Overview of the Uplift Weathering Hypothesis Archived from the original on 2008 10 22 Eduard Y Osipov Oleg M Khlystov Glaciers and meltwater flux to Lake Baikal during the Last Glacial Maximum Archived 2016 03 12 at the Wayback Machine Black R 9 January 2012 Carbon emissions will defer Ice Age BBC News Science and Environment Portals nbsp Geology nbsp Paleontology Retrieved from https en wikipedia org w index php title Ice age amp oldid 1193849209, wikipedia, wiki, book, books, library,

article

, read, download, free, free download, mp3, video, mp4, 3gp, jpg, jpeg, gif, png, picture, music, song, movie, book, game, games.