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Encyclopedia > Ice Age
Ice sheets expand during an ice age. This image is of the Antarctic ice sheet.
Ice sheets expand during an ice age. This image is of the Antarctic ice sheet.
Variations in temperature, CO2, and dust from the Vostok ice core over the last 400,000 years
Variations in temperature, CO2, and dust from the Vostok ice core over the last 400,000 years

An ice age is a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ice age is used to refer to colder periods with extensive ice sheets over the North American and Eurasian continents: in this sense, the most recent ice age ended about 11,000 years ago. This article will use the term ice age in the former, glaciological, sense: glacials for colder periods during ice ages and interglacials for the warmer periods. Image File history File links Emblem-important. ... The Pleistocene epoch (IPA: ) on the geologic timescale is the period from 1,808,000 to 11,550 years BP. The Pleistocene epoch had been intended to cover the worlds recent period of repeated glaciations. ... // The Paleolithic is a prehistoric era distinguished by the development of stone tools. ... Ice age or Ice Age may mean any of the following: A period of major glaciation on Earth: Ice age An animated movie: Ice Age (movie) A progressive rock music band: Ice Age (band) A series of expansion cards in Magic: The Gathering and related story lines: Ice Age (Magic... Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Graph of Vostok CO2/T/dust from Petit 1999 paper. ... Graph of Vostok CO2/T/dust from Petit 1999 paper. ... Vostok, Antarctica is a Russian research station located near the Geomagnetic South Pole (see South Pole), at the center of the East Antarctic Ice Sheet. ... For other uses, see Temperature (disambiguation). ... This article is about Earth as a planet. ... An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² (19,305 mile²).[1] The only current ice sheets are in Antarctica and Greenland; during the last ice age at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much... Perito Moreno Glacier Patagonia Argentina Aletsch Glacier, Switzerland Icebergs breaking off glaciers at Cape York, Greenland This article is about the geological formation. ... Lateral moraine on a glacier joining the Gorner Glacier, Zermatt, Switzerland. ... A satellite composite image of Antarctica The Antarctic ice sheet is the largest single mass of ice on Earth. ... North American redirects here. ... For other uses, see Eurasia (disambiguation). ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... An Interglacial is a geological interval of warmer global average temperature that separates glacials, or ice ages. ...

Contents

Origin of ice age theory

The idea that in the past glaciers had been far more extensive was folk knowledge in some alpine regions of Europe: Imbrie and Imbrie (1979) quote a woodcutter by name of Jean-Pierre Perraudin[1] telling Jean de Charpentier of the former extent of the Swiss Grimsel glacier.[2] Macdougall (2004) claims the person was a Swiss engineer named Ignaz Venetz,[3] but no single person invented the idea.[4] Between 1825 and 1833, Charpentier assembled evidence in support of the concept. In 1836 Charpentier, Venetz and Karl Friedrich Schimper convinced Louis Agassiz, and Agassiz published the hypothesis in his book Étude sur les glaciers (Study on Glaciers) of 1840.[5] According to Macdougall (2004), Charpentier and Venetz disapproved of the ideas of Agassiz who extended their work claiming that most continents were once covered by ice. Jean de Charpentier (December 8, 1786 - December 12, 1855) was a German-Swiss geologist who studied Swiss glaciers. ... View from the pass on Grimselsee, Grimsel Hospice und Räterichsbodensee The Grimsel Pass (German: Grimselpass) is a Swiss alpine pass between the valley of the Rhone River (Canton of Valais) and the Haslital (upper valley of the Aar river) in Canton of Berne, at 46°33. ... Ignaz Venetz (1788–1859) was a Swiss engineer, naturalist, and glaciologist. ... Louis Agassiz Jean Louis Rodolphe Agassiz (May 28, 1807-December 14, 1873) was a Swiss-American zoologist and geologist, the husband of educator Elizabeth Cabot Cary Agassiz, and one of the first world-class American scientists. ...


At this early stage of knowledge, what was being studied were the glacial periods within the past few hundred thousand years, during the current ice age. The existence of ancient ice ages was as yet unsuspected.


Evidence for ice ages

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, making it difficult to interpret. It took some time for the current theory to be worked out. Moraine is the general term for debris of all sorts originally transported by glaciers or ice sheets that have since melted away. ... Drumlin in Cato, New York A drumlin (Gaelic druim the crest of a hill) is an elongated whale-shaped hill formed by glacial action. ... Glacial till with tufts of grass Till is an unsorted glacial sediment. ... A Glacial erratic is a piece of rock carried by glacial ice some distance from the rock outcrop from which it came. ...


The chemical evidence mainly consists of variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks, ocean sediment cores, and for the most recent glacial periods, ice cores. Because water containing heavier isotopes has a higher heat of evaporation, its proportion decreases with colder conditions[6]. This allows a temperature record to be constructed. However, this evidence can be confounded by other factors recorded by isotope ratios; for example, a mass extinction increases the proportion of lighter isotopes in sediments and ice because biological processes preferentially use lighter isotopes so a reduction in land or ocean biomass makes larger quantities of lighter isotopes available for deposition. Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... Ice Core sample taken from drill. ... Molar heat content of zinc above 298. ... An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. ... For the use of the term in ecology, see Biomass (ecology). ...


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 are squeezed into lower latitudes. This evidence is also difficult to interpret because it requires (1) sequences of sediments which cover a long time-span and wide range of latitudes and 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, which requires a lot of luck.


Despite the difficulties, analyses of ice cores and ocean sediment cores clearly show the 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

Ice age map of northern central Europe. Red: maximum limit of Weichselian ice age; yellow: Saale ice age at maximum (Drenthe stage); blue: Elster ice age maximum glaciation.
Ice age map of northern central Europe. Red: maximum limit of Weichselian ice age; yellow: Saale ice age at maximum (Drenthe stage); blue: Elster ice age maximum glaciation.

There have been at least four major ice ages in the Earth's past. Outside these periods, the Earth seems to have been ice-free even in high latitudes. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article is about Earth as a planet. ...


The earliest hypothesized ice age, called the Huronian, was around 2.7 to 2.3 billion years ago during the early Proterozoic Eon. The Huronian glaciation was from 2400 mya to 2100 mya, during the Siderian and Rhyacian periods of the Paleoproterozoic era. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ...


The earliest well-documented ice age, and probably the most severe of the last 1 billion years, occurred from 850 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which permanent ice covered the entire globe. This ended very rapidly as water vapor returned to Earth's atmosphere. It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian Explosion, though this theory is recent and controversial. The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... One computer simulation of conditions during the Snowball Earth period. ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... Air redirects here. ... The Ediacaran[5][6]  â€¢  â€¢  | Neoproterozoic (last æon of the Precambrian) Phanerozoic Axis scale: millions of years ago. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ...

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

A minor ice age, the Andean-Saharan, occurred from 460 to 430 million years ago, during the Late Ordovician and the Silurian period. There were extensive polar ice caps at intervals from 350 to 260 million years ago, during the Carboniferous and early Permian Periods, associated with the Karoo Ice Age. Description Expansion of changes during the recent sequence of glacials and interglacials This figure shows the climate record of Lisiecki and Raymo (2005) [1] constructed by combining measurements from 57 globally distributed deep sea sediment cores. ... Description Expansion of changes during the recent sequence of glacials and interglacials This figure shows the climate record of Lisiecki and Raymo (2005) [1] constructed by combining measurements from 57 globally distributed deep sea sediment cores. ... The Andean-Saharan glaciation was from 450 mya to 420 mya, during most of the Silurian period and the beginning of the Devonian period. ... The Late Ordovician, also called the Upper Ordovician by geologists, is the third epoch of the Ordovician period. ... For other uses, see Silurian (disambiguation). ... An ice cap is a dome-shaped ice mass that covers less than 50,000 km² of land area (usually covering a highland area). ... President Bush- Deres gold in dem dere mines The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... The Permian is a geologic period that extends from about 299. ... The Karoo Ice Age from 350-250 million years ago was the second major period of Glaciation of the Phanerozoic Era. ...


The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica. It intensified during the late Pliocene, around 3 million years ago, with the spread of ice sheets in the Northern Hemisphere, and has continued in the Pleistocene. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales. The most recent glacial period ended about ten thousand years ago. The Pliocene epoch (spelled Pleiocene in some older texts) is the period in the geologic timescale that extends from 5. ... The Pleistocene epoch (IPA: ) on the geologic timescale is the period from 1,808,000 to 11,550 years BP. The Pleistocene epoch had been intended to cover the worlds recent period of repeated glaciations. ...


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. Note that the maximum extent of the ice is not maintained for the full interval. Unfortunately, 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. It is possible that glacial periods other than those above, especially in the Precambrian, have been overlooked because of scarcity of exposed rocks from high latitudes from older periods. The Wisconsin (in North America), Weichsel (in Scandinavia), Devensian (in the British Isles), Midlandian (in Ireland) or Würm glaciation (in the Alps) is the most recent period of the Ice Age, and ended some 10,000 Before Present (BP). ... Alp redirects here. ... The Precambrian (Pre-Cambrian) is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. ...


Glacials and interglacials

See also: Interglacial
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials

Within the ice ages (or at least within the last one), more temperate and more severe periods occur. The colder periods are called glacial periods, the warmer periods interglacials, such as the Eemian interglacial era. Glaciation, often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... Description Expanded record of temperature change since the end of the last glacial period Extended record of climate change during the last 5 Myr This figure shows the Antarctic temperature changes during the last several glacial/interglacial cycles of the present ice age and a comparison to changes in global... Description Expanded record of temperature change since the end of the last glacial period Extended record of climate change during the last 5 Myr This figure shows the Antarctic temperature changes during the last several glacial/interglacial cycles of the present ice age and a comparison to changes in global... The Eemian interglacial era (Sangamon era in North America) is the second-to-latest interglacial era of the Ice age. ...


Glacials are characterized by cooler and drier climates over most of the 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. Since the Earth has significant continental glaciation in the Arctic and Antarctic, we are currently in a glacial minimum of a glaciation. Such a period between glacial maxima is known as an interglacial. For other uses, see Mountain (disambiguation). ... The snow line is the point above which, or poleward of which, snow and ice cover the ground throughout the year. ...


The Earth has been in an interglacial period known as the Holocene for more than 11,000 years. It was conventional wisdom that "the typical interglacial period lasts about 12,000 years," but this has been called into question recently. For example, an article in Nature[7] argues that the current interglacial might be most analogous to a previous interglacial that lasted 28,000 years. Predicted changes in orbital forcing suggest that the next glacial period would not begin before about 50,000 years from now, regardless of man-made global warming [8] (see Milankovitch cycles). Moreover, anthropogenic forcing from increased greenhouse gases might outweigh orbital forcing for as long as intensive use of fossil fuels continues[9]. The Holocene epoch is a geological period, which began approximately 11,550 calendar years BP (about 9600 BC) and continues to the present. ... Orbital forcing, or Milankovitch theory, describes the effect on climate of slow changes in the tilt of the Earths axis and shape of the orbit. ... Global warming refers to the increase in the average temperature of the Earths near-surface air and oceans in recent decades and its projected continuation. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... Top: Increasing atmospheric levels as measured in the atmosphere and ice cores. ...


Positive and negative feedbacks in glacial periods

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 feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... This article does not cite any references or sources. ...


Processes which make glacial periods more severe

Ice and snow increase the Earth's albedo, i.e. they make it reflect more of the sun's energy and absorb less. Hence, when the air temperature decreases, ice and snow fields grow, and this continues until an equilibrium is reached. Also, the reduction in forests caused by the ice's expansion increases albedo. For other uses, see Albedo (disambiguation). ... Taiga (SAMPA /[email protected]/, from Russian тайга́) is a biome characterized by its coniferous forests. ...


Another theory has 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. (Current projected consequences of global warming include a largely ice-free Arctic Ocean within 50 years.) Additional fresh water flowing into the North Atlantic during a warming cycle may also reduce the global ocean water circulation (see Shutdown of thermohaline 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. It has also been suggested that during an extensive ice age glaciers may move through the Gulf of Saint Lawrence, extending into the North Atlantic ocean to an extent that the Gulf Stream is blocked. Sublimation of an element or substance is a conversion between the solid and the gas phases with no intermediate liquid stage. ... This article is about arid terrain. ... Global warming refers to the increase in the average temperature of the Earths near-surface air and oceans in recent decades and its projected continuation. ... A simplified summary of the path of the Thermohaline Circulation. ... Shutdown or slowdown of the thermohaline circulation is a possible effect of global warming. ... For the album by Ocean Colour Scene, see North Atlantic Drift (album) The Gulf Stream is orange and yellow in this representation of water temperatures of the Atlantic. ... Bathymetry of the Gulf, with the Laurentian Channel visible Gulf of Saint Lawrence (French: golfe du Saint-Laurent), the worlds largest estuary, is the outlet of North Americas Great Lakes via the Saint Lawrence River into the Atlantic Ocean. ...


Processes which mitigate glacial periods

Ice sheets that form during glaciations cause erosion of the land beneath them. After some time, this will reduce land below sea level and thus diminish the amount of space on which ice sheets can form. This mitigates the albedo feedback, as does the lowering in sea level that accompanies the formation of ice sheets. For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ...


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.


Causes of ice ages

The causes of ice ages remain controversial for both the large-scale ice age periods and the smaller ebb and flow of glacial–interglacial periods within an ice age. The consensus is that several factors are important: atmospheric composition (the concentrations of carbon dioxide, methane; changes in the Earth's orbit around the Sun known as Milankovitch cycles (and possibly the Sun's orbit around the galaxy); the motion of tectonic plates resulting in changes in the relative location and amount of continental and oceanic crust on the Earth's surface, which could affect wind and ocean currents; variations in solar output; the orbital dynamics of the Earth-Moon system; and the impact of relatively large meteorites, and volcanism including eruptions of supervolcanoes. Air redirects here. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Methane is a chemical compound with the molecular formula . ... Sol redirects here. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... For other uses, see Milky Way (disambiguation). ... The tectonic plates of the world were mapped in the second half of the 20th century. ... For other uses, see Wind (disambiguation). ... An ocean current is any more or less permanent or continuous, directed movement of ocean water that flows in one of the Earths oceans. ... Atmospheric circulation is the large-scale movement of air, and the means (together with the ocean circulation, which is smaller [1]) by which heat is distributed on the surface of the Earth. ... 20 years of solar irradiance data from satellites Solar variation refers to fluctuation in the amount of energy emitted by the Sun. ... Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ... A supervolcano is a volcano that produces the largest and most voluminous kinds of eruption on Earth. ...


Some of these factors are causally related to 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). Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earths atmosphere. ...


William Ruddiman, Maureen Raymo, 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.[10][11] William F. Ruddiman is a palaeoclimatologist and Professor Emeritus at the university of Virginia. ... The Colorado Plateau, also called the Colorado Plateaus Province, is a physiographic region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. ...


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 vulcanism. Top: Increasing atmospheric levels as measured in the atmosphere and ice cores. ...


The Snowball Earth hypothesis maintains that the severe freezing in the late Proterozoic was ended by an increase in CO2 levels in the atmosphere, and some supporters of Snowball Earth argue that it was caused by a reduction in atmospheric CO2. The hypothesis also warns of future Snowball Earths. One computer simulation of conditions during the Snowball Earth period. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ...


William Ruddiman has proposed the early anthropocene hypothesis, according to which the anthropocene era, as some people call the most recent period in the Earth's history when the activities of the human race first began to have a significant global impact on the Earth's climate and ecosystems, did not begin in the 18th century with the advent of the Industrial Era, but dates back to 8,000 years ago, due to intense farming activities of our early agrarian ancestors. It was at that time that atmospheric greenhouse gas concentrations stopped following the periodic pattern of the Milankovitch cycles. In his overdue-glaciation hypothesis Ruddiman claims that an incipient ice age would probably have begun several thousand years ago, but the arrival of that scheduled ice age was forestalled by the activities of early farmers. William F. Ruddiman is a palaeoclimatologist and Professor Emeritus at the university of Virginia. ... The early anthropocene hypothesis (sometimes called Early Anthropogenic) is a theory proposed by William Ruddiman. ... The term Anthropocene is used by some scientists to describe the most recent period in the Earths history, starting in the 18th century where the activities of the human race first began to have a significant global effect on the Earths climate and ecosystems. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... The overdue-glaciation hypothesis is a theory proposed by William Ruddiman that the end of the current interglacial warm period is already overdue; that is, according to astronomical models that have successfully characterized the pattern of past glaciations due to variations in the earths orbit known as Milankovitch cycles...


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 the 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. Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ... For other uses, see Albedo (disambiguation). ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... Wikinews has related news: Scientists warn thawing Siberia may trigger global meltdown A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ...


There are three known configurations of the continents which block or reduce the flow of warm water from the equator to the poles:

  • 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. In geology, Rodinia (from the Russian родина, or motherland) refers to one of the oldest known supercontinents, which contained most or all of Earths then-current landmass. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ...


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 CO2 is washed out of the atmosphere, decreasing the greenhouse effect. 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. For the movie Himalaya, see Himalaya (film). ...  The Indo-Australian plate, shown in dull orange The Indo-Australian Plate is an overarching name for two tectonic plates that include the continent of Australia and surrounding ocean extending northwest to include the Indian subcontinent and adjacent waters. ...  The Eurasian plate, shown in green The Eurasian Plate is a tectonic plate covering Eurasia (a landmass consisting of the traditional continents of Europe and Asia) except that it does not cover the Indian subcontinent, the Arabian subcontinent, and the area east of the Verkhoyansk Range in East Siberia. ... hfajhfiudshfas == == == --24. ...


Other important aspects which contributed to ancient climate regimes are the ocean currents, which are modified by continent position 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.[12]


Variations in Earth's orbit (Milankovitch cycles)

The Milankovitch cycles are a set of cyclic variations in characteristics of the 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. Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the...


It is very unlikely that the Milankovitch cycles can start or end an ice age (series of glacial periods):

  • Even when their effects reinforce each other they are not strong enough.
  • The "peaks" (effects reinforce each other) and "troughs" (effects cancel each other) are much more regular and much more frequent than the observed ice ages.

In contrast, there is strong evidence that the Milankovitch cycles affect the occurrence of glacial and interglacial periods within an ice age. The present ice ages are 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 the Earth's axis, and the changing tilt of the Earth's axis redistribute the sunlight received by the Earth. Of particular importance are changes in the tilt of the 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 25% (from 400 W/m² to 500 W/m², see graph at [1]). 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 workers believe that the strength of the orbital forcing is too small to trigger glaciations, but feedback mechanisms like CO2 may explain this mismatch. Ice Core sample taken from drill. ... This article is about divisions of a year. ... This article is about the geographical term. ... For other uses, see Watt (disambiguation). ...


While Milankovitch forcing predicts that cyclic changes in the Earth's orbital parameters 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 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 the Earth's climate system. Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ... For the science fiction novella by William Shunn, see Inclination (novella). ... Axial tilt is an astronomical term regarding the inclination angle of a planets rotational axis in relation to its orbital plane. ...


The "traditional" Milankovitch explanation struggles to explain the dominance of the 100,000-year cycle over the last 8 cycles. Richard A. Muller and Gordon J. MacDonald [2] [3] [4] 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 the 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 [5]. Richard Muller Richard A. Muller (January 6, 1944 -) of San Francisco, California, USA, is a physicist who works at the University of California, Berkeley and Lawrence Berkeley National Laboratory. ... Not to be confused with insulation. ...


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 (23,000-year cycle) combined with greenhouse gas feedbacks in the 41,000- and 23,000-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 the 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. This theory is consistent with the existing uncertainties in dating, but not widely accepted at present (Nature 434, 2005, [6]). William F. Ruddiman is a palaeoclimatologist and Professor Emeritus at the university of Virginia. ...


Variations in the Sun's energy output

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

  • In the very long term, astrophysicists believe that the sun's output increases by about 10% per billion (109) years. In about one billion years the additional 10% will be enough to cause a runaway greenhouse effect on Earth—rising temperatures produce more water vapour, water vapour is a greenhouse gas (much stronger than CO2), the temperature rises, more water vapour is produced, etc.
  • Shorter-term variations, some possibly caused by hunting. Since the Sun is huge, the effects of imbalances and negative feedback processes take a long time to propagate through it, so these processes overshoot and cause further imbalances, etc.—"long time" in this context means thousands to millions of years.

The long-term increase in the Sun's output cannot be a cause of ice ages. Wikinews has related news: Scientists warn thawing Siberia may trigger global meltdown A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ... Hunting is a self-exciting oscillation of a physical system, commonly that of systems incorporating feedback. ... Sol redirects here. ... This article does not cite any references or sources. ...


The best known shorter-term variations are sunspot cycles, especially the Maunder minimum, which is associated with the coldest part of the Little Ice Age. Like the Milankovitch cycles, sunspot cycles' effects are too weak and too frequent to explain the start and end of ice ages but very probably help to explain temperature variations within them. For other uses, see Sunspot (disambiguation). ... The Maunder minimum in a 400 year history of sunspot numbers The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time. ... The Little Ice Age (LIA) was a period of cooling occurring after a warmer era known as the Medieval climate optimum. ...


Volcanism

It is theoretically possible that undersea volcanoes could end an ice age by causing global warming. 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. There appears to be no geological evidence for such eruptions at the right time, but this does not prove they did not happen. Climate change during the last 65 million years. ... Methane is a chemical compound with the molecular formula . ... A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ... Wikinews has related news: Scientists warn thawing Siberia may trigger global meltdown A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ...


It is harder to see how volcanism could cause an ice age, since its cooling effects would have to be stronger than and to outlast its warming effects. This would require dust and aerosol clouds which would stay in the upper atmosphere blocking the sun for thousands of years, which seems very unlikely. Undersea volcanoes could not produce this effect because the dust and aerosols would be absorbed by the sea before they reached the atmosphere. Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ...


Recent glacial and interglacial phases

There have been four major periods of glaciation in the Earths past. ... Image File history File links This is a lossless scalable vector image. ...

Glacial stages in North America

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

The major glacial stages of the current ice age in North America were the Nebraskan, Kansan, Illinoian, and Wisconsin glaciation. They were divided by the Aftonian, Yarmouth, and Sangamon interglacial stages. Image File history File links Download high-resolution version (2236x1640, 305 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Ice age Maps of the World Geological history of Minnesota ... Image File history File links Download high-resolution version (2236x1640, 305 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Ice age Maps of the World Geological history of Minnesota ... Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 20 centimeters per century (2 mm/year). ... The Beestonian stage is the name for an early Pleistocene glacial stage used in the British Isles. ... The Kansan Glaciation (known in UK as the Anglian Glaciation and sometimes referred to as the Illinoian Glaciation, Elster glaciation in northern Europe and the Mindel glaciation in the Alps) was a very severe glacial period in the Pleistocene. ... The Wolstonian glaciation is a name for an ice age period which occurred between 200,000 and 125,000 years ago. ... The Wisconsin (in North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), and Weichsel (in northern central Europe) glaciations are the most recent glaciations of the Pleistocene epoch, which ended around 10,000 BCE. The general glacial advance began about 70,000 BCE, and... The Cromerian interglacial is a name for an interglacial period which occurred between 600,000 and 450,000 years ago. ... The Hoxnian interglacial (and is analogous to the Yarmouth interglacial in North America, the Holstein interglacial in northern Europe and the Mindel-Riss interglacial in the Alps) is a name for an interglacial period which occurred between 300,000 and 200,000 years ago. ...


During the most recent North American glaciation, the Wisconsin glaciation (70,000 to 10,000 years ago), ice sheets extended to about 45 degrees north latitude. These sheets were 3 to 4 km thick.


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 the Niagara, 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 Great Lakes from space The Great Lakes are a group of five large lakes on or near the United States-Canadian border. ... The Finger Lakes, a major tourist destination in the west-central section of Upstate New York, are actually eleven in number, but only seven of the largest are commonly identified as such. ... The Teays River was an important pre-glacial river that drained much of the area now drained by the Ohio River, and more. ... View of Pittsburgh, the largest metropolitan area on the Ohio River, where the Allegheny River (left) and the Monongahela River (right) join at Point State Park to form the Ohio River Cincinnati, Ohio is a well known city along the Ohio River, historically known for its riverboats. ... For other uses, see Niagara Falls (disambiguation). ... The Lake and the cliff of the ancient waterfall in the park Clark Reservation State Park is a state park in Onondaga County, New York in the USA. The park is in the Town of DeWitt, south of Syracuse. ... Nickname: Location of Syracuse within the state of New York Coordinates: , City Government  - Mayor Matthew Driscoll (D) Area  - City 66. ...


Long Island 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. Isostatic rebound continues to reshape the Great Lakes and other areas formerly under the weight of the ice sheets. This article is about the island in New York State. ... Glacial till with tufts of grass Till is an unsorted glacial sediment. ... Canadian Shield Canadian Shield Landform. ... This article or section does not cite any references or sources. ... The Missouri River is a tributary of the Mississippi River in the United States. ... Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process known as isostatic depression. ... The Great Lakes from space The Laurentian Great Lakes are a group of five large lakes in North America on or near the Canada-United States border. ...


The Driftless Zone, a portion of western and southwestern Wisconsin along with parts of adjacent Minnesota, Iowa, and Illinois, was not covered by glaciers. The Driftless Area is an area of about 20,000 square miles in southwestern Wisconsin and northeastern Iowa which was by-passed by the continental glaciers. ... Capital Saint Paul Largest city Minneapolis Largest metro area Minneapolis-St. ... This article is about the U.S. state. ... Official language(s) English[1] Capital Springfield Largest city Chicago Largest metro area Chicago Metropolitan Area Area  Ranked 25th  - Total 57,918 sq mi (140,998 km²)  - Width 210 miles (340 km)  - Length 390 miles (629 km)  - % water 4. ...

See also: Glacial history of Minnesota

Northern Hemisphere glaciation during the last ice ages. ...

Effects of glaciation

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 landscape in Canada, Greenland, northern Eurasia and Antarctica. The erratic boulders, till, drumlins, eskers, 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 the earth's crust and mantle. After the ice sheets melted, the ice-covered land rebounded (see Post-glacial rebound). Due to the high viscosity of the Earth, 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 today. Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process...


During glaciation, water was taken from the oceans to form the ice at high latitudes, thus global sea level drops by about 120 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.


The redistribution of ice-water on the surface of the Earth and the flow of mantle rocks causes the gravitational field and the Moment of Inertia of the Earth to change. Changes in the moment of inertia result in a change in the rotational motion of the Earth. The redistribution of surface mass induced stress within the Earth and caused earthquakes (see Post-glacial rebound), according to some scientists. However, many mainstream geologists are doubtful that the effect on rotational motion, at least at the end of the last glacial maximum, was sufficient to create significant earthquake effect. That does not remove the possibility that the rebound itself generated regional tectonic effects. Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process...


References

  1. ^ Die Eiszeit…, Museum of Neuchatel, Switzerland, p. 3 (pdf 125 Kb)
  2. ^ Imbrie, John and Katherine Palmer Imbrie. Ice ages: Solving the Mystery. Cambridge, Massachusetts: Harvard University Press, 1979, 1986 (reprint). ISBN 0-89490-020-X; ISBN 0-89490-015-3; ISBN 0-674-44075-7. p. 25
  3. ^ Doug Macdougall, Frozen Planet: The Once and Future Story of Ice Ages, University of California Press, 2004. ISBN 0-520-24824-4
  4. ^ Aber Sandusky, James. Birth of the Glacial Theory. Emporia State University. Retrieved on 2006-08-04.
  5. ^ Louis Agassiz: Études sur les glaciers, Neuchâtel 1840. Digital book on Wikisource. Accessed on February 25, 2008.
  6. ^ How are past temperatures determined from an ice core?, Scientific American, September 20, 2004
  7. ^ EPICA community members (2004-06-10). "Eight glacial cycles from an Antarctic ice core". Nature. doi:10.1038/nature02599. 
  8. ^ CLIMATE: An Exceptionally Long Interglacial Ahead?. Science (2002). Retrieved on 2007-03-11.
  9. ^ Next Ice Age Delayed By Rising Carbon Dioxide Levels. ScienceDaily (2007). Retrieved on 2008-02-28.
  10. ^ Ruddiman, W.F. and J.E. Kutzbach. 1991. Plateau Uplift and Climate Change. Scientific American 264:66-74
  11. ^ Raymo, M.E., W.F. Ruddiman, and P.N. Froelich (1988) Influence of late Cenozoic mountain building on ocean geochemical cycles. Geology, v. 16, p. 649-653.
  12. ^ We are all Panamanians - formation of Isthmus of Panama may have started a series of climatic changes that led to evolution of hominids

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 216th day of the year (217th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... is the 161st day of the year (162nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 70th day of the year (71st in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 59th day of the year in the Gregorian calendar. ...

See also

This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... The International Union for Quaternary Research (INQUA) was founded in 1928. ... It is known that during the Ice Age, probably on more than one occasion, a huge glacier referred to as The Irish Sea Glacier flowed southwards from its source areas in Scotland and Northern Ireland and across the Isle of Man, Anglesey and Pembrokeshire. ... Temperature proxies for the last 40,000 years The Last Glacial Maximum refers to the time of maximum extent of the ice sheets during the last glaciation, approximately 21 thousand years ago. ... The Little Ice Age (LIA) was a period of cooling occurring after a warmer era known as the Medieval climate optimum. ... Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process... There have been four major periods of glaciation in the Earths past. ...

External links

Wikimedia Commons has media related to:
Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... An ice cap is a dome-shaped ice mass that covers less than 50,000 km² of land area (usually covering a highland area). ... Glaciation, often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... A stadial is a period of even-colder temperatures during an ice age. ... The Older Dryas was a somewhat variable cold, dry Blytt-Sernander period of North Europe, roughly equivalent to Pollen zone 1c. ... Three temperature records, the GRIP one clearly showing the Younger Dryas event at around 11 kyr BP The Younger Dryas stadial, named after the alpine / tundra wildflower Dryas octopetala, and also referred to as the Big Freeze [1], was a brief (approximately 1300 ± 70 years [1]) cold climate period following... The Little Ice Age (LIA) was a period of cooling occurring after a warmer era known as the Medieval climate optimum. ...

  Results from FactBites:
 
Ice age - Wikipedia, the free encyclopedia (2040 words)
Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist).
The earliest well-documented ice age, and probably the most severe of the last 1 billion years, occurred from 800 to 600 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended to or very near the equator.
The present ice ages are 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.
BIGpedia - Ice age - Encyclopedia and Dictionary Online (2002 words)
An ice age is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ("glaciation").
The earliest well-documented ice age, and probably the most severe of the last 1000 million years, occurred from 800 to 600 million years ago (the Cryogenian period) and it has been suggested that it produced a Snowball Earth in which permanent sea ice extended to or very near the equator.
The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica, but intensified during the Pleistocene (starting around 3 million years ago) with the spread of ice sheets in the Northern Hemisphere.
  More results at FactBites »

 
 

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