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{{Short description|Period of long-term reduction in temperature of Earth's surface and atmosphere}} | {{Short description|Period of long-term reduction in temperature of Earth's surface and atmosphere}} | ||
{{About|glacial periods in general|specific recent glacial periods often referred to as the "Ice Age"|Last Glacial Period|and|Pleistocene|and|Quaternary glaciation|other uses}} | {{About|glacial periods in general|specific recent glacial periods often referred to as the "Ice Age"|Last Glacial Period|and|Pleistocene|and|Quaternary glaciation|the current ice age|Late Cenozoic Ice Age|other uses|Ice Age (disambiguation){{!}}Ice Age}} | ||
{{pp-semi-indef}} | {{pp-semi-indef}} | ||
{{pp-move|small=yes}} | {{pp-move|small=yes}} | ||
[[File:IceAgeEarth.jpg|thumb|upright=1.35|An artist's impression of ice age Earth at [[Pleistocene]] glacial maximum]] | [[File:IceAgeEarth.jpg|thumb|upright=1.35|An artist's impression of ice age Earth at [[Pleistocene]] glacial maximum]] | ||
An '''ice age''' is a | An '''ice age''' is a period of time when the lower temperature of [[Earth]]'s surface and atmosphere results in the presence or expansion of continental and polar [[ice sheet]]s and alpine [[glacier]]s. The term is applied in several different senses to very long and comparatively short periods of cooling. Colder periods are called glacials or ice ages, and warmer periods are called interglacials. | ||
Earth's climate alternates between [[Greenhouse and icehouse Earth|icehouse and greenhouse periods]] based on whether there are glaciers on the planet, and for most of Earth's history it has been in a greenhouse period with little or no permanent ice. Over the very long term, Earth is currently in an icehouse period called the [[Late Cenozoic Ice Age]], which started 34 million years ago. There have been colder and warmer periods within this ice age, and the term is also applied to the [[Quaternary glaciation]], which started 2.58 million years ago. Within this period, the [[Last Interglacial]] ended 115,000 years ago, and was followed by the [[Last Glacial Period]] (LGP), which gave way to the current warm [[Holocene]], which started 11,700 years ago. The most severe cold period of the LGP was the [[Last Glacial Maximum]], which reached its maximum between 26,000 and 20,000 years ago. The most recent glaciation was the [[Younger Dryas]] between 12,800 and 11,700 years ago. | |||
==History of research== | ==History of research== | ||
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<!--[[File:AntarcticaDomeCSnow.jpg|thumb|left|upright=1.15|The [[Antarctic ice sheet]]. Ice sheets expand during an ice age.]] | <!--[[File:AntarcticaDomeCSnow.jpg|thumb|left|upright=1.15|The [[Antarctic ice sheet]]. Ice sheets expand during an ice age.]] | ||
[[File:Vostok Petit data.svg|thumb|left|upright=1.15|Variations in temperature, {{CO2}}, and dust from the [[Vostok, Antarctica|Vostok]] ice core over the last 400,000 years]]--> | [[File:Vostok Petit data.svg|thumb|left|upright=1.15|Variations in temperature, {{CO2}}, and dust from the [[Vostok, Antarctica|Vostok]] ice core over the last 400,000 years]]--> | ||
[[File:Haukalivatnet.JPG|thumb|Haukalivatnet lake (50 meters above sea level) where [[Jens Esmark]] in 1823 discovered similarities to [[moraine]]s near existing glaciers in the high mountains]] | [[File:Haukalivatnet.JPG|thumb|Haukalivatnet lake (50 meters — 164 feet — above sea level) where [[Jens Esmark]] in 1823 discovered similarities to [[moraine]]s 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.<ref>{{harvnb|Krüger|2013|pp=91–6}}</ref> 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]].<ref>{{Cite journal|last=Hestmark|first=Geir|date=2018|title=Jens Esmark's mountain glacier traverse 1823 − the key to his discovery of Ice Ages|journal=Boreas|language=en|volume=47|issue=1|pages=1–10|doi=10.1111/bor.12260|bibcode=2018Borea..47....1H |issn=1502-3885|quote=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.|doi-access=free|hdl=10852/67376|hdl-access=free}}</ref><ref>{{Citation|last=Berg|first=Bjørn Ivar|title=Jens Esmark|date=2020-02-25|url=http://nbl.snl.no/Jens_Esmark|work=Norsk biografisk leksikon|language=nb|access-date=2021-02-28|archive-date=2021-03-07|archive-url=https://web.archive.org/web/20210307220710/https://nbl.snl.no/Jens_Esmark|url-status=live}}</ref><ref>{{Cite web|last=Hverven|first=Tom Egil|title=Isens spor|url=https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|access-date=2021-02-28|website=Klassekampen|archive-date=2021-04-17|archive-url=https://web.archive.org/web/20210417172110/https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|url-status=live}}</ref> | 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.<ref>{{harvnb|Krüger|2013|pp=91–6}}</ref> 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]].<ref>{{Cite journal|last=Hestmark|first=Geir|date=2018|title=Jens Esmark's mountain glacier traverse 1823 − the key to his discovery of Ice Ages|journal=Boreas|language=en|volume=47|issue=1|pages=1–10|doi=10.1111/bor.12260|bibcode=2018Borea..47....1H |issn=1502-3885|quote=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.|doi-access=free|hdl=10852/67376|hdl-access=free}}</ref><ref>{{Citation|last=Berg|first=Bjørn Ivar|title=Jens Esmark|date=2020-02-25|url=http://nbl.snl.no/Jens_Esmark|work=Norsk biografisk leksikon|language=nb|access-date=2021-02-28|archive-date=2021-03-07|archive-url=https://web.archive.org/web/20210307220710/https://nbl.snl.no/Jens_Esmark|url-status=live}}</ref><ref>{{Cite web|last=Hverven|first=Tom Egil|title=Isens spor|url=https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|access-date=2021-02-28|website=Klassekampen|archive-date=2021-04-17|archive-url=https://web.archive.org/web/20210417172110/https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|url-status=live}}</ref> | ||
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).<ref>{{cite journal |first=Bjørn G. |last=Andersen |year=1992 |title=Jens Esmark—a pioneer in glacial geology |journal=[[Boreas (journal)|Boreas]] |volume=21 |pages=97–102 |doi=10.1111/j.1502-3885.1992.tb00016.x|title-link=Jens Esmark |issue=1 |bibcode=1992Borea..21...97A }}</ref> Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark.<ref>{{cite book |author=Davies, Gordon L. |title=The Earth in Decay. A History of British Geomorphology 1578–1878 |url=https://archive.org/details/earthindecayhist0000herr |url-access=registration |location=London |year=1969 |pages=267f|publisher=New York, American Elsevier Pub. Co |isbn= | 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).<ref>{{cite journal |first=Bjørn G. |last=Andersen |year=1992 |title=Jens Esmark—a pioneer in glacial geology |journal=[[Boreas (journal)|Boreas]] |volume=21 |pages=97–102 |doi=10.1111/j.1502-3885.1992.tb00016.x|title-link=Jens Esmark |issue=1 |bibcode=1992Borea..21...97A }}</ref> Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark.<ref>{{cite book |author=Davies, Gordon L. |title=The Earth in Decay. A History of British Geomorphology 1578–1878 |url=https://archive.org/details/earthindecayhist0000herr |url-access=registration |location=London |year=1969 |pages=267f|publisher=New York, American Elsevier Pub. Co |isbn=978-0-444-19701-6 }}<br />{{cite book |author=Cunningham, Frank F. |title=James David Forbes. Pioneer Scottish Glaciologist |publisher=Scottish Academic Press |location=Edinburgh |year=1990 |isbn=978-0-7073-0320-8 |page=15}}</ref> In Germany, Albrecht Reinhard Bernhardi (1797–1849), a geologist and professor of forestry at an academy in Dreissigacker (since incorporated in the southern [[Thuringia]]n 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.<ref>{{harvnb|Krüger|2013|pp=142–47}}</ref> | ||
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.<ref>{{cite book|last=Wood |first=Gillen | 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.<ref>{{cite book|last=Wood |first=Gillen D'Arcy |title=Tambora, the Eruption that Changed the World|pages=160–167 |publisher=Princeton University Press |location =Princeton, NJ |year=2014|isbn=978-0-691-16862-3}}</ref> | ||
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.<ref>{{harvnb|Krüger|2013|pp=155–59}}</ref> 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.<ref>{{harvnb|Krüger|2013|pp=167–70}}</ref> At the beginning of 1837, Schimper coined the term "ice age" (''"Eiszeit"'') for the period of the glaciers.<ref>{{harvnb|Krüger|2013|p=173}}</ref> 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.<ref>{{harvnb|Krüger|2013|pp=177–78}}</ref> | 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.<ref>{{harvnb|Krüger|2013|pp=155–59}}</ref> 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.<ref>{{harvnb|Krüger|2013|pp=167–70}}</ref> At the beginning of 1837, Schimper coined the term "ice age" (''"Eiszeit"'') for the period of the glaciers.<ref>{{harvnb|Krüger|2013|p=173}}</ref> 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.<ref>{{harvnb|Krüger|2013|pp=177–78}}</ref> | ||
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[[File:GlaciationsinEarthExistancelicenced annotated.jpg|thumb|upright=2.75|right|Timeline of glaciations, shown in blue]] | [[File:GlaciationsinEarthExistancelicenced annotated.jpg|thumb|upright=2.75|right|Timeline of glaciations, shown in blue]] | ||
There have been at least five major ice ages in Earth's history (the [[Huronian glaciation|Huronian]], [[Cryogenian]], [[Andean-Saharan]], [[late Paleozoic icehouse|late Paleozoic]], and the latest [[Quaternary glaciation|Quaternary Ice Age]]). Outside these ages, Earth was previously thought to have been ice-free even in high latitudes;<ref>{{cite journal |author=Lockwood, J.G. |title=The Antarctic Ice-Sheet: Regulator of Global Climates?: Review |journal=The Geographical Journal |volume=145 |issue=3 |pages=469–471 |date=November 1979 |jstor=633219 |doi=10.2307/633219 |last2=Zinderen-Bakker |first2=E. M. van|author-link2=Eduard Meine van Zinderen-Bakker}}</ref><ref>{{cite book |url=https://books.google.com/books?id=ihny39BvVhIC&pg=PA289 |title=Evaporites: sediments, resources and hydrocarbons |first=John K. |last=Warren |publisher=Birkhäuser |year=2006 |isbn=978-3-540-26011-0 |page=289}}</ref> such periods are known as [[Greenhouse and icehouse Earth#Greenhouse Earth|greenhouse periods]].<ref>{{cite book |last=Allaby |first=Michael |date=January 2013 |title=A Dictionary of Geology and Earth Sciences |edition=Fourth |url=https://oxfordindex.oup.com/view/10.1093/acref/9780199653065.013.3641 |access-date=17 Sep 2019 |publisher=Oxford University Press |isbn= | There have been at least five major ice ages in Earth's history (the [[Huronian glaciation|Huronian]], [[Cryogenian]], [[Andean-Saharan]], [[late Paleozoic icehouse|late Paleozoic]], and the latest [[Quaternary glaciation|Quaternary Ice Age]]). Outside these ages, Earth was previously thought to have been ice-free even in high latitudes;<ref>{{cite journal |author=Lockwood, J.G. |title=The Antarctic Ice-Sheet: Regulator of Global Climates?: Review |journal=The Geographical Journal |volume=145 |issue=3 |pages=469–471 |date=November 1979 |jstor=633219 |doi=10.2307/633219 |last2=Zinderen-Bakker |first2=E. M. van|author-link2=Eduard Meine van Zinderen-Bakker}}</ref><ref>{{cite book |url=https://books.google.com/books?id=ihny39BvVhIC&pg=PA289 |title=Evaporites: sediments, resources and hydrocarbons |first=John K. |last=Warren |publisher=Birkhäuser |year=2006 |isbn=978-3-540-26011-0 |page=289}}</ref> such periods are known as [[Greenhouse and icehouse Earth#Greenhouse Earth|greenhouse periods]].<ref>{{cite book |last=Allaby |first=Michael |date=January 2013 |title=A Dictionary of Geology and Earth Sciences |edition=Fourth |url=https://oxfordindex.oup.com/view/10.1093/acref/9780199653065.013.3641 |access-date=17 Sep 2019 |publisher=Oxford University Press |isbn=978-0-19-965306-5 }}{{Dead link|date=May 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> However, other studies dispute this, finding evidence of occasional glaciations at high latitudes even during apparent greenhouse periods.<ref name=":0">{{Cite journal |last1=Bornemann |first1=André |last2=Norris |first2=Richard D. |last3=Friedrich |first3=Oliver |last4=Beckmann |first4=Britta |last5=Schouten |first5=Stefan |last6=Damsté |first6=Jaap S. Sinninghe |last7=Vogel |first7=Jennifer |last8=Hofmann |first8=Peter |last9=Wagner |first9=Thomas |date=2008-01-11 |title=Isotopic Evidence for Glaciation During the Cretaceous Supergreenhouse |url=https://www.science.org/doi/10.1126/science.1148777 |journal=Science |language=en |volume=319 |issue=5860 |pages=189–192 |doi=10.1126/science.1148777 |pmid=18187651 |bibcode=2008Sci...319..189B |s2cid=206509273 |issn=0036-8075 |access-date=2023-10-26 |archive-date=2023-11-25 |archive-url=https://web.archive.org/web/20231125035757/https://www.science.org/doi/10.1126/science.1148777 |url-status=live |url-access=subscription }}</ref><ref name=":1">{{Cite journal |last1=Ladant |first1=Jean-Baptiste |last2=Donnadieu |first2=Yannick |date=2016-09-21 |title=Palaeogeographic regulation of glacial events during the Cretaceous supergreenhouse |journal=Nature Communications |language=en |volume=7 |issue=1 |article-number=12771 |doi=10.1038/ncomms12771 |pmid=27650167 |pmc=5036002 |bibcode=2016NatCo...712771L |issn=2041-1723|doi-access=free }}</ref> | ||
[[File:EisrandlagenNorddeutschland.png|thumb|right|Ice age map of northern Germany and its northern neighbours. Red: maximum limit of [[Weichselian]] glacial; yellow: [[Saale glaciation|Saale]] glacial at maximum (Drenthe stage); blue: [[Anglian glaciation|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 {{convert|10 to 100|km|0|sp=us}} north of the north shore of Lake Huron, extending from near [[Sault Ste. Marie, Ontario|Sault Ste. Marie]] to Sudbury, northeast of Lake Huron, with giant layers of now-lithified till beds, [[dropstone]]s, [[varve]]s, [[glacial outwash|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]].<ref>{{Cite journal|last=Kopp|first=Robert|date=14 June 2005|title=The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis|journal=PNAS|volume=102|issue=32|pages=11131–6|doi=10.1073/pnas.0504878102|pmid=16061801|pmc=1183582|bibcode=2005PNAS..10211131K|doi-access=free}}</ref> | [[File:EisrandlagenNorddeutschland.png|thumb|right|Ice age map of northern Germany and its northern neighbours. Red: maximum limit of [[Weichselian]] glacial; yellow: [[Saale glaciation|Saale]] glacial at maximum (Drenthe stage); blue: [[Anglian glaciation|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 {{convert|10 to 100|km|0|sp=us}} north of the north shore of Lake Huron, extending from near [[Sault Ste. Marie, Ontario|Sault Ste. Marie]] to Sudbury, northeast of Lake Huron, with giant layers of now-lithified till beds, [[dropstone]]s, [[varve]]s, [[glacial outwash|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]].<ref>{{Cite journal|last=Kopp|first=Robert|date=14 June 2005|title=The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis|journal=PNAS|volume=102|issue=32|pages=11131–6|doi=10.1073/pnas.0504878102|pmid=16061801|pmc=1183582|bibcode=2005PNAS..10211131K|doi-access=free}}</ref> | ||
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{{See also|Glacial period|Interglacial}} | {{See also|Glacial period|Interglacial}} | ||
[[File:Ice Age Temperature.png|right|thumb|upright=1.35| | [[File:Ice Age Temperature.png|right|thumb|upright=1.35|Pattern of temperature and ice volume changes associated with recent glacials and interglacials]] | ||
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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|Eemian Stage]].<ref name="ehlers-gibbard-2011"/> There is evidence that similar '''glacial cycles''' occurred in previous glaciations, including the Andean-Saharan<ref>{{cite journal |last1=Ghienne |first1=Jean-François |title=Late Ordovician sedimentary environments, glacial cycles, and post-glacial transgression in the Taoudeni Basin, West Africa |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=January 2003 |volume=189 |issue=3–4 |pages=117–145 |doi=10.1016/S0031-0182(02)00635-1|bibcode=2003PPP...189..117G }}</ref> and the late Paleozoic ice house. The glacial cycles of the late Paleozoic ice house are likely responsible for the deposition of [[cyclothems]].<ref>{{cite book |last1=Heckel |first1=P.H. |year=2008 |chapter=Pennsylvanian cyclothems in Midcontinent North America as far-field effects of waxing and waning of Gondwana ice sheets |title=Resolving the Late Paleozoic Ice Age in Time and Space |editor-last1=Fielding |editor-first1=C.R. |editor-last2=Frank |editor-first2=T.D. |editor-last3=Isbell |editor-first3=J.L. |pages=275–290}}</ref> | 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|Eemian Stage]].<ref name="ehlers-gibbard-2011">{{cite book|year=2011|doi=10.1007/978-90-481-2642-2_423|title = Encyclopedia of Snow, Ice and Glaciers|pages=873–882|series = Encyclopedia of Earth Sciences Series|last1 = Ehlers|first1 = Jürgen|last2=Gibbard|first2=Philip|chapter=Quaternary Glaciation |isbn=978-90-481-2641-5}}</ref> There is evidence that similar '''glacial cycles''' occurred in previous glaciations, including the Andean-Saharan<ref>{{cite journal |last1=Ghienne |first1=Jean-François |title=Late Ordovician sedimentary environments, glacial cycles, and post-glacial transgression in the Taoudeni Basin, West Africa |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=January 2003 |volume=189 |issue=3–4 |pages=117–145 |doi=10.1016/S0031-0182(02)00635-1|bibcode=2003PPP...189..117G }}</ref> and the late Paleozoic ice house. The glacial cycles of the late Paleozoic ice house are likely responsible for the deposition of [[cyclothems]].<ref>{{cite book |last1=Heckel |first1=P.H. |year=2008 |chapter=Pennsylvanian cyclothems in Midcontinent North America as far-field effects of waxing and waning of Gondwana ice sheets |title=Resolving the Late Paleozoic Ice Age in Time and Space |editor-last1=Fielding |editor-first1=C.R. |editor-last2=Frank |editor-first2=T.D. |editor-last3=Isbell |editor-first3=J.L. |pages=275–290}}</ref> | ||
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. | 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. | ||
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}}</ref> 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 gas]]es is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2007/08/070829193436.htm |title=Next Ice Age Delayed By Rising Carbon Dioxide Levels |access-date=2008-02-28 |year=2007 |website=ScienceDaily |archive-date=2008-03-02 |archive-url=https://web.archive.org/web/20080302083828/http://www.sciencedaily.com/releases/2007/08/070829193436.htm |url-status=live }}</ref><ref name="PIK2016"/><ref name="LiveScience2007"/> | }}</ref> 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 gas]]es is estimated to potentially outweigh the orbital forcing of the Milankovitch cycles for hundreds of thousands of years.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2007/08/070829193436.htm |title=Next Ice Age Delayed By Rising Carbon Dioxide Levels |access-date=2008-02-28 |year=2007 |website=ScienceDaily |archive-date=2008-03-02 |archive-url=https://web.archive.org/web/20080302083828/http://www.sciencedaily.com/releases/2007/08/070829193436.htm |url-status=live }}</ref><ref name="PIK2016">{{cite web|url=https://www.pik-potsdam.de/news/press-releases/human-made-climate-change-suppresses-the-next-ice-age|title=Human-made climate change suppresses the next ice age|year=2016|publisher=Potsdam Institute for Climate Impact Research in Germany|access-date=2019-01-07|archive-date=2020-08-18|archive-url=https://web.archive.org/web/20200818202438/https://www.pik-potsdam.de/news/press-releases/human-made-climate-change-suppresses-the-next-ice-age}}</ref><ref name="LiveScience2007">{{cite web|url=https://www.livescience.com/1846-global-warming-good-news-ice-ages.html|title=Global Warming Good News: No More Ice Ages|year=2007|publisher=LiveScience|last1=Thomson|first1=Andrea|access-date=2019-01-07|archive-date=2020-11-12|archive-url=https://web.archive.org/web/20201112000544/https://www.livescience.com/1846-global-warming-good-news-ice-ages.html|url-status=live}}</ref> | ||
==Feedback processes== | ==Feedback processes== | ||
Each glacial period is subject to [[positive feedback]] mechanisms, which makes it more severe, and [[negative feedback]] which dampens the overall climate response to different types of forcing. In the case of Quaternary ice ages, Earth's high [[albedo]] from ice sheets and atmospheric dust as well as low concentrations of atmospheric {{CO2}} contributed to cold glacial climates.<ref>{{Citation | vauthors=((Hain, M. P.)), ((Chalk, T. B.)) | year=2025 | | Each glacial period is subject to [[positive feedback]] mechanisms, which makes it more severe, and [[negative feedback]] which dampens the overall climate response to different types of forcing. In the case of Quaternary ice ages, Earth's high [[albedo]] from ice sheets and atmospheric dust as well as low concentrations of atmospheric {{CO2}} contributed to cold glacial climates.<ref>{{Citation | vauthors=((Hain, M. P.)), ((Chalk, T. B.)) | title=Encyclopedia of Quaternary Science | year=2025 | chapter=Greenhouse gas effects on Quaternary climates | pages=143–157 | publisher=Elsevier | chapter-url=https://earth-system-biogeochemistry.net/wp-content/uploads/2025/01/Hain-and-Chalk-2024-EQS-Milankovitch-vs-CO2.pdf | doi=10.1016/b978-0-323-99931-1.00271-3 | isbn=978-0-443-29997-1 }}</ref> | ||
[[File:Fig3 Q-climate-CO2-feedbacks V2.png|thumb|Diagram of key climate-carbon cycle feedbacks linking Quaternary climates and temperatures, Generalized Milankovitch Theory (GMT), to atmospheric {{CO2}} and ice sheets.<ref>{{Citation | vauthors=((Hain, M. P.)), ((Chalk, T. B.)) | year=2025 | | [[File:Fig3 Q-climate-CO2-feedbacks V2.png|thumb|Diagram of key climate-carbon cycle feedbacks linking Quaternary climates and temperatures, Generalized Milankovitch Theory (GMT), to atmospheric {{CO2}} and ice sheets.<ref>{{Citation | vauthors=((Hain, M. P.)), ((Chalk, T. B.)) | title=Encyclopedia of Quaternary Science | year=2025 | chapter=Greenhouse gas effects on Quaternary climates | pages=143–157 | publisher=Elsevier | chapter-url=https://earth-system-biogeochemistry.net/wp-content/uploads/2025/01/Hain-and-Chalk-2024-EQS-Milankovitch-vs-CO2.pdf | doi=10.1016/b978-0-323-99931-1.00271-3 | isbn=978-0-443-29997-1 }}</ref> Positive feedbacks amplify and negative feedbacks dampen environmental change, with slow-acting responses shown as dashed arrows.]] | ||
===Positive=== | ===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 [[Boreal forest|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. | 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 [[Boreal forest|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. | ||
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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.<ref>{{Cite web |url=https://www.smithsonianmag.com/science-nature/complicated-role-iron-ocean-health-and-climate-change-180973893/ |title=The Complicated Role of Iron in Ocean Health and Climate Change |access-date=2022-08-02 |archive-date=2022-08-02 |archive-url=https://web.archive.org/web/20220802125320/https://www.smithsonianmag.com/science-nature/complicated-role-iron-ocean-health-and-climate-change-180973893/ |url-status=live }}</ref> | 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.<ref>{{Cite web |url=https://www.smithsonianmag.com/science-nature/complicated-role-iron-ocean-health-and-climate-change-180973893/ |title=The Complicated Role of Iron in Ocean Health and Climate Change |access-date=2022-08-02 |archive-date=2022-08-02 |archive-url=https://web.archive.org/web/20220802125320/https://www.smithsonianmag.com/science-nature/complicated-role-iron-ocean-health-and-climate-change-180973893/ |url-status=live }}</ref> | ||
In 1956, Ewing and Donn<ref>{{Cite journal|last1=Ewing|first1=M.|last2=Donn|first2=W. L.|date=1956-06-15|title=A Theory of Ice Ages|journal=Science|volume=123|issue=3207|pages=1061–1066|doi=10.1126/science.123.3207.1061|issn=0036-8075|pmid=17748617|bibcode=1956Sci...123.1061E}}</ref> 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 (phase transition)|sublimation]] and the polar regions are quite dry in terms of precipitation, comparable to the amount found in mid-latitude [[desert]]s. 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 [[Arctic sea ice decline#Ice-free summer vs. ice-free winter|a brief ice-free Arctic Ocean period by 2050]].) Additional fresh water flowing into the North Atlantic during a warming cycle may also [[shutdown of thermohaline circulation|reduce]] the [[Thermohaline circulation|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.<ref>{{cite book|last=Garrison|first=Tom|title=Oceanography: An Invitation to Marine Science|publisher=Cengage Learning|edition=7th|date=2009| | In 1956, Ewing and Donn<ref>{{Cite journal|last1=Ewing|first1=M.|last2=Donn|first2=W. L.|date=1956-06-15|title=A Theory of Ice Ages|journal=Science|volume=123|issue=3207|pages=1061–1066|doi=10.1126/science.123.3207.1061|issn=0036-8075|pmid=17748617|bibcode=1956Sci...123.1061E}}</ref> 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 (phase transition)|sublimation]] and the polar regions are quite dry in terms of precipitation, comparable to the amount found in mid-latitude [[desert]]s. 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 [[Arctic sea ice decline#Ice-free summer vs. ice-free winter|a brief ice-free Arctic Ocean period by 2050]].) Additional fresh water flowing into the North Atlantic during a warming cycle may also [[shutdown of thermohaline circulation|reduce]] the [[Thermohaline circulation|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.<ref>{{cite book|last=Garrison|first=Tom|title=Oceanography: An Invitation to Marine Science|publisher=Cengage Learning|edition=7th|date=2009|page=582|isbn=978-0-495-39193-7}}</ref><ref>{{cite journal|doi=10.1038/nature04385 |author=Bryden, H.L. |author2=H.R. Longworth |author3=S.A. Cunningham |title=Slowing of the Atlantic meridional overturning circulation at 25° N|journal=Nature|issue=7068|pages=655–657|year=2005|pmid=16319889|volume=438|bibcode = 2005Natur.438..655B |s2cid=4429828 }}</ref><ref>{{cite journal|doi=10.1126/science.1109477 |author=Curry, R. |author2=C. Mauritzen|author2-link= Cecilie Mauritzen |title=Dilution of the northern North Atlantic in recent decades|journal=Science|volume=308|issue=5729 |pages=1772–1774|year=2005|bibcode = 2005Sci...308.1772C|pmid=15961666|s2cid=36017668 }}</ref> It has also been suggested{{by whom|date=November 2020}} 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=== | ===Negative=== | ||
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Another important contribution to ancient climate regimes is the variation of [[ocean current]]s, 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.<ref>{{cite journal |url=http://discovermagazine.com/1996/apr/weareallpanamani743 |title=We are all Panamanians |author=Svitil, K. A. |date=April 1996 |journal=Discover |access-date=2012-04-23 |archive-date=2014-02-03 |archive-url=https://web.archive.org/web/20140203183832/http://discovermagazine.com/1996/apr/weareallpanamani743 |url-status=live }}—formation of Isthmus of Panama may have started a series of climatic changes that led to evolution of hominids</ref> | Another important contribution to ancient climate regimes is the variation of [[ocean current]]s, 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.<ref>{{cite journal |url=http://discovermagazine.com/1996/apr/weareallpanamani743 |title=We are all Panamanians |author=Svitil, K. A. |date=April 1996 |journal=Discover |access-date=2012-04-23 |archive-date=2014-02-03 |archive-url=https://web.archive.org/web/20140203183832/http://discovermagazine.com/1996/apr/weareallpanamani743 |url-status=live }}—formation of Isthmus of Panama may have started a series of climatic changes that led to evolution of hominids</ref> | ||
Analyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations. During the last glacial period the sea-level fluctuated | Analyses suggest that ocean current fluctuations can adequately account for recent glacial oscillations. During the last glacial period the sea-level fluctuated {{convert|20|to|30|m|0}} 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 metres – 165 feet – 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.<ref name=Hu2010>{{Cite journal |last1=Hu |first1=Aixue |last2=Meehl |first2=Gerald A. |author2-link=Gerald Meehl |last3=Otto-Bliesner |first3=Bette L. |author-link3=Bette Otto-Bliesner |last4=Waelbroeck |first4=Claire |author5=Weiqing Han |last6=Loutre |first6=Marie-France |last7=Lambeck |first7=Kurt |last8=Mitrovica |first8=Jerry X. |last9=Rosenbloom |first9=Nan |title=Influence of Bering Strait flow and North Atlantic circulation on glacial sea-level changes |journal=Nature Geoscience |volume=3 |issue=2 |pages=118–121 |year=2010 |doi=10.1038/ngeo729 |bibcode=2010NatGe...3..118H |hdl=1885/30691 |url=http://www.cgd.ucar.edu/ccr/publications/ngeo729.pdf |citeseerx=10.1.1.391.8727 |access-date=2017-10-24 |archive-date=2017-08-11 |archive-url=https://web.archive.org/web/20170811021943/http://www.cgd.ucar.edu/ccr/publications/ngeo729.pdf }}</ref> | ||
According to a study published in ''[[Nature (journal)|Nature]]'' in 2021, all [[glacial period]]s of ice ages over the last 1.5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns, [[Oceanic carbon cycle|leading to more CO<sub>2</sub> 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.<ref>{{cite news |title=Melting icebergs key to sequence of an ice age, scientists find |url=https://phys.org/news/2021-01-icebergs-key-sequence-ice-age.html |access-date=12 February 2021 |work=phys.org |language=en |archive-date=27 January 2021 |archive-url=https://web.archive.org/web/20210127163116/https://phys.org/news/2021-01-icebergs-key-sequence-ice-age.html |url-status=live }}</ref><ref>{{cite journal |last1=Starr |first1=Aidan |last2=Hall |first2=Ian R. |last3=Barker |first3=Stephen |last4=Rackow |first4=Thomas |last5=Zhang |first5=Xu |last6=Hemming |first6=Sidney R. |last7=Lubbe |first7=H. J. L. van der |last8=Knorr |first8=Gregor |last9=Berke |first9=Melissa A. |last10=Bigg |first10=Grant R. |last11=Cartagena-Sierra |first11=Alejandra |last12=Jiménez-Espejo |first12=Francisco J. |last13=Gong |first13=Xun |last14=Gruetzner |first14=Jens |last15=Lathika |first15=Nambiyathodi |last16=LeVay |first16=Leah J. |last17=Robinson |first17=Rebecca S. |last18=Ziegler |first18=Martin |title=Antarctic icebergs reorganize ocean circulation during Pleistocene glacials |journal=Nature |date=January 2021 |volume=589 |issue=7841 |pages=236–241 |doi=10.1038/s41586-020-03094-7 |pmid=33442043 |bibcode=2021Natur.589..236S |hdl=10261/258181 |s2cid=231598435 |url=https://www.nature.com/articles/s41586-020-03094-7 |access-date=12 February 2021 |language=en |issn=1476-4687 |hdl-access=free |archive-date=4 February 2021 |archive-url=https://web.archive.org/web/20210204185828/https://www.nature.com/articles/s41586-020-03094-7 |url-status=live }}</ref> | According to a study published in ''[[Nature (journal)|Nature]]'' in 2021, all [[glacial period]]s of ice ages over the last 1.5 million years were associated with northward shifts of melting Antarctic icebergs which changed ocean circulation patterns, [[Oceanic carbon cycle|leading to more CO<sub>2</sub> 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.<ref>{{cite news |title=Melting icebergs key to sequence of an ice age, scientists find |url=https://phys.org/news/2021-01-icebergs-key-sequence-ice-age.html |access-date=12 February 2021 |work=phys.org |language=en |archive-date=27 January 2021 |archive-url=https://web.archive.org/web/20210127163116/https://phys.org/news/2021-01-icebergs-key-sequence-ice-age.html |url-status=live }}</ref><ref>{{cite journal |last1=Starr |first1=Aidan |last2=Hall |first2=Ian R. |last3=Barker |first3=Stephen |last4=Rackow |first4=Thomas |last5=Zhang |first5=Xu |last6=Hemming |first6=Sidney R. |last7=Lubbe |first7=H. J. L. van der |last8=Knorr |first8=Gregor |last9=Berke |first9=Melissa A. |last10=Bigg |first10=Grant R. |last11=Cartagena-Sierra |first11=Alejandra |last12=Jiménez-Espejo |first12=Francisco J. |last13=Gong |first13=Xun |last14=Gruetzner |first14=Jens |last15=Lathika |first15=Nambiyathodi |last16=LeVay |first16=Leah J. |last17=Robinson |first17=Rebecca S. |last18=Ziegler |first18=Martin |title=Antarctic icebergs reorganize ocean circulation during Pleistocene glacials |journal=Nature |date=January 2021 |volume=589 |issue=7841 |pages=236–241 |doi=10.1038/s41586-020-03094-7 |pmid=33442043 |bibcode=2021Natur.589..236S |hdl=10261/258181 |s2cid=231598435 |url=https://www.nature.com/articles/s41586-020-03094-7 |access-date=12 February 2021 |language=en |issn=1476-4687 |hdl-access=free |archive-date=4 February 2021 |archive-url=https://web.archive.org/web/20210204185828/https://www.nature.com/articles/s41586-020-03094-7 |url-status=live }}</ref> | ||
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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 core]]s 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 of rotation|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 [[65th parallel north|65 degrees north]] [[latitude]] varies by as much as 22% (from 450 W/m<sup>2</sup> to 550 W/m<sup>2</sup>). 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. | 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 core]]s 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 of rotation|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 [[65th parallel north|65 degrees north]] [[latitude]] varies by as much as 22% (from 450 W/m<sup>2</sup> to 550 W/m<sup>2</sup>). 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 [[Perturbation (astronomy)|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.<ref>{{cite web|url=https://news.brown.edu/articles/2017/01/iceages|title=Earth's orbital variations and sea ice synch glacial periods|access-date=2017-01-29|archive-date=2019-02-17|archive-url=https://web.archive.org/web/20190217084915/https://news.brown.edu/articles/2017/01/iceages|url-status=live}}</ref><ref>{{cite web|url=http://www.sciforums.com/threads/ice-age-explanation.158750/|title=Ice-Age Explanation - Sciforums|website=www.sciforums.com|date=28 January 2017|access-date=29 January 2017|archive-date=2 February 2017|archive-url=https://web.archive.org/web/20170202051228/http://www.sciforums.com/threads/ice-age-explanation.158750/|url-status=live}}</ref> | 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 [[Perturbation (astronomy)|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.<ref>{{cite web|url=https://news.brown.edu/articles/2017/01/iceages|title=Earth's orbital variations and sea ice synch glacial periods|date=26 January 2017 |access-date=2017-01-29|archive-date=2019-02-17|archive-url=https://web.archive.org/web/20190217084915/https://news.brown.edu/articles/2017/01/iceages|url-status=live}}</ref><ref>{{cite web|url=http://www.sciforums.com/threads/ice-age-explanation.158750/|title=Ice-Age Explanation - Sciforums|website=www.sciforums.com|date=28 January 2017|access-date=29 January 2017|archive-date=2 February 2017|archive-url=https://web.archive.org/web/20170202051228/http://www.sciforums.com/threads/ice-age-explanation.158750/|url-status=live}}</ref> | ||
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]],<ref>{{Cite journal|last1=Muller|first1=R. A.|last2=MacDonald|first2=G. J.|date=1997-08-05|title=Spectrum of 100-kyr glacial cycle: orbital inclination, not eccentricity|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=94|issue=16|pages=8329–8334|doi=10.1073/pnas.94.16.8329|issn=0027-8424|pmc=33747|pmid=11607741|bibcode=1997PNAS...94.8329M|doi-access=free}}</ref><ref>{{cite web |author=Richard A. Muller |url=http://muller.lbl.gov/pages/glacialmain.htm |title=A New Theory of Glacial Cycles |publisher=Muller.lbl.gov |access-date=2012-08-07 |archive-date=2013-04-29 |archive-url=https://web.archive.org/web/20130429203041/http://muller.lbl.gov/pages/glacialmain.htm |url-status=live }}</ref><ref>{{Cite journal|last=Muller|first=R. A.|date=1997-07-11|title=Glacial Cycles and Astronomical Forcing|journal=Science|volume=277|issue=5323|pages=215–218|doi=10.1126/science.277.5323.215|bibcode=1997Sci...277..215M|url=https://zenodo.org/record/1231114|access-date=2020-05-03|archive-date=2020-08-01|archive-url=https://web.archive.org/web/20200801205823/https://zenodo.org/record/1231114|url-status=live}}</ref> 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.<ref>{{cite journal |author=Rial, J.A. |title=Pacemaking the ice ages by frequency modulation of Earth's orbital eccentricity |journal=Science |volume=285 |issue=5427 |pages=564–8 |date=July 1999 |pmid=10417382 |url=http://pangea.stanford.edu/Oceans/GES290/Rial1999.pdf |doi=10.1126/science.285.5427.564 | 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]],<ref>{{Cite journal|last1=Muller|first1=R. A.|last2=MacDonald|first2=G. J.|date=1997-08-05|title=Spectrum of 100-kyr glacial cycle: orbital inclination, not eccentricity|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=94|issue=16|pages=8329–8334|doi=10.1073/pnas.94.16.8329|issn=0027-8424|pmc=33747|pmid=11607741|bibcode=1997PNAS...94.8329M|doi-access=free}}</ref><ref>{{cite web |author=Richard A. Muller |url=http://muller.lbl.gov/pages/glacialmain.htm |title=A New Theory of Glacial Cycles |publisher=Muller.lbl.gov |access-date=2012-08-07 |archive-date=2013-04-29 |archive-url=https://web.archive.org/web/20130429203041/http://muller.lbl.gov/pages/glacialmain.htm |url-status=live }}</ref><ref>{{Cite journal|last=Muller|first=R. A.|date=1997-07-11|title=Glacial Cycles and Astronomical Forcing|journal=Science|volume=277|issue=5323|pages=215–218|doi=10.1126/science.277.5323.215|bibcode=1997Sci...277..215M|url=https://zenodo.org/record/1231114|access-date=2020-05-03|archive-date=2020-08-01|archive-url=https://web.archive.org/web/20200801205823/https://zenodo.org/record/1231114|url-status=live}}</ref> 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.<ref>{{cite journal |author=Rial, J.A. |title=Pacemaking the ice ages by frequency modulation of Earth's orbital eccentricity |journal=Science |volume=285 |issue=5427 |pages=564–8 |date=July 1999 |pmid=10417382 |url=http://pangea.stanford.edu/Oceans/GES290/Rial1999.pdf |doi=10.1126/science.285.5427.564 |archive-url=https://web.archive.org/web/20081015123309/http://pangea.stanford.edu/Oceans/GES290/Rial1999.pdf |archive-date=2008-10-15 }}</ref> | ||
[[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.<ref>{{Cite journal|last1=Huybers|first1=Peter|last2=Wunsch|first2=Carl|date=2005-03-24|title=Obliquity pacing of the late Pleistocene glacial terminations|journal=Nature|volume=434|issue=7032|pages=491–494|doi=10.1038/nature03401|issn=1476-4687|pmid=15791252|bibcode=2005Natur.434..491H|s2cid=2729178|url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:3382978|hdl=1912/555|hdl-access=free}}</ref> This theory is consistent with a simple empirical multi-state model proposed by [[Didier Paillard]].<ref>{{cite journal |author=Paillard, D. |title=The timing of Pleistocene glaciations from a simple multiple-state climate model |journal=Nature |volume=391 |issue=6665 |pages=378–381 |date=22 January 1998 |doi=10.1038/34891 |bibcode = 1998Natur.391..378P|s2cid=4409193 }}</ref> 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 [[orbit]]al forcing, while in the early Pleistocene the 41,000-year glacial cycles resulted from jumps between only two climate states. A dynamical | [[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.<ref>{{Cite journal|last1=Huybers|first1=Peter|last2=Wunsch|first2=Carl|date=2005-03-24|title=Obliquity pacing of the late Pleistocene glacial terminations|journal=Nature|volume=434|issue=7032|pages=491–494|doi=10.1038/nature03401|issn=1476-4687|pmid=15791252|bibcode=2005Natur.434..491H|s2cid=2729178|url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:3382978|hdl=1912/555|hdl-access=free|url-access=subscription}}</ref> This theory is consistent with a simple empirical multi-state model proposed by [[Didier Paillard]].<ref>{{cite journal |author=Paillard, D. |title=The timing of Pleistocene glaciations from a simple multiple-state climate model |journal=Nature |volume=391 |issue=6665 |pages=378–381 |date=22 January 1998 |doi=10.1038/34891 |bibcode = 1998Natur.391..378P|s2cid=4409193 }}</ref> 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 [[orbit]]al 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.<ref>{{cite journal |author=Ditlevsen, P.D. |title=Bifurcation structure and noise-assisted transitions in the Pleistocene glacial cycles |journal=Paleoceanography |volume=24 |pages=PA3204 |year=2009 |doi=10.1029/2008PA001673 |url=http://www.agu.org/pubs/crossref/2009/2008PA001673.shtml |bibcode=2009PalOc..24.3204D |issue=3 |arxiv=0902.1641 |access-date=2012-06-09 |archive-date=2012-11-01 |archive-url=https://web.archive.org/web/20121101101821/http://www.agu.org/pubs/crossref/2009/2008PA001673.shtml | model explaining this behavior was proposed by Peter Ditlevsen.<ref>{{cite journal |author=Ditlevsen, P.D. |title=Bifurcation structure and noise-assisted transitions in the Pleistocene glacial cycles |journal=Paleoceanography |volume=24 |pages=PA3204 |year=2009 |doi=10.1029/2008PA001673 |url=http://www.agu.org/pubs/crossref/2009/2008PA001673.shtml |bibcode=2009PalOc..24.3204D |issue=3 |article-number=2008PA001673 |arxiv=0902.1641 |access-date=2012-06-09 |archive-date=2012-11-01 |archive-url=https://web.archive.org/web/20121101101821/http://www.agu.org/pubs/crossref/2009/2008PA001673.shtml }} as [http://www.gfy.ku.dk/~pditlev/papers/2008PA001673.pdf PDF] {{Webarchive|url=https://web.archive.org/web/20110927153529/http://www.gfy.ku.dk/~pditlev/papers/2008PA001673.pdf |date=2011-09-27 }}</ref> 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=== | ===Variations in the Sun's energy output=== | ||
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===Volcanism=== | ===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 CO<sub>2</sub> in the atmosphere. Carbon dioxide from volcanoes probably contributed to periods with highest overall temperatures.<ref>{{cite web|last=Rieke|first=George|title=Long Term Climate|url=http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm|access-date=25 April 2013|archive-date=2 June 2015|archive-url=https://web.archive.org/web/20150602033750/http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm | 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 CO<sub>2</sub> in the atmosphere. Carbon dioxide from volcanoes probably contributed to periods with highest overall temperatures.<ref>{{cite web|last=Rieke|first=George|title=Long Term Climate|url=http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm|access-date=25 April 2013|archive-date=2 June 2015|archive-url=https://web.archive.org/web/20150602033750/http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/climate.htm}}</ref> One suggested explanation of the [[Paleocene–Eocene Thermal Maximum]] is that undersea volcanoes released [[methane]] from [[clathrate]]s and thus caused a large and rapid increase in the [[greenhouse effect]].<ref>{{Cite web|url=https://www.wunderground.com/climate/PETM.asp|title=PETM: Global Warming, Naturally |website=Weather Underground |access-date=2016-12-02|archive-url=https://web.archive.org/web/20161202234346/https://www.wunderground.com/climate/PETM.asp|archive-date=2016-12-02}}</ref> 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== | ==Recent glacial and interglacial phases== | ||
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[[File:Northern icesheet hg.png|thumb|upright=1.25|Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a [[sea level rise|sea level lowering]] of about 120 m.]] | [[File:Northern icesheet hg.png|thumb|upright=1.25|Northern hemisphere glaciation during the last ice ages. The setup of 3 to 4 kilometer thick ice sheets caused a [[sea level rise|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,<ref name="ICSchart2013"/> is marked by warm and cold episodes, cold phases called [[Glacial period|glacials]] ([[Quaternary glaciation|Quaternary ice age]]) lasting about 100,000 years, and warm phases called [[interglacial]]s lasting 10,000–15,000 years. The last cold episode of the [[Last Glacial Period]] ended about 10,000 years ago.<ref>{{cite magazine|url=https://www.nationalgeographic.com/science/prehistoric-world/quaternary|archive-url=https://web.archive.org/web/20170320053318/http://www.nationalgeographic.com/science/prehistoric-world/quaternary/ | The current geological period, the [[Quaternary]], which began about 2.6 million years ago and extends into the present,<ref name="ICSchart2013">{{cite web |last1=Cohen |first1=K .M. |last2=Finney |first2=S. C. |last3=Gibbard |first3=P. L. |last4=Fan |first4=J.-X. |title=International Chronostratigraphic Chart 2013 |url=http://www.stratigraphy.org/icschart/chronostratchart2013-01.pdf |website=stratigraphy.org |publisher=ICS |access-date=7 January 2019 |ref=ICS2013 |archive-date=17 July 2013 |archive-url=https://web.archive.org/web/20130717121504/http://www.stratigraphy.org/ICSchart/ChronostratChart2013-01.pdf |url-status=live }}</ref> is marked by warm and cold episodes, cold phases called [[Glacial period|glacials]] ([[Quaternary glaciation|Quaternary ice age]]) lasting about 100,000 years, and warm phases called [[interglacial]]s lasting 10,000–15,000 years. The last cold episode of the [[Last Glacial Period]] ended about 10,000 years ago.<ref>{{cite magazine|url=https://www.nationalgeographic.com/science/prehistoric-world/quaternary|archive-url=https://web.archive.org/web/20170320053318/http://www.nationalgeographic.com/science/prehistoric-world/quaternary/|archive-date=March 20, 2017|title=Quaternary Period|magazine=National Geographic|date=2017-01-06}}</ref> Earth is currently in an interglacial period of the Quaternary, called the [[Holocene]]. | ||
===Glacial stages in North America=== | ===Glacial stages in North America=== | ||
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The [[Driftless Area]], a portion of western and southwestern Wisconsin along with parts of adjacent [[Minnesota]], [[Iowa]], and [[Illinois]], was not covered by glaciers. | The [[Driftless Area]], a portion of western and southwestern Wisconsin along with parts of adjacent [[Minnesota]], [[Iowa]], and [[Illinois]], was not covered by glaciers. | ||
==Effects of glaciation== | ==Effects of glaciation== | ||
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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 boulder]]s, [[till]], [[drumlin]]s, [[esker]]s, [[fjord]]s, [[kettle lake]]s, [[moraine]]s, [[cirque]]s, [[Glacial horn|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 [[Post-glacial rebound|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. | 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 boulder]]s, [[till]], [[drumlin]]s, [[esker]]s, [[fjord]]s, [[kettle lake]]s, [[moraine]]s, [[cirque]]s, [[Glacial horn|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 [[Post-glacial rebound|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 [[Proglacial lake|ice dams]] resulting in [[salinity|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 region|Baltic]] and [[Scandinavia]]n 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.<ref>{{cite book |last1=Andersen |first1=Bjørn G. |last2=Borns |first2=Harold W. Jr. |title=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 |year=1997 |url=http://www.universitetsforlaget.no/boker/realfagogit/biologi_geologi_og_miljoefag/katalog?productId=674197 |archive-url=https://archive.today/20130112093533/http://www.universitetsforlaget.no/boker/realfagogit/biologi_geologi_og_miljoefag/katalog?productId=674197 | 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 [[Proglacial lake|ice dams]] resulting in [[salinity|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 region|Baltic]] and [[Scandinavia]]n 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.<ref>{{cite book |last1=Andersen |first1=Bjørn G. |last2=Borns |first2=Harold W. Jr. |title=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 |year=1997 |url=http://www.universitetsforlaget.no/boker/realfagogit/biologi_geologi_og_miljoefag/katalog?productId=674197 |archive-url=https://archive.today/20130112093533/http://www.universitetsforlaget.no/boker/realfagogit/biologi_geologi_og_miljoefag/katalog?productId=674197 |archive-date=2013-01-12 |publisher=[[Universitetsforlaget]] |location=Oslo |isbn=978-82-00-37683-5 |access-date=2013-10-14 }}</ref> | ||
The redistribution of ice-water on the surface of Earth and the flow of mantle rocks causes changes in the [[Gravity of Earth|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 of rotation|axis]], and wobble of Earth's rotation. | The redistribution of ice-water on the surface of Earth and the flow of mantle rocks causes changes in the [[Gravity of Earth|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 of rotation|axis]], and wobble of Earth's rotation. | ||
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{{Main|Next glacial period}} | {{Main|Next glacial period}} | ||
Based on past estimates for interglacial durations of about 10,000 years, there was some concern in the 1970s that the next glacial period would be imminent.<ref>{{cite news |title=The Fiction Of Climate Science |url=https://www.forbes.com/2009/12/03/climate-science-gore-intelligent-technology-sutton.html |work=Forbes |date=4 December 2009}}</ref> [[Human impact on the environment|Human impact]] is now seen as possibly extending what would already be an unusually long warm period.<ref>{{cite news |title=Our next ice age is due in 10,000 years, but there's a catch |url=https://www.dw.com/en/earths-next-ice-age-is-due-in-10000-years-but-theres-a-catch/a-71786018 |work=Deutsche Welle |date=3 March 2025}}</ref><ref>{{cite news |title=Study Shows How | Based on past estimates for interglacial durations of about 10,000 years, there was some concern in the 1970s that the next glacial period would be imminent.<ref>{{cite news |title=The Fiction Of Climate Science |url=https://www.forbes.com/2009/12/03/climate-science-gore-intelligent-technology-sutton.html |work=Forbes |date=4 December 2009}}</ref> [[Human impact on the environment|Human impact]] is now seen as possibly extending what would already be an unusually long warm period.<ref>{{cite news |title=Our next ice age is due in 10,000 years, but there's a catch |url=https://www.dw.com/en/earths-next-ice-age-is-due-in-10000-years-but-theres-a-catch/a-71786018 |work=Deutsche Welle |date=3 March 2025}}</ref><ref>{{cite news |title=Study Shows How Earth's Orbit Affects Ice Ages |url=https://learningenglish.voanews.com/a/study-shows-how-earth-s-orbit-affects-ice-ages/7997495.html |work=[[Voice of America]] |date=10 March 2025}}</ref> Ice ages go through cycles of about 100,000 years, but the next one may well be avoided due to human carbon dioxide emissions.<ref name="PIK2016" /> According to Stephen Barker of [[Cardiff University]], without human interference, the next glaciation of the Earth would "occur within the next 11,000 years, and it would end in 66,000 years' time."<ref>{{cite news |title=Human-caused emissions have delayed Earth's next ice age, study says. But by how long? |url=https://www.euronews.com/green/2025/02/28/human-caused-emissions-have-delayed-earths-next-ice-age-study-says-but-by-how-long |work=Euronews |date=28 February 2025}}</ref> | ||
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 | 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 | ||
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* [https://www.pbs.org/wgbh/nova/ice/ Cracking the Ice Age] {{Webarchive|url=https://web.archive.org/web/20170904171146/http://www.pbs.org/wgbh/nova/ice/ |date=2017-09-04 }} from PBS | * [https://www.pbs.org/wgbh/nova/ice/ Cracking the Ice Age] {{Webarchive|url=https://web.archive.org/web/20170904171146/http://www.pbs.org/wgbh/nova/ice/ |date=2017-09-04 }} from PBS | ||
* {{cite web |title=Scientists unveil 'best-preserved Ice Age animal ever found' |author=Rina Torchinsky |website=AccuWeather |date=9 Aug 2021 |url=https://www.accuweather.com/en/weather-news/28000-year-old-lion-cub-best-preserved-ice-age-animal-ever-found/995878#:~:text=28%2C000%2Dyear%2Dold%20Lion%20cub,AccuWeather |access-date=9 August 2021 |archive-date=9 August 2021 |archive-url=https://web.archive.org/web/20210809172900/https://www.accuweather.com/en/weather-news/28000-year-old-lion-cub-best-preserved-ice-age-animal-ever-found/995878#:~:text=28%2C000%2Dyear%2Dold%20Lion%20cub,AccuWeather |url-status=live }} | * {{cite web |title=Scientists unveil 'best-preserved Ice Age animal ever found' |author=Rina Torchinsky |website=AccuWeather |date=9 Aug 2021 |url=https://www.accuweather.com/en/weather-news/28000-year-old-lion-cub-best-preserved-ice-age-animal-ever-found/995878#:~:text=28%2C000%2Dyear%2Dold%20Lion%20cub,AccuWeather |access-date=9 August 2021 |archive-date=9 August 2021 |archive-url=https://web.archive.org/web/20210809172900/https://www.accuweather.com/en/weather-news/28000-year-old-lion-cub-best-preserved-ice-age-animal-ever-found/995878#:~:text=28%2C000%2Dyear%2Dold%20Lion%20cub,AccuWeather |url-status=live }} | ||
* {{cite web |author=Raymo, M. |title=Overview of the Uplift-Weathering Hypothesis |date=July 2011 |url=http://www.moraymo.us/uplift_overview.php | * {{cite web |author=Raymo, M. |title=Overview of the Uplift-Weathering Hypothesis |date=July 2011 |url=http://www.moraymo.us/uplift_overview.php |archive-url=https://web.archive.org/web/20081022085754/http://www.moraymo.us/uplift_overview.php |archive-date=2008-10-22 }} | ||
* [https://ice.tsu.ru/index.php?option=com_content&view=category&layout=blog&id=43&Itemid=88&limitstart=5 Eduard Y. Osipov, Oleg M. Khlystov. Glaciers and meltwater flux to Lake Baikal during the Last Glacial Maximum.] {{Webarchive|url=https://web.archive.org/web/20160312054118/http://ice.tsu.ru/index.php?id=43&itemid=88&layout=blog&limitstart=5&option=com_content&view=category |date=2016-03-12 }} | * [https://ice.tsu.ru/index.php?option=com_content&view=category&layout=blog&id=43&Itemid=88&limitstart=5 Eduard Y. Osipov, Oleg M. Khlystov. Glaciers and meltwater flux to Lake Baikal during the Last Glacial Maximum.] {{Webarchive|url=https://web.archive.org/web/20160312054118/http://ice.tsu.ru/index.php?id=43&itemid=88&layout=blog&limitstart=5&option=com_content&view=category |date=2016-03-12 }} | ||
* {{cite news |author=Black, R. |title=Carbon emissions 'will defer Ice Age' |publisher=[[BBC News]] |department=Science and Environment |date=9 January 2012 |url=https://www.bbc.co.uk/news/science-environment-16439807 |access-date=20 June 2018 |archive-date=23 October 2018 |archive-url=https://web.archive.org/web/20181023223334/https://www.bbc.co.uk/news/science-environment-16439807 |url-status=live }} | * {{cite news |author=Black, R. |title=Carbon emissions 'will defer Ice Age' |publisher=[[BBC News]] |department=Science and Environment |date=9 January 2012 |url=https://www.bbc.co.uk/news/science-environment-16439807 |access-date=20 June 2018 |archive-date=23 October 2018 |archive-url=https://web.archive.org/web/20181023223334/https://www.bbc.co.uk/news/science-environment-16439807 |url-status=live }} | ||