Editing Ice age (section)

==Glacials and interglacials==
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{{See also|Glacial period|Interglacial}}
[[File:Ice Age Temperature.png|right|thumb|upright=1.35|Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials.]]
{{multiple image
| align = right
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| width = 230
| header = Minimum and maximum glaciation
| image1 = Iceage north-intergl glac hg.png
| caption1 = Minimum (interglacial, black) and maximum (glacial, grey) glaciation of the [[Northern Hemisphere|northern hemisphere]]
| image2 = Iceage south-intergl glac hg.png
| caption2 = Minimum (interglacial, black) and maximum (glacial, grey) glaciation of the [[Southern Hemisphere|southern hemisphere]]
}}

Within the current glaciation, more temperate and more severe periods have occurred. The colder periods are called ''glacial periods'', the warmer periods ''interglacials'', such as the [[Eemian|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>

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

Earth has been in an interglacial period known as the [[Holocene]] for around 11,700 years,<ref name="Walker, M. 2009. pp. 3">{{cite journal |last1 = Walker |first1 = M. |last2 = Johnsen |first2 = S. |last3 = Rasmussen |first3 = S. O. |last4 = Popp |first4 = T. |last5 = Steffensen |first5 = J.-P. |last6 = Gibbard |first6 = P. |last7 = Hoek |first7 = W. |last8 = Lowe |first8 = J. |last9 = Andrews |first9 = J. |last10 = Bjo |last11 = Cwynar |first11 = L. C. |last12 = Hughen |first12 = K. |last13 = Kershaw |first13 = P. |last14 = Kromer |first14 = B. |last15 = Litt |first15 = T. |last16 = Lowe |first16 = D. J. |last17 = Nakagawa |first17 = T. |last18 = Newnham |first18 = R. |last19 = Schwander |first19 = J. |year = 2009 |title = Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records |url = http://www.stratigraphy.org/GSSP/Holocene.pdf |journal = J. Quaternary Sci. |volume = 24 |issue = 1 |pages = 3–17 |doi = 10.1002/jqs.1227 |bibcode = 2009JQS....24....3W |doi-access = free |access-date = 2017-07-26 |archive-date = 2013-11-04 |archive-url = https://web.archive.org/web/20131104131948/http://www.stratigraphy.org/GSSP/Holocene.pdf |url-status = live }}</ref> and an article in ''Nature'' in 2004 argues that it might be most analogous to a previous interglacial that lasted 28,000 years.<ref>{{cite journal
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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"/>