Editing Climate variability and change (section)

=== Changes in the cryosphere ===

==== Glaciers and ice sheets ====
[[Glacier]]s are considered among the most sensitive indicators of a changing climate.<ref name="Seiz-2007">{{cite report|last=Seiz |first=G. |author2=N. Foppa |title=The activities of the World Glacier Monitoring Service (WGMS) |year=2007 |url=http://www.meteoswiss.admin.ch/web/en/climate/climate_international/gcos/inventory/wgms.Par.0008.DownloadFile.tmp/gcosreportwgmse.pdf |access-date=21 June 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090325100331/http://www.meteoswiss.admin.ch/web/en/climate/climate_international/gcos/inventory/wgms.Par.0008.DownloadFile.tmp/gcosreportwgmse.pdf |archive-date=25 March 2009 }}</ref> Their size is determined by a [[mass balance]] between snow input and melt output. As temperatures increase, glaciers retreat unless snow precipitation increases to make up for the additional melt. Glaciers grow and shrink due both to natural variability and external forcings. Variability in temperature, precipitation and hydrology can strongly determine the evolution of a glacier in a particular season.

The most significant climate processes since the middle to late [[Pliocene]] (approximately 3 million years ago) are the glacial and [[interglacial]] cycles. The present interglacial period (the [[Holocene]]) has lasted about 11,700 years.<ref name="ICS-2008">{{cite web|url=http://www.stratigraphy.org/column.php?id=Chart/Time%20Scale|title=International Stratigraphic Chart|year=2008|publisher=International Commission on Stratigraphy|access-date=3 October 2011|url-status=dead|archive-url=https://web.archive.org/web/20111015042711/http://www.stratigraphy.org/column.php?id=Chart%2FTime%20Scale|archive-date=15 October 2011}}</ref> Shaped by [[Milankovitch cycles|orbital variations]], responses such as the rise and fall of [[Continental climate|continental]] ice sheets and significant sea-level changes helped create the climate. Other changes, including [[Heinrich event]]s, [[Dansgaard–Oeschger event]]s and the [[Younger Dryas]], however, illustrate how glacial variations may also influence climate without the [[orbital forcing]].

==== Sea level change ====
During the [[Last Glacial Maximum]], some 25,000 years ago, sea levels were roughly 130 m lower than today. The deglaciation afterwards was characterized by rapid sea level change.{{Sfn|Burroughs|2007|p=279}} In the early [[Pliocene]], global temperatures were 1–2˚C warmer than the present temperature, yet sea level was 15–25 meters higher than today.<ref>{{cite web|url=http://www.giss.nasa.gov/research/briefs/hansen_15/|archive-url=https://web.archive.org/web/20110724050602/http://www.giss.nasa.gov/research/briefs/hansen_15/|url-status=dead|archive-date=24 July 2011|title=Science Briefs: Earth's Climate History|last=Hansen|first=James|publisher=NASA GISS|access-date=25 April 2013}}</ref>

==== Sea ice ====
[[Sea ice]] plays an important role in Earth's climate as it affects the total amount of sunlight that is reflected away from the Earth.<ref>{{Cite journal|last1=Belt|first1=Simon T.|last2=Cabedo-Sanz|first2=Patricia|last3=Smik|first3=Lukas|last4=Navarro-Rodriguez|first4=Alba|last5=Berben|first5=Sarah M. P.|last6=Knies|first6=Jochen|last7=Husum|first7=Katrine|display-authors=3|date=2015|title=Identification of paleo Arctic winter sea ice limits and the marginal ice zone: Optimised biomarker-based reconstructions of late Quaternary Arctic sea ice|journal=Earth and Planetary Science Letters|volume=431|pages=127–39|doi=10.1016/j.epsl.2015.09.020|bibcode=2015E&PSL.431..127B|issn=0012-821X|hdl=10026.1/4335|hdl-access=free}}</ref> In the past, the Earth's oceans have been almost entirely covered by sea ice on a number of occasions, when the Earth was in a so-called [[Snowball Earth]] state,<ref>{{Cite journal|last1=Warren|first1=Stephen G.|last2=Voigt|first2=Aiko|last3=Tziperman|first3=Eli|last4=Sadler|first4=Peter M.|last5=Rose|first5=Catherine V.|last6=Rose|first6=Brian E. J.|last7=Ramstein|first7=Gilles|last8=Partin|first8=Camille A.|last9=Maloof|first9=Adam C.|display-authors=3|date=1 November 2017|title=Snowball Earth climate dynamics and Cryogenian geology-geobiology|journal=Science Advances|volume=3|issue=11|pages=e1600983|doi=10.1126/sciadv.1600983|pmid=29134193|issn=2375-2548|pmc=5677351|bibcode=2017SciA....3E0983H}}</ref> and completely ice-free in periods of warm climate.<ref>{{Cite journal|last1=Caballero|first1=R.|last2=Huber|first2=M.|date=2013|title=State-dependent climate sensitivity in past warm climates and its implications for future climate projections|journal=Proceedings of the National Academy of Sciences|volume=110|issue=35|pages=14162–67|doi=10.1073/pnas.1303365110|pmid=23918397|pmc=3761583|bibcode=2013PNAS..11014162C|issn=0027-8424|doi-access=free}}</ref> When there is a lot of sea ice present globally, especially in the tropics and subtropics, the climate is [[Climate sensitivity|more sensitive to forcings]] as the [[ice–albedo feedback]] is very strong.<ref>{{Cite journal|last1=Hansen James|last2=Sato Makiko|last3=Russell Gary|last4=Kharecha Pushker|date=2013|title=Climate sensitivity, sea level and atmospheric carbon dioxide|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=371|issue=2001|pages=20120294|doi=10.1098/rsta.2012.0294|pmc=3785813|pmid=24043864|arxiv=1211.4846|bibcode=2013RSPTA.37120294H}}</ref>