Editing Permafrost (section)

=== Continuity of coverage ===
Permafrost typically forms in any [[climate]] where the mean annual air temperature is lower than the freezing point of water. Exceptions are found in [[taiga|humid boreal forests]], such as in Northern [[Scandinavia]] and the North-Eastern part of [[European Russia]] west of the [[Ural Mountains|Urals]], where snow acts as an insulating blanket. Glaciated areas may also be exceptions. Since all glaciers are warmed at their base by geothermal heat, [[Glacier#Types|temperate glaciers]], which are near the [[pressure melting point]] throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost.<ref>{{cite book |last=Sharp |first=Robert Phillip |author-link=Robert P. Sharp |title=Living Ice: Understanding Glaciers and Glaciation |publisher=Cambridge University Press |page=[https://archive.org/details/livingiceunderst0000shar/page/27 27] |url=https://archive.org/details/livingiceunderst0000shar |url-access=registration |isbn=978-0-521-33009-1 |date=1988 }}</ref> "Fossil" cold anomalies in the [[geothermal gradient]] in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in [[borehole]]s in North America and Europe.<ref>{{Cite journal |last=Majorowicz |first=Jacek |title=Permafrost at the ice base of recent pleistocene glaciations – Inferences from borehole temperatures profiles |journal=Bulletin of Geography. Physical Geography Series |series=Physical Geography Series |date=28 December 2012 |doi=10.2478/v10250-012-0001-x |volume=5 |pages=7–28 |doi-access = free }}</ref>

==== Discontinuous permafrost ====
[[File:Digging in permafrost.jpg|thumb|left|Excavating ice-rich permafrost with a [[jackhammer]] in [[Alaska]].]]
The below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth due to the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below {{convert|0|°C|°F|abbr=on}}, permafrost will form only in spots that are sheltered (usually with a northern or southern [[aspect (geography)|aspect]], in the north and south hemispheres respectively) creating discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between {{convert|-5|and|0|C|F}}. In the moist-wintered areas mentioned before, there may not even be discontinuous permafrost down to {{convert|-2|°C|°F}}. Discontinuous permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between {{convert|-2|and|-4|C|F}}, and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between {{convert|0|and|-2|C|F}}.<ref name="BrownPéwé">{{Cite journal |last1=Brown |first1=Roger J. E. |last2=Péwé |first2=Troy L. |title=Distribution of permafrost in North America and its relationship to the environment: A review, 1963–1973 |journal=Permafrost: North American Contribution – Second International Conference |volume=2 |pages=71–100 |year=1973 |isbn=978-0-309-02115-9 |url=https://books.google.com/books?id=SjErAAAAYAAJ&pg=PA72}}</ref>

In soil science, the sporadic permafrost zone is abbreviated '''SPZ''' and the extensive discontinuous permafrost zone '''DPZ'''.<ref>{{Cite report |first= S. D. |last= Robinson |editor-last=Phillips |contribution= Permafrost and peatland [[carbon sink]] capacity with increasing latitude |title= Permafrost |year=2003 |pages=965–970 |publisher=Swets & Zeitlinger |url=http://www.arlis.org/docs/vol1/ICOP/55700698/Pdf/Chapter_169.pdf |isbn=90-5809-582-7 |display-authors=etal |display-editors=etal |access-date=18 August 2023 |archive-url=https://web.archive.org/web/20140302190815/http://www.arlis.org/docs/vol1/ICOP/55700698/Pdf/Chapter_169.pdf |archive-date=2 March 2014 |url-status=live }}</ref> Exceptions occur in un-glaciated [[Siberia]] and [[Alaska]] where the present depth of permafrost is a [[Relict (geology)|relic]] of climatic conditions during glacial ages where winters were up to {{convert|11|C-change}} colder than those of today.

==== Continuous permafrost ====
{| class="wikitable floatright"
|+ Estimated extent of alpine permafrost by region<ref name="BockhMunr" />
|-
! Locality
! Area<br />
|-
| [[Qinghai-Tibet Plateau]]
| style="text-align:right;" | {{convert|1300000|km2|mi2|abbr=on}}
|-
| [[Khangai Mountains|Khangai]]-[[Altai Mountains]]
| style="text-align:right;" | {{convert|1000000|km2|mi2|abbr=on}}
|-
| [[Brooks Range]]
| style="text-align:right;" | {{convert|263000|km2|mi2|abbr=on}}
|-
| [[Siberia#Mountain ranges|Siberian Mountains]]
| style="text-align:right;" | {{convert|255000|km2|mi2|abbr=on}}
|-
| [[Greenland]]
| style="text-align:right;" | {{convert|251000|km2|mi2|abbr=on}}
|-
| [[Ural Mountains]]
| style="text-align:right;" | {{convert|125000|km2|mi2|abbr=on}}
|-
| [[Andes]]
| style="text-align:right;" | {{convert|100000|km2|mi2|abbr=on}}
|-
| [[Rocky Mountains]] (US and Canada)
| style="text-align:right;" | {{convert|100000|km2|mi2|abbr=on}}
|-
| [[Alps]]
| style="text-align:right;" | {{convert|80000|km2|mi2|abbr=on}}
|-
| [[Fennoscandian]] mountains
| style="text-align:right;" | {{convert|75000|km2|mi2|abbr=on}}
|-
| Remaining
| style="text-align:right;" | <{{convert|50000|km2|mi2|abbr=on}}
|}
At mean annual soil surface temperatures below {{convert|-5|C}} the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost (abbreviated to '''CPZ''') forms. A line of continuous permafrost in the [[Northern Hemisphere]]<ref>{{cite book |title=Frozen ground engineering |first1=Orlando B. |last1=Andersland |first2=Branko |last2=Ladanyi |publisher=Wiley |year=2004 |page=5 |isbn=978-0-471-61549-1 |edition=2nd}}</ref> represents the most southern border where land is covered by continuous permafrost or glacial ice. The line of continuous permafrost varies around the world northward or southward due to regional climatic changes. In the [[southern hemisphere]], most of the equivalent line would fall within the [[Southern Ocean]] if there were land there. Most of the [[Antarctica|Antarctic continent]] is overlain by glaciers, under which much of the terrain is subject to basal [[pressure melting point|melting]].<ref>{{Cite journal |last=Zoltikov |first=I. A. |title=Heat regime of the central Antarctic glacier |journal=Antarctica, Reports of the Commission, 1961 |pages=27–40 |year=1962 |language=ru }}</ref> The exposed land of Antarctica is substantially underlain with permafrost,<ref>{{Cite book |first1=Iain B. |last1=Campbell |first2=Graeme G. C. |last2=Claridge |editor-last=Margesin |editor-first=Rosa |contribution=Antarctic Permafrost Soils |isbn=978-3-540-69370-3  |title = Permafrost Soils |volume=16 |year=2009 |pages=17–31 |place = Berlin |publisher=Springer |doi=10.1007/978-3-540-69371-0_2 |series=Soil Biology }}</ref> some of which is subject to warming and thawing along the coastline.<ref>{{Cite news |last=Heinrich |first=Holly |title=Permafrost Melting Faster Than Expected in Antarctica |publisher=[[National Public Radio]] |date=25 July 2013 |url=https://stateimpact.npr.org/texas/2013/07/25/permafrost-melting-faster-than-expected-in-antarctica/ |access-date=23 April 2016 |archive-url=https://web.archive.org/web/20160503120018/https://stateimpact.npr.org/texas/2013/07/25/permafrost-melting-faster-than-expected-in-antarctica/ |archive-date=3 May 2016 |url-status=live }}</ref>