Editing Cryosphere (section)

== Components ==

=== Glaciers and ice sheets ===
{{Main|Glacier|Ice sheet}}
[[File:1249 Finsteraarhorn.jpg|thumb|Representation of glaciers on a [[National Maps of Switzerland|topographic map]]]]
[[File:Wildspitze_seen_from_Hinterer_Brunnkogel,_with_visible_ascent_track_of_ski_mountaineer.jpg|thumb|The Taschachferner [[glacier]] in the [[Ötztal Alps]] in [[Austria]]. The mountain to the left is the [[Wildspitze]] (3.768 m), second highest in Austria. To the right is an area with open [[crevasse]]s where the glacier flows over a kind of large [[cliff]].<ref>[https://www.google.com/maps/dir/Wildspitze,+6458,+%C3%96sterreich/Hinterer+Brochkogel,+6458,+%C3%96sterreich/@46.8693351,10.8649167,14z/data=!3m1!4b1!4m14!4m13!1m5!1m1!1s0x4782d399aa449a3b:0xc81bf75a6575685b!2m2!1d10.8672595!2d46.8854289!1m5!1m1!1s0x4782d388c6e336af:0xa4fff85a8397f10c!2m2!1d10.85!2d46.8833333!3e0 Google Maps: Distance between Wildspitze and Hinterer Brochkogel], cf. image scale at lower edge of screen</ref>]]

[[Ice sheet]]s and [[glacier]]s are flowing ice masses that rest on solid land. They are controlled by snow accumulation, surface and basal melt, calving into surrounding oceans or lakes and internal dynamics. The latter results from gravity-driven creep flow ("[[Ice flow dynamics|glacial flow]]") within the ice body and sliding on the underlying land, which leads to thinning and horizontal spreading.<ref name="GreveBlatter2009">{{cite book |author1=Greve, R. |title=Dynamics of Ice Sheets and Glaciers |author2=Blatter, H. |publisher=Springer |year=2009 |isbn=978-3-642-03414-5 |doi=10.1007/978-3-642-03415-2}}</ref> Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies.[[File:Greenland-ice_sheet_hg.jpg|thumb|Aerial view of the [[ice sheet]] on [[Greenland]]'s east coast]]Relationships between global climate and changes in ice extent are complex. The mass balance of land-based glaciers and ice sheets is determined by the accumulation of snow, mostly in winter, and warm-season [[ablation]] due primarily to net radiation and turbulent heat fluxes to melting ice and snow from warm-air advection<ref name="paterson">
Paterson, W. S. B., 1993: World sea level and the present mass balance of the Antarctic ice sheet. In: W.R. Peltier (ed.), Ice in the Climate System, NATO ASI Series, I12, Springer-Verlag, Berlin, 131–140.</ref><ref name="vandenbroeke">
Van den Broeke, M. R., 1996: The atmospheric boundary layer over ice sheets and glaciers. Utrecht, Universitiet Utrecht, 178 pp.</ref> Where ice masses terminate in the [[ocean]], iceberg [[Ice calving|calving]] is the major contributor to mass loss. In this situation, the ice margin may extend out into deep water as a floating [[ice shelf]], such as that in the [[Ross Sea]].

{{excerpt|glacier|paragraphs=1-3|file=no}}

{{excerpt|ice sheet|file=no}}
=== Sea ice ===
{{Main|Sea ice}}
[[File:Arctic ice.jpg|thumb|Broken pieces of Arctic sea ice with a snow cover]]
[[File:Seaice.jpg|thumb|Satellite image of sea ice forming near [[St. Matthew Island]] in the Bering Sea]]
[[Sea ice]] covers much of the polar oceans and forms by freezing of sea water. [[Satellite]] data since the early 1970s reveal considerable seasonal, regional, and interannual variability in the sea ice covers of both hemispheres. Seasonally, sea-ice extent in the [[Southern Hemisphere]] varies by a factor of 5, from a minimum of 3–4 million km<sup>2</sup> in February to a maximum of 17–20 million km<sup>2</sup> in September.<ref name="zwally">Zwally, H. J., J. C. Comiso, C. L. Parkinson, W. J. Campbell, F. D. Carsey, and P. Gloersen, 1983: Antarctic Sea Ice, 1973–1976: Satellite Passive-Microwave Observations. NASA SP-459, National Aeronautics and Space Administration, Washington, D.C., 206 pp.</ref><ref name="gloersen">Gloersen, P., W. J. Campbell, D. J. Cavalieri, J. C. Comiso, C. L. Parkinson, and H. J. Zwally, 1992: Arctic and Antarctic Sea Ice, 1978–1987: Satellite Passive-Microwave Observations and Analysis. NASA SP-511, National Aeronautics and Space Administration, Washington, D.C., 290 pp.</ref> The seasonal variation is much less in the Northern Hemisphere where the confined nature and high latitudes of the [[Arctic Ocean]] result in a much larger perennial ice cover, and the surrounding land limits the equatorward extent of wintertime ice. Thus, the seasonal variability in [[Northern Hemisphere]] ice extent varies by only a factor of 2, from a minimum of 7–9 million km<sup>2</sup> in September to a maximum of 14–16 million km<sup>2</sup> in March.<ref name="gloersen" /><ref name="parkinson">Parkinson, C. L., J. C. Comiso, H. J. Zwally, D. J. Cavalieri, P. Gloersen, and W. J. Campbell, 1987: Arctic Sea Ice, 1973–1976: Satellite Passive-Microwave Observations, NASA SP-489, National Aeronautics and Space Administration, Washington, D.C., 296 pp.</ref>

The ice cover exhibits much greater regional-scale interannual variability than it does hemispherical. For instance, in the region of the [[Sea of Okhotsk]] and [[Japan]], maximum ice extent decreased from 1.3 million km<sup>2</sup> in 1983 to 0.85 million km<sup>2</sup> in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km<sup>2</sup>.<ref name="gloersen" /> The regional fluctuations in both hemispheres are such that for any several-year period of the [[satellite]] record some regions exhibit decreasing ice coverage while others exhibit increasing ice cover.<ref name="parkinson1995">Parkinson, C. L., 1995: Recent sea-ice advances in Baffin Bay/Davis Strait and retreats in the Bellinshausen Sea. Annals of Glaciology, 21, 348–352.</ref>

=== Frozen ground and permafrost ===
{{excerpt|permafrost|paragraphs=1-3}}

=== Snow cover ===
{{Main|Snow}}
[[File:Snow-covered_fir_trees.jpg|thumb|Snow-covered trees in [[Kuusamo]], [[Finland]]]]
[[File:Long Mynd snowdrift.jpeg|right|thumb|Snow drifts forming around downwind obstructions]]
Most of the Earth's snow-covered area is located in the [[Northern Hemisphere]], and varies seasonally from 46.5 million km<sup>2</sup> in January to 3.8 million km<sup>2</sup> in August.<ref name="robinson">Robinson, D. A., K. F. Dewey, and R. R. Heim, 1993: Global snow cover monitoring: an update. Bull. Amer. Meteorol. Soc., 74, 1689–1696.</ref>

[[Snow]] cover is an extremely important storage component in the water balance, especially seasonal [[snowpack]]s in mountainous areas of the world. Though limited in extent, seasonal [[snowpack]]s in the [[Earth]]'s mountain ranges account for the major source of the runoff for stream flow and [[groundwater]] recharge over wide areas of the midlatitudes. For example, over 85% of the annual runoff from the [[Colorado River]] basin originates as snowmelt. [[Snowmelt]] runoff from the Earth's mountains fills the rivers and recharges the aquifers that over a billion people depend on for their water resources.{{citation needed|date=September 2023}}

Furthermore, over 40% of the world's protected areas are in mountains, attesting to their value both as unique [[ecosystem]]s needing protection and as recreation areas for humans.{{citation needed|date=September 2023}}

=== Ice on lakes and rivers ===
{{See also|Ice#On lakes|Ice#On rivers and streams}}
[[Ice]] forms on [[river]]s and [[lake]]s in response to seasonal cooling. The sizes of the ice bodies involved are too small to exert anything other than localized climatic effects. However, the freeze-up/break-up processes respond to large-scale and local weather factors, such that considerable interannual variability exists in the dates of appearance and disappearance of the ice. Long series of lake-ice observations can serve as a proxy climate record, and the monitoring of freeze-up and break-up trends may provide a convenient integrated and seasonally-specific index of climatic perturbations. Information on river-ice conditions is less useful as a climatic proxy because ice formation is strongly dependent on river-flow regime, which is affected by precipitation, snow melt, and watershed runoff as well as being subject to human interference that directly modifies channel flow, or that indirectly affects the runoff via land-use practices.{{citation needed|date=September 2023}}

Lake freeze-up depends on the heat storage in the lake and therefore on its depth, the rate and temperature of any [[inflow (hydrology)|inflow]], and water-air energy fluxes. Information on lake depth is often unavailable, although some indication of the depth of shallow lakes in the [[Arctic]] can be obtained from airborne [[radar imagery]] during late winter (Sellman ''et al.'' 1975) and spaceborne optical imagery during summer (Duguay and Lafleur 1997). The timing of breakup is modified by snow depth on the ice as well as by ice thickness and freshwater inflow.{{citation needed|date=September 2023}}