Editing Cryosphere (section)

== Properties and interactions ==
[[File:Climate-system.jpg|alt=|thumb|330x330px|The cryosphere (bottom left) is one of five components of the [[climate system]]. The others are the [[Atmosphere of Earth|atmosphere]], the [[hydrosphere]], the [[lithosphere]] and the [[biosphere]].<ref name=":0"> {{cite book |last=Planton |first=S. |title=Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. |year=2013 |editor-last=Stocker |editor-first=T.F. |chapter=Annex III: Glossary |editor-last2=Qin |editor-first2=D. |editor-last3=Plattner |editor-first3=G.-K. |editor-last4=Tignor |editor-first4=M. |editor-last5=Allen |editor-first5=S.K. |editor-last6=Boschung |editor-first6=J. |editor-last7=Nauels |editor-first7=A. |editor-last8=Xia |editor-first8=Y. |editor-last9=Bex |editor-first9=V. |chapter-url=https://www.ipcc.ch/site/assets/uploads/2018/08/WGI_AR5_glossary_EN.pdf |editor-first10=P.M. |editor-last10=Midgley}}</ref>{{rp|1451}}]]There are several fundamental physical properties of snow and ice that modulate energy exchanges between the surface and the [[atmosphere]]. The most important properties are the surface reflectance ([[albedo]]), the ability to transfer heat (thermal diffusivity), and the ability to change state ([[latent heat]]). These physical properties, together with surface roughness, [[emissivity]], and [[dielectric]] characteristics, have important implications for observing snow and ice from space. For example, surface roughness is often the dominant factor determining the strength of [[radar]] [[backscatter]].<ref name="hall">{{cite book |last1=Hall |first1=Dorothy K. |author-link=Dorothy Hall (scientist)|title=Remote Sensing of Ice and Snow |date=1985 |publisher=Springer Netherlands |location=Dordrecht |isbn=978-94-009-4842-6}}</ref> Physical properties such as [[crystal]] structure, density, length, and liquid water content are important factors affecting the transfers of heat and water and the scattering of [[microwave]] [[energy]].

=== Residence time and extent ===
The residence time of water in each of the cryospheric sub-systems varies widely. Snow cover and freshwater ice are essentially seasonal, and most sea ice, except for ice in the central [[Arctic]], lasts only a few years if it is not seasonal. A given water particle in glaciers, ice sheets, or ground ice, however, may remain frozen for 10–100,000 years or longer, and deep ice in parts of [[East Antarctica]] may have an age approaching 1 million years.{{citation needed|date=September 2023}}

Most of the world's ice volume is in [[Antarctica]], principally in the [[East Antarctic Ice Sheet]]. In terms of areal extent, however, [[Northern Hemisphere]] winter snow and ice extent comprise the largest area, amounting to an average 23% of hemispheric surface area in January. The large areal extent and the important climatic roles of snow and [[ice]] is related to their unique physical properties. This also indicates that the ability to observe and model snow and ice-cover extent, thickness, and [[Properties of water#Physics and chemistry|physical properties]] (radiative and thermal properties) is of particular significance for [[Climatology|climate research]].<ref>{{Cite web |title=Properties of Snow – Our Winter World |url=https://ourwinterworld.org/snow-science/properties-of-snow/ |archive-url=http://web.archive.org/web/20250115030453/https://ourwinterworld.org/snow-science/properties-of-snow/ |archive-date=2025-01-15 |access-date=2025-03-06 |website=ourwinterworld.org |language=en-US}}</ref>

=== Surface reflectance ===
The surface reflectance of incoming [[solar radiation]] is important for the surface energy balance (SEB). It is the ratio of reflected to incident solar radiation, commonly referred to as [[albedo]]. Climatologists are primarily interested in albedo integrated over the [[Shortwave radiation|shortwave]] portion of the [[electromagnetic spectrum]] (~300 to 3500&nbsp;nm), which coincides with the main solar energy input. Typically, albedo values for non-melting snow-covered surfaces are high (~80–90%) except in the case of forests.{{citation needed|date=September 2023}} 

The higher albedos for snow and ice cause rapid shifts in surface [[reflectivity]] in autumn and spring in high latitudes, but the overall climatic significance of this increase is spatially and temporally modulated by [[cloud cover]]. (Planetary albedo is determined principally by cloud cover, and by the small amount of total solar radiation received in high [[latitudes]] during winter months.) Summer and autumn are times of high-average cloudiness over the [[Arctic Ocean]] so the albedo [[feedback]] associated with the large seasonal changes in sea-ice extent is greatly reduced. It was found that snow cover exhibited the greatest influence on [[Earth's energy budget|Earth's radiative balance]] in the spring (April to May) period when incoming [[solar radiation]] was greatest over snow-covered areas.<ref name="groisman">{{cite journal |last1=Groisman |first1=Pavel Ya. |last2=Karl |first2=Thomas R. |last3=Knight |first3=Richard W. |title=Observed Impact of Snow Cover on the Heat Balance and the Rise of Continental Spring Temperatures |journal=Science |date=14 January 1994 |volume=263 |issue=5144 |pages=198–200 |doi=10.1126/science.263.5144.198 |pmid=17839175 |bibcode=1994Sci...263..198G |s2cid=9932394 |url=https://www.science.org/doi/10.1126/science.263.5144.198 |access-date=25 February 2022}}</ref>

=== Thermal properties of cryospheric elements ===
The [[Heat|thermal]] properties of cryospheric elements also have important climatic consequences.{{citation needed|date=September 2023}} Snow and ice have much lower thermal diffusivities than [[air]]. [[Thermal diffusivity]] is a measure of the speed at which temperature waves can penetrate a substance. Snow and ice are many [[orders of magnitude]] less efficient at diffusing heat than air. Snow cover insulates the ground surface, and sea ice insulates the underlying ocean, decoupling the surface-atmosphere interface with respect to both heat and moisture fluxes. The flux of moisture from a water surface is eliminated by even a thin skin of ice, whereas the flux of heat through thin ice continues to be substantial until it attains a thickness in excess of 30 to 40&nbsp;cm. However, even a small amount of snow on top of the ice will dramatically reduce the heat flux and slow down the rate of ice growth. The insulating effect of snow also has major implications for the [[hydrological cycle]]. In non-permafrost regions, the insulating effect of snow is such that only near-surface ground freezes and deep-water drainage is uninterrupted.<ref name="lynch">Lynch-Stieglitz, M., 1994: The development and validation of a simple snow model for the GISS GCM. J. Climate, 7, 1842–1855.</ref>

While snow and ice act to insulate the surface from large energy losses in winter, they also act to retard warming in the spring and summer because of the large amount of energy required to melt ice (the [[latent heat]] of fusion, 3.34 x 10<sup>5</sup> J/kg at 0&nbsp;°C). However, the strong static stability of the atmosphere over areas of extensive snow or ice tends to confine the immediate cooling effect to a relatively shallow layer, so that associated atmospheric anomalies are usually short-lived and local to regional in scale.<ref name="cohen">Cohen, J., and D. Rind, 1991: The effect of snow cover on the climate. J. Climate, 4, 689–706.</ref> In some areas of the world such as [[Eurasia]], however, the cooling associated with a heavy snowpack and moist spring soils is known to play a role in modulating the summer [[monsoon]] circulation.<ref name="vernekar">Vernekar, A. D., J. Zhou, and J. Shukla, 1995: The effect of Eurasian snow cover on the Indian monsoon. J. Climate, 8, 248–266.</ref>

=== Climate change feedback mechanisms ===
{{Main|Climate change feedback}}
There are numerous cryosphere-climate feedbacks in the [[global climate]] system. These operate over a wide range of spatial and temporal scales from local seasonal cooling of air temperatures to hemispheric-scale variations in ice sheets over time scales of thousands of years. The feedback mechanisms involved are often complex and incompletely understood. For example, Curry ''et al.'' (1995) showed that the so-called "simple" sea ice-albedo feedback involved complex interactions with lead fraction, melt ponds, ice thickness, snow cover, and sea-ice extent.<ref>{{Cite journal |last1=Curry |first1=Judith A. |last2=Schramm |first2=Julie L. |last3=Ebert |first3=Elizabeth E. |date=1995 |title=Sea Ice-Albedo Climate Feedback Mechanism |journal=Journal of Climate |language=en |volume=8 |issue=2 |pages=240–247 |doi=10.1175/1520-0442(1995)008<0240:SIACFM>2.0.CO;2 |issn=0894-8755|doi-access=free |bibcode=1995JCli....8..240C }}</ref>

The role of snow cover in modulating the monsoon is just one example of a short-term cryosphere-climate feedback involving the land surface and the atmosphere.<ref name="vernekar" />{{citation needed|date=September 2023}}