Editing Cryosphere (section)

=== 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>