The Cryosphere is the collective term for all parts of Earth where water exists in solid form for substantial periods, including snow cover, glaciers, ice sheets, sea ice, ice shelves, frozen lakes and rivers, and frozen ground. It is a component of the Earth system rather than a single geographical region. Cryospheric features occur from polar environments to high mountains and, seasonally, in many temperate areas.
Their duration can range from days for temporary snow to hundreds of thousands of years for some deep ice. The Cryosphere is important because frozen water stores freshwater, reflects incoming solar radiation, influences atmospheric and oceanic processes, affects ecosystems and landscapes, and interacts with the global climate system.
Snow is one of the most widespread and variable components of the Cryosphere. It forms when atmospheric water vapour or cloud water freezes and accumulates as ice crystals or aggregates at the surface. Snow properties depend on temperature, humidity, wind, crystal structure, compaction, metamorphism, and age. Fresh snow can have high reflectivity, while older or dirty snow may absorb more solar energy. Seasonal snow cover can insulate underlying ground, influence soil temperature, store water, and control the timing of spring runoff. In mountainous areas, snow accumulation is also a major source of seasonal water for rivers and downstream ecosystems.
Glaciers and ice sheets are long lasting bodies of land based ice formed from accumulated snowfall that has survived through successive seasons and compacted into dense ice. Glaciers generally occupy valley or mountain environments, while ice sheets cover very large areas of continental land. Ice flows under gravity and internal deformation, with movement also influenced by basal sliding and subglacial water. Ice thickness, temperature, surface slope, bed conditions, snowfall, melting, and calving all influence mass balance and flow. When accumulation exceeds losses over a sustained period, ice mass can increase; when losses exceed gains, it can decrease.
Sea ice is frozen seawater and therefore differs fundamentally from land based ice. When seawater freezes, salts are largely excluded from the forming ice lattice, leaving the surrounding water relatively saltier and denser. Sea ice can therefore influence ocean circulation as well as surface energy balance. Its seasonal expansion and contraction affect marine habitats, navigation, atmospheric heat exchange, and coastal conditions. Sea ice can also contain brine channels and inclusions that create specialised habitats and influence chemical exchange between ocean and atmosphere.
The Cryosphere has a major role in Earth's energy balance. Snow and ice generally have high surface reflectivity compared with darker land and open water, meaning that a substantial fraction of incoming solar radiation can be reflected back to space. Changes in snow or ice cover can therefore modify the amount of energy absorbed by the surface. Frozen surfaces also regulate heat and moisture exchange between the atmosphere, land, and ocean. However, the magnitude and direction of these effects depend on season, surface properties, cloud conditions, latitude, and the specific type of frozen material involved.
Frozen ground is another important part of the Cryosphere. It includes soil and rock that remain frozen for extended periods, with permafrost representing ground that stays at or below the freezing threshold for at least two consecutive years. Seasonal thawing of the upper active layer supports biological processes and hydrological movement. Changes in frozen ground can affect landscapes through subsidence, thermokarst development, erosion, landslides, and altered drainage. Infrastructure built on frozen ground can also be affected when thermal conditions change, because melting ground ice can reduce mechanical stability and cause uneven settlement.
The Cryosphere interacts continuously with the water cycle. Snow and ice store water that may otherwise enter rivers, lakes, groundwater, and oceans. Seasonal melting can produce strong pulses of freshwater, while glacier and ice sheet runoff can contribute to long term sea level change. Freezing and melting also alter the timing and distribution of water availability. In high mountain environments, stored snow and glacier ice can provide important seasonal water supplies. In polar environments, changes in frozen water can influence ocean salinity and circulation. These interactions demonstrate that the Cryosphere is an active part of the hydrological system rather than a passive reservoir.
Scientific investigation of the Cryosphere uses satellite observations, aircraft surveys, automatic weather stations, ice cores, snow measurements, ground penetrating radar, satellite altimetry, gravimetry, GPS measurements, ocean observations, and numerical models. Ice cores can preserve information about past atmospheric composition, temperature related indicators, volcanic events, dust, and snowfall over long periods. Remote sensing can measure changes in surface area, thickness, motion, snow extent, and sea ice concentration across regions that are difficult to access directly. Understanding the Cryosphere therefore requires combining observations at many spatial and temporal scales, from individual snow crystals and ice layers to entire continental ice sheets and global climate processes.
