The cryosphere is the collective term for the frozen components of Earth: surface snow, glaciers, ice sheets, sea ice, lake and river ice, and frozen ground, including permafrost. It overlaps with the hydrosphere wherever water occurs as ice and interacts with the land, oceans, and atmosphere. Rather than forming a continuous shell, it consists of geographically scattered systems whose extent changes seasonally and over longer periods. These systems store freshwater, influence climate, and preserve evidence of past environmental conditions. (nsidc.org)
Components and distribution
Snow cover is widespread at middle and high latitudes and in mountains, including high elevations near the equator. Much of it melts annually, whereas persistent accumulation can develop into glacial ice. Snow cover is therefore distinct from glaciers: it may be temporary, shallow, and stationary rather than a long-lived, flowing mass. In the surface-based definition used by the National Snow and Ice Data Center, falling snow becomes part of the cryosphere once it reaches the ground. (nsidc.org)
A glacier forms where accumulated snowfall survives successive melt seasons, compacts into ice, and moves under its own weight. Glaciers occur in mountain ranges and polar regions. An ice sheet is a continental-scale body of glacial ice exceeding 50,000 square kilometres. Earth’s two present ice sheets cover most of Greenland and Antarctica; together they contain more than 99 percent of its land ice. Smaller dome-shaped bodies are called ice caps. (nsidc.org)
Sea ice forms through the freezing of seawater, principally in the Arctic Ocean and the Southern Ocean. It differs from an ice shelf, a floating extension of land-based glacial ice attached to the coast. Ice shelves receive ice flowing from glaciers and can lose fragments as icebergs. Lakes and rivers also develop seasonal or persistent ice covers, linking the cryosphere to freshwater environments. (nsidc.org)
Permafrost is ground—soil, sediment, or rock—that remains at or below 0°C for at least two consecutive years. Its definition depends on temperature, not on a minimum ice content. It occurs across northern high latitudes, in high mountains, and beneath parts of the Arctic continental shelves. The overlying active layer freezes and thaws seasonally. Ground that freezes in winter but thaws each year is seasonally frozen ground, not permafrost. (nsidc.org)
Climate and physical processes
Snow and ice influence the Earth’s energy budget through their high albedo, or reflectivity. Compared with dark land or open water, they generally reflect more incoming sunlight. When warming removes snow or sea ice, the exposed surface absorbs more solar energy, encouraging additional warming and melting. This ice–albedo feedback helps connect changes in the cryosphere with broader climate change. Its strength varies with season, sunlight, and surface conditions. (science.nasa.gov)
Snow also insulates the ground, while sea ice modifies exchanges between the ocean and atmosphere. Consequently, cryospheric change involves more than the disappearance of reflective surfaces: it alters heat exchange, ocean biology, and circulation. The effects depend on which component changes, its location, and the timing of freezing and melting. (nsidc.org)
Glaciers and ice sheets are assessed through their mass balance: the difference between gains, principally from snowfall, and losses through melting and ice discharge. Their movement redistributes accumulated ice toward lower elevations or the coast. Floating ice shelves can restrain the discharge of grounded ice; thinning or retreat can weaken this restraint and allow upstream glaciers to accelerate. (nsidc.org)
Water, sea level, and carbon
The cryosphere is an important reservoir within the water cycle. Seasonal snowmelt and glacier melt supply rivers, influencing the amount and timing of downstream flow. Glacier shrinkage can initially increase meltwater production, but continued loss ultimately reduces the remaining ice reservoir. Changes in snow and glacier storage therefore affect water availability, agriculture, and hydropower in dependent drainage basins. (ipcc.ch)
Loss of land ice contributes to sea-level rise when water previously stored on land enters the ocean. Melting floating ice has a much smaller direct effect because it already displaces seawater. Nevertheless, ice-shelf loss can indirectly raise sea level by increasing discharge from grounded glaciers. Ocean warming also raises sea level through thermal expansion, independently of cryospheric mass loss. (nsidc.org)
Permafrost connects the cryosphere with the carbon cycle. Frozen soils preserve organic material that can undergo microbial decomposition after thawing, releasing carbon dioxide or methane. Such releases can reinforce warming, although their magnitude depends on moisture, vegetation, thaw processes, and other local conditions. Thawing ice-rich ground can also subside, changing drainage and damaging infrastructure. (ipcc.ch)
Observed change and investigation
Observations show widespread cryospheric responses to climate change. The Intergovernmental Panel on Climate Change reported in its 2021 assessment that Northern Hemisphere spring snow cover had declined since the late 1970s, alongside permafrost warming and thawing. Arctic sea ice has declined across the satellite record beginning in 1979, with particularly strong reductions in September. Satellite gravimetry also documents net mass loss from both major ice sheets since 2002. Regional and year-to-year variations remain important when interpreting these trends. (ipcc.ch)
Scientists combine field measurements with remote sensing. Satellite and airborne instruments measure ice extent, elevation, movement, and changes in gravitational attraction associated with ice mass. These observations constrain estimates of mass loss and support projections of future change. Ice cores provide a complementary archive for paleoclimatology: trapped air records earlier atmospheric composition, while isotope ratios and other properties help reconstruct past temperatures and environmental conditions. (science.nasa.gov)