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Cryosphere
Cryosphere
Cryosphere
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Overview of the cryosphere and its larger components[1]

The cryosphere is an umbrella term for those portions of Earth's surface where water is in solid form. This includes sea ice, ice on lakes or rivers, snow, glaciers, ice caps, ice sheets, and frozen ground (which includes permafrost). Thus, there is an overlap with the hydrosphere. The cryosphere is an integral part of the global climate system. It also has important feedbacks on the climate system. These feedbacks come from the cryosphere's influence on surface energy and moisture fluxes, clouds, the water cycle, atmospheric and oceanic circulation.

Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. Approximately 10% of the Earth's surface is covered by ice, but this is rapidly decreasing.[2] Current reductions in the cryosphere (caused by climate change) are measurable in ice sheet melt, glaciers decline, sea ice decline, permafrost thaw and snow cover decrease.

Definition and terminology

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The cryosphere describes those portions of Earth's surface where water is in solid form. Frozen water is found on the Earth's surface primarily as snow cover, freshwater ice in lakes and rivers, sea ice, glaciers, ice sheets, and frozen ground and permafrost (permanently frozen ground).

The cryosphere is one of five components of the climate system. The others are the atmosphere, the hydrosphere, the lithosphere and the biosphere.[3]: 1451 

The term cryosphere comes from the Greek word kryos, meaning cold, frost or ice and the Greek word sphaira, meaning globe or ball.[4]

Cryospheric sciences is an umbrella term for the study of the cryosphere. As an interdisciplinary Earth science, many disciplines contribute to it, most notably geology, hydrology, and meteorology and climatology; in this sense, it is comparable to glaciology.

The term deglaciation describes the retreat of cryospheric features.

Properties and interactions

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The cryosphere (bottom left) is one of five components of the climate system. The others are the atmosphere, the hydrosphere, the lithosphere and the biosphere.[3]: 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.[5] 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

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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]

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 physical properties (radiative and thermal properties) is of particular significance for climate research.[6]

Surface reflectance

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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 portion of the electromagnetic spectrum (~300 to 3500 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]

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 radiative balance in the spring (April to May) period when incoming solar radiation was greatest over snow-covered areas.[7]

Thermal properties of cryospheric elements

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The thermal properties of cryospheric elements also have important climatic consequences.[citation needed] 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 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.[8]

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 105 J/kg at 0 °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.[9] 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.[10]

Climate change feedback mechanisms

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Main article: 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.[11]

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.[10][citation needed]

Components

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Glaciers and ice sheets

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Main articles: Glacier and Ice sheet
Representation of glaciers on a topographic map
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 crevasses where the glacier flows over a kind of large cliff.[12]

Ice sheets and glaciers 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 ("glacial flow") within the ice body and sliding on the underlying land, which leads to thinning and horizontal spreading.[13] Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies.

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[14][15] Where ice masses terminate in the ocean, iceberg 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.

This section is an excerpt from Glacier.[edit]

A glacier (US: /ˈɡleɪʃər/; UK: /ˈɡlæsiə/ or /ˈɡleɪsiə/) is a persistent body of dense ice, a form of rock,[16] that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as crevasses and seracs, as it slowly flows and deforms under stresses induced by its weight. As it moves, it abrades rock and debris from its substrate to create landforms such as cirques, moraines, or fjords. Although a glacier may flow into a body of water, it forms only on land[17][18][19] and is distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand. Between latitudes 35°N and 35°S, glaciers occur only in the Himalayas, Andes, and a few high mountains in East Africa, Mexico, New Guinea and on Zard-Kuh in Iran.[20] With more than 7,000 known glaciers, Pakistan has more glacial ice than any other country outside the polar regions.[21][22] Glaciers cover about 10% of Earth's land surface. Continental glaciers cover nearly 13 million km2 (5 million sq mi) or about 98% of Antarctica's 13.2 million km2 (5.1 million sq mi), with an average thickness of ice 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers.[23] The volume of glaciers, not including the ice sheets of Antarctica and Greenland, has been estimated at 170,000 km3.[24]

Glacial ice is the largest reservoir of fresh water on Earth, holding with ice sheets about 69 percent of the world's freshwater.[25][26] Many glaciers from temperate, alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. However, within high-altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater.
This section is an excerpt from Ice sheet.[edit]

In glaciology, an ice sheet, also known as a continental glacier,[27] is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi).[28] The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.

Although the surface is cold, the base of an ice sheet is generally warmer due to geothermal heat. In places, melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels in the ice sheet — these are ice streams.

Even stable ice sheets are continually in motion as the ice gradually flows outward from the central plateau, which is the tallest point of the ice sheet, and towards the margins. The ice sheet slope is low around the plateau but increases steeply at the margins.[29]

Increasing global air temperatures due to climate change take around 10,000 years to directly propagate through the ice before they influence bed temperatures, but may have an effect through increased surface melting, producing more supraglacial lakes. These lakes may feed warm water to glacial bases and facilitate glacial motion.[30]

In previous geologic time spans (glacial periods) there were other ice sheets. During the Last Glacial Period at Last Glacial Maximum, the Laurentide Ice Sheet covered much of North America. In the same period, the Weichselian ice sheet covered Northern Europe and the Patagonian Ice Sheet covered southern South America.

Sea ice

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Main article: Sea ice
Broken pieces of Arctic sea ice with a snow cover
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 km2 in February to a maximum of 17–20 million km2 in September.[31][32] 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 km2 in September to a maximum of 14–16 million km2 in March.[32][33]

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 km2 in 1983 to 0.85 million km2 in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km2.[32] 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.[34]

Frozen ground and permafrost

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This section is an excerpt from Permafrost.[edit]
Extent and types of permafrost in the Northern Hemisphere as per International Permafrost Association

Permafrost (from perma- 'permanent' and frost) is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more; the oldest permafrost has been continuously frozen for around 700,000 years.[35] Whilst the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than 1,500 m (4,900 ft).[36] Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions.[37] The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which freezes and thaws depending on the season.[38]

Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost,[39] covering a total area of around 18 million km2 (6.9 million sq mi).[40] This includes large areas of Alaska, Canada, Greenland, and Siberia. It is also located in high mountain regions, with the Tibetan Plateau being a prominent example. Only a minority of permafrost exists in the Southern Hemisphere, where it is consigned to mountain slopes like in the Andes of Patagonia, the Southern Alps of New Zealand, or the highest mountains of Antarctica.[37][35]

Permafrost contains large amounts of dead biomass that has accumulated throughout millennia without having had the chance to fully decompose and release its carbon, making tundra soil a carbon sink.[37] As global warming heats the ecosystem, frozen soil thaws and becomes warm enough for decomposition to start anew, accelerating the permafrost carbon cycle. Depending on conditions at the time of thaw, decomposition can release either carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback.[41][42][43] The emissions from thawing permafrost will have a sufficient impact on the climate to impact global carbon budgets. It is difficult to accurately predict how much greenhouse gases the permafrost releases because the different thaw processes are still uncertain. There is widespread agreement that the emissions will be smaller than human-caused emissions and not large enough to result in runaway warming.[44] Instead, the annual permafrost emissions are likely comparable with global emissions from deforestation, or to annual emissions of large countries such as Russia, the United States or China.[45]

Snow cover

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Main article: Snow
Snow-covered trees in Kuusamo, Finland
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 km2 in January to 3.8 million km2 in August.[46]

Snow cover is an extremely important storage component in the water balance, especially seasonal snowpacks in mountainous areas of the world. Though limited in extent, seasonal snowpacks 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]

Furthermore, over 40% of the world's protected areas are in mountains, attesting to their value both as unique ecosystems needing protection and as recreation areas for humans.[citation needed]

Ice on lakes and rivers

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See also: Ice § On lakes, and Ice § On rivers and streams

Ice forms on rivers and lakes 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]

Lake freeze-up depends on the heat storage in the lake and therefore on its depth, the rate and temperature of any 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]

Changes caused by climate change

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This section is an excerpt from Effects of climate change § Ice and snow.[edit]
The cryosphere, the area of the Earth covered by snow or ice, is extremely sensitive to changes in global climate.[47] There has been an extensive loss of snow on land since 1981. Some of the largest declines have been observed in the spring.[48] During the 21st century, snow cover is projected to continue its retreat in almost all regions.[49]: 39–69 

Ice sheet melt

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2023 projections of how much the Greenland ice sheet may shrink from its present extent by the year 2300 under the worst possible climate change scenario (upper half) and of how much faster its remaining ice will be flowing in that case (lower half)[50]
This section is an excerpt from Greenland ice sheet.[edit]

The Greenland ice sheet is an ice sheet which forms the second largest body of ice in the world. It is an average of 1.67 km (1.0 mi) thick and over 3 km (1.9 mi) thick at its maximum.[51] It is almost 2,900 kilometres (1,800 mi) long in a north–south direction, with a maximum width of 1,100 kilometres (680 mi) at a latitude of 77°N, near its northern edge.[52] The ice sheet covers 1,710,000 square kilometres (660,000 sq mi), around 80% of the surface of Greenland, or about 12% of the area of the Antarctic ice sheet.[51] The term 'Greenland ice sheet' is often shortened to GIS or GrIS in scientific literature.[53][54][55][56]

If all 2,900,000 cubic kilometres (696,000 cu mi) of the ice sheet were to melt, it would increase global sea levels by ~7.4 m (24 ft).[51] Global warming between 1.7 °C (3.1 °F) and 2.3 °C (4.1 °F) would likely make this melting inevitable.[56] However, 1.5 °C (2.7 °F) would still cause ice loss equivalent to 1.4 m (4+1⁄2 ft) of sea level rise,[57] and more ice will be lost if the temperatures exceed that level before declining.[56] If global temperatures continue to rise, the ice sheet will likely disappear within 10,000 years.[58][59] At very high warming, its future lifetime goes down to around 1,000 years.[60]

Beneath the Greenland ice sheet are mountains and lake basins.
This section is an excerpt from Climate change in Antarctica.[edit]
The West Antarctic ice sheet is likely to completely melt[61][62] unless temperatures are reduced by 2 °C (3.6 °F) below 2020 levels.[63] The loss of this ice sheet would take between 500 and 13,000 years.[64][65] A sea-level rise of 3.3 m (10 ft 10 in) would occur if the ice sheet collapses, leaving ice caps on the mountains, and 4.3 m (14 ft 1 in) if those ice caps also melt.[66] The far-stabler East Antarctic ice sheet may only cause a sea-level rise of 0.5 m (1 ft 8 in) – 0.9 m (2 ft 11 in) from the current level of warming, a small fraction of the 53.3 m (175 ft) contained in the full ice sheet.[67] With global warming of around 3 °C (5.4 °F), vulnerable areas like Wilkes Basin and Aurora Basin may collapse over around 2,000 years,[64][65] potentially adding up to 6.4 m (21 ft 0 in) to sea levels.[68]

Decline of glaciers

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This section is an excerpt from Retreat of glaciers since 1850.[edit]
Alaska's McCarty Glacier retreated about 15 kilometres (9.3 mi) in less than a century, and dense, diverse vegetation has become established on the slopes.[69]

The retreat of glaciers since 1850 is a well-documented effect of climate change. The retreat of mountain glaciers provides evidence for the rise in global temperatures since the late 19th century. Examples include mountain glaciers in western North America, Asia, the Alps in central Europe, and tropical and subtropical regions of South America and Africa. Since glacial mass is affected by long-term climatic changes, e.g. precipitation, mean temperature, and cloud cover, glacial mass changes are one of the most sensitive indicators of climate change. The retreat of glaciers is also a major reason for sea level rise. Excluding peripheral glaciers of ice sheets, the total cumulated global glacial losses over the 26 years from 1993 to 2018 were likely 5500 gigatons, or 210 gigatons per year.[70]: 1275 

On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions. Glaciers also exist in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand. Glacial bodies larger than 50,000 km2 (19,000 sq mi) are called ice sheets.[71] They are several kilometers deep and obscure the underlying topography.

Sea ice decline

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This section is an excerpt from Effects of climate change § Sea ice decline.[edit]
Reporting the reduction in Antarctic sea ice extent in mid 2023, researchers concluded that a "regime shift" may be taking place "in which previously important relationships no longer dominate sea ice variability".[72]

Sea ice reflects 50% to 70% of the incoming solar radiation back into space. Only 6% of incoming solar energy is reflected by the ocean.[73] As the climate warms, the area covered by snow or sea ice decreases. After sea ice melts, more energy is absorbed by the ocean, so it warms up. This ice-albedo feedback is a self-reinforcing feedback of climate change.[74] Large-scale measurements of sea ice have only been possible since satellites came into use.[75]

Sea ice in the Arctic has declined in recent decades in area and volume due to climate change. It has been melting more in summer than it refreezes in winter. The decline of sea ice in the Arctic has been accelerating during the early twenty-first century. It has a rate of decline of 4.7% per decade. It has declined over 50% since the first satellite records.[76][77][78] Ice-free summers are expected to be rare at 1.5 °C (2.7 °F) degrees of warming. They are set to occur at least once every decade with a warming level of 2 °C (3.6 °F).[79]: 8  The Arctic will likely become ice-free at the end of some summers before 2050.[80]: 9 

Sea ice extent in Antarctica varies a lot year by year. This makes it difficult to determine a trend, and record highs and record lows have been observed between 2013 and 2023. The general trend since 1979, the start of the satellite measurements, has been roughly flat. Between 2015 and 2023, there has been a decline in sea ice, but due to the high variability, this does not correspond to a significant trend.[81]

Permafrost thaw

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This section is an excerpt from Permafrost § Impacts of climate change.[edit]
Recently thawed Arctic permafrost and coastal erosion on the Beaufort Sea, Arctic Ocean, near Point Lonely, Alaska in 2013.

Snow cover decrease

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Shrinkage of snow cover duration in the Alps, starting ca. end of the 19th century, highlighting climate change adaptation needs[82]

Studies in 2021 found that Northern Hemisphere snow cover has been decreasing since 1978, along with snow depth.[83] Paleoclimate observations show that such changes are unprecedented over the last millennia in Western North America.[84][85][83]

North American winter snow cover increased during the 20th century,[86][87] largely in response to an increase in precipitation.[88]

Because of its close relationship with hemispheric air temperature, snow cover is an important indicator of climate change.[citation needed]

Global warming is expected to result in major changes to the partitioning of snow and rainfall, and to the timing of snowmelt, which will have important implications for water use and management.[citation needed] These changes also involve potentially important decadal and longer time-scale feedbacks to the climate system through temporal and spatial changes in soil moisture and runoff to the oceans.(Walsh 1995). Freshwater fluxes from the snow cover into the marine environment may be important, as the total flux is probably of the same magnitude as desalinated ridging and rubble areas of sea ice.[89] In addition, there is an associated pulse of precipitated pollutants which accumulate over the Arctic winter in snowfall and are released into the ocean upon ablation of the sea ice.[citation needed]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Cryosphere

View on Grokipedia
from Grokipedia
The cryosphere denotes those portions of Earth's surface where water exists in solid form, encompassing ice sheets, glaciers, ice caps, permafrost, sea ice, frozen lakes and rivers, and seasonal snow cover. This frozen subsystem of the Earth system covers variable extents seasonally, reaching a maximum area of approximately 78 million square kilometers in January and a minimum of 59 million square kilometers in August, primarily influencing global climate through its high albedo that reflects incoming solar radiation and thereby moderates planetary temperatures. The cryosphere stores roughly 70% of Earth's freshwater, with the Antarctic and Greenland ice sheets holding the vast majority of this volume—equivalent to over 58 meters of potential sea-level rise if fully melted—while also regulating ocean circulation, supporting ecosystems, and providing freshwater to billions via glacial melt and snowmelt. Empirical observations from satellite altimetry and ground measurements reveal ongoing mass losses in land ice components, particularly from Greenland and Antarctic ice sheets, alongside fluctuations in sea ice extent and permafrost thaw, which amplify climate feedbacks through reduced albedo and methane release, though regional variations persist due to natural forcings like atmospheric circulation patterns.

Definition and Fundamentals

Definition and Scope

The cryosphere comprises those parts of Earth's surface where is in frozen form, including continental ice sheets, glaciers, , seasonal cover, river and lake ice, and . This frozen realm exists under sub-zero temperatures that maintain 's solid state, distinguishing it from liquid or vapor phases in the broader . The term "cryosphere" derives from "kryos," signifying cold, frost, or ice, combined with "sphaira," meaning globe or sphere, thus denoting the planet's cold, icy envelope. Geographically, the cryosphere spans polar regions, high mountain chains, and even mid-latitude areas during winter, occurring in roughly one hundred countries across all latitudes, though concentrated in the , , and alpine zones. Permanent ice from glaciers and ice sheets covers about 10% of Earth's land area, while seasonal elements like and expand its temporary footprint significantly. These components interact dynamically with the atmosphere, oceans, and land, influencing global energy balance through high and freshwater storage—holding approximately 70% of Earth's freshwater reserves. The scope excludes atmospheric ice like clouds or hail, focusing solely on surface and near-surface frozen water, which varies in scale from vast ice sheets (spanning 14 million km²) to transient river ice formations. This delineation underscores the cryosphere's role as a distinct subsystem within Earth's machinery, responsive to forcings yet integral to long-term hydrological cycles.

Terminology and Classification

The term cryosphere originates from the Greek word krios, meaning "icy cold," and denotes the portions of Earth's surface where water exists in solid form due to temperatures at or below 0°C, encompassing all frozen elements of the hydrologic cycle. This includes both perennial and seasonal features, such as ice sheets covering vast continental areas and transient snow accumulations. Key components are defined by their physical state, location, and persistence. Ice sheets are expansive masses of land-based ice exceeding 50,000 km² in area, exemplified by the Antarctic and Greenland ice sheets, which store over 70% of Earth's freshwater as ice. Glaciers and ice caps, smaller than ice sheets, consist of compacted snow that deforms and flows under its own weight; ice caps are distinguished as those under 50,000 km², often atop mountains or plateaus. Sea ice forms from frozen seawater in polar oceans, freezing at approximately -1.8°C due to salinity effects, and is categorized by age into first-year (one season) and multi-year ice. Permafrost refers to ground remaining below 0°C for at least two consecutive years, underlying about 24% of the Northern Hemisphere's land surface, while seasonally frozen ground thaws annually above a permafrost active layer. Snow cover arises from precipitated ice crystals, providing insulation and high albedo, whereas lake and river ice covers freshwater bodies in colder regions. Classification schemes typically divide the cryosphere into terrestrial and marine domains to reflect interactions with land and systems. Terrestrial components include land ice (glaciers, ice sheets, ice caps), (permafrost and seasonal frost), and snow cover, which dominate freshwater storage and continental . Marine components, primarily , influence circulation and atmospheric heat exchange without contributing to sea-level rise upon melting, unlike land ice. Additional categorizations consider —perennial (e.g., ice sheets, ) versus seasonal (e.g., snow cover, river ice)—or by form, such as freshwater ice (lakes, s) distinct from saline . These distinctions aid in monitoring cryospheric responses to temperature variations, with organizations like the Global Cryosphere Watch standardizing terminology across components including , freshwater ice, glaciers, ice sheets, and .

Physical Properties

Thermal and Mechanical Properties

Ice in the cryosphere exhibits distinct properties that influence and phase changes. Pure ice has a of approximately 2.097 J/g/K at 0°C, decreasing to 1.741 J/g/K at -50°C, which is roughly half that of liquid . Its thermal conductivity is about 2.3 W/m/K, enabling efficient conduction compared to air but varying with impurities and . The of fusion for is 334 kJ/kg, absorbing significant during without change, a critical to cryospheric balances. Snow and firn display lower thermal conductivities due to their porous structures, acting as insulators. 's thermal conductivity ranges from 0.33 to 0.47 W/m/, with a median of 0.39 W/m/ in Arctic conditions, reducing heat flux from underlying surfaces to the atmosphere by up to orders of magnitude relative to bare ground. , transitional between snow and , has conductivity increasing with density, reaching up to 2.4 W/m/ at ice densities, affecting in ice sheets. incorporates brine pockets, lowering effective conductivity and altering transfer during freeze-thaw cycles. In permafrost regions, snow cover's insulation preserves ground by limiting winter conductive heat loss, with conductivity schemes varying by snow type influencing modeled permafrost stability. Mechanically, cryospheric ice behaves as a viscoelastic material, combining elastic, delayed elastic, and viscous responses under stress. Glacier ice deforms primarily through creep, following Glen's flow law where strain rate is proportional to the third power of deviatoric stress, enabling slow plastic flow over geological timescales. At low strain rates, viscous creep dominates, while higher rates induce brittle fracture or elastic behavior, as seen in sea ice floe interactions. Polycrystalline ice strength depends on grain size, fabric, and temperature; colder ice (-50°C) resists deformation more than temperate ice near 0°C due to reduced dislocation mobility. Brine inclusions in sea ice weaken mechanical integrity, promoting frictional sliding and ridging under compressive forces. These properties govern cryospheric dynamics, from glacier surging to sea ice pack deformation, with flow laws calibrated against laboratory data spanning 70 years confirming non-linear viscous rheology for ice sheets.

Extent, Volume, and Residence Time

The cryosphere encompasses diverse frozen components with varying spatial extents. The covers approximately 14 million km², while the spans about 1.71 million km². Glaciers and ice caps outside these major ice sheets occupy roughly 706,000 to 726,000 km² globally. underlies 14 to 23 million km² in the , representing 15% to 24% of exposed land there. extent varies seasonally: averages 14-15 million km² at winter maximum and 4-5 million km² at summer minimum, while reaches 17-18 million km² maximum and 2-3 million km² minimum. snow cover averages 24 million km² annually. Ice volumes are dominated by continental ice sheets. The holds about 26.5 million km³, equivalent to 58 meters of global if fully melted. The contains approximately 2.9 million km³, corresponding to 7.4 meters equivalent. Glaciers outside ice sheets store 158,000 to 170,000 km³, or 0.32 to 0.4 meters equivalent after adjusting for below sea level. Sea ice volumes are smaller and seasonal, with Arctic peaks around 15,000-20,000 km³ and Antarctic higher but variable. ground ice volume is estimated in tens of thousands of km³ but dispersed in soil. Total land ice volume exceeds 29 million km³, primarily from ice sheets. Residence times differ markedly across components, reflecting formation and persistence timescales. Snow cover persists seasonally, from days to months. has residence times of 1 to 10 years, with first-year ice turning over annually and older multi-year ice rarer. Glaciers exhibit decadal to centennial turnover, depending on size and location. Ice sheets involve millennial to multimillennial scales, with deep interior ice aged tens of thousands of years. can remain frozen for thousands to millions of years, though active layer thaws annually. These timescales influence cryospheric responses to climatic forcing, with shorter-residence elements more sensitive to annual variations.

Surface Properties

The surfaces of cryospheric components exhibit high , typically reflecting 50% to 90% of incoming solar , which plays a critical role in Earth's energy balance by limiting absorption of shortwave . Fresh albedo ranges from 0.80 to 0.90, while snow-covered can reach up to 0.90, enhancing reflectivity compared to bare ice. Bare albedo is generally 0.65 to 0.70, decreasing to 0.5 or lower during melt seasons due to , grain , and impurities like that reduce reflectivity. Albedo variations are influenced by factors such as , surface microstructure, and , with small-scale roughness potentially lowering total albedo by up to 0.10 through increased multiple and trapping of light. Aerodynamic , quantified by the z0z_0, governs and exchange between the cryosphere and atmosphere, affecting turbulent fluxes in models of evolution and ice-atmosphere interactions. For fresh under rough flow conditions, z0z_0 averages approximately 0.24 mm, while smoother surfaces like interior ice sheets exhibit values as low as 10−410^{-4} m, escalating to 10−110^{-1} m over hummocky or sastrugi-formed terrain. These parameters are derived from field measurements and data, underscoring the need for site-specific parameterization in simulations, as dynamic roughness alters thermal profiles and rates. In the thermal , cryospheric surfaces display high , approximating blackbody behavior and facilitating efficient longwave radiation emission. and reaches 0.98 to 0.99, enabling accurate retrieval of surface skin temperatures from sensors, though values vary slightly with , viewing angle, and contaminants. This property contrasts with lower microwave emissivities used in detection, highlighting wavelength-dependent radiative behavior essential for and energy budget calculations.

Components of the Cryosphere

Glaciers and Ice Sheets

Glaciers form where the accumulation of exceeds melting and sublimation over multiple years, leading to the compaction of snow into that deforms plastically and flows downslope under its own weight due to . This flow occurs through internal deformation of crystals and basal sliding over the underlying , with rates varying from centimeters to hundreds of meters per year depending on , thickness, and . Ice sheets represent the largest class of glaciers, defined as contiguous ice masses exceeding 50,000 km² that blanket entire continents or large islands, overriding underlying and spreading radially outward from high-elevation domes. The two extant ice sheets are the and the , which together store approximately 68% of global and influence regional climate through effects and freshwater discharge. The covers about 13.61 million km², encompassing nearly 98% of the , with an average thickness of 1.9 km and maximum depths exceeding 4.5 km in . Its volume totals roughly 26.5 million km³, equivalent to 58.3 meters of global mean if fully melted. The , comprising 80% of the total, is largely stable or gaining mass in interior regions due to increased snowfall, while the shows greater variability and net loss primarily from enhanced calving and surface melting. assessments from altimetry, , and input-output methods indicate a net loss of 2,720 ± 1,390 gigatons from 1992 to 2020, with the rate accelerating to 142 ± 49 Gt yr⁻¹ in the , though uncertainties remain high due to challenges in partitioning accumulation changes and oceanic forcing. These losses contribute to but are modulated by compensatory snowfall increases linked to warmer atmospheric moisture capacity. The spans 1.71 million km², with an average thickness of 1.6 km and maxima up to 3.4 km near the summit. Its volume is approximately 2.96 million km³, corresponding to 7.4 meters of equivalent. Unlike , experiences significant surface in summer, amplified by feedback from melt ponds, with mass loss dominated by runoff (about 50%) and calving (about 50%) in recent decades. The Inter-comparison Exercise (IMBIE) reports a cumulative loss of 4,890 Gt from 1992 to 2020, with an average rate of 169 Gt yr⁻¹ increasing to 234 Gt yr⁻¹ after , driven by marine-terminating outlet glaciers' rapid retreat and thinning. Interior accumulation has risen slightly from enhanced , offsetting some peripheral losses, but net imbalance persists, with gravimetric data confirming acceleration linked to submarine from Atlantic Water intrusion. Beyond ice sheets, glaciers number approximately 215,000 worldwide outside and , covering a total area of about 680,000 km² as of inventories from the early , though ongoing retreat has reduced this extent. These include valley glaciers, ice caps, and piedmont glaciers primarily in mountain ranges like the , , , and , where they respond sensitively to and changes. Global glacier mass loss averaged -1.0 m water equivalent per year from 2000 to 2019, totaling over 21,000 Gt, equivalent to 58 mm of , with acceleration in low-latitude regions due to reduced accumulation and increased melt. Observations from repeat airborne and satellite surveys, such as those by NASA's Oceans Melting (OMG) mission, highlight causal drivers including black carbon deposition lowering and geothermal beneath thin ice. Regional variations exist, with some temperate glaciers showing surging behavior from hydrological feedbacks, underscoring that is not uniformly negative but governed by local and .
Major Ice MassesArea (million km²)Volume (million km³)Sea Level Equivalent (m)Primary Mass Loss Mechanism
13.6126.558.3Calving and basal melt
1.712.967.4Surface melt and calving
Non-polar Glaciers0.680.240.63Surface
Glacial dynamics involve a zone of accumulation at higher elevations feeding a zone of lower down, with equilibrium maintained when annual inputs balance outputs; disequilibrium leads to advance or retreat. For s, divide structures into slow-flowing interiors and fast-flowing margins via ice streams, where enhanced basal lubrication from subglacial accelerates discharge. Empirical data from GPS and seismic networks reveal that stability hinges on and grounding line position, with marine-based sectors vulnerable to unstable retreat if temperatures rise, as evidenced by paleo-records of past collapses. However, first-principles modeling indicates that snowfall accumulation, which scales with atmospheric , can counteract melt in a warming world up to certain thresholds, challenging simplistic narratives of inevitable disintegration.

Sea Ice

Sea ice consists of frozen that forms and floats on the surface in polar regions. It develops through the freezing of , which occurs at temperatures below -1.8°C due to the presence of salts, lower than the freezing point of pure at 0°C. This process rejects , creating a porous structure with lower than the underlying , typically around 4-5 parts per thousand compared to 's 35. Sea ice exhibits pronounced seasonal variability, expanding during winter and contracting in summer in both the and . In the , which is semi-enclosed, sea ice reaches its maximum extent in March, covering up to 14-16 million square kilometers historically, and minimum in . The , surrounding the , sees maximum extent in , historically around 18-20 million square kilometers, and minimum in . Multi-year ice persists in the , while is predominantly annual. Physically, has a of about 920 kg/m³, causing it to float with roughly 10% above . Thickness varies from thin nilas (centimeters) to deformed ridges exceeding 10 meters, though average thickness is 1-3 meters and 0.5-1 meter. Its high , ranging from 0.5 to 0.7 for snow-covered ice, contrasts sharply with the ocean's 0.06, reflecting most incoming solar radiation. also insulates the underlying ocean, limiting winter heat loss to the atmosphere by up to 90%. Observed trends show sea ice extent declining markedly since satellite records began in 1979, with summer minima decreasing at approximately 13% per decade. The 2025 maximum extent on March 22 was the lowest in the 47-year record, while the September minimum of 4.60 million square kilometers ranked among the ten lowest. trends were modestly positive until the mid-2010s but have since shown variability with recent record lows; the 2025 maximum of 17.81 million square kilometers on September 30 was the third lowest on record. Volume estimates indicate losses exceeding 50% since 1979, driven primarily by thinning. In the , modulates energy exchanges by enhancing planetary , reducing absorbed solar heat in polar regions. Its retreat amplifies warming via the ice-albedo feedback, where exposed darker ocean absorbs more radiation, further melting ice. Additionally, formation drives through brine rejection, producing dense water that sinks and contributes to global ocean overturning. It barriers wind-driven mixing and influences atmospheric moisture and salinity fluxes.

Permafrost and Frozen Ground

consists of , sediment, rock, and included or organic material that remains at or below 0°C continuously for at least two consecutive years. This perennial frozen state distinguishes it from seasonally , which thaws annually and freezes for more than 15 days per year, or intermittently frozen ground that freezes for fewer than 15 days. Above the lies the active layer, a surface zone that thaws during summer and refreezes in winter, typically ranging from 30 cm to several meters in depth depending on , , and properties. Permafrost underlies approximately 14 to 16 million km² of the Northern Hemisphere's exposed land surface, equivalent to about 15% of the total, with continuous in polar regions and discontinuous or sporadic zones toward lower latitudes and elevations. It also occurs in subsea s beneath continental shelves, high mountain ranges like the and Rockies, and limited areas in . Ground within permafrost exists in forms such as pore filling voids, segregated lenses formed by migration, and massive wedges or blocks resulting from contraction cracks. content varies widely, from ice-poor dry permafrost to ice-rich layers exceeding 90% volume by weight in some lowlands, influencing stability and thaw susceptibility. Permafrost regions store an estimated 1,460 to 1,700 petagrams of organic carbon, roughly twice the amount currently in Earth's atmosphere, accumulated over millennia in frozen soils and . Thawing , driven by rising air temperatures, can release this carbon as and through microbial decomposition, potentially amplifying global warming, while also causing ground , thermokarst lake formation, and infrastructure instability in affected areas. Recent observations indicate active layer thickening and permafrost temperature increases of up to 0.3–0.4°C per decade in continuous zones since the .

Snow Cover and Seasonal Ice

Snow cover constitutes the seasonal accumulation of solidified on terrestrial surfaces, forming a transient yet extensive component of the cryosphere that influences regional , , and energy budgets. In the , where the majority of seasonal occurs, maximum extent typically reaches 46 to 47 million square kilometers during , covering roughly 10% of the land surface and spanning and . Minimum extent contracts to about 2 million square kilometers by late summer, primarily residual in high-latitude or high-elevation regions. snow cover remains limited, averaging 0.5 to 2 million square kilometers annually, concentrated in the , , and coastal areas during austral winter. Satellite observations, initiated in 1967 by NOAA and processed by Rutgers University's Global Snow Lab, provide the primary record of Northern Hemisphere snow cover extent (SCE), combining weekly charts from 1967 to 1999 with daily visible-band imagery thereafter. These data reveal a pronounced seasonal cycle, with accumulation driven by winter precipitation and ablation governed by spring warming, resulting in snow persistence durations of 100 to 250 days across mid-to-high latitudes. Regional variations are stark: Eurasia hosts over 60% of NH maximum SCE due to vast continental interiors, while North American cover correlates more closely with mid-latitude storm tracks. Snow water equivalent (SWE), a measure of stored water volume, peaks at 200 to 500 millimeters in continental interiors but exhibits high interannual variability tied to precipitation anomalies. Seasonal ice, encompassing ephemeral formations such as ice crusts, depth hoar layers within snowpacks, and aufeis (spring-fed ice sheets in permafrost margins), integrates with snow cover to modulate subsurface heat exchange and runoff. These features arise from freeze-thaw cycles, with ice lenses forming via capillary action in porous snow or soil, enhancing structural stability but accelerating melt through insulation effects. In Arctic and subarctic zones, seasonal ground ice contributes to active layer dynamics, thawing annually to depths of 0.3 to 2 meters while preserving underlying permafrost. Observational trends from 1981 to 2018 indicate negative SCE anomalies in the across all months, with rates exceeding 50,000 square kilometers per year in , , , and May, attributed to warmer spring temperatures advancing melt onset by 1 to 2 weeks per decade in many regions. mass, a proxy for pre-melt storage, declined 4.3% per decade through 2016, reflecting reduced accumulation efficiency amid variable precipitation. However, annual maximum SCE exhibits relative stability since the 1970s, with fluctuations linked to large-scale modes like the North Atlantic Oscillation rather than monotonic decline. These patterns underscore snow cover's sensitivity to hemispheric circulation shifts, with low-elevation sites showing more pronounced reductions than high-elevation refugia. Monitoring continues via passive microwave sensors (e.g., SSM/I) for all-weather SWE estimates and MODIS optical data for fractional cover, enabling detection of sub-grid variability down to 500-meter resolution.

Lake and River Ice

Lake and river forms on inland water bodies in regions where sustained subfreezing air s cause surface cooling and eventual solidification, typically in the Northern Hemisphere's higher latitudes and altitudes. This seasonal cover influences local heat exchange, hydrological regimes, and ecosystems by insulating water from atmospheric conditions during winter. Unlike perennial cryospheric components such as glaciers, lake and undergoes annual freeze-up, maximum extent, and break-up cycles driven primarily by air thresholds around 0°C, modulated by factors like water depth, currents, snowfall, and solar radiation. The phenological cycle begins with freeze-up, when ice nucleation spreads across the surface, often starting in shallow margins and progressing inward; this process can take days to weeks depending on and . Maximum thickness, typically 0.5–2 meters in temperate lakes and thinner on fast-flowing rivers, accumulates through thermodynamic growth and snow loading before break-up initiates via rising temperatures, , and mechanical forces like wave action or ice jams. duration varies regionally: in zones, it spans 4–6 months, while in milder climates like the , it averages 2–3 months with interannual variability tied to winter severity. Historical records, compiled in databases like the Global Lake and River Ice Database encompassing 865 sites, reveal consistent trends toward diminished ice seasons across the . Analysis of 3510 from 678 water bodies indicates later freeze-up dates by approximately 1–2 days per decade and earlier break-up by 2–3 days per decade over the , shortening ice-covered periods by 2–5 days per decade on average. Longer paleorecords, some extending to the , show initial reductions in ice cover accelerating post-1850, with a notable regime shift in North American lakes around the late 1980s coinciding with amplified warming. For rivers, 56% of monitored segments exhibit delayed freeze-up by 2.7 days per decade, though trends are less uniform due to hydrological influences like . Monitoring employs a mix of in-situ observations, such as thermistor chains and visual logs, alongside techniques including passive microwave radiometry for freeze-thaw detection and (SAR) for mapping ice extent and thickness. datasets, like ESA's Initiative lake records since 2001, provide near-global coverage at resolutions down to 250–500 meters, enabling daily tracking of phenology. Web-based cameras and unmanned aerial vehicles supplement these for real-time river ice dynamics, particularly jam formation risks. These methods confirm ongoing declines, with projections under warming scenarios estimating 10–28 additional days of loss per century in vulnerable regions.

Role in Global Systems

Climate Feedbacks

The exerts significant influence on Earth's through various feedback mechanisms, predominantly positive ones that amplify warming. These feedbacks arise from interactions between , , , and atmospheric processes, altering energy balances and concentrations. Empirical observations and modeling indicate that reductions in cryospheric extent enhance , with changes and carbon releases contributing substantially to global temperature sensitivity. A primary feedback is the ice-albedo effect, where melting of high-albedo surfaces like sea ice and snow exposes darker ocean or land, increasing solar absorption and accelerating melt. In the Arctic, sea ice loss has decreased regional albedo by approximately 3% per decade in August, intensifying local warming through this positive loop. Ice sheet-albedo feedback alone amplifies the total climate feedback parameter by 42%, equivalent to 0.55 W/m² per Kelvin of warming. Cloud-albedo interactions further enhance Greenland Ice Sheet sensitivity in recent climate models. Permafrost thaw triggers a carbon feedback by releasing stored as CO₂ and CH₄ upon , potentially adding 6 to 118 petagrams of carbon by 2100 under varying scenarios. This process is gradual, spanning decades to centuries, and is regulated by , carbon quantity, and content, with abrupt thaw events exacerbating emissions in vulnerable regions like . Such releases could reduce carbon budgets for limiting warming to 1.5°C or 2°C by up to 20-22%. Additional feedbacks include ice sheet elevation changes, where surface lowering reduces atmospheric lapse rates, exposing to warmer air and hastening mass loss, as seen in simulations. Sea ice decline also perturbs ocean circulation and moisture fluxes, potentially altering and hemispheric energy transport. While some negative feedbacks exist, such as increased freshwater stabilizing stratification, positive mechanisms dominate, contributing to observed since the 20th century.

Hydrological and Biogeochemical Cycles

The cryosphere constitutes a primary in the Earth's hydrological cycle, storing roughly 69% of global freshwater, with the and ice sheets alone accounting for over 68% of this total. Glaciers, seasonal cover, and further regulate water distribution by sequestering in solid form and releasing it via melt processes, which influence discharge, infiltration, and ocean salinity gradients. In high-latitude and mountain catchments, cryospheric melt synchronizes peak freshwater availability with periods of highest demand, such as summer low- seasons, thereby stabilizing downstream hydrologic regimes. Seasonal snowpacks, in particular, accumulate winter snowfall—equivalent to 10-20% of annual in many mid-latitude basins—and release it gradually in spring, functioning as a temporal buffer that supports , , and ecosystems for more than one-sixth of the world's population. Glacial melt contributes to proglacial rivers, with rates varying by region; for instance, in the Hindu Kush-Himalaya, it supplies 10-30% of annual discharge to major rivers like the Indus and during dry months. Perturbations, such as earlier or glacier mass loss, observed at rates of 200-300 Gt per year globally since the 1990s, can advance peak runoff timing by 1-4 weeks, compressing the and increasing risks while exacerbating late-season deficits. In biogeochemical cycles, the cryosphere exerts control over carbon storage and flux, with permafrost soils containing an estimated 900-1,000 Gt of organic carbon in the upper 3 meters alone, vulnerable to upon thaw. Thawing exposes this material to microbial oxidation, releasing CO₂ and CH₄; field measurements indicate efflux rates of 1-2 Gt C per year from permafrost regions, with deeper destabilization potentially mobilizing additional hundreds of Gt over centuries. modulates ocean carbon uptake by limiting vertical mixing and , reducing CO₂ solubility in underlying waters during winter expansion; its decline correlates with enhanced but variable net due to stratification effects. Glacial meltwaters deliver micronutrients like bioavailable iron (Fe) and manganese (Mn) to coastal oceans via sediment-laden runoff, fertilizing phytoplankton blooms in high-nutrient, low-Fe environments such as the Southern Ocean, where inputs from icebergs alone may supply 0.1-0.5 μmol Fe per liter in melt plumes. However, retreating tidewater glaciers reduce fine-particle ("rock flour") production from bedrock abrasion, potentially lowering nutrient concentrations in discharge by 20-50% per unit volume, as evidenced by Alaskan fjord observations from 2010-2020. Permafrost degradation further perturbs nitrogen and phosphorus cycles, with thaw mobilizing 10-50 kg N per hectare annually into Arctic rivers, elevating export to shelves and risking downstream eutrophication. These dynamics underscore the cryosphere's dual role as stabilizer and potential amplifier in elemental cycling, contingent on thaw extent and microbial response rates.

Sea Level and Ocean Dynamics

The land-based components of the cryosphere, principally glaciers and ice sheets, drive barystatic sea level rise by transferring solid ice mass into ocean water upon melting, distinct from steric rise caused by thermal expansion of seawater. Sea ice, being afloat, contributes negligibly to global mean sea level changes, as its melt displaces equivalent volume without net mass addition. Empirical assessments from satellite gravimetry, such as NASA's GRACE-FO mission, quantify ice sheet mass losses as a primary barystatic driver: the Greenland Ice Sheet averaged 266 ± unknown gigatons per year (Gt/yr) of net loss in recent years, equating to approximately 0.73 mm/yr of sea level equivalent after accounting for the conversion factor of roughly 362 Gt per mm. The Antarctic Ice Sheet contributed an average of 135 Gt/yr, or about 0.37 mm/yr. Glaciers and ice caps outside the major sheets add another ~0.7 mm/yr collectively, making land cryosphere melt responsible for over half of barystatic rise, which forms roughly 40-50% of total observed global mean sea level increase (around 3.7 mm/yr from 2006-2018). Variability persists; for instance, Greenland's 2024 mass loss dropped to 55 ± 35 Gt due to elevated snowfall, the lowest since 2013, underscoring the role of precipitation in modulating annual balances. Cryospheric meltwater inputs influence dynamics by injecting low-salinity freshwater into high-latitude surface layers, reducing and promoting stratification that inhibits vertical mixing and deep-water formation. In the and North Atlantic, this freshening—exacerbated by both land ice discharge and melt—alters the , potentially weakening the Atlantic Meridional Overturning Circulation (AMOC) by limiting convective sinking of saline water. Observations indicate Arctic surface declines of 0.1-0.5 practical salinity units per decade in recent decades, correlating with increased runoff and loss, which sustains shallower haloclines and shifts transport patterns. Antarctic contributions, though smaller in freshwater volume, similarly affect Weddell and polynyas, where melt-driven circulation enhances basal melting under ice shelves while exporting freshwater southward, influencing overturning and global carbon uptake efficiency. These perturbations propagate via wave adjustments, with modeled and observed responses showing reduced poleward fluxes in stratified scenarios, though empirical quantification remains challenged by sparse polar observations and model uncertainties in eddy-resolving simulations.

Historical Evolution

Geological Timescales

The cryosphere has exhibited episodic expansions and contractions over Earth's 4.5 billion-year history, primarily during periods of driven by factors such as atmospheric CO₂ drawdown, continental configurations, and orbital variations. for ancient glaciations derives from sedimentary deposits including tillites, striated pavements, and dropstones in rock records, corroborated by oxygen ratios in marine sediments indicating expanded ice volumes. The oldest documented glaciations occurred during the Huronian Supergroup in , dated to approximately 2.4 to 2.1 billion years ago (Ga), associated with the that reduced greenhouse gases via oxygen-mediated weathering. In the Neoproterozoic Era, the Cryogenian Period (720 to 635 million years ago, Ma) featured severe "" events, with the spanning roughly 720 to 660 Ma and the Marinoan from 650 to 635 Ma, evidenced by equatorial glacial deposits and cap carbonates signaling rapid post-glacial warming. These episodes involved near-global ice cover, potentially down to at low latitudes, as inferred from geological proxies like banded iron formations and paleomagnetic data. Paleozoic glaciations included the Late (around 450 to 440 Ma) and the extensive Carboniferous-Permian () Ice Age (360 to 260 Ma), linked to supercontinent assembly () and vascular plant evolution enhancing silicate weathering, with tillites preserved across southern continents. Mesozoic records show minimal cryospheric persistence, with hothouse conditions limiting ice to transient mountain glaciers. The marks the establishment of modern polar cryosphere components, initiating the around 34 Ma with the onset of the , driven by opening, thermal isolation of , and declining CO₂ levels below 600 ppm, as evidenced by benthic foraminiferal δ¹⁸O shifts and fossil wood assemblages indicating permanent glaciation in by 33.7 Ma. glaciation emerged later, with initial alpine ice around 7-5 Ma in , intensifying to continental ice sheets by 3.3 to 2.7 Ma during the Pliocene-Pleistocene transition, tied to Panama Isthmus closure altering ocean circulation and further CO₂ decline. The Quaternary Period (2.58 Ma to present) encompasses 50+ glacial-interglacial cycles, with ice sheets covering up to 30% of land surface at maxima, reconstructed from cores and cosmogenic nuclides. and seasonal snow likely expanded concurrently with these glaciations, though direct geological evidence is sparser due to post-thaw erosion.

Paleoclimate Records from Cryosphere

Ice cores from polar ice sheets provide high-resolution paleoclimate records spanning hundreds of thousands of years, capturing temperature variations through stable isotopes like deuterium (δD) and oxygen-18 (δ¹⁸O), atmospheric composition via trapped gas bubbles, and dust flux as indicators of aridity. In Antarctica, the European Project for Ice Coring in Antarctica (EPICA) Dome C core extends to 800,000 years before present (BP), revealing eight glacial-interglacial cycles with temperature shifts of up to 10°C between cold stadials and warm interglacials, corroborated by CO₂ concentrations fluctuating between 180 and 300 ppm. Greenland cores, such as GISP2 and GRIP, offer records up to approximately 110,000 years BP with finer millennial-scale variability, including Dansgaard-Oeschger events characterized by abrupt warmings of 8-15°C over decades followed by gradual coolings. Glacial moraines and erratics serve as terrestrial proxies for past extents, dated via cosmogenic nuclides like ¹⁰Be to reconstruct timings of advances during cold phases. In tropical and mid-latitude regions, such as the and , chronologies indicate synchronized maxima around 20,000-18,000 years BP during the (LGM), aligning with global volume peaks and lowered sea levels of 120-130 meters. These records highlight regional responses to orbital forcings, with phases correlating to rising insolation and atmospheric CO₂, though local modulates response times. Permafrost sequences preserve multiproxy evidence of past ground thermal regimes, including ice-wedge polygons for extreme winter cold, fossil pollen for shifts, and stable isotopes in syngenetic ice for sources. Reconstructions from lowlands show widespread during the LGM, with rates exceeding 1 mm/year, but highly restricted near-surface during warmer interglacials like the Eemian (130,000-115,000 years BP), where proxy data indicate thaw depths exceeding modern limits. In alpine settings, lake sediments from the Last Interglacial reveal pollen assemblages suggesting warmer, wetter conditions with reduced ice-cemented , challenging models of uniform high-latitude freezing. Snow cover duration reconstructions, often derived from tree-ring width and maximum latewood density in high-elevation sensitive to melt-out dates, extend back several centuries to millennia. In the European Alps, a 600-year proxy from shrubs indicates that recent snowpack reductions since the mid-19th century are unprecedented in magnitude and persistence, with modeled durations declining by 20-30 days relative to the maxima around 1650-1850 CE. These proxies link shorter snow seasons to warmer springs, influencing regional and , though uncertainties arise from site-specific elevation effects and proxy calibration against instrumental data post-1834 CE.

Holocene Variations

The Holocene epoch (approximately 11,700 years ago to present) marked a transition from deglaciation to more stable but variable cryospheric conditions, driven primarily by orbital forcings, solar variability, and volcanic activity that modulated insolation and temperatures. Following the abrupt warming at the end of the stadial around 11,700 years (BP), continental ice sheets in the , including the Laurentide and Fennoscandian sheets, underwent rapid retreat, contributing to a global mean (GMSL) rise of about 40-50 meters by 7,000 BP. Glaciers in extratropical regions similarly diminished, with many mid-latitude systems, such as those in the and , approaching near-minimal extents during the Holocene Thermal Maximum (HTM, roughly 9,000-5,000 BP), when summer insolation peaked due to . This period saw reduced cryospheric coverage globally, with proxy records from moraines, cosmogenic nuclides (e.g., 10Be dating), and lake sediments indicating glacier fronts retreating to higher elevations or disappearing in some sectors. In polar regions, ice sheet dynamics reflected these trends: the (GrIS) experienced enhanced and thinning in its margins during the early-to-mid , contributing to GMSL elevations 2-3 meters above present levels around 6,000-4,000 BP, as evidenced by records and glacio-isostatic modeling. ice cores and marine sediments suggest the (WAIS) surface lowered by up to 500 meters since the early due to warmer seasonal temperatures, though overall volume remained relatively stable compared to the . reconstructions from biomarkers (e.g., IP25) and dinocysts indicate perennial Arctic persisted in key areas like the northern through the HTM, despite regional air temperatures 1-2°C warmer than today, implying wind-driven formation and ocean heat transport limited summer melt. In the sector of , cover showed contrasting patterns, with reduced coastal ice during warmer intervals but increased open-ocean extent tied to efficiency of katabatic winds and . Permafrost responded to early warming with widespread thaw in discontinuous zones, particularly in ; pollen and peat records from West Siberia document permafrost retreat and expansion by 10,000-8,000 , amplifying release via formation and woody shrub encroachment that reduced . By the mid-to-late , cooling trends associated with decreasing insolation fostered permafrost in northern s, with late- shrubification signaling stabilized frozen ground in continuous zones. Snow cover duration, reconstructed from tree-ring widths in the , exhibited millennial-scale variability, with shorter seasonal persistence during the HTM and extensions during Neoglacial cooling phases starting around 5,000 , correlating with glacier readvances. The late (post-5,000 BP) initiated the Neoglaciation, characterized by progressive glacier expansions in response to orbital-driven cooling and amplified by internal feedbacks like ice-albedo effects; advances culminated in the (circa 1450-1850 CE), when Alpine glaciers reached maximum extents, overtopping historical moraines and impounding new lakes, as dated by and historical records. extent likely increased during this interval, with proxy data showing thicker multi-year ice in the northern North Atlantic, though reconstructions remain sparse due to proxy limitations like biomarker sensitivity to open water. These variations underscore regional asynchronies—e.g., earlier HTM warmth in the versus delayed peaks in the —highlighting the role of ocean circulation (e.g., stability) and topography in modulating cryospheric responses to hemispheric forcings. Overall, cryosphere extents were often more limited than present during warm phases, challenging uniform anthropogenic attribution for recent changes. ![Holocene snow cover duration reconstruction for the Alps from tree-ring data][center]

Modern Observations and Monitoring

Measurement Methods and Advances

In-situ measurements form the foundation for cryosphere monitoring, providing direct data on properties such as ice velocity, snow density, and permafrost temperature. For glaciers and ice sheets, techniques include ablation stakes drilled into ice surfaces to track surface mass balance through periodic height and density measurements, often combined with GPS for velocity profiling. Permafrost monitoring relies on borehole thermistor strings, which record ground temperatures at depths from 10 to over 30 meters, enabling detection of thaw layers and thermal gradients; these are standardized for network-scale observations to ensure comparability across sites. Sea ice and lake/river ice studies employ ice coring for thickness and salinity profiles, supplemented by electromagnetic induction devices for rapid surveys. These methods, while precise at local scales, are labor-intensive and limited by logistical challenges in remote polar regions. Remote sensing has revolutionized cryosphere observations by enabling global, repetitive coverage. Optical and multispectral satellites, such as Landsat series, delineate extents and cover through reflectance analysis, achieving resolutions down to 15-30 meters. Microwave sensors provide all-weather capabilities: passive microwave radiometers like SSM/I measure concentration via brightness temperature differences, with extents defined at 15% threshold. (SAR) on platforms like detects ice deformation and ridging patterns insensitive to clouds or darkness. For mass and elevation, gravimetry via satellites tracks mass loss through monthly gravity field variations, revealing Greenland's net loss of about 280 Gt/year from 2002-2021. Altimetry missions measure height changes: CryoSat-2's radar altimeter derives freeboard and thickness by subtracting depth assumptions, with mean thicknesses around 1-2 meters in winter. Recent advances integrate multi-sensor data and novel techniques to enhance accuracy and resolve fine-scale processes. ICESat-2, launched in 2018, employs photon-counting lidar for sub-meter vertical precision, enabling first-time measurements of thin Arctic sea ice (<0.5 meters) and vegetation-penetrating canopy heights over permafrost. Drift-aware algorithms now correct sea ice thickness retrievals from CryoSat-2 by incorporating motion vectors, improving daily maps and reducing biases in dynamic regions; a 2025 method using Envisat/CryoSat data reconstructed Arctic thicknesses declining from 1.61 m in 1992 to 1.08 m in 2022. For permafrost, autonomous electrical resistivity tomography (A-ERT) and passive seismic interferometry offer non-invasive, continuous monitoring of thaw dynamics, complementing boreholes with spatial coverage over kilometers. Machine learning enhances data fusion, such as reconstructing continuous ice sheet elevations from 2003-2021 using Envisat, ICESat, and ICESat-2 inputs. Unmanned aerial vehicles (UAVs) bridge scales, providing high-resolution velocity fields, as demonstrated in 2020 Eqip Sermia Glacier surveys. These developments, validated against in-situ data, reduce uncertainties but highlight persistent challenges like snow depth estimation in altimetry, which can introduce 10-20% errors in thickness derivations. Satellite observations since document a pronounced decline in extent, particularly during summer minima, with September extents shrinking at a rate of 12.2% per decade relative to the 1981–2010 baseline. Multiyear ice has also decreased, remaining below pre-2005 levels despite short-term fluctuations. In the , extent exhibited a modest increase from to 2014, but transitioned to sharp declines thereafter, recording the four lowest minima in the satellite era from to 2025. Mountain glaciers globally have retreated since the end of the around 1850, with mass loss rates accelerating through the and reaching historically unprecedented levels in the early based on glaciological and geodetic records spanning over 5,200 observations since 1850. In the European Alps, retreat and downwasting intensified post-1980, while peripheral glaciers in doubled their retreat rates over the last two decades compared to the . The has experienced accelerating mass loss, shedding an average of 280 gigatons per year from 2002 to 2021 as measured by GRACE satellites, with rates increasing decade by decade into the . in the has warmed at 0.6°F per decade overall, with thaw accelerating in boreal regions since the mid-20th century, particularly in peatlands where late-century warming drove deeper active layers. Northern Hemisphere snow cover extent has trended downward since the mid-20th century, with spring declines most evident: April at 1.32% per decade, May at 4.1% per decade, and June at 12.95% per decade from 1967 to 2022. These observational trends reflect a transition from 20th-century variability to more consistent reductions in cryospheric components amid rising global temperatures, though regional exceptions persist, such as variable Antarctic sea ice dynamics.

Regional and Component-Specific Changes

In the , sea ice extent has declined markedly since satellite observations began in 1979, with the September 2024 minimum reaching 4.28 million square kilometers, the seventh lowest on record and 12.4% below the 1981-2010 average per decade trend. The March 2025 maximum extent set a record low, reflecting persistent thinning and loss of multi-year ice, which now constitutes less than 5% of the pack compared to over 25% in the 1980s. In contrast, extent has shown greater variability, with overall increases through the early 2010s but sharp declines since 2016, approaching record lows in 2024 austral summer minima. The has experienced accelerating mass loss, averaging 280 gigatons per year from 2002 to 2021 based on GRACE , contributing 0.8 millimeters annually to global , with 177 gigatons lost in 2023 alone due to enhanced surface melt and outlet dynamics. mass , per the 2023 IMBIE assessment covering 1992-2020, indicates cumulative losses of 2,671 gigatons, accelerating to 107 gigatons per year in the , though with regional gains in offsetting West Antarctic and Peninsula losses; 2023 saw a net loss of 57 gigatons. Global glaciers have lost mass at an accelerating rate, with annual losses averaging 335 billion tons over the past three decades per World Glacier Monitoring Service data, and 2023-2024 marking the highest three-year loss on record at over 80 gigatons above prior peaks, affecting all 19 monitored regions including the , , and . in the , covering about 12.5 million square kilometers as of the 2010s, has warmed at 0.3°C per decade since the 1980s, with thawing accelerating in the 2020s, leading to ground , coastal rates up to 1-2 meters per year in sites, and release of stored carbon equivalent to 30-85% of near-surface layers under 3°C global warming scenarios. Northern Hemisphere snow cover extent has trended downward, particularly in spring and summer, with declines of 1.32% per from 1967-2022 and losses exceeding 12% per , driven by earlier melt onset; 2024 November extent was slightly below average at 34.32 million square kilometers. Regional variations persist, such as stable or increasing winter in parts of amid overall hemispheric contraction.

Drivers of Variability and Change

Natural Drivers

Astronomical forcing through —variations in Earth's , (obliquity), and —drives long-term fluctuations in seasonal insolation, profoundly influencing cryosphere extent over tens to hundreds of thousands of years. These cycles initiate glacial-interglacial transitions by altering the distribution of solar radiation, particularly in the summers, which controls the buildup or retreat of continental s and glaciers; for instance, reduced summer insolation during periods of high and low obliquity promotes ice accumulation, as seen in paleoclimate records linking these forcings to Pleistocene ice volume changes of up to 70 meters in equivalent. The cryosphere responds with , where ice sheet margins exhibit multistability, requiring sustained insolation shifts to cross thresholds between expanded and contracted states. Solar variability, including cycles in total solar irradiance (TSI) such as the 11-year Schwabe cycle, modulates cryospheric parameters on decadal to centennial scales, though its global is modest at approximately 0.1–1 W/m² peak-to-peak. During low solar activity phases, like the (1645–1715), reduced TSI correlates with cooler temperatures and expanded snow cover or glacier advances in regions sensitive to insolation changes, such as the and ; paleoclimate proxies from ice cores indicate these variations amplified cooling in mass balances during the . In the , solar minima have been linked to multidecadal variability, with low activity periods enhancing ice extent through stratospheric pathways influencing winter circulation. Volcanic eruptions inject stratospheric aerosols that reflect sunlight, inducing short-term of 0.1–0.5°C lasting 1–3 years, which temporarily boosts and snow cover extents. Major events like the 1963 , 1982 , and 1991 Pinatubo eruptions increased area by 5–10% in subsequent winters due to and altered atmospheric dynamics, with sensitivity heightened under pre-eruption warmer conditions. In glacierized regions, this cooling reduces summer melt rates, preserving , as evidenced by reduced in Alpine glaciers post-Pinatubo; however, ash deposition from proximal eruptions can lower surface , counteracting cooling via enhanced absorption in some cases. Internal climate oscillations, such as the El Niño-Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), and Pacific Decadal Oscillation (PDO), generate regional cryosphere variability through teleconnections altering temperature, precipitation, and circulation. ENSO's warm phases (El Niño) typically reduce extent by 1–2 million km² via anomalous warming and weakened , while enhancing variability in snow cover; conversely, La Niña phases expand . The positive AMO phase, characterized by warmer North Atlantic sea surface temperatures, correlates with reduced sea ice volume and accelerated glacier retreat in and over multidecadal periods, contributing up to 20–30% of observed variability in ice extent since 1850. Similarly, the PDO's cool phases promote greater Alaskan mass gain and expanded ice, with phase shifts explaining interdecadal fluctuations independent of long-term trends. These modes interact, amplifying or damping cryospheric responses; for example, concurrent positive AMO and PDO phases have historically aligned with reduced pan- ice minima.

Anthropogenic Factors

Human activities, principally through emissions of long-lived greenhouse gases such as and from combustion, production, , and land-use changes, have increased atmospheric concentrations to levels unprecedented in at least 800,000 years, enhancing the and causing rise of approximately 1.1°C since pre-industrial times. This anthropogenic warming is the primary driver of recent cryosphere changes, with high to very high confidence in attribution based on detection-attribution studies comparing observed trends to natural variability and model simulations under anthropogenic forcing scenarios. For instance, century-scale warming trends have substantially increased the likelihood of rapid mass loss events, with synthetic experiments indicating that without human forcing, extreme annual losses observed in regions like the or would be far less probable. Global retreat since the 1990s is very likely driven by human-induced atmospheric and oceanic warming, overriding natural variability such as post-Little Ice Age recovery; mass loss accelerated to 266 Gt yr⁻¹ from 2000 to 2019, accounting for about 4% of volume lost since 2000 and contributing 17.1 mm to global mean from 1993 to 2019. Attribution analyses estimate that 36 ± 8% of present-day mass is committed to loss due to cumulative emissions to date, with regional examples including 23% greater mass loss in northeast from 1980–2014 compared to 1910–1978 under anthropogenic influence. In the , more than 50% of observed summer extent decline since 1979—equating to a roughly 13% per decade reduction—is attributable to forcing, as evidenced by strong correlations (R² 0.76–0.92) with cumulative CO₂ emissions and model simulations isolating anthropogenic signals from internal variability like the Atlantic Multidecadal . Recent modeling indicates that while internal variability has temporarily offset some forced loss in the 2000s–2020s, the long-term trend remains dominated by human emissions, with projections of near ice-free September conditions before 2050 under all if emissions exceed 1000 Gt CO₂ post-2020. Ice sheet dynamics in and reflect anthropogenic influences through amplified surface melting and basal/ocean-driven discharge; lost 4890 Gt of mass from to (rate peaking at 243 Gt yr⁻¹ in 2010–2019), with high that human forcing has enhanced surface deficits via elevated air temperatures and reduced snowfall efficiency. mass loss totaled 2670 Gt over the same period (148 Gt yr⁻¹ in 2010–2019), primarily from ocean warming-induced ice shelf thinning and calving, where greenhouse gas-driven heat uptake in the has facilitated Circumpolar Deep Water intrusion beneath shelves. thaw, affecting ~22 million km² of near-surface ground, has seen temperatures rise 0.29°C per from 2007 to 2016, directly linked to anthropogenic warming with high , potentially releasing ~25% of volume per 1°C global increase and altering stability through ground . Secondary factors include anthropogenic aerosols: sulfate aerosols have masked some warming via cooling effects, while deposition reduces snow/ice , accelerating melt in polluted regions like parts of the and by up to 20–50% locally in deposition hotspots. spring snow cover has declined since 1978 at a rate of -1.9 million km² per 1°C warming, attributable to human-induced increases with very high observational .

Interactions and Feedback Loops

The cryosphere interacts with the atmosphere through exchanges of , heat, and moisture, influencing regional and global patterns. Ice and surfaces exhibit high values of approximately 0.8, reflecting up to 80% of incoming solar radiation and thereby exerting a cooling effect on the lower atmosphere. processes release and freshwater vapor, which can enhance formation and alter regimes, particularly in polar regions where reduced cover increases open water evaporation. These interactions are bidirectional, as atmospheric warming accelerates cryospheric melt while cryospheric changes modify , such as through strengthened heat fluxes from exposed ocean surfaces. A primary mechanism is the ice- effect, wherein diminishing ice extent lowers planetary reflectivity, permitting greater absorption of shortwave radiation and further amplifying local warming and melt rates. Empirical observations indicate this feedback has contributed to a 3% per decade decline in summer since satellite records began, with components alone amplifying the total feedback parameter by 0.55 W/m² per degree of warming. This process operates across , glaciers, and continental s, though its magnitude varies regionally; for instance, sensitivity to changes has increased in recent coupled model assessments due to enhanced feedbacks. Cryospheric-ocean interactions involve substantial freshwater fluxes that alter marine salinity, density stratification, and circulation. Annual discharge from the totals about 1,174 km³, predominantly entering the North Atlantic via fjords and shelves, which can suppress deep convection and weaken the Atlantic Meridional Overturning Circulation (AMOC) by freshening surface layers. Antarctic contributions, projected to rise under warming scenarios, similarly influence Southern Ocean and heat redistribution, with melt adding variable salt rejection during formation and dilution during retreat. These fluxes create feedbacks by modulating heat uptake, potentially delaying but intensifying as stratified waters trap heat near the surface. Permafrost degradation within the cryosphere represents another potent via carbon release, as thawing exposes to microbial , emitting CO₂ and CH₄ that enhance greenhouse forcing. Northern regions store 1,460–1,600 Gt of soil organic carbon, with estimates suggesting that even partial thaw could release emissions equivalent to offsetting a significant portion of global terrestrial sinks by mid-century. Observations link talik formation—unfrozen ground layers beneath —to elevated cold-season respiration, accelerating net carbon losses in ecosystems like . While vegetation greening may partially mitigate this through enhanced uptake, empirical data indicate net positive forcing, with feedbacks potentially amplifying transient climate response to cumulative emissions. Overall, cryospheric feedbacks are predominantly amplifying, though quantitative uncertainties persist due to nonlinear thresholds and interactions with responses.

Debates and Uncertainties

Attribution of Recent Changes

Detection and attribution analyses seek to distinguish human-induced influences from natural variability in cryosphere changes, employing methods such as comparing observed trends to simulations with anthropogenic forcings versus natural-only scenarios. The (IPCC) assesses that human activities have contributed to widespread cryosphere alterations since the mid-20th century, including Arctic sea ice loss and glacier retreat, with medium confidence in attribution for many components. However, these assessments rely on models that exhibit discrepancies with observations, such as underestimating historical variability, which introduces uncertainty in partitioning causes. For Arctic sea ice, the post-1979 decline in summer extent is substantial, averaging a loss of about 13% per decade through 2010, but attribution debates center on the interplay of greenhouse gas forcing and internal variability modes like the Atlantic Multidecadal Oscillation (AMO) and (NAO). Studies indicate that natural variability explains 30–50% of the observed September extent decline, with anthropogenic forcing dominating the remainder in multi-model ensembles. Recent data reveal a slowdown in melt rates since approximately 2007, with minimal net loss over the past two decades, consistent with internal variability offsetting forced trends; climate simulations suggest this pause results from multidecadal fluctuations rather than a reversal in anthropogenic influence. Such episodes underscore low confidence in precise attribution for short-term trends, as models often fail to capture episodic natural accelerations or stabilizations in ice loss. Global glacier mass loss, totaling around 150–200 gigatons per year in recent decades, began accelerating in the late , predating substantial industrial emissions. Attribution estimates for the period 1851–2010 assign only 25% ± 35% of the loss to anthropogenic warming, attributing the majority to natural fluctuations in temperature and precipitation, including the end of the . Regional variations complicate this: tropical glaciers show retreat rates unprecedented in millennia, more directly linked to post-1950 warming, while mid-latitude glaciers exhibit stronger natural signals from modes like the . Formal attribution remains limited by sparsity before satellite era and model biases in simulating pre-industrial variability, leading to debates over whether recent accelerations exceed natural baselines or reflect amplified forcing. Permafrost thaw, affecting up to 20% of permafrost by active layer deepening since 1980, correlates with air temperature rises of 0.3–0.5°C per decade in the , but quantitative attribution to anthropogenic versus natural drivers is hindered by heterogeneous ground conditions and limited long-term monitoring. While warming from greenhouse gases is deemed the primary trigger for widespread degradation, natural factors such as wildfires, drainage changes, and decadal oscillations contribute significantly to abrupt thaw events, with studies noting that internal variability can account for up to half of regional temperature trends. Uncertainties persist in projecting carbon release feedbacks, as models overestimate thaw rates compared to data, potentially inflating human-attributable impacts. Ice sheet contributions to , with losing 270 ± 14 Gt/year and 150 ± 20 Gt/year on average from 2000–2020, show higher attribution confidence to anthropogenic warming via enhanced surface melt and dynamics, yet variability modulates rates; for instance, AMO-positive phases have amplified discharge independently of forcing. Detection studies confirm emergence of human signals in since the , but pre-satellite reconstructions reveal prior fluctuations, questioning the uniqueness of recent changes. Overall, while anthropogenic forcing is detectable in aggregated cryosphere trends, the magnitude of its role versus variability—estimated at 20–50% across components—remains debated, with source biases in consensus reports potentially underemphasizing model-observation mismatches.

Model Reliability and Predictions

Climate models, particularly those from the Phase 6 (CMIP6), exhibit mixed reliability in simulating historical cryosphere changes, with notable biases affecting predictive accuracy. For sea ice, many CMIP6 models underestimate the observed rate of summer extent decline since the late , as satellite records show faster losses than hindcast simulations, attributed to inadequate representation of feedbacks like and ocean heat transport. In contrast, these models often overestimate processes such as sea ice melt and growth when compared to in-situ measurements, highlighting deficiencies in ice dynamics and parameterization. simulations show consistent biases in concentration and compactness, with models struggling to reproduce observed expansions in the early despite projections of decline. Ice sheet and glacier models face deeper uncertainties due to incomplete physics, such as marine ice cliff instability and rapid calving, leading to discrepancies between simulated and observed . models project accelerating melt but underestimate historical surface losses when driven by reanalysis data, while projections reveal substantial spread across CMIP ensembles, contributing to "deep uncertainty" in sea-level rise estimates. models in CMIP6 generally capture broad thaw trends but underestimate active layer deepening in some regions, influenced by biases in thermal properties and feedbacks. Overall, while models reliably hindcast large-scale warming-driven losses, quantitative predictions remain challenged by structural errors and parameter tuning, as evidenced by inter-model spread exceeding observational variability in key metrics. Future cryosphere projections under (SSPs) anticipate continued decline, with Arctic summer sea ice potentially reaching occasional ice-free conditions by mid-century in high-emission scenarios, though timing varies widely due to internal variability and model biases. contributions to sea-level rise by 2100 range from 0.1 to 0.9 meters under SSP5-8.5, dominated by uncertain Antarctic dynamics, prompting calls for hybrid approaches integrating emulators and elicitation to quantify deep uncertainties beyond ensemble means. mass loss is projected more robustly, with global volume reductions of 18-36% by 2100 across scenarios, but regional predictions for permafrost carbon release carry low confidence owing to nonlinear thaw processes. These projections underscore the need for improved process representation, as current models may understate risks from abrupt shifts while overemphasizing gradual trends in vulnerable components like polar .

Exaggerations in Public Discourse

Public discourse on the cryosphere has occasionally amplified predictions of imminent and catastrophic melt that subsequent observations have not substantiated. In December 2009, former U.S. Vice President stated at the United Nations Climate Change Conference in that computer modeling indicated the could become nearly ice-free during summer as early as 2014, citing research by Wieslaw Maslowski. Maslowski's model suggested a high probability of low ice conditions by 2016 under continued warming, but emphasized it was a projection based on extrapolated trends rather than a validated forecast. In reality, the sea ice minimum extent in September 2014 reached 5.02 million square kilometers, the sixth lowest on record but far from ice-free, with persistent multi-year ice persisting in the region. Such statements, while rooted in model outputs, contributed to narratives of an accelerating "death spiral" that overstated near-term probabilities, as sea ice extent has exhibited high interannual variability rather than linear collapse. A prominent institutional error involved the Intergovernmental Panel on Climate Change's ( in 2007, which asserted that Himalayan glaciers were projected to disappear by 2035 if present trends continued, potentially threatening supplies for of millions. This claim originated from a World Wildlife Fund report citing anecdotal observations rather than peer-reviewed modeling, and the IPCC later acknowledged it as "poorly substantiated" with no rigorous scientific basis. The projection was retracted in 2010 amid criticism, highlighting vulnerabilities in IPCC review processes where non-peer-reviewed sources influenced high-confidence statements. Empirical data since then shows Himalayan s retreating at rates of 0.3 to 0.6 meters per year on average, with regional variations but no evidence of wholesale disappearance by mid-century. Media amplification of this unsubstantiated timeline fueled alarm over Asia's "water towers," despite assessments indicating sustained glacier volume for decades under moderate warming scenarios. Coverage of Greenland Ice Sheet dynamics has also featured distortions, such as 2019 reports claiming the sheet "melted nearly four trillion tons" in days, implying existential threat. These figures referred to surface volume from a heatwave, much of which refroze or ran off without net mass loss equivalent to sheet disintegration; actual annual loss for 2019 was about 532 gigatons, consistent with decadal trends but not unprecedented. Similarly, some outlets extrapolated localized glacial retreat to forecast rapid total melt, overlooking interior accumulation gains that partially offset peripheral losses. For , early 2000s media emphasized West Antarctic shelf thinning while downplaying overall expansion, which reached record highs in 2014 before recent declines. These patterns reflect a tendency to prioritize dramatic endpoints over measured variability, where cryospheric components respond to multifaceted forcings including currents and feedbacks, rather than unidirectional . Such exaggerations, often from advocacy-driven reporting, contrast with satellite data showing cumulative loss but within bands of long-term projections.

Implications and Future Outlook

Environmental and Ecological Impacts

The retreat of sea ice has disrupted marine ecosystems by reducing habitat for ice-dependent species such as and ringed seals, leading to declines in body condition and population shifts, while enabling range expansions of sub- species like killer whales that prey on ice-associated marine mammals. These changes cascade through food webs, altering primary productivity and distributions, with observed reductions in that underpin . thaw in the , affecting approximately 25% of land, mobilizes stored organic carbon, with models estimating that 4% to 8% of newly thawed carbon—equivalent to tens of gigatons—could be emitted as CO2 and CH4 by 2100, potentially amplifying regional warming and stressing vegetation and microbial communities. Glacier mass loss, documented at an average rate of -267 ± 16 Gt yr⁻¹ globally from 2000 to 2023, alters downstream freshwater ecosystems by increasing turbidity and nutrient inputs, initially enhancing planktonic in proglacial lakes but risking long-term oligotrophication and as seasonal flows diminish. In high-mountain regions, this shift threatens endemic aquatic adapted to cold, stable flows, with cascading effects on riparian habitats and fisheries. The cryosphere's feedback exacerbates these ecological pressures by reducing surface reflectivity, absorbing more solar radiation, and accelerating warming that desynchronizes phenological events like plant flowering and in and alpine zones. Loss of lake and river ice cover, observed across northern latitudes, exposes ecosystems to prolonged , diminishing winter refugia for and while promoting proliferation and altering nutrient cycling, with projections indicating widespread impacts on boreal by mid-century. In systems, intensified glacial calving introduces freshwater plumes that stratify waters, suppressing and affecting benthic communities, as evidenced in where cryosphere meltdown has driven shifts in microbial and macrofaunal assemblages since the 1990s. These interconnected changes underscore the cryosphere's role in modulating stability, though empirical data reveal variability, with some diversity buffered by herbivore grazing amid warming.

Human Societal Effects

Changes in the cryosphere, particularly the retreat of glaciers and thawing of , threaten freshwater availability for human populations dependent on glacial . Glaciers in mountain regions contribute significantly to seasonal river flows, supporting , , and for over one billion people, with mountains providing up to 60% of global annual freshwater. Accelerated melting has led to initial increases in in some areas, but long-term projections indicate peak water availability followed by declines, exacerbating scarcity in regions like the and , where two billion people face risks to and by mid-century. Thawing undermines infrastructure in and sub-Arctic regions, causing , , and structural failures. In , projected costs for repairing damage to buildings and roads from permafrost thaw range from $37 billion to $51 billion by 2100 under moderate to high emissions scenarios, driven by ground settlement and development. Across the broader , including pipelines, airports, and railroads, cumulative repair expenses could reach $276 billion by 2050 due to accelerated thaw from rising temperatures. These effects disproportionately impact remote communities reliant on stable ground for housing and transportation. Melting of land-based contributes to global , posing risks to coastal settlements through inundation, erosion, and storm surges. Since 1880, sea levels have risen 8-9 inches globally, with and melt accounting for a substantial portion alongside ; Greenland's loss alone drove much of the recent acceleration. Low-lying coastal areas, home to hundreds of millions, face heightened flooding, with projections indicating faster rises in tropical and mid-latitude regions due to gravitational effects from loss. Loss of and snow cover disrupts indigenous livelihoods in the , shortening safe hunting and travel seasons on ice-dependent ecosystems. Declining has curtailed seal-hunting periods in northern , increasing travel risks and contributing to food insecurity rates among indigenous groups that exceed national averages. from reduced ice buffering has threatened 31 Alaska Native villages with relocation, amplifying vulnerabilities to storms and undermining cultural practices tied to traditional lands. Economic sectors face mixed but predominantly challenging shifts from cryospheric changes. Winter in alpine areas suffers from reduced snow reliability, impacting resorts dependent on consistent cover for and related revenues. Fisheries in polar regions experience alterations in prey distribution due to sea ice variability, affecting commercial catches and indigenous subsistence. Conversely, diminished extends navigable shipping seasons in the , potentially lowering transport costs via routes like the , though this benefit is offset by increased risks from unstable ice conditions. retreat also heightens hazards such as lake outburst floods, damaging downstream and in vulnerable valleys.

Projections with Uncertainty Ranges

Projections for cryospheric components under CMIP6 scenarios, particularly SSP5-8.5, forecast substantial declines in ice volume and extent by 2100, driven primarily by atmospheric warming, though ice sheet dynamics introduce the dominant uncertainties in sea-level rise estimates. Global glacier mass is expected to decrease by 26 ± 6% relative to 2015 under +1.5°C warming or 41 ± 11% under +4°C, contributing 79 to 159 mm to sea level in low- versus high-emission pathways, with climate model spread and glacier-specific responses accounting for much of the variance. The Greenland Ice Sheet's projected sea-level contribution ranges from 5 to 33 cm by 2100 across ensemble models, with recent climate disequilibrium committing at least 27.4 ± 6.8 cm from an area of 59 ± 15 × 10³ km² retreat, though ice flow models often underestimate observed mass loss due to inadequacies in capturing outlet glacier dynamics. Uncertainty in basal friction and surface mass balance feedbacks amplifies projections, with ISMIP6 intercomparisons showing spreads driven by these parameters under high-emission scenarios. Antarctic Ice Sheet projections exhibit deeper uncertainties, potentially contributing up to 28 cm by 2100, but with internal climate variability influencing 45% to 93% of the sea-level signal depending on the CMIP6 model, and marine ice sheet instability potentially skewing outcomes toward higher-end estimates if thresholds are crossed. East Antarctic dynamics dominate under strong warming, where ice flow instabilities could elevate contributions beyond structured models, as evidenced by ISMIP6 assessments where climate model choice contributes up to 13% of 2100 uncertainty. Arctic sea ice projections from CMIP6 indicate an ice-free September Arctic by mid-century in high-emission scenarios, but models systematically underestimate historical loss, leading to overly conservative timelines; emergent constraints narrow the first ice-free year spread, yet multidecadal variability and circulation biases persist as key uncertainty sources. Permafrost thaw is projected to release carbon equivalent to emissions from a major nation, with abrupt thaw in 20% of permafrost areas amplifying releases, though microbial decomposition efficiencies and abrupt versus gradual thaw pathways yield budgets reduced by up to 20-22% for 1.5-2°C targets due to feedbacks. Northern Hemisphere snow cover extent is anticipated to decline further, with historical trends of -3.6 ± 2.7% annually extending into projections of reduced duration and mass, particularly in mid-latitudes, where model interquartile spreads highlight uncertainties from surface feedbacks and phase changes. Overall, processes, especially dynamical instabilities, overshadow other cryospheric uncertainties in long-term sea-level projections, underscoring the need for improved process representation in models to refine ranges.

References

  1. https://sealevel.nasa.gov/glossary/
  2. https://svs.gsfc.nasa.gov/api/detailspage/4400/recommended/display?id=details_page_4400_rec_pages&
  3. https://www.researchgate.net/figure/Global-Cryosphere-Area-and-Volume_tbl1_245820334
  4. https://oceanservice.noaa.gov/facts/cryosphere.html
  5. https://wmo.int/topics/cryosphere
  6. https://www.antarcticglaciers.org/glaciers-and-climate/what-is-the-global-volume-of-land-ice-and-how-is-it-changing/
  7. https://ntrs.nasa.gov/api/citations/20060026200/downloads/20060026200.pdf
  8. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JC020848
  9. https://nsidc.org/learn/what-cryosphere
  10. https://mynasadata.larc.nasa.gov/basic-page/about-cryosphere
  11. https://globalcryospherewatch.org/about-the-cryosphere/
  12. https://nsidc.org/learn/parts-cryosphere
  13. https://pubs.usgs.gov/publication/fs20243043
  14. https://globalcryospherewatch.org/
  15. https://doi.org/10.1016/B978-0-12-817129-5.00007-X
  16. https://courses.washington.edu/ess431/LECTURES/LECTURE_2016/Lect_02_Physical_properties_2016.pdf
  17. https://online.ucpress.edu/elementa/article/12/1/00086/200266/Snow-thermal-conductivity-and-conductive-flux-in
  18. https://www.cambridge.org/core/journals/journal-of-glaciology/article/thermal-conductivity-of-polar-firn/CB3DAA0407417233A1DEEA0B6D344B7E
  19. https://nsidc.org/learn/parts-cryosphere/sea-ice/science-sea-ice
  20. https://tc.copernicus.org/articles/19/1539/2025/
  21. https://link.springer.com/chapter/10.1007/978-3-642-81434-1_10
  22. https://www.nature.com/articles/s41561-025-01661-z
  23. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL084896
  24. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021RG000743
  25. https://www.sciencedirect.com/science/article/abs/pii/S0012821X06008430
  26. https://arctic.noaa.gov/report-card/report-card-2024/greenland-ice-sheet-2024/
  27. https://www.nature.com/articles/s41586-024-08545-z
  28. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021jf006123
  29. https://arcticportal.org/education/quick-facts/environment-and-science/3523-permafrost
  30. https://nsidc.org/sea-ice-today/analyses/arctic-sea-ice-extent-levels-2024-minimum-set
  31. https://www.climate.gov/news-features/event-tracker/2024-antarctic-sea-ice-winter-maximum-second-lowest-record
  32. https://globalcryospherewatch.org/snow-assessments-2024/
  33. https://nsidc.org/learn/parts-cryosphere/ice-sheets/ice-sheet-quick-facts
  34. https://www.antarcticglaciers.org/glaciers-and-climate/estimating-glacier-contribution-to-sea-level-rise/
  35. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012JF002523
  36. https://scripps.ucsd.edu/system/files/2025-04/SIO%2520115%2520Fricker%2520SP%252025.pdf
  37. http://www.climatedata.info/forcing/albedo/
  38. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023JD040667
  39. https://tc.copernicus.org/articles/15/793/2021/
  40. https://link.springer.com/article/10.1007/s10546-011-9623-3
  41. https://tc.copernicus.org/articles/15/2601/2021/
  42. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022JD037032
  43. https://pmc.ncbi.nlm.nih.gov/articles/PMC6501920/
  44. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JD035677
  45. https://nsidc.org/learn/parts-cryosphere/sea-ice
  46. https://earthobservatory.nasa.gov/features/SeaIce
  47. https://www.meereisportal.de/en/learn-more/sea-ice-physics
  48. https://earthobservatory.nasa.gov/world-of-change/sea-ice-antarctic
  49. https://podaac.jpl.nasa.gov/SeaIce
  50. https://nsidc.org/sea-ice-today/analyses/arctic-sea-ice-sets-record-low-maximum-2025
  51. https://nsidc.org/news-analyses/news-stories/antarctic-sea-ice-maximum-third-lowest-2025
  52. https://nsidc.org/sea-ice-today/analyses/2025-arctic-sea-ice-minimum-squeezes-ten-lowest-minimums
  53. https://nsidc.org/learn/parts-cryosphere/sea-ice/why-sea-ice-matters
  54. https://nsidc.org/learn/parts-cryosphere/frozen-ground-permafrost
  55. https://science.nasa.gov/kids/earth/what-is-permafrost/
  56. https://education.nationalgeographic.org/resource/permafrost/
  57. https://www.epa.gov/climate-indicators/climate-change-indicators-permafrost
  58. https://www.sciencedirect.com/science/article/pii/S0012825218305907
  59. https://essd.copernicus.org/preprints/essd-2022-144/essd-2022-144.pdf
  60. https://arctic.noaa.gov/report-card/report-card-2019/permafrost-and-the-global-carbon-cycle/
  61. https://www.nature.com/articles/s43017-021-00230-3
  62. https://cpo.noaa.gov/emissions-from-thawing-permafrost-add-trillions-in-economic-impacts/
  63. https://nsidc.org/learn/parts-cryosphere/snow/why-snow-matters
  64. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2007gl031474
  65. https://tc.copernicus.org/articles/14/2495/2020/
  66. https://climatedataguide.ucar.edu/climate-data/snow-cover-extent-northern-hemisphere-climate-data-record-rutgers
  67. https://www.ncei.noaa.gov/products/climate-data-records/snow-cover-extent
  68. https://arctic.noaa.gov/report-card/report-card-2016/terrestrial-snow-cover-7/
  69. https://www.ipcc.ch/srocc/
  70. https://www.sciencedirect.com/science/article/abs/pii/S2352938525002150
  71. https://tc.copernicus.org/articles/15/2211/2021/
  72. https://pmc.ncbi.nlm.nih.gov/articles/PMC3357771/
  73. https://tc.copernicus.org/articles/16/2493/2022/
  74. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JG006275
  75. https://www.sciencedirect.com/science/article/pii/S0022169424018432
  76. https://www.glerl.noaa.gov/data/ice/
  77. https://nsidc.org/data/lake_river_ice/
  78. https://pubmed.ncbi.nlm.nih.gov/10976066/
  79. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023WR036392
  80. https://www.sciencedirect.com/science/article/abs/pii/S003442572400364X
  81. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022WR031939
  82. https://www.mdpi.com/2306-5338/11/8/126
  83. https://climate.esa.int/en/projects/lakes/data/
  84. https://www.researchgate.net/publication/245293342_Monitoring_River_Ice_Conditions_Using_Web-Based_Cameras
  85. https://www.nature.com/articles/s41598-025-07321-x
  86. https://pmc.ncbi.nlm.nih.gov/articles/PMC3357779/
  87. https://iccinet.org/pan-cryosphere-feedbacks-albedo-permafrost-melt-sea-level-rise/
  88. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029%252F2024GL109953
  89. https://tc.copernicus.org/articles/18/475/2024/
  90. https://www.pnas.org/doi/10.1073/pnas.2100163118
  91. https://www.nature.com/articles/nature14338
  92. https://www.annualreviews.org/doi/10.1146/annurev-environ-012220-011847
  93. https://www.sciencespo.fr/psia/chair-sustainable-development/2025/08/01/how-emissions-from-thawing-permafrost-reshape-carbon-budgets/
  94. https://tc.copernicus.org/articles/19/2289/2025/
  95. https://www.usgs.gov/programs/ecosystems-land-change-science-program/science/cryosphere-earths-snow-ice-and-permafrost
  96. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023WR034690
  97. https://tc.copernicus.org/articles/16/3531/2022/
  98. https://www.sciencedirect.com/science/article/pii/S1674927822000387
  99. https://esd.copernicus.org/articles/16/347/2025/
  100. https://essd.copernicus.org/articles/5/393/2013/essd-5-393-2013-relations.html
  101. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EF003293
  102. https://www.geomar.de/en/news/article/icebergs-as-a-source-of-nutrients
  103. https://scripps.ucsd.edu/news/retreating-glaciers-may-send-fewer-nutrients-ocean
  104. https://sealevel.nasa.gov/understanding-sea-level/regional-sea-level/ice-sheets/
  105. https://science.nasa.gov/earth/explore/earth-indicators/ice-sheets/
  106. https://svs.gsfc.nasa.gov/10503/
  107. https://journals.ametsoc.org/view/journals/phoc/29/9/1520-0485_1999_029_2370_tiomio_2.0.co_2.xml
  108. https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016JC012509
  109. https://oceanservice.noaa.gov/facts/sea-ice-climate.html
  110. https://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/
  111. https://www.science.org/doi/10.1126/sciadv.1600983
  112. https://geo.libretexts.org/Bookshelves/Geology/Environmental_Geology_%28Earle%29/04%253A_Glaciation/4.01%253A_Glacial_Periods_in_Earths_History
  113. https://www.bas.ac.uk/media-post/the-dawn-of-the-antarctic-ice-sheets/
  114. https://www.imperial.ac.uk/news/254678/study-reveals-where-when-antarctic-sheet/
  115. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022RG000793
  116. https://www.ncei.noaa.gov/access/paleo-search/study/9971
  117. https://doi.pangaea.de/10.1594/PANGAEA.683655
  118. https://www.ncei.noaa.gov/access/paleo-search/study/17796
  119. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JD042810
  120. https://www.ncei.noaa.gov/access/paleo-search/study/37178
  121. https://www.ncei.noaa.gov/access/paleo-search/study/26612
  122. https://www.ncei.noaa.gov/access/paleo-search/study/36253
  123. https://epic.awi.de/41976/
  124. https://www.pnas.org/doi/10.1073/pnas.2301954120
  125. https://cp.copernicus.org/preprints/cp-2024-74/cp-2024-74.pdf
  126. https://www.nature.com/articles/s41558-022-01575-3
  127. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL107385
  128. https://www.nature.com/articles/s41586-025-09600-z
  129. https://www.sciencedirect.com/science/article/pii/S0277379114004788
  130. https://academiccommons.columbia.edu/doi/10.7916/D8H99GX3/download
  131. https://www.nature.com/articles/s41467-024-54535-0
  132. https://www.nature.com/articles/s41586-022-05411-8
  133. https://www.nature.com/articles/s43247-021-00191-x
  134. https://www.nature.com/articles/s41467-017-01455-x
  135. https://www.nature.com/articles/s43247-021-00238-z
  136. https://www.sciencedirect.com/science/article/pii/S0277379123001038
  137. https://www.usgs.gov/publications/holocene-vegetation-dynamics-circum-arctic-permafrost-peatlands
  138. https://www.researchgate.net/publication/375577331_Holocene_glacier_variations_in_the_Alps
  139. https://www.sciencedirect.com/science/article/abs/pii/S027737912100456X
  140. https://www.nature.com/articles/s41467-025-61793-z
  141. https://journals.ametsoc.org/view/journals/clim/35/4/JCLI-D-21-0099.1.pdf
  142. https://www.mdpi.com/2072-4292/16/10/1709
  143. https://gtnp.arcticportal.org/data/measurement-standards-and-monitoring-guidelines
  144. https://link.springer.com/article/10.1007/s10712-023-09781-0
  145. https://ntrs.nasa.gov/api/citations/20180003555/downloads/20180003555.pdf
  146. https://climatedataguide.ucar.edu/climate-data/sea-ice-thickness-data-sets-overview-comparison-table
  147. https://gracefo.jpl.nasa.gov/resources/37/two-new-missions-set-to-study-one-of-earths-most-critically-changing-regions/
  148. https://tc.copernicus.org/articles/17/809/2023/tc-17-809-2023-relations.html
  149. https://svs.gsfc.nasa.gov/5100/
  150. https://tc.copernicus.org/articles/19/3785/2025/
  151. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL105770
  152. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022JF007020
  153. https://gi.copernicus.org/articles/9/1/2020/
  154. https://tc.copernicus.org/articles/19/731/2025/
  155. https://science.nasa.gov/earth/explore/earth-indicators/arctic-sea-ice-minimum-extent/
  156. https://nsidc.org/sea-ice-today/analyses/antarctic-sea-ice-minimum-hits-near-record-low-again
  157. https://www.cambridge.org/core/journals/journal-of-glaciology/article/historically-unprecedented-global-glacier-decline-in-the-early-21st-century/2F1E3ACB111A03F9BA83D11439F5D681
  158. https://www.nature.com/articles/s41467-020-16818-0
  159. https://www.nature.com/articles/s41558-023-01855-6
  160. https://grace.jpl.nasa.gov/resources/30/greenland-ice-loss-2002-2021/
  161. https://link.springer.com/article/10.1007/s10584-005-4785-y
  162. https://www.climate.gov/news-features/understanding-climate/climate-change-spring-snow-cover-northern-hemisphere
  163. https://nsidc.org/sea-ice-today/analyses/antarctic-sea-ice-extent-hits-third-low-row
  164. https://www.[nasa](/page/NASA).gov/earth/arctic-winter-sea-ice-at-record-low/
  165. https://earthobservatory.[nasa](/page/NASA).gov/images/153457/arctic-and-antarctic-sea-ice-approached-historic-lows
  166. https://climate.copernicus.eu/climate-indicators/ice-sheets
  167. https://essd.copernicus.org/articles/15/1597/2023/
  168. https://wgms.ch/sea-level-rise/
  169. https://www.climate.gov/news-features/understanding-climate/climate-change-mountain-glaciers
  170. https://www.sciencedirect.com/science/article/pii/S1674927825000590
  171. https://www.ncei.noaa.gov/access/monitoring/monthly-report/global-snow/202411
  172. https://journals.ametsoc.org/view/journals/hydr/24/6/JHM-D-22-0182.1.xml
  173. https://pubs.geoscienceworld.org/gsl/books/edited-volume/2338/chapter/132175436/Impact-of-a-northern-hemispherical-cryosphere-on
  174. https://cp.copernicus.org/articles/20/151/2024/
  175. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL024518
  176. https://www.climate.gov/news-features/understanding-climate/climate-change-incoming-sunlight
  177. https://nap.nationalacademies.org/read/4778/chapter/4
  178. https://www.geomar.de/en/news/article/sun-controlled-climate-during-ice-ages
  179. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JD027038
  180. https://tc.copernicus.org/articles/14/4581/2020/tc-14-4581-2020.pdf
  181. https://nsidc.org/sea-ice-today/studying-sea-ice
  182. https://nsidc.org/learn/ask-scientist/climate-change-or-variability-what-rules-arctic-sea-ice
  183. https://www.nature.com/articles/s41598-019-48178-1
  184. https://www.nature.com/articles/s41598-020-57472-2
  185. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007gl031584
  186. https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-3/
  187. https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-9/
  188. https://tc.copernicus.org/articles/16/2725/2022/
  189. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL116175
  190. https://www.nature.com/articles/s43247-022-00546-y
  191. https://www.meereisportal.de/en/glossary/Ice-albedo%2520feedback
  192. https://acp.copernicus.org/articles/19/2015/2019/
  193. https://tos.org/oceanography/article/increasing-freshwater-fluxes-from-the-greenland-ice-sheet-observed-from-space
  194. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL111250
  195. https://tc.copernicus.org/articles/12/123/2018/
  196. https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1714/
  197. https://www.cato.org/blog/natural-variabilitys-role-arctic-sea-ice-decline-strengthens-case-lukewarming
  198. https://www.nature.com/articles/s41467-025-63520-0
  199. https://www.climate.gov/news-features/understanding-climate/five-things-understand-about-ice-free-arctic
  200. https://pubmed.ncbi.nlm.nih.gov/25123485/
  201. https://www.science.org/doi/10.1126/science.adg7546
  202. https://www.nature.com/articles/s41467-023-37276-4
  203. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024EF005153?af=R
  204. https://www.nature.com/articles/s43247-025-02092-9
  205. https://journals.ametsoc.org/view/journals/clim/aop/JCLI-D-23-0647.1/JCLI-D-23-0647.1.pdf
  206. https://gmd.copernicus.org/articles/18/3041/2025/gmd-18-3041-2025-relations.html
  207. https://tc.copernicus.org/articles/12/365/2018/
  208. https://www.nature.com/articles/s41467-022-34414-2
  209. https://www.science.org/doi/10.1126/sciadv.add7082
  210. https://journals.ametsoc.org/view/journals/hydr/26/10/JHM-D-24-0124.1.xml
  211. https://tc.copernicus.org/articles/19/3259/2025/
  212. https://www.nature.com/articles/s43247-024-01799-5
  213. https://tc.copernicus.org/articles/15/5705/2021/
  214. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025AV001698
  215. https://www.npr.org/sections/thetwo-way/2009/12/al_gore_trips_on_artic_ice_mis.html
  216. https://www.timesunion.com/news/article/gore-predicts-ice-free-arctic-sea-555712.php
  217. https://www.reuters.com/article/fact-check/al-gore-did-not-predict-ice-caps-melting-by-2013-but-misrepresented-data-idUSL1N2RV0K6/
  218. https://www.nasa.gov/news-release/2014-arctic-sea-ice-minimum-sixth-lowest-on-record/
  219. https://nsidc.org/sea-ice-today/analyses/arctic-sea-ice-minimum-ties-tenth-lowest
  220. https://www.realclimate.org/index.php/archives/2025/09/but-you-said-the-ice-was-going-to-disappear-in-10-years/
  221. https://www.theguardian.com/environment/2010/jan/20/ipcc-himalayan-glaciers-mistake
  222. https://www.science.org/content/article/ipcc-expresses-regret-over-glaciers-error
  223. https://yaleclimateconnections.org/2010/02/anatomy-of-ipccs-himalayan-glacier-year-2035-mess/
  224. https://www.cnn.com/2010/WORLD/asiapcf/01/20/glacier.himalayas.ipcc.error/
  225. https://www.cato.org/policy-analysis/false-alarm-over-retreat-himalayan-glaciers
  226. https://www.jpl.[nasa](/page/NASA).gov/news/nasa-study-more-greenland-ice-lost-than-previously-estimated/
  227. https://climatefeedback.org/evaluation/article-by-cnn-exaggerates-studys-implications-for-future-greenland-ice-loss/
  228. https://www.epw.senate.gov/public/index.cfm/press-releases-all?ID=F1F2F75F-802A-23AD-4701-A92B4EBBCCBF
  229. https://www.nationalgeographic.com/science/article/140513-antarctic-ice-sheet-[collapse](/page/Collapse)-in-perspective
  230. https://pmc.ncbi.nlm.nih.gov/articles/PMC5008214/
  231. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013RG000431
  232. https://phys.org/news/2024-12-permafrost-century-carbon.html
  233. https://jpl.nasa.gov/news/nasa-helps-find-thawing-permafrost-adds-to-near-term-global-warming/
  234. https://pmc.ncbi.nlm.nih.gov/articles/PMC4747089/
  235. https://www.usgs.gov/programs/climate-adaptation-science-centers/glacier-change-impacts-alaskas-coastal-ecosystems
  236. https://www.nature.com/articles/s43247-021-00227-2
  237. https://www.science.org/doi/10.1126/science.adl3211
  238. https://www.nature.com/articles/s43247-025-02251-y
  239. https://www.science.org/doi/10.1126/science.add2679
  240. https://www.unesco.org/en/articles/glaciers-and-mountains-melting-water-towers-will-aggravate-global-crises-report
  241. https://www.theguardian.com/environment/2025/mar/20/glacier-meltdown-risks-food-and-water-supply-of-2bn-people-says-un
  242. https://www.nature.com/articles/s43247-025-02191-7
  243. https://alaskabeacon.com/2023/02/16/arctic-permafrost-thaw-expected-to-impose-heavy-costs-on-roads-airport-runways/
  244. https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level
  245. https://sealevel.nasa.gov/understanding-sea-level/global-sea-level/ice-melt/
  246. https://www.arcticwwf.org/the-circle/stories/retreating-sea-ice-threatens-indigenous-way-of-life/
  247. http://toolkit.climate.gov/arctic-peoples-and-ecosystems
  248. https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2019.00091/full
  249. https://weekly.chinacdc.cn/en/article/doi/10.46234/ccdcw2025.062
  250. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf
  251. https://www.science.org/doi/10.1126/science.abo1324
  252. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019EF001470
  253. https://www.science.org/doi/10.1126/sciadv.aav9396
  254. https://www.nature.com/articles/s41558-022-01441-2
  255. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022JF006914
  256. https://esd.copernicus.org/articles/16/293/2025/
  257. https://www.science.org/doi/10.1126/science.adt9619
  258. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EF002772
  259. https://tc.copernicus.org/articles/17/5197/2023/
  260. https://journals.ametsoc.org/view/journals/clim/37/23/JCLI-D-23-0647.1.xml
  261. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EF002708
  262. https://permafrost.woodwellclimate.org/mitigation-policy/
  263. https://www.nature.com/articles/s41598-022-16743-w
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