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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 a 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.
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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. 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
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.: 1451
The term cryosphere comes from the Greek word kryos, meaning cold, frost or ice and the Greek word sphaira, meaning globe or ball.
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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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. Physical properties such as crystal structure, density, length, and liquid water content are important factors affecting the transfers of heat and water and the scattering of microwave energy.
Residence time and extent
The residence time of water in each of the cryospheric sub-systems varies widely. Snow cover and freshwater ice are essentially seasonal, and most sea ice, except for ice in the central Arctic, lasts only a few years if it is not seasonal. A given water particle in glaciers, ice sheets, or ground ice, however, may remain frozen for 10–100,000 years or longer, and deep ice in parts of East Antarctica may have an age approaching 1 million years.[citation needed]
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.[citation needed]
Surface reflectance
The surface reflectance of incoming solar radiation is important for the surface energy balance (SEB). It is the ratio of reflected to incident solar radiation, commonly referred to as albedo. Climatologists are primarily interested in albedo integrated over the shortwave 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.
Thermal properties of cryospheric elements
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.
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. 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.
Climate change feedback mechanisms
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.
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.[citation needed]
Components
Glaciers and ice sheets
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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. Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies.
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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 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.
A glacier (US: /ˈɡleɪʃər/; UK: /ˈɡlæsiə/ or /ˈɡleɪsiə/) is a persistent body of dense ice, a form of rock, 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 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. With more than 7,000 known glaciers, Pakistan has more glacial ice than any other country outside the polar regions. 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. The volume of glaciers, not including the ice sheets of Antarctica and Greenland, has been estimated at 170,000 km3.In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). 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.
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.
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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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. 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.
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. 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.
Frozen ground and permafrost
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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. 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). Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. 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.
Around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, covering a total area of around 18 million km2 (6.9 million sq mi). 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.
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. 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. 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 of 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. 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.Snow cover
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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.
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
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
Ice sheet melt
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Every summer, parts of the surface melt and ice cliffs calve into the sea. Normally the ice sheet would be replenished by winter snowfall, but due to global warming the ice sheet is melting two to five times faster than before 1850, and snowfall has not kept up since 1996. If the Paris Agreement goal of staying below 2 °C (3.6 °F) is achieved, melting of Greenland ice alone would still add around 6 cm (2+1⁄2 in) to global sea level rise by the end of the century. If there are no reductions in emissions, melting would add around 13 cm (5 in) by 2100,: 1302 with a worst-case of about 33 cm (13 in). For comparison, melting has so far contributed 1.4 cm (1⁄2 in) since 1972, while sea level rise from all sources was 15–25 cm (6–10 in) between 1901 and 2018.: 5
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). Global warming between 1.7 °C (3.1 °F) and 2.3 °C (4.1 °F) would likely make this melting inevitable. 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, and more ice will be lost if the temperatures exceed that level before declining. If global temperatures continue to rise, the ice sheet will likely disappear within 10,000 years. At very high warming, its future lifetime goes down to around 1,000 years.Decline of glaciers
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The retreat of glaciers since 1850 is a well-documented effect of climate change. The retreat of mountain glaciers provide 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.: 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. They are several kilometers deep and obscure the underlying topography.Sea ice decline
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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. 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. Large-scale measurements of sea ice have only been possible since satellites came into use.
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. 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).: 8 The Arctic will likely become ice-free at the end of some summers before 2050.: 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.Permafrost thaw
Snow cover decrease
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Studies in 2021 found that Northern Hemisphere snow cover has been decreasing since 1978, along with snow depth.Paleoclimate observations show that such changes are unprecedented over the last millennia in Western North America.
North American winter snow cover increased during the 20th century, largely in response to an increase in precipitation.
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. 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
- Cryobiology
- International Association of Cryospheric Sciences (IACS)
- Polar regions of Earth
- Special Report on the Ocean and Cryosphere in a Changing Climate
- Water cycle
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External links
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- Canadian Cryospheric Information Network
- Near-real-time overview of global ice concentration and snow extent
- National Snow and Ice Data Center
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 a 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 Overview of the cryosphere and its larger components 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 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 terminologyThe 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 1451 The term cryosphere comes from the Greek word kryos meaning cold frost or ice and the Greek word sphaira meaning globe or ball 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 interactionsThe cryosphere bottom left is one of five components of the climate system The others are the atmosphere the hydrosphere the lithosphere and the biosphere 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 Physical properties such as crystal structure density length and liquid water content are important factors affecting the transfers of heat and water and the scattering of microwave energy Residence time and extent The residence time of water in each of the cryospheric sub systems varies widely Snow cover and freshwater ice are essentially seasonal and most sea ice except for ice in the central Arctic lasts only a few years if it is not seasonal A given water particle in glaciers ice sheets or ground ice however may remain frozen for 10 100 000 years or longer and deep ice in parts of East Antarctica may have an age approaching 1 million years citation needed 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 citation needed Surface reflectance The surface reflectance of incoming solar radiation is important for the surface energy balance SEB It is the ratio of reflected to incident solar radiation commonly referred to as albedo Climatologists are primarily interested in albedo integrated over the shortwave 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 Thermal properties of cryospheric elements 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 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 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 Climate change feedback mechanisms 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 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 citation needed ComponentsGlaciers and ice sheets Representation of glaciers on a topographic mapThe Taschachferner glacier in the Otztal 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 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 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 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 ˈ ɡ l eɪ ʃ er UK ˈ ɡ l ae s i e or ˈ ɡ l eɪ s i e is a persistent body of dense ice a form of rock 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 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 With more than 7 000 known glaciers Pakistan has more glacial ice than any other country outside the polar regions 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 The volume of glaciers not including the ice sheets of Antarctica and Greenland has been estimated at 170 000 km3 This section is an excerpt from Ice sheet edit In glaciology an ice sheet also known as a continental glacier is a mass of glacial ice that covers surrounding terrain and is greater than 50 000 km2 19 000 sq mi 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 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 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 Broken pieces of Arctic sea ice with a snow coverSatellite 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 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 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 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 Frozen ground and permafrost 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 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 Similarly the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions 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 Around 15 of the Northern Hemisphere or 11 of the global surface is underlain by permafrost covering a total area of around 18 million km2 6 9 million sq mi 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 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 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 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 of 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 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 Snow cover Snow covered trees in Kuusamo FinlandSnow 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 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 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 changeThis 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 There has been an extensive loss of snow on land since 1981 Some of the largest declines have been observed in the spring During the 21st century snow cover is projected to continue its retreat in almost all regions 39 69 Ice sheet melt 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 This section is an excerpt from Greenland ice sheet edit Every summer parts of the surface melt and ice cliffs calve into the sea Normally the ice sheet would be replenished by winter snowfall but due to global warming the ice sheet is melting two to five times faster than before 1850 and snowfall has not kept up since 1996 If the Paris Agreement goal of staying below 2 C 3 6 F is achieved melting of Greenland ice alone would still add around 6 cm 2 1 2 in to global sea level rise by the end of the century If there are no reductions in emissions melting would add around 13 cm 5 in by 2100 1302 with a worst case of about 33 cm 13 in For comparison melting has so far contributed 1 4 cm 1 2 in since 1972 while sea level rise from all sources was 15 25 cm 6 10 in between 1901 and 2018 5 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 Global warming between 1 7 C 3 1 F and 2 3 C 4 1 F would likely make this melting inevitable 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 and more ice will be lost if the temperatures exceed that level before declining If global temperatures continue to rise the ice sheet will likely disappear within 10 000 years At very high warming its future lifetime goes down to around 1 000 years This section is an excerpt from Climate change in Antarctica edit The West Antarctic ice sheet is likely to completely melt unless temperatures are reduced by 2 C 3 6 F below 2020 levels The loss of this ice sheet would take between 2 000 and 13 000 years although several centuries of high greenhouse emissions could shorten this time to 500 years 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 Isostatic rebound may contribute an additional 1 m 3 ft 3 in to global sea levels over another 1 000 years 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 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 potentially adding up to 6 4 m 21 ft 0 in to sea levels The complete melting and disappearance of the East Antarctic ice sheet would require at least 10 000 years and would only occur if global warming reaches 5 C 9 0 F to 10 C 18 F Decline of glaciers This section is an excerpt from Retreat of glaciers since 1850 edit Example of a mountain glacier retreat White Chuck Glacier WashingtonWhite Chuck Glacier in the United States in 1973Same vantage point in 2006 at the same time of the year The glacier retreated 1 9 kilometres 1 2 mi in 33 years The retreat of glaciers since 1850 is a well documented effect of climate change The retreat of mountain glaciers provide 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 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 They are several kilometers deep and obscure the underlying topography Sea ice decline 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 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 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 Large scale measurements of sea ice have only been possible since satellites came into use 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 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 8 The Arctic will likely become ice free at the end of some summers before 2050 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 Permafrost thaw 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 Shrinkage of snow cover duration in the Alps starting ca end of the 19th century highlighting climate change adaptation needs Studies in 2021 found that Northern Hemisphere snow cover has been decreasing since 1978 along with snow depth Paleoclimate observations show that such changes are unprecedented over the last millennia in Western North America North American winter snow cover increased during the 20th century largely in response to an increase in precipitation 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 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