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105-521: Cryologists describe how ice patches, such the rare Yukon alpine region ice patches, differ from glaciers. The latter are constantly moving; they gradually build up mass over time until they reach a certain size, when they slowly flow downhill. Unlike glaciers, ice patches do not move. As some of the snow remaining from winter accumulation melts, the rest is gradually compressed into ice. Ice patches do not achieve enough mass to flow downhill so any artifacts within are preserved intact without being crushed. In

210-487: A climate change feedback if it is gradually released through meltwater, thus increasing overall carbon dioxide emissions . For comparison, 1400–1650 billion tonnes are contained within the Arctic permafrost . Also for comparison, the annual human caused carbon dioxide emissions amount to around 40 billion tonnes of CO 2 . In Greenland, there is one known area, at Russell Glacier , where meltwater carbon

315-518: A continental glacier , is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km (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 km are termed an ice cap . An ice cap will typically feed

420-581: A 1 m tidal oscillation can be felt as much as 100 km from the sea. During larger spring tides , an ice stream will remain almost stationary for hours at a time, before a surge of around a foot in under an hour, just after the peak high tide; a stationary period then takes hold until another surge towards the middle or end of the falling tide. At neap tides, this interaction is less pronounced, and surges instead occur approximately every 12 hours. Increasing global air temperatures due to climate change take around 10,000 years to directly propagate through

525-425: A buttressing effect on the ice sheet, the so-called back stress increases and the grounding line is pushed backwards. The ice sheet is likely to start losing more ice from the new location of the grounding line and so become lighter and less capable of displacing seawater. This eventually pushes the grounding line back even further, creating a self-reinforcing mechanism . Because the entire West Antarctic Ice Sheet

630-426: A higher level of warming. Isostatic rebound of ice-free land may also add around 1 m (3 ft 3 in) to the global sea levels over another 1,000 years. The East Antarctic Ice Sheet (EAIS) lies between 45° west and 168° east longitudinally. It was first formed around 34 million years ago, and it is the largest ice sheet on the entire planet, with far greater volume than the Greenland ice sheet or

735-461: A latitude of 77°N , near its northern edge. 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 . The term 'Greenland ice sheet' is often shortened to GIS or GrIS in scientific literature . The retreat of glaciers since 1850 is a well-documented effect of climate change . The retreat of mountain glaciers provide evidence for

840-432: A much greater area than this minimum definition, measuring at 1.7 million km and 14 million km , respectively. Both ice sheets are also very thick, as they consist of a continuous ice layer with an average thickness of 2 km (1 mi). This ice layer forms because most of the snow which falls onto the ice sheet never melts, and is instead compressed by the mass of newer snow layers. This process of ice sheet growth

945-705: A portion of the ice sheet collapses. External factors might also play a role in forcing ice sheets. Dansgaard–Oeschger events are abrupt warmings of the northern hemisphere occurring over the space of perhaps 40 years. While these D–O events occur directly after each Heinrich event, they also occur more frequently – around every 1500 years; from this evidence, paleoclimatologists surmise that the same forcings may drive both Heinrich and D–O events. Hemispheric asynchrony in ice sheet behavior has been observed by linking short-term spikes of methane in Greenland ice cores and Antarctic ice cores. During Dansgaard–Oeschger events ,

1050-430: 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

1155-430: 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

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1260-460: A shallow fjord and stabilized) could have involved MICI, but there weren't enough observations to confirm or refute this theory. The retreat of Greenland ice sheet 's three largest glaciers - Jakobshavn , Helheim , and Kangerdlugssuaq Glacier - did not resemble predictions from ice cliff collapse at least up until the end of 2013, but an event observed at Helheim Glacier in August 2014 may fit

1365-426: 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

1470-407: 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. Historically, ice sheets were viewed as inert components of the carbon cycle and were largely disregarded in global models. In 2010s, research had demonstrated

1575-517: Is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more: the oldest permafrost had 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

1680-406: 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

1785-399: 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 . Through these feedback processes, the cryosphere plays a significant role in

1890-409: Is about 1 million years old. Due to anthropogenic greenhouse gas emissions , the ice sheet is now the warmest it has been in the past 1000 years, and is losing ice at the fastest rate in at least the past 12,000 years. 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

1995-399: 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

2100-469: 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. 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

2205-925: 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 . Most of the Earth's snow-covered area is located in the Northern Hemisphere , and varies seasonally from 46.5 million km in January to 3.8 million km in August. Snow cover

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2310-571: 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

2415-427: Is an important indicator of climate change. 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. 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

2520-456: Is believed that the loss of the ice sheet would take place between 2,000 and 13,000 years in the future, although several centuries of high emissions may shorten this to 500 years. 3.3 m (10 ft 10 in) of sea level rise would occur if the ice sheet collapses but leaves ice caps on the mountains behind. Total sea level rise from West Antarctica increases to 4.3 m (14 ft 1 in) if they melt as well, but this would require

2625-534: 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

2730-468: Is evidence of large glaciers in Greenland for most of the past 18 million years, these ice bodies were probably similar to various smaller modern examples, such as Maniitsoq and Flade Isblink , which cover 76,000 and 100,000 square kilometres (29,000 and 39,000 sq mi) around the periphery. Conditions in Greenland were not initially suitable for a single coherent ice sheet to develop, but this began to change around 10 million years ago , during

2835-483: Is grounded below the sea level, it would be vulnerable to geologically rapid ice loss in this scenario. In particular, the Thwaites and Pine Island glaciers are most likely to be prone to MISI, and both glaciers have been rapidly thinning and accelerating in recent decades. As the result, sea level rise from the ice sheet could be accelerated by tens of centimeters within the 21st century alone. The majority of

2940-432: 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

3045-431: 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 . The term cryosphere comes from

3150-724: Is known to vary on seasonal to interannual timescales. The Wilkes Basin is the only major submarine basin in Antarctica that is not thought to be sensitive to warming. Ultimately, even geologically rapid sea level rise would still most likely require several millennia for the entirety of these ice masses (WAIS and the subglacial basins) to be lost. A related process known as Marine Ice Cliff Instability (MICI) posits that ice cliffs which exceed ~ 90 m ( 295 + 1 ⁄ 2  ft) in above-ground height and are ~ 800 m ( 2,624 + 1 ⁄ 2  ft) in basal (underground) height are likely to collapse under their own weight once

3255-400: 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. Lake freeze-up depends on the heat storage in the lake and therefore on its depth,

Yukon Ice Patches - Misplaced Pages Continue

3360-501: 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, with

3465-777: 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 km in September to a maximum of 14–16 million km in March. The ice cover exhibits much greater regional-scale interannual variability than it does hemispherical. For instance, in

3570-448: 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 km (6.9 million sq mi). This includes large areas of Alaska , Canada , Greenland , and Siberia . It

3675-455: 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 . 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

3780-487: Is released into the atmosphere as methane , which has a much larger global warming potential than carbon dioxide. However, it also harbours large numbers of methanotrophic bacteria, which limit those emissions. Normally, the transitions between glacial and interglacial states are governed by Milankovitch cycles , which are patterns in insolation (the amount of sunlight reaching the Earth). These patterns are caused by

3885-484: Is still occurring nowadays, as can be clearly seen in an example that occurred in World War II . A Lockheed P-38 Lightning fighter plane crashed in Greenland in 1942. It was only recovered 50 years later. By then, it had been buried under 81 m (268 feet) of ice which had formed over that time period. Even stable ice sheets are continually in motion as the ice gradually flows outward from the central plateau, which

3990-524: Is still open for debate. The icing of Antarctica began in the Late Palaeocene or middle Eocene between 60 and 45.5 million years ago and escalated during the Eocene–Oligocene extinction event about 34 million years ago. CO 2 levels were then about 760 ppm and had been decreasing from earlier levels in the thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm,

4095-458: 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 10 J/kg at 0 °C). However, the strong static stability of the atmosphere over areas of extensive snow or ice tends to confine

4200-707: Is the segment of the continental ice sheet that covers West Antarctica , the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere . It is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf , the Ronne Ice Shelf , and outlet glaciers that drain into

4305-456: 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. This difference in slope occurs due to an imbalance between high ice accumulation in the central plateau and lower accumulation, as well as higher ablation , at the margins. This imbalance increases the shear stress on a glacier until it begins to flow. The flow velocity and deformation will increase as

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4410-512: The Amundsen Sea . As a smaller part of Antarctica, WAIS is also more strongly affected by climate change . There has been warming over the ice sheet since the 1950s, and a substantial retreat of its coastal glaciers since at least the 1990s. Estimates suggest it added around 7.6 ± 3.9 mm ( 19 ⁄ 64  ±  5 ⁄ 32  in) to the global sea level rise between 1992 and 2017, and has been losing ice in

4515-503: 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. The thermal properties of cryospheric elements also have important climatic consequences. Snow and ice have much lower thermal diffusivities than air . Thermal diffusivity

4620-536: 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

4725-816: 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 km (5 million sq mi) or about 98% of Antarctica 's 13.2 million km (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

4830-713: 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 . An ice sheet is a body of ice which covers a land area of continental size - meaning that it exceeds 50,000 km . The currently existing two ice sheets in Greenland and Antarctica have

4935-644: The West Antarctic Ice Sheet (WAIS), from which it is separated by the Transantarctic Mountains . The ice sheet is around 2.2 km (1.4 mi) thick on average and is 4,897 m (16,066 ft) at its thickest point. It is also home to the geographic South Pole , South Magnetic Pole and the Amundsen–Scott South Pole Station . The surface of the EAIS is the driest, windiest, and coldest place on Earth. Lack of moisture in

5040-551: The Younger Dryas period which appears consistent with MICI. However, it indicates "relatively rapid" yet still prolonged ice sheet retreat, with a movement of >200 km (120 mi) inland taking place over an estimated 1100 years (from ~12,300 years Before Present to ~11,200 B.P.) In recent years, 2002-2004 fast retreat of Crane Glacier immediately after the collapse of the Larsen B ice shelf (before it reached

5145-423: 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. The cryosphere describes those portions of Earth 's surface where water

5250-548: 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

5355-482: 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 : / ˈ ɡ l eɪ ʃ ər / ; UK : / ˈ ɡ l æ s i ər , ˈ ɡ l eɪ s i ər / ) is a persistent body of dense ice that is constantly moving downhill under its own weight. A glacier forms where

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5460-501: 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 . Ice sheet#Melting due to climate change In glaciology , an ice sheet , also known as

5565-510: 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

5670-629: The 1990s "during a period of extremely warm summer temperatures" with ice patches melting, the Yukon Ice Patch Project began. In September 1997, Gerald W. Kuzyk discovered the first of the Yukon ice patches artifacts, an atlatl dart fragment, on mountain Thandlät at an elevation of 1,850 m (6,070 ft). The Yukon Ice Patches are studied by archaeologists in partnership with six Yukon First Nations, on whose traditional territory

5775-555: The 2010s at a rate equivalent to 0.4 millimetres (0.016 inches) of annual sea level rise. While some of its losses are offset by the growth of the East Antarctic ice sheet , Antarctica as a whole will most likely lose enough ice by 2100 to add 11 cm (4.3 in) to sea levels. Further, marine ice sheet instability may increase this amount by tens of centimeters, particularly under high warming. Fresh meltwater from WAIS also contributes to ocean stratification and dilutes

5880-502: The Antarctic winter is cooler at the surface than in its middle layers. Consequently, greenhouse gases actually trap heat in the middle atmosphere and reduce its flow towards the surface while the temperature inversion lasts. Due to these factors, East Antarctica had experienced slight cooling for decades while the rest of the world warmed as the result of climate change . Clear warming over East Antarctica only started to occur since

5985-412: 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). The Arctic will likely become ice-free at

6090-500: The Earth's mountains fills the rivers and recharges the aquifers that over a billion people depend on for their water resources. 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. 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,

6195-510: The East Antarctic Ice Sheet would not be affected. Totten Glacier is the largest glacier there which is known to be subject to MISI - yet, its potential contribution to sea level rise is comparable to that of the entire West Antarctic Ice Sheet. Totten Glacier has been losing mass nearly monotonically in recent decades, suggesting rapid retreat is possible in the near future, although the dynamic behavior of Totten Ice Shelf

6300-503: The Ice Patch artifacts...Oral history tells us that a corral, or caribou fence was located on the east side of the lake, between the lake and the mountain." Cryologists 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

6405-656: The SLR was greater than 6 m ( 19 + 1 ⁄ 2  ft). As of 2023, the most recent analysis indicates that the Last Interglacial SLR is unlikely to have been higher than 2.7 m (9 ft), as higher values in other research, such as 5.7 m ( 18 + 1 ⁄ 2  ft), appear inconsistent with the new paleoclimate data from The Bahamas and the known history of the Greenland Ice Sheet. The West Antarctic Ice Sheet (WAIS)

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6510-422: 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

6615-412: The air, high albedo from the snow as well as the surface's consistently high elevation results in the reported cold temperature records of nearly −100 °C (−148 °F). It is the only place on Earth cold enough for atmospheric temperature inversion to occur consistently. That is, while the atmosphere is typically warmest near the surface and becomes cooler at greater elevation, atmosphere during

6720-416: The base of the glacier in as little as 2–18 hours – lubricating the bed and causing the glacier to surge . Water that reaches the bed of a glacier may freeze there, increasing the thickness of the glacier by pushing it up from below. As the margins end at the marine boundary, excess ice is discharged through ice streams or outlet glaciers . Then, it either falls directly into the sea or is accumulated atop

6825-427: The boulders and other continental rocks they carried, leaving layers known as ice rafted debris . These so-called Heinrich events , named after their discoverer Hartmut Heinrich , appear to have a 7,000–10,000-year periodicity , and occur during cold periods within the last interglacial. Internal ice sheet "binge-purge" cycles may be responsible for the observed effects, where the ice builds to unstable levels, then

6930-477: The case of forests. 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

7035-605: 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. 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

7140-541: 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. Sea ice covers much of

7245-604: 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

7350-402: The collapse of Larsen B, in context. In the 1970s, Johannes Weertman proposed that because seawater is denser than ice, then any ice sheets grounded below sea level inherently become less stable as they melt due to Archimedes' principle . Effectively, these marine ice sheets must have enough mass to exceed the mass of the seawater displaced by the ice, which requires excess thickness. As

7455-515: The continent since the 1957. 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. 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. The ice sheet covers 1,710,000 square kilometres (660,000 sq mi), around 80% of

7560-505: The definition. Further, modelling done after the initial hypothesis indicates that ice-cliff instability would require implausibly fast ice shelf collapse (i.e. within an hour for ~ 90 m ( 295 + 1 ⁄ 2  ft)-tall cliffs), unless the ice had already been substantially damaged beforehand. Further, ice cliff breakdown would produce a large number of debris in the coastal waters - known as ice mélange - and multiple studies indicate their build-up would slow or even outright stop

7665-558: The end of some summers before 2050. 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

7770-522: The equilibrium line between these two processes is approached. This motion is driven by gravity but is controlled by temperature and the strength of individual glacier bases. A number of processes alter these two factors, resulting in cyclic surges of activity interspersed with longer periods of inactivity, on time scales ranging from hourly (i.e. tidal flows) to the centennial (Milankovich cycles). On an unrelated hour-to-hour basis, surges of ice motion can be modulated by tidal activity. The influence of

7875-498: The existence of uniquely adapted microbial communities , high rates of biogeochemical and physical weathering in ice sheets, and storage and cycling of organic carbon in excess of 100 billion tonnes. There is a massive contrast in carbon storage between the two ice sheets. While only about 0.5-27 billion tonnes of pure carbon are present underneath the Greenland ice sheet, 6000-21,000 billion tonnes of pure carbon are thought to be located underneath Antarctica. This carbon can act as

7980-406: The floating ice shelves . Those ice shelves then calve icebergs at their periphery if they experience excess of ice. Ice shelves would also experience accelerated calving due to basal melting. In Antarctica, this is driven by heat fed to the shelf by the circumpolar deep water current, which is 3 °C above the ice's melting point. The presence of ice shelves has a stabilizing influence on

8085-528: The formation of salty Antarctic bottom water , which destabilizes Southern Ocean overturning circulation . In the long term, the West Antarctic Ice Sheet is likely to disappear due to the warming which has already occurred. Paleoclimate evidence suggests that this has already happened during the Eemian period, when the global temperatures were similar to the early 21st century. It

8190-448: 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

8295-529: The glacier behind them, while an absence of an ice shelf becomes destabilizing. For instance, when Larsen B ice shelf in the Antarctic Peninsula had collapsed over three weeks in February 2002, the four glaciers behind it - Crane Glacier , Green Glacier , Hektoria Glacier and Jorum Glacier - all started to flow at a much faster rate, while the two glaciers (Flask and Leppard) stabilized by

8400-409: The ice as well as by ice thickness and freshwater inflow. 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. 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

8505-437: 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. Lakes of a diameter greater than ~300 m are capable of creating a fluid-filled crevasse to the glacier/bed interface. When these crevasses form, the entirety of the lake's (relatively warm) contents can reach

8610-599: 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. 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

8715-881: The ice patches were found. They include the Carcross/Tagish First Nation , the Kwanlin Dün First Nation , the Ta’an Kwäch’än Council , the Champagne and Aishihik First Nations , the Kluane First Nation , and the Teslin Tlingit Council . "At [the Kusawa Lake] location, a small fragment of wooden dart shaft was recovered and radiocarbon dated to 4360 ± 50 14C yr BP (TO 6870). Also reported

8820-415: The ice sheet melts and becomes thinner, the weight of the overlying ice decreases. At a certain point, sea water could force itself into the gaps which form at the base of the ice sheet, and marine ice sheet instability (MISI) would occur. Even if the ice sheet is grounded below the sea level, MISI cannot occur as long as there is a stable ice shelf in front of it. The boundary between the ice sheet and

8925-538: The ice sheets of Antarctica and Greenland, has been estimated at 170,000 km . 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 km (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 km are termed an ice cap . An ice cap will typically feed

9030-440: The ice shelf, known as the grounding line , is particularly stable if it is constrained in an embayment . In that case, the ice sheet may not be thinning at all, as the amount of ice flowing over the grounding line would be likely to match the annual accumulation of ice from snow upstream. Otherwise, ocean warming at the base of an ice shelf tends to thin it through basal melting. As the ice shelf becomes thinner, it exerts less of

9135-406: 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. There are numerous cryosphere-climate feedbacks in

9240-466: The instability soon after it started. Some scientists - including the originators of the hypothesis, Robert DeConto and David Pollard - have suggested that the best way to resolve the question would be to precisely determine sea level rise during the Last Interglacial . MICI can be effectively ruled out if SLR at the time was lower than 4 m (13 ft), while it is very likely if

9345-474: 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 . The surface reflectance of incoming solar radiation

9450-408: The monsoon is just one example of a short-term cryosphere-climate feedback involving the land surface and the atmosphere. 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

9555-475: The northern hemisphere warmed considerably, dramatically increasing the release of methane from wetlands, that were otherwise tundra during glacial times. This methane quickly distributes evenly across the globe, becoming incorporated in Antarctic and Greenland ice. With this tie, paleoclimatologists have been able to say that the ice sheets on Greenland only began to warm after the Antarctic ice sheet had been warming for several thousand years. Why this pattern occurs

9660-415: The peripheral ice stabilizing them is gone. Their collapse then exposes the ice masses following them to the same instability, potentially resulting in a self-sustaining cycle of cliff collapse and rapid ice sheet retreat - i.e. sea level rise of a meter or more by 2100 from Antarctica alone. This theory had been highly influential - in a 2020 survey of 106 experts, the paper which had advanced this theory

9765-402: 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 km in February to a maximum of 17–20 million km in September. The seasonal variation

9870-453: 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

9975-546: The region of the Sea of Okhotsk and Japan , maximum ice extent decreased from 1.3 million km in 1983 to 0.85 million km in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km . 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. Permafrost (from perma-  ' permanent ' and frost )

10080-569: The remnants of the ice shelf did not accelerate. The collapse of the Larsen B shelf was preceded by thinning of just 1 metre per year, while some other Antarctic ice shelves have displayed thinning of tens of metres per year. Further, increased ocean temperatures of 1 °C may lead to up to 10 metres per year of basal melting. Ice shelves are always stable under mean annual temperatures of −9 °C, but never stable above −5 °C; this places regional warming of 1.5 °C, as preceded

10185-554: The retreat of cryospheric features. 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

10290-404: The southern Yukon. The artifacts range in age from a 9000-year-old (calendar) dart shaft to a 19th-century musket ball...Of particular interest is the description of three different techniques for the construction of throwing darts and the observation of stability in the hunting technology employed in the study area over seven millennia. Radiocarbon chronologies indicate that this period of stability

10395-448: The surface of Greenland , or about 12% of the area of the Antarctic ice sheet . The term 'Greenland ice sheet' is often shortened to GIS or GrIS in scientific literature . Greenland has had major glaciers and ice caps for at least 18 million years, but a single ice sheet first covered most of the island some 2.6 million years ago. Since then, it has both grown and contracted significantly. The oldest known ice on Greenland

10500-535: The variations in shape of the Earth's orbit and its angle relative to the Sun, caused by the gravitational pull of other planets as they go through their own orbits. For instance, during at least the last 100,000 years, portions of the ice sheet covering much of North America, the Laurentide Ice Sheet broke apart sending large flotillas of icebergs into the North Atlantic. When these icebergs melted they dropped

10605-460: The year 2000, and was not conclusively detected until the 2020s. In the early 2000s, cooling over East Antarctica seemingly outweighing warming over the rest of the continent was frequently misinterpreted by the media and occasionally used as an argument for climate change denial . After 2009, improvements in Antarctica's instrumental temperature record have proven that the warming over West Antarctica resulted in consistent net warming across

10710-639: Was a caribou dung pellet dating to 2450 ± 14C yr BP (TO 6871) collected from a nearby ice core 1.6 m (5.2 ft) below the surface (Kuzyk et al., 1999:214). That first brief research report represented one of the earliest accounts of ancient, non-glacial ice in North America and drew attention to the potential of alpine ice to be a productive source of paleobiological and archaeological information" The 43 Yukon Ice Patches in southern Yukon included "more than 207 archaeological objects and 1700 faunal remains have been recovered from 43 melting ice patches in

10815-886: Was considered more important than even the year 2014 IPCC Fifth Assessment Report . Sea level rise projections which involve MICI are much larger than the others, particularly under high warming rate. At the same time, this theory has also been highly controversial. It was originally proposed in order to describe how the large sea level rise during the Pliocene and the Last Interglacial could have occurred - yet more recent research found that these sea level rise episodes can be explained without any ice cliff instability taking place. Research in Pine Island Bay in West Antarctica (the location of Thwaites and Pine Island Glacier ) had found seabed gouging by ice from

10920-553: Was followed by an abrupt technological replacement of the throwing dart by the bow and arrow after 1200 BP." The artifacts are curated by the Yukon Archaeology Program, Government of Yukon. In the Kusawa Lake area, there are no longer any caribou , but in her 1987 interviews, Elder Mary Ned (born 1890s-) spoke about caribou being “all over this place.” Evidence of this was proven by the nearby discovery of

11025-527: Was the primary agent forcing Antarctic glaciation. The glaciation was favored by an interval when the Earth's orbit favored cool summers but oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an ice age of some size. The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO 2 levels to have been more important. While there

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