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 a series of glaciers around its periphery.
196-482: 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
392-424: A cirque landform (alternatively known as a corrie or as a cwm ) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes ) – which collects and compresses through gravity the snow that falls into it. This snow accumulates and the weight of the snow falling above compacts it, forming névé (granular snow). Further crushing of the individual snowflakes and squeezing
588-487: 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
784-581: 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
980-487: A 28-square-kilometre (11 sq mi) iceberg breaking off in 2008, and then a 260 square kilometres (100 sq mi) iceberg calving from ice shelf in August 2010. This became the largest Arctic iceberg since 1962, and amounted to a quarter of the shelf's size. In July 2012, Petermann glacier lost another major iceberg, measuring 120 square kilometres (46 sq mi), or twice the area of Manhattan . As of 2023,
1176-425: 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
1372-505: A combination of high temperatures and unsuitable cloud cover led to an even larger mass melting event, which ultimately covered over 300,000 sq mi (776,996.4 km) at its greatest extent. Predictably, 2019 set a new record of 586 Gt net mass loss. In July 2021, another record mass melting event occurred. At its peak, it covered 340,000 sq mi (880,596.0 km), and led to daily ice losses of 88 Gt across several days. High temperatures continued in August 2021, with
1568-522: A glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area is snow-covered at the end of the melt season, and they have a terminus with a vigorous flow. Following the Little Ice Age 's end around 1850, glaciers around the Earth have retreated substantially . A slight cooling led to
1764-601: 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
1960-411: A glacier via moulins . Streams within or beneath a glacier flow in englacial or sub-glacial tunnels. These tunnels sometimes reemerge at the glacier's surface. Most of the important processes controlling glacial motion occur in the ice-bed contact—even though it is only a few meters thick. The bed's temperature, roughness and softness define basal shear stress, which in turn defines whether movement of
2156-482: 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
SECTION 10
#17327655094302352-506: A hypothetical future would greatly increase ice loss, but still wouldn't melt the entire ice sheet within the study period. On the ice sheet, annual temperatures are generally substantially lower than elsewhere in Greenland: about −20 °C (−4 °F) at the south dome (latitudes 63° – 65°N ) and −31 °C (−24 °F) near the center of the north dome (latitude 72°N (the fourth highest "summit" of Greenland ). On 22 December 1991,
2548-408: A kilometer per year. Eventually, the ice will be surging fast enough that it begins to thin, as accumulation cannot keep up with the transport. This thinning will increase the conductive heat loss, slowing the glacier and causing freezing. This freezing will slow the glacier further, often until it is stationary, whence the cycle can begin again. The flow of water under the glacial surface can have
2744-456: A kilometer with the tide. It has been suggested that if similar processes can occur at the other glaciers, then their eventual rate of mass loss could be doubled. There are several ways in which increased melting at the surface of the ice sheet can accelerate lateral retreat of outlet glaciers. Firstly, the increase in meltwater at the surface causes larger amounts to flow through the ice sheet down to bedrock via moulins . There, it lubricates
2940-404: A large effect on the motion of the glacier itself. Subglacial lakes contain significant amounts of water, which can move fast: cubic kilometers can be transported between lakes over the course of a couple of years. This motion is thought to occur in two main modes: pipe flow involves liquid water moving through pipe-like conduits, like a sub-glacial river; sheet flow involves motion of water in
3136-460: A lower heat conductance, meaning that the basal temperature is also likely to be higher. Bed temperature tends to vary in a cyclic fashion. A cool bed has a high strength, reducing the speed of the glacier. This increases the rate of accumulation, since newly fallen snow is not transported away. Consequently, the glacier thickens, with three consequences: firstly, the bed is better insulated, allowing greater retention of geothermal heat. Secondly,
3332-460: A marked increase in glacial earthquakes between 1993 and 2005. Since then, it has remained comparatively stable near its 2005 position, losing relatively little mass in comparison to Jakobshavn and Kangerlussuaq, although it may have eroded sufficiently to experience another rapid retreat in the near future. Meanwhile, smaller glaciers have been consistently losing mass at an accelerating rate, and later research has concluded that total glacier retreat
3528-432: 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
3724-493: A net loss of −44 ± 53 gigatonnes per year. Annual ice losses from the Greenland ice sheet accelerated in the 2000s, reaching ~187 Gt/yr in 2000–2010, and an average mass loss during 2010–2018 of 286 Gt per year. Half of the ice sheet's observed net loss (3,902 gigatons (Gt) of ice between 1992 and 2018, or approximately 0.13% of its total mass) happened during those 8 years. When converted to sea level rise equivalent,
3920-466: A phase of [[North Atlantic oscillation]] increasing snowfall. Every summer, a so-called snow line separates the ice sheet's surface into areas above it, where snow continues to accumulate even then, with the areas below the line where summer melting occurs. The exact position of the snow line moves around every summer, and if it moves away from some areas it covered the previous year, then those tend to experience substantially greater melt as their darker ice
4116-648: 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 ,
SECTION 20
#17327655094304312-407: 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
4508-400: A small chance of the ice sheet gaining mass and thus reducing the sea levels by around 2 cm (1 in). Some scientists, led by James Hansen , have claimed that the ice sheets can disintegrate substantially faster than estimated by the ice sheet models , but even their projections also have much of Greenland, whose total size amounts to 7.4 m (24 ft) of sea level rise, survive
4704-559: A temperature of −69.6 °C (−93.3 °F) was recorded at an automatic weather station near the topographic summit of the Greenland Ice Sheet, making it the lowest temperature ever recorded in the Northern Hemisphere . The record went unnoticed for more than 28 years and was finally recognized in 2020. These low temperatures are in part caused by the high albedo of the ice sheet, as its bright white surface
4900-488: A thin layer. A switch between the two flow conditions may be associated with surging behavior. Indeed, the loss of sub-glacial water supply has been linked with the shut-down of ice movement in the Kamb ice stream. The subglacial motion of water is expressed in the surface topography of ice sheets, which slump down into vacated subglacial lakes. The speed of glacial displacement is partly determined by friction . Friction makes
5096-410: A tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by climate change than other glaciers. Thermally, a temperate glacier is at a melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing threshold from the surface to its base, although
5292-562: A very likely range ( 5–95% confidence level ) of 5–23 cm (2–9 in)), while the "moderate" SSP2-4.5 scenario adds 8 cm (3 in) with a likely and very likely range of 4–13 cm ( 1 + 1 ⁄ 2 –5 in) and 1–18 cm ( 1 ⁄ 2 –7 in), respectively. The optimistic scenario which assumes that the Paris Agreement goals are largely fulfilled, SSP1-2.6, adds around 6 cm ( 2 + 1 ⁄ 2 in) and no more than 15 cm (6 in), with
5488-593: A whole. Further, more precipitation in the northwest had been falling as rain instead of snow, with a fourfold increase in rain since 1980. Rain is warmer than snow and forms darker and less thermally insulating ice layer once it does freeze on the ice sheet. It is particularly damaging when it falls due to late-summer cyclones, whose increasing occurrence has been overlooked by the earlier models. There has also been an increase in water vapor , which paradoxically increases melting by making it easier for heat to radiate downwards through moist, as opposed to dry, air. Altogether,
5684-407: 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
5880-687: 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. 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
6076-443: Is about 0.5-27 billion tonnes of pure carbon underneath the entire ice sheet, and much less within it. This is much less than the 1400–1650 billion tonnes contained within the Arctic permafrost , or the annual anthropogenic emissions of around 40 billion tonnes of CO 2 .) Yet, the release of this carbon through meltwater can still act as a climate change feedback if it increases overall carbon dioxide emissions. There
Greenland ice sheet - Misplaced Pages Continue
6272-409: 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
6468-405: 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
6664-456: Is above or at freezing at the interface and is able to slide at this contact. This contrast is thought to a large extent to govern the ability of a glacier to effectively erode its bed , as sliding ice promotes plucking at rock from the surface below. Glaciers which are partly cold-based and partly warm-based are known as polythermal . Glaciers form where the accumulation of snow and ice exceeds ablation . A glacier usually originates from
6860-407: Is affected by factors such as slope, ice thickness, snowfall, longitudinal confinement, basal temperature, meltwater production, and bed hardness. A few glaciers have periods of very rapid advancement called surges . These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous movement state. These surges may be caused by the failure of the underlying bedrock,
7056-411: Is because these peaks are located near or in the hyperarid Atacama Desert . Glaciers erode terrain through two principal processes: plucking and abrasion . As glaciers flow over bedrock, they soften and lift blocks of rock into the ice. This process, called plucking, is caused by subglacial water that penetrates fractures in the bedrock and subsequently freezes and expands. This expansion causes
7252-456: 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
7448-406: Is by basal sliding, where meltwater forms between the ice and the bed itself. Whether a bed is hard or soft depends on the porosity and pore pressure; higher porosity decreases the sediment strength (thus increases the shear stress τ B ). Porosity may vary through a range of methods. Bed softness may vary in space or time, and changes dramatically from glacier to glacier. An important factor
7644-434: Is called glaciology . Glaciers are important components of the global cryosphere . Glaciers are categorized by their morphology, thermal characteristics, and behavior. Alpine glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier , or alternatively, an alpine glacier or mountain glacier . A large body of glacial ice astride a mountain, mountain range, or volcano
7840-416: Is called rock flour and is made up of rock grains between 0.002 and 0.00625 mm in size. Abrasion leads to steeper valley walls and mountain slopes in alpine settings, which can cause avalanches and rock slides, which add even more material to the glacier. Glacial abrasion is commonly characterized by glacial striations . Glaciers produce these when they contain large boulders that carve long scratches in
8036-429: 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
Greenland ice sheet - Misplaced Pages Continue
8232-468: 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
8428-407: Is expected to overtake that of Greenland later this century. Retreat of outlet glaciers as they shed ice into the Arctic is a large factor in the decline of Greenland's ice sheet. Estimates suggest that losses from glaciers explain between 49% and 66.8% of observed ice loss since the 1980s. Net loss of ice was already observed across 70% of the ice sheet margins by the 1990s, with thinning detected as
8624-691: Is exposed. Uncertainty about the snow line is one of the factors making it hard to predict each melting season in advance. A notable example of ice accumulation rates above the snow line is provided by Glacier Girl , a Lockheed P-38 Lightning fighter plane which had crashed early in World War II and was recovered in 1992, by which point it had been buried under 268 ft ( 81 + 1 ⁄ 2 m) of ice. Another example occurred in 2017, when an Airbus A380 had to make an emergency landing in Canada after one of its jet engines exploded while it
8820-483: 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
9016-647: Is higher, and the mountains above 5,000 m (16,400 ft) usually have permanent snow. Even at high latitudes, glacier formation is not inevitable. Areas of the Arctic , such as Banks Island , and the McMurdo Dry Valleys in Antarctica are considered polar deserts where glaciers cannot form because they receive little snowfall despite the bitter cold. Cold air, unlike warm air, is unable to transport much water vapor. Even during glacial periods of
9212-665: 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
9408-437: 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
9604-431: 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
9800-455: Is one known area, at Russell Glacier , where meltwater carbon is released into the atmosphere in the form of methane (see arctic methane emissions ), which has a much larger global warming potential than carbon dioxide. However, the area also harbours large numbers of methanotrophic bacteria, which limit those methane emissions. In 2021, research claimed that there must be mineral deposits of mercury (a highly toxic heavy metal ) beneath
9996-445: Is over 20 mi (32 km) long, 4.5 mi (7 km) wide and around 1 km ( 1 ⁄ 2 mi) thick, which makes it the third largest glacier in Greenland. Between 1993 and 1998, parts of the glacier within 5 km (3 mi) of the coast lost 50 m (164 ft) in height. Its observed ice flow speed went from 3.1–3.7 mi (5–6 km) per year in 1988–1995 to 8.7 mi (14 km) per year in 2005, which
SECTION 50
#173276550943010192-487: 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
10388-424: 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
10584-524: 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,
10780-502: Is stopped by a sufficiently large obstacle, such as a mountain . Greenland has many mountains near its coastline , which normally prevent the ice sheet from flowing further into the Arctic Ocean . The 11 previous episodes of glaciation are notable because the ice sheet grew large enough to flow over those mountains. Nowadays, the northwest and southeast margins of the ice sheet are the main areas where there are sufficient gaps in
10976-897: Is termed an ice cap or ice field . Ice caps have an area less than 50,000 km (19,000 sq mi) by definition. Glacial bodies larger than 50,000 km (19,000 sq mi) are called ice sheets or continental glaciers . Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces. The only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of freshwater, enough that if both melted, global sea levels would rise by over 70 m (230 ft). Portions of an ice sheet or cap that extend into water are called ice shelves ; they tend to be thin with limited slopes and reduced velocities. Narrow, fast-moving sections of an ice sheet are called ice streams . In Antarctica, many ice streams drain into large ice shelves . Some drain directly into
11172-413: Is the region where there is a net loss in glacier mass. The upper part of a glacier, where accumulation exceeds ablation, is called the accumulation zone . The equilibrium line separates the ablation zone and the accumulation zone; it is the contour where the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. In general, the accumulation zone accounts for 60–70% of
11368-707: 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
11564-577: 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
11760-456: 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
11956-402: Is the underlying geology; glacial speeds tend to differ more when they change bedrock than when the gradient changes. Further, bed roughness can also act to slow glacial motion. The roughness of the bed is a measure of how many boulders and obstacles protrude into the overlying ice. Ice flows around these obstacles by melting under the high pressure on their stoss side ; the resultant meltwater
SECTION 60
#173276550943012152-552: Is then forced into the cavity arising in their lee side , where it re-freezes. As well as affecting the sediment stress, fluid pressure (p w ) can affect the friction between the glacier and the bed. High fluid pressure provides a buoyancy force upwards on the glacier, reducing the friction at its base. The fluid pressure is compared to the ice overburden pressure, p i , given by ρgh. Under fast-flowing ice streams, these two pressures will be approximately equal, with an effective pressure (p i – p w ) of 30 kPa; i.e. all of
12348-522: Is underestimated unless the smaller glaciers are accounted for. By 2023, the rate of ice loss across Greenland's coasts had doubled in the two decades since 2000, in large part due to the accelerated losses from smaller glaciers. Since the early 2000s, glaciologists have concluded that glacier retreat in Greenland is accelerating too quickly to be explained by a linear increase in melting in response to greater surface temperatures alone, and that additional mechanisms must also be at work. Rapid calving events at
12544-645: Is very effective at reflecting sunlight. Ice-albedo feedback means that as the temperatures increase, this causes more ice to melt and either reveal bare ground or even just to form darker melt ponds, both of which act to reduce albedo, which accelerates the warming and contributes to further melting. This is taken into account by the climate models , which estimate that a total loss of the ice sheet would increase global temperature by 0.13 °C (0.23 °F), while Greenland's local temperatures would increase by between 0.5 °C (0.90 °F) and 3 °C (5.4 °F). Even incomplete melting already has some impact on
12740-512: 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
12936-993: The Andes , the Himalayas , the Rocky Mountains , the Caucasus , Scandinavian Mountains , and the Alps . Snezhnika glacier in Pirin Mountain, Bulgaria with a latitude of 41°46′09″ N is the southernmost glacial mass in Europe. Mainland Australia currently contains no glaciers, although a small glacier on Mount Kosciuszko was present in the last glacial period . In New Guinea, small, rapidly diminishing, glaciers are located on Puncak Jaya . Africa has glaciers on Mount Kilimanjaro in Tanzania, on Mount Kenya , and in
13132-459: The Atlantic meridional overturning circulation (AMOC). Ice cores provide valuable information about the past states of the ice sheet, and other kinds of paleoclimate data. Subtle differences in the oxygen isotope composition of the water molecules in ice cores can reveal important information about the water cycle at the time, while air bubbles frozen within the ice core provide a snapshot of
13328-644: The Faroe and Crozet Islands were completely glaciated. The permanent snow cover necessary for glacier formation is affected by factors such as the degree of slope on the land, amount of snowfall and the winds. Glaciers can be found in all latitudes except from 20° to 27° north and south of the equator where the presence of the descending limb of the Hadley circulation lowers precipitation so much that with high insolation snow lines reach above 6,500 m (21,330 ft). Between 19˚N and 19˚S, however, precipitation
13524-760: 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
13720-713: 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
13916-562: The Quaternary , Manchuria , lowland Siberia , and central and northern Alaska , though extraordinarily cold, had such light snowfall that glaciers could not form. In addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high (4,500 to 6,900 m or 14,800 to 22,600 ft) and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This
14112-535: The Rwenzori Mountains . Oceanic islands with glaciers include Iceland, several of the islands off the coast of Norway including Svalbard and Jan Mayen to the far north, New Zealand and the subantarctic islands of Marion , Heard , Grande Terre (Kerguelen) and Bouvet . During glacial periods of the Quaternary, Taiwan , Hawaii on Mauna Kea and Tenerife also had large alpine glaciers, while
14308-644: 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
14504-551: 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
14700-432: The effects of climate change on the water cycle could increase snowfall over Greenland, and thus further delay this transition. This hypothesis was difficult to test in the 2000s due to the poor state of long-term precipitation records over the ice sheet. By 2019, it was found that while there was an increase in snowfall over southwest Greenland, there had been a substantial decrease in precipitation over western Greenland as
14896-462: The firn layer at night, which can increase total meltwater runoff by over 30%. Thin, water-rich clouds have the worst impact, and they were the most prominent in July 2012. Ice cores had shown that the last time a melting event of the same magnitude as in 2012 took place was in 1889, and some glaciologists had expressed hope that 2012 was part of a 150-year cycle. This was disproven in summer 2019, when
15092-437: The sea ice and icebergs immediately off-shore were able to survive for longer, and thus helped to stabilize the glacier. Likewise, the rapid retreat and then slowdown of Helheim and Kangerdlugssuaq has also been connected to the respective warming and cooling of nearby currents. At Petermann Glacier, the rapid rate of retreat has been linked to the topography of its grounding line, which appears to shift back and forth by around
15288-418: The 1970s were the last decade when the Greenland ice sheet grew, gaining about 47 gigatonnes per year. From 1980–1990 there was an average annual mass loss of ~51 Gt/y. The period 1990–2000 showed an average annual loss of 41 Gt/y, with 1996 being the last year the Greenland ice sheet saw net mass gain. As of 2022, the Greenland ice sheet had been losing ice for 26 years in a row, and temperatures there had been
15484-448: The 1990s and 2000s. In a study using data from January 1993 through October 2005, more events were detected every year since 2002, and twice as many events were recorded in 2005 as there were in any other year. Ogives or Forbes bands are alternating wave crests and valleys that appear as dark and light bands of ice on glacier surfaces. They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals
15680-555: 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
15876-532: The 21st century. A 2016 paper from Hansen claimed that Greenland ice loss could add around 33 cm (13 in) by 2060, in addition to double that figure from the Antarctic ice sheet , if the CO 2 concentration exceeded 600 parts per million , which was immediately controversial amongst the scientific community, while 2019 research from different scientists claimed a maximum of 33 cm (13 in) by 2100 under
16072-538: The AMOC would weaken by around 18% (with a range of potential weakening between 3% and 34%) under Representative Concentration Pathway 4.5, which is most akin to the current trajectory, while it would weaken by 37% (with a range between 15% and 65%) under Representative Concentration Pathway 8.5, which assumes continually increasing emissions. If the two scenarios are extended past 2100, then the AMOC ultimately stabilizes under RCP 4.5, but it continues to decline under RCP 8.5:
16268-502: 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
16464-463: The Arctic, including Greenland, to warm three to four times more than the global average: thus, while a period like the Eemian interglacial 130,000–115,000 years ago was not much warmer than today globally, the ice sheet was 8 °C (14 °F) warmer, and its northwest part was 130 ± 300 meters lower than it is at present. Some estimates suggest that the most vulnerable and fastest-receding parts of
16660-510: 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
16856-416: The Greenland ice sheet contributed about 13.7 mm since 1972. Between 2012 and 2017, it contributed 0.68 mm per year, compared to 0.07 mm per year between 1992 and 1997. Greenland's net contribution for the 2012–2016 period was equivalent to 37% of sea level rise from land ice sources (excluding thermal expansion). These melt rates are comparable to the largest experienced by the ice sheet over
17052-585: 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)
17248-482: The absence of existing large crevasses that are normally thought to be necessary for their formation. Currently, the total accumulation of ice on the surface of Greenland ice sheet is larger than either outlet glacier losses individually or surface melting during the summer, and it is the combination of both which causes net annual loss. For instance, the ice sheet's interior thickened by an average of 6 cm (2.4 in) each year between 1994 and 2005, in part due to
17444-412: The advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous. Glaciers move downhill by the force of gravity and the internal deformation of ice. At the molecular level, ice consists of stacked layers of molecules with relatively weak bonds between layers. When the amount of strain (deformation) is proportional to
17640-520: The air from the snow turns it into "glacial ice". This glacial ice will fill the cirque until it "overflows" through a geological weakness or vacancy, such as a gap between two mountains. When the mass of snow and ice reaches sufficient thickness, it begins to move by a combination of surface slope, gravity, and pressure. On steeper slopes, this can occur with as little as 15 m (49 ft) of snow-ice. In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice called firn . Under
17836-412: 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
18032-430: The amount of melting at surface of the glacier, the faster the ice will flow. Basal sliding is dominant in temperate or warm-based glaciers. The presence of basal meltwater depends on both bed temperature and other factors. For instance, the melting point of water decreases under pressure, meaning that water melts at a lower temperature under thicker glaciers. This acts as a "double whammy", because thicker glaciers have
18228-713: The annual movement of the glacier. Ogives are formed when ice from an icefall is severely broken up, increasing ablation surface area during summer. This creates a swale and space for snow accumulation in the winter, which in turn creates a ridge. Sometimes ogives consist only of undulations or color bands and are described as wave ogives or band ogives. Glaciers are present on every continent and in approximately fifty countries, excluding those (Australia, South Africa) that have glaciers only on distant subantarctic island territories. Extensive glaciers are found in Antarctica, Argentina, Chile, Canada, Pakistan, Alaska, Greenland and Iceland. Mountain glaciers are widespread, especially in
18424-542: The average decline by 2290–2300 is 74%, and there is 44% likelihood of an outright collapse in that scenario, with a wide range of adverse effects. In 2021, the IPCC Sixth Assessment Report estimated that under SSP5-8.5 , the scenario associated with the highest global warming, Greenland ice sheet melt would add around 13 cm (5 in) to the global sea levels (with a likely (17%–83%) range of 9–18 cm ( 3 + 1 ⁄ 2 –7 in) and
18620-416: 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
18816-399: The base of the glaciers and generates higher basal pressure, which collectively reduces friction and accelerates glacial motion , including the rate of ice calving . This mechanism was observed at Sermeq Kujalleq in 1998 and 1999, where flow increased by up to 20% for two to three months. However, some research suggests that this mechanism only applies to certain small glaciers, rather than to
19012-432: The bedrock has frequent fractures on the surface, glacial erosion rates tend to increase as plucking is the main erosive force on the surface; when the bedrock has wide gaps between sporadic fractures, however, abrasion tends to be the dominant erosive form and glacial erosion rates become slow. Glaciers in lower latitudes tend to be much more erosive than glaciers in higher latitudes, because they have more meltwater reaching
19208-445: The bedrock. By mapping the direction of the striations, researchers can determine the direction of the glacier's movement. Similar to striations are chatter marks , lines of crescent-shape depressions in the rock underlying a glacier. They are formed by abrasion when boulders in the glacier are repeatedly caught and released as they are dragged along the bedrock. The rate of glacier erosion varies. Six factors control erosion rate: When
19404-427: 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
19600-582: The calving front. While the models generally consider the impact from meltwater run-off as secondary to ocean warming, observations of 13 glaciers found that meltwater plumes play a greater role for glaciers with shallow grounding lines. Further, 2022 research suggests that the warming from plumes had a greater impact on underwater melting across northwest Greenland. Finally, it has been shown that meltwater can also flow through cracks that are too small to be picked up by most research tools - only 2 cm (1 in) wide. Such cracks do not connect to bedrock through
19796-411: The central Greenland ice sheet, even the most extensive melting event can only affect a small fraction of it before the start of the freezing season, and so they are considered "short-term variability" in the scientific literature. Nevertheless, their existence is important: the fact that the current models underestimate the extent and frequency of such events is considered to be one of the main reasons why
19992-486: The coastal glaciers are lost. Sea level rise from Greenland does not affect every coast equally. The south of the ice sheet is much more vulnerable than the other parts, and the quantities of ice involved mean that there is an impact on the deformation of Earth's crust and on Earth's rotation . While this effect is subtle, it already causes East Coast of the United States to experience faster sea level rise than
20188-402: 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
20384-515: 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
20580-571: The created ice's density. The word glacier is a loanword from French and goes back, via Franco-Provençal , to the Vulgar Latin glaciārium , derived from the Late Latin glacia , and ultimately Latin glaciēs , meaning "ice". The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation . The corresponding area of study
20776-467: The deep profile of fjords , which can reach a kilometer in depth as ice is topographically steered into them. The extension of fjords inland increases the rate of ice sheet thinning since they are the principal conduits for draining ice sheets. It also makes the ice sheets more sensitive to changes in climate and the ocean. Although evidence in favor of glacial flow was known by the early 19th century, other theories of glacial motion were advanced, such as
20972-434: The deeper levels of snow to firn and then to solid glacier ice over hundreds of years. Once the ice sheet formed in Greenland, its size remained similar to its current state. However, there have been 11 periods in Greenland's history when the ice sheet extended up to 120 km (75 mi) beyond its current boundaries; with the last one around 1 million years ago. The weight of the ice causes it to slowly "flow", unless it
21168-505: 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
21364-483: The deformation to become a plastic flow rather than elastic. Then, the glacier will begin to deform under its own weight and flow across the landscape. According to the Glen–Nye flow law , the relationship between stress and strain, and thus the rate of internal flow, can be modeled as follows: where: The lowest velocities are near the base of the glacier and along valley sides where friction acts against flow, causing
21560-400: The disparate ice caps to connect and cover most of the island. The base of the ice sheet may be warm enough due to geothermal activity to have liquid water beneath it. This liquid water, under pressure from the weight of ice above it, may cause erosion , eventually leaving nothing but bedrock below the ice sheet. However, there are parts of the Greenland ice sheet, near the summit, where
21756-506: The entire ice sheet but may still reach several hundred meters down from the surface. Their presence is important, as it weakens the ice sheet, conducts more heat directly through the ice, and allows it to flow faster. This recent research is not currently captured in models. One of the scientists behind these findings, Alun Hubbard, described finding moulins where "current scientific understanding doesn’t accommodate" their presence, because it disregards how they may develop from hairline cracks in
21952-522: 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
22148-418: The essentially correct explanation in the 1840s, although it was several decades before it was fully accepted. The top 50 m (160 ft) of a glacier are rigid because they are under low pressure . This upper section is known as the fracture zone and moves mostly as a single unit over the plastic-flowing lower section. When a glacier moves through irregular terrain, cracks called crevasses develop in
22344-498: 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
22540-503: The first team of researchers as a reagent . However, there is still a risk of toxic waste being released from Camp Century , formerly a United States military site built to carry nuclear weapons for the Project Iceworm . The project was cancelled, but the site was never cleaned up, and it now threatens to pollute the meltwater with nuclear waste , 20,000 liters of chemical waste and 24 million liters of untreated sewage as
22736-406: 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
22932-476: 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
23128-475: The fracture zone. Crevasses form because of differences in glacier velocity. If two rigid sections of a glacier move at different speeds or directions, shear forces cause them to break apart, opening a crevasse. Crevasses are seldom more than 46 m (150 ft) deep but, in some cases, can be at least 300 m (1,000 ft) deep. Beneath this point, the plasticity of the ice prevents the formation of cracks. Intersecting crevasses can create isolated peaks in
23324-461: The gas and particulate composition of the atmosphere through time.When properly analyzed, ice cores provide a wealth of proxies suitable for reconstructing the past temperature record , precipitation patterns, volcanic eruptions , solar variation , ocean primary production , and even changes in soil vegetation cover and the associated wildfire frequency. The ice cores from Greenland also record human impact, such as lead production during
23520-529: 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
23716-502: The glacier disintegrated, and the glacier shed 94 square kilometres (36 sq mi) of ice between 2001 and 2005. The ice flow reached 45 metres (148 ft) per day in 2012, but slowed down substantially afterwards, and showed mass gain between 2016 and 2019. Northern Greenland's Petermann Glacier is smaller in absolute terms, but experienced some of the most rapid degradation in recent decades. It lost 85 square kilometres (33 sq mi) of floating ice in 2000–2001, followed by
23912-453: The glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. However, within high-altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater. Since glacial mass is affected by long-term climatic changes, e.g., precipitation , mean temperature , and cloud cover , glacial mass changes are considered among
24108-428: The glacier will be accommodated by motion in the sediments, or if it'll be able to slide. A soft bed, with high porosity and low pore fluid pressure, allows the glacier to move by sediment sliding: the base of the glacier may even remain frozen to the bed, where the underlying sediment slips underneath it like a tube of toothpaste. A hard bed cannot deform in this way; therefore the only way for hard-based glaciers to move
24304-456: The glacier's ice shelf had lost around 40% of its pre-2010 state, and it is considered unlikely to recover from further ice loss. In the early 2010s, some estimates suggested that tracking the largest glaciers would be sufficient to account for most of the ice loss. However, glacier dynamics can be hard to predict, as shown by the ice sheet's second largest glacier, Helheim Glacier . Its ice loss culminated in rapid retreat in 2005, associated with
24500-510: The glacier's surface area, more if the glacier calves icebergs. Ice in the accumulation zone is deep enough to exert a downward force that erodes underlying rock. After a glacier melts, it often leaves behind a bowl- or amphitheater-shaped depression that ranges in size from large basins like the Great Lakes to smaller mountain depressions known as cirques . The accumulation zone can be subdivided based on its melt conditions. The health of
24696-421: The glaciers started to lose height. Between 1998 and 2006, thinning occurred four times faster for coastal glaciers compared to the early 1990s, falling at rates between 1 m ( 3 + 1 ⁄ 2 ft) and 10 m (33 ft) per year, while the landlocked glaciers experienced almost no such acceleration. One of the most dramatic examples of thinning was in the southeast, at Kangerlussuaq Glacier . It
24892-441: The global average. At the same time, Greenland itself would experience isostatic rebound as its ice sheet shrinks and its ground pressure becomes lighter. Similarly, a reduced mass of ice would exert a lower gravitational pull on the coastal waters relative to the other land masses. These two processes would cause sea level around Greenland's own coasts to fall, even as it rises elsewhere. The opposite of this phenomenon happened when
25088-623: The highest in the entire past last millennium – about 1.5 °C (2.7 °F) warmer than the 20th century average. Several factors determine the net rate of ice sheet growth or decline. These are: When the IPCC Third Assessment Report was published in 2001, the analysis of observations to date had shown that the ice accumulation of 520 ± 26 gigatonnes per year was offset by runoff and bottom melting equivalent to ice losses of 297±32 Gt/yr and 32±3 Gt/yr, and iceberg production of 235±33 Gt/yr, with
25284-413: The historical record, which spans from late 19th century to present. Some research suggests that Greenland's meltwater mainly benefits marine productivity not by adding carbon and iron, but through stirring up lower water layers that are rich in nitrates and thus bringing more of those nutrients to phytoplankton on the surface. As the outlet glaciers retreat inland, the meltwater will be less able to impact
25480-562: The ice at the bottom of the glacier move more slowly than ice at the top. In alpine glaciers, friction is also generated at the valley's sidewalls, which slows the edges relative to the center. Mean glacial speed varies greatly but is typically around 1 m (3 ft) per day. There may be no motion in stagnant areas; for example, in parts of Alaska, trees can establish themselves on surface sediment deposits. In other cases, glaciers can move as fast as 20–30 m (70–100 ft) per day, such as in Greenland's Jakobshavn Isbræ . Glacial speed
25676-437: 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
25872-419: The ice sheet (compared to 4% for Kangerlussuaq), at speeds of ~20 metres (66 ft) per day. While it lost enough ice to retreat around 30 km (19 mi) between 1850 and 1964, its mass gain increased sufficiently to keep it in balance for the next 35 years, only to switch to rapid mass loss after 1997. By 2003, the average annual ice flow speed had almost doubled since 1997, as the ice tongue in front of
26068-555: The ice sheet gained mass during the Little Ice Age : increased weight attracted more water and flooded certain Viking settlements, likely playing a large role in the Viking abandonment soon afterwards. Notably, the ice sheet's massive size simultaneously makes it insensitive to temperature changes in the short run, yet also commits it to enormous changes down the line, as demonstrated by paleoclimate evidence. Polar amplification causes
26264-451: The ice sheet have already passed "a point of no return" around 1997, and will be committed to disappearance even if the temperature stops rising. A 2022 paper found that the 2000–2019 climate would already result in the loss of ~3.3% volume of the entire ice sheet in the future, committing it to an eventual 27 cm ( 10 + 1 ⁄ 2 in) of SLR, independent of any future temperature change. They have additionally estimated that if
26460-530: The ice sheet lost approximately 0.1% of its total mass (2900 Gt) during that year's melting season, with the net loss (464 Gt) setting another record. It became the first directly observed example of a "massive melting event", when the melting took place across practically the entire ice sheet surface, rather than specific areas. That event led to the counterintuitive discovery that cloud cover, which normally results in cooler temperature due to their albedo , actually interferes with meltwater refreezing in
26656-415: 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
26852-502: The ice sheet slides over a basal layer of ice which had frozen solid to the ground, preserving ancient soil , which can then be recovered by drilling. The oldest such soil was continuously covered by ice for around 2.7 million years, while another, 3 kilometres (1.9 mi) deep ice core from the summit has revealed ice that is around ~1,000,000 years old. Sediment samples from the Labrador Sea provide evidence that nearly all of
27048-420: The ice sheets of Antarctica and Greenland, has been estimated at 170,000 km . Glacial ice is the largest reservoir of fresh water on Earth, holding with ice sheets about 69 percent of the world's freshwater. Many glaciers from temperate , alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause
27244-440: 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
27440-556: The ice to act as a lever that loosens the rock by lifting it. Thus, sediments of all sizes become part of the glacier's load. If a retreating glacier gains enough debris, it may become a rock glacier , like the Timpanogos Glacier in Utah. Abrasion occurs when the ice and its load of rock fragments slide over bedrock and function as sandpaper, smoothing and polishing the bedrock below. The pulverized rock this process produces
27636-488: The ice, called seracs . Crevasses can form in several different ways. Transverse crevasses are transverse to flow and form where steeper slopes cause a glacier to accelerate. Longitudinal crevasses form semi-parallel to flow where a glacier expands laterally. Marginal crevasses form near the edge of the glacier, caused by the reduction in speed caused by friction of the valley walls. Marginal crevasses are largely transverse to flow. Moving glacier ice can sometimes separate from
27832-449: The ice-albedo feedback. Besides the formation of darker melt ponds, warmer temperatures enable increasing growth of algae on the ice sheet's surface. Mats of algae are darker in colour than the surface of the ice, so they absorb more thermal radiation and increase the rate of ice melt. In 2018, it was found that the regions covered in dust , soot , and living microbes and algae altogether grew by 12% between 2000 and 2012. In 2020, it
28028-411: The idea that meltwater, refreezing inside glaciers, caused the glacier to dilate and extend its length. As it became clear that glaciers behaved to some degree as if the ice were a viscous fluid, it was argued that "regelation", or the melting and refreezing of ice at a temperature lowered by the pressure on the ice inside the glacier, was what allowed the ice to deform and flow. James Forbes came up with
28224-418: The increased pressure can facilitate melting. Most importantly, τ D is increased. These factors will combine to accelerate the glacier. As friction increases with the square of velocity, faster motion will greatly increase frictional heating, with ensuing melting – which causes a positive feedback, increasing ice speed to a faster flow rate still: west Antarctic glaciers are known to reach velocities of up to
28420-423: The infrared OH stretching mode of the water molecule. (Liquid water appears blue for the same reason. The blue of glacier ice is sometimes misattributed to Rayleigh scattering of bubbles in the ice.) A glacier originates at a location called its glacier head and terminates at its glacier foot, snout, or terminus . Glaciers are broken into zones based on surface snowpack and melt conditions. The ablation zone
28616-466: 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
28812-427: The largest glaciers match what was first described as the "Jakobshavn effect" in 1986: thinning causes the glacier to be more buoyant, reducing friction that would otherwise impede its retreat, and resulting in a force imbalance at the calving front, with an increase in velocity spread across the mass of the glacier. The overall acceleration of Jakobshavn Isbrae and other glaciers from 1997 onwards had been attributed to
29008-418: The largest outlet glaciers, and may have only a marginal impact on ice loss trends. Secondly, once meltwater flows into the ocean, it can still impact the glaciers by interacting with ocean water and altering its local circulation - even in the absence of any ocean warming. In certain fjords , large meltwater flows from beneath the ice may mix with ocean water to create turbulent plumes that can be damaging to
29204-473: The local fjords , and further out in the Labrador Sea , where 40% of the total primary production had been attributed to nutrients from meltwater. Since the 1950s, the acceleration of Greenland melt caused by climate change has already been increasing productivity in waters off the North Icelandic Shelf, while productivity in Greenland's fjords is also higher than it had been at any point in
29400-407: The lower layers, which implies that benefit from the meltwater will diminish even as its volume grows. The impact of meltwater from Greenland goes beyond nutrient transport. For instance, meltwater also contains dissolved organic carbon , which comes from the microbial activity on the ice sheet's surface, and, to a lesser extent, from the remnants of ancient soil and vegetation beneath the ice. There
29596-413: The melt extent staying at 337,000 sq mi (872,826.0 km). At that time, rain fell for 13 hours at Greenland's Summit Station, located at 10,551 ft (3,215.9 m) elevation. Researchers had no rain gauges to measure the rainfall, because temperatures at the summit have risen above freezing only three times since 1989 and it had never rained there before. Due to the enormous thickness of
29792-636: The melt progresses. Finally, increased quantities of fresh meltwater can affect ocean circulation . Some scientists have connected this increased discharge from Greenland with the so-called cold blob in the North Atlantic , which is in turn connected to Atlantic meridional overturning circulation , or AMOC, and its apparent slowdown. In 2016, a study attempted to improve forecasts of future AMOC changes by incorporating better simulation of Greenland trends into projections from eight state-of-the-art climate models . That research found that by 2090–2100,
29988-424: The melt zone below the snow line, where summer warmth turns snow and ice into slush and melt ponds , has been expanding at an accelerating rate since the beginning of detailed measurements in 1979. By 2002, its area was found to have increased by 16% since 1979, and the annual melting season broke all previous records. Another record was set in July 2012, when the melt zone extended to 97% of the ice sheet's cover, and
30184-430: The middle Miocene , when the two passive continental margins which now form the uplands of West and East Greenland experienced uplift , and ultimately formed the upper planation surface at a height of 2000 to 3000 meter above sea level . Glacier 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
30380-479: The middle Miocene , when the two passive continental margins which now form the uplands of West and East Greenland experienced uplift , and ultimately formed the upper planation surface at a height of 2000 to 3000 meter above sea level . Later uplift, during the Pliocene , formed a lower planation surface at 500 to 1000 meters above sea level. A third stage of uplift created multiple valleys and fjords below
30576-679: The most deformation. Velocity increases inward toward the center line and upward, as the amount of deformation decreases. The highest flow velocities are found at the surface, representing the sum of the velocities of all the layers below. Because ice can flow faster where it is thicker, the rate of glacier-induced erosion is directly proportional to the thickness of overlying ice. Consequently, pre-glacial low hollows will be deepened and pre-existing topography will be amplified by glacial action, while nunataks , which protrude above ice sheets, barely erode at all – erosion has been estimated as 5 m per 1.2 million years. This explains, for example,
30772-445: The most sensitive indicators of climate change and are a major source of variations in sea level . A large piece of compressed ice, or a glacier, appears blue , as large quantities of water appear blue , because water molecules absorb other colors more efficiently than blue. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing
30968-479: The mountains to enable the ice sheet to flow out to the ocean through outlet glaciers . These glaciers regularly shed ice in what is known as ice calving . Sediment released from calved and melting ice sinks accumulates on the seafloor, and sediment cores from places such as the Fram Strait provide long records of glaciation at Greenland. While there is evidence of large glaciers in Greenland for most of
31164-491: The near future. It is also known that at a certain level of global warming, effectively the entirety of the Greenland Ice Sheet will eventually melt. Its volume was initially estimated to amount to ~2,850,000 km (684,000 cu mi), which would increase the global sea levels by 7.2 m (24 ft), but later estimates increased its size to ~2,900,000 km (696,000 cu mi), leading to ~7.4 m (24 ft) of sea level rise. Ice sheet Although
31360-475: 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
31556-532: The observed ice sheet decline in Greenland and Antarctica tracks the worst-case rather than the moderate scenarios of the IPCC Fifth Assessment Report 's sea-level rise projections . Some of the most recent scientific projections of Greenland melt now include an extreme scenario where a massive melting event occurs every year across the studied period (i.e. every year between now and 2100 or between now and 2300), to illustrate that such
31752-407: The past 12,000 years. Currently, the Greenland ice sheet loses more mass every year than the Antarctic ice sheet , because of its position in the Arctic , where it is subject to intense regional amplification of warming . Ice losses from the West Antarctic Ice Sheet have been accelerating due to its vulnerable Thwaites and Pine Island Glaciers , and the Antarctic contribution to sea level rise
31948-408: 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
32144-415: 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
32340-574: The planation surfaces. This uplift intensified glaciation due to increased orographic precipitation and cooler surface temperatures , allowing ice to accumulate and persist. As recently as 3 million years ago, during the Pliocene warm period, Greenland's ice was limited to the highest peaks in the east and the south. Ice cover gradually expanded since then, until the atmospheric CO2 levels dropped to between 280 and 320 ppm 2.7–2.6 million years ago, by which time temperatures had dropped sufficiently for
32536-674: The pooling of meltwater at the base of the glacier — perhaps delivered from a supraglacial lake — or the simple accumulation of mass beyond a critical "tipping point". Temporary rates up to 90 m (300 ft) per day have occurred when increased temperature or overlying pressure caused bottom ice to melt and water to accumulate beneath a glacier. In glaciated areas where the glacier moves faster than one km per year, glacial earthquakes occur. These are large scale earthquakes that have seismic magnitudes as high as 6.1. The number of glacial earthquakes in Greenland peaks every year in July, August, and September and increased rapidly in
32732-410: The pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacier ice is slightly more dense than ice formed from frozen water because glacier ice contains fewer trapped air bubbles. Glacial ice has a distinctive blue tint because it absorbs some red light due to an overtone of
32928-569: 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
33124-567: The sea, often with an ice tongue , like Mertz Glacier . Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica, Baffin , Devon , and Ellesmere Islands in Canada, Southeast Alaska , and the Northern and Southern Patagonian Ice Fields . As the ice reaches the sea, pieces break off or calve, forming icebergs . Most tidewater glaciers calve above sea level, which often results in
33320-476: The seas annually, which was substantially larger than the liquid meltwater input from the Antarctic ice sheet , and equivalent to 0.7% of freshwater entering the oceans from all of the world's rivers . This meltwater is not pure, and contains a range of elements - most notably iron , about half of which (around 0.3 million tons every year) is bioavailable as a nutrient for phytoplankton . Thus, meltwater from Greenland enhances ocean primary production , both in
33516-404: The smaller glaciers were losing more ice to such melting than normal calving processes, leading to rapid retreat. Conversely, Jakobshavn Isbrae is sensitive to changes in ocean temperature as it experiences elevated exposure through a deep subglacial trench. This sensitivity meant that an influx of cooler ocean water to its location was responsible for its slowdown after 2015, in large part because
33712-506: The south Greenland ice had melted around 400,000 years ago, during Marine Isotope Stage 11 . Other ice core samples from Camp Century in northwestern Greenland, show that the ice there melted at least once during the past 1.4 million years, during the Pleistocene , and did not return for at least 280,000 years. These findings suggest that less than 10% of the current ice sheet volume was left during those geologically recent periods, when
33908-528: The southern half of the ice sheet, and just the three of them are expected to add 9.1–14.9 mm under RCP 8.5. Similarly, 2013 estimates suggested that by 2200, they and another large glacier would add 29 to 49 millimetres by 2200 under RCP 8.5, or 19 to 30 millimetres under RCP 4.5. Altogether, the single largest contribution to 21st century ice loss in Greenland is expected to be from the northwest and central west streams (the latter including Jakobshavn), and glacier retreat will be responsible for at least half of
34104-441: The southwestern ice sheet, because of the exceptional concentrations in meltwater entering the local fjords . If confirmed, these concentrations would have equalled up to 10% of mercury in all of the world's rivers. In 2024, a follow-up study found only "very low" concentrations in meltwater from 21 locations. It concluded that the 2021 findings were best explained by accidental sample contamination with mercury(II) chloride , used by
34300-409: The stagnant ice above, forming a bergschrund . Bergschrunds resemble crevasses but are singular features at a glacier's margins. Crevasses make travel over glaciers hazardous, especially when they are hidden by fragile snow bridges . Below the equilibrium line, glacial meltwater is concentrated in stream channels. Meltwater can pool in proglacial lakes on top of a glacier or descend into the depths of
34496-520: The start of the Industrial Revolution and its impact on global carbon dioxide levels) and a trend of strong warming starting around 1979, in line with concurrent observed Arctic sea ice decline . In 1995– 1999, central Greenland was already 2 °C (3.6 °F) warmer than it was in the 1950s. Between 1991 and 2004, average winter temperature at one location, Swiss Camp, rose almost 6 °C (11 °F). Consistent with this warming,
34692-423: The stress being applied, ice will act as an elastic solid. Ice needs to be at least 30 m (98 ft) thick to even start flowing, but once its thickness exceeds about 50 m (160 ft) (160 ft), stress on the layer above will exceeds the inter-layer binding strength, and then it'll move faster than the layer below. This means that small amounts of stress can result in a large amount of strain, causing
34888-438: The surface snowpack may experience seasonal melting. A subpolar glacier includes both temperate and polar ice, depending on the depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is often described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface and is thus frozen to the underlying substrate. A warm-based glacier
35084-403: 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
35280-448: 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
35476-436: 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
35672-447: 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. Ice sheets form through a process of glaciation , when the local climate is sufficiently cold that snow is able to accumulate from year to year. As the annual snow layers pile up, their weight gradually compresses
35868-492: The temperatures were less than 2.5 °C (4.5 °F) warmer than preindustrial conditions. This contradicts how climate models typically simulate the continuous presence of solid ice under those conditions. Analysis of the ~100,000-year records obtained from 3 km (1.9 mi) long ice cores drilled between 1989 and 1993 into the summit of Greenland's ice sheet, had provided evidence for geologically rapid changes in climate, and informed research on tipping points such as in
36064-490: The then-record melting seen on the ice sheet in 2012 were to become its new normal, then the ice sheet would be committed to around 78 cm ( 30 + 1 ⁄ 2 in) SLR. Another paper suggested that paleoclimate evidence from 400,000 years ago is consistent with ice losses from Greenland equivalent to at least 1.4 m ( 4 + 1 ⁄ 2 ft) of sea level rise in a climate with temperatures close to 1.5 °C (2.7 °F), which are now inevitable at least in
36260-502: The time of Ancient Greece and the Roman Empire . From the 1960s to the 1980s an area in the North Atlantic which included southern Greenland was one of the few locations in the world which showed cooling rather than warming. This location was relatively warmer in the 1930s and 1940s than in the decades immediately before or after. More complete data sets have established trends of warming and ice loss starting from 1900(well after
36456-446: The total ice loss, as opposed to earlier studies which suggested that surface melting would become dominant later this century. If Greenland were to lose all of its coastal glaciers, though, then whether or not it will continue to shrink will be entirely determined by whether its surface melting in the summer consistently outweighs ice accumulation during winter. Under the highest-emission scenario, this could happen around 2055, well before
36652-535: 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
36848-489: The warming of North Atlantic waters which melt the glacier fronts from underneath. While this warming had been going on since the 1950s, 1997 also saw a shift in circulation which brought relatively warmer currents from the Irminger Sea into closer contact with the glaciers of West Greenland. By 2016, waters across much of West Greenland's coastline had warmed by 1.6 °C (2.9 °F) relative to 1990s, and some of
37044-417: The weight of the ice is supported by the underlying water, and the glacier is afloat. Glaciers may also move by basal sliding , where the base of the glacier is lubricated by the presence of liquid water, reducing basal shear stress and allowing the glacier to slide over the terrain on which it sits. Meltwater may be produced by pressure-induced melting, friction or geothermal heat . The more variable
37240-477: The worst-case climate change scenario. As with the present losses, not all parts of the ice sheet would contribute to them equally. For instance, it is estimated that on its own, the Northeast Greenland ice stream would contribute 1.3–1.5 cm by 2100 under RCP 4.5 and RCP 8.5, respectively. On the other hand, the three largest glaciers - Jakobshavn, Helheim, and Kangerlussuaq - are all located in
37436-460: 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
37632-429: Was above Greenland; the engine's massive air intake fan was recovered from the ice sheet two years later, when it was already buried beneath 4 ft (1 m)of ice and snow. While summer surface melting has been increasing, it is still expected that it will be decades before melting will consistently exceed snow accumulation on its own. It is also hypothesized that the increase in global precipitation associated with
37828-831: 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
38024-479: Was demonstrated that the presence of algae, which is not accounted for by ice sheet models unlike soot and dust, had already been increasing annual melting by 10–13%. Additionally, as the ice sheet slowly gets lower due to melting, surface temperatures begin to increase and it becomes harder for snow to accumulate and turn to ice, in what is known as surface-elevation feedback. Even in 1993, Greenland's melt resulted in 300 cubic kilometers of fresh meltwater entering
38220-527: 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
38416-480: Was then the fastest known flow of any glacier. The retreat of Kangerlussuaq slowed down by 2008, and showed some recovery until 2016–2018, when more rapid ice loss occurred. Greenland's other major outlet glaciers have also experienced rapid change in recent decades. Its single largest outlet glacier is Jakobshavn Isbræ ( Greenlandic : Sermeq Kujalleq ) in west Greenland, which has been observed by glaciologists for many decades. It historically sheds ice from 6.5% of
#429570