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80-630: Because the East Antarctic ice sheet is over 10 times larger than the West Antarctic ice sheet and located at a higher elevation , it is less vulnerable to climate change than the WAIS. In the 20th century, EAIS had been one of the only places on Earth which displayed limited cooling instead of warming, even as the WAIS warmed by over 0.1 °C/decade from 1950s to 2000, with an average warming trend of >0.05 °C/decade since 1957 across

160-518: A geographic location is its height above or below a fixed reference point, most commonly a reference geoid , a mathematical model of the Earth 's sea level as an equipotential gravitational surface (see Geodetic datum § Vertical datum ). The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above

240-543: A more literal translation). For a long time, the term referred only to glacial periods. Over time, this developed into the concept that they were all part of a much longer ice age. The concept that the Earth is currently in an ice age that began around 30 million years ago can be dated back to at least 1966. As a geologic time period, the Late Cenozoic Ice Age was used at least as early as 1973. The last greenhouse period began 260 million years ago during

320-645: A much-larger West-Antarctica warming of 2.4 °C (4.3 °F) since 1958, or around 0.46 °C (0.83 °F) per decade, although there has been uncertainty about it. In 2022, a study narrowed the warming of the Central area of the West Antarctic Ice Sheet between 1959 and 2000 to 0.31 °C (0.56 °F) per decade, and conclusively attributed it to increases in greenhouse gas concentrations caused by human activity. Between 2000 and 2020, local changes in atmospheric circulation patterns like

400-552: A period of around 2,000 years, which would add up to 6.4 m (21 ft 0 in) to sea levels. The loss of the entire ice sheet would require global warming in a range between 5 °C (9.0 °F) and 10 °C (18 °F), and a minimum of 10,000 years. The Antarctic ice sheet covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice. A cubic kilometer of ice weighs approximately 0.92 metric gigatonnes, meaning that

480-542: A role as well though models of the changes suggest declining CO 2 levels to have been more important. The Western Antarctic ice sheet declined somewhat during the warm early Pliocene epoch, approximately five to three million years ago; during this time the Ross Sea opened up. But there was no significant decline in the land-based Eastern Antarctic ice sheet. 90°S 0°E  /  90°S 0°E  / -90; 0 Elevation The elevation of

560-406: A way which would be difficult to reverse and constitute an example of tipping points in the climate system . This would be similar to some projections for Atlantic meridional overturning circulation (AMOC), which is also affected by the ocean warming and by meltwater flows from the declining Greenland ice sheet . However, Southern Hemisphere is only inhabited by 10% of the world's population, and

640-471: Is 70 m (230 ft) lower than it would be without the ice sheets of Antarctica and Greenland. Based on the Milankovitch cycles, the current interglacial period is predicted to be unusually long, continuing for another 25,000 to 50,000 years beyond present times. There are also high concentrations of greenhouse gases in the atmosphere from human activity, and it is almost certain to get higher in

720-405: Is a major reason for why Antarctica has such an exceptionally cold climate. The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. At this point, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, CO 2 levels had dropped to 750 ppm. This

800-465: Is also possible, but it would require very high warming and a lot of time: In 2022, an extensive assessment of tipping points in the climate system published in Science Magazine concluded that the ice sheet would take a minimum of 10,000 years to fully melt. It would most likely be committed to complete disappearance only once the global warming reaches about 7.5 °C (13.5 °F), with

880-630: Is bounded by the Ross Ice Shelf , the Filchner-Ronne Ice Shelf , and outlet glaciers that drain into the Amundsen Sea . Thwaites Glacier and Pine Island Glacier are the two most important outlet glaciers. Antarctica is the coldest, driest continent on Earth, and has the highest average elevation. Antarctica's dryness means the air contains little water vapor and conducts heat poorly. The Southern Ocean surrounding

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960-499: Is defined by the ICAO as the highest point of the landing area. It is often measured in feet and can be found in approach charts of the aerodrome. It is not to be confused with terms such as the altitude or height. GIS or geographic information system is a computer system that allows for visualizing, manipulating, capturing, and storage of data with associated attributes. GIS offers better understanding of patterns and relationships of

1040-462: Is developing a 3D Elevation Program (3DEP) to keep up with growing needs for high quality topographic data. 3DEP is a collection of enhanced elevation data in the form of high quality LiDAR data over the conterminous United States, Hawaii, and the U.S. territories. There are three bare earth DEM layers in 3DEP which are nationally seamless at the resolution of 1/3, 1, and 2 arcseconds. Late Cenozoic Ice Age The Late Cenozoic Ice Age falls within

1120-481: Is due to the Milankovitch cycles . These are cycles that have to do with Earth's axial tilt and orbital eccentricity. Earth is currently tilted at 23.5 degrees. Over a 41,000 year cycle, the tilt oscillates between 22.1 and 24.5 degrees. When the tilt is greater (high obliquity), the seasons are more extreme. During times when the tilt is less (low obliquity), the seasons are less extreme. Less tilt also means that

1200-588: Is open to interpretation because the IPCC does not specify 1850-1829 as being the present, or give any exact set of years as being the present. It also does not state whether or not they agree with the figures given by Berkeley Earth. According to the United States Geographical Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level

1280-657: Is the Quaternary , which started 2.58 million years ago. It is divided into the Pleistocene , which ended 11,700 years ago, and the current Holocene . The Quaternary is also divided into alternating stadials (colder periods) and interstadials (warmer periods) The last stadial reached its peak in the Last Glacial Maximum , between 26,000 and 20,000 years ago, and the Earth is now in an interstadial. The oscillation between glacial and interglacial periods

1360-431: Is to lower the global temperature to 1 °C (1.8 °F) below the pre-industrial level, to 2 °C (3.6 °F) below the temperature of 2020. Other researchers said a climate engineering intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give the environment more time to adapt. This is an uncertain proposal and would be one of the most-expensive projects ever attempted. Otherwise,

1440-538: The CMIP6 models - the most advanced generation available as of early 2020s. One study suggests that the circulation would lose half its strength by 2050 under the worst climate change scenario , with greater losses occurring afterwards. It is possible that the South Ocean overturning circulation may not simply continue to weaken in response to increased warming and freshening, but will eventually collapse outright, in

1520-695: The Cenozoic Era which started 66 million years ago. The Cenozoic Era is part of the Phanerozoic Eon which started ~538.8 million years ago. The Late Cenozoic Ice Age , or Antarctic Glaciation , began 34 million years ago at the Eocene-Oligocene Boundary and is ongoing. It is Earth's current ice age or icehouse period . Its beginning is marked by the formation of the Antarctic ice sheets. Six million years after

1600-550: The Eemian , and about 0.9 m (2 ft 11 in) between 318,000 and 339,000 years ago, during the Marine Isotope Stage 9 . Neither Wilkes nor the other subglacial basins were lost entirely, but estimates suggest that they would be committed to disappearance once the global warming reaches 3 °C (5.4 °F) - the plausible temperature range is between 2 °C (3.6 °F) and 6 °C (11 °F). Then,

1680-582: The Eocene Epoch , summer high temperatures in Antarctica were around 25 °C (77 °F). Temperatures during winter were around 10 °C (50 °F). It did not frost during the winter. The climate was so warm that trees grew in Antarctica. Arecaceae (palm trees) grew on the coastal lowlands, and Fagus (beech trees) and Pinophyta (conifers) grew on the hills just inland from

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1760-678: The Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) slowed or partially reversed the warming of West Antarctica , with the Antarctic Peninsula experiencing cooling from 2002. While a variability in those patterns is natural, ozone depletion had also led the SAM to be stronger than it had been in the past 600 years of observations. Studies predicted a reversal in

1840-611: The Northern Hemisphere , which means that there is more ice on Earth than there was during the first 31 million years of the Late Cenozoic Ice Age. During that time, only the Antarctic ice sheets existed. Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice according to the USGS. The total volume of ice presently on Earth is about 33,000,000 km (7,900,000 cu mi) (as of 2004). The current sea level (as of 2009)

1920-460: The Quaternary glaciation developed with decreasing mean temperatures and increasing amplitudes between glacials and interglacials. During the glacial periods of the Pleistocene, large areas of northern North America and northern Eurasia have been covered by ice sheets. In 1837, German naturalist Karl Friedrich Schimper coined the term Eiszeit , meaning ice age (or ice time for

2000-461: The seafloor and the base of the ice sheet once the sheet is no longer heavy enough to displace such flows. Marine ice-cliff instability may cause ice cliffs taller than 100 m (330 ft) to collapse under their own weight once they are no longer buttressed by ice shelves. This process has never been observed and it only occurs in some models. By 2100, these processes may increase sea-level rise caused by Antarctica to 41 cm (16 in) under

2080-541: The 20th century satellite temperature measurements began in 1981 and are typically limited to cloud-free conditions. Thus, datasets representing the entire continent only began to appear by the very end of the 20th century. The exception was the Antarctic Peninsula , where warming was pronounced and well-documented; it was eventually found to have warmed by 3 °C (5.4 °F) since the mid 20th century. Based on this limited data, several papers published in

2160-556: The Antarctic ice sheets were similar in size and volume to present times. Glaciers were starting to form in the mountains of the Northern Hemisphere. Between 3.6 and 3.4 million years ago, there was a sudden but brief warming period. The glaciation of the Arctic in the Northern Hemisphere commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago). The current period

2240-605: The EAIS in addition to the erosion of the WAIS. This Antarctica-only sea level rise would be in addition to ice losses from the Greenland ice sheet and mountain glaciers , as well as the thermal expansion of ocean water. If the warming were to remain at elevated levels for a long time, then the East Antarctic Ice Sheet would eventually become the dominant contributor to sea level rise, simply because it contains

2320-720: The EAIS would play an increasingly larger role in sea level rise occurring after 2100. According to the most recent reports of the Intergovernmental Panel on Climate Change ( SROCC and the IPCC Sixth Assessment Report ), the most intense climate change scenario , where the anthropogenic emissions increase continuously, RCP8.5 , would result in Antarctica alone losing a median of 1.46 m (4 ft 9 in) ( confidence interval between 60 cm (2.0 ft) and 2.89 m (9 ft 6 in)) by 2300, which would involve some loss from

2400-459: The Gamburtsev ice cap was now much larger due to the colder climate. CO 2 continued to fall and the climate continued to get colder. At 28.1 million years ago, the Gamburtsev and Transantarctic ice caps merged into a main central ice cap. At this point, ice was now covering a majority of the continent. The Dronning Maud ice cap merged with the main ice cap 27.9 million years ago. This was

2480-458: The Homo sapiens and Neanderthals interbred. Currently, persons of European descent are two to four percent Neanderthal. With the exception of this small amount of Neanderthal DNA that exists today, Neanderthals became extinct 30,000 years ago. The Last Glacial Maximum ran from 26,500 years ago to 20,000 years ago. Although different ice sheets reached maximum extent at somewhat different times, this

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2560-574: The Intergovernmental Panel On Climate Change (IPCC) estimate a slightly lower global temperature than the figures given by the Zurich University of Applied Sciences. However, these figures are not exact figures and are open more to interpretation. According to the IPCC, average global temperatures increased by 5.5 ± 1.5 °C (9.9 ± 2.7 °F) since the last glacial maximum, and the rate of warming

2640-501: The Pleistocene epoch. Between 9,000 and 5,000 years ago there was a warm period called the Holocene climatic optimum . Being in an interglacial, there is less ice than there was during the last glacial period. However, the last glacial period was just one part of the ice age that still continues today. Even though Earth is in an interglacial, there is still more ice than times outside of ice ages. There are also currently ice sheets in

2720-726: The SAM once the ozone layer began to recover following the Montreal Protocol , starting from 2002, and these changes are consistent with their predictions. As these patterns reversed, the East Antarctica interior demonstrated clear warming over those two decades. In particular, the South Pole warmed by 0.61 ± 0.34 °C per decade between 1990 and 2020, which is three times the global average. The Antarctica-wide warming trend continued after 2000, and in February 2020,

2800-522: The Southern Ocean overturning circulation has historically received much less attention than the AMOC. Some preliminary research suggests that such a collapse may become likely once global warming reaches levels between 1.7 °C (3.1 °F) and 3 °C (5.4 °F), but there is far less certainty than with the estimates for most other tipping points in the climate system . Even if initiated in

2880-496: The West Antarctic ice sheet would cause around 3.3 m (10 ft 10 in) of sea-level rise. This kind of collapse is now considered almost inevitable because it appears to have occurred during the Eemian period 125,000 years ago, when temperatures were similar to those in the early 21st century. The Amundsen Sea also appears to be warming at rates that, if continued, make the ice sheet's collapse inevitable. The only way to reverse ice loss from West Antarctica once triggered

2960-504: The West Antarctic ice sheet, which is much smaller than the East Antarctic ice sheet and is grounded deep below sea level, is considered highly vulnerable. The melting of all of the ice in West Antarctica would increase global sea-level rise to 4.3 m (14 ft 1 in). Mountain ice caps that are not in contact with water are less vulnerable than the majority of the ice sheet, which is located below sea level. The collapse of

3040-410: The beginning of records in 1850 until 1929. The average temperature during these years was 13.8 °C (56.8 °F). When subtracting 5.5 ± 1.5 °C (9.9 ± 2.7 °F) from the 1850-1929 average, the average temperature for the last glacial maximum comes out to 8.3 ± 1.5 °C (46.9 ± 2.7 °F). This is about 6.7 ± 1.5 °C (12.0 ± 2.7 °F) colder than the 2011-2020 average. This figure

3120-643: The book at the time, but it was mentioned in a 2006 US Senate hearing in support of climate change denial . Peter Doran published a statement in The New York Times decrying the misinterpretation of his work. The British Antarctic Survey and NASA also issued statements affirming the strength of climate science after the hearing. By 2009, researchers were able to combine historical weather-station data with satellite measurements to create consistent temperature records going back to 1957 that demonstrated warming of >0.05 °C/decade since 1957 across

3200-692: The coast. As the global climate became cooler, the planet was seeing a decrease in forests, and an increase in savannas. Animals were evolving to have a larger body size. Australia drifted away from Antarctica forming the Tasmanian Passage , and South America drifted away from Antarctica forming the Drake Passage . This caused the formation of the Antarctic Circumpolar Current , a current of cold water surrounding Antarctica. This current still exists today, and

3280-466: The coming decades. This will lead to higher temperatures. In 25,000 to 50,000 years, the climate will begin to cool due to the Milankovich cycles. However, the high levels of greenhouse gases are predicted to keep it from getting cold enough to build up enough ice to meet the criteria of a glacial period. This would effectively extend the current interglacial period an additional 100,000 years placing

Antarctic ice sheet - Misplaced Pages Continue

3360-414: The continent is far more effective at absorbing heat than any other ocean. The presence of extensive, year-around sea ice , which has a high albedo (reflectivity), adds to the albedo of the ice sheets' own bright, white surface. Antarctica's coldness means it is the only place on Earth where an atmospheric temperature inversion occurs every winter; elsewhere on Earth, the atmosphere is at its warmest near

3440-483: The continent recorded its highest temperature of 18.3 °C, which is one degree higher than the previous record of 17.5 °C in March 2015. By 2100, net ice loss from Antarctica is expected to add about 11 cm (4.3 in) to global sea-level rise. Other processes may cause West Antarctica to contribute more to sea-level rise. Marine ice-sheet instability is the potential for warm water currents to enter between

3520-409: The continent, with cooling in East Antarctica offset by the average temperature increase of at least 0.176 ± 0.06 °C per decade in West Antarctica. Subsequent research confirmed clear warming over West Antarctica in the 20th century, with the only uncertainty being the magnitude. During 2012-2013, estimates based on WAIS Divide ice cores and revised temperature records from Byrd Station suggested

3600-451: The disappearance of the West Antarctic ice sheet would take an estimated 2,000 years. The loss of West Antarctica ice would take at least 500 years and possibly as long as 13,000 years. Once the ice sheet is lost, the isostatic rebound of the land previously covered by the ice sheet would result in an additional 1 m (3 ft 3 in) of sea-level rise over the following 1,000 years. If global warming were to reach higher levels, then

3680-650: The early 2000s said there had been an overall cooling over continental Antarctica outside the Peninsula. A 2002 analysis led by Peter Doran received widespread media coverage after it also indicated stronger cooling than warming between 1966 and 2000, and found the McMurdo Dry Valleys in East Antarctica had experienced cooling of 0.7 °C per decade, a local trend that was confirmed by subsequent research at McMurdo. Multiple journalists said these findings were "contradictory" to global warming, even though

3760-402: The end of the Antarctic winter. Early climate models predicted temperature trends over Antarctica would emerge more slowly and be more subtle than those elsewhere. There were fewer than twenty permanent weather stations across the continent and only two in the continent's interior. Automatic weather stations were deployed relatively late, and their observational record was brief for much of

3840-560: The formation of the East Antarctic Ice Sheet . Global refrigeration set in 22 million years ago. About 15 million years ago was the warmest part of the Late Cenozoic Ice Age, with average global temperatures around 18.4 °C (65.1 °F). Atmospheric CO 2 levels were around 700 ppm. This time period was called the Mid-Miocene Climatic Optimum (MMCO). By 14 million years ago,

3920-457: The global sea levels over another 1,000 years. On the other hand, the East Antarctic ice sheet is far more stable and may only cause 0.5 m (1 ft 8 in) - 0.9 m (2 ft 11 in) of sea level rise from the current level of warming, which is a small fraction of the 53.3 m (175 ft) contained in the full ice sheet. Around 3 °C (5.4 °F), vulnerable locations like Wilkes Basin and Aurora Basin may collapse over

4000-529: The ice sheet weighs about 24,380,000 gigatonnes. This ice is equivalent to around 61% of all fresh water on Earth. The only other currently existing ice sheet on Earth is the Greenland ice sheet in the Arctic . The Antarctic ice sheet is divided by the Transantarctic Mountains into two unequal sections called the East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS). Some glaciologists consider ice cover over

4080-582: The landscape at different scales. Tools inside the GIS allow for manipulation of data for spatial analysis or cartography. A topographical map is the main type of map used to depict elevation, often through contour lines . In a Geographic Information System (GIS), digital elevation models (DEM) are commonly used to represent the surface (topography) of a place, through a raster (grid) dataset of elevations. Digital terrain models are another way to represent terrain in GIS. USGS (United States Geologic Survey)

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4160-430: The largest amount of ice. Sustained ice loss from the EAIS would begin with the significant erosion of the so-called subglacial basins, such as Totten Glacier and Wilkes Basin , which are located in vulnerable locations below the sea level. Evidence from the Pleistocene shows that Wilkes Basin had likely lost enough ice to add 0.5 m (1 ft 8 in) to sea levels between 115,000 and 129,000 years ago, during

4240-665: The late Permian Period at the end of the Karoo Ice Age . It lasted all through the time of the non-avian dinosaurs during the Mesozoic Era , and ended 33.9 million years ago in the middle of the Cenozoic Era (the current Era). This greenhouse period lasted 226.1 million years. The hottest part of the last greenhouse earth was the Late Paleocene - Early Eocene. This was a hothouse period that lasted from 65 to 55 million years ago. The hottest part of this torrid age

4320-408: The limited recovery during 2010s. Since the 1970s, the upper cell has strengthened by 3-4 sverdrup (Sv; represents a flow of 1 million cubic meters per second), or 50-60% of its flow, while the lower cell has weakened by a similar amount, but because of its larger volume, these changes represent a 10-20% weakening. While these effects weren't fully caused by climate change, with some role played by

4400-414: The low-emission scenario and by 57 cm (22 in) under the high-emission scenario. Ice loss from Antarctica also generates more fresh meltwater , at a rate of 1100-1500 billion tons (GT) per year. This meltwater then mixes back into the Southern Ocean, which makes its water fresher. This freshening of the Southern Ocean results in increased stratification and stabilization of its layers, and this has

4480-506: The middle latitudes of the Northern Hemisphere. The Toba eruption 75,000 years ago in present-day Sumatra , Indonesia has been linked to a bottleneck in the human DNA, although such a causal link remains highly controversial. 50,000 years ago, Homo sapiens migrated out of Africa. They began replacing other Hominins in Asia. They also began replacing Neanderthals in Europe. However, some of

4560-620: The minimum and the maximum range between 5 °C (9.0 °F) and 10 °C (18 °F). Another estimate suggested that at least 6 °C (11 °F) would be needed to melt two thirds of its volume. 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

4640-469: The most-recent reports of the Intergovernmental Panel on Climate Change ( SROCC and the IPCC Sixth Assessment Report ), there will be a median rise of 16 cm (6.3 in) and maximum rise of 37 cm (15 in) under the low-emission scenario. The highest-emission scenario results in a median rise of 1.46 m (5 ft) with a minimum of 60 cm (2 ft) and a maximum of 2.89 m ( 9 + 1 ⁄ 2  ft). Over longer timescales,

4720-459: The natural cycle of Interdecadal Pacific Oscillation , they are likely to worsen in the future. As of early 2020s, climate models ' best, limited-confidence estimate is that the lower cell would continue to weaken, while the upper cell may strengthen by around 20% over the 21st century. A key reason for the uncertainty is limited certainty about future ice loss from Antarctica and the poor and inconsistent representation of ocean stratification in even

4800-616: The near future, the circulation's collapse is unlikely to be complete until close to 2300, Similarly, impacts such as the reduction in precipitation in the Southern Hemisphere , with a corresponding increase in the North , or a decline of fisheries in the Southern Ocean with a potential collapse of certain marine ecosystems , are also expected to unfold over multiple centuries. Sea levels will continue to rise long after 2100 but potentially at very different rates. According to

4880-532: The paper noted the limited data and found warming over 42% of the continent. What became known as the Antarctic Cooling Controversy received further attention in 2004, when Michael Crichton wrote that novel State of Fear , which said a conspiracy among climate scientists to make up global warming, and said Doran's study definitively proved there was no warming in Antarctica outside of the Peninsula. Relatively few scientists responded to

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4960-450: The polar regions receive less light from the sun. This causes a colder global climate as ice sheets start to build up. The shape of Earth's orbit around the Sun affects the Earth's climate. Over a 100,000 year cycle, Earth oscillates between having a circular orbit to having a more elliptical orbit. From 2.58 million years ago to about 1.73 million ± 50,000 years ago, the degree of axial tilt

5040-582: The present. Some coastal areas also have exposed bedrock that is not covered by ice. During the Late Cenozoic Ice Age , many of those areas had been covered by ice as well. The EAIS rests on a major land mass, but the bed of the WAIS is, in places, more than 2,500 meters (8,200 feet) below sea level . It would be seabed if the ice sheet were not there. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies below sea level and its edges flow into floating ice shelves. The WAIS

5120-559: The relatively small Antarctic Peninsula (also in West Antarctica) to be the third ice sheet in Antarctica, in part because its drainage basins are very distinct from the WAIS. Collectively, these ice sheets have an average thickness of around 2 kilometres (1.2 mi), Even the Transantarctic Mountains are largely covered by ice, with only some mountain summits and the McMurdo Dry Valleys being ice-free in

5200-464: The saline Antarctic bottom water , which weakens the lower cell of the Southern Ocean overturning circulation and may even contribute to its collapse, although this will likely take place over multiple centuries. Paleoclimate research and improved modelling show that the West Antarctic ice sheet is very likely to disappear even if the warming does not progress any further, and only reducing

5280-441: The sea level leaves it vulnerable to marine ice sheet instability , which is difficult to simulate in ice sheet models . If instability is triggered before 2100, it has the potential to increase total sea level rise caused by Antarctica by tens of centimeters more, particularly with high overall warming. Ice loss from Antarctica also generates fresh meltwater , at a rate of 1100-1500 billion tons (GT) per year. This meltwater dilutes

5360-404: The single largest impact on the long-term properties of Southern Ocean circulation. These changes in the Southern Ocean cause the upper cell circulation to speed up, accelerating the flow of major currents, while the lower cell circulation slows down, as it is dependent on the highly saline Antarctic bottom water , which already appears to have been observably weakened by the freshening, in spite of

5440-466: The start of the Late Cenozoic Ice Age, the East Antarctic Ice Sheet had formed, and 14 million years ago it had reached its current extent. In the last three million years, glaciations have spread to the northern hemisphere. It commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago) During the Pleistocene Epoch (starting 2.58 Ma ago),

5520-595: The subglacial basins would gradually collapse over a period of around 2,000 years, although it may be as fast as 500 years or as slow as 10,000 years. Their loss would ultimately add between 1.4 m (4 ft 7 in) and 6.4 m (21 ft 0 in) to sea levels, depending on the ice sheet model used. Isostatic rebound of the newly ice-free land would also add 8 cm (3.1 in) and 57 cm (1 ft 10 in), respectively. The entire East Antarctic Ice Sheet holds enough ice to raise global sea levels by 53.3 m (175 ft). Its complete melting

5600-404: The surface and becomes cooler as elevation increases. During the Antarctic winter, the surface of central Antarctica becomes cooler than middle layers of the atmosphere; this means greenhouse gases trap heat in the middle atmosphere, and reduce its flow toward the surface and toward space, rather than preventing the flow of heat from the lower atmosphere to the upper layers. This effect lasts until

5680-424: The surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface. Elevation is not to be confused with the distance from the center of the Earth. Due to the equatorial bulge , the summits of Mount Everest and Chimborazo have, respectively, the largest elevation and the largest geocentric distance. In aviation, the term elevation or aerodrome elevation

5760-423: The thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm, 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

5840-518: The warming to 2 °C (3.6 °F) below the temperature of 2020 may save it. It is believed that the loss of the ice sheet would take between 2,000 and 13,000 years, 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, and 4.3 m (14 ft 1 in) if those melt as well. Isostatic rebound may also add around 1 m (3 ft 3 in) to

5920-414: The whole continent. As of early 2020s, there is still net mass gain over the EAIS (due to increased precipitation freezing on top of the ice sheet), yet the ice loss from the WAIS glaciers such as Thwaites and Pine Island Glacier is far greater. By 2100, net ice loss from Antarctica alone would add around 11 cm (5 in) to the global sea level rise . Further, the way WAIS is located deep below

6000-399: Was about 10 times slower than that of the 20th century. It appears that they are defining the present as the early period of instrumental records when temperatures were less affected by human activity, but they do not specify exact years, or give a temperature for the present. Berkeley Earth publishes a list of average global temperatures by year. It shows that temperatures were stable from

6080-408: Was about 125 m (410 ft) lower than in present times (2012). The volume of ice on Earth was around 17,000,000 cu mi (71,000,000 km ), which is about 2.1 times Earth's current volume of ice. The Earth is currently in an interglacial period called the Holocene epoch. However, there is debate as to whether it is actually a separate epoch or merely an interglacial period within

6160-664: Was the Paleocene–Eocene Thermal Maximum , 55.5 million years ago. Average global temperatures were around 30 °C (86 °F). This was only the second time that Earth reached this level of warmth since the Precambrian . The other time was during the Cambrian Period , which ran from 538.8 million years ago to 485.4 million years ago. During the early Eocene , Australia and South America were connected to Antarctica. 53 million years ago during

6240-646: Was the beginning of the Late Cenozoic Ice Age. This was when the ice sheets reached the ocean, the defining point. At 29.2 million years ago, there were three ice caps in the high elevations of Antarctica. One ice cap formed in the Dronning Maud Land . Another ice cap formed in the Gamburtsev Mountain Range . Another ice cap formed in the Transantarctic Mountains . At this point, the ice caps weren't very big yet. Most of Antarctica wasn't covered by ice. By 28.7 million years ago,

6320-411: Was the main cause of glacial and interglacial periods. Around 850,000 ± 50,000 years ago, the degree of orbital eccentricity became the main driver of glacial and interglacial periods rather than the degree of tilt, and this pattern continues to present-day. The Last Glacial Period began 115,000 years ago and ended 11,700 years ago. This time period saw the great advancement of polar ice sheets into

6400-426: Was the time when ice sheets overall were at maximum extent. According to Blue Marble 3000 (a video by the Zurich University of Applied Sciences), the average global temperature around 19,000 BCE (about 21,000 years ago) was 9.0 °C (48.2 °F). This is about 4.8 °C (8.6 °F) colder than the 1850-1929 average, and 6.0 °C (10.8 °F) colder than the 2011-2020 average. The figures given by

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