Query: In the early 2000s, ice shelves began disintegrating in several parts of Antarctica, and scientists realized that process could greatly accelerate the demise of the vastly larger ice sheets themselves.

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Retreat of glaciers since 1850 <=SEP=> The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use , mountain recreation , animals and plants that depend on glacier-melt , and , in the longer term , the level of the oceans . Studied by glaciologists , the temporal coincidence of glacier retreat with the measured increase of atmospheric greenhouse gases is often cited as an evidentiary underpinning of global warming . Mid-latitude mountain ranges such as the Himalayas , Alps , Rocky Mountains , Cascade Range , and the southern Andes , as well as isolated tropical summits such as Mount Kilimanjaro in Africa , are showing some of the largest proportionate glacial losses .   Glacier mass balance is the key determinant of the health of a glacier . If the amount of frozen precipitation in the accumulation zone exceeds the quantity of glacial ice lost due to melting or in the ablation zone a glacier will advance ; if the accumulation is less than the ablation , the glacier will retreat . Glaciers in retreat will have negative mass balances , and if they do not find an equilibrium between accumulation and ablation , will eventually disappear .   The Little Ice Age was a period from about 1550 to 1850 when the world experienced relatively cooler temperatures compared to the present . Subsequently , until about 1940 , glaciers around the world retreated as the climate warmed substantially . Glacial retreat slowed and even reversed temporarily , in many cases , between 1950 and 1980 as global temperatures cooled slightly . Since 1980 , a significant global warming has led to glacier retreat becoming increasingly rapid and ubiquitous , so much so that some glaciers have disappeared altogether , and the existences of many of the remaining glaciers are threatened . In locations such as the Andes of South America and Himalayas in Asia , the demise of glaciers in these regions has the potential to affect water supplies in those areas .   The retreat of mountain glaciers , notably in western North America , Asia , the Alps and tropical and subtropical regions of South America , Africa and Indonesia , provide evidence for the rise in global temperatures since the late 19th century . The acceleration of the rate of retreat since 1995 of key outlet glaciers of the Greenland and West Antarctic ice sheets may foreshadow a rise in sea level , which would affect coastal regions .

Ice shelf <=SEP=> An ice shelf is a thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface . Ice shelves are only found in Antarctica , Greenland , Canada and the Russian Arctic . The boundary between the floating ice shelf and the grounded ( resting on bedrock ) ice that feeds it is called the grounding line . The thickness of ice shelves ranges from about 100 to 1000 meters .   In contrast , sea ice is formed on water , is much thinner ( typically less than 3m ) , and forms throughout the Arctic Ocean . It also is found in the Southern Ocean around the continent of Antarctica .   Ice shelves are principally driven by gravity-driven pressure from the grounded ice . That flow continually moves ice from the grounding line to the seaward front of the shelf . The primary mechanism of mass loss from ice shelves was thought to have been iceberg calving , in which a chunk of ice breaks off from the seaward front of the shelf . A study by NASA and university researchers - published in the June 14 , 2013 issue of Science - found however that ocean waters melting the undersides of Antarctic ice shelves are responsible for most of the continent 's ice shelf mass loss .   Typically , a shelf front will extend forward for years or decades between major calving events . Snow accumulation on the upper surface and melting from the lower surface are also important to the mass balance of an ice shelf . Ice may also accrete onto the underside of the shelf .   The density contrast between glacial ice , which is denser than normal ice , and liquid water means that only about 1/9 of the floating ice is above the ocean surface . The world 's largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica .   The term captured ice shelf has been used for the ice over a subglacial lake , such as Lake Vostok .

Antarctica <=SEP=> Antarctica ( UK English -LSB- ænˈtɑːktɪkə -RSB- or -LSB- ænˈtɑːtɪkə -RSB- , US English -LSB- æntˈɑːrktɪkə -RSB- ) is Earth 's southernmost continent . It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere , almost entirely south of the Antarctic Circle , and is surrounded by the Southern Ocean . At 14000000 km2 , it is the fifth-largest continent . For comparison , Antarctica is nearly twice the size of Australia . About 98 % of Antarctica is covered by ice that averages 1.9 km in thickness , which extends to all but the northernmost reaches of the Antarctic Peninsula .   Antarctica , on average , is the coldest , driest , and windiest continent , and has the highest average elevation of all the continents . Antarctica is a desert , with annual precipitation of only 200 mm ( 8 in ) along the coast and far less inland . The temperature in Antarctica has reached − 89.2 ° C ( − 128.6 ° F ) , though the average for the third quarter ( the coldest part of the year ) is − 63 ° C ( − 81 ° F ) . Anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent . Organisms native to Antarctica include many types of algae , bacteria , fungi , plants , protista , and certain animals , such as mites , nematodes , penguins , seals and tardigrades . Vegetation , where it occurs , is tundra .   Although myths and speculation about a Terra Australis ( `` Southern Land '' ) date back to antiquity , Antarctica is noted as the last region on Earth in recorded history to be discovered and colonised by humans , being only first sighted in 1820 by the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on Vostok and Mirny , who sighted the Fimbul ice shelf . The continent , however , remained largely neglected for the rest of the 19th century because of its hostile environment , lack of easily accessible resources , and isolation . In 1895 , the first confirmed landing was conducted by a team of Norwegians .   Antarctica is a de facto condominium , governed by parties to the Antarctic Treaty System that have consulting status . Twelve countries signed the Antarctic Treaty in 1959 , and thirty-eight have signed it since then . The treaty prohibits military activities and mineral mining , prohibits nuclear explosions and nuclear waste disposal , supports scientific research , and protects the continent 's ecozone . Ongoing experiments are conducted by more than 4,000 scientists from many nations .