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Ice sheets are bigger than Ice Shelves or Glacier s. Masses of ice covering less than 50,000 km&2 are termed an Ice Cap . An ice cap will typically feed a series of glaciers around its periphery. Although the surface is cold, the base of an ice sheet is generally warmer, in places it melts 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 Stream s. The present-day polar ice sheets are relatively young in geological terms. The Antarctic Ice Sheet first formed as a small Ice Cap (maybe several) in the early Oligocene , but retreating and advancing many times until the Pliocene , when it came to occupy almost all of Antarctica. The Greenland ice sheet did not develop at all until the late Pliocene, but apparently developed ''very rapidly'' with the first continental Glaciation . This had the unusual effect of allowing Fossil s of Plant s that once grew on present-day Greenland to be much better preserved than with the slowly forming Antarctic ice sheet. ANTARCTIC ICE SHEET The the ice sheet rests on a major land mass, but in West Antarctica the bed is in places more than 2,500 meters below Sea Level . It would be Seabed if the ice sheet were not there. GREENLAND ICE SHEET The 's Gravity Recovery And Climate Experiment (GRACE) satellite, launched in 2002, as reported by BBC News, 11 August 2006 . PREDICTED EFFECTS OF GLOBAL WARMING Both the Antarctic and Greenland ice sheets have been losing mass recently, because losses due to melting and outlet glaciers have exceeded accumulation due to snowfall. According to the IPCC , loss of Antarctic ice sheet mass and Greenland ice sheet mass each contributed about .21 mm/year to the Sea Level Rise between 1993 and 2003.http://www.ipcc.ch/SPM2feb07.pdf The IPCC projects that ice mass loss from melting of the Greenland ice sheet will continue to outpace accumulation from snowfall. Accumulation from snowfall on the Antarctic ice sheet is projected to outpace losses from melting. However, loss of ice mass on the Antarctic ice sheet may continue, if there is sufficient loss of ice mass via outlet glaciers. According to the IPCC, scientific understanding of dynamical ice flow processes is currently "limited". EXTERNAL LINKS REFERENCES |
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