Ice sheets January 12, 2018 An ice sheet is a mass of glacial land ice extending more than 50,000 square kilometers (20,000 square miles). The two ice sheets on Earth today cover most of Greenland and Antarctica. Ice sheets are constantly in motion, slowly flowing downhill under their own weight. Near the coast, most of the ice moves through relatively fast-moving outlets called ice streams, glaciers, and ice shelves. As long as an ice sheet accumulates the same mass of snow as it loses to the sea, it remains stable. Importance of Ice sheets • The Antarctic and Greenland ice sheets contain more than 99 percent of the freshwater ice on Earth. • The presence of the high ice sheet and the polar location make Antarctica a powerful heat sink that strongly affects the climate of the whole Earth. • It modulates exchanges of heat, moisture, and gases between the atmosphere and ocean and, forces the formation of cold oceanic bottom waters that spread out under the world’s oceans. Alterations to this system are likely to affect climate all over the planet. • Large high-altitude plateaus on the ice caps alter storm tracks and create cold downslope winds close to the ice surface. • If the Antarctic Ice Sheet melted, sea level would rise by about 60 meters. Difference between Antarctica and Arctic Ice sheets Antarctic land ice is the ice which has accumulated over thousands of years on the Antarctica landmass itself through snowfall. This land ice therefore is actually stored ocean water that once fell as precipitation. Sea ice in Antarctica is quite different as it is ice which forms in salt water primarily during the winter months. When land ice melts and flows into the oceans global sea levels rise on average; when sea ice melts sea levels do not change measurably. In Antarctica, sea ice grows quite extensively during winter but nearly completely melts away during the summer. That is where the important difference between Antarctic and Arctic sea ice exists as much of the Arctic's sea ice lasts all the year round. During the winter months it increases and before decreasing during the summer months, but an ice cover does in fact remain in the North which includes quite a bit of ice from previous years. Essentially Arctic sea ice is more important for the earth's energy balance because when it increasingly melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged.