There are currently only two ice sheets in the world: the Greenland ice sheet and the Antarctic ice sheet. However, during the last glacial period, there were more ice sheets covering the majority of Earth's land mass. An ice sheet is a large mass of glacial ice that covers an area greater than 50,000 km2 and is also known as a continental glacier. The Bering Glacier is the only other existing ice sheet, with the rest of Earth's ice shelves collapsing. These ice sheets have smoothed and shaped the terrain and are important indicators of climate change. The Antarctic continent has three separate ice sheets: the Antarctic Peninsula Ice Sheet, West Antarctic Ice Sheet, and East Antarctic Ice Sheet. Climate change is causing a decline in Earth's ice cover as seen in the Global Ice Viewer, and ice sheets are typically warmer at their base than on the surface due to various factors.