The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea. Description It is estimated that the volume of the Antarctic ice sheet is about 25.4 million km3 (6.1 million cu mi), and the WAIS contains just under 10% of this, or 2.2 million km3 (530,000 cu mi). The weight of the ice has caused the underlying rock to sink by between in a process known as isostatic depression. Under the force of its own weight, the ice sheet deforms and flows. The interior ice flows slowly over rough bedrock. In some circumstances, ice can flow faster in ice streams, separated by slow-flowing ice ridges. The inter-stream ridges are frozen to the bed while the bed beneath the ice streams consists of water-saturated sediments. Many of these sediments were deposited before the ice sheet occupied the region, when much of West Antarctica was covered by the ocean. The rapid ice-stream flow is a non-linear process still not fully understood; streams can start and stop for unclear reasons. When ice reaches the coast, it either calves or continues to flow outward onto the water. The result is a large, floating ice shelf affixed to the continent. Climate change Warming and net ice loss The West Antarctic ice sheet (WAIS) has warmed by more than /decade in the last fifty years, and the warming is the strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this effect was restricted to the 1980s and 1990s. The continent-wide average surface temperature trend of Antarctica is positive and statistically significant at >/decade since 1957. This warming of WAIS is strongest in the Antarctic Peninsula. In 2012, the temperature records for the ice sheet were reanalyzed with a conclusion that since 1958, the West Antarctic ice sheet had warmed by , almost double the previous estimate. Some scientists now fear that the WAIS could now collapse like the Larsen B Ice Shelf did in 2002. Indications that