Melting Ice Sheets From Below

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A new study of ice sheets in West Antarctica has made major news this week with the announcement that the ice melt in this region is unstoppable and may raise sea levels by more than 1.2 meters. Part of what makes the ice sheet so unstable is the local topography, shown schematically in the animation above. The land on which the glacier sits lies well below sea level, and the grounding line marks where the ice, sea, and land meet. Part of the glacier projects outward as a sheet, with seawater between it and the land; this is not unusual, but it can encourage melting if the water under the ice sheet is warmer. A major problem for this region, though, is that the slope of the underlying land tilts downward. This means that, as warmer water begins circulating under the ice sheet, it causes the grounding line to retreat and expose a greater volume for warm water to fill beneath the ice. More warm water melts more ice and the process continues unabated. (Video credit: NASA/JPL; h/t to jtotheizzoe, jshoer)

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