Greenland faces a great risk of losing substantial amounts of its glaciers, which could result in more sea level rise. One of these immense glaciers that drain the vast Greenland ice sheet has recently begun to retreat. It could eventually contribute half a metre to sea level rise. Some of Greenland's glaciers rest in deep fjords, and as the water warms, their leading edges melt. The ice within them is also moving towards the sea faster ─ so more is being dumped in the sea. The process began with the vast Jakobshavn glacier in the west, followed by the Petermann and Humboldt in the north. Recently, it has been announced that the Zachariæ Isstrøm glacier in the north-east began to retreat in 2012 and its flow towards the sea has also accelerated. "Now it's unstable and it's going to retreat even more," says Jeremie Mouginot of the University of California. The next glacier to the north, Nioghalvfjerdsfjorden, could follow suit. The floating ice shelf that protects it is thinning and could soon be lost. Most of the ice shelves in the seas around Greenland have already disappeared. "The melt will add millimetres to sea levels over the coming decades," says Mouginot.