The huge ice sheet covering Greenland, which is the world’s largest island, provides a habitat for many arctic species and holds nearly 8 per cent of the world’s freshwater. It is, on average, 5,000 feet thick and is constantly being replaced as snow falls each winter. Over the course of centuries, the snow compacts into ice, which slides towards the ocean. In recent years, higher atmospheric concentrations of heat-trapping gases have accelerated that process. As temperatures rise, the top layers melt, giving way to darker, heat-absorbing ice and liquid water. The meltwater seeps down to the rock below, lubricating the ice mass and speeding its slide into the sea.