According to the passage, when the top layers of the ice sheet melt, ----.

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.