Greenland's shrinking ice sheet has a new threat: warm waters.  Flowing in from the Atlantic, it strikes Greenland's glaciers every second, melting it from below, according to a new study.  

"This melting of the glacier ice may increase if the temperature of the (relatively) warm water becomes warmer which is possible as part of global warming," Dr Wilken-Jon von Appen from the Alfred Wegener Institute, tells MEA WorldWide (MEAWW).

This means we could risk losing Greenland's ice sheet in the future. In fact, over the past 50 years, the ice sheet has already lost enough mass to add about half an inch of water to the world’s oceans. Compared to the 1990s, the glacier is melting seven times faster now.

And if the entire ice sheet melts, scientists fear that it could release about 25 feet of water to the world’s oceans. A previous study suggests that the entire ice mass of Greenland could be wiped out if temperatures rise by as little as 2°C.

Ice melts on the surface because it is exposed to the Sun and rising temperatures. But it has now also begun melting from below — including in northeast Greenland. But scientists did not understand why, until now.

To uncover this underwater mystery, Appen and his colleagues studied an ice structure called 'ice tongues'.  Each tongue is a strip of ice that floats on the ocean's water though it remains attached to the land ice. 

One of these ice tongues, which is part of the '79° North Glacier', is about 80 km long. It has been shrinking over the past 20 years, losing its mass and thickness, thanks to melting on the surface and from below, explain the researchers.  

A detailed ship-based survey of the ocean floor near the glacier revealed the cause: a 325m deep sill, which controls the inflow of ocean water.  "If there was no sill (or its depth would be greater), the inflow would be stronger and could melt more glacier ice. If the sill was shallower, the inflow would be smaller and less glacier ice could be melted," explains von Appen.

These effects were not restricted only to the '79° North Glacier'. Their study showed that an ice tongue attached to another glacier, the Zachariæ Isstrøm, is also experiencing the same. 

"The glacier tongue of Zachariæ Isstrøm has broken off half a decade ago and we have seen that the temperature of the warm water has become warmer at 79North Glacier, therefore, it is likely that the ice tongue of 79° North Glacier will also disappear in our lifetime," says von Appen.

"These two glaciers account for 1/5 of Greenland's discharge and Greenland has accounted for about half of the recent sea-level rise," he adds.

The study has been published in Nature Geoscience.