The last edge of the Greenland ice sheet that had resisted global warming has now become unstable, adding billions of tonnes of meltwater to rising seas, scientists say.

In a study published in the journal Nature Climate Change, they say a surge in temperature from 2003 has eased the brakes on a long "river" of ice that flows to the coast in northeastern Greenland.

Greenland's ice sheet is melting.

Known as an ice stream, the "river" takes ice from a vast basin and slowly shifts it to the sea - in the same way the Amazon River drains water.

In the past, the flow from this ice stream was constrained by massive buildups of ice debris choking its mouth.