Sea levels could rise by up to seven metres if greenhouse gas emissions were not scaled back, a panel of leading geoscientists has told the US Congress.
The warning came as a vast ice shelf, about 260 square kilometres in size, continued to fall away from Greenland's Petermann glacier, the largest iceberg shed by the island in half a century.
The geoscientists told Congress Greenland might cease to exist, with the island rapidly approaching a tipping point that would see much larger masses of ice melting, pushing up the average level of oceans around the world. Temperature rises of between two and seven degrees Celsius - which are considered likely by the end of the century due to human-induced carbon emissions - would force the change, they said.
A leading Australian sea level rise researcher, Dr John Church, broadly agreed with the US assessment. ''We are seeing something significant, and it's something our coastal cities have not experienced before,'' said Dr Church, a lead author of the most recent global assessment by the Intergovernmental Panel on Climate Change. ''We're beginning to move outside the range of what we have become used to seeing as normal variability, and see an acceleration of both greenhouse gas levels and sea level rise.''
But there was still a great deal of uncertainty about the timing and extent of the disintegration of Greenland's ice sheets, Dr Church said.
''We are looking at a process that will be going on for centuries,'' he said. ''It may be that we do cross that threshold relatively soon, but there is a lot of uncertainty around it, in my view.''
Professor Richard Alley, a geoscientist at Pennsylvania State University, told the US House of Representatives committee on energy independence and global warming a sea level rise of seven metres was a realistic possibility.
''Some time in the next decade we may pass that tipping point, which would put us warmer than temperatures that Greenland can survive,'' Professor Alley said.
The current threshold at which Greenland would melt is a temperature rise of between two and four degrees, according to the UN's current estimate.
The Australian government is currently planning for a sea level rise of 90 centimetres by the end of the century.
Dr Ryan McAllister, a scientist from the CSIRO's climate adaptation division, said planning for sea level rises needed to become more flexible to take uncertainty into account.
''We also need to broaden our perspective on planning so we can adapt to different stages of climate change as they emerge,'' Dr McAllister said.