Rising sea levels and melting polar ice-sheets are at upper limits of projections, leaving some human population centers already unable to cope, top world scientists say as they analyze latest satellite data.
A United Nations report by the Intergovernmental Panel on Climate Change (IPCC) in February projected sea level gains of 18-59 centimeters (7-23 inches) this century from temperature rises of 1.8-4.0 Celsius (3.2-7.8 Farenheit).
"Observations are in the very upper edge of the projections," leading Australian marine scientist John Church told Reuters.
"I feel that we're getting uncomfortably close to threshold," said Church, of Australia's CSIRO Marine and Atmospheric Research said.
Past this level, parts of the Antarctic and Greenland would approach a virtually irreversible melting that would produce sea level rises of meters, he said.
There has been no repeat in the Antarctic of the 2002 break-up of part of the Larsen ice shelf that created a 500 billion ton iceberg as big as Luxembourg.
But the Antarctic Peninsula is warming faster than anywhere else on Earth, and glaciers are in massive retreat.