Before the industrial revolution, sea levels were rising at 1 millimetre a year but now they are rising by 3 millimetres annually because of a combination of global warming, polar ice-melting and long natural cycles of sea level change.

Eric Lindstrom, head of oceanography at the National Aeronautics and Space Administration (NASA), said, at a global oceans conference in Hobart, that the indications were that the increase would get faster.

Rapid advances in science in the past five years on polar ice-sheet dynamics had yet to filter through into scientific models, Lindstrom said.

He also pointed to huge splits in Antarctic ice shelves in 2002, then seen as once-in-100-year events that created icebergs bigger than some small countries.

The mega icebergs were first thought not to affect global sea levels because the ice broke off from shelves already floating on the surface of the ocean.

But the disintegration of ice shelves that had blocked the flow of ice from the Antarctic continent could allow sudden flows by glaciers into the ocean, raising sea-levels.

A report by the U.N. climate panel released last month cited six models with core projections of sea level rises ranging from 28 to 43 cms (11.0-16.9 inches) by 2100.

The Intergovernmental Panel on Climate Change also said temperatures were likely to rise by 2-4.5 Celsius (3.6-8.1 Fahrenheit) above pre-industrial levels if carbon dioxide concentrations are kept at 550 parts per million in the atmosphere, against about 380 now. The "best estimate" for the rise is about 3C (5.4F).

The report, which brought together 2,500 researchers from more than 130 nations, said Antarctica was likely to stay too cold for wide surface melting and is expected to gain in mass due to more snow.