Alarm grows over big melt in Antarctica

Antarctica is shrinking more quickly than expected and the pace is increasing, a conference has been told.

Professor Peter Barrett of Victoria University's Antarctic Research Centre summarised the latest findings at the Annual Antarctic Conference.

Recent satellite pictures showed the frozen continent was calving glaciers from its edges at a rate adding up to about 0.4mm of sea-level rise a year.

That might not sound like much, he said, but the rate of ice loss was increasing quickly - up 75 per cent since 1996.

The Antarctic ice sheet has been stable for a million years and until recently had seemed too large and too cold to be vulnerable.

But Dr Barrett said scientists now believed it could change significantly in a matter of decades. A new assessment adding up global ice loss from Greenland, Antarctica and other glaciers suggested sea levels would rise between 80cm and 2m by 2100, he said.

Governments have been worried about losing polar ice, mostly because of the possible effects of rising sea levels on towns and cities.

Dr Barrett said the loss of ice would also affect sealife by making oceans warmer and more acidic.

Vonda Cummings, an ecologist with the National Institute for Water and Atmospheric Research, told the conference a team of researchers had been studying Antarctic shellfish, starfish and other creatures living in the Ross Sea to see how climate change might affect them.

They would feed details of the creatures' living conditions into computer models over the next six months to see how changes in ice cover and food supplies might play out.

Meanwhile, the director of Victoria University's Antarctic Research Centre, Professor Tim Naish, says he will issue new information on Tuesday showing that changes to the west Antarctic ice sheet could eventually raise sea levels by up to 5m.

Dr Naish led a team of researchers who drilled deep into the Antarctic rock and uncovered ancient records from the last time atmospheric CO2 reached the level it is now approaching.

The project found that 3 million to 5 million years ago, seas were warm enough to melt a large chunk of Antarctica's ice when atmospheric CO2 was only slightly higher than today.

The team has been studying the rock cores to find out how warm the sea was when a Texas-sized chunk of the ice sheet last melted.

Sea levels would rise 58m were the Antarctic ice to melt completely, something scientists believe is very unlikely this century.

West Antarctica's ice would melt before the larger east Antarctic ice sheet because it sits below sea level and warms with the ocean.

Dr Barrett said the drill cores raised unresolved questions about how much atmospheric CO2 would need to rise to increase temperatures by 2C or more.

CO2 concentration in the atmosphere is now around 387 parts per million, up from about 280ppm at the start of the Industrial Revolution.

Modelling by the Intergovernmental Panel on Climate Change predicts temperatures would rise 3C if atmospheric CO2 doubled. But the drilling project found temperatures were 3C warmer than they are today when CO2 levels were less than 400ppm, only slightly higher than today.

Dr Barrett said the findings suggested the European Union's target of keeping temperature rise to 2C by reining in CO2 to a maximum of 450ppm might be optimistic.

Modelling suggested CO2 would remain long after humans stopped burning fossil fuels.