Melbourne, Oct 19 (IANS): A jump in global average temperatures of 1.5 degree Celsius to two degrees Celsius will see the collapse of Antarctic ice shelves, the floating margins of the Antarctic ice sheet, and lead to hundreds and even thousands of years of sea level rise, warns new research.

Using computer modelling, the researchers simulated the ice sheet's response to a warming climate under a range of greenhouse gas emission scenarios.

They found in all but one scenario (that of significantly reduced emissions beyond 2020) large parts of the Antarctic ice sheet were lost, resulting in a substantial rise in global sea level.

"The long reaction time of the Antarctic ice sheet -- which can take thousands of years to fully manifest its response to changes in environmental conditions -- coupled with the fact that CO2 lingers in the atmosphere for a very long time means that the warming we generate now will affect the ice sheet in ways that will be incredibly hard to undo," said lead researcher Nicholas Golledge from Victoria University of Wellington, New Zealand.

The findings suggest that to avoid the loss of the Antarctic ice shelves, and a long-term commitment to many metres of sea level rise, atmospheric warming needs to be kept below two degree Celsius above present levels.

"Missing the two degree Celsius target will result in an Antarctic contribution to sea level rise that could be up to 10 metres higher than today," Golledge said.

"The stakes are obviously very high -- 10 percent of the world's population lives within 10 metres of present sea level," Golledge noted.

"The striking thing about these findings is that we have taken the most conservative estimates possible," study co-author Chris Fogwill from the University of New South Wales in Australia pointed out.

The last time CO2 concentrations in the atmosphere were similar to present levels was about three million years ago, Golledge said.

"At that time average global temperatures were two or three degrees warmer, large parts of the Antarctic ice sheet had melted, and sea levels were a staggering 20 metres higher than they are now," he noted.

"We are currently on track for a global temperature rise of a couple of degrees which will take us into that ballpark, so there may well be a few scary surprises in store for us, possibly within just a few hundred years," Golledge said.

The study was published in the journal Nature.