Scientists are filling in more of the details about the collapse of the Western Antarctic Ice Sheet (WAIS), an event that is now expected to begin in 60 years under current greenhouse warming conditions, and eventually boost sea levels by three metres.

In 2014, climate researchers at the University of Washington reported in the journal Science that the melting of two glaciers — Thwaite's and Pine Island — in the West Antarctic, was underway and would lead to the destabilisation of the larger ice sheet from which they arise.

Today's study in the journal Proceedings of the National Academy of Sciences (PNAS), uses a computer model for a more long-term and larger-scale prediction. It found that the destabilisation of the entire ice sheet would be irreversible if current conditions do not change by 2075.

"We now, for the first time, show that if you destabilise the region, then you get a chain reaction, and the entire WAIS is discharged into the ocean," said Anders Levermann, professor of climate dynamics at the Potsdam Institute for Climate Impact Research in Germany.

"We can now say how much sea level rise that will imply, which is three metres. But it will take a long time."

Dr Leverman said that the entire WAIS melting could take several hundred to thousands of years. The WAIS accounts for about 10 per cent of the volume of the Antarctic ice continent.

The computer model used in this new study takes into account conditions on the whole continent, rather than just the small area of the two glaciers that are currently retreating, Dr Levermann said.

For this reason, the time scales are not exact, although the results are.

"We can say that to our knowledge there is nothing that will hold [the ice sheet] once it is destabilised," Dr Levermann said.

"And it's unlikely that once this [happens], that it will stop."

Dr Levermann was careful to say that the model still needed more observational data about the topography of the ice surface, and more information about the bedrock upon which the WAIS sits.

The frictional forces between the ice and the rock underneath are key to understanding how quickly the ice will break up.

University of California climate scientist Eric Rignot said the German model added more proof that Antarctica is in trouble.

"It adds to the critical debate of how long it will take for ice to retreat from West Antarctica," Dr Rignot said.

"The real advance here is to put on the table yet another model projection that shows very rapid retreat, i.e. less than 100 years."

The author of the 2014 Science paper, University of Washington's Polar Science Centre researcher Ian Joughin, said the melting may occur even faster.

"This paper does confirm what we hypothesised, which was that knocking out Pine Island Glacier and Thwaites takes down the rest of WAIS," Dr Joughin said.

"Because of the resolution limitations of the model, however, I think the time scale over which this collapse will occur is too long (it's more likely measured in centuries rather than millennia).

"Certainly present observations indicate collapse is already underway at [a] substantially faster pace."

This story was first published on Discovery.com