A new study from the University of New South Wales shows historical patterns of rapid ice loss in the Antarctic ice sheet could contribute to rising sea levels this century and millennium.
Published in Nature Communications on Thursday, the study used geological data from Antarctica combined with computer modelling and statistical analyses to determine how changes date back thousands of years.
What they found was when the Antarctic ice sheet retreated, periods of rapid mass loss 'switched on' rapidly, within a decade or two.
"Interestingly, after the ice sheet continued to retreat for several hundred years, it 'switched off' again, also only taking a couple of decades," co-author Dr Zoe Thomas said.
Dr Thomas added that the Antarctic ice sheet went through many of these on/off episodes, each time contributing to rising global sea levels at the end of the last ice age, approximately 20,000 years ago.
The researchers' findings confirm computer modelling indicating the diminishing ice sheet had passed a critical tipping point leading to irreversible loss of parts of the ice sheet below sea level.
"We have already observed over the last two decades that the Antarctic Ice Sheet has suddenly started losing ice which has contributed to rising sea levels around the world," co-author Professor Chris Turney said.
"But the satellite data showing this speed-up only go back about 40 years, so we needed longer records to put this change in context."
By using sediment release from melting icebergs onto the sea floor in their analysis, scientists were able to identify eight phases with high amounts of debris which they interpreted as retreat phases of the ice sheet.
Combining the sediment record with computer models of ice sheet behaviour, the team showed that each episode of increased iceberg calving reflected increased loss of ice from the interior of the ice sheet, not just changes in the already-floating ice shelves.
They also confirmed via computer analysis that "tipping points" did exist, and current behaviours of the ice sheet indicate a point of no return.
"Our findings are consistent with a growing body of evidence suggesting the acceleration of Antarctic ice-mass loss in recent decades may mark the beginning of a self-sustaining and irreversible period of ice sheet retreat and substantial global sea level rise," said Dr Michael Weber, from the Institute of Geosciences at the University of Bonn.
"When we might see the eventual stabilisation of the ice sheet is unknown, because it will depend significantly on how much future climate warming occurs."