“If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary,” said a scientist who set out to determine whether Greenland or Antarctica will introduce more melting water to rising sea levels.
Many scientists have assumed that the Greenland ice sheet was the main culprit for sea level rise during the Last Interglacial Period, at which time the oceans were at least 4 metres – and possile as much as 6.5 metres – higher than they are now.
However, after studying sedimentary runoff off the coast of Greenland, Carlson now thinks that Greenland is the more stable of the two massive ice sheets.
“The Greenland Ice Sheet is melting faster and faster,” says Carlson, who is also a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies, but, “there’s a clear need to understand how it has behaved in the past, and how it has responded to warmer-than-present summers in the past,” because despite clear observations, estimates of just how much the Greenland ice sheet will melt and how much it will contribute to sea level rise by the end of the century are unreliable at best, ranging from a few centimetres to several metres.
Carlson and his team sought out a way to determine whether ice remained on Greenland during the Last Interglacial Period, approximately 125,000 years ago, so as to determine ice sheet behaviour and understanding. The researchers analysed silt from an ocean-floor core taken from a region off the southern tip of Greenland that receives sediments carried by meltwater streams off the Greenland ice sheet, and found that the ice sheet had not completely disappeared.
“The ice definitely retreated to smaller than present extent and definitely raised sea level to higher than present” and continued to melt throughout the warm period, he adds, but the sediment analysis indicates that “the ice sheet seems to be more stable than some of the greater retreat values that people have presented.”
Comparing their results to existing models of the melting of Greenland’s ice sheet from the Last Interglacial Period, the researchers found that their findings matched up with Greenland being responsible for a sea level rise of 1.6 to 2.2 metres, at most. This comes in at roughly half that of the minimum four metre increase.
This leaves the Antarctic ice sheet as the main culprit.
“The implication of our results is that West Antarctica likely was much smaller than it is today,” and responsible for much more of the sea level rise than many scientists have thought, he says. “If West Antarctica collapsed, that means it’s more unstable than we expected, which is quite scary.”