A recent study has analyzed several proxies for sea surface temperature (SST) and other indicators captured at a site in the Labrador sea just off southern Greenland. Over the past 450,000 years, there have been four interglacials; Marine Isotope Stage (MIS) 5e from 117,900 to 128,200, MIS 7e from 232,600 to 243,200, MIS 9e from 320,900 to 333,100 ka and MIS 11c from 394,700 to 424,200 years ago.
The analysis reveals that significant loss of Greenland ice occurred under climate conditions only slightly warmer than present. Partial deglaciation of southern Greenland occurred during three of these interglacials, but in the oldest interglacial, MIS 11c, there was nearly complete deglaciation of southern Greenland. The summer sea surface temperature (SST) data shows that MIS 9e was the warmest of the four deglacial periods, but southern Greenland remained ice covered. In contrast during MIS 11c, which was cooler but persisted longer then MIS 9e, southern Greenland was nearly completely deglaciated. This suggests that that the near disappearance of the southern Greenland ice sheet was the result of the extended duration of warmer than present conditions rather than crossing a threshold that would lead irrevocably to ice sheet collapse. MIS 11c was over 0.8 °C warmer for longer, about 3,000 years longer than MIS 9e and longer than the other two. This suggests that the near disappearance of the southern Greenland ice sheet was the result of the extended duration of warmer than present conditions rather than crossing a threshold that would lead irrevocably to ice sheet collapse.
A low climate threshold for south Greenland Ice Sheet demise during the Late Pleistocene, Nil Irval?, Eirik V. Galaasen, Ulysses S. Ninnemann, Yair Rosenthal, Andreas Born, and Helga F. Kleiven, PNAS January 7, 2020 117 (1) 190-195. doi/10.1073/pnas.1911902116