Northwestern Greenland was ice-free 400,000 years ago, according to Camp Century sediments

Sediments recovered from the base of the Camp Century ice core show that northwestern Greenland was ice-free during a period of history known to have exhibited some of the lowest global ice volumes -- the Marine Isotope Stage (MIS) 11 interglacial period. The absence of ice at that location means that the Greenland Ice Sheet must have contributed more 1.4 meters of sea-level equivalent to global sea level during the interglacial – a period in which average global air temperature was similar to what we’ll soon experience, given human-caused climate warming. The climate conditions of past interglacials – periods during Earth’s climatic history characterized by warmer global temperatures and reduced global ice coverage – provide opportunities to better understand how Earth’s cryosphere will respond to our warming climate and contribute to sea level rise. However, well-dated sedimentary records from areas formally ice-free during interglacial periods are rare or difficult to obtain due to present-day ice cover. One notable exception is the Camp Century ice core from northwestern Greenland, which contained rare frozen subglacial sediments suggesting that the region was ice-free at some point during the Pleistocene. Using luminescence dating and cosmogenic nuclide data, Andrew Christ and colleagues analyzed the sediments and found they were deposited by flowing water in an ice-free tundra environment during the MIS 11 interglacial (~416 thousand years ago) after first being exposed at the surface and to sunlight less than 16,000 years earlier. Then, to better understand the deglaciation of Greenland during MIS 11, Christ et al. used an ensemble of ice sheet models and found that for the Camp Century location to be ice-free, melting of the ice sheet would have contributed to at least 1.4 meters of sea-level equivalent to the global mean sea level of the interglacial, which was between 6 and 13 meters higher than present. “If moderate warmth for 29 [thousand years] during MIS 11 resulted in significant ice loss from Greenland, then rapid, prolonged, and considerable anthropogenic Arctic warming will likely cause melting of the [Greenland Ice Sheet], raise sea level, and trigger additional climate feedbacks in the coming centuries,” write Christ et al.