Understanding how warmer climates affected Greenland in the past helps in determining how future warming will impact it. The Greenland Ice Sheet (GIS) has retreated during recent interglacials, suggesting a critical survival threshold within a few degrees of modern temperatures. Defining this temperature threshold requires records of the past climates responsible for GIS demise. Using microfossil temperature reconstructions, we show that the current interglacial is unusually moderate and that all 4 previous interglacials were warmer than present near Greenland. Both magnitude and duration of past warmth were important influences on the ice sheet. Notably, the critical temperature threshold for past GIS decay will likely be surpassed this century. The duration for which this threshold is exceeded will determine Greenland’s fate.

Abstract

The Greenland Ice Sheet (GIS) has been losing mass at an accelerating rate over the recent decades. Models suggest a possible temperature threshold between 0.8 and 3.2 °C, beyond which GIS decline becomes irreversible. The duration of warmth above a given threshold is also a critical determinant for GIS survival, underlining the role of ocean warming, as its inertia prolongs warmth and triggers longer-term feedbacks. The exact point at which these feedbacks are triggered remains equivocal. Late Pleistocene interglacials provide potential case examples for constraining the past response of the GIS to a range of climate states, including conditions warmer than present. However, little is known about the magnitude and duration of warming near Greenland during these periods. Using high-resolution multiproxy surface ocean climate records off southern Greenland, we show that the previous 4 interglacials over the last ∼450 ka all reached warmer than present climate conditions and exceeded the modeled temperature threshold for GIS collapse but by different magnitudes and durations. Complete deglaciation of the southern GIS in Marine Isotope Stage 11c (MIS 11c; 394.7 to 424.2 ka) occurred under climates only slightly warmer than present (∼0.5 ± 1.6 °C), placing the temperature threshold for major GIS retreat in the lower end of model estimates and within projections for this century.