Holocene thinning in central Greenland controlled by the Northeast Greenland Ice Stream.

Ice-core records from the interior of the Greenland ice sheet suggest widespread thinning during the Holocene. However, the recurring underestimation of this thinning in numerical models raises concerns about both the veracity of such reconstructions and the reliability of glaciological models. Recent work suggests the 8000-year-old Northeast Greenland Ice Stream (NEGIS), including a now-extinct northern tributary, may have been an early influence on Greenland ice-sheet dynamics.

Overshooting the critical threshold for the Greenland ice sheet.

Melting of the Greenland ice sheet (GrIS) in response to anthropogenic global warming poses a severe threat in terms of global sea-level rise (SLR). Modelling and palaeoclimate evidence suggest that rapidly increasing temperatures in the Arctic can trigger positive feedback mechanisms for the GrIS, leading to self-sustained melting, and the GrIS has been shown to permit several stable states. Critical transitions are expected when the global mean temperature (GMT) crosses specific thresholds, with substantial hysteresis between the stable states.

Time-scale synchronisation of oscillatory responses can lead to non-monotonous R-tipping.

Rate-induced tipping (R-tipping) describes the fact that, for multistable dynamic systems, an abrupt transition can take place not only because of the forcing magnitude, but also because of the forcing rate. In the present work, we demonstrate through the case study of a piecewise-linear oscillator (PLO), that increasing the rate of forcing can make the system tip in some cases but might also prevent it from tipping in others. This counterintuitive effect is further called non-monotonous R-tipping (NMRT) and has already been observed in recent studies.

MIS-11 duration key to disappearance of the Greenland ice sheet.

Palaeo data suggest that Greenland must have been largely ice free during Marine Isotope Stage 11 (MIS-11). However, regional summer insolation anomalies were modest during this time compared to MIS-5e, when the Greenland ice sheet likely lost less volume. Thus it remains unclear how such conditions led to an almost complete disappearance of the ice sheet.

Iceberg discharges of the last glacial period driven by oceanic circulation changes.

Proxy data reveal the existence of episodes of increased deposition of ice-rafted detritus in the North Atlantic Ocean during the last glacial period interpreted as massive iceberg discharges from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence of the crucial role that the ocean plays both for past and future behavior of the cryosphere suggests a climatic control of these ice surges. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures.