Overshooting the critical threshold for the Greenland ice sheet

Abstract

Melting of the Greenland ice sheet (GrIS) in response to anthropogenic global warming poses a severe threat in terms of global sea level rise of more than 7~m for its complete loss (Allan et al., 2021), but also in terms of North Atlantic freshening that in turn destabilises the Atlantic Overturning Circulation (Boers, 2021). Modelling and paleoclimate evidence suggest that rapidly increasing temperatures in the Arctic can trigger positive feedback mechanisms, and the GrIS is hypothesised to exhibit multiple stable states (Gregory et al., 2020). Consequently, critical transitions are expected when the global mean surface temperature crosses specific thresholds, and there is substantial hysteresis between the alternative stable states (Robinson et al., 2012). Here, we investigate the impact of different overshoot scenarios with varying peak and convergence temperatures for a broad range of warming and subsequent cooling rates. Our results show that both the maximum GMT and the time span of overshooting given global mean temperature (GMT) targets are critical in determining GrIS stability. We find a threshold GMT around 4.5°C above pre-industrial levels for an abrupt loss of the ice sheet, preceded by several intermediate stable states. We show that overshoots of up to 7.5°C GMT above pre-industrial levels might be tolerable if GMTs are subsequently reduced below 1.5°C GMT above pre-industrial levels within a few centuries. However, our results also show that even temporarily overshooting the temperature threshold, without a transition to a new ice sheet state, still leads to dramatic sea-level rise up to several metres during the time span before returning to moderate GMTs.

Rate-induced tipping cascades arising from interactions between the Greenland Ice Sheet and the Atlantic Meridional Overturning Circulation

“…At present, the ice sheet's mass loss is accelerating (Shepherd et al, 2020), and there is limited evidence that its western parts may already be approaching a critical transition (Boers and Rypdal, 2021). While the crossing of the critical temperature threshold itself does not imply a fast collapse, the time needed to melt the ice sheet on Greenland decreases with a higher temperature level above its tipping point (as qualitatively obtained with our model as well as quantified using a three-dimensional polythermal ice sheet model by Robinson et al, 2012;Bochow et al, 2023). As a consequence, the future level of warming controls the rates of mass loss from Greenland even if having transgressed the threshold.…”

“…the freshwater input and the AMOC response timescale . In particular, the rate of melting of the ice sheet on Greenland was suggested to depend on the magnitude of the surface warming above its tipping point (Robinson et al, 2012;Bochow et al, 2023). Such a rate-induced cascade induced by crossing critical rates of environmental change complements the commonly suspected tipping cascades involving bifurcationinduced tipping (Dekker et al, 2018;Klose et al, 2021;Wunderling et al, 2021).…”

Cryosphere tipping elements decisive for tipping risks and cascading effects in the Earth system

“…For example, many climate models do not include a coupled ice sheet and although these are fundamentally very difficult to couple to a climate model, even a simplified ice sheet component coupled to the climate model may provide a very fruitful way forward 35 .…”