Overshooting the critical threshold for the Greenland ice sheet

• Published in: Nature (London) 2023-10, Vol.622 (7983), p.528-536
• Main Authors: Bochow, Nils, Poltronieri, Anna, Robinson, Alexander, Montoya, Marisa, Rypdal, Martin, Boers, Niklas
• Format: Article
• Language: English
• Subjects: 21st century; 704/106/125; 704/106/694/2739; 704/106/694/2786; Climate change; Climate Models; Cooling; Cooling rate; Freezing; Global sea level; Global temperatures; Global Warming - statistics & numerical data; Greenland; Greenland ice sheet; Humanities and Social Sciences; Ice; Ice Cover - chemistry; Ice sheet melting; Ice sheet models; Ice sheets; Mean temperatures; multidisciplinary; Paleoclimate; Positive feedback; Science; Science (multidisciplinary); Sea Level Rise; Temperature; Time Factors
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-023-06503-9

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) 1 . 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 2 – 4 , and the GrIS has been shown to permit several stable states 5 . Critical transitions are expected when the global mean temperature (GMT) crosses specific thresholds, with substantial hysteresis between the stable states 6 . Here we use two independent ice-sheet models to 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 the maximum GMT and the time span of overshooting given GMT targets are critical in determining GrIS stability. We find a threshold GMT between 1.7 °C and 2.3 °C above preindustrial levels for an abrupt ice-sheet loss. GrIS loss can be substantially mitigated, even for maximum GMTs of 6 °C or more above preindustrial levels, if the GMT is subsequently reduced to less than 1.5 °C above preindustrial 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 a peak in SLR of up to several metres. Simulations using two state-of-the-art ice-sheet models show that abrupt melting of the Greenland ice sheet following overshooting of the global mean temperature critical threshold can be mitigated by subsequent cooling to below 1.5 °C.