Polar ice sheets contribute decisively to uncertainty in climate change projections

Earth's climate is a complex system including key components such as Arctic sea ice in the summer and the El Niño Southern Oscillation, along with climate-inclining elements including polar ice caps, the Atlantic meridian, and the Amazon rainforest. Exceeding the threshold values of these elements can lead to a qualitatively different climatic condition that threatens human societies. Elements of the cryosphere are vulnerable to current levels of global warming (1.3°C), while also having long response times and high uncertainty. We assess the impact of interacting components of the Earth system on overturning risks using an established conceptual network model of these components. The polar ice sheets (the Greenland and West Antarctic ice sheets) are critical to the tilt probability and cascading effects within our model. At a global warming level of 1.5°C, neglecting the polar ice sheets can change the expected number of spiked features by a factor of more than 2. This is worrying because exceeding 1.5°C global warming becomes inevitable, while the current state-of-the-art IPCC-type models do not (yet) include dynamic ice sheets. Our results suggest that polar ice sheets are critical to better understanding the risks of overturning and cascading effects. Therefore, improved observations and integrated model development are key. (Jonathan P. Rosser, Ricarda Winkelmann & Nico Wunderling, more at nature.com)