Arctic ice loss causes extinction.
Huggel ’22 [Christian; September; Professor of Glaciology and Geomorphodynamics at the University of Zurich, Lead Author for the IPCC 6th Assessment Report, Ph.D. in Geology from the University of Zurich; Dr. Laurens M. Bouwer, Senior Scientist at the Climate Service Center Germany, Ph.D. in Flood Risk and Climate Change from Vrije University Amsterdam; Dr. Sirkku Juhola, Professor of Urban Environmental Policy in the Ecosystems and Environment Research Program at the University of Helsinki, Ph.D. in International Development Studies from the University of Sussex; Dr. Reinhard Mechler, Lead of the Systemic Risk and Resilience Group at the International Institute for Applied System Analysis, Ph.D. in Economics from Karlsruhe University of Technology; Dr. Veruska Muccione, Senior Scientist of Glaciology and Geomorphodynamics at the University of Zurich, Ph.D. in Astrophysics from the University of Geneva, M.Sc. in Sustainable Development and Environmental Management from SOAS University of London; Dr. Ben Orlove, Co-director of the Center for Research on Environmental Decisions & Associate Director of the Climate and Society Master’s Program at Columbia University, Ph.D. in International and Public Affairs from the University of California, Berkeley; Dr. Ivo Wallimann‑Helmer, Professor of Environmental Humanities at the University of Fribourg, Director of the Environmental Sciences and Humanities Institute at the University of Fribourg, Ph.D. in Philosophy from the University of Zurich, “The Existential Risk Space of Climate Change,” Climactic Change, Vol. 174, Iss.8, p.4-5]
In the recently published IPCC AR6 report of Working Group II, broadly speaking, there are three narratives in which existential threat or risk is explicitly used (IPCC 2022): (i) sea-level rise posing an existential threat to Small Island States and low-lying coasts; (ii) Loss and Damage, in line with the analysis and discourse mentioned above for the IPCC SR15; (iii) relocation which can pose existential threats to sense of place, identity, and citizenship.
The IPCC AR5 introduced the concept of key risks that can potentially have severe adverse consequences for humans and socio-ecological systems (Oppenheimer et al. 2014). Criteria for identifying key risks include probability, timing, magnitude, systems affected and irreversibility of corresponding risks, and limitations to reduce risks through mitigation and adaptation (O’Neill et al. 2017). Notably, none of these key risks reaches a level where human civilization would be threatened, as it would be by GCR. The key risks were also intended to inform the Reasons for Concern (RFC), which are probably the risks treated in current and past IPCC reports that have the strongest resemblance to (sensu GCR).
The five RFCs are (Oppenheimer et al. 2014; O’Neill et al. 2022) risks to unique and threatened (eco-) systems (RFC1); risks from extreme climate events (RFC2); distribution of impacts (RFC3); aggregate (economic) impacts (RFC4); and risks from future largescale discontinuities (RFC5) (Smith et al. 2001).
RFC1 and RFC5 encompass a number of disruptive processes in climate, cryosphere, and ecological systems with global-scale consequences, namely the collapse of the West Antarctic Ice Sheet (WAIS), the irreversible loss of the Greenland Ice Sheet, or the ecological transformation of the Amazon or boreal forest systems (Smith et al. 2009; O’Neill et al. 2017). The IPCC AR6 assessed the transition from low to moderate or high risks at lower temperature levels than previous IPCC Reports, e.g., RFC2 risks start to transition to a high level when global warming reached 1°C, or RFC5 transitions to moderate levels of risk already at 1°C warming, and to high risk levels between 1.5 and 2.5°C (O’Neill et al. 2022). RFC5 is underlaid by the concept of tipping points in climate and other natural and ecological systems which imply irreversible, large-scale processes with positive, self-reinforcing mechanisms if certain thresholds of warming are crossed. Global tipping cascades, involving for instance ice sheet collapse, Amazon rainforest transformation, or Arctic sea ice loss and permafrost thaw, are of particular concern and would pose an existential threat to civilization, as Lenton et al. (2019) suggest.