High-impact climate events and tipping dynamics: assessing scientific understanding and future challenges

Le résumé fourni par la source

This paper is motivated by growing concern about tipping dynamics and processes that can cause abrupt, self-amplifying, and irreversible changes across the Earth system and societies. It assesses current scientific understanding of the most severe climate outcomes, and proposes ways to address the deep uncertainty surrounding them. We find substantial, though difficult-to-quantify, probabilities of major disruptions to large-scale ocean circulation, including the Atlantic Meridional Overturning Circulation and the Southern Ocean Abyssal Circulation, with the potential to cause global climate shifts. The probability of ice sheet instability in vulnerable sectors, particularly Antarctica's marine-based sectors, is already high and could accelerate sea level rise over centennial to multi-centennial timescales. Permafrost thaw is underway, with the potential for accelerated greenhouse gas release. Tropical forests face increasing risks of widespread tree mortality, with major consequences for biodiversity, regional climate, and water availability. Coral reef dieback and mountain glacier loss are also underway, while severe compound marine events may trigger irreversible ecosystem changes. Even gradual climate change can produce nonlinear, abrupt impacts when hazards breach physiological or socioecological thresholds, disrupting health, food, or economic systems. It is essential to determine how the probability of such outcomes depends on the level and rate of warming. Current modelling systems challenge our ability to reliably quantify these risks. Sustained investment in observations, process understanding and next-generation earth system modelling is critical to identify precursors and improve early warning. Decision frameworks are needed to support proactive, flexible, anticipatory adaptation. Effective mitigation reduces risks of these highly disruptive outcomes.

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