How can the catastrophic risk potential of unseen climate extremes be understood?

The Earth’s climate is heading into unprecedented territory, with the global mean surface temperature reaching record-breaking levels in 2024. Meanwhile, on regional scales, extreme events are becoming both more frequent and more severe, with some events being without precedent in the observational record. These types of ‘unseen’ events could result in very high-impact, potentially catastrophic impacts for society on a variety of temporal and spatial scales. However, due to the inherent uncertainty in the complex climate system, we have a poor understanding of the risk of unprecedented events, including what is physically and statistically plausible, and the role of critical thresholds in both the physical climate and societal responses. We also have limited capacity to imagine and anticipate events with no historical precedent. Given the risk of very high societal impacts, including mortality, morbidity, and other socio-economic vulnerabilities already possible under present climate conditions, and the potential for a substantial increase in the number of people exposed to these threats under climate change, it is critical that we improve our understanding of these unknown-likelihood unseen events.

In late 2024, a workshop was hosted at King’s College London to address the question of how to reduce the catastrophic risk potential from unseen climate extremes. Twenty-seven researchers participated from a range of disciplines to solicit a variety of perspectives on the question. This included, amongst others, contributions from physical climate scientists, researchers in existential threats, and social scientists. Here, we present the outcomes from these interdisciplinary discussions, including perspectives on the framing and definition of the problem, open research questions, and a research agenda to advance toward a more comprehensive understanding of risk and improved societal preparedness to facilitate pragmatic policy decisions. Areas of discussion included developments in large ensemble climate modelling; modelling of connected systems; counterfactual thinking; and risk-based limits to adaptation; as well as wider philosophical questions regarding what constitutes a catastrophic or existential risk and how this should be defined in a climate context.