Significant sociopolitical fragmentation and/or state failure along with the relatively rapid, enduring, and significant loss capital, and systems identity this can lead to large-scale increases in mortality and morbidity. The potential for smaller damages to spiral into global catastrophic or extinction risk due to societal vulnerabilities, risk cascades, and maladaptive responses. The probability of human extinction within a given timeframe.Ī plausible and significant contributor to total extinction risk. Mean global surface temperature rise of 3 ☌ or more above preindustrial levels by 2100. The potential for individual disruptions or failures to cascade into a system-wide failure. Risk that is dormant under one set of conditions but becomes active under another set of conditions.Ĭhains of risk occurring when an adverse impact triggers a set of linked risks ( 3). Temperature rise is crucially dependent on the overall dynamics of the Earth system, not just the anthropogenic emissions trajectory. Particularly worrying is a “tipping cascade” in which multiple tipping elements interact in such a way that tipping one threshold increases the likelihood of tipping another ( 20). Such changes are evident in Earth’s geological record, and their impacts cascaded across the coupled climate–ecological–social system ( 19). Instead, abrupt and/or irreversible changes may be triggered at a temperature threshold. These are likely to not be proportional to warming, as is sometimes assumed. Examples include Arctic permafrost thawing that releases methane and CO 2 ( 15), carbon loss due to intense droughts and fires in the Amazon ( 16), and the apparent slowing of dampening feedbacks such as natural carbon sink capacity ( 17, 18). There are feedbacks in the carbon cycle and potential tipping points that could generate high GHG concentrations ( 14) that are often missing from models. The proposed agenda covers four main questions: 1) What is the potential for climate change to drive mass extinction events? 2) What are the mechanisms that could result in human mass mortality and morbidity? 3) What are human societies' vulnerabilities to climate-triggered risk cascades, such as from conflict, political instability, and systemic financial risk? 4) How can these multiple strands of evidence-together with other global dangers-be usefully synthesized into an “integrated catastrophe assessment”? It is time for the scientific community to grapple with the challenge of better understanding catastrophic climate change.Įven if anthropogenic GHG emissions start to decline soon, this does not rule out high future GHG concentrations or extreme climate change, particularly beyond 2100. We outline current knowledge about the likelihood of extreme climate change, discuss why understanding bad-to-worst cases is vital, articulate reasons for concern about catastrophic outcomes, define key terms, and put forward a research agenda. Analyzing the mechanisms for these extreme consequences could help galvanize action, improve resilience, and inform policy, including emergency responses. Yet there are ample reasons to suspect that climate change could result in a global catastrophe. Could anthropogenic climate change result in worldwide societal collapse or even eventual human extinction? At present, this is a dangerously underexplored topic. Yet, for climate change, such potential futures are poorly understood. Prudent risk management requires consideration of bad-to-worst-case scenarios.

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