In January, the Intergovernmental Panel on Climate Change (IPCC), the world’s most authoritative body for the assessment of climate science, met to plan the seventh iteration of its reports to international policymakers. As that work gets underway, the IPCC will have to ensure its assessment of the science continues to provide insights to policymakers on the most pressing policy issues. 

One such issue is the potential for climate change to trigger catastrophic or even existential risks to humanity. 

Despite all the rhetoric on climate catastrophe among scientists, policymakers, media, and civil society, the IPCC has had surprisingly little to say on this important topic. Across the more than 10,000 pages of the IPCC’s most recent Sixth Assessment Report, the terms “catastrophic” or “existential” are used sparingly. The IPCC’s reports are well known for their rigorous documentation of observed and projected climate change impacts, and they identify a number of “key risks” such as impacts on low-lying coastal areas and heat-related mortality. 

For over three decades, the IPCC has produced assessments on the state of knowledge regarding climate change science, consequences, and risk management. The work of the IPCC is meant to provide a level playing field of foundational knowledge that informs international negotiations regarding future climate policy.

Yet, the IPCC does not define what constitutes a catastrophic or existential risk or provide a framework for interpreting this information for decisionmakers. At what point does a key risk become a catastrophe and what criteria does one use to make that judgement? Without such criteria, these terms are used inconsistently, which lessens their relevance to policymakers.   

There are a variety of reasons why IPCC reports might limit the use of such language. First, the concept of a catastrophe has a subjective nature to it. The Working Group II report on climate change impacts, for example, notes that “What constitutes ‘dangerous’ or ‘severe’ risks is partly a value judgement and can therefore vary widely across people, communities or countries.” Given that ambiguity authors may opt to use less subjective terminology when reporting on the impacts of climate change. 

Second, IPCC authors could be pulling their punches in their assessment of the science. Thousands of studies have been published that refer explicitly to “catastrophic risk”, “catastrophic threat” or “climate catastrophe.” No doubt, IPCC authors are reading these studies, but the language of catastrophe is being filtered out in the process, despite those same authors being among those most alarmed by the climate’s current trajectory. If United Nations Secretary General Antonia Guterres wants the IPCC’s assessments to be interpreted as “a code red for humanity,” then the assessments would benefit from a clear and explicit communication regarding catastrophic risk.  

Third, IPCC authors and the scientific community may simply lack the language to effectively communicate about catastrophic and existential risks. For example, the AR6 Working Group II report itself states that “there has been less and often implicit discussion on the existential dimension of climate-related risk.” A recent study by Christian Huggel and others has also noted that “the high end of the risk, i.e., where risks become existential, is poorly framed, defined, and analyzed in the scientific literature.” 

Given the importance of high-end consequences for the negotiation of international agreements and the design and implementation of climate adaptation efforts, the credibility and thought leadership of the IPCC could be harnessed to bring structure and clarity to these concepts in the Seventh Assessment Report. 

Specifically, IPCC authors could pursue the following goals:

• Develop common language around the concepts of catastrophic and existential risk: Climate researchers have made some attempts to develop calibrated language around different scales of risk. Building on these efforts to develop common understanding and technical descriptions regarding scales of risk would help to enhance clarity. One specific opportunity is to update IPCC’s guidance on the assessment of risk to include calibrated language and criteria for different magnitudes of risk that explicitly includes catastrophic and existential risks. 

• Enhance consideration for high-end scenarios: Since the 2015 Paris Agreement, much of the IPCC’s assessment efforts have focused on the agreement’s policy objective of limiting warming to less than 2°C or event 1.5°C. Scientists appear reluctant to engage in conversations around futures where this threshold is exceeded. Yet, clarifying the emissions pathways under which catastrophic and existential risks are likely to occur would benefit negotiations around greenhouse gas mitigation as well as adaptation strategies that hedge against high-end risks. 

• Clarify Impact Pathways Leading to Catastrophic and Existential Risks: While the IPCC suggests climate change could pose global catastrophic or existential threats, there is a lack of understanding regarding the mechanisms by which such consequences would arise. Greater investment in tracing the paths by which the effects of climate change scale-up to create large-scale risk would aid efforts to assess and manage risk. 

An estimated 2,356 jurisdictions with a population of over a billion people across 40 countries have declared a climate emergency, and recent years have seen both scientists and national security agencies find common cause in referring to climate change as an existential threat. As illustrated by the Global Catastrophic Risk Management Act of 2022, governments are increasingly thinking critically about such threats. Meanwhile, climate anxiety in on the rise as civil society leans heavily into the narrative that the situation is hopeless.

The IPCC is well-positioned to tackle the global threats posed by the climate emergency. What is needed is a concerted effort to confront the stark realities of catastrophic risk and interpret that literature through a policy-relevant lens. The seventh cycle of the IPCC is underway, but authors have yet to be selected and writing has yet to commence. Now is the time for IPCC leadership to orient the assessment toward filling gaps in knowledge that affect the policy arena. The potential for high-end risk stands as one such gap.