Natural climate change, through its influence on agriculture, has been central to the rise and fall of civilisations throughout history. Anthropogenic climate change poses an unprecedented challenge and existential risk but, unlike natural climate change, it is a threat that contemporary society can prevent if we so choose. Despite consensus amongst climate scientists, concern across society and knowledge of solutions, anthropogenic emissions continue to rise, threatening the welfare of current and future generations globally. The recent failure of COP26 to ‘flick the switch’ on urgent climate action demonstrates the need for a paradigm shift in the way that we think about the threat of climate change.

Good risk management requires consideration and communication of tangible worst-case impacts. The mainstream framing of ‘global warming’, in terms of imperceptible temperature increases, does neither. For humanity, tangible worst-case impacts take the form of human suffering, societal collapse or extinction. However, consideration and communication of these concerning outcomes, with respect to climate change, is underdeveloped. This thesis is motivated by the idea that reframing the threat of climate change to embody more tangible risk of everyday relevance to society may support better risk management. And so, a three-part investigation is undertaken to improve our understanding of the complex risk landscape of climate change, food insecurity and societal collapse.

The first contribution looks to the past to examine how systematically documenting historical evidence may improve our understanding of the complex risk landscape. An original empirical evidence base is established and structured using a novel format causal loop diagram. Thousands of feedback loops are unfurled, demonstrating fragile interdependencies that may see climate change undermine agricultural productivity and food supply chains. This may lead to cascading or synchronous sociocultural unrest, economic loss and political dysfunction as well as starvation, migration and conflict, with the potential to trigger a reinforcing ‘global systems death spiral’. The novel format enables swift identification of data-driven methods used to establish empirical evidence and existing gaps. This systematic documentation of multidisciplinary evidence facilitates succinct visual consideration and communication of feedback loops and intervention points critical to managing the threat of climate change.

The second contribution looks to the future to examine how surveying ‘end-game’ climate change may improve our understanding of the complex risk landscape. An original quantitative model is developed to illustrate an ‘extreme global warming’ scenario. It is shown that we may face societal collapse as early as 2050, with population plummeting to 32% of current numbers by 2100, under high-range (8°C+) global warming. The distribution of risk will not be equal, with the least prepared countries of the developing Global South hit the hardest, experiencing 93% of cumulative human suffering by 2100. Emerging superpowers have a unique role to play in mitigating climate change, not only in the best interests of the rest of the world but for their own sake, with China and India alone at risk of 1.2 billion and 1.6 billion starvation deaths by 2100. These insights emphasise the danger of societal collapse should we not act with haste to reduce emissions, build resilience and decrease vulnerability.

The third contribution looks to the present to examine how climate policy and socioeconomic development decision-making may influence the complex risk landscape. An original quantitative model is used to conduct a comparative analysis of decision-factors under 15 mainstream scenarios of low- to mid-range (1.5–4.5°C) global warming. Depending on decision-making in the present, up to 2.5 billion people may face starvation, conflict or migration by 2100. Climate policy should prioritise urgent mitigation through behavioural disruption, while supporting slow-burn technological solutions. Socioeconomic development supporting education, gender and income equality, social cohesion and sustainable infrastructure and services is needed to build resilience and decrease vulnerability. High emitters hold a moral responsibility to address inequalities that may manifest global climate injustice. These insights emphasise that strong global coordination and international cooperation is needed to tackle climate change with proactive and well-balanced decisions if we are to minimise human suffering.

Collectively, the contributions to knowledge contained in this thesis provide a systematic and quantitative study of climate change, food insecurity and societal collapse, highlighting the danger of indirect cascading effects and synchronous failures as well as the potential for technological and socio-politico-economic interventions to backfire or have unintended consequences. It demonstrates the importance of future work to develop a deeper understanding of the worst-case impacts of climate change, which has broader implications for society in terms of articulating more tangible risk of everyday relevance to individuals, businesses and governments, to support better risk management.