Climate and agriculture have played an interconnected role in the rise and fall of historical civilizations. Our modern food system, based on open-environment production and globalised supply chains, is vulnerable to a litany of abiotic and biotic stressors exacerbated by anthropogenic climate change. Despite this evidence, greenhouse gas emissions continue to rise. Current trajectories suggest global warming of ∼2.0–4.9 °C by 2100, however, a worst-case emissions scenario with rapid combustion of all available fossil fuels could cause a rise of ∼12 °C. Even if emissions decline, unprecedented atmospheric CO2-e concentrations risk triggering tipping points in climate system feedbacks that may see global warming exceed 8 °C. Yet, such speculative ‘runaway global warming’ has received minimal attention compared to mainstream low- to mid-range scenarios. This study builds on The Limits to Growth to provide new insights into the international risk of mass mortality due to food insecurity based on a higher-resolution illustration of World3’s ‘runaway global warming’ scenario (∼8–12 °C+). Our simulation indicates rapid decline in food production and unequal distribution of ∼6 billion deaths due to starvation by 2100. We highlight the importance of including high-resolution simulations of high-range global warming in climate change impact modelling to make well-informed decisions about climate change mitigation, resilience and adaptation.