Abstract The simulated effects of anthropogenic global warming have become important in many fields and most models agree that significant impacts are becoming unavoidable in the face of slow action. Improvements to model accuracy rely primarily on the refinement of parameter sensitivities and on plausible future carbon emissions trajectories. Carbon emissions are the leading cause of global warming, yet current considerations of future emissions do not consider structural limits to fossil fuel supply, invoking a wide range of uncertainty. Moreover, outdated assumptions regarding the future abundance of fossil energy could contribute to misleading projections of both economic growth and climate change vulnerability. Here we present an easily replicable mathematical model that considers fundamental supply-side constraints and demonstrate its use in a stochastic analysis to produce a theoretical upper limit to future emissions. The results show a significant reduction in prior uncertainty around projected long term emissions, and even assuming high estimates of all fossil fuel resources and high growth of unconventional production, cumulative emissions tend to align to the current medium emissions scenarios in the second half of this century. This significant finding provides much-needed guidance on developing relevant emissions scenarios for long term climate change impact studies.