Forecasting Lives Lost to Climate Change

Nigel Peter Howard , Peter Newman

This review synthesises empirical evidence linking global mean surface temperature to climate mortality through undernourishment, heat, extreme events, conflict, and disease, and introduces an exploratory precautionary metric: cumulative climate-related deaths per cumulative megatonne of greenhouse gas emissions (CO₂-e), intended to support policy evaluation under deep uncertainty. Using observed CO₂-driven warming relationships and globally available population vulnerability data, we estimate that continued business-as-usual emissions would impose very large, geographically concentrated mortality burdens this century, with risks escalating nonlinearly beyond 2 °C. While uncertainty remains substantial, especially for undernourishment and conflict pathways, the direction and scale of risk are robust, providing a broad exploratory framework for approximating climate-related mortality. Expressing mortality per Mt CO₂-e allows the metric to be applied across all greenhouse gases and policy contexts. The resulting estimates should be interpreted as scenario-based approximations contingent on the assumptions and historical relationships used in the model. The results imply that treating climate change primarily as an economic externality understates its consequences, and that precautionary policy assessment should explicitly account for human lives at risk or saved due to decarbonization. (Full derivation provided in Supplementary Information S3).