Increasing risk of mass human heat mortality if historical weather patterns recur

The potential death toll of severe extreme heat events is crucial for climate risk analysis and adaptation planning but may not be captured by existing projections. We estimate this quantity for Europe using machine learning to calculate the intensity of historical heat waves if they occur at present or future global temperatures, combined with empirical exposure-response functions to quantify the resulting mortality. Each event is projected to generate tens of thousands of excess deaths. If August 2003 meteorological conditions recur at the current global temperature anomaly of 1.5 °C, we project 17,800 excess deaths across Europe in one week, rising to 32,000 at 3 °C. This mortality is comparable to peak COVID-19 mortality in Europe and is not substantially reduced by ongoing climate adaptation. Our results suggest that while mitigating further global warming can reduce heat mortality, mass mortality events remain plausible at near-future temperatures despite current adaptations to heat.