Christopher Callahan, Jared Trok, Andrew Wilson, Carlos Gould, Sam Heft-Neal, Noah S Diffenbaugh, Marshall Burke

The potential death toll of worst-case extreme heat events is crucial for climate risk analysis and adaptation planning. 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. For example, if July 1994 or August 2003 meteorological conditions recur at the current global temperature anomaly of 1.5 °C, we project 14,000 or 17,300 excess deaths across Europe in a single week, respectively. At 3 °C, mortality rises to 26,800 or 31,500 per week. These death rates are comparable to peak COVID-19 mortality in Europe and are not substantially reduced by ongoing climate adaptation. Our results suggest that avoiding mass heat mortality in Europe will require significant and novel adaptation to heat.