The evolution of heat exposure in changing societies and a changing climate from 1960 to 2100

Andreas Maximilian Schaefer^*Patrick LudwigSusanna MohrSvea KrikauBernhard MührSusanne BenzMichael Kunz

• Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

With climate change, human exposure to heat has increased over recent decades and is expected to substantially increase in the future. This study introduces a novel metric —- namely, the exponentially weighted degree-day approach – to assess population-weighted heat exposure at the national level, incorporating both static and dynamic population scenarios. Using ERA5 reanalysis and CMIP6 climate projections under the SSP2-4.5 and SSP5-8.5 scenarios, we analyze and categorize global heat exposure and its trends from 1960 until 2100. Our findings reveal a significant rise in heat exposure over past decades, disentangling the contributions of climate and demographic changes. Furthermore, a thorough analysis of biases across different datasets and model dimensions provides a global perspective based on daily maximum and daily mean temperatures. This analysis forms the basis for quantifying current and future heat exposure, together with a qualitative heat zone classification scheme. The results underscore the urgent need for targeted adaptation strategies and improved climate metrics to better assess and mitigate future heat-related risks.