Heat stress caused by high levels of air temperature and humidity is rising globally due to climate change. Various indicators for heat stress have been developed to quantify different facets of how heat impacts people. We use data from climate models to calculate the future evolution of eight heat stress indicators for highly populated regions of the world. The trends of the different indicators vary substantially, with some indicators showing large increases while others only increase modestly. For estimating the severity of heat stress, we calculate how often each indicator exceeds threshold values that indicate different heat stress severity. Many thresholds will be exceeded much more often with rising temperatures. The increases are particularly large for some indicators while others only show small increases. Moreover, the indicators with the strongest trends are often not the ones that show the highest increase in threshold exceedances. For quantifying the impacts of heat stress caused by climate change it is thus important to choose indicators that are appropriate for the respective application. While several indicators were tested on small scales (e.g., in cities or single countries), for global heat stress assessments it is necessary to have more validation studies on regional‐to‐global scales.

The research conducted by the researchers in the EXHAUSTION consortium, published in Earth’s Future was recently highlighted under the Research Spotlight of EOS.org.

These maps show the frequency with which three heat stress indicators exceed their “very high” and “extreme” thresholds. for a global warming level of 3°C, which is the most likely outcome given current policies. While there is a clear trend of increasing high-heat stress frequency with greater warming, how that stress manifests depends on the selected indicator. Schwingshackl et al.