The evolution of the global population experiencing unprecedented exposure and its age of emergence.

In climate change attribution, unprecedented magnitudes of extreme events can be defined on the basis of thresholds in the pre-industrial distributions of event magnitudes. This notion of unprecedented levels of climate change impacts has been extended toward the lifetime exposure to extreme events by evaluating exposure frequency. Unprecedented exposure to extreme events is assessed by comparing average lifetime exposure under different climate scenarios to an upper percentile of exposure in a pre-industrial climate. Here we combine simulations of climate change impacts under different climate forcing scenarios with country-level demography datasets to estimate the fraction of the global population experiencing unprecedented exposure to extreme events. This is done for 29 global mean temperature trajectories taken from the AR6 scenario explorer and multiple extreme event categories such as heatwaves, floods and droughts. Further, we assess the age of emergence at which birth cohorts reach unprecedented levels of exposure.