Global age-dependent population exposure to multiple future climate extremes

In the last decades, climate extremes have become more frequent and severe over most regions of the World. Combined with poor adaptation measures and limited mitigation strategies, such extremes have progressively caused large socioeconomic impacts. Given the projected increase of global temperature, climate extremes are likely to see a further increase during the 21^st century, to the point that what we see as an extreme today might become the new normal, especially within scenarios characterized by high emissions and insufficient mitigation as the SSP3 and SSP5.

In the first part this study, we analysed, at global scale, the evolution of single and multiple climate extremes, focusing in particular on heatwaves, meteorological droughts, and heavy rainfall and snowfall events. As input data, we selected a combination of datasets for past reconstruction (ERA5, GPCC, CRU, and Berkeley Earth) and an ensemble of ten bias-adjusted simulations from the ISIMIP3b family. Firstly, we analysed the projected changes in extremes – at gridded (0.5°), country, and macro-regional scales -, then we investigated the timing of the emergence of unprecedented extremes, and eventually we selected the hotspots where the current extremes will become the new climate normal, i.e. occurring any other year. All the analyses are separated by the SSP, in this study we used four (SSP1, SSP2, SSP3, and SSP5) plus two overshoot-based SSPs (SSP1-1.9, and SSP5-3.4ov).

In the second part, we estimated the exposed population to robust increase of extremes, to the occurrence of unprecedented events (with a special attention to combined drought-heatwaves and heavy rainfall-snowfall), and we quantified the global and continental number of people that will live in hotspot areas with climate extremes as the new normal. The input population data derive from multiple datasets (WorldPop, GW-POP, GHSL, IIASA, and HYDE), but we performed the analyses adding age-dependent classes, namely young (< 5 years), adult (5-69) and old (> 69 years) people, in order to account the possible inhomogeneous evolution of climate change affecting the segments of the population at higher risk. We therefore repeated the analysis introducing econometrics and focusing on age-dependent population living above and below a dynamic poverty line.