Abstract

Extreme heat events are one of the most dangerous climate hazards and they are projected to increase in frequency, intensity and duration as this century progresses. Change in future exposure to extreme heat events depends not only on climate change, but also on changes to future population size and the areas this population inhabits. This study explores exposure to the heat event known as a tropical night. Using a CMIP6 multi-model ensemble, coupled with population projections, this study projects exposure for the four alternative futures described by SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. Exposure is quantified annually at both the global and regional scale, relative to a preindustrial baseline. By the end of the twenty-first century global annual exposure to tropical nights will total 1338-2674 billion person-days depending on the pathway followed. Of the four pathways, globally change in exposure from the pre-industrial is avoided most under SSP1-2.6, which, when compared to SSP3-7.0 which projects the greatest change, is a reduction of 1336 billion person-days annually. Exposure reduction varies at the regional level, yet in the majority of cases, SSP1-2.6 remains the more desirable future in terms of minimising future exposure. Moreover, this study finds that changes in climate versus changes in population do not equally influence changes in exposure, and their contributions vary regionally. Irrespective of the future pathway followed, human exposure is set to increase at the global scale and for the vast majority of regions.