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.