This paper models long-term changes in minimum mortality temperatures (MMT), a well-established metric denoting the lowest risk of heat-related mortality, as a function of climate change and socio-economic progress across 3820 cities. The analysis notes that human adaptation to heat should be accounted in inferring on the magnitude of future heat-related mortality due to climate change. Depending on the combination of climate trajectories and socio-economic pathways evaluated, by 2100 the risk to human health is expected to decline in 60% to 80% of the cities against contemporary conditions. This is caused by an average global increase in MMTs driven by long-term human acclimatisation to future climatic conditions and economic development of countries.
The study finds that a stable and sustainable socio-economic pathway SSP1 will equip most world cities with a moderately high adaptation. In contrast, a rapid socio-economic growth based on fossil fuels along with high forcing (RCP8.5/SSP5) will reach higher adaptation levels in 2100 for most cities against a sustainable future. The high socio-economic level driven by fossil-fuel exploitation can only partly compensate for its own negative consequences for human health. A future according to RCP8.5/SSP5 would critically endanger cities in arid and semi-arid climates. All exhibit small gains in adaptation while heat exposures are projected to increase. Even though tropical and subtropical cities show relatively small and climate-driven increments in adaptation change until 2100, they profit from small exposure changes in a sustainable scenario. The study bears some limitations, namely the premise that adaptation to heat, especially the wealth-enabled share, is instantaneous. The study also attempts to account for a lag in physiological acclimatisation by using mean climate variables over a 30-year period ending in 2094. Further, the SSPs rely on assumptions and could be source of uncertainty in the study's projections. Still, the SSPs originate from an established framework developed to analyse different climate and socio-economic futures.