Increasing old people in poor region will be threatened by early emergence of heat waves

As the global temperature rises, heat wave (HW), which can produce numerous vital and economic loss, will become stronger, last longer, and occurs frequently. However, a time when change in HW will emerge from natural variability - defined here as the time of emergence (ToE) for HW - is unclear. Here we estimate ToE for each individual HW aspects (frequency, duration, and amplitude) using two kinds of HW determined by daily maximum and minimum temperature (indicating daytime and nighttime HW, respectively) from projections of 21 global climate models (GCMs) under the Representative Concentration Pathways (RCPs) RCP8.5. The ensemble median ToE occurs earlier for HW frequency and duration than HW amplitude for both daytime and nighttime HW. ToE for all HW aspects occurs much earlier in tropics: frequency and duration of HW will emerge before the ensemble median global warming reaches 1.5 °C, also ToE for HW amplitude is earlier than time of 2 °C global warming. Low economic growth and rapid increase in the elderly (age ≥ 65) in tropical countries can amplify heat-related disease and mortality. Therefore, mitigation is timely needed in tropical countries to reduce potential health risks according to the likelihood of significantly strong, long, and frequent HW.