The hidden burden of dual climate threats: Region-specific additive impacts of PM2.5 and temperature extremes on cardiovascular and respiratory mortality in a tropical climate

Abstract

Background

Climate change has increased the frequency and intensity of extreme temperature events (ETEs; heat and cold waves), alongside fluctuations in PM_2.5. However, limited research has explored the additive interaction between ETEs and PM_2.5 on mortality, especially in tropical regions where interactions may differ from temperate settings.

Methods

A two-stage time-series using distributed lag non-linear models was applied to estimate region-specific relative risks (RRs) of ETEs and PM_2.5 on daily cardiovascular and respiratory mortality. Additive interaction was quantified using the Relative Excess Risk due to Interaction (RERI).

Results

Cold waves had the strongest effect in the central region (cardio RR = 1.044, lag0) and the south (respiratory RR = 1.038, lag21). In the north, heat waves showed the highest risks (cardio = 1.032, lag0; respiratory = 1.041, lag0). PM_2.5 significantly elevated mortality in all regions, especially the south (cardio = 1.013, lag0) and east (respiratory = 1.018, lag0). Cold wave-PM_2.5 interaction was greatest in the central region (respiratory RERI = 0.308; cardio = 0.203), followed by Bangkok (respiratory = 0.019; cardio = 0.070). Heat wave-PM_2.5 interaction was also significant in Bangkok and the south. Bangkok residents were vulnerable to both ETEs; the south experienced only heat wave-PM_2.5 effects. In sensitive subgroups, interactions heightened cardiovascular susceptibility among females (cold wave = 0.117; heat wave = 0.045), older adults ≥65 (cold wave = 0.066; heat wave = 0.031), and in sub-diseases like pulmonary heart disease (cold wave = 0.054; heat wave = 0.141) and lung diseases from external causes (cold wave = 0.264; heat wave = 0.306).

Conclusions

Interactions between ETEs and PM_2.5 significantly increased mortality risks in tropical subpopulations, particularly during cold waves. These findings support urgent global preparedness to mitigate health impacts from the convergence of climate extremes and air pollution in tropical contexts.