Western Pacific Ocean Warming Intensifies Heat–Ozone Compound Extremes and Population Health Risks in China

Compound heatwave–high ozone pollution events (CHOPs) represent an emerging climate–health challenge, yet their drivers and long-term population impacts remain insufficiently quantified. Using 2000–2022 high-resolution climate and environmental datasets, together with updated epidemiological evidence for compound heat–ozone risks and machine-learning diagnostics, we show that CHOP occurrences in Eastern–Northern China (ENC) have risen by nearly 3.7‐fold since 2013—far exceeding the increases in isolated heatwaves (1.85-fold) and ozone events (2.66-fold). We identify Western Pacific Warm Pool (WPWP) warming as a dominant climatic precursor that strengthens tropical–midlatitude ocean–atmosphere coupling and reinforces a persistent barotropic high-pressure ridge over ENC. This circulation pattern produces simultaneous heat accumulation, stagnant ventilation, and enhanced photochemical ozone formation, thereby amplifying compound extremes beyond the sum of their individual components. The intensified CHOPs have markedly elevated health burdens. Among older adults, CHOP-related mortality risks have nearly quadrupled, while the associated economic losses now exceed 14.3 billion CNY annually—an increase of more than threefold compared to the early 2000s. These disproportionate impacts highlight the vulnerability of aging populations to compounding climate and air-quality stressors. By revealing the teleconnection pathways that modulate CHOP variability and quantifying their escalating human and economic costs, this study provides a scientific foundation for climate-informed seasonal forecasts, targeted early-warning systems, and equitable adaptation strategies. Our findings underscore the necessity of integrating large-scale climate precursors into compound-risk assessments to safeguard public health under a warming climate.