Global health impacts of the 2018–2019 heatwaves and air pollution events under warmer climates

Extreme temperatures and ambient air pollution are closely linked and impose substantial global health burdens, yet their regional responses to additional warming remain poorly understood across the world. Using a storyline approach based on the exceptionally warm years 2018 and 2019, we examine how heatwaves (HWs), fine particulate matter (PM 2.5 ), ozone (O 3 ), and their separately estimated mortality burdens respond to two counterfactual climates at +2 K and +2.75 K warming levels. The storylines keep the global circulation patterns and anthropogenic emissions fixed at 2018–2019 levels, while biogenic emissions and meteorological conditions evolve in response to the warmer climate. Present-day exposure-response functions, population, baseline mortality, vulnerability, and adaptation are held constant across storylines. The mortality evaluation for the factual year 2018 reveals regional disparities: in Asia (with 100.5 per million, 95% CI: 68.1 to 131.5) and Africa (62.2; 42.1-81.5), PM 2.5 attributable deaths far outweighs HWs and O 3 , whereas HWs attributable mortality is highest in Europe (155.8; 153.5–158.2) and Australia (24.2; 21.7–31.7). Similar regional patterns, with quantitative differences, occurred in 2019. Compared with the factual world, HW-attributable mortality shows the largest increase across the two warmer storylines. Under +2.75 K warming, the 2018–2019 average increase exceeds 95% in South America, followed by Africa (81.6%), Australia (66.5%), North America (58.6%), Asia (45.1%) and Europe (36.6%), respectively. In contrast, pollution attributable mortality generally decreases under a +2.75 K warmer world, although responses vary by pollutant and region. These findings highlight the need for region-specific strategies integrating heat adaptation and air quality management to reduce the associated health burdens.