A groundbreaking study by Karolinska Institutet’s Institute of Environmental Medicine reveals that extreme heat combined with high air pollution levels drastically increases the risk of death in Indian cities—far more than each factor on its own. Published in Environment International, the study analyzed over 3.6 million deaths from 10 major Indian cities between 2008 and 2019.

Using sophisticated spatiotemporal models, researchers assessed daily exposure to temperature and fine particulate matter (PM2.5). They discovered a striking synergy: a 10 μg/m³ rise in PM2.5 resulted in a 4.6% increase in daily deaths on extremely hot days, compared to just 0.8% on moderately warm ones.

Even more alarming: when PM2.5 reached 100 μg/m³, the risk of death skyrocketed by 64% during extreme heat events—highlighting a deadly interaction between air and climate hazards.

Time-series analyses using advanced regression models helped map how these environmental threats work together. The research underscores a pressing need for coordinated action to reduce pollution and tackle climate change simultaneously.

“This study shows the urgent need for integrated warning systems and aggressive emissions control,” said lead researcher Jeroen de Bont. Co-author Petter Ljungman added that immediate pollution reduction can deliver rapid health benefits.

With climate change intensifying heat waves and urban air remaining toxic, Indian cities must act fast to safeguard public health.