The number of people exposed to both heat waves and wildfire smoke on the same days has increased by 287 million worldwide over two decades highlighting the growing health risks posed by overlapping climate extremes, according to a study by researchers at Monash University in Australia.
Published in the journal Science Advances, the study examined global patterns of exposure to heat waves and pollution from landscape fires between 2000 and 2019. The research was led by Dr Yao Wu, alongside professors Yuming Guo and Shanshan Li.
The findings show that more than half of the global population experienced exposure to these combined events during the 20 year study period. In populated areas 52.4% of people experienced increasing exposure while the proportion was nearly 56% across the global population.
The researchers estimated that around 916 million people experienced at least one day of combined exposure each year, when heat wave conditions and wildfire related air pollution occurred simultaneously.
The annual global average reached 1.3 days of combined exposure per person. It increased from an average of one day per person annually during 2000–2009 to 1.7 days during 2010–2019.
The study identified the Democratic Republic of the Congo, Indonesia, Mexico, Brazil and the Russian Federation among the five countries with the highest annual averages of person days of combined exposure to heat waves and wildfire smoke.
Heat waves and wildfire smoke can pose serious health risks individually, but their simultaneous occurrence can intensify the effects on human health. Extreme temperatures place additional strain on the cardiovascular system, while smoke contains fine particles and other pollutants that can irritate the respiratory system and worsen existing health conditions.
Combined exposure can therefore increase the risk of respiratory and cardiovascular problems particularly among older people, children, outdoor workers and individuals with pre-existing illnesses.
The researchers warned that exposure could continue to increase as global warming contributes to more frequent or intense heat extremes and changes the conditions that influence landscape fires. The extent of future exposure will also depend on regional climate patterns, vegetation, land management and population distribution.
The findings underline the need for public health and disaster management systems to prepare for heat waves and wildfire smoke together rather than treating them as separate hazards.
Measures such as heat health warning systems, timely smoke alerts access to cleaner indoor air, public cooling facilities and coordinated emergency responses could help reduce risks during periods when extreme heat and fire related pollution coincide.
As climate related hazards increasingly overlap, the study highlights the importance of understanding their combined effects on communities and strengthening preparedness to protect public health.