Synergy effect of heat and air pollution: mortality risk almost doubles

“The mortality effect of exposure to extreme temperatures and pollution is greater than the sum of their individual effects.” That’s how Md Mostafijur Rahman, PhD, summarizes the results of a study done by researchers at the Keck School of Medicine of USC.

The findings have high relevance as the exposure to heat, and air pollution will grow with climate change. Wildfires add another level because they create heat and air pollution, which sum up with weather conditions and other sources of air pollution and heat.

The researchers found that on days with extreme heat only, the mortality risks increased by 6.1% and on days with high air pollution, the mortality risks increased by 5%. When extreme heat and high air pollution coincide, deaths are 21% more likely. Thus the mortality risk almost doubles with this synergy effect. Not surprisingly, people over age 75 are more affected than younger ones. The study also found that the risk of death due to cardiovascular problems increased by 29.9%, and the risk of death due to respiratory issues increased by 38% on double-extreme days.

The results stress the urgency of mitigating the health risks related to climate change. Countermeasures may start with risk warnings for the risk groups and behavioural recommendations. Medium-term urban planning must focus on avoiding heat islands, air pollution hotspots and exposure-reduced mobility.

The study has been published in the American Journal of Respiratory and Critical Care Medicine .