18.7% of heat-related deaths in Spain are due to pollution

What happened?

A team of researchers from the Institute of Health Carlos III (ISCIII) and the Center for Energy, Environmental and Technological Research (CIEMAT) has published a preliminary study that statistically separates the effects of temperature and pollution on mortality in Spain. The main conclusion is that 18.7% of deaths historically attributed to heat are actually caused by air pollutants such as NO₂, tropospheric ozone and PM2.5 particles, which accumulate during heat waves due to atmospheric stagnation.

The study, still pending formal review, uses mortality data from the MoMo system of the Ministry of Health and covers all Spanish provinces. The results were advanced by journalist Javier Jiménez in Xataka.

Why is it important?

For decades, public health policies have focused on mitigating the direct impact of heat, but this finding reveals that a significant portion of mortality is preventable by reducing pollution. In August 2003, for example, 6,600 people died in the first fortnight and almost 13,000 by the end of the month, but only 141 were from direct heat stroke. The rest died from worsening cardiovascular, respiratory and kidney diseases. Now we know that almost a fifth of those deaths were not due to heat, but to poor air quality.

This implies that climate change adaptation strategies must integrate pollution control measures, especially during episodes of high temperatures. It also underscores the need to review mortality attribution models and update health alerts.

Consequences for public health

The study suggests that reducing air pollution could decrease heat-related mortality more effectively than purely thermal measures. Authorities should consider implementing traffic restrictions, limitations on industrial emissions, and awareness campaigns on air quality during heat waves. Likewise, early warning systems should include pollution indices to activate protection protocols.

In 2025, the MoMo system recorded 3,832 deaths attributable to heat in Spain, 87.6% more than in 2024, and May 2026 already marks a historical record of heat-related mortality for that month. If 18.7% of those deaths are explained by pollution, we are talking about hundreds of lives that could be saved with cleaner air.

What should readers know?

That extreme heat and air pollution are two sides of the same meteorological coin. During a heat wave, air stagnation prevents the dispersion of pollutants, multiplying the health risk. Therefore, protecting yourself from heat is not enough: you also need to avoid exposure to pollution, using FFP2 masks, reducing outdoor activity during hours of high ozone concentration, and keeping windows closed during traffic peaks.

Furthermore, it is important that citizens demand integrated climate and air quality policies from their governments, and that the media report on both factors when warning of heat waves.

Historical context and comparison

This study adds to previous research that already pointed to the interaction between heat and pollution, but it is the first to quantify the percentage of deaths attributable to pollution in Spain. Globally, the World Health Organization estimates that 7 million premature deaths per year are due to air pollution, and climate change will worsen this problem. In Europe, the European Environment Agency has warned that heat waves will become more frequent and intense, making it urgent to act on emissions.

The finding also has implications for the attribution of responsibilities: while heat is a natural phenomenon amplified by climate change, pollution has specific human sources (traffic, industry, heating) that can be regulated.

Reactions and next steps

The authors of the study, who receive funding from FECYT and public bodies, hope that their work will help redesign public health policies. The MoMo system is already integrating pollution variables to improve its predictions. The full results are expected to be published in a peer-reviewed scientific journal in the coming months.