June heatwave may have killed around 20,000 people in Europe

The recent heatwave across Europe, one of the most severe on record, may have resulted in the deaths of between 17,000 and 25,000 people, according to early estimates based on historical heat-related fatalities in the area.

Christopher Callahan from Indiana University notes, “These numbers are preliminary, but they underscore the urgent need for investments in rapid adaptation to prevent such impacts in the future.”

Callahan’s projections stem from a study his team released last year, which analyzed temperature and mortality data across Europe. “We examine how high temperatures correlate with excess mortality rates,” explains Callahan. “Using this correlation, we infer the mortality impact of a specific heatwave over Europe.”

According to Callahan, the heatwave from June 22 to June 28, 2026, resulted in approximately 20,390 deaths, including 5,210 in France, 4,543 in Germany, 3,163 in Spain, 2,709 in Germany, and 862 in the UK. These figures exceed the direct death counts reported so far, which is not surprising, as collecting and analyzing death data takes time.

Raquel Nunes from the University of Warwick in the UK points out, “This figure is a modeled estimate rather than a final count. It will take months before the true toll is confirmed, partly because heat rarely appears on a death certificate.”

On June 28, the head of the World Health Organization, Tedros Adhanom Ghebreyesus, reported over 1,300 excess deaths, based largely on a statement from Public Health France, which noted around 1,000 more deaths than expected from June 24 to June 26.

This statement clarified that the figure is based on an incomplete computerized death certificate system, recording 80% of hospital deaths, 45% of deaths in long-term care, and 25% of deaths at home. “Mortality will consequently be higher than these initial figures suggest,” the statement indicated.

Some experts believe Callahan’s estimates might be too high. Dann Mitchell from the University of Bristol in the UK comments, “Twenty-thousand for a single week seems very large. We’d need to examine the modeling details more closely.”

Callahan’s methodology, while sound, is based on data from 2015 to 2019, according to Marcin Walkowiak of Poznań University of Medical Sciences in Poland. People might be less vulnerable now due to ongoing adaptations like increased air conditioning access. Walkowiak’s rough estimate suggests the actual death toll might be around 15,000.

Callahan remains firm on his estimate. “We lack strong evidence that the relationship between temperature and mortality has dramatically changed over time,” he says. “So, it’s not obvious that it differs now from ten years ago.”

He adds, “Our statistical estimates generally yield higher numbers than direct ground reporting because such reporting can miss people who die from heat when the cause isn’t immediately clear.”

Conversely, Walkowiak argues that Callahan’s estimate does not consider that heatwaves are more lethal in early summer than later. “By late summer, the especially vulnerable population has already diminished,” he says.

Mitchell also notes that Callahan’s approach only accounts for immediate deaths, ignoring long-term effects such as increased domestic violence, suicides, and kidney failure. “The health impacts of heat vary significantly over time,” he explains.

Nunes emphasizes the importance of preventing further deaths as the planet continues to warm and heat becomes more intense. “Heat is now the deadliest weather hazard we face, and most of these deaths are preventable,” she states. “We can forecast these events accurately, but we haven’t built the necessary systems across health, housing, social care, and transport to translate forecasts into protection. Adaptation is lagging behind the risk.”