An unusually early and intense heat wave across Europe this year may have caused more than 10,000 additional deaths, according to early data collected from several countries.

Researchers say deaths rose sharply in late June, when many parts of Europe experienced record-breaking temperatures. Scientists measure this using "excess mortality"—the number of deaths above what would normally be expected during a given period.

Experts caution that the actual toll may be even higher because many heat-related deaths are never officially recorded as being caused by extreme heat. For example, a heart attack triggered by high temperatures may simply be listed as a heart attack on a death certificate.

The figures raise fresh concerns as Europe enters the summer season. The continent has experienced several deadly heat waves in recent years, although the 2003 heat wave remains the worst on record, with around 70,000 deaths. Scientists say climate change, driven largely by the burning of fossil fuels, is making heat waves more frequent and more severe.

Sharp rise in deaths during one week

EuroMOMO, a European mortality monitoring network that collects data from two dozen countries, estimated 14,260 excess deaths from all causes during the week ending June 28. More than 12,000 of those deaths were among people aged 65 and above. A total of 84,583 deaths were recorded that week, while excess mortality was much lower in the weeks before and after.

Lasse Vestergaard of Denmark's Statens Serum Institut, which coordinates EuroMOMO, said the spike was most likely linked to the widespread heat wave because there was no other clear explanation for such a large increase in deaths.

He described such a high number of excess deaths in a single week as "highly unusual."

According to EuroMOMO, France, Belgium and Germany recorded the highest rates of excess mortality during the period.

Individual countries have also released their own estimates, although the methods used vary.

Germany

Germany's Robert Koch Institute estimated that 6,830 people died from heat-related causes through early July, including 6,470 people aged 65 or older.

Late June temperatures reached 41.7 degrees Celsius, the highest ever recorded in the country, according to the German Weather Service.

United Kingdom

Britain's Met Office estimated that about 2,700 people died from heat-related causes during heat waves in England and Wales in May and June.

Around 550 of those deaths occurred during a late-May heat wave, while about 2,200 were linked to the late-June heat wave.

The UK also recorded its hottest May and June on record.

France

France's public health agency reported at least 2,000 more deaths during the week of June 22-28 compared with the previous week.

The country experienced its hottest days on record on June 24 and 25, with more than 40% of France recording temperatures above 40 degrees Celsius.

Spain

Spain's Carlos III Health Institute estimated that 937 deaths in June were linked to extreme heat.

According to the national weather agency AEMET, June was the country's second-hottest on record, with average temperatures 3.2 degrees Celsius above normal. Temperatures exceeded 40 degrees Celsius during a five-day heat wave.

Belgium

Belgium's public health institute Sciensano estimated 1,747 excess deaths between June 18 and July 1.

The institute said higher mortality is expected during heat waves, but described the June 2026 event as exceptional because of its intensity and widespread impact.

The country's highest temperature during the heat wave reached 35.5 degrees Celsius on June 26.

Netherlands

Dutch public health authorities estimated 480 more deaths than expected during the June heat wave.

The increase was greatest in the eastern and southern parts of the country, where temperatures were highest.

The Netherlands also recorded its hottest June temperature on record at 36.8 degrees Celsius, breaking a record that had stood since 1947.