The vast majority — more than 9,000 — were among people aged 65 and above, according to data published by EuroMOMO, a network backed by the European Centre for Disease Prevention and Control and the World Health Organization.
Extreme heat can kill by causing heat stroke, or aggravating cardiovascular and respiratory diseases, with older people among the most vulnerable.
"To have this kind of excess at this time of year is unusual. It’s really high," Lasse Vestergaard, Chief Physician at Denmark's Statens Serum Institut, which hosts EuroMOMO, told Reuters.
"It is difficult to explain this high excess mortality by anything but the extreme heat," Vestergaard added.
Scientists have said the late-June heatwave would have been "virtually impossible" without human-caused climate change, which is making heatwaves more frequent and intense.
The data, pooled from national mortality statistics in 27 European countries, included excess deaths from all causes, not just heat-related ones, during the week of June 22 to 28, when the heatwave peaked in France, Spain, Britain and other countries.
But scientists said there were no other known major factors, such as COVID-19 outbreaks, that would have contributed to the spike to 10,650 excess deaths in that week.
