More than 10,000 excess deaths were recorded across Europe during the record-breaking heatwave that struck the west of the continent in late June, according to official data.

The vast majority, more than 9,000, were among people aged 65 and above, according to data published by EuroMOMO, the European mortality surveillance network backed by the European Centre for Disease Prevention and Control (ECDC) and the World Health Organisation (WHO).

Extreme heat can be fatal, triggering heatstroke or aggravating existing cardiovascular and respiratory conditions, with older people among the most vulnerable groups.

“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,” he added.

Scientists estimate the heatwave in the final days of June would have been almost impossible without human-induced climate change, which is making such events increasingly frequent and severe.

The data, pooled from national mortality statistics in 27 European countries, covers excess deaths from all causes, not only those directly linked to heat, for the week of June 22 to 28, when the heatwave peaked in France, Spain, the United Kingdom and other parts of Western Europe.

Scientists said no other significant factor, such as a Covid-19 surge or another outbreak, could explain the spike to 10,650 excess deaths in that single week. By comparison, the same countries had recorded around 500 fewer deaths per week than usual, on average, over the previous eight weeks. EuroMOMO cautioned that the figures may be revised as further data is incorporated.

The late-June heatwave caused widespread disruption across Europe, triggering power outages, forcing school closures and breaking historic temperature records in France, Spain and the UK.

EuroMOMO does not publish country-by-country excess mortality figures, but noted that France and Belgium were the only two countries to record “very high excess” mortality in the last week of June. In Belgium, according to the public health institute Sciensano, the heatwave produced the highest excess mortality recorded during any heatwave since data collection began in 2000.

Separately, a study published on Monday by Imperial College London, the UK Met Office and the London School of Hygiene & Tropical Medicine estimated that around 2,700 people died from heat-related causes in England and Wales during the May and June heatwaves. The researchers attributed 42% of those deaths to the additional burden caused by global warming, which intensified the severity of the extreme weather.