The figures analyzed by POLITICO include around 2,000 excess deaths in France, 1,740 in Belgium, 6,800 in Germany and 480 in the Netherlands, as well as 810 specifically heat-related fatalities in Spain and an estimated 2,200 heat deaths in the United Kingdom.

A separate dataset published Monday by EuroMOMO, a mortality monitoring service supported by the European Centre for Disease Prevention and Control and the World Health Organization, showed that its 27 member countries reported 10,650 excess deaths between June 22 and June 28. Those figures could still change as more data trickles in.

Excess deaths represent the increase in mortality compared to average levels. Although the figures capture fatalities from all causes, this measure is used to swiftly assess the toll of heat waves; getting a precise count of heat-related deaths is painstaking work, as high temperatures kill not only through heat stroke, but also by exacerbating existing conditions.

“It’s very plausible that these figures are primarily related to heat,” said Lasse Skafte Vestergaard, chief physician at Denmark’s Statens Serum Institut, which hosts EuroMOMO, of the service’s findings.

“There are no other obvious explanations or public health threats currently in Europe that could explain this,” he told POLITICO. “And the figures are really quite unusual in terms of the magnitude.”

EuroMOMO’s figures do not include a country-level breakdown, though the service noted that excess deaths were particularly high in France and Belgium in late June.