Some 2,300 people are likely to have died of heat-related causes across 12 European cities during a severe heatwave that ended last week, with two-thirds of the deaths directly linked to climate change, according to a new study, Al Jazeera reported.

The analysis, published on Wednesday, focused on the 10-day period between June 23 and July 2, during which large parts of Western Europe were hit by extreme heat, with temperatures breaching 40 degrees Celsius (104 Fahrenheit) in Spain and wildfires breaking out in France.

It covered 12 cities with a combined population of more than 30 million, including Barcelona, Madrid, London and Milan, where the study said climate change had increased heatwave temperatures by up to 4C (39.2F).

Of the 2,300 people estimated to have died during this period, 1,500 deaths were linked to climate change, which made the heatwave more severe, said the study conducted by more than a dozen researchers from five European institutions in the United Kingdom, Netherlands, Denmark and Switzerland.

“Climate change has made it significantly hotter than it would have been, which in turn makes it a lot more dangerous,” said Ben Clarke, a researcher at Imperial College London, one of the institutions involved in the study.