A new study shows that human-caused climate change made Europe’s recent heatwave up to 4°C hotter in many cities. The extreme heat likely led to higher deaths, especially among vulnerable groups like the elderly.

Humanity’s burning of fossil fuels directly led to the deaths of at least 1,500 people in a European heatwave last week, a landmark study said.

The study targeted the 10 days, ending July 2, during which large parts of Western Europe were hit by extreme heat, with temperatures breaching 40 degrees Celsius in Spain and wildfires breaking out in France.