LONDON, July 9 — Human-induced climate change intensified the recent European heatwave by as much as 4°C in many cities, significantly raising temperatures into life-threatening levels for vulnerable populations, according to a new scientific study published Wednesday.

The rapid assessment, conducted by over a dozen researchers from five European institutions, concluded that the extreme heat likely caused significantly more deaths than would have occurred without global warming.

The study analyzed temperature data across 12 major European cities between June 23 and July 2, when an early-summer heatwave sent temperatures soaring above 40°C in several regions, triggering public health alerts.

According to Copernicus, the EU’s climate monitoring agency, western Europe experienced its hottest June on record. In many places, schools were closed and tourist sites shuttered as authorities tried to manage the extreme heat.

To determine the impact of climate change, researchers used historical climate data to simulate how intense the heatwave would have been in a pre-industrial climate without human influence. Their findings showed that, in 11 out of the 12 cities studied, temperatures would have been 2 to 4 degrees cooler without the warming effect of greenhouse gas emissions.

This additional heat pushed health risks into dangerous territory, particularly in urban centers like Paris, London, Rome, and Madrid — cities with a combined population exceeding 30 million.

“What that does is bring certain groups of people into more dangerous territory,” said lead author Ben Clarke from Imperial College London. “For some people, it's still just warm weather. But for many others, it’s deadly.”