The analysis was published by World Weather Attribution, a partnership made up of several university and governmental weather and climate bodies looking at the possible influence of climate change on extreme weather events.
Their findings were based on data collected in Toulouse, France, over the three hottest days of the year so far, June 26-28.
Acting Director of the Environmental Change Institute at Oxford University Friederike Otto, who contributed to the research, told CNN that the findings give the most conservative assessment of the impact of human activity on the heatwave.
“It’s important to stress the ‘at least’. It’s likely to be much higher but this is hard to quantify. Our best estimate is that it’s 100 times more. We give the most conservative estimate,” Otto said.
Using a combination of historical records and climate model statistics, the World Weather Attribution group estimates the early summer heat wave was roughly a 1-in-30-year event, and similar heat waves occurring a century ago would have likely been about 4 degrees Celsius cooler.
Researcher at the Royal Netherlands Meteorological Institute Geert Jan van Oldenborgh, who also took part in the analysis, told CNN Tuesday: “We looked at records of heatwaves in France from 1947 until now. We were surprised at how quickly heatwaves in June in France were getting warmer – they were stronger than they were before”.
France recorded its highest-ever temperature on Friday, with the mercury reaching 45.9 degrees Celsius (114.6 Fahrenheit) in Gallargues-le-Montueux in the Gard department in southern France, according to the French national weather service Météo-France.
This is 1.8 degrees higher than the previous record from 2003.
Meanwhile, Germany, Poland and the Czech Republic each recorded their highest-ever June temperatures last Wednesday.
While temperatures around 100 degrees Fahrenheit may not seem too high, they are way above seasonal averages for the region, and episodes of intensely hot weather are more common during July and August.
The heat wave was also unusual because of its timing. Such episodes of intensely hot weather are more common during July and August.
Worldwide, last month was the hottest June ever recorded, satellite data taken by the EU-ran Copernicus Climate Change Service (C3S) showed Tuesday. The European-average temperature for June was more than 2°C above normal, C3S reported, and the global-average temperature was about 0.1C warmer than the previous June record, in 2016.