PARIS • The record-breaking heatwave that gripped France last week was made at least five times more likely by climate change, scientists have said as other data showed that last month was the hottest June worldwide in history.
Compared with weather stretching back more than a century, the three-day temperature peak from June 26 to June 28 in France was 4 deg C warmer than an equally rare June heatwave would have been in 1900, the World Weather Attribution (WWA) team told journalists in a briefing on Tuesday.
Global readings, meanwhile, taken by the EU's Copernicus Climate Change Service (C3S) showed European temperatures were around 2 deg C hotter than normal.
Globally, Earth was 0.1 deg C hotter than the previous June record.
The heatwave last week smashed national records for the hottest single day as scorching weather spread across Europe from the Sahara.
It was so intense that temperatures were as much as 10 deg C higher than normal across France, Germany, northern Spain and Italy, C3S said.
Global warming probably amplified France's devastating hot spell by far more than five times, said Dr Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford, who contributed to the research published by WWA.
The heatwave last week smashed national records for the hottest single day as scorching weather spread across Europe from the Sahara. It was so intense that temperatures were as much as 10 deg C higher than normal across France, Germany, northern Spain and Italy.
"Models are very good at representing large-scale seasonal changes in temperatures," she explained. "On localised scales, climate models tend to underestimate the increase in temperature."
The findings, presented as a report and to be published in a peer-reviewed journal, focused on metropolitan France and the southern city of Toulouse, where climate statisticians were coincidentally meeting during the heatwave.
Based purely on temperature records, extreme scorchers like the one last week are now 100 times more likely than in 1900, said Dr Geert Jan van Oldenborgh, a senior researcher at the Royal Netherlands Meteorological Institute and co-author of the new report.
"But we are unable to say that this is just because of climate change," he said.
Air pollution, the "urban heat island" effect, soil moisture, cloud cover and a host of other factors can also affect the intensity of heatwaves. And models designed to work on a different scale are consistently "biased" such that they underestimate temperature peaks.
Dr Otto told the Agence France-Presse: "Given what we know about the observation data and the biases of the models, this is our most conservative estimate as to the contribution of climate change.
"The likely role is much higher."
Merging satellite data with historic temperature charts, the Copernicus team found that last month was 3 deg C hotter across Europe than the baseline average between 1850-1900.
"Our data show that the temperatures over the south-western region of Europe during the last week of June were unusually high," said Dr Jean-Noel Thepaut, head of C3S.
"Although this was exceptional, we are likely to see more of these events in the future due to climate change."