Compared to June weather stretching back more than a century, the three-day peak from June 26th to June 28th was 4C warmer than an equally rare heatwave would have been in 1900, the World Weather Attribution team told journalists in a briefing.
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Global readings taken by the EU-run Copernicus Climate Change Service (C3S) showed European temperatures were around 2C hotter than normal, and globally Earth was 0.1C 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 10C higher than normal across France, Germany, northern Spain and Italy.
The Copernicus team said it was difficult to attribute the record-breaking month “directly” to climate change, but a separate analysis from an international team of scientists said global warming had made the heatwave at least five times more likely.
“Our data show that the temperatures over the southwestern region of Europe during the last week of June were unusually high,” said 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.”
The role of global warming is probably much greater, said Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford.
“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 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.
By Thursday last week almost the whole of France was covered by weather warnings over extreme heat while four départements in the south of the country were placed a red weather alert – the first time this has ever been issued for heat.
Dozens of town across the country recorded their highest ever temperature and in areas including Paris and the Dordogne authorities enacted their emergency heat plans.
Across France, Italy, Spain and some central European nations, dozens of deaths attributed to the week-long heatwave.
The final death toll is likely to be far higher, but will only show up months from now in statistical records as “excess deaths”.
A 2003 heatwave in France claimed at least 15,000 lives, according to government figures.