When large parts of Western Europe groaned under a heat wave in mid-July, temperatures in England also rose to unprecedented levels. Three stations recorded more than 40 degrees Celsius: Gringely on the Hill in Nottinghamshire, St James’s Park in central London and Coningsby in Lincolnshire, which peaked at 40.3 degrees on July 19. Nearly four dozen stations were above the previous record set in 2019, with many others showing three or even four degrees more than ever recorded in the series.
“Such temperatures would have been extremely unlikely without climate change,” says Friedericke Otto from the University of Oxford. “At most of the individual measuring stations, they would even have been impossible.” The German physicist and a team of 20 other scientists from nine countries have just completed a so-called Attribution or attribution study on the extreme event presented. It should answer the frequently asked question: Was it due to climate change?
The answer is obvious in this case, but the loosely composed research association World Weather Attribution calculates the numbers. Friedericke Otto played a leading role in developing the method for such studies. To do this, the working group compares the current weather development with historical measurements and with climate simulations in the supercomputer, in which the greenhouse gases emitted by mankind are switched on or off.
Would it have been two or rather four degrees cooler without warming?
The results of the two methods are somewhat contradictory in this case, which complicates things. “If you look at the measurements, this heat wave was four degrees warmer than it would have been without it because of climate change,” says Otto. “However, the climate models only show a difference of two degrees because of climate change.” All that allows the research team to say is that global warming has made the heat wave “at least tenfold” more likely. Previous analysis of other extreme events has provided factors of 30, for example the heatwave in India in March. “The ‘at least’ is particularly important here, because it was certainly more than ten times as likely.”
According to Otto, the reason for the discrepancy between the two analysis methods lies in a well-known weakness of the global climate models: They underestimated the trend in regional heat waves in Western Europe, although they depict average temperatures or extreme rains well. “For us, that means we could get higher temperatures even faster than expected,” says the physicist.
The analysis confirms calculations made by the British weather service Met Office released in 2020. According to the study at the time, temperatures of 40 degrees Celsius or more would have occurred in Great Britain every 1,000 to 10,000 years at best if the atmosphere was still in its pre-industrial composition. But in today’s climate, which has already warmed by 1.2 degrees, the extreme heat is likely to repeat itself every 100 to 300 years. And if climate change continues unabated, such a summer would be expected every three to four years after 2100.
“It is very sobering that something like this should happen so soon after this study,” said Fraser Lott of the Met Office. “But our new study confirms the results of the old one.” Average temperatures such as those reached during the heat wave on July 18 and 19 and the night in between could be repeated every hundred years in today’s climate, according to Friedericke Otto’s team. The peak values of individual stations, on the other hand, remain less likely and have statistical repetition times of around 1000 years at the respective locations. “But we don’t live in a stable climate that has warmed up by 1.2 degrees, it’s changing dynamically,” says Otto. The danger of temperature extremes is therefore constantly increasing. “The role of climate change is big in any heat wave these days.”
The Met Office, like other weather services, had seen the heatwave coming many days in advance. The orange warning level was in effect for six days before the authority declared the red warning level for heat danger for the first time in its history. After Estimate by Antonio Gasparrini by the London School of Hygiene, the heatwave could have resulted in 840 premature deaths extrapolating from historical data. However, since there were many warnings and the British authorities have taken protective measures, he wrote on Twitter, the count should be lower afterwards.