The United Kingdom has experienced two record-shattering heatwaves in the space of two months, the first time such a pair of extreme events has occurred before August since 1911. A red extreme heat warning, only the second of its kind since the system was introduced in 2021, was issued for the June heatwave, and forecasters say more extreme heat is likely before the summer is over.
The May heatwave
Between May 22 and 31, a heat dome settled over the UK, breaking temperature records across multiple days. On May 25, Kew Gardens in London recorded 34.8 degrees Celsius (94.6 degrees Fahrenheit), breaking the previous UK May record of 32.8 degrees Celsius set in 1922 and equaled in 1944. The next day, that new record was shattered when Kew reached 35.1 degrees Celsius (95.2 degrees Fahrenheit).
The May heatwave also set national records for Wales (32.9 degrees Celsius at Bute Park, Cardiff) and Jersey (34.2 degrees Celsius), as well as the highest minimum temperature ever recorded in the UK for May, 21.3 degrees Celsius at Kenley Airfield in Surrey.
At least 19 people died during the May heatwave, all in water-related incidents.
The June heatwave
Three weeks later, another heatwave began building. Between June 19 and 28, temperatures climbed higher still. On June 24, the UK recorded its hottest June day on record, 36.1 degrees Celsius in Gosport, Hampshire. That record lasted one day: June 25 brought 36.7 degrees Celsius at Merryfield in Somerset. And on June 26, Santon Downham in Suffolk reached 37.3 degrees Celsius (99.1 degrees Fahrenheit), the highest June temperature ever recorded in the UK, breaking a record that had stood since 1957.
The previous June record of 35.6 degrees Celsius was set in 1957 and equaled in 1976.
A red extreme heat warning was issued on June 22, covering parts of the Midlands, south-east Wales, and southern England. The warning was in force from June 24 to June 25, with an amber warning extending the coverage. The Met Office’s Deputy Chief Forecaster, Mark Sidaway, said the warning was “reserved for the most severe events,” with “health impacts likely for many, even beyond those who are normally more vulnerable.” It marked the first time red extreme heat warnings had been issued on three consecutive days.
The Guardian reported that two-thirds of Europe’s population was affected by the broader June heatwave, which brought record-breaking temperatures to France, Italy, and Spain as well. The Channel Islands recorded their hottest day ever, 39.3 degrees Celsius (102.7 degrees Fahrenheit) in Jersey on June 25. Guernsey also set an all-time record of 36.4 degrees Celsius.
The odds are changing
The Met Office states that a hotter summer is now twice as likely as it was during the 1991-2020 baseline period. In practical terms, while the chance of a summer being “hotter than normal” was roughly 33% during the reference period, by definition, one-third of summers fall in the upper tercile, it has now shifted to approximately 66%.
The number of UK days above 28 degrees Celsius has more than doubled compared to the 1961-1990 average, and days above 30 degrees Celsius have more than tripled. The UK’s average highest maximum temperature for the 2015-2024 period was 35.9 degrees Celsius, 2.3 degrees higher than the 1991-2020 average and 4.5 degrees higher than the 1961-1990 average.
World Weather Attribution issued a rapid analysis on June 26 concluding that the June European heatwave would have been “virtually impossible” in the climate of 1976, and is now tens to hundreds of times more likely than during the 2003 baseline. Daytime temperatures were approximately 3.5 degrees Celsius hotter than a comparable event would have been in 1976.
“Human induced climate change has made events like this more likely and more intense,” said Professor Stephen Belcher, the Met Office’s Chief Scientist. “To see temperatures like this in the UK in June is sobering.”
What comes next
The Met Office’s three-month outlook expects July and August to bring above-average temperatures and “significant bursts” of heat. By 2050, if current warming trends continue, mid-40s degrees Celsius become a serious possibility for the UK, according to the BBC’s Weather team.
Dr. Akshay Deoras of the University of Reading is quoted: ‘Unless we drastically cut down the emission of greenhouse gases, global warming is not going to stop.’
The numbers tell a stark story. The UK has already broken 19 temperature records this summer. Four of the five warmest summers for England have occurred since 2003. And a hotter summer is now, as the Met Office puts it, “twice as likely than the period of 1991-2020, which is consistent with our warming climate.”
Source: BBC Weather, based on reporting by Simon King and Sarah Keith-Lucas, with additional data from the Met Office and World Weather Attribution.