Chances of extremely high temperatures in the UK could increase significantly by the end of the century, new research has found.
Met Office Hadley Centre researchers have investigated whether exceeding 40C is within the possibilities of Britain's climate.
It comes after the highest temperature ever recorded in the UK hit 38.7C in Cambridge in July last year.
Their study, published in the journal Nature Communications, suggests that the current chance of seeing days above 40C is extremely low.
However, by 2100 the UK could see 40C days every 3-4 years under a high emissions scenario, their research showed.
Co-author of the research and head of the Met Office National Climate Information Centre Dr Mark McCarthy, warned that "urgent action" to reduce emissions now could help stop extreme high temperatures hitting the UK in the future.
If emissions are reduced in line with the Paris climate agreement, the future probabilities are expected to be considerably lower, the scientists said.
The return time for the 40C threshold is reduced to around 15 years by 2100 under a medium-emissions scenario, they added.
Lead author Dr Nikolaos Christidis, said “We found that the likelihood of extremely hot days in the UK has been increasing and will continue to do so during the course of the century, with the most extreme temperatures expected to be observed in the south east of England.
New research published today shows the chances of 40°C days in the UK are increasing rapidly due to #GlobalWarming
With high greenhouse gas emissions 40°C could be recorded as frequently as every 3-4 years by 2100
Read more in our news release here: https://t.co/JeLXlw6V5h pic.twitter.com/RXaT1gseZK
— Met Office (@metoffice)
“Climate change has already influenced the likelihood of temperature extremes in the UK.
"The chances of seeing 40C days in the UK could be as much as 10 times more likely in the current climate than under a natural climate unaffected by human influence.
"The likelihood of exceeding 40C anywhere in the UK in a given year has also been rapidly increasing, and, without curbing of greenhouse gas emissions, such extremes could be taking place every few years in the climate of 2100.”
The study took advantage of the new high-resolution HadUK-Grid dataset to make more precise local predictions of future hot spells.
Summers with daily maximum temperatures exceeding 35C currently happen once every five years on average, but could happen almost every other year by 2100 under a high emissions scenario.
Dr McCarthy also said: “This research shows human-caused climate change has set us on a course to see temperature extremes in the UK that would be highly unlikely under a ‘natural’ climate, although urgent action to reduce emissions now can significantly reduce the occurrence of extreme high temperatures in the UK in the future.
“Analysis shows that in some parts of the south east between 1960 and 2019 the hottest days of the year have already increased by 1C each decade, showing the UK is already on a warming trend when it comes to heat extremes.”
The chances of 40C days are focused around the south east of the UK, with temperatures above 35C becoming increasingly common in this region too.
However, the study also found that by 2100 many areas in the north for which 30C is currently extremely rare or unlikely may exceed 30C at least once per decade.
The findings from this research are important to help plan for future extremes, informing effective adaptation and mitigation strategies to limit impacts on UK society.
The outcomes are consistent with the headline findings from the UKCP18 climate projections, which show a greater chance of hotter, drier summers in the UK and that under certain emissions pathways exceedances of 40C in the UK may become common by the end of the century.