The extremes, which can be fatal to healthy people in six hours, could affect hundreds of millions unused to such conditions. As a result, heat deaths could rise quickly without urgent and serious efforts to prepare populations, the researchers said.
The human body cools itself by producing sweat, which evaporates and takes heat away. But when humidity is high, evaporation is reduced.
The new study used a limit based on experiments on people showing that when combined heat and humidity, as measured by so-called wet bulb temperature, passes 31.5C, the body is no longer able to cool itself.
The researchers called this threshold "non-compensable heat stress", as sweating cannot compensate for the extreme conditions. Without cooling aids, such as cold water, fans or air conditioning, death is likely within hours.
The research analysed data from thousands of global weather stations to show 4% had already experienced at least one six-hour period of this extreme heat stress since 1970, with the frequency of such events doubling by 2020. However, these have been confined to date to hot places including the Gulf in the Middle East, Red Sea and north Indian plain, where people expect extreme heat.
The new analysis, which also used climate models, shows that extreme heat stress will spread rapidly to other regions with global heating of 2C. The climate crisis has already raised global temperature by about 1.2C. At 2C, more than 25% of the weather stations would suffer the extreme heat stress once a decade on average.
Denne historien er fra September 09, 2023-utgaven av The Guardian.
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Denne historien er fra September 09, 2023-utgaven av The Guardian.
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Bajrami and McCausland to the fore as Rangers seal impressive victory
Rangers made a storming start to their Europa League campaign with a 2-0 win over Malmö in Sweden that should have been even more emphatic. Nedim Bajrami scored his first goal for the Ibrox club in less than a minute and Philippe Clement's side passed up several chances to add a second before the interval.
Thames credit ratings cut to lower levels of junk as default fears grow
Thames Water's debt rating has been slashed to the lower levels of junk by two major credit rating agencies, piling further pressure on the UK's biggest water company, which is rapidly running through cash and fighting to stave off renationalisation.
Austria Fears rise over prospect of far-right election win
After topping the Austrian poll in June's EU elections, the far-right Freedom party (FPÖ) seized the moment, calling for the appointment of an EU \"remigration\" commissioner to be tasked with the forced return of migrants and citizens with a migration background to their countries of origin.
'Cold and direct' Fayed's security chief accused of facilitating abuse
It was May 1991 and Mohamed AI Fayed was in a foul mood. \"I told you, no sex with anybody else, no relationship with anybody else,\" he ranted.
Allegations made over tycoon's years at Fulham FC
Sexual assault allegations have been made relating to Mohamed AI Fayed's 16 years of ownership of Fulham Football Club, lawyers representing his accusers have said.
'No sane people are going' Leadership race casts pall over Tory conference
On Tuesday, four candidates will make their pitches to lead the Conservative party from a conference stage in Birmingham. Their immediate challenge after the Tory rout this summer will be to reinvigorate demoralised MPs and members.
Pandemic as deadly as Covid-19 'a certainty', says Whitty
Another pandemic as big as the Covid crisis that killed 7 million people worldwide was \"a certainty\", Prof Sir Chris Whitty warned yesterday, as he said the UK's lack of intensive care capacity for the sickest patients was a \"political choice\".
Naomi Campbell banned as charity trustee for five years
Naomi Campbell has been banned from being a charity trustee after a watchdog investigation uncovered widespread evidence of financial misconduct at the poverty relief charity she founded.
Family haunted by last moments of teenager killed by 12-year-olds
The family of a man killed by the UK's youngest knife murderers have said they are haunted by thoughts of his last moments and \"how scared he must have been\".
London rail stations to be shut for up to eight days over festive period
Some of London's main railway stations will be closed and train services diverted at Christmas time, Network Rail has said.