Human body ‘close to thermal limits’ due to extreme heatwaves caused by climate change, scientist says

Extreme global temperatures are pushing the human body “close to thermal limits”, according to a climate scientist.

Record-breaking heat has swept through Europe this week with temperatures topping 40C in a number of countries.

However, in places such as South Asia and the Persian Gulf, people are already enduring temperatures reaching up to 54C.

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Despite all the body's thermal efficiencies, these areas could soon be uninhabitable, according to Loughborough University climate scientist Dr Tom Matthews in The Conversation.

When air temperature exceeds 35C, the body relies on sweating to keep core temperatures at a safe level. However, when the “wet bulb” temperature – which reflects the ability of moisture to evaporate – reaches 35C, this system no longer works.

“The wet bulb temperature includes the cooling effect of water evaporating from the thermometer, and so is normally much lower than the normal (“dry bulb”) temperature reported in weather forecasts,” Dr Matthews wrote.

Shape Created with Sketch. UK heatwave rolls in as temperatures soar Show all 44 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. UK heatwave rolls in as temperatures soar 1/44 Bournemouth Hundreds of people at the beach in Bournemouth, as the UK could encounter the hottest July day on record PA 2/44 Manchester Hamza and Haris splash in the water feature beside the National Football Museum PA 3/44 Derbyshire People play in the water at Hathersage Outdoor Swimming Pool PA 4/44 Whitley Bay Sunrise at St Mary's Lighthouse PA 5/44 Margate Families fish for crabs from a sea wall Getty Images 6/44 Surrey People leap from a bridge at Taggs Island, near Hampton Court PA 7/44 London Ireland's players in a drinks break during the second day of the test match against England at Lord's AP 8/44 London People sunbathe in Hyde Park PA 9/44 Manchester People splash in the fountains in Piccadilly Gardens PA 10/44 Margate Families make their way to the beach Getty Images 11/44 Cambridge People use umbrellas to shield from the sun as they punt along on the River Cam PA 12/44 Brighton People enjoy the hot weather on the beach PA 13/44 London England's Jack Leach cools down with a towel in a drinks break AP 14/44 Margate Getty Images 15/44 Northumberland Kadie Lane, 10, cools off in the fountain at Alnwick Gardens. The UK is bracing itself for what could be its hottest ever day after lightning storms triggered fires and rail disruption PA 16/44 Hampshire Lightening striking as a thunder storm passes over Basingstoke lanttans/PA 17/44 Northumberland Visitors sit in deckchairs in the sun at Alnwick Gardens PA 18/44 West Yorkshire Sisters, Nyam May (left) and Ciara May (right), jump into the water at Ilkley outdoor pool and lido PA 19/44 An African white lion sunbathes at West Midlands Safari Park PA 20/44 Liverpool Lightening strikes as a thunder storm passes over houses in Lee Park PA 21/44 Northumberland Children sit in the sun by 'The Friendly Giant', a pond sculpture situated in Alnwick Gardens PA 22/44 Northumberland Reuben Humphreys, 4 , cools off in the fountain at Alnwick Gardens PA 23/44 West Yorkshire PA 24/44 Pembrokeshire Holidaymakers shelter under umbrellas on the South Beach,Tenby Reuters 25/44 Lincolnshire A thunder storm passes over Holbeach St Marks wiker_1971/PA 26/44 Pembrokeshire Swimmers have fun in the sea on a giant inflatable Flamingo, South Beach Reuters 27/44 Folkestone Sunbathers relax PA 28/44 West Yorkshire PA 29/44 Kent Broadstairs beach PA 30/44 Pembrokeshire South Beach,Tenby Reuters 31/44 Dog owners warned about heatstroke American Bulldog Finlay, receiving urgent cooling treatment at PDSA's Pet Hospital, after was left fighting for his life after his body temperature soared to a life-threatening 42.2C (108F) during recent hot weather PA 32/44 Folkestone A couple, seen through heat haze PA 33/44 Ilkley Freddie Ward jumps into the water at Ilkley outdoor pool and lido in West Yorkshire as the UK is expected to edge towards its hottest ever July day PA 34/44 Pembrokeshire North Beach,Tenby REUTERS 35/44 Pembrokeshire REUTERS 36/44 Canterbury People enjoy punting through Westgate Gardens as temperatures rise across the UK this week PA 37/44 Pembrokeshire REUTERS 38/44 Ilkley People play in the water at Ilkley outdoor pool and lido PA 39/44 Canterbury Isla Stanton enjoys the sunshine in Westgate Gardens PA 40/44 Pembrokeshire REUTERS 41/44 Oxford PA 42/44 Pembrokeshire REUTERS 43/44 Warwickshire People enjoy a trip in a boat along the river in Stratford Upon Avon PA 44/44 Stratford Upon Avon PA 1/44 Bournemouth Hundreds of people at the beach in Bournemouth, as the UK could encounter the hottest July day on record PA 2/44 Manchester Hamza and Haris splash in the water feature beside the National Football Museum PA 3/44 Derbyshire People play in the water at Hathersage Outdoor Swimming Pool PA 4/44 Whitley Bay Sunrise at St Mary's Lighthouse PA 5/44 Margate Families fish for crabs from a sea wall Getty Images 6/44 Surrey People leap from a bridge at Taggs Island, near Hampton Court PA 7/44 London Ireland's players in a drinks break during the second day of the test match against England at Lord's AP 8/44 London People sunbathe in Hyde Park PA 9/44 Manchester People splash in the fountains in Piccadilly Gardens PA 10/44 Margate Families make their way to the beach Getty Images 11/44 Cambridge People use umbrellas to shield from the sun as they punt along on the River Cam PA 12/44 Brighton People enjoy the hot weather on the beach PA 13/44 London England's Jack Leach cools down with a towel in a drinks break AP 14/44 Margate Getty Images 15/44 Northumberland Kadie Lane, 10, cools off in the fountain at Alnwick Gardens. The UK is bracing itself for what could be its hottest ever day after lightning storms triggered fires and rail disruption PA 16/44 Hampshire Lightening striking as a thunder storm passes over Basingstoke lanttans/PA 17/44 Northumberland Visitors sit in deckchairs in the sun at Alnwick Gardens PA 18/44 West Yorkshire Sisters, Nyam May (left) and Ciara May (right), jump into the water at Ilkley outdoor pool and lido PA 19/44 An African white lion sunbathes at West Midlands Safari Park PA 20/44 Liverpool Lightening strikes as a thunder storm passes over houses in Lee Park PA 21/44 Northumberland Children sit in the sun by 'The Friendly Giant', a pond sculpture situated in Alnwick Gardens PA 22/44 Northumberland Reuben Humphreys, 4 , cools off in the fountain at Alnwick Gardens PA 23/44 West Yorkshire PA 24/44 Pembrokeshire Holidaymakers shelter under umbrellas on the South Beach,Tenby Reuters 25/44 Lincolnshire A thunder storm passes over Holbeach St Marks wiker_1971/PA 26/44 Pembrokeshire Swimmers have fun in the sea on a giant inflatable Flamingo, South Beach Reuters 27/44 Folkestone Sunbathers relax PA 28/44 West Yorkshire PA 29/44 Kent Broadstairs beach PA 30/44 Pembrokeshire South Beach,Tenby Reuters 31/44 Dog owners warned about heatstroke American Bulldog Finlay, receiving urgent cooling treatment at PDSA's Pet Hospital, after was left fighting for his life after his body temperature soared to a life-threatening 42.2C (108F) during recent hot weather PA 32/44 Folkestone A couple, seen through heat haze PA 33/44 Ilkley Freddie Ward jumps into the water at Ilkley outdoor pool and lido in West Yorkshire as the UK is expected to edge towards its hottest ever July day PA 34/44 Pembrokeshire North Beach,Tenby REUTERS 35/44 Pembrokeshire REUTERS 36/44 Canterbury People enjoy punting through Westgate Gardens as temperatures rise across the UK this week PA 37/44 Pembrokeshire REUTERS 38/44 Ilkley People play in the water at Ilkley outdoor pool and lido PA 39/44 Canterbury Isla Stanton enjoys the sunshine in Westgate Gardens PA 40/44 Pembrokeshire REUTERS 41/44 Oxford PA 42/44 Pembrokeshire REUTERS 43/44 Warwickshire People enjoy a trip in a boat along the river in Stratford Upon Avon PA 44/44 Stratford Upon Avon PA

“Once this wet bulb temperature threshold is crossed, the air is so full of water vapour that sweat no longer evaporates,” he said.

This means the human body cannot cool itself enough to survive more than a few hours.

“Without the means to dissipate heat, our core temperature rises, irrespective of how much water we drink, how much shade we seek, or how much rest we take,” he explained.

Some areas – which are among the most densely populated on Earth – could pass this threshold by the end of the century, according to Dr Matthews.

There is already evidence wet bulb temperatures are occurring in Southwest Asia.

With climate change starting to profoundly alter weather systems, rising temperatures could soon make parts of the world uninhabitable.

If electricity can be maintained, living in chronically heat-stressed conditions may be possible but a power outage could be catastrophic.

In a recent paper published in Nature Climate Change, Dr Matthews and his team looked at the probability of a “grey swan” event in the case of extreme heat coinciding with massive blackouts.

Mega blackouts sometimes follow powerful tropical cyclones. Researchers found that dangerously hot temperatures during a period with no electricity could have catastrophic consequences.

“We looked at tropical cyclones, which have already caused the biggest blackouts on Earth, with the months-long power failure in Puerto Rico after Hurricane Maria among the most serious,” Dr Matthews wrote.

“We found that as the climate warms, it becomes ever more likely that these powerful cyclones would be followed by dangerous heat, and that such compound hazards would be expected every year if global warming reaches 4C.

“During the emergency response to a tropical cyclone, keeping people cool would have to be as much a priority as providing clean drinking water.”

Heat-stressed countries are likely to see the largest absolute increases in humid-heat and they are often the least well-prepared to deal with the hazard. This could drive mass migration, which would make heat a worldwide issue – even for countries that are not experiencing scorching temperatures.

Dr Matthews wrote: “The challenges ahead are stark. Adaptation has its limits. We must therefore maintain our global perspective on heat and pursue a global response, slashing greenhouse gas emissions to keep to the Paris warming limits.

“In this way, we have the greatest chance of averting deadly heat – home and abroad.”