Deadly humid heatwaves spread rapidly as climate warms – study | Climate crisis

Life-threatening periods of high heat and humidity will spread rapidly around the world with only a small increase in global temperatures, a study finds, potentially causing a sharp acceleration in the number of deaths from the climate crisis.

These extremes, which can be fatal to healthy people within six hours, can affect hundreds of millions of people unaccustomed to such conditions. As a result, heat-related deaths could rise rapidly unless serious efforts are made to prepare the population urgently, the researcher said.

Normally, the human body cools itself by producing sweat, which evaporates and removes heat. But when humidity is high, evaporation decreases. The study used a limit based on experiments on people that showed that when the combined heat and humidity, as measured by the so-called wet-bulb temperature, exceeded 31.5 degrees Celsius, the body was no longer able to cool itself.

The researchers dubbed this threshold “irreversible heat stress”, where sweating cannot compensate for the extreme conditions. Without refrigeration, such as cold water, fans or air conditioners, death is likely to occur within hours.

The research analyzed data from thousands of weather stations worldwide to show that 4% had already experienced at least six hours of such extreme heat stress since 1970, with the frequency of such events doubling by 2020. However, it has been reported that These events have so far been confined to hot places, including the Gulf region in the Middle East, the Red Sea and the northern Indian plain, where people expect extreme heat.

The analysis, which also used climate models, shows that extreme heat stress will quickly spread to other regions where the global temperature is just 2 degrees Celsius. The climate crisis has already raised global temperatures by about 1.2 degrees Celsius. At 2°C, more than 25% of weather stations will experience severe heat stress once every decade on average.

East Coast regions, the Midwest of the United States, and Central Europe, including Germany, are among the places that may see the arrival of unprecedented heat stress conditions. And in already hot places like Arizona, Texas and parts of California, periods of extreme heat stress will become annual events at 2°C.

The lack of mass deaths in places already exposed to extreme heat stress showed that cooling measures could be effective in preventing deaths, the researcher said. But they said the rapid arrival of these conditions in places where people historically did not need cool buildings or air conditioning, and were therefore unprepared, is worrying.

“Of all the different aspects of climate change, heat is the one that personally worries me the most, and these results have made me even more concerned,” said Carter Powis, from the University of Oxford, UK, who led the study with colleagues. At the Woodwell Climate Research Center in the United States.

“All is well until it isn’t, and there are limits to what the human body can tolerate when it comes to heat,” he said. “Things will continue to accelerate until we get past those limits, and then all of a sudden things won’t be so good. All of a sudden, you’ll see an acceleration in the death rate.”

“My concern is that our bodies and our society will be more vulnerable to small changes than we think,” Boyce said. “This is just another (study) that says we need to start cutting emissions – but this is what we need to do.”

Dr Colin Raymond, from the University of California, Los Angeles, who was not part of the study team, said: ‘Many regions are only slightly below the irreplaceable temperature level now, so as the planet continues to warm, the overall increase in exposure will Exponential.

“We know the broad outlines of what lies ahead, but not every fluctuation is the last,” he said. “But the seriousness of the extreme heat threat means it is extremely important not to prepare by surprise, and to treat heatwaves near or above the irreversible limit like other life-threatening disasters. For potentially more severe events in the coming decades, lives will depend on the availability artificial cooling.

Previous research on extreme heat and humidity has used the human body’s theoretical upper limit, a wet temperature of 35 degrees Celsius, at which even cooling devices cannot take heat away from the body. These studies have shown the extent to which people in the Gulf, India, and China are exposed to extreme temperature and humidity conditions. Worldwide, scientists estimate that the climate crisis has already caused millions of premature deaths in the past three decades.

The study, published in the journal Science Advances, used detailed data from weather stations and broader data produced by climate modelling, and found “very good agreement”, giving confidence in the results, Powis said.

“The geographic extent and frequency of irreversible extreme heat waves will increase rapidly, given the continuing only moderate increase in global mean temperatures,” the researchers concluded. “This means that in the near future, a significant portion of the world’s population will be exposed to these irreversible environmental conditions.” To compensate.

They said there was a “real risk” of widespread exposure with “hundreds of millions of people” affected before they had adequately adapted to the heat to avoid associated increases in deaths and illness. Scientists were unable to evaluate Europe and Japan using climate models in this study due to known difficulties in representing high levels of temperature in Europe and humidity in Japan.

Even if adaptation measures are taken to protect health, extreme heat stress will still prevent many people from working or going outside, Boyce said.

“Even in cases where it is not fatal, the impacts on quality of life will be enormous.”