Wet-bulb temperatures
Wet-bulb temperature combines dry air temperature with humidity. Once wet-bulb temperature hits 35°C, humans are unable to cool themselves and are more likely to die from heat stress. Because of human-caused global warming, certain areas are hitting wet-bulb temperatures more frequently and becoming increasingly uninhabitable.
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“A wet-bulb temperature of 35°C is regarded as the theoretical limit of what humans can endure. It would be reached at an actual temperature of 45°C if relative humidity were 50%, or at about 39°C if humidity were 75%. Beyond this point it becomes impossible for sweat to cool the body down, causing people to overheat and in effect cook. Cells swell, proteins are deformed and organ systems fail, resulting in death. At wet-bulb temperatures above 35°C, it is thought that even young healthy people wearing light clothing—regardless of whether they are parked in front of a fan, in the shade or have unlimited water to drink—will die in about six hours.
Even slightly lower wet-bulb temperatures can be dangerous. At a wet-bulb temperature of 32°C, it is risky to do anything that raises body temperature, such as walking or working outside…
Average global temperatures are currently 1.1-1.3°C warmer than pre-industrial levels. The same team of American and British researchers found that extreme levels of humidity and heat now occur twice as often than they did in 1979. Even if countries stick to their promises to curb emissions and scrub carbon from the atmosphere, the world is on track for temperatures to rise by the same amount again by the end of the century.
Humans’ ability to regulate their temperature—through sweating, clothing, housing and more—has allowed them to live, and thrive, in almost every environment on Earth, from tundras to deserts. In modern times technology, such as air-conditioning, does what the body cannot. It will continue to perform that role. But parts of the world will nevertheless get harder and harder to bear.”
The Economist, The increasing frequency of fatal wet-bulb temperatures
“Climate models project that combinations of heat and humidity could reach deadly thresholds for anyone spending several hours outdoors by the end of the 21st century. However, new research says these extremes are already happening — decades before anticipated — due to global warming to date.
The study, “The emergence of heat and humidity too severe for human tolerance,” published today in Science Advances shows for the first time that some locations have already reported combined heat and humidity extremes above humans’ survivability limit. Dangerous extremes only a few degrees below this limit have occurred thousands of times globally — including in parts of the southwestern and southeastern United States — and have more than doubled in frequency since 1979.”
NOAA, Dangerous humid heat extremes occurring decades before expected
”In March, April and May this year, India and its neighbours endured repeated heatwaves that exposed more than a billion people to dangerously hot conditions. India broke several temperature records. The warmest March in more than a century was recorded across the country and a new high of more than 49C was hit in Delhi in May.
Record-breaking heat has also been recorded elsewhere this year, including the UK, which smashed its previous record by an incredible 1.6C, reaching more than 40C. Portugal reached 47C on the 21st of this month, the hottest July day on record, while several places in France recorded new highs.
These heatwaves have reignited the debate about how we can protect people from rising temperatures – and how high we can stand them to go. But the headline figures do not give the whole story when it comes to the impact of high temperatures on humans, because humidity, which is not factored into these figures, plays a huge role in how we actually experience heat.”
The Guardian, Why you need to worry about the ‘wet-bulb temperature’
“If the air becomes too humid and is combined with record-breaking high temperatures causing the body’s sweat to inhibit evaporation from the body, the ability to cool itself is dangerously compromised. The phenomenon is known as the wet-bulb temperature, and the threshold of humidity and heat in Celsius is 35 degrees and Fahrenheit 95 degrees. That threshold will be pushed to the outer limits in India, warn experts.”
Daily Kos, India may tip this year to a wet-bulb temperatures threshold that will test human survival
“At least 13 people have died from heatstroke in India’s western Maharashtra state after attending a state award ceremony on Sunday at which a senior government official was present, police officials have confirmed.
In Navi Mumbai, the city where the ceremony was held, between 50 to 60 people were hospitalized, according to a city police official, who asked to not be named as he is not authorized to speak to the media.
The total number of those impacted by the searing temperatures at the event is believed to be much higher, as many may have sought medical care in their local district…
Heat waves in India usually take place between March and July, but in recent years these hot spells have become more intense, more frequent and longer.”
CNN, India heatstroke: 13 people die after attending government award ceremony
More Reading:
The Conversation, Why 40°C is bearable in a desert but lethal in the tropics