High temperatures are known to be a killer, and historically, it is not unusual for extreme heat to cause tens of thousands of deaths. Climate change is making extremely hot temperatures more common around the world as well. While many people are familiar with the heat index, which estimates how hot it feels and takes humidity levels into account, researchers have developed another measure of extreme heat called wet bulb temperature.
Wet bulb temperature is the reading on a thermometer that is wrapped in a wet cloth, and is meant to describe the lowest temperature at which a person can still cool down by sweating. It can become so humid and hot the body can no longer cool down. Some researchers have estimated that the human body has a difficult time withstanding anything over a wet bulb temperature of 35C, around 95F, and depending on humidity. Other studies have determined more recently that a wet bulb temperature of 27C (about 86F to 105F, and depending on humidity), can cause death.
A new study has found that wet bulb temperatures of 23C may be the most dangerous, however, because they happen far more often and there is a higher degree of cumulative exposure.
It's also been assumed that elderly people fare the worst in extremely hot conditions. But this recent work has analyzed data from Mexico that included wet bulb temperatures and excess mortality data. Researchers determined that younger people are particularly vulnerable to heat. About 75 percent of heat-related deaths happened to people under the age of 35, who might have been expected to be less affected by extremely hot temperatures compared to other age groups. The findings have been reported in Science Advances.
"It's a surprise. These are physiologically the most robust people in the population," said senior study author Jeffrey Shrader of the Center for Environmental Economics and Policy, an affiliate of Columbia University's Climate School. "I would love to know why this is so."
In Mexico, there were around 3,300 deaths related to heat every year between 1998 and 2019. People aged 50 t0 70 were found to have the lowest mortality, while children under five years old and those 18 to 35 were particularly affected.
This study has suggested that as the world gets warmer and more heat-related deaths happen, young people will be most affected, said co-corresponding study author R. Daniel Bressler, a graduate candidate in Columbia's Sustainable Development program.
These results may be due to a number of factors. Younger people tend to work outdoors in agricultural or construction jobs, where dehydration is more likely and access to air-conditioning is less likely. Younger people are also more likely to play sports outside in hot temperatures.
The research also determined that older people are more vulnerable to colder temperatures. Cold is also still the primary cause of temperature-related deaths in Mexico and in the world, however. (In the US, experts differ on whether heat or cold kills more Americans.) Scientists are expecting heat-related deaths to increase globally, however.
Now the scientists want to learn more about who is most affected by extreme temperatures in other countries besides Mexico.
Sources: Columbia Climate School, Science Advances
