Written by Scott Dance for the Washington Post.
In an average June, just a few days reach 90 degrees in Detroit. But by the time the year’s first blast of summer breaks in the Motor City this weekend, nearly a week of intense heat will have passed.
Published on June 21, 2024
And some of the most dangerous heat waves are those just like the one gripping parts of the Midwest and Northeast this week: hitting early in the season, when people have had less time to adjust to the conditions, and in places well outside the Sun Belt where people don’t often experience such sustained levels of tropical-like warmth.
“We’re starting pretty early in the year,” said Abdul El-Sayed, health officer for Wayne County, Mich. “People aren’t as used to heat this early in the summer.”
As global temperatures rise, intense heat is arriving sooner and raising risks of illnesses and death among people who aren’t acclimatized to it, experts said. In many cases, heat can overwhelm the body well before a person realizes it, they added — especially at this time of year, when memories of heat-beating strategies are stale and physiological adaptations to heat need a jump-start.
When the body is adjusted to heat, it manages by initiating sweating sooner, sending more blood to the skin, increasing thirst sensations and retaining more salt, said Jennifer Vanos, an associate professor in the Global Futures Laboratory at Arizona State University.
But in the first heat wave of the season — or even when another strikes weeks after a previous bout of heat — those adjustments don’t happen immediately. That is true of people who haven’t felt heat in months, as well as those who might live in a hot environment but spend most of their time in air conditioning, Vanos said.
“In order to have those adaptations, we have to expose ourselves to the heat,” she said.
At the same time, people who aren’t used to the heat are also less likely to take precautions or behave in ways needed to keep themselves cool, researchers said. They might overestimate how much heat they can withstand while working outside or sunning on a beach, for example.
After enduring multiple days of extreme heat in a row, “people start to get dehydrated and they don’t realize they haven’t caught up,” El-Sayed said.
Many people underestimate the toll that heat may be taking on the human body, said Kristie Ebi, a professor at the Center for Health and the Global Environment at the University of Washington. There is no strong feedback mechanism to make us aware if our core body temperature is starting to rise, she said. Making that more difficult to discern: that the first symptom is often confusion.
“People can get in trouble with heat before they’re even aware they’re having heat stress,” Ebi said.
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People in urban centers are especially vulnerable to extreme heat. Many people underestimate the toll that heat may be taking on the human body, said Kristie Ebi, a professor at the Center for Health and the Global Environment at the University of Washington.