“At 10:51 p.m. the heat index was 95 — that’s pretty incredible,” Mr. Crouch said. “That’s a hot heat index in the middle of the summer, in the middle of the day, for New York.”
Short-term weather conditions are not the same as long-term changes to the climate, and a few hot days do not prove a trend. But the unusual heat and humidity that appeared to strain Federer are in keeping with the changes that atmospheric scientists are seeing under human-caused global warming.
Normally this time of year, the daytime high temperature tops out at 80 degrees, with overnight temperatures in the 60s.
Humidity at high temperatures stymies a key cooling mechanism for the body, sweating.
“When we exercise, our primary means of cooling ourselves off is to sweat,” said Lacy Alexander, an associate professor of kinesiology at Pennsylvania State University. “For every gram of sweat we evaporate, we liberate heat.”
But when the air is too humid, the sweat doesn’t evaporate; it drips. “It provides no cooling capacity for the body,” Dr. Alexander said.
“You have soaking wet pants, soaking wet everything,” Federer said after the match.
He also said Millman might have had an advantage because “he maybe comes from one of the most humid places on earth.” Millman is from Brisbane, Australia, which is cooler but steamier than Federer’s off-season training base in Dubai.
The body has some capacity to adapt to warmer temperatures through exposure. But being maladapted to heat is mostly a problem for non-athletes, Dr. Alexander said.
For an athlete like Federer, “that high level of training on a day-to-day basis imparts a degree of heat acclimation just because of high fitness,” she said.
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