July 22, 2024—The way we measure outdoor temperatures is “seriously flawed” and doesn’t reflect how hot it actually feels, according to Harvard T.H. Chan School of Public Health’s Joseph Allen.
In a July 15 opinion piece in The Washington Post, Allen, associate professor of environmental health, said that we should be measuring something called “wet-bulb globe temperature,” which incorporates not just air temperature, but also radiant heat, humidity, and air movement—providing the most accurate read on heat and its potential danger.
To explain why using wet-bulb temperatures matters, Allen offered examples of recent heat waves in Fresno, California and New York City. By standard measures, Fresno’s “dry temperature” was predicted to reach 102 degrees on July 16, compared to 98 degrees in New York City. But New York City’s wet-bulb temperature was predicted to be 88 degrees that day—eight degrees hotter than in Fresno, where the humidity is low.
“I’m not writing to minimize the heat waves in the West,” Allen wrote. “I just want to stress that we cannot ignore the even more dangerous weather happening elsewhere that might be less obvious. A worker heading outside on the East Coast seeing only the dry temperature might incorrectly think it’s not a big deal. If they see only the heat index, they won’t realize that assumes they’re in the shade and resting.”
Allen acknowledged that it may take time for people to become familiar with wet-bulb temperatures because they’re generally lower than dry temperatures and heat indexes and can be prone to misinterpretation. But he noted that athletic organizations, the military, and federal regulators have used wet-bulb temperature for decades, and that it provides the best data on which to base policies that protect people from the threat posed by heat.
“We have the tools to measure [heat] correctly,” Allen wrote. “We just need to use them.”
Read the opinion piece: We need to change the way we think about outdoor temperatures
Image: iStock/Marc Bruxelle