In much of the United States, the high 80s in Fahrenheit is hot, but it’s not hot-hot. It could even be a day of sweet relief in the South, maybe time for a family picnic. But last month, across the United Kingdom, headlines warned of temperatures that could hit 31 degrees Celsius. When Americans found out that translated to 88 degrees Fahrenheit, they quickly concluded: “Europeans are weak.” And while temperatures in Europe kept going up, eventually hitting levels even Texans would find daunting and killing thousands of people across the continent, the question of how a temperature could mean serious danger in one place while being an average summer Saturday in another remained.
The temperature may be an objective number, but how we experience it is not. Culture influences the biology and psychology of thermal comfort, shaping what our bodies are used to dealing with and how our homes and businesses are set up to adapt. In fact, the very numbers of thermal comfort aren’t even universal. There are dozens of ways to measure what a hot summer day actually feels like; different countries do it differently, and how you measure affects how we communicate and understand risk.
What’s more, the climate is changing faster than our cultural and subjective experience of it. So if you’re ever tempted to flex on people in other parts of the world for not being able to take the heat, maybe it’s time to recognize that you and they are living in very different kitchens.
Most of the time, when you check the daily weather report, you’re looking at the air temperature — a measurement of heat in the air around you. But that measurement doesn’t tell the whole story of human experience. What you feel like when you open the door — and how the situation you find outside affects your body — depends on more than temperature, said Margaret Sugg, a professor of geography and planning at Appalachian State University. Humidity, air speed and direction, how hot it usually is compared to right now, and even how much the air cooled during the previous night: These factors all play a role in determining whether 88 degrees Fahrenheit feels comfortable or crushing. How we talk about our thermal comfort is both cultural and scientific.
For example, we use the heat index in the United States to measure the difference between real and perceived temperature. This is a formula that combines air temperature and humidity to give people a better indication of when they might be at risk of heat stroke. The heat index tells us that 88 degrees with 40 percent humidity feels like 88 degrees, and while there is risk there if you’re out in the sun being active for a long time, it’s not a huge deal. In contrast, 88 degrees with 90 percent humidity feels like 113 degrees — cramps and exhaustion are likely, and activity could put you on the path to heat stroke.
But “there’s a ton of metrics out there, you could spend forever researching them,” Sugg said. Another researcher, Salman Shooshtarian, a design and social context lecturer at Australia’s Royal Melbourne Institute of Technology, told me more than 116 different indices are used in different contexts. Heat index just happens to be one for which you can gather data cheaply, Sugg said. These indices can vary by country. Canada uses one called Humidex, which also combines temperature and humidity but uses a different formula and categorizes its results based on degree of comfort rather than risk of heat sickness. Another system, called the wet bulb globe temperature, takes many more factors into account, including cloud cover, wind speed and sun angle, and frames its results around how long you can work in direct sunlight before feeling ill and how long a break you need each hour. (The Occupational Safety and Health Administration is a big fan of that one.) There are even proprietary versions with secret math formulas, like AccuWeather’s “RealFeel.”
These different indices matter because they’re all telling you something slightly different and presenting their results in ways that leave you with different understandings of what’s at risk and what you should do about it. And studies have shown that they have to be recalibrated to correctly define “normal” and “safe” in different countries. The dangers of heat, in other words, are at least partially determined by culture. And that’s not the only way temperature — a thing that seems so basic, so absolute — can be pretty subjective.
“I’m from Wisconsin, and I live in Tennessee,” said Alisa Hass, a professor of geography at Middle Tennessee State University. “Moving south is a huge shock to the body.” That’s because your body acclimatizes to the temperature range it’s used to — literally, your physiology changes. People accustomed to spending time outside in higher temperatures sweat more and have increased blood flow to the skin, two changes that can help the body offload excess heat. These are short-term effects and can go away if the person gets de-acclimatized, a process that helps explain why lower high temperatures in spring can produce the same levels of heat sickness as higher highs later in the summer, Sugg said.
But there’s long-term acclimatization, as well, with people used to living in hotter climates feeling more comfortable at higher temperatures — even if their health risks are actually larger. For example, in a comparison of outdoor workers in Mississippi and North Carolina, Sugg found that the Mississippi workers believed their jobs had lower heat risks but were also the ones experiencing more heat-strain events. Another study that compared the temperature and local perception of temperature across a bunch of European cities found that what people considered “neutral” in comfort corresponded pretty well with local temperature ranges and was, in fact, closer to the local maximum temperatures than the local mean.
There’s a whole host of studies showing that where you grew up and what you’re used to affects what temperatures you perceive as comfortable and safe. The reasons seem to range from physiological acclimatization to behavioral adaptations chosen based on the normal climate — like the fact that more than 80 percent of Tennessee households have central air conditioning, compared to 60 percent of Wisconsin households and less than 5 percent of homes in the U.K. Even sex and gender can affect whether you feel comfortable at a certain temperature. There are decades of literature showing women are more comfortable at warmer temperatures indoors (where office air conditioning is often calibrated by a metric designed with male bodies and male clothing in mind) and out. The same study that found differences in local perception of temperature across Europe found that women in the study consistently reported a higher neutrally comfortable temperature than men, no matter where they lived.
And the subjective nature of temperature only gets messier as climates change. Quite quickly, the climates people have acclimatized to over their whole lives have become much hotter and wetter. So what happens to a place with the cultural infrastructure adaptations of the U.K. when it starts to have the comfort index of Wisconsin or Tennessee? Well, that’s what we saw last month. The good news, Shooshtarian said, is that acclimatizing to heat seems to take less time than acclimating to cold. But climate change also complicates our efforts to adapt. After all, Shooshtarian pointed out, people in the U.K. could install more central air, but that energy use will make climate change worse. To survive and thrive, the future might need a new culture all its own — one that adapts to rising temperatures and to the causes of them.