Scientists May Have Found the Secret Environmental Factor Behind Your Personality

To arrive at this conclusion, the researchers ran two separate studies assessing the personalities of subjects in China and the United States. In the first one, 5,587 university students from across China completed a personality survey online. In the second, 1,660,638 Americans filled out a survey in return for a customized personality evaluation.

They also collected meteorological data on the 59 home cities of the Chinese participants and, in the U.S. study, for the 12,449 ZIP codes where participants had grown up. After controlling for age, gender, population density, GDP per capita, and other factors—even humidity and wind speed—they found a “robust” connection between enjoying a balmy hometown temperature in childhood and being more agreeable and extraverted as an adult.

Brad Bushman, a social psychologist at Ohio State University who was not involved in the study, called it “a significant contribution to the literature” in an email.

“The fact that the basic findings replicate in two different countries”—one collectivist and the other individualistic—“is impressive,” he wrote. “The theoretical [rationale] for predicting personality differences is convincing.”

Rentfrow has spent much of his career investigating geographic differences in personality (sometimes in collaboration with CityLab’s Richard Florida). In a 2013 report, after collecting data from 1.5 million people in 48 states, Rentfrow and his co-authors wrote that they had observed a strong geographic clustering of people with similar personalities within the United States.

They drew a psychological map of the U.S. with three distinct—but not always geographically contiguous—regions: “Friendly and Conservative,” stretching from the Great Plains to the Deep South; “Relaxed and Creative,” comprising the West Coast, the Rockies, and parts of the Eastern seaboard; and “Temperamental and Uninhibited,” in New England, the Mid-Atlantic, and, interestingly, Texas. No one who’s seen a New Yorker chew out a stranger on the street would be surprised by that last one, but fewer of us associate the state of barbecue and rodeos with mercurial tempers. (“Sometimes the stereotypes do hold up with data, sometimes not so much,” Rentfrow said.)

The recent study in Nature Human Behaviour is in the same genre, but has a narrower focus. The connection it makes between an ideally pleasant temperature (22 degrees Celsius, or 72 degrees Fahrenheit) and a pleasant disposition has a neat symmetry to it, which is probably one reason it has generated a considerable amount of press, much of it with an upbeat spin.   

“Perhaps, in this warming world, we will all become a little more agreeable and a little more open,” wrote The Washington Post’s Angela Fritz when summarizing the findings. A public relations firm touted the study before Valentine’s Day with the headline, “Climate Change Could Explain the Personality of Your Significant Other.”

It’s tantalizing to think that climate change could smooth out our personal rough spots, or that rising temperatures will gradually turn gruff New Englanders into laid-back Californians. But don’t count on it. Rentfrow is careful to qualify the report’s prediction of possible personality impacts. “Any changes that might happen as a result of climate change would probably end up being over generations,” he said. And perhaps more significantly, “not all places are going to become warmer,” he added. “Some places will experience harsher winters, while others get hotter and drier.”

This is why Bushman finds the implications of the research not at all cheery, but “frightening.” He wrote in an email, “As climate change makes temperatures more extreme, people should become less sociable.” His own research predicts that global warming will increase crime, on the theory that living at lower temperatures, with more seasonal variation, requires groups to focus on the future and exercise more self-control, which in turn inhibits aggression and violence.

Not every social scientist is convinced that the link between climate and personality is so dramatic. And there is reason to be cautious about reading too much into it. Montesquieu, you’ll recall, argued that cold weather made people more vigorous. The corollary was the exact opposite: That hot weather made them listless and passive. “The heat of the climate may be so excessive as to deprive the body of all vigor and strength,” Montesquieu wrote. “Then the faintness is communicated to the mind: there is no curiosity, no enterprise, no generosity of sentiment; the inclinations are all passive.” Referring to India, he noted that “the inhabitants … have much greater need than the European nations of a wise legislator” because of their heat-induced torpor.

The belief that people raised in hot climates were lazy, and generally inferior to inhabitants of cold climates, spread throughout the West. It was deployed to help justify colonial rule in Africa and chattel slavery in America. To be clear, research that finds a correlation between friendliness and balmy temperatures is a far cry from scientific racism. But the possibility of “climate determinism” being used for destructive ends has not gone away.

Andrew Mathews, an environmental anthropologist at the University of California, Santa Cruz, expressed skepticism about some of the recent study’s assumptions. He pointed out that China and the U.S. are big countries, and each is culturally diverse. So it’s possible that cultural differences may underlie some of the personality differences recorded. And a “psychophysiological comfort optimum” of precisely 22 Celsius or 72 Fahrenheit is too narrow, he said.