American pop culture often splits its characters into two broad stereotypes: the easygoing, friendly West Coaster, and the acerbic, uptight East Coaster. Most people know to take those tropes with a grain of salt — not everyone who grew up along the Pacific is as chill as Snoop Dogg, and thankfully their Atlantic counterparts aren’t all cranky Larry Davids — but a study published in Nature Human Behavior on Monday suggests there’s some scientific truth behind the old stereotypes.

In the study, the team of American and Chinese researchers show that there actually is a link between personality type and geography — specifically, the ambient temperature of the geographical location in which people spent the majority of their life before college. They hypothesized that people in warmer, more “clement” regions would generally be more social and open to new experiences because they would be more likely to venture outdoors and do things with others than people who grew up in colder environments.

“Clement (that is, mild) temperatures encourage individuals to explore the outside environment, where both social interactions and new experiences abound; by contrast, when the ambient temperature is either too hot or too cold, individuals are less likely to go outside (for example, to meet up with friends, or to try new activities),” they write.

Their explanation is in line with “attachment theories” — the idea that people who are comfortable in their environment are more willing to branch out and try new things. This sense of comfort has largely been attributed to emotional and psychological factors, but this study shows it may rely on physical comfort as well.

Snoop Dogg
Snoop Dogg may be this chill because he grew up in a clement environment.

In other words, clement parts of the world — where the ambient temperature is close to the human “psychophysiological comfort optimum” of 22 °C (71.7 °F) — increase person’s scores on their “Big Five” personality traits, which include agreeableness, conscientiousness, emotional stability, extraversion, and openness to experience. It also boosts scores on two more broadly defined traits, aptly named the “socialization factor” and the “personal growth factor.”

Previous experiments have suggested that social contact boosts scores in these traits, the researchers note, and since warm weather makes people more likely to socialize, then warm weather must be able to shift a person’s personality, at least to some extent.

On this map of China, yellow bars represent clement temperatures, and taller bars represent higher scores in sociability (left) and stability (right) assessments.

The first part of their study, conducted using data on 5,587 people across 59 cities in China, showed that the researchers were on the right track. Participants whose home cities had a higher ambient temperature showed higher scores “on personality factors related to socialization and stability (agreeableness, conscientiousness, and emotional stability) and personal growth and plasticity (extraversion and openness to experience).”

The researchers repeated their analysis with a bigger data set covering the personality types of almost 1.7 million people across 12,499 ZIP-code level locations in the U.S., a country that’s not only larger but also much more culturally diverse. Again, warmer temperatures were linked to higher scores on traits linked to sociability and emotional stability, leading the researchers to conclude that temperature clemency really is an “important predictor” of personality.

Larry David
Larry David's lack of openness and emotional stability might be linked to the temperature of Brooklyn, his hometown.

Of course, temperature clemency isn’t the only predictor of personality, and this study’s results, based only on data from two countries, are far from conclusive. But the relationship is interesting to consider, especially seeing as the pattern is consistent across two very large, very different nations. What’s more, they note, is that the study gives us a glimpse into how personalities may change as the world’s climate shifts.

“As climate change continues across the world, we may also observe concomitant changes in human personality,” the researchers write, hinting at one unexpected consequence of a warming planet — that everyone gets a little bit friendlier.