As I mentioned on Sunday, I’ve been itching to do a deep dive in to this new paper about how people who grow up in cold regions tend to have different personalities than those who don’t. As someone who grew up in the New England area, it’s pretty striking to me how every warmer weather city in the US seems more outgoing than what I’m used to. Still, despite my initial belief I was curious how one goes about proving that people in cold-weather cities are less agreeable. While the overall strategy is pretty simple (give personality tests to different people in different climates, compare answers) I figured there’d likely be some interesting nuance I’d be interested in.

Now that I’ve finally read the paper, here’s what I found out:

1. To make the findings more broadly applicable, study multiple countries One of the first things I noticed when I pulled up the paper is that there were a surprising number of Chinese names among the author list. I had assumed this was just a US based study, but it turns out it was actually a cross-cultural study using both the US and China for data sets. This makes the findings much stronger than they would be otherwise.
2. There are 3 possible mechanisms for climate effecting personality I’ve talked about the rules for proving causality before, and the authors wasted no time in introducing a potential mechanism to explain a cold weather/agreeableness link. There are three main theories: people in cold weather were more likely to be herders which requires less cooperation than farming or fishing, people in cold weather are more susceptible to pathogens so they unconsciously avoid each other, and people may migrate to areas that fit their (group) personalities. Thus, it’s possible that the cold doesn’t make people disagreeable, but rather that disagreeable people move to cold climates. Insert joke about Bostonians here.
3. The personality difference were actually present for every one of the Big 5 traits. Interestingly, every one of the Big 5 personality traits was higher in those who lived in nicer climates: extraversion, agreeableness, openness to new experience, conscientiousness and emotional stability. The difference in agreeableness was not statistically significant for the Chinese group. Here are the differences, along with what variables appear to have made a difference (note: “temperature clemency” means how far off the average temperature is from  72 degrees):
4. Reverse causality was controlled for One of the interesting things about the findings is that the authors decided to control for the factors listed in #2 to determine what was causing what. They specifically asked people about where they grew up to control for selective (adult) migration, and in the Chinese part of the study actually asked about prior generations as well. They controlled for things like influenza incidence (as a proxy for pathogen presence) as well. Given that the finding persisted after these controls, it seems more likely that weather causes these other factors.
5. Only cold climates were examined One of the more interesting parts of this to me is what wasn’t studied: uncomfortably warm temperatures. Both China and the US are more temperate to the south and colder to the north. The “temperature clemency” variable looked specifically at temperatures that deviated from 72 degrees, but only in the low temperature direction. It would be interesting to see what unreasonably hot temperatures did to personalities….is it a linear effect? Do some personality traits drop off again? I’d be curious.

Overall I thought this was an interesting study. I always appreciate it when multiple cultures are considered, and I thought the findings seemed pretty robust. Within the paper and in the notes at the end, the authors repeatedly mentioned that they tried most of the calculations a few different ways to make sure that their findings were robust and didn’t collapse with minor changes. That’s a great step in the right direction for all studies. Stay warm everyone!