I'm fairly good at keeping my anger down to a simmer, but on the few occasions where I've found myself snapping at people, I can trace the cause back to hot, humid weather. I wish I wasn't cursed to be at the whim of something none of us can control, but the heat takes any small irritation I have and dials it up to 100.
But I'm not alone in this — several studies have shown that while warmth and sunshine can make people more agreeable and happy, that attitude can disappear once it's sweltering outside.
In a study from 2017, researchers looked at retail workers at a chain store, and found that they were 50% less likely to actively engage with customers when it was uncomfortably hot outside.
In a second part of the study, the researchers divided college management course students into two groups. One group was put into a humid, hot classroom, and the other in a cool, air-conditioned room (with a 15% difference in room temperature). The researchers then had the students fill out a survey for an organization to help underprivileged people in the community, but only 64% of participants in the hot room agreed to answer at least one question, compared to 95% in the cooler room. This led the researchers to conclude that the heat really can affect your perceptions, emotions, and the way you behave towards other people.
Past studies have also linked hot weather to violence and aggression.
There are a couple of theories about why people get so worked up when it's stiflingly hot. For one thing, you're more likely to get dehydrated when you're hot, and dehydration definitely impacts your mood. A 2012 study that looked at young women found that after losing about 1.5% of their body’s normal water volume, the study's participants were tired and had difficulty concentrating, and they were more tense and anxious.
Plus, being overheated can lead to a heatstroke, symptoms of which include confusion, agitation, and irritability. And more anecdotally, hot weather is harder to escape — when it's cold, you can at least put on more layers and bundle up. When it's hot out, you're basically doomed to be uncomfortable unless you have an air conditioner, or you actually enjoy sweating all your fluids out. The heat can also make it more difficult for you to fall and stay asleep, and we all know what sleep deprivation can do to your mood.