If sweating your shirt off in the extreme summer heat makes you angry, you’re not alone. In fact, research shows that there is a direct correlation between high temperatures and temper, and that anger can sometimes lead to bad behavior.
Violent crimes such as murder, manslaughter and rape, terrorist attacks and mass shootings are much more likely when temperatures rise, studies show. There are higher rates of civil wars and riots. Even in controlled environments such as prisons, a 2021 study found an 18% increase in inmate-on-inmate violence on really hot days. People can also turn their anger on themselves; there is a higher risk of suicide on hotter days.
There could be many reasons for these links, but recent research has confirmed that some people became angrier and lashed out more when they felt hot. One experiment found that people who played video games in a hot room, under certain circumstances, were consistently more cruel to their fellow players than those in a room with a more moderate temperature.
Hot Room Experiment Reveals Alarming Aggression in ‘Joy of Destruction’ Game
The experiment was conducted with 2,000 college students in California and Kenya who were randomly assigned to play in a hot or warmer room. The heat did not seem to change the outcomes of those who played a game involving general economic decisions, but when they played a game called “Joy of Destruction,” some students in the hot room in Kenya became more aggressive.
In that game, players earn points that can be redeemed for real gift cards. But points can also be taken away randomly by the computer or by a fellow player acting anonymously. The research found that Kenyan players in the hot room were consistently more willing to harm other players by reducing their winnings.
“There was no personal gain in doing this. It was simply the ‘joy of destruction,’ as the name implies,” said study co-author Dr. Ian Bolliger, a member of the Energy and Resources Group at the University of California, Berkeley. “That was something that surprised us.”
Bolliger noted that the heat did not seem to change the behavior of students at Berkeley, so he believes that temperature alone does not make people aggressive. Rather, the difference may have been what was happening outside the hot room in Kenya.
The experiment took place in late September 2017 and ran through early 2018. Kenya had just held a contentious election in which the vote was split along ethnic lines. Feeling cheated, the losing side accused the winners of stealing the election. Video game players who aligned themselves with the losing candidate had “significant grievances,” the study found.
“That was the group that exhibited all this aggressive behavior, whereas in Berkeley and with the other ethnic group, we didn’t see an increase in aggressive behavior, even in the hot room,” Bolliger said.
It’s a finding the researchers said they would like to investigate further.
“It may be that temperature itself is not a direct cause of aggression, but it’s actually a multiplier,” Bolliger said. “So, if you’re already feeling aggrieved for some reason, being in a stressed environment could allow those aggrievances to manifest.”
A similar 2011 study found that when temperatures were high, Major League Baseball pitchers were much more likely to retaliate and intentionally hit a batter if someone on the pitcher’s team had been hit by a pitch earlier in the game.
Dr. Curtis Craig, a Human Factors Research Associate in the HumanFIRST Lab, Department of Mechanical Engineering at the University of Minnesota, tracked temperatures and the number of penalties in NFL games for a 2016 study. The hotter it got, the more players committed infractions.
The home team received the most penalties, so, as with the video game experiment, Craig believes that while the heat was a factor, the circumstances during the game also mattered. In this case, the players may have felt more support from the fans and that allowed them to give in to the aggressive feelings they may have had because they were hot.
“We don’t like to be hot,” Craig said. “High temperatures increase discomfort. It increases negative emotions, especially if you already have a negative association with something else.”
The Science Behind Heat-Induced Aggression: Insights from Experts
None of these studies can really explain why heat can make people more aggressive and misbehave, but scientists have theories.
Dr. Joseph Taliercio, Research Coordinator and licensed psychologist at Cognitive and Behavioral Consultants, believes that when it’s hot outside, the body may not have its usual defenses in place to keep aggressive impulses in check.
The body needs to expend energy to cool down, and some of that energy may come from the part of the brain that consumes the most energy: the prefrontal cortex, which helps people self-regulate. It’s the same part that shuts down when people drink alcohol, he said, and that can lead to impulsive behavior.
“It’s like when you watch a science fiction show or movie and they talk about how they have to redirect energy to the frontal shields. Our brain has to redirect power when it’s hot and, as a result, we will become more impulsive and act more without thinking,” Taliercio said.
Dr. Susan Yeargin, who studies the connection between heat and behavior as an associate professor of Exercise Science at the University of South Carolina, said that just as the body diverts blood to the skin to help release heat, it would make sense that energy would be diverted from the brain.
“Anything that deviates from homeostasis, the brain will not be happy and will react in some way,” he said. In the case of heat stroke, for example, one symptom is central nervous system dysfunction, “which simply means the person is not making good decisions.”
Heat also causes the body to sweat and lose nutrients, which play a role in self-regulation and mental health. “It’s like we’re trying to run the machine using the wrong fuel, or at least using the wrong balance of fuel,” Taliercio said.
Climate Impact on Mental Health: Insights from Dr. Amruta Nori-Sarma’s 2022 Study
Dr. Amruta Nori-Sarma, an assistant professor in the Department of Environmental Health at Boston University School of Public Health, found in a 2022 study that many more adults went to the emergency room for mental health problems in hot climates. That doesn’t suggest that people with mental health problems are angry or violent, but that heat can affect a person’s mental well-being.
“Initially, I think people were a little surprised to see an increase in rates of mental health Emergency Department visits in the summer,” Nori-Sarma said. With seasonal affective disorder and the isolation that comes with extreme cold, some scientists expected emergency rooms to be full of mental health patients in the winter. “However, now that what we know about violence and aggression increases as temperatures rise, this may make more sense.”
Higher temperatures can increase anxiety levels, Nori-Sarma said. Even anticipating higher temperatures can cause anxiety. One reason may be that people don’t sleep as well in hot weather, and lack of sleep can cause irritation and affect decision-making ability.
“Sleep is one of the best things we can do to self-regulate emotions,” Taliercio said.
Not everyone will become angry, aggressive or even violent in high temperatures, he said, and everyone will have a different level at which the heat can make them more aggressive. But, he said, “irritability will show up in many people when it’s hot.”
As the weather gets hotter, people may need to periodically check weather forecasts before heading out, Taliercio said.
“Ask yourself, ‘Based on my own personality, should I be more alert so I’m not potentially irritable today because it’s hot outside?” asked Taliercio.
He compared it to checking whether face masks were needed this summer as Canadian wildfires caused widespread air pollution.
“Maybe put less time in the schedule when temperatures are high, or hang out with people who irritate you less,” Taliercio said. “Maybe even reschedule important meetings for cooler days. With the climate crisis and rising temperatures, this is certainly something more people will have to keep in mind.”