But establishing cause and effect when it comes to human behavior in an uncontrolled world is complicated. The correlation could be a result of any number of factors, or combination:
In summer, people may be more likely to be outdoors, at parties and concerts or other situations where they’re more likely to get into trouble. There’s a greater chance alcohol will be around, which any police officer or EMT will tell you drastically increases the chances for bad behavior in humans.
But what about the heat itself? Is there something happening to our bodies and minds in the heat that makes us more prone to violence? That question is even trickier to study.
“We can't really do a true experiment in a field where the outcome variable is an assault or something because that would be ethically impossible to do that kind of a study,” said Craig Anderson, who runs the Center for the Study of Violence at Iowa State University, and has been studying human aggression for decades. “But you can study what happens in the real world.”
And statistics from the real world often show that correlation between increased assaults and hotter temperatures. Anderson said a lot of other variables come into play, but even when they’re taken into consideration, heat remains a significant factor.
“All of those studies tend to produce the same outcome in this case that heat is associated with increased aggression including violent behavior,” he said.
Anderson said sports can help us understand more specifically how this heat-related aggression plays out. “The baseball studies are some of my favorites.” One crunched the numbers from more than 50,000 games, comparing how often pitchers intentionally beaned batters on hot days versus cool ones.
“Baseball pitchers are more likely to hit batter with a pitched ball on hotter days than cooler days, even after you statistically control for things like how good was the pitcher's control that day.”
This kind of evidence supports what researchers call the heat hypothesis: simply put, higher temperatures make people more aggressive. Another study showed a correlation between higher temperatures and more fouls in NFL games.
Common sense might tell us that heat makes people uncomfortable, and uncomfortable people are more likely to be more angry and therefore more violent.
But there’s more to it than that.
“It isn't that anyone goes out said, “Gee, I'm hot, therefore I'm going to smack somebody,” right?” Anderson said, laughing. “That's not what happens.”
The heat doesn’t instigate, it escalates. The heat increases the chances a pitcher will retaliate by hitting the other team’s batter AFTER theirs has been hit.
You can see it play out in this Red Sox versus New York Yankees game, played on a day that hit 91 degrees: after the Sox pitchers hit four Yankee batters, the Yankees retaliate by hitting Big Papi. It’s the kind of thing that might have happened anyway, but the heat effect increases the chances. Studies from our more mundane lives seem to bear this out as well — one indicates you’re more likely to honk your horn at a slow driver on hot days.
Anderson said studies in the lab show the heat seems to actually change one’s perception in these instances.
“People who are uncomfortably warm perceive more aggression in this interaction than people who are comfortable,” he said. “They perceive more aggression in the world than what might actually be there.”
A comment could more easily be taken as an insult — and, since the person you’re interacting with is ALSO hot, they’re more likely to take offense at your offense, and a vicious cycle of heat-induced escalation can ensue.
“Once that starts,” Anderson said, “something that should've been relatively innocuous can accelerate into something that eventually leads to ... a fist fight, or guns, or knives, or whatever that then show up in terms of assault statistics or homicide statistics.”
Anderson said understanding the extent to which your environment affects your perceptions and decisions might help you override the angry impulse.
“But it is such a subtle effect that people don't really believe that they're angry because they're hot,” he said. They think, “they’re angry because so-and-so just said something to them that was inappropriate. It's really hard to look into your own internal brain functions and say ‘Oh, no no, I'm reacting this way simply because I'm uncomfortable.'"
When police are called to a conflict, they need to de-escalate the aggression, and many are now trained to do just that.
Christine Elow is the superintendent in charge of operations for the Cambridge Police Department, and a 22-year veteran. She said in her days on patrol, she had to play the role of conflict mediator almost daily.
“And it's really interesting when it comes down to the police responding, because a lot of times people just respond to the police in a negative manner. They see us and sometimes, in certain communities, the presence of the police can actually escalate the situation,” Elow said.
The approach to de-escalation varies with each situation, Elow said. Calming down hot and angry people requires communication on multiple levels.
“Verbal communication is huge, but it's also your body language,” she said. “So you can say one thing, but if you're in a specific stance where you look like you're ready for a fight that means something. So we've done a lot of work on how people interpret our words and our actions, and how do we effectively engage.”
Part of that engagement is having an existing presence, and involvement in the community they’re patrolling.
“What we're really trying to do is engage at the neighborhood level,” Elow said.
When people know you, it’s easier to de-escalate a situation, and play that role of interpreter without being misinterpreted — even when everybody is hot and bothered.