Summer in Chicago: Does the heat really make people violent?

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“Ma, did you see the guys in the car?”


“I did!”

“What did the guys in the car do?”

“They shot me.”

That was  four-year-old Jacele Johnson telling her mother Trennetta Gresham about the moment she was shot in the head. That Friday night, only a few hours into Memorial Day weekend and the unofficial start of summer, the family was at a prom party in Chicago’s Englewood neighborhood. Jacele played behind the wheel of Gresham’s parked car when it happened.

It didn’t take long. A car pulled up, windows rolled down, and fired. The bullet hit Jacele in the left side of her head, her 17-year-old cousin was shot in neck and chest, and a 15-year-old girl was shot in the head. No arrests have been made.

As temperatures hit the 80s and schools close, Chicago is bracing for a violent season.


About a week ago, on June 7th, the city recorded its 1,000th shooting victim of the year. That’s nearly double the number of people shot in New York and Los Angeles over the same period. (In 2014, 933 people had been shot in the city by that time.) Homicides are up, too: there have been 170 so far, a 14 percent increase from last year.

This happens every year in Chicago: the temperatures rise, and so do the shootings. Must be the heat, right? That’s what Romeo and Juliet (“For now, these hot days, is the mad blood stirring”) and Spike Lee’s Do the Right Thing would have you believe. But the truth is more complicated.

Violent crime does tend to increase along with temperatures, a relationship that’s been studied for hundreds of years. As far back as the 1800s, astronomer Adolphe Quetelet found that violent crime in France peaked in the summer. And there is some research, like this often-cited paper from 2001, that concludes aggression increases with heat.

The chart below, from the Chicago Police Department’s 2011 report Chicago Murder Analysis, shows the murder victims by month from 1991-2011. There’s an uptick during the hotter portion of the year.


But correlation doesn’t equal causation. That is, just because crime increases with heat doesn’t mean that heat causes crime.


Ellen G. Cohn, associate professor of Criminal Justice at Florida International University, gathers data on 911 calls to link the exact time of a crime with weather data, since temperature changes over the course of a day. She told Fusion that while crime does get a distinct, well-documented bump from heat—unlike barometric pressure, humidity, and precipitation—just saying the Chicago summer is hot and miserable does not explain violent behavior.

Committing a crime is still a choice. Cohn explained the “routine activities theory,” the idea that for crime to happen three things must come together: a motivated offender, a suitable target, and the absence of a capable guardian. On evenings, weekends, and summer—when school is out, people are on the street, tourism spikes, and alcoholic consumption is up—routines evaporate, our lives are generally less structured, and the likelihood that the three ingredients of crime collide increases.


Excessive heat can even deter crime, Cohn said. When the temperature rises high enough, the urge to flee the heat outweighs the desire to be violent. “It’s just too darn hot to commit a crime,” she told Fusion. “You’d rather go find a cold beer or something. Or air conditioning.”

This interactive analysis of more than 5 million crime reports and weather data from 2001 to at least 2013, shows crime drop off at 89 degrees in Chicago.


“You can’t blame anything on the weather changes,” activist Andrew Holmes, who spent time with Gresham and her family in the hospital, told Fusion. “Even when it’s cold out here, you still have people shooting people and people losing their lives.” He said that for gun violence to really change, people need to stop shooting each other.


The other thing that’s complicated about the “murder season” myth: crime in Chicago is actually at its lowest rates in four decades. And despite the high shooting and homicide numbers, it’s nowhere near the murder capital of the United States when adjusting for population (2.7 million residents make the city the third largest in America).


Furthermore, violence is concentrated in pockets in the South and West sides. A neighborhood like Englewood where Jacele was shot can have an annual homicide rate more than 20 times that of a “safe” northwest neighborhood. The Tribune’s interactive map of shootings this year illustrates how the violence is isolated.


Still, Chicago is often referred to as a war zone. The city has been nicknamed for “Chiraq” for its gun violence. That’s also the working title for Spike Lee’s next film, shooting now in the city, about black-on-black violence in Englewood. The film is rumored to be an adaptation of the Greek comedy Lysistrata, in which women withhold sex to stop violence. Mayor Rahm Emanuel has told Lee that he is not happy with the title.

And for those like Gresham, the violence—which the police says is fueled by illegal gun trafficking and gangs—is suffocating.


Police have said that Jacele’s shooting was gang-related, but Trennetta hasn’t seen any evidence. When she saw a photo of herself at the crime scene, her white pants drenched in her daughter’s blood, she stared in disbelief. Jacele asked what she was looking at.


“Look at mommy,” Gresham told her. “I was cute.” She laughed. Gresham said she didn’t realize she was covered in blood until she was at the hospital. An officer gave her green scrubs to change into. Jacele’s father drove overnight from Minneapolis to be by his daughter’s side.


After 40 minutes of surgery, doctors said it was too dangerous to remove a bullet fragment from Jacele’s brain. Fragments of her skull, however, were taken out and are expected to grow back in a few months. For now, Jacele is back at a hospital in Minnesota. She can walk and use her left hand. Her days are spent in hours of therapy until at least July 1. Gresham says that her nephew and the young lady who were also shot that night are recovering and back to “being silly and normal teenagers.”


Gresham, born and raised in the South Side, had lived in Minneapolis for seven years before heading back to Chicago three months ago to help launch a daycare. But because of the violence in the city, she had planned to move back to Minneapolis after Memorial Day. Then Jacele was shot.

Since then, a 13-year-old, 11-year-old, and 2-year-old are among dozens of shooting victims. Gresham said that for her daughter to take a bullet and survive isn’t just a miracle—it’s a message to the city. “It has to stop, it has to stop,” she said. “We’re going to kill off all our kids.”