Heat of the moment: Why does violent crime spike in the summer?

Rush Hour

CHICAGO, IL (NewsNation) — Ask any police officer who’s worried about the violent crime in their city today and they’ll likely tell you a version of the same thing: It’s about to get worse.

That’s because rates of violent crime typically go up during the warm weather months.

For decades, criminologists have debated why certain crimes, specifically violent ones, consistently increase during the summer.

Explanations run the gamut. Teens are out of school unsupervised with nothing to do, so they get in trouble. Nice weather means more people are outside, which leads to more social encounters that could potentially turn violent. Others argue that hot temperatures directly increase levels of aggression and hostility.

In recent weeks, Chicago has seen a number of violent incidents linked to large gatherings of teenagers in public spaces.

Last week, Mayor Lori Lightfoot imposed a weekend curfew for minors at one of the city’s most oft-visited areas, Millennium Park. The day before, a 16-year-old boy was shot and killed after hundreds of young people descended on the park near “The Bean.”

Despite the headlines, it’s unclear whether the uptick in violent crime during the summer is directly tied to kids being out of school. Data suggests it may not be.

In general, juveniles between the ages of 7 and 17 were more likely to commit violent crime (murder, sexual assault, robbery, aggravated assault) on school days than on non-school days, according to FBI data for 2018 and 2019.

Other studies have found the seasonal spike may have more to do with changes in human behavior brought on by warmer weather.

“It has less to do with the heat and it being really hot and bothering people and far more to do with the opportunities for disagreements to blow up into violence,” Daniel Semenza, a criminology professor at Rutgers University, told NewsNation Friday.

As the reasoning goes, when the weather gets nice, more people go outside, days are longer and that creates more opportunity for interpersonal conflict — there’s simply a greater number of interactions that could go wrong.

Which begs the question: Does violent crime increase on days when the weather is warm not during the summer months? Some studies suggest it does.

In 2017, researchers at Drexel University analyzed daily crime data in Philadelphia over a 10-year period and found higher rates of violent crime and disorderly conduct on days when the weather was warmer. In fact, the effect of temperature on crime rates was most pronounced on days when the weather was warm during traditionally cold months, not during the summer.

A more recent 2019 study from researchers at the University of Southern California examined the relationship between temperature and violent crime in Los Angeles. It found violent crime rates rose, on average, 5.7% on days when the temperature was above 85 degrees. The researchers also noted that “the heat-crime relationship is more pronounced in low-income neighborhoods.”

Others have found that warm weather itself can increase aggressive motives and behaviors in individuals. The “heat hypothesis” asserts that people can become more easily aggravated and hostile in hot temperatures. In turn, those feelings may contribute to factors that spur violent crime.

Whatever the underlying cause, police departments in America’s largest cities are bracing for a violent summer.

Homicides linked to firearms hit the highest rate in 26 years in the United States in 2020, according to the Centers for Disease Control and Prevention.

In Chicago, robberies are up 17% compared to this time last year. So far, 207 people have been murdered in the city this year, a slight decrease from the 223 killed over the same period last year.

In New York, the murder rate is down 13 percent but violent crime overall is up 42 percent compared to this same time a year ago.

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