The New Orleans Times-Picayune ran a piece last Friday attempting to answer a question the entire world has been asking: Should ice cream be blamed for murders? “The correlation between homicides and ice cream sales—when ice cream sales increase, the rate of homicides also increases—has long been a topic in statistics and science classrooms,” writes John Harper, citing several recent cases of ice cream-related crime.
In the second paragraph of his piece, Harper thankfully reminds readers that correlation is not causation, and that ice cream’s relationship to homicide is a mere statistical coincidence. The idea that frozen treats cause crime is obviously ridiculous, unless you’re talking about that addictive Cocaine Chip ice cream I’ve heard so much about. But it does stand to reason that ice cream sells better in warm weather, and there is in fact plenty of evidence to suggest that murder rates rise when temperatures rise.
In 2009 a New York Times article on summer killings in New York City cited a CDC study that found a national increase in homicide numbers between the months of July and September. The Times analyzed some New York Police Department data itself, and found a similar trend: “when the temperatures rise, people hit the streets, and New York becomes a more lethal place.” Why?
Summer is when people get together. More specifically, casual drinkers and drug users are more likely to go to bars or parties on weekends and evenings, as opposed to a Tuesday morning. These people in the social mix, flooding the city’s streets and neighborhood bars, feed the peak times for murder, experts say.
Similar trends have been spotted in other cities. In Chicago violent crimes consistently spike with higher temperatures—more than 70 people were shot and at least 12 were killed during this exceedingly warm Independence Day weekend in Chicago. In a 2012blog post for Chicago magazine, Whet Moser speculated on several reasons for this correlation, one of which was that people might just be more prone to anger when it’s warm outside. (“Heat also contributes to the ‘are you lookin’ at me’ effect, as initially proven by Taxi Driver,” Moser noted.)
Saying that warm weather causes crime is just as simplistic as saying ice cream causes crime. I was in Chicago this past weekend, and I didn’t kill anybody. (I ate a lot of ice cream, too, for what it’s worth.) But the correlation between temperature levels and violent crime rates is worth remembering the next time that some showboating police chief holds a press conference in March to brag that he’s solved the city’s murder problem. If the gains he’s touting hold through the summer, then there might be something to brag about.
Justin Peters writes a crime blog for Slate.