Does Chicago’s homicide rate rise and fall with cold winter weather?

By Dean DeChiaro

There’s evidence to support the conventional wisdom that as temperatures in Chicago increase, so does crime. But that narrative usually focuses on spring and summer, when statistics show violent crimes, including homicide, occur most frequently. But do those summer patterns also hold true for a particularly mild winter?

According to information compiled by the Chicago Tribune, 145 shootings took place in Chicago this January, compared with 100 shootings in January 2014. This January also saw seven more homicides. Temperature-wise, 2015 was on average 7 degrees warmer than 2014. So in a city known for its brutal cold, do more homicides occur when Mother Nature lets up a bit?

The numbers don’t exactly say no, but they say probably not. According to information gathered from RedEye’s Chicago homicide tracker and Weather Underground, the number of January homicides over the past decade has ranged from 20 to 44, while the average mean temperature ranges from 16 to 36 degrees. The number of homicides generally rises and falls with the temperatures, but with notable exceptions — for instance, January 2006 was the warmest of the past decade, but only 27 homicides were recorded, as opposed to 41 in 2012, the next warmest.

(Weather Underground and RedEye, Dean DeChiaro/Medill)

Derral Cheatwood, a professor emeritus of sociology at the University of Texas at San Antonio, has written about the correlations between violent crime and weather in urban settings and said he doesn’t see the same patterns in Chicago’s winter numbers that one typically finds in summer statistics.

“It doesn’t seem as if very cold weather dampens the homicide rate,” Cheatwood said, noting that Chicago’s frigid climate might prevent it from experiencing what he calls the “cold floor,” meaning a temperature below which crime tends to taper off.

(Weather Underground and RedEye, Dean DeChiaro/Medill)

Cheatwood also suggested a reason that, despite a few outlying years, Chicago’s January homicide rates don’t always correlate with its fluctuating temperatures.

“In cities with such extreme cold, you basically adjust to the weather around you,” he said. “There is impact of heat [on crime rates], and I tend to think there is a dampening effect with cold. Up there it’s like, ‘Hey, it’s a Chicago winter, whatever.’”

In San Antonio, Cheatwood said, you might see the opposite effect.

“It gets up to 90 degrees in Chicago in the summer and that’s a heat wave, but in San Antonio that’s nothing,” he said. “If it got as cold down here as it does in Chicago, I’m not sure what would happen.”

Cheatwood also emphasized the importance of societal factors — especially those related to criminal networks — that could affect crime rates measured on a month-to-month basis.

“When you disrupt a criminal market or start a gang war, these numbers can go way up or down,” he said. “There could be one homicide that takes three or four lives. I’d be surprised if [years with more homicides] aren’t just statistical oddities.”

Eric van Zanten, a Chicago-based Web developer and self-described “civic-minded hacker,” has created an online tool for viewing the frequency of crime in Chicago as it relates to temperature.

“You have this concept about crime and weather, and every spring people are going to say that summer’s coming and crime will increase,” van Zanten said. “I’m kind of a skeptical person so I tried to prove that.”

And though the results show that the rates of most violent crimes tend to increase with temperature, Cheatwood and van Zanten were reluctant to say whether they believed police could benefit from tracking crime and weather together.

“I think police will use weather loosely,” Cheatwood said. “It becomes a minor consideration most, if not all, of the time.”

A spokesman for the Chicago Police Department did not respond to an email requesting comment.

Van Zanten said that the data could be used to fuel other initiatives, pointing out the city’s One Summer youth jobs program that showed a 43 percent reduction in violent-crime arrests by participants.

“I think there’s more nuance to reducing crime than figuring out whether it’s going to be hot,” he said. “But there’s a lot sitting in that crime data, and stuff like this will become more useful.”

Photo at top: Violent crime rates tend to decrease in the winter in neighborhoods such as Lake View when fewer people are outside. (Dean DeChiaro/Medill)