From the massacre at a Texas school to a hospital shooting in Tulsa and far fewer reported incidents, a recent wave of gun violence across America is confirming a trend law enforcement has long sworn to: homicides are increasing in warmer weather.
The link has been written about by criminologists for decades, with more recent research examining the precise relationship between temperature and crime rates.
For those who have studied the question, there is both common sense and possibly less obvious mechanisms at play.
First, the more obvious: “It’s hard to shoot someone when no one is around,” David Hemenway, a professor of health policy at Harvard’s TH Chan School of Public Health, told AFP, and explained why gun crime is lower in bad weather.
A second, more controversial idea is that heat itself — unlike weather that encourages people to go outside — can fuel conflict.
While there are many causes for the increasing gun violence in the United States, weather could play an increasingly important role in a world that is rapidly warming due to climate change.
Warm days in cold months
Hemenway said he has long been interested in the relationship between heat and higher crime, given the stereotypes about the north-south divide within the United States and Italy, as well as between the northern European states of Scandinavia and the southern Mediterranean countries.
In 2020, he co-wrote a paper in Injury Epidemiology, led by his then graduate student Paul Reeping, examining the city of Chicago between 2012 and 2016.
The newspaper used reports from the Chicago Tribune to get the number of shootings per day, then matched that with daily high temperature, humidity, wind speed, temperature difference from the historical average, and precipitation type and amount.
They found that a 10 degrees Celsius higher temperature was significantly associated with 34 percent more weekday shots and 42 percent more weekend or holiday shots.
They also found that a temperature 10°C higher than the average temperature was associated with a 33.8 percent higher number of shootings.
In other words, Hemenway said, it’s not just heat that matters, but also relative heat: “In the winter, there were more shootings on those days that wouldn’t be hot in the summer, but warm for the winter.”
Another recent paper, led by Leah Schinasi of Drexel University and published in the Journal of Urban Health in 2017, looked at violent crime in Philadelphia.
“I live in Philadelphia and I remember riding my bike home from work on a really hot day and seeing how grumpy everyone seemed. I was interested to see if this observation translated into higher crime rates on hot days,” she said. to AFP.
Indeed, she and co-author Ghassan Hamra found that violent crimes occurred more frequently in the warmer months — May to September — and were highest on the hottest days.
The contrast was most noticeable on comfortable days in the colder months — October to April — compared to colder days in those months.
When temperatures reached 21C (70F) during that period, daily violent crime rates were 16 percent higher compared to 6C (43F) days, the median for those months.
‘Limitation of damage’
Hemenway believes that both of the main hypotheses on the subject—that more people being outside opens up more opportunities for hostile interactions, and that heat itself makes people more aggressive—could be true.
A notable study published by the National Bureau of Economic Research in 2019 involved placing college students in Kenya and California in hot or cold rooms and measuring the impact on a number of behavioral categories.
It found that “heat significantly affects individuals’ willingness to voluntarily destroy other participants’ assets” in the form of gift cards and vouchers.
When it comes to the general problem of gun violence, there are far bigger drivers than temperature, Hemenway acknowledged.
These include the fact that there were an estimated 393 million guns in circulation in the United States in 2020, more than the number of people, while many states have moved in recent years to relax rather than tighten restrictions.
But a better understanding of its relationship to the weather could have policy implications, for example by finding more activities for young men to keep them off street corners on the hottest summer days, and strengthening police presence in key areas on the road. based on predictions.
“It’s kind of damage mitigation,” Hemenway said. “But even if this wasn’t a weapons issue, I suspect we’d find the same if we had evidence about combat and assault. What the weapons do is make hostile interactions more deadly.”
(Except for the headline, this story has not been edited by NDTV staff and has been published from a syndicated feed.)