From a Texas school massacre to a Tulsa hospital shooting and many less-reported incidents, a recent wave of gun violence across America confirms a trend that police departments have long sworn to: murders are rising by warm weather.
The link has been written about for decades by criminologists, with more recent research on the precise relationship between temperature and crime rates.
For those who have studied the matter, there is common sense as well as potentially less obvious mechanics at play.
First, the most obvious: “It’s hard to shoot someone if there’s no one around,” David Hemenway, professor of health policy at Harvard TH Chan School, told AFP. of Public Health, explaining why gun crime is lower in bad weather.
A second, more controversial idea is that the heat itself – as opposed to the weather which encourages people to go out – could rekindle conflict.
While there are many causes behind the rise in gun violence in the United States, the weather could play an increasingly important role in a rapidly warming world due to climate change.
Hot days during cold months
Hemenway said he has long been interested in the relationship between heat and crime, given stereotypes about the north-south divide in the United States and Italy, as well as between northern states. Europe, Scandinavia, and southern Mediterranean countries.
In 2020, he co-authored a paper on 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 compared them to the daily high temperature, humidity, wind speed, temperature difference from the historical average and the type and amount of precipitation.
They found that a 10 degree Celsius higher temperature was significantly associated with 34% more shots on weekdays and 42% more shots on weekends or holidays.
They also found that a temperature 10°C above average was associated with a 33.8% higher firing rate.
In other words, Hemenway said, it’s not just the heat that’s important, but the relative heat: “In the winter, there were more shoots on those days that wouldn’t have been hot in the summer. but which were warm for the winter.”
Another recent paper, led by Drexel University’s Leah Schinasi and published in the Journal of Urban Health in 2017, examined violent crime in Philadelphia.
“I live in Philadelphia, and I remember riding my bike home from work on a very hot day and observing how grumpy everyone seemed. I was curious to see if that observation translated by higher crime rates in hot weather,” she told AFP.
She and co-author Ghassan Hamra found that violent crime happened more often during the hottest months – May to September – and was highest on the hottest days.
The contrast was most striking on the comfortable days of the colder months – October through April – compared to the colder days of those months.
When temperatures reached 21°C (70°F) during this period, daily violent crime rates were 16% higher compared to days of 6°C (43°F), the median for those months.
Hemenway thinks the two main hypotheses on the subject — that more people outdoors opens up more possibilities for hostile interactions, and that heat itself makes people more aggressive — might be true.
A striking study published by the National Bureau of Economic Research in 2019 involved placing university students in Kenya and California in hot or cold rooms and measuring the impact on a number of behavioral categories.
He 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 overall problem of gun violence, there are far more important factors than the weather, Hemenway acknowledged.
These include the fact that there were an estimated 393 million firearms in circulation in the United States in 2020, more than the number of people, as many states have taken steps in recent years to ease instead only to tighten restrictions.
But a better understanding of the relationship to the weather could have policy implications – for example, finding more activities for young men to keep them away from street corners on the hottest summer days and increasing police presence. in key areas based on forecasts.
“It’s kind of harm reduction,” Hemenway said. “But even if it wasn’t a gun problem, I suspect we’d find the same thing if we had evidence of fights and assaults. What guns do is make the more deadly hostile interactions.”
(Except for the title, this story has not been edited by NDTV staff and is published from a syndicated feed.)