The comprehensive study reveals that nearly seven percent of shootings can be attributed to above-average daily temperatures, even after adjusting for seasonal patterns. The findings indicate that the Northeast and Midwest regions experience the sharpest increases in gun violence on hotter-than-normal days.

“Our study provides strong evidence that daily temperature plays a meaningful role in gun violence fluctuations,” says study senior author Dr. Jonathan Jay, assistant professor of community health sciences at BUSPH, director of BUSPH’s Research on Innovations for Safety and Equity (RISE) Lab, and a partnering faculty member of Boston University’s Center for Climate and Health (BU CCH). “Even though some regions showed larger or smaller effects, the general pattern is remarkably consistent across cities.” …

For the study, Dr. Jay, Dr. Lyons, and colleagues utilized publicly available data from the Gun Violence Archive, a national repository of gun violence information. The team analyzed daily temperatures and more than 116,000 shootings from 2015 to 2020, in the top 100 US cities with the highest number of assault-related shootings in the country.

Accounting for seasonality and regional climate differences, they found that 7,973 shootings were attributable to above-average temperatures. The temperatures associated with increased gun violence varied considerably across cities. For example, both Seattle and Las Vegas experienced the highest elevated risk of gun violence during days when the temperature soared within the 96th percentile range of average daily temperatures—but for Seattle, that temperature was 84 degrees, while in Las Vegas, it was 104 degrees.

“Cities with high rates of firearm violence should continue to implement firearm-prevention strategies broadly including credible messenger programs and hospital-based violence intervention programs,” Dr. Lyons says. “What our study suggests is that for cities with more heat-attributable shootings, implementing heat adaptation strategies at the community level—such as greening efforts that have been effective at reducing urban heat islands and have some association with reductions in firearm violence—may be particularly important.”

So what might be driving this association between heat and gun violence? “It could be that heat causes stress, which makes people more likely to use aggression,” Dr. Jay says. “Or it could be that people are more likely to get out on warmer days and have more interactions, which creates more opportunities for conflict and violence. Most likely, it’s a combination of both.”

— Boston University in Warm Days are Contributing to Gun Violence Surge Across the US, Says Study of 100 Cities