As cities try to reduce gun violence, they may face an unexpected roadblock: heat.

A recent study finds that hotter-than-normal days come with a higher risk of shootings.

Researchers looked at data from a hundred U.S. cities over a six-year period. They found that as temperatures increased, so did the rate of gun violence.

“I think the key finding from the study is that almost 7% of shootings in U.S. cities are attributable to daily temperature differences,” says Jonathan Jay, a public health researcher at Boston University and one of the study authors.

The exact link between heat and gun violence is not yet clear, but Jay says that when it’s hot and people are uncomfortable, they’re more likely to act aggressively.

And on warmer days, people are also more likely to be outside, interacting with others.

“Pretty simple interpersonal disputes are the single most common reason that gun violence occurs,” he says.

So the study suggests that as the climate warms, cities may have to contend with more gun violence. But they can work to counter the trend by planting trees and taking other steps to reduce urban heat.

“This is just one more important reason to address climate change,” Jay says.

Reporting credit: Ethan Freedman/ChavoBart Digital Media