Some of the first hints that hot temperatures can mess up minds, however, came from studies on humans. Back in the 1800s, Belgian astronomer Adolphe Quetelet noticed that violent crime in France peaked in the summer. Later studies linked high temperatures with gun violence, mental-health-related hospital admissions, suicide, and gambling. When it’s hot, people have trouble making decisions, and their memory suffers. For students at schools without air conditioning, a school year just one degree Fahrenheit hotter reduces test scores by 1 percent, a study found.
Increasingly, there’s evidence that other species may also be more aggressive when mercury shoots up. A 2023 study that combed through nearly 70,000 reports of dogs biting people across eight US cities, from Chicago to Baltimore, found that such incidents were more likely to happen on hot, sunny, and smoggy days. The risk was 10 percent higher on a 90° F day than on a 60° F day—and not only because people are more apt to venture out for walks when the sun is shining (the researchers controlled for seasonal effects in their data).
Still, the scientists were unable to determine whether dogs get more aggressive as it gets hot, or if cranky humans provoke more attacks. “It’s likely that both humans and dogs get stressed and more irate at higher temperatures,” said Clas Linnman, a neuroscientist at the University of Miami and a coauthor on the study.
And it’s not only dogs: A 2025 study out of China showed that many animals, including snakes and cats, are more inclined to bite people when it gets hot.
Animals also seem to lose their cool with each other, especially if there is food involved. Scientists used binoculars and spotting scopes to spy on wild goat-like chamois that feed on protein-rich plants on the slopes of the Italian Apennine Mountains. More than 1,600 hours of observations over two summers revealed that when temperatures rose from 54° to 64° F, vegetation grew scarcer, and chamois aggression in turn shot up. The animals became territorial over patches of food, they assumed threatening postures, chased each other—attacks that, at times, escalated. The study authors predict that chamois aggression will go up 50 percent by 2080 due to climate change.