"It's a simple but crucial fact that people tend to get out and about more when it's pleasant out," he said. "During the winter months, people can't get out. There aren't as many opportunities to interact."
Warm weather lets people mix socially, he said. And it is only a matter of probability that sometimes that mixture may prove volatile.
"More opportunity for violent crime means more violent crime," he said....Yet two American psychologists, Ellen Cohn and James Rotton, both of Florida State University, found their tipping point at a much lower temperature threshold. By analyzing violent crime rates over a two-year period, classifying assaults according to time, day of the week, month and temperature, they found that violence rose as the temperature rose to about 80 degrees Fahrenheit -- and then declined.