Hot tempers and hot weather — playwrights sensed the connection and made poetry of it. And it’s playing out again this week on our bloody streets.

For more than 100 years social scientists have researched and recorded it so that it is now almost a commonplace: aggression and violence increase as the temperature rises.

James Alan Fox, a professor of criminology at Northeastern University, collected data correlating daily temperatures with violent crime in Columbus, Ohio, in 2007. He showed there was more crime during the summer months and less as the weather cooled.