Hotter it is, the cooleryou are

We can speculate, of course. When it gets to 100 degrees in the shade, who can wear a hooded sweat shirt? Perhaps a .22 revolver feels icky-sticky. Nor are the criminally minded the only ones affected. As we weigh whether to slug the guy who spills beer on us in a bar, at a certain temperature we apparently conclude there is something to be said for having an ice-cold beverage trickle down our torsos.

It wasn8217;t always this way. Theories about the connection between temperature and aggression have been around for centuries. The Belgian social statistician Adolphe Quetelet concluded in the 19th century that people in hotter countries were more violent than people in colder countries.

The English language and the law have long assumed a linear relationship between heat and crime. Killing someone in 8216;8216;cold blood8217;8217; is seen as worse than murders committed in the 8216;8216;heat8217;8217; of passion, because we know that being hot or hot-blooded makes people lose control. People often say that when provoked their blood boils.

All this heat and bloodlust makes intuitive sense, but the relationship apparently breaks down when the temperature gets too hot. When scientists tracked the connection between the temperature and 911 calls for violent assault in two US cities, Minneapolis and Dallas, they found a curvilinear relationship8212;crime rose up to a point, then fell8212;making the shape of an inverted 8216;8216;U8217;8217;.

It is important to remember that temperature is not the only factor that affects fluctuations in the crime rate. The time of day, day of the week, population density, even whether a major holiday is underway, all have effects on crime. The temperature effect is overlaid on all these other factors, said Ellen Cohn, a criminologist at Florida International University.

Air-conditioning plays a role, too. If you remove the effects of sky-high heat in homes and office buildings, you bring people back into the range where they may be prone to slug each other. So does alcohol. If people drink a lot of beer because it is super hot, you might not see the decrease in crime at very high temperatures because alcohol raises the risk of assaults. There are times of the day when the inverted 8216;8216;U8217;8217; is more curvy, and times when it is nearly straight.

Cohn said the curious relationship between heat and assaults is most pronounced in the evenings, say between 6 and 9 p.m. If you compare 911 calls during that time on balmy, hot and very hot days, violent crime seems to rise at first, then fall when it gets very hot.

The theory has its critics. University of Michigan psychologist Brad Bushman says the relationship between hot weather and crime is linear8212;as it gets hotter, people get more aggressive, period. But laboratory experiments suggest Cohn might be onto something. When you get volunteers into a room and ask them to administer a painful shock to someone in response to an insult, the hotter you make the room, the stronger the shock that people are willing to administer. But when the room gets too hot, you start to see the same curious effect8212;people administer weaker shocks as they become very uncomfortable. At a certain point, people prefer to leave rather than fight, said psychologist Paul Bell at Colorado State University.

Shankar Vedantam