I’ve just tested the temperature outside my open window and it is a pleasant 18C (64F). So I’m bolting it shut, because these lethal spring conditions are a crucible for crime.

High temperatures have long been linked with violence. Hotter countries tend to experience higher violent crime rates, riots tend to break out in high summer and “PC Rain” has long been regarded by police officers as a reliably effective crime-fighter.

An analysis of 6.6m police records covering a decade in Manchester by Peter Langmead-Jones of the Greater Manchester police suggests a more nuanced picture, however: that crime rises with the temperature, but peaks at 18C, and gradually falls thereafter.

“Thank God for Manchester weather,” tweeted one of the city’s police officers at the Society of Evidence-Based Policing conference last month, where the findings were unveiled.

If crime peaks at 18C in Manchester, it appears that criminals beyond northern England are less easily reformed by warmer weather. Psychologists Ellen Cohn and James Rotton studied assaults in Minneapolis and concluded that they rose with the temperature but only started to fall when it exceeded 24C.

Despite many studies suggesting hotter weather triggers a rise in crime – until it gets too hot – the association between crime and sunshine is still much debated. In Britain, for example, the modest decline in crime when temperatures rise above 18C has been attributed to the fact that many would-be offenders are on holiday.

Some criminologists have found that particular types of crime, such as domestic violence or antisocial behaviour, go on rising with temperatures, becoming more common the hotter things get. Others argue that apparent correlations between criminality and temperature don’t take account of the influence of time of day: crime is lower in the day, when temperatures are higher but people are working or at school, and highest in the evening, when people have time to themselves and temperatures are actually lower. US criminologists have argued that these influences disguise the fact that offences continue to rise with temperatures – and so hot summer evenings offer the perfect blend of opportunity and antagonism: windows left open and irascible people having the spare time to commit crime.

Perhaps the correlation between temperature and criminal behaviour will weaken or even reverse as we enter an era where most crimes are committed online, but some scientists suggest global warming will only make matters worse. If so, rather than equip police with thermometers, it might be best to take heed of the 1976 study that said the likelihood of physical aggression declines if hot people are given a nice cool drink.