According to an expansive new study, when the temperature rises, so does our propensity to commit crime.



recent United Nations report confirmed what most already know – that more action is required to prevent the catastrophic effects of global warming.

Meanwhile, an exhaustive study of crime data over a 10-year period suggests that violent crime and disorderly conduct are most prevalent on hotter-than-average days.


The study

Researchers from Drexel University in Philadelphia analysed crime rates in the state from 2006 to 2015.

They found the rate of crime was consistently highest in the warmest months of the year – from May to September in the United States – and further that crime was the most prevalent on hotter-than-average days, regardless of the season.

The study found that when the heat index – which uses temperature and humidity to determine comfort – was 98 degrees, rates of violent crime were 9% higher than on days when the index was 57 degrees. Rates of public disorder offences were 7% higher on 98-degree days than on 57-degree days.

It further found that in the colder months – October through to April – rates of violent crime were 16% higher on days when the index was above 70 degrees, compared to the median level of 43 degrees. Rates of disorderly conduct were found to be 23% higher.


Other research

A previous study in Chicago found that between 2012 and 2017, rates of battery, shootings, theft and criminal damage increased significantly on the hotter days. Only drug crimes and homicides remained consistent.

The trend was also found to be evident in the United Kingdom, with data from the London Metropolitan Police suggesting that between April 2010 and June 2018, violent crime was on average 14% higher when the temperature was above 20 degrees than when it was below 10C. Harassment and weapons possession offences were each found to be 16% higher.

A study in Mexico similarly found that over a 16 year period, 1 degree Celsius increase in temperature correlated with an increase across all crime types of 1.3%. It also found there were over 30% more accusations of crime on days hotter than 32C than on days cooler than 10C.

Researcher John Simister reasons that relative rather than absolute temperature is the determining factor – finding that rises in temperature rather than the temperature itself are what corresponds with increases in crime, regardless of whether a nation is generally hot or cold.


Social gathering theory

The lead researcher of the Drexel University study, Dr Leah Schinasi, speculates that a reason for the disparity is simply that most people stay indoors when it is cold.

“As temperatures become more comfortable, more people are outdoors, which presents greater opportunity for crime,” she remarks.

John Roman, a senior fellow at the Urban Institute’s Justice Policy Center, similarly states: “When it’s warmer and when people want to go out more, they’re putting themselves in places in which they’re more likely to be victimised.”

He additionally points out that there are modest rises in crime rates during school breaks and public holidays.

However, Dr Schinasi notes that crime rates rose when it was warmer than average at times when it was still too cool to venture outside.


Physiological theory

Criminologist Larry Siegel suggests the relationship between warmer weather and crime may be partially a result of hormonal changes linked to stress and tension.

He points out that the body generates the stress hormones of adrenaline and testosterone in response to excessive heat, and that these are linked to aggressive behaviour.

Another study published by the Association for Psychological Science found that baseball pitchers in the United States are more likely to hit opposition players in retribution when the temperature is warmer.

And research by the University of California found that a drop in happiness between a day in the range of 15 to 20 degrees Celsius and a day in the range of 27 to 32 degrees Celsius was comparable to the drop in happiness that the average American feels from Sunday to Monday, which is suggests may contribute to aggression and crime.





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