According to studies, an increase in testosterone and metabolic “fight or flight” changes indicate a possible link between violent crime and rising temperatures.



Many of us will admit to getting a little irritable and short-tempered in the sweltering heat. But is there evidence to support a correlation between hot weather and violent crime?

With temperatures soaring in Sydney and Melbourne, we thought we’d explore this idea. In short, the answer is yes – but it’s not as straightforward as that.


Hot weather and rising crime

The most interesting data to support the idea that rising temperatures increase violent crime rates comes from overseas.

There are studies from the US which suggest a clear link between violent crime and the heat, and it all comes down to biology.

In hot weather, the human body changes – our heart rates increase, we sweat, and there are metabolic changes too. These are associated with our sympathetic nervous system activity, which is linked to the “fight or flight” response in our brains.

Hot weather also increases testosterone production, and this tends to tilt the body towards “fight” rather than “flight”. Studies also suggest that in hot weather, people are more likely to interpret neutral signals as hostile, and are less likely to condemn violence. Put simply: overheated people have trouble thinking straight.

Matthew Ranson is an economist and statistician with an interest in health and the environment. He has conducted research into the probability of an increase in crime (not just violent crime) and global warming and predicts that in the US between 2010 and 2099, climate change will cause an additional 22,000 murders, 180,000 cases of sexual assault, 1.2 million aggravated assaults, 2.3 million simple assaults, 260,000 robberies, 1.2 million burglaries, 2.2 million cases of larceny and 580,000 cases of vehicle theft.

Many see Ranson’s findings as far-fetched, but there are other studies which add weight to the argument that hot weather increases the propensity towards violent crime. One such study is Heat and Violence by Professor Craig Anderson from the University of Iowa, which found that there are 2.6% more murders and assaults in the US in the summer than during winter, and that “hot summers produce a bigger increase in violence than cooler summers.”


Hot weather increases testosterone production, and there are metabolic changes associated with our sympathetic nervous system activity, which is linked to “fight or flight”. Put simply: overheated people have trouble thinking straight.


Another study, conducted by psychologists Ellen Cohn and James Rotton of Florida State University, looked at violent crime over a two-year period in Minneapolis, Minnesota. That study also found that violent crime increases with temperature, but only up to a point. The authors found that if the temperature rose too much – above about 30ºC – then a kind of heat-induced lethargy seems to set in and rather than fight, people tend to want to “flee”.

The problem with these studies however, is they don’t seem to take account of the fact that there may be more events which increase the likelihood of conflict – more music festivals and other outdoor events, more barbecues and gatherings which may give rise to family violence and so on.


Closer to home

Although the evidence is scant in Australia, figures from the Australian Institute of Criminology suggest that assault offences are seasonal, with numbers peaking between October and February.

Of course, if there is a direct relationship between heat and crime then it would stand to reason that the hottest places would also be the most violent, such as the Northern Territory in Australia.

On the face of it, the numbers do indeed support this notion: NT has the highest temperature – an average of 32ºC year-round, and for the past decade, it has also had the highest rates of murder and manslaughter in Australia – six times the national average. But as researchers point out, other socio-economic factors that come into play, such as poverty, homelessness, family break-downs, lack of education and alcohol consumption, which are prevalent in the territory.

And figures released in 2016 suggest that the state of Victoria was the murder capital of Australia. A year later, South Australia received the same honour. So, while it is possible that there is some link between heat and violence, it remains a relatively tenuous one.

Overall, the figures paint a positive picture for Australia – violent crime rates are in significant decline nationally. Murders and assaults have decreased over the past decade, as have break and enter offences, motor vehicle theft, robbery and general stealing offences.

But despite the decline and tenuous link between heat and crime, it’s probably a good idea to crank up the air-con and stay cool and calm on hot summer days.





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