Donders Wonders Blog

Heat makes us more aggressive and violent

This post is also available in Dutch.

The Netherlands is recovering from what was the warmest May in three centuries and more heat will come our way soon. High temperatures don’t only make you sweat, but according to research it also makes us more aggressive! How does that work?

The warmth heats us up, literally and figuratively.
Picture: CC0, Pexels

Various scientists have studied this interesting question: the influence of warmth on aggression and violence. They pretty much all come to the same conclusion: as the temperature rises, aggression and violence increase.

Warm countries and cities have higher crime rates
Let us begin with research on areas with different climates. This shows that the closer you live to the equator, the more violent it is: for every 100.000 people there are 26 murders in Central-America, 18 in Central-Africa, and 5 in Europe and North-America. Of course these areas differ from each other in more than one way. However, this pattern can also be seen within countries. For example, mafia-related crimes are far more frequent in southern Italy than in the north. Additionally, crime rates in the USA are higher in warmer cities than in cooler ones, even when controlling for social and cultural factors.

Warm days, months and years come with more aggression
Apart from temperature differences between areas, periodical differences in temperature also influence aggression and violence. An American longitudinal study spanning 45 years shows that violent attacks increase in warm years and seasons. Non-violent crimes were unaffected by temperature. Additionally, Veilig Verkeer Nederland (VVN, or ‘Safe Traffic Netherlands’) observed that in our country traffic-related death and injury rates are 30% higher in the summer compared to the winter. The VVN indicates that this is probably due to increased aggressive-driving behaviors in the summer, since driving conditions are then more optimal.

Climate change and crime
Now that we know that higher temperatures are associated with more aggression and higher crime rates, we can also predict how climate change might affect this. Most climate change experts predict that the temperature will increase from 1-4.5°C in the year 2050. According to researchers, in America this will lead to a 25.000 to 80.000 increase in crime and murder rates. So, this is an additional reason to fight climate change.

Why do we become more aggressive when temperatures rise?
People become more aggressive in warm conditions because their body temperature also increases. An increase in body temperature is accompanied by increased heart rate and blood pressure, sweating of the skin, and heavy respiration. Researchers call this an increase in arousal. But we are not always aware of why this happens: unconsciously you might attribute this warmth-related increase in arousal to something else (because your neighbor really acted horribly today!), which then makes you angry. Due to this so-called excitation transfer an increase in body temperature can wrongly be interpreted as anger which leads to more aggression and violence.

So, for the upcoming hot summer days: if you notice you are becoming a bit more sensitive and aroused, keep in mind that this may not be caused by the people or events around you. High arousal might very well be the result of the heat. Try to find some shade to keep your head cool!

Blog was written by Angelique, edited by Annelies, and translated by Felix.

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