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Hot and Bothered: Does Heat Make People Aggressive?

Reaching your "boiling point" may in fact be an accurate description.

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Yesterday, we had the first really hot, humid day of the year in Western Illinois. This followed a very long, difficult winter and a cold, rainy spring. Given how much I looked forward to warmer weather, one would think I would have relished the heat.

Instead, I found myself feeling, for want of a better word, cranky. I was sweating and tired, and in general my emotional reactions to the weather were more negative than positive. This got me to reflecting a bit on how the weather—especially hot temperatures—affects our feelings and behavior.

The relationship between heat and aggression is complicated. During the 1960s, the civil disturbances and riots that raged throughout the United States during the summer months gave rise to the journalistic expression “long hot summer.” This phrase reflected the common belief that hot weather made people behave aggressively and that the amount of violence was closely related to the temperature. However, it is hard to say for sure if heat was directly causing the problem. It's possible, for example, that in warmer weather there are simply more people out and about, resulting in more interaction and a greater likelihood of getting swept up in whatever ruckus might be occurring in the neighborhood.

Wanting to explore the nature of the relationship between heat and aggression in a more scientific way was the impetus behind an extensive program of laboratory research. Most of these studies placed individuals in situations where they could behave aggressively, often by administering electric shocks to another person. Usually, these “sham-shock” studies (no one was actually getting shocked, although the subjects did not know that) uncovered an “inverted U-shaped” relationship in which aggression increases with temperature up to a certain point (somewhere in the very high 80-degrees Fahrenheit range), but then decreases if temperatures start going even higher.

The conclusion of the laboratory research is at odds with the results of field research, which indicates that rising temperatures are always accompanied by increases in violent behaviors. Psychologist Craig Anderson used archival sources from cities across the United States to gather data on the rates of murder, rape, assault, robbery, burglary, and motor vehicle theft. He confirmed that violent crime increases with temperature but that nonviolent crime does not. In such field studies, hotter regions of the world and hotter years, seasons, months, and days are all linked with more aggression. Some studies even suggest that baseball pitchers throw more aggressively in hot weather, as there is an increase in the number of batters hit by pitches on hot days. This does not appear to occur because pitchers are fatigued or wilder, as there are not more walks or wild pitches in hot weather—it looks as if the pitchers are simply hitting more batters intentionally.

High temperatures may lead to a reduced attraction toward other people who we encounter, especially when the heat is accompanied by crowding; this makes us less helpful as well. Individuals who are exposed to warm temperatures in the laboratory are less likely to do nice things for others, even after the experiment is over, and extreme temperatures in winter or summer make people less willing to help others. In fact, drivers are more likely to honk their horns at stalled cars if they do not have air-conditioning in their own cars on hot days.

And heat can also have negative effects on health. This is especially true in cities where the heat from air conditioners, motor vehicle engines, and industrial sources make cities more than ten degrees hotter than the surrounding countryside. The effects of prolonged heat stress can range from exhaustion and headaches to delirium, heart attacks, and death. In other words, heat does not only make us angry—it can also make us sick.

The take-home message is that responding to heat in a negative way is very much a human thing—so if you find yourself getting a little testy with those around you this summer, relax; it isn’t just you. And stay cool!

More from Frank T. McAndrew Ph.D.
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More from Frank T. McAndrew Ph.D.
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