For more than a week, the Environment Canada website for the Victoria forecast pronounced: “Be prepared for … HEAT!”
Normally, the notices above the daily weather predictions warn of coming high winds, storms, freezing temperatures, thick fog or heavy rains. This time, it cautioned us to expect a heat wave.
Caution, indeed, is needed when so many studies document a link between high temperatures and aggression. Aggression can range from snappish impatience at home, at work or in line at the grocery store, to road rage, verbal abuse and violent crimes such as assault and murder.
The link shows up in our language. The words “temper” and “temperature” share the same Latin origin, temperare — meaning to restrain or to mix. In that wonderful way the English language moulds and changes words and their meanings, the definition of temper — anger — has deviated from the original definition. In fact, temper (anger) often has little to do with restraint.
Common expressions reinforce the link between heat and aggression in English. “Tempers flare,” “a hot temper,” “hot under the collar,” “hot-headed,” “short fuse,” “slow burn,” “let off steam” and “smouldering resentment” come to mind.
Psychologists and sociologists who study how heat influences emotions and behaviour believe high temperatures exacerbate already near-boiling levels of stress in people, bringing them closer to losing control.
Heat is, in itself, a stressor. It makes people uncomfortable, leading to impatience. It can lead to dehydration, which affects the brain’s ability to function and reason. The combination of discomfort and dehydration interferes with a person’s ability to regulate emotions. It causes the brain’s fright-fight-flight centre to react to even mild events, and short-circuits the reasoning part of the brain that would normally temper (restrain) temper (anger).
And that’s looking at heat’s effects at an individual level. Warming temperatures and climate appear to also affect peace and well-being across entire societies.
Researchers from Princeton University and the University of California-Berkeley analyzed 60 studies exploring the connection between weather and violence.
They examined information from archeology, criminology, economics, psychology and many other fields of study to calculate the risk that violence could increase under hotter and wetter climate conditions. The data they drew on included events in human history dating from 12,000 years ago to the present.
They examined three categories of violence. Personal violence and crime includes murder, assault, rape and domestic violence. Intergroup violence and political instability includes events such as civil wars, riots, ethnic violence and land invasions. Institutional breakdowns include abrupt and major changes in governments or the collapse of civilizations.
Based on these analyses, the researchers concluded that even slight increases in temperature and precipitation have greatly increased the risk of personal violence and social upheaval throughout human history. They found that shifts in climate predictably amplified violence in all three categories of violence, regardless of geography, societal wealth or the time in history.
For instance, aberrantly warm climate coincided with incidents that included spikes in domestic violence in India and Australia; increased assaults and murders in the U.S. and Tanzania; ethnic violence in Europe and South Asia; and wars and displacement in Middle Ages Europe.
Most alarming of all, the climate shifts need not be extreme. Warming a country in Africa, for example, by 0.3 C for one year, or a region in a country like the U.S. by 3 C for just a month, boosts the risk of a riot, civil war or ethnic conflict in the region by an average of 14 per cent. Both those examples equal one standard-deviation shift away from normal temperatures.
Most climate-change models predict an average of two to four standard-deviation shifts in global climate conditions by 2050.
So, with seasons expected to become more extreme, our individual and collective tempers may also rise with summer temperatures.
