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Some of the most interesting and informative aspects of criminal investigations are the motives and social or environmental conditions that contributed to specific criminal acts. From substance use to socioeconomic background and exposure to violent media, experts have attempted to understand the factors that make particular types of crimes more likely or that correlate to an increased overall crime rate. Studies in this area have made it clear that the circumstances that promote violence and crime are just as complex as the motivations of the perpetrators.

Recent research has tied a rise in crime rates to an environmental factor: the weather. Between extended cold spells to blistering summer heat, temperature and weather conditions have taken the blame for increased criminal activity in many different news stories covering a range of locations. In many cases, law enforcement officers and others seem convinced that atmospheric factors play a role in crime rates, but does the evidence actually show a correlation between weather and crime?

WHAT THE DATA SAYS ABOUT CRIME RATES AND TEMPERATURE

Fortunately, multiple studies have been completed to determine whether there is any truth to the claims that weather conditions in either extreme contribute to an increased likelihood of criminal activity. These studies have provided important insights into the ways that temperature influence the frequency of certain crimes.

WARM WEATHER LEADS TO HIGHER CRIME RATES

Tracking ambient temperature and crime rates, a Finland study used nearly two decades of data to identify a possible connection between them. Researchers found that temperature changes were responsible for 10 percent of fluctuations in the nation’s crime rates — a 1.7 percent increase in criminal activity for each degree centigrade rise in the temperature. More specifically, the study found that increased serotonin levels resulting from high temperature likely contributed to increased impulsivity and a higher risk of crimes.

A recent comparison of crime and temperature data across ten major U.S. cities echoed the findings of the Finland study. Looking only at the number of shootings, the investigation found that as temperatures rose, so did the number of shooting victims in nine out of the ten cities (the outlier, San Francisco, has weather patterns that are notably more moderate). Additional details provided by the city of Philadelphia reveal that the crime increase comes solely from outdoor incidents – the number of indoor shootings stayed the same despite dramatic changes in temperature.

CERTAIN CRIMES ARE MORE CLOSELY RELATED TO WEATHER CONDITIONS

Another major American city, Chicago, provides further insights into the impact of weather and temperature on crime rates. Police crime data from the City of Chicago Data Portal indicates that within the annual summer crime peak, certain types of crime appear more weather-dependent. Out of seven major crime categories, theft, along with shootings and other battery, saw the greatest increase as temperatures rose, with nine additional incidents for every 10-degree temperature increase.

Other categories of crime are correlated to a lesser extent, including criminal damage (five more incidents per 10-degree increase) and assault (three additional incidents). Burglary, narcotics and homicide were significantly impacted by weather variations, limiting the correlation of temperature to certain types of crime.

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OTHER WEATHER CONDITIONS SHOW LITTLE CORRELATION TO HIGH CRIME RATES

This trend of violent crimes rising with the temperature has been corroborated by several studies across the globe, but it appears to be the only weather condition that relates to an increase in crime. Data collected in the South African city of Tshwane found significantly higher rates of violent, sexual and property crimes on the hottest days; violent crimes in particular rose 50 percent compared to the city’s coldest days. Rainfall had a much less noticeable relationship to crime rates, with a decrease in violent and sexual crimes, and only a 2 percent increase in property crimes.

Similarly, during cold weather conditions (ranging from standard winter to brutal blizzard conditions), crime instances tend to decrease. Knowing that hot weather is a factor in crime rates is valuable for law enforcement, and even more important is understanding why temperature seems to have such an influence on violence.

HOW HOT TEMPERATURES MAY INFLUENCE CRIME

Current research and scholarship around the connection between temperature and crime, especially the most violent crimes, provides insights into the reason behind this intriguing correlation. Two main theories have been presented as the key reasons that hot temperatures may encourage additional criminal activity: the increase in opportunities for crime and the changes in temperament that result from warmer weather.

TEMPERATURE AND OPPORTUNITY

One of the most obvious explanations for weather’s apparent impact on crime is that warmer temperatures in general provide more opportunities for crime. Especially compared to cold or stormy weather, warm summer days encourage more time spent away from the home and more outdoor activities.

Along with increased opportunities for property-related crimes, there is an increase in interactions between people. Statistically speaking, more interactions provide a higher likelihood of a violent or criminal encounter. The Philadelphia study mentioned above is clear evidence of this connection between weather and opportunity.

TEMPERATURE AND HUMAN TEMPERAMENT

The other element that is often referenced in warm weather’s influence on crime is a change in temperament that occurs along with the change in temperature. In the Finland study, hot temperatures were linked to changes in brain chemistry that made impulse and aggressive actions more likely — and it is far from the only research to make this connection.

Craig Anderson, leader of Iowa’s Center for the Study of Violence and expert in human aggression, explains that heat doesn’t cause violence but does tend to encourage it. As an example, hot temperatures make it more likely a pitcher will hit the player at-bat, but only after a batter on the pitcher’s team has been hit. The heat escalates situations by causing people to perceive more aggression in certain acts than may be intended. In other words, the mental effect of a warm day that makes you more likely to honk your horn is the same one that contributes to greater violence in the heat of summer.

WHY A CONNECTION BETWEEN WEATHER AND CRIME MATTERS

The insight that hot temperatures do, in fact, have a connection to higher crime rates is important for several reasons. For those in law enforcement and related fields, this knowledge will help them prepare for the rise in violent acts that comes with a higher temperature. It can also provide a better understanding of the mental factors that contributed to the commission of a crime.

For environmentalists, the correlation between hot weather and crime is a valuable aspect of understanding the full impact of environmental changes on individuals. With the threat of global warming, temperature’s effect on crime rates becomes an even greater concern, and yet another reason to pay better attention to the environment.

Of course, temperature is just a part of the factors involved in an understanding of criminal justice and the environment, and it’s just one way that the two are connected to each other. At Virginia Wesleyan University, our online criminal justice degree and online environmental studies program are designed for students who want to explore this topic further. Our programs teach you the real-world skills you’ll need to succeed in your career, and we emphasize flexibility so that you can fit your education into your already busy life.

This article was originally published on the website of Virginia Wesleyan University and was re-posted with permission.