Temperature and Violent Crime: Implications of Climate Change?

Exploring the link between outdoor temperature and violent crime in American cities.

By Janet L. Gamble, Ph.D.

Dallas, Texas

Has a hot and humid day ever made you cranky?  If so, you might ask this question: can hotter days lead to more human conflict?  Scientists at the U.S. EPA and the Emory University School of Medicine are investigating whether hotter temperatures affect violent crimes, such as assault, robbery, rape, and murder.

According to the Federal Bureau of Investigation, many factors influence violent crime, including weather, age, population density, family cohesiveness and divorce rates, effectiveness of law enforcement, and others. Weather is of particular interest due to an observed association between crime and temperature. This relationship raises the question of whether the hotter temperatures that are expected to accompany climate change may contribute to increased rates of violent crime.

In our recent paper published in the Western Journal of Emergency Medicine, “Temperature and Violent Crime in Dallas, Texas: Relationships and Implications of Climate Change,” we examined the relationship between daily temperature and daily incidence of violent crime in Dallas from 1993 to 1999.

We determined that the relationship in Dallas is not simply a linear function. Rather, while we found that daily rates of violent crime increase as temperatures rise in the low to moderate range, they begin to level off at temperatures above 80°F, and actually decrease above 90°F. In other words, we observe that as it gets very hot there are fewer violent crimes (see Figure 1).

Figure 1. According to analyses of violent crime and temperature in Dallas TX, we found that aggravated assaults and other violent crimes decrease at high ambient temperatures.

We were a bit surprised by our results, because prior studies have found linear and increasing crime rates even at very high temperatures. To explain our findings, we hypothesize that when it gets very hot people stay indoors where it is cooler. As a result, street crime and other crimes of opportunity are decreased. If this is correct, the higher temperatures expected to accompany climate change are unlikely to result in an increased rate of violent crime.

Yet, this is just one city and one study.  Would we get the same results in different cities with different ranges of daily temperatures? To answer this question, we are conducting analyses of multiple U.S. cities: Atlanta, Denver, Houston, and Chicago and re-doing the analysis for Dallas using more recent data. Stay tuned for more information as our climate change research continues.

About the Author: Dr. Gamble is a research scientist in the National Center for Environmental Assessment in the Office of Research and Development at the U.S. EPA.