Effects of temperature on violent crime in Dallas, Texas: Implications for climate change

Purpose. This study examines the relationship between mean ambient temperatures and violent crime in a large U.S. city. Study Question. We ask whether warmer ambient temperatures may be associated with increased aggression and whether that relationship is best described as an increasing linear function, as reported in prior studies. We also ask whether the warming that may accompany climate change is likely to be significantly associated with increased violence. Methods. Time series piece-wise regression and plots of daily data are used to analyze daily fluctuations in mean temperature and other meteorological and temporal variables and their relationships to four categories of violent crime reported in Dallas Texas from 1993-1999. Results. Daily mean temperatures ranged from 19°F to 97°F. Mean daily counts of aggravated assaults were 111.7 with slightly higher means in summer (120.0) than winter (100.4). We find that daily mean ambient temperature is related in a non-linear fashion to daily records of violent crimes (including aggravated assaults, homicides, rapes, and suicide). Regression results and plots of mean temperature and daily counts of aggravated assaults support a curvilinear hypothesis, showing a positive relationship that begins to moderate slightly beyond mean temperatures of 80°F and then turns negative beyond 90°F. Conclusions. This analysis contradicts studies that find a consistently positive linear association between temperature and aggression and project increases in violent crime with global warming. This study finds, instead, that aggression moderates or even decreases at high ambient temperatures. We conclude that higher temperatures may encourage people to seek shelter in cooler indoor spaces, and that “street” crime is subsequently decreased. This finding also suggests that the higher ambient temperatures associated with climate change may not be expected to be accompanied by higher rates of violent crime. Additional studies in locales with a variety of daily temperatures are indicated.