On chilly autumn days like today, I remember why I love the warmth of the summer so much. It always takes me by surprise when the season for thick jackets and heavy boots comes around. Personally, freezing in the cold outside air isn’t my cup of tea, so I’d rather stay heated indoors in the warmth of a blanket and a cup of hot tea. It’s safe to say that this mentality is shared with the majority of people, as I’ve noticed few people walking leisurely on the streets here in Toronto compared to the pleasant summer months. Coincidentally, I also find that crime reports aren’t as frequent on the news compared to the summer. This leads me to inquire if it’s truly a coincidence or if high temperatures induce higher crime rates.
Since frigid temperatures discourage people from going outside, it puts less people at risk of being the victim of a crime. During the colder months homes are less likely to be robbed since people will be occupying them. Empirical data gathered by the University of North Carolina suggests that a 1 degree Fahrenheit increase in temperature variation increases the amplitude of violent crime by 4.9%. Crime is 22% higher in the summer than winter, and tends to peak on August 1st . The impact of temperature could be through either: the fact that more people are outside during warm weather or the hot-head theory – people get aggravated more quickly in the hot temperatures. Simply put, there is a strong positive relationship between temperature and criminal behavior. Crime has a price tag. The burden falls on the government as well as taxpayers. According to the Department of Justice’s 2008 report, the total cost of Criminal Code offenses in Canada is about $99.6 billion. Of this total, tangible costs – social and economic – came up to $68.2 billion and intangible costs – pain, suffering, and loss of life – summed up to $31.4 billion (2008 CAD).
With temperature projected to increase due to climate change, this could lead to rising crime rates. Economist Matthew Ranson conducted a study  on the FBI’s Uniform Crime Reports  and estimated that between the years 2010 and 2099, climate change, in the United States alone, will cause an additional:
·200,000 cases of rape,
·1.3 million cases of vehicle theft,
·1.4 million aggravated assaults,
·2.2 million simple assaults,
·3.0 million cases of larceny
·3.2 million burglaries
Projects such as planting street trees, installing green roofs, or even replacing asphalt with permeable pavement can naturally cool cities, leading to reduced heat-induced crimes.The benefit of adding greenery and vegetation to a city can be analyzed in AutoCASE. Suppose you plant 1 million full-grown trees in Baltimore , our models estimate that this reduces temperatures in the city by an average of 0.33 Fahrenheit. Currently we only look at the mortality impact of this change in temperature, but, we are working on expanding the number of benefits linked to the urban heat island effect. In this case, a 0.33 degree reduction in temperatures would reduce violent crime by about 1.61%, according to the literature . This crime reduction is valued at $0.18 (2011 USD) per tree, and with 1 million trees this would lead to a total benefit of $180,000 per year . This is an impact we are currently considering adding to AutoCASE after a more in-depth review of the relevant literature.
It’s important to point out that other factors may affect the crime rate, such as changes in the unemployment rate, culture, the number of drinking/entertainment establishes, population density, and social organization. For example, a 1% increase in the percentage of divorce rates is correlated with a 7% increase in the violent crime rate . So crime cannot be solved by focusing on just one solution. But on the individual level, we can do our part by landscaping our outdoor spaces and rooftops to cool down our cities. With each household and building that adopts greenery, we can potentially minimize the impact that the urban heat island effect has on crime, and promote a safer community to live in.
 Hipp, et al., “Crimes of Opportunity or Crimes of Emotion? Testing Two Explanations of Seasonal Change in Crime”(Social Forces, June 2004)
 Zhang, “Costs of Crime in Canada, 2008”(Department of Justice Canada, 2008)
 Ranson, “Crime, Weather, and Climate Change”(Harvard Kennedy School M-RCBG Associate Working Paper Series No. 8, November 2012)
 United States. Federal Bureau of Investigation, “Uniform Crime Reports”(U.S. Department of Justice, 2010)
 United States. United States Census Bureau, “Annual Estimates of the Resident Population for Incorporated Places of 50,000 or More, Ranked by July 1, 2014 Population: April 1, 2010 to July 1, 2014” (U.S. Census Bureau, 2014)