New research published in the Journal of Urban Health has analyzed crime data in Philadelphia for 10 years and found that rates of violent crime and disorderly conduct are higher when the weather is warmer and more pleasant, even rising sharply during warmer-than-typical winter days.
When the heat index (a metric that uses temperature and humidity to represent human comfort) was 98 degrees, rates of violent crime were 9% higher compared to days when the temperature was 57 degrees. When it came to rates of disorderly conduct, they were 7% higher on 98-degree days than on 57-degree days.
During the year's colder months, the contrast of high versus low rates of crime on more comfortable versus cooler temperature days was more striking. When temperatures reached 70 degrees during that time period, daily rates of violent crime were 16% higher and disorderly conduct rates were 23% higher, compared to 43 degree days, the median heat index for that period.
The researchers also looked at deviations of daily temperatures from seasonal averages in trying to determine the effect of anomalies on crime rates. For example, during cool months, days that were 55 degrees warmer than the seasonal average were associated with 7% higher rates of disorderly conduct.
The study findings are reasonable when you think about social behaviour. When temperatures are extremely cold or hot, people stay indoors. But as temperatures become more comfortable, more people are outdoors, which presents greater opportunity for crime. Following that more pleasant weather results in more crime, it could be assumed that cooler days in hot weather months would result in more crime.
But that does not seem to be the case, as crime rates remained fairly static during the hotter–weather months when temperatures dip below the seasonal average. Overall, these results still reflect that higher rates of crime occur when temperatures are warmer. Additional analyses that tease apart these effects will help us to better understand these findings and seasonal trends.
The team suggested additional research into the locations of crime and the particulars of the areas, like infrastructure and neighbourhood characteristics, would divulge more insight. Regardless, seeing increases in crime during warmer days is particularly concerning when taking climate change into account. The research is potentially a picture of what could happen if warmer days become the norm.
It is important to recognize the implications of these climate change effects for public health, including changes in crime rates. Although these results back up police officers' anecdotal reports about the relationship between temperature and crime, it's nice to have data to confirm these reports. The study results might help inform local law enforcement about ways to allocate resources during different seasons and with consideration of the local climate.