With Warmer Winters Comes More Violent Crime

If stronger hurricanes can't convince you that climate change is dangerous, how about the increased odds of getting mugged?
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Researchers found higher rates of both violent and property crimes during periods of higher winter temperatures.

Researchers found higher rates of both violent and property crimes during periods of higher winter temperatures.

It can be difficult to get conservatives—especially those in America—to acknowledge the dangers of climate change. When it comes to personal perils, they are more inclined to be preoccupied with crime.

Here's a talking point that may resonate with these Americans: It turns out the two threats are related. New research finds that warmer winters are associated with higher levels of crime.

"During mild winters, more people are out and about, creating the key ingredient for interpersonal crimes: opportunity," lead author Ryan Harp, of the University of Colorado–Boulder, said in announcing the findings.

Using a huge data set, Harp and co-author Kristopher Karnauskas found higher rates of both violent and property crimes during periods of higher winter temperatures. This association was not found for the summer months.

The researchers used monthly crime data from the Federal Bureau of Investigation's Uniform Crime Reporting program, which covers more than 16,000 American cities from 1979 to 2016, and includes data on a variety of crimes, including murder, rape, aggravated assault, burglary, and motor-vehicle theft. Year-to-year climate fluctuations for each city were estimated using data from the National Oceanic and Atmospheric Administration.

Somewhat to their surprise, the researchers found that average temperatures had a strong impact on crime rates—but only in the traditionally colder months. "We were expecting to find a more consistent relationship," said Harp, a doctoral candidate in the university's Department of Atmospheric and Oceanic Sciences.

Specifically, for both violent and property crimes, "the relationship strength peaks with statistically significant relationships in the winter months," the researchers write in the journal GeoHealth, "but is reduced and loses statistical significance during the summer and fall."

As the researchers note, these results throw cold water on the theory that crime increases in periods of intense heat because of heat-induced irritation. Rather, they suggest that weather affects crime to the extent that it influences behavior patterns.

In other words, milder winter temperatures, which some see as the sole positive outcome of climate change, are not uniformly positive. Muggy weather is unpleasant, but we may need to worry more about mugging weather.

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