Nav: Home

Violent crime rates rise in warmer winters

November 13, 2018

As global temperatures climb, warmer winters in parts of the country may set the scene for higher rates of violent crimes such as assault and robbery, according to a new CIRES study.

"During mild winters, more people are out and about, creating the key ingredient for interpersonal crimes: opportunity," said Ryan Harp, a CIRES/CU Boulder Ph.D. student and lead author of the study published today in the AGU's cross-disciplinary journal, GeoHealth.

In an innovative new assessment, Harp and his advisor, CIRES Fellow Kris Karnauskas, used powerful climate analysis techniques to investigate the relationship between year-to-year fluctuations in climate and violent crime rates in U.S. cities since 1979. Their methods accounted for the fact that crime rates have dropped significantly since the 1990s in most places. These long-term trends, driven by many societal factors, create the "baseline" for the new analysis. "Consequently, we considered the crime rate differences from that baseline," said Karnauskas, who is also an Associate Professor of Atmospheric and Oceanic Sciences at the University of Colorado Boulder.

He and Harp obtained monthly violent and property crime data for over 16,000 cities directly from the FBI, specifically the Uniform Crime Reporting (UCR) Program. The database, which was snail-mailed to Karnauskas' lab after only a few phone calls and extraction from tape drives at a FBI data center in West Virginia, included all types of violent crimes including murder, rape, robbery, aggravated assault, burglary, larceny, and motor vehicle theft. The scientists relied on historical climate data from NOAA's North American Regional Reanalysis (NARR).

They divvied data up by broad climate regions in the United States, and then measured the strength of the relationship between climate variables and crime in each region.

Combining these data sets revealed a strong relationship between crime and temperature, in particular, including a much stronger correlation in winter than in summer months. For example, in winter in the northeastern United States, the relationship was so tight that temperature changes alone could explain more than half of the year-to-year ups and downs in crime rates. In the summer, the relationship between temperature and crime patterns diminished.

The strength of the wintertime correlation was surprising, Harp said, given that crime rates vary for all kinds of reasons.

"It's highly unusual to find correlations this high in big, messy data sets, especially spanning disciplines like climate and health or sociology. The initial disbelief forced us to recheck our work more than a couple of times," Karnauskas added.

Part of the power in the new research approach, he and Harp said, was "zooming out" from a city-by-city approach to look at all cities within a climate region. When researchers study only a single city, a local change in, for example, policing or demographics might have made it harder to pick out the impact of temperatures on crime. By aggregating thousands of cities into a region that simultaneously experiences similar year-to-year fluctuations, the connection between temperature and crime became obvious.

The new assessment also provides insight into why climate anomalies affect crime rates, including some of the strongest evidence to date in support of one theory about how crime patterns may be linked with weather and climate: The Routine Activities Theory. That theory states that despite the complexity of human behavior and external forces, interpersonal crime is driven by a relatively simple combination of ingredients: a motivated offender, a suitable target, and the absence of a guardian who could prevent a violation. So pleasant weather may increase the chances of all three factors converging; lousy weather may decrease it.

In addition to Routine Activities is the Temperature-Aggression Hypothesis, which suggests that people act more aggressively in extreme heat. Because Harp and Karnauskas found that the relationship between temperature and crime rates loosened during summer, Routine Activities Theory likely explains what we're seeing, Harp said. During mild winters, more people are out and about more often than during colder times, creating the opportunity for interaction.

These findings imply that in some regions of the United States, warming temperatures due to anthropogenic climate change could exacerbate crime rates, especially in winter, Harp said. He and his colleagues are now dissecting data and building models with an eye to predicting future crime rates, as well as how crime might be affected by the world's changing climate.

"This study is significant because it broadens our thinking on connections between climate and human health, to encompass a very real and dangerous threat to our bodily safety and, therefore, health," said Karnauskas.
-end-


University of Colorado at Boulder

Related Climate Articles:

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.
Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.
How aerosols affect our climate
Greenhouse gases may get more attention, but aerosols -- from car exhaust to volcanic eruptions -- also have a major impact on the Earth's climate.
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
How trees could save the climate
Around 0.9 billion hectares of land worldwide would be suitable for reforestation, which could ultimately capture two thirds of human-made carbon emissions.
Climate undermined by lobbying
For all the evidence that the benefits of reducing greenhouse gases outweigh the costs of regulation, disturbingly few domestic climate change policies have been enacted around the world so far.
Climate education for kids increases climate concerns for parents
A new study from North Carolina State University finds that educating children about climate change increases their parents' concerns about climate change.
Inclusion of a crop model in a climate model to promote climate modeling
A new crop-climate model provides a good tool to investigate the relationship between crop development and climate change for global change studies.
Natural climate solutions are not enough
To stabilize the Earth's climate for people and ecosystems, it is imperative to ramp up natural climate solutions and, at the same time, accelerate mitigation efforts across the energy and industrial sectors, according to a new policy perspective published today in Science.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
More Climate News and Climate Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at Radiolab.org/donate.