Dear EarthTalk:

What's the connection, if any, between the onset of global warming and an increase in violent human behavior?

Robert C., Southampton, MA

It's not uncommon to hear talk about the dire consequences of global warming—rising-sea levels, extreme weather and ecological disruptions. But there's another dimension to this crisis that doesn’t get much attention but is equally concerning: the link between global warming and increased violent behavior.

Indeed, a new study from University of Washington and Boston University researchers that surveyed data from 100 U.S. cities found that hotter-than-normal days—which we are getting more of every year thanks to global warming—coincide with higher incidences of gun violence. Several other previous studies underscore the connection between warmer temperatures and violence, with murder, rape and assault rates higher across the board during warmer-than-average stretches of days, months, seasons and years. 

How does this add up? Researchers believe that prolonged exposure to climate change-related stressors can lead to anxiety, depression, and even post-traumatic stress disorder (PTSD)—and that those experiencing these mental health issues may be more susceptible to engaging in violent behaviors as a coping mechanism or due to their altered mental state.

According to Iowa State University psychology researcher Craig Anderson, higher temperatures cause the brain to divert resources to other parts of the body in order to cool down. When this happens, parts of the brain are not running at full capacity, making it harder to process new information, manage emotions and control impulses. People who are hot are also more likely to perceive others as behaving aggressively, which increases the odds of hostile confrontations. “Heat stress primes people to act more aggressively,” reports Anderson. “We can see this play out on a larger scale across geographic regions and over time.”

While it’s clear that hotter temperatures can rile people up more than usual, the ripple effect on society at large is more troubling. The predicted decline in crop yields and scarcity of drinking water in a fast-warming world could act like a multiplier effect on our tendency to get short-tempered when we heat up, and regional violent conflicts over essential resources—food and water—are the likely result.

Historians point to the 2011 civil war in Syria as an example of climate change catalyzing violent conflict. Prolonged warming-induced droughts there contributed to crop failures and displacement of rural communities which exacerbated existing social and political tensions creating an environment that erupted into full-scale civil war. These types of conflicts are likely to become more and more common as we continue to add more and more greenhouse gasses into the atmosphere.

One way to minimize warming-induced violence at the meta level is to reduce warming by reducing our carbon footprints. And we can also take other steps to ensure a more peaceful future regardless of our ability to rein in emissions. Building resilient communities and food systems can go a long way towards reducing violence in the face of climate-related stressors. And we should prioritize mental health services and support systems to assist individuals in coping with the psychological impacts of climate change.

CONTACTS

• Analysis of Daily Ambient Temperature and Firearm Violence in 100 US Cities, https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2799635
• Climate as a risk factor for armed conflict, https://www.nature.com/articles/s41586-019-1300-6.