Does hot weather lead to increased violence? These researchers found a connection

High temperatures can cause the brain to divert resources to other parts of the body to cool down, according to researchers. This makes it harder for a person to process information and control emotions, as areas of the brain are not running at full capacity. This would be a direct impact of hotter temperatures on thoughts and behaviors.

"One of the things I learned very early on was that seemingly simple variables - such as how hot you are - have implications for how likely people are, to behave violently. In fact, my first publication looked at the relationship between ambient temperature and the likelihood of a riot," Craig A. Anderson, Professor of Psychology at Iowa State University, tells IE.

He found that hotter regions in the U.S. and around the world have higher rates of violent crime. Previous research, led by Anderson himself, demonstrated a significant connection between hotter periods and violence. 

If natural climate variability can trigger violent emotions, imagine the consequences when the world is impacted by extreme weather changes. In short, the psychological implications of climate change are extensive.

And if the direct consequences of temperature rises can increase violence on an individual level, the indirect outcomes could be more damaging than you think.

Think it sounds too far-fetched? Read on.

Anthropogenic climate change has far-reaching consequences

Policymakers and commentators are aware that drought caused by climate change was a contributing factor in the Syrian civil war which began in 2011.

The general public? Perhaps not.

An extreme drought between 2006 and 2010 in the region, combined with poor agricultural and water-use policies, led to crop failures that resulted in a large proportion of the rural population migrating to urban areas in search of jobs, food, and water. This then created social stresses which eventually resulted in the uprising against President Bashar al-Assad in March 2011 which set off the larger conflict.

This extreme drought was not due to natural climate variability, but was part of a century-long trend toward drier conditions in the Eastern Mediterranean, according to scientists. 

The Syrian government, which was already affected by the influx of 1.5 million refugees from Iraq, was ill-prepared for the added pressure, which led to competition over basic resources like food, jobs, and housing. The drought exacerbated poor governance and other factors, contributing to the political unrest that led to the devastating civil war. The violence in Syria, in turn, led to large-scale migration to Europe, which in turn placed more pressure on those areas and governments. 

The disruption caused by climate change also acts as what the U.S. military has described as a “threat multiplier” that may lead to greater instability in some affected regions. According to Anderson and Andreas Miles-Novelo, an Iowa State psychology graduate student, the conflict in Syria is a classic example of an indirect effect of climate change, known as intergroup conflict. 

Their recently published book Climate Change and Human Behavior bridges the gap between climate science and psychology by explaining how a rapidly warming planet can lead to increases in aggression and violence.

Matters of the psyche

Anderson published his first paper on the relationship between temperature and aggression in 1979 when he was still in graduate school. At the time, he did not connect it to climate change, but he thought it was an interesting theoretical phenomenon. He worked on several studies. "You know, different kinds of field studies, correlational studies, and crime data to investigate that phenomenon," he says.

It turned out to be a very robust phenomenon.

But it wasn't until many years later, when a greater awareness of global warming emerged, that Anderson began work connecting it to increases in aggression and violent behavior. 

"I started reading the Intergovernmental Panel on Climate Change reports in my spare time. That's when it hit me that this could be related to changes in human behavior, in a more violent direction. And no one was talking about this at the time," he says.

He researched the risk factors for violent behavior at multiple levels. "At an individual level, what makes a child grow up to be a violence-prone adult? And at an even broader level, what do we know about the kinds of triggers such as civil wars, intergroup aggression, and violence?" Anderson found himself wondering.

As he delved deeper into the literature, it was evident that one of the major consequences of rapid global warming could be an increase in violent behavior at multiple levels. 

Though he wrote several pieces that explicitly talked about the multiple ways that rapid climate change played a role in the likelihood of violent behavior, there was a lot of resistance in the psychology community.

"In the broader scientific community, no one was paying attention and we couldn't get into the top journals in the field. People weren't interested, or didn't believe in it," says Anderson.

With the release of their book, Anderson and Miles-Novelo hope that they can contribute to the conversation on the role between climate change and violence. And perhaps how psychology can play a role in reducing both the amount of global warming and human violence problems that arise from the climate crisis.

Effects of climate change at multiple levels

Psychology is relevant to understanding how to persuade people, and change attitudes, beliefs, and behavior in a positive direction.

Anderson says that the situation became much more important when Donald Trump was elected President. "Because he, essentially, along with the whole right-wing movement, were explicitly denying that there was any climate change, that this was just a normal, temporary kind of thing. And then they denied that it was human-caused. Within the United States, there are huge portions of the general population that are still ignorant of what the scientific facts are," he says.

So, one of the things they wanted to do was produce a book that was accessible to the general population.

"One that would have some impact, and in a sense, alert the climate science community, to think about the long term impact on humans and the multiple tools that can be used to mitigate some of the problems of climate change. Convince populations to elect politicians who will take positive action towards reducing the amount of temperature increase that we're going to see. So, you know, we have multiple goals here," he explains.

Though the direct impact of climate change is relatively easy for people to understand, Anderson also stresses the indirect ways in which climate change and extreme weather events can lead to violence.

"By indirect effects, global warming ... is influencing other variables that in turn influence humans," he says.

The reports on climate change that were coming out of the United Nations discussed some of the effects of temperature increases on extreme weather, droughts, and flooding, says Anderson. And these effects could wreak havoc in many parts of the world. "So we're going to see increased periods of no rain, which will create [drought and] famines. And the same region may very well have increased rainfall, that produces flooding," he says.

These events could then lead to increases in human aggression and violence. 

"The idea of ecological disasters forcing large populations to move to new locations, because their former homes are no longer sustainable, results in eco-migration. They're either underwater or flooded so frequently that people can no longer live there. We're already seeing huge numbers of eco migrants around the world. From there we get to what I think of as the two indirect paths to violence," he explains.

The larger picture

At the individual level, it starts with prenatal health, which could create conditions that make it more likely for a child to grow into a violence-prone adult.

"Prenatal and post-natal nutrition is very important, both to mothers and children. [Poor nutrition] has negative consequences for physical development, especially the brain development of the child. So at that very basic biological level, several risk factors are known to be important in predicting who's going to become violent. We know the proportion of children in that situation is increasing. And it's going to get much worse with the rise in drought and flooding," he says.

Extreme weather conditions can also impact family structure and stability.

"One of the things that happen in migration is that the family gets destabilized. Very often the father leaves first to try to find work to pay for food and housing. The absence of the father is a risk factor for growing stress in the family. By the time the children are adults, their emotional and intellectual skills have been affected in a harmful way that makes them more likely to resort to violence to get what they want and need," explains Anderson.

The third route, as aforementioned with the situation in Syria, is intergroup conflict.

"When people migrate, they naturally choose [to move to] a place that has a lot of resources. The thing to be noted here is that people in those places have their own set of struggles," he says.

They may end up competing with the large influx of people taking a greater share of resources. This resource competition can in turn lead to intergroup conflict.

"And that's especially true if the groups are of a different race, a different religion, or just differences in citizenship. There are a lot of historical examples of these kinds of population pressures eventually leading to civil or international war," Anderson explains.

It isn't just the neighboring countries that are reluctant to take the new eco-migrants, he says. It also extends to a reluctance of wealthy countries to take in economic migrants.

Act now

"From a psychological standpoint, we talk about this to some extent in this book. Affluent countries need to do a much better job of learning how to bring in eco-migrants in ways that don't stigmatize them and enable them to become productive citizens," he says.

Anderson argues that psychology can be a valuable tool in reducing the risk factors of climate-induced violence and mass migration. 

"We're trying to do a lot of things by bringing social psychology to the climate crisis itself. And getting more behavioral science people doing the appropriate research that's needed to, you know, to fully understand what will likely work, what will likely not work. We're trying to educate politicians," Anderson tells us. "Yes, it's gonna be bad. No, don't stick your head in the sand, do something," he says.

Despite all this, Anderson is hopeful about the future. "There are things that we can do as a species. We know how to reduce energy use, we have some fairly cost-effective technologies. So, in that sense, I'm optimistic."

At the same time, he's also realistic. 

"I just hope that my grandkids actually will be able to look at pictures of the North Pole and or the South Pole and see that there's some ice left," he adds.