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Dr. Craig Anderson,
2017 Kurt Lewin Award Winner

Global Warming and Human Violence

Craig A. Anderson
Distinguished Professor of Liberal Arts and Sciences
Department of Psychology
Iowa State University

Rapid Global Warming is already having devastating economic, political, and social consequences worldwide. My presentation at the 2017 SPSSI conference in Albuquerque briefly summarized some of the environmental consequences that are already taking place, and then linked them to increased human violence through three very different pathways.

Key environmental consequences of rapid global warming (rapid in geological terms) concern habitability of high-density regions of the world. The first, obviously, is that even temperature climates will experience increases in the frequency of uncomfortably hot days. A second is increases in severe droughts and consequent decline in food and water availability. A third is increased sea level and intensity of storms, both of which dramatically increase flood disasters. Combined, all three of these rapid environmental changes force both small-scale and large-scale migrations (called eco-migration). In brief, much of the populated world is becoming uninhabitable (e.g., more desserts in already-stressed populated regions of Africa, inundated coastal regions worldwide).

The first of the three pathways that link global warming to increased violence is one that I’ve studied many years; it involves the direct effect of heat-induced irritability on aggression and violence. Basically, evidence going back to the late 1800s and as recent as last year shows that heat-stress increases aggressive and violent behavior tendencies. In field studies, hot regions and hotter cities have higher violent crime rates than cooler regions and cities within the same country, even when a dozen or more demographic and cultural variables are statistically controlled. Similarly, within the same region, city, or country, hot days, hot months, hot seasons, and hot years yield greater violence rates than cooler days, months, seasons, and years. Interestingly, nonviolent crimes do not show these heat effects. Laboratory studies suggest that the heat effect on aggressive and violent behavior is largely the result of increased irritability. Despite my own involvement in this literature, dating back to my first publication in 1979, I think that this pathway is the least important of the three.

The second pathway involves the many known pre-and post-natal risk factors for creating violence-prone adults. Many of those risk factors—such as poor nutrition, poverty, famine, disease, neighborhood disorganization, broken home, academic failure, separation from one or both parents— will increasingly occur to a larger proportion of fetuses, infants, children, and adolescents. Much of this increased exposure results directly from the ecological disasters and from consequent eco-migration and refugee crises. Increased violence resulting from this pathway is slightly delayed, because it takes roughly 15 years for a fetus to become old enough to engage in truly violent behavior, whether that be “common” criminal violence or more organized violence as child soldiers participating in civil or international wars, or as ethnic cleansing movements.

The third pathway involves the more direct and immediate effects of ecological disasters on eco-migration and consequent political instability—various types of intergroup violence and war (civil or international). Basically, groups fight over resources, and when some groups are forced to move because of ecological disasters, they often come into conflict with neighboring groups who already live and use the resources that are being sought by the migrants and refugees. There are multiple examples of such climate-change influenced wars, including the current civil war in Syria.

These climate-change exacerbated problems are going to get much worse over the next 50 – 200 years, as was predicted by U.S. military leaders over a decade ago. But, there are actions that we can take to mitigate these problems. The most obvious is to try to minimize the amount of global warming that actually takes place. SPSSI members and others can aid in this by their own green actions (e.g., installing solar panels on your house, reducing gasoline use…), and by doing Lewinian “action” research to change attitudes and behaviors of others, including voters. Other actions that nations can take involve getting prepared to take in and support large numbers of refugees and internally displaced persons.


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