War, murder and other acts of violence are likely to become more common in the coming decades, as the effects of global warming trigger outbreaks of aggression around the world, according to an article published in the American edition of 7 Days.
The study, detailed in the journal Science, summarizes the findings of work spanning fields from archeology to economics to create a clearer picture of how changes associated with rising temperatures and precipitation can trigger aggression.
While scientists do not know exactly why global warming is provoking violence, the evidence suggests that it is another important impact of climate change, in addition to rising ocean levels and intensifying periods of unusually hot weather.
"This study shows that the benefits of reducing greenhouse gas emissions are actually greater than we previously thought," said study lead author Solomon Xiang, an economist at Princeton University in New Jersey.
To complete their analysis, Xiang and his colleagues reviewed hundreds of studies in a variety of fields, including climatology, archeology, economics, political science, and psychology.
Ultimately, the team settled on 60 studies related to climate, conflict, temperature, violence and crime and reanalyzed the data from those studies using a common statistical framework.
The results were striking: even relatively small deviations from normal temperature or rainfall significantly increase the risk of conflict at different levels, ranging from individual aggression such as murder and rape, to political instability at the level of one country and international wars.
The survey data covered all major regions of the world and at different intervals of time, from non-slip hours and years to decades and centuries. As a result, scientists have found similar patterns of human aggression caused by climatic factors.
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Examples include spikes in domestic violence in India and Australia, increased beatings and killings in the United States and Tanzania, ethnic violence in Europe and South Asia, and the use of force in the Netherlands.
Among the studies was work linking the increased political instability and wars of the ancient Maya civilization with prolonged droughts caused by climate shifts, which were caused by global warming in the areas near the Pacific Ocean.
"That's when the classic period of the Mayan civilization ended," says study co-author Edward Miguel, professor of economics at the University of California, Berkeley.
Another study linked the collapse of the ancient Khmer civilization in 14th century Cambodia, which built the Angkor Wat temple, to a decades-long drought interspersed with heavy monsoon rains.
Brad Bushman, a professor of communications and psychology at Ohio State University who specializes in human aggression and violence, called the study "impressive." “Hopefully this study will raise awareness that climate change is sprawling across many areas of human endeavor, including war,” he says.
Bushman believes that sudden changes in temperature and rainfall make people look more morose. “When people are in a bad mood, they are more prone to aggression,” he said.
Another theory is that a lack or excess of rainfall could lead to economic collapse. When the people have very low incomes or the economy of the region collapses, this changes the person's motivation - for example, he decides to join an insurgent group.
