A warmer world could be a more violent world.
Take the evidence: cops perceive more of a threat to themselves when it is hotter and are more likely to use force. Some civil wars have happened at times of severe climate stress. Such case studies are fodder for a new meta-analysis that finds climate change will play a key role in future conflicts.
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The analysis, published today in the journal Science, wades into a contentious arena where scientists are entrenched in opposing battle camps. Some believe the link between climate change and conflict is obvious. Others refute the idea that human society could be influenced so greatly by a physical force.
"That raises the hackles for people who think its wrong that people are victims of their environment rather than shaping their environment," said Marc Levy, deputy director of the Center for International Earth Science Information Network at Columbia University, who is unaffiliated with the study.
Solomon Hsiang, a researcher at Princeton University, and his colleagues wanted to resolve the question once and for all. They collected all the research that solidly linked weather and violence from 1,000 B.C.E. onwards. The studies included the collapse of the Mayan civilization due to multi-year droughts, the collapse of major kingdoms in China supposedly due to reduced rainfall, and even controlled experiments such as one where cops placed in heated chambers responded with greater aggression than normal.
One study looked at periods of colder weather, such as the Little Ice Age, when Europe went bananas with wars, social unrest, economic and political upheavals.
The scientists re-analyzed 60 studies and found that there is a clear scientific consensus that climate change has a role to play in conflicts.
That's a careful statement, analogous to saying rain increases the risk of car accidents. Rain may contribute to a wreck; it may lead to an accident; it can even be the primary cause of damage (flash floods). Accidents do happen when it is not raining. And conflicts can happen without climate change.
The Hsiang paper is unlikely to be the final say in this debate. That's because its boundaries are confined by the papers it is based on, and it does not say how, exactly, climate increases the risk of conflict.
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"Unfortunately, this study brings us no closer to understanding whether, where, and under what conditions climate might increase the risk of violent conflict," said Halvard Buhaug, director at Peace Research Institute Oslo, who has published previously refuting the climate-conflict link.
Richard Potts, director of the Smithsonian Institution's Human Origins Program, looks at conflict from a deep time perspective, and recognizes that historically, climate instability has presented the greatest threat to human survival. Societies that can adapt sociologically, technologically or economically tend to prosper, while others - the Mayans, for example - decline.
But it would be simplistic to say climate causes the human conflict and subsequent decline, he wrote in an e-mail from Kenya. He was at a remote field site, writing on a solar-powered laptop by waning battery.
"The effects of climate instability always pass through the lens of how societies, their institutions, technologies, economic and political systems, are able to adjust to changing landscapes, resource uncertainty, population density, among other factors," he wrote.
Our modern day society may learn to adapt to the new norm of warmer climate and evade its worst effects. For instance, if conflict is caused by a weaker economy (mediated by climate), some technological change could help us evade the effects.
In that case, we may yet avoid the worst of it.