When you think about civil violence in countries worldwide, consider that one factor may be changes in climate.
A new study in the journal Nature finds that the climate event El Niño Southern Oscillation played a role in 21% of civil conflicts from 1950 to 2004. This is seen most prominently in the poorer countries of the tropics, such as Sudan and Rwanda. Wealthier nations affected by El Niño, such as Australia, do not appear to have civil conflict related to climate change.
The study authors are not saying that El Niño Southern Oscillation causes civil conflict, but it seems to be a contributing factor in many cases, especially in the tropics. They find the probability of a new civil conflict breaking out in the tropics doubles during El Niño years, which are associated with warming ocean temperatures in the Equatorial Pacific, relative to La Niña years, which are associated with cooling of those temperatures. El Niño occurs about every four to five years, and lasts about one year.
This is analogous to the way that you might find an increase in car accidents on icy roads; the ice itself doesn't cause wrecks, but it's part of a situation that feeds into them, said study co-author Solomon Hsiang, postdoctoral research associate at Princeton University.
"Even in modern society, the global climate is a major factor in determining the global pattern of violence," Hsiang said. "Not only is the effect something that we can observe, it’s a very large and important effect that would explain a lot of the conflict."
What is El Niño, and why might it lead to violence?
El Niño refers to a large movement of water in the Pacific Ocean, Hsiang explains. During a normal year, there’s a certain pattern in which the wind blows a lot of the water on the surface of the tropical ocean to the west.
But sometimes that pattern changes, and the warm water sloshes toward the eastern Pacific, releasing a lot of energy into the atmosphere and heating it. That causes a wave in the atmosphere that's trapped in the tropics around the equator, resulting in warming and drying that's associated with El Niño. During La Niña, the trend is the opposite, with cooler temperatures in the equatorial Pacific.
El Niño can have several effects that might influence civil unrest. For instance, warming patterns can lead to water shortage and large crop losses that negatively impact a country's economy enormously, particularly one in which populations are dependent on subsistence agriculture. This can affect the labor market, making fewer jobs available. Changes in climate can also promote the spread of disease and contribute to famine. In these desperate situations, fighting for resources may seem a viable or necessary option.
Previous research suggests warmer weather may have psychological effects, too. Studies suggest that hot temperatures make people more aggressive, provoking hostile feelings and thoughts. This idea feeds into indications that violent crime is more likely when it's warm outside, too.
More research needs to be done into the actual mechanisms of the role that El Niño plays in violent conflict, but the premise is solid, said Thomas Homer-Dixon, political scientist at the Balsillie School of International Affairs in Waterloo, Canada.
"I’ve looked at the methods pretty closely; this is as close to an air-tight argument as it gets," says Homer-Dixon, who was not involved with the Nature study, but has also done research on these issues. "Now there’s a lot more than needs to be done. This is only the beginning."
So what about global warming?
The new study does not prove that warming from human-induced climate change will cause violence, and study authors caution that El Niño patterns are distinct from global warming.
But the implication is certainly there that if this influence of climate change on violence can be observed from El Niño, human-induced global warming patterns may potentially also contribute to violence. In fact, we may seeing that in the case of the Arab Spring, Homer-Dixon said. The Middle East does not experience climate variations related to El Niño, but a recent unexpected warming (which he suggests could be related to human-induced climate change) in a different world region may have contributed to unrest.
The situation can be viewed this way, Homer-Dixon said: Unusual high temperatures Russia in the summer of 2010 (potentially from global warming) caused droughts and hampered food production, which drove up food prices. The resulting economic turmoil is one factor driving the recent instability in the Middle East.
"The kind of climate phenomenon these authors have been looking at in the past is not dissimilar to the kind of climate shock that appears to have contributed to the Middle East uprising," he said.
What can be done
Armed with the knowledge that El Niño is associated with greater violent conflict in the tropics, people in affected areas may be able to take certain preventative measures before outbreaks occur, Hsiang said.
Humanitarian groups could increase their fundraising efforts in preparation for an El Niño event, and prepare resources more effectively to reach people before a crisis occurs. Spreading the word across a population can also help. For instance, a farmer who knows there's a greater chance of drought might save up more water to keep crops from dying.
According to the latest data from the National Weather Service Climate Prediction Center, our planet's northern hemisphere is currently in an "ENSO-neutral" state, which will remain through fall 2011 and probably heading toward La Niña next. So, we will not have an El Niño event this year.
In the meantime, nations can take steps to mitigate the threat of human-induced climate change, Homer-Dixon said. It's true that violence tied to warmer climate shifts seems to impact chiefly poor societies that depend on the food they grow themselves, but there are spillover effects to civil violence that threaten national and global security. There may even be violent outbreaks in the United States as dire droughts set in.
"To think that we can wall ourselves off from this stuff is real folly," Homer-Dixon said.