The idea that anthropogenic climate change might cause a war or two sometime in the future is not new. It’s been a subject of hot debate in the science community for much of the past decade. The National Intelligence Council even evaluated the topic in 2008. But recent headlines (such as “Climate cycles are driving wars“) may have you thinking that such a link has now been proved. You’d be wrong, however. The story is far more complex.

The recent headlines are the result of a study published last week in the journal Nature. The study didn’t look at anthropogenic climate change or war in general. Instead, researchers from Columbia University examined the potential role of the El Niño/Southern Oscillation (ENSO) in civil conflicts, defined as a country that experiences “more than 25 battle-related deaths…in a new civil dispute between a government and another organized party over a stated political incompatibility.” The scientists then split all the nations in the world into two categories—those affected by ENSO cycles and those unaffected by ENSO—and examined ENSO patterns and timing of civil conflicts between 1950 and 2004 to see if a conflict was more likely to be associated with an ENSO event than not.

They did find that association; in the countries affected by ENSO, the rate of conflict was about 6 percent in El Niño years and only 3 percent in La Niña years. The researchers conclude that “ENSO may have had a role in 21 percent of all civil conflicts since 1950.” But that doesn’t mean that El Niño caused any of those conflicts. The scientists write:

Precipitation, temperature, sunlight, humidity and ecological extremes can adversely influence both agrarian and non-agrarian economies. In addition, ENSO variations affect natural disasters, such as tropical cyclones, and trigger disease outbreaks. All of these have adverse economic effects, such as loss of income or increasing food prices, and it is thought that economic shocks can generate civil conflict through a variety of pathways. Furthermore, altered environmental conditions stress the human psyche, sometimes leading to aggressive behaviour. We hypothesize that El Niño can simultaneously lead to any of these adverse economic and psychological effects, increasing the likelihood of conflict.

They also caution that there results “might not generalize to gradual trends in average temperature or particular characteristics of anthropogenic climate change.”

However, we can conclude from this study that changes in weather patterns can contribute to conflict. And that’s a story that emerges from other recent studies on the topic of climate or weather and conflict. Studies have linked the fall of the Roman Empire and Angkor Wat to changes in climate. A 2007 PNAS study found that “long-term fluctuations in war frequency and population changes followed the cycles of temperature change.” A 2008 PNAS study found that climate warming increased the risk of civil wars in Africa (a conclusion that was quickly disputed, showing the level of debate on this topic).

We can also see from these studies that there are no easy answers in this arena. Any conflict—even one as simple as an argument with a neighbor that ends in a fistfight—has a complex set of factors that work together to foster the violence. The assassination of Archduke Ferdinand may have started World War I, but it didn’t cause it. And countries aren’t going to go to war with each other because their local climate has slowly changed over decades. But those changes could contribute to other internal and international strife and have consequences we cannot foresee. As one intelligence source told Wired in 2008, “Climate change is a threat multiplier in the world’s most unstable regions….It’s like a match to the tinder.”