Five Conflicts and Collapses That May Have Been Spurred by Climate Change

The history of China is often told in dynastic cycles, where one family takes control of the country for hundreds of years until, for social or political reasons, they fall from power. Dynastic collapses were almost always followed by years of turmoil, which eventually led to the introduction of another ruling family.

But there's another crucial cycle that has ruled China for thousands of years: the monsoon. In 2008, researchers found a 2,000-year-old record of China's monsoon activity, in the form of a stalagmite that grew continuously between A.D. 190 and 2003. Stalagmites form as mineral-rich water drips onto the floor of a cave, so the chemical signatures in successive layers gave the researchers a glimpse of China's monsoon cycles over two millennia. When compared with China's historical record, periods of strong monsoon activity coincided with periods of prosperity—increased agricultural production, increased population and general peace. In contrast, periods of low monsoon activity lined up with periods of drought—and the turbulent declines of three major Chinese dynasties. 

The Maya grew during a time when the Central American region was very wet, from A.D. 440 to 660. Writings and pictographs on the ruins of Maya cities tell the story of three stages of collapse, with the empire contracting abruptly as inhabitants moved from cities near the edge of the empire to cities closer to its center. Proposed reasons for the decline vacillate between the very plausible, such as foreign invasion, and the outlandish, including alien interference. 

In 2003, a group of scientists looked at ocean sediment cores from the Cariaco basin, which lies off the northern coast of Venezuela. The concentration of titanium and iron swept to sea by rainfall in the various layers allowed the team to build a picture of the climate, and especially the rainfall amounts, during the Maya civilization's decline. The three contractions lined up pretty closely with three major drought events. One drought period in particular—from the years 600 to 1000—seems to have been especially marked by social conflict. Archaeologists have found stone monuments built between A.D. 750 and 775 that honor of 39 different rulers, evidence that those 25 years were filled with "rivalry, war and strategic alliances."

The Little Ice Age was a period between about 1300 and 1870 when the Northern Hemisphere saw markedly colder winters, and glaciers expanded on mountains in various locations. The intervals of regional drying and cooling that happened during this time might have contributed to periods of increased violence. Looking at temperatures between 1400 and 1900, a group of scientists spearheaded by David Zhang at the University of Hong Kong found that "periods of relative peace and turbulence during those 500 years were a global phenomenon seemingly linked to temperature change." 

The study looked at how cold, dry periods affected the land's ability to produce ample resources. A decrease in temperature and rainfall, the scientists noted, is likely to adversely affect agricultural production, which in turn can lead to famines, epidemics and armed conflicts. For instance, the Thirty Years’ War, the most violent conflict in Europe’s history, occurred during the coldest period of the Little Ice Age. 

Modern society often has the benefit of industrial agriculture, such as better irrigation or drought-resistant crop varieties. The hope is that these technologies will lessen the threat of conflict due to agricultural failings. "There is a lot of optimism with innovation in agriculture, and some of that is warranted, because we've done some amazing things," Hsiang says. "But some things we can't fix." Corn, for example, has become more sensitive to heat and drought—even with technological advances in planting and genetics. 

The Center for Climate and Security argues that modern, human-induced climate change is already having violent repercussions, such as the recent Syrian uprising. "[The Bashar al-]Assad regime’s failure to effectively manage water and land resources, the drought, and the subsequent displacement of close to 1.5 million people contributed to social unrest," the center says in a 2012 report. Looking toward the future, U.S. security officials worry that Asia-Pacific, which could face the displacement of millions of people due to sea-level rise, might be the next location to face a breakdown in security due to climate change.

But it's not necessarily all violence on the horizon; some research has shown that countries are far more likely to cooperate over water shortages than go to war because of them, which is an encouraging precedent for a world on the brink of unprecedented change.