Is climate change a matter of national security? In a warming world, sea-level rise, drought and soil degradation are putting basic human needs such as food and shelter at risk. In March, the U.S. Department of Defense called climate change a "threat multiplier," saying that competition for resources "will aggravate stressors abroad such as poverty, environmental degradation, political instability and social tensions—conditions that can enable terrorist activity and other forms of violence."
Connecting climate change to a global increase in violence is tricky, and attempts to make such a link receive a fair amount of criticism. A hotter planet doesn't automatically become a more conflict-ridden one. The 2000s, for instance, saw some of the highest global temperatures in recorded history—and some of the lowest rates of civil conflict since the 1970s.
But there are historical examples of civilizations that did not fare well when faced with drastic environmental change, and those examples may offer a window into the future—and even help prevent catastrophe. "We can never know with 100-percent certainty that the climate was the decisive factor [in a conflict]," says Solomon Hsiang, assistant professor of public policy at the University of California, Berkeley. "But there's a lot of cases where things look pretty conspicuous."
The Akkadian Empire
Around 2350 B.C., the Akkadian empire conquered and united the various city-states of Sumer in Mesopotamia. For almost two centuries, this powerful empire stretched from the Mediterranean Sea to what is now inner Iran, setting up vast stretches of agricultural land and trade routes. Then, around 2100 B.C., the empire collapsed, and the land remained unsettled for nearly 300 years.
Archaeologists attributed the empire's abrupt end to invasions and political strife. But in one region, formerly the center of the empire’s grain production, the soil also held an intriguing clue: a thin layer of volcanic ash covered by a thicker layer of wind-blown silts. That region, it seemed, suffered from a sudden shift to more arid conditions.
In 2000, an international group of scientists studied marine sediment cores taken from the Gulf of Oman, more than 1,000 miles from what would have been the heart of the Akkadian empire. From these cores, the scientists were able to create a holistic picture of climate in the region. They found distinct peaks of the minerals calcite and dolomite beginning around 2025 B.C. that lasted approximately 300 years. These minerals are transported to the ocean as dust from dry, arid regions, so their abundance suggests that the collapse of the Akkadian empire must have been caused, at least in part, by a rapid and unprecedented drying, which in turn led to mass migrations, overcrowded cities and eventually, internal violence within the empire.