Climate variations may have had a large role in the progression of agrarian states in Mexico and Peru. According to a press release from Penn State, Douglas Kennett, a professor of environmental archaeology and his research team have compared historical climate data with archaeological and anthropological history to determine the effect climate had on the rise and fall of agricultural city states.

“We are arguing that the climate information in both areas is good enough to establish that climate is playing some role in the rise and fall of these city states,” Kennett says. “Now we need to further refine the archaeological data.”

Kennett collaborated with climatologist and statistician Norbert Marwan of the Potsdam Institute for Climate Impact Research in Germany to sift through climate records in central Mexico gathered from a stalagmite found in Juxtlahuaca Cave. They pulled their climate data from the Quelccaya ice cap in the Cordillera Vilcanota region of the Andes Mountains in Peru.

In both regions, the researchers based their records on oxygen isotope measurements taken from ice and cave samples. The samples showed that the rainfall and temperature changed in these two regions over a period of 2,000 years.

“There is a long tradition of archaeology in both central Mexico and the Peruvian Highlands,” Kennett says. “There are also new high resolution climate records available that have not yet been capitalized on by archaeologists.”

The data fell in line with the rise and fall of three agrarian states in Mexico, and two from Peru. The ability of a society to grow depended strongly on climate stability, and the ability to produce food. When conditions worsened in these five states, the populations diminished and ultimately dispersed. People followed the good growing conditions, and this created and destroyed entire city-states over the centuries.