Climate variability is one of the major forces in the rise and fall of agrarian states in Mexico and Peru, according to a team of researchers looking at both climate and archaeological records.

"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," said Douglas Kennett, professor of environmental archaeology at Penn State. "Now we need to further refine the archaeological data."

Kennett, working with Norbert Marwan, climatologist and statistician, Potsdam Institute for Climate Impact Research, Germany, looked at climate records for central Mexico gleaned from a stalagmite collected from Juxtlahuaca Cave in the state of Guerrero. They also looked at the climate record preserved in the Quelccaya ice cape in the Cordillera Vilcanota portion of the Peruvian Andes.

In both cases the climate records are based on oxygen isotope measurements on datable layers of ice or stalagmite cave deposition. These records show annual changes in rainfall and temperature for 2,000 years in Mexico and 1,800 years in Peru.

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