Turn of the tides: PSU researchers find links between climate change and political, human impacts

The role of climate change in the development and demise of classic Maya civilization, ranging from AD 300 to 1000, has been controversial for decades because of a lack of well-dated climate and archaeological evidence. But our international team of archaeologists and earth science researchers has now compiled a precisely dated, high-resolution climate record of 2,000 years that shows how Maya political systems developed and disintegrated in response to climate change.

Starting in 2006, our team members reconstructed rainfall records from stalagmite samples collected from Yok Balum Cave, located less than a mile from the ancient city of Uxbenka, in the tropical Maya Lowlands in southern Belize. Some of the stalagmites in the cave yielded high-resolution oxygen isotope records reflecting changes in rainfall through time. The stalagmites’ exceptional quality allowed us to collect two samples per year over a 2,000-year period. That yielded a robust and continuous record of wet and dry events, with fewer potential errors than earlier studies.

Then, our team compared these findings to the rich political histories carved on stone monuments at Maya cities throughout the region. These well-dated stone monuments celebrated rulers and depicted wars. By comparing these political histories to our rainfall record, we were able to examine the role of climate change in the Maya’s rise and fall.

Unusually high amounts of rainfall favored an increase in food production and an explosion in the population between AD 450 and 660. This led to the proliferation of cities like Tikal, Copan and Caracol across the Maya lowlands. The new climate data show that this salubrious period was followed by a general drying trend lasting four centuries. It was punctuated by a series of major droughts that triggered a decline in agricultural productivity and contributed to societal fragmentation and political collapse.

The most severe drought (AD 1020 and 1100) in the record occurs after the widespread collapse of Maya state centers (referred to as the Maya collapse) and may be associated with widespread population decline in the region.

Over the centuries, the cities suffered a decline in their populations, and Maya kings lost their power and influence. The linkage between an extended 16th century drought, crop failures, death, famine and migration in Mexico provides a historic analog — supported by the cave stalagmite samples — for the socio-political tragedy and human suffering experienced periodically by the Classic Period Maya.

Our findings published in a recent issue of the journal Science have attracted national and international media attention and public discussions in several countries. This unique project brought together anthropologists, archaeologists, historians, linguists and climate science researchers from Eidgenössische Technische Hochschule Zürich, Zurich, Switzerland; the University of New Mexico; the National Institute of Culture and History, Belize; the University of Durham, United Kingdom; University of Oregon; University of California, Davis; Potsdam Institute for Climate Impact Research, Germany. In addition, the study attracted funding from National Science Foundation, European Research Council, German Science Foundation, and the Alphawood Foundation.

Overall, we have learned that climate matters in terms of development of complex societies like the ones we live in today. The unique climate conditions that set up the Maya’s social and political systems also lured them into a very vulnerable situation when conditions started to dry.

The rich archaeological and historical records of the Maya provided an opportunity to examine the long-term effects of climate change for both the development and disintegration of complex sociopolitical systems like our own.

The effects of climate change are complex and play out over multiple time scales. Abrupt climate change is only part of the story. In addition to climate drying and drought, the preceding conditions stimulating societal complexity and population expansion helped set the stage for later stress on their societies and the fragmentation of political institutions.