To document the rainfall amounts, the group analyzed a stalagmite from Yok Balum cave in Belize. They precisely tracked an increase in rainfall between A.D. 450 and 600, then a decline in rainfall, punctuated by a series of short droughts 200 years later.
"This correlates with explosive growth and rapid expansion of Maya states across the lowlands, the proliferation of kings, and of carved monuments that talk about their successes," said Keith Prufer, associate professor of Anthropology at UNM and one of the principal investigators. "Starting around the middle of the seventh century you see a decline in rainfall, corresponding with increasing incidents of warfare between competing states. There were a series of short droughts simultaneous with a collapse of polities in the southern lowlands of Belize and Guatemala. The northern part of the Maya culture in the Yucatan Peninsula continued to flourish well into the ninth century when a massive protracted drought beginning in the 11th century corresponds with a dramatic collapse at Chichen Itza and may have prevented the recovery of extant complex political systems."
The precise chronological reconstruction of the climate record was conducted at the Radiogenic Isotope Laboratory at UNM Earth and Planetary Sciences, directed by Principal Investigator Yemane Asmerom along with Senior Research Scientist Victor Polyak and anthropology doctoral student Valorie Aquino. Some of the technical work was done by Aquino who drilled tiny trenches in the stalagmite and measured ratios of Uranium and Thorium isotopes from powders to accurately date the age of different layers linked to climate change.
"The link between changes in climate and culture, especially as it relates to the Maya Civilization, has been of long-standing scientific interest," said Asmerom. "What makes our findings in this regard unique is the fact that we can document timing of climate transitions with unprecedented precision, thanks to technical developments in uranium-series dating for which our lab is one of the leading labs in the world, and the very detailed and exhaustive field-based work done by our groups."
Prufer says the group was uniquely able to document the effects of climate change on the rise and collapse of an entire culture. But the research team wants to move further.
"One of the goals is to see if we could begin to model human responses to climate change in ways that could apply generally," he says. "The Maya are an excellent empirical case study given the long history of archaeological research in the area and the presence of explicit texts detailing the activities of kings and dates when they were in power."
Co-authors of the article include Douglas Kennett, Penn State; Sebastian F.M. Breitenbach, Eidgenössische Technische Hochschule Zürich, Zurich, Switzerland; Jaime Awe, National Institute of Culture and History, Belize; James Baldini, University of Durham, UK; Patrick Bartlein, University of Oregon; Brendan Culleton, Claire Ebert, and Christopher Jazwa, Penn State; Martha Macri, University of California, Davis; Norbert Marwan, Potsdam Institute for Climate Impact Research, Germany; Harriet Ridley, University of Durham; Harald Sodemann, Eidgenössische Technische Hochschule Zürich; Bruce Winterhalder, University of California, Davis; and Gerald Haug, Eidgenössische Technische Hochschule Zürich.
The study was funded by the U.S. National Science Foundation, European Research Council, Swiss National Science Foundation, German Science Foundation and the Alphawood Foundation.
Media contacts: Keith Prufer (505) 918-6763; email: firstname.lastname@example.org or Yemane Asmeron (505) 379-4850; email: email@example.com