May 17, 2001

Researchers Link Past Recurrent Droughts To Collapse Of Mayan Civilization

LIVERMORE, Calif.— A researcher at Lawrence Livermore National Laboratory along with scientists at the University of Florida at Gainesville have attributed the end of the Mayan civilization on the north-central Yucatan Peninsula to a recurrent series of droughts that spanned the last 2,600 years.

Through analysis of sediments taken from Lake Chichancanab and Punta Laguna, LLNL researcher Thomas Guilderson, who is part of a team with University of Florida colleagues David Hodell, Mark Brenner and Jason Curtis, determined that the terminal Classic drought in the Maya Lowlands, said to have occurred from 800 to 1000 AD, was only one in a recurrent pattern of droughts that spanned the last 2.6 millennia.

Their findings will be published in an article entitled "Solar Forcing of Drought Frequency in the Maya Lowlands" in the May 18 edition of Science Magazine.
Sediments taken from Lake Chichancanab and Punta Laguna provide a highly sensitive record of past climate changes. The sediment samples display stratigraphic variation in the proportions of organic matter, calcium carbonate and gypsum. Under drought conditions, gypsum is precipitated and preserved in the sediment record and provided documentation of past increases in evaporation.

The researchers were able to carbon date the sediments taken from the lake and show that there has been a persistent bicentennial drought frequency. One of the more severe droughts reflected by high gypsum concentrations, between 125 and 210 AD, is consistent with pedological and archaeological evidence for a severe dry period at El Mirador in northern Guatemala and may have contributed to the site’s abandonment near 150 AD. Furthermore, this same drought coincides with preclassic site abandonment in the Maya Lowlands that may have been a response to widespread drought on the Yucatan Peninsula. The Maya were highly dependent on rainfall and surface reservoirs as their principle water supply. Hence, these multi-decadal to multi-century-scale fluctuations in rain probably had a detrimental impact on Maya food production and culture.

The 208-year drought cycle appears to be correlated with enhanced solar activity. Increased evaporation (droughts) occurred during times of high solar activity. The mechanisms by which such a small change in solar activity (incoming solar radiation) yields dramatic climate change are not known and require a significant amplifying mechanism.

"The paleoclimate record is replete with indications of centennial scale droughts, which are much worse than anything recorded in the instrumental or modern record," said Guilderson. "By studying past climates we can begin to understand how a subtle change in forcing (such as a small increase in incoming radiation due to solar variability) is amplified and propagated through the climate system. The system is too complex to rely on climate models alone. Whether this is a direct corollary to increased greenhouse gases is debatable, but the connection between climate change, water resources, and human culture is not."