DROUGHT AND THE MAYA COLLAPSE Richardson B. Gill a , Paul A. Mayewski b , Johan Nyberg c , Gerald H. Haug d , and Larry C. Peterson e a 7707 Broadway 11A, San Antonio, TX 78209, USA b Climate Change Institute, University of Maine, 133 Sawyer Environmental Research Center, Orono, ME 04469, USA c Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden d Institut fu ¨r Geowissenschaften, Universita ¨t Potsdam, Postfach 601553, 14415 Potsdam, Germany e Rosenstiel School of Marine and Atmospheric Science, Marine Geology and Geophysics, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA Abstract Between A.D. 760 and 930, millions of Maya disappeared from the Earth. We examine changes in the physical environment in which the Maya lived. The ice-core evidence from Greenland indicates that around the time of the Maya Collapse, a minimum in solar insolation and a low in solar activity occurred, accompanied by severe cold and dryness over Greenland, indicating hemispheric climatic conditions propitious for drought in the Maya Lowlands. In the northeastern Caribbean, sea-surface salinity (SSS) was lowered. The most severe drought of the past 7,000 years devastated the Yucatan Peninsula. Large Maya cities collapsed in four phases of abandonment spaced about fifty years apart around A.D. 760, 810, 860, and 910. A new core taken from Lake Chichancanab in Quintana Roo showsthree peak episodes of brutal drought within a 150- to 200-year drought. A marine core from the Cariaco Basin off Venezuela precisely dates four severe drought episodes to 760, 810, 860, and 910, coincident with the four phases of abandonment of cities. The long-term drought appearsto have lasted from 760 to 930 in the Cariaco Basin. The climatic changes were the most drastic the Maya had faced in the preceding 1,500 years and the most severe of the preceding 7,000 years. THERMODYNAMICS Leslie White and Betty Meggers proposed that human societies are thermodynamic systems and are subject to the laws of physics. Ilya Prigogine demonstrated, based on his Nobel Prize –winning theory of self-organization and dissipative structures, that all self-organized systems, including hierarchical human civilizations, require strong, consistent, stable flows of energy through them, enabling the systems to organize themselves. If the strong flow of energy is cut off, a system collapses to a level of hierarchical organization that can be supported by the available energy (Meggers 1955; Prigogine 1980; White 1959). Prigogine showed that the history of all self-organized systems is characterized by alternating periods of stability interspersed with periods of catastrophic chaos. He also demonstrated that self- organized systems are in constant, two-way interaction with their physical environment. Not only do the systems affect their environ- ment, but the environment will also affect the system, completely independently of any internal processes within the system and com- pletely independently of the actions of human beings themselves (see Gill 2000:39– 71 for a more complete discussion). CLIMATE AND DEMOGRAPHY To what extent it is reasonable to conclude that independent climate changes directly affect the health and vitality of a population? Numerous studies have been done to try to answer this question using historical weather records and historical demographic data from preindustrial Europe during the seventeenth and eighteenth centuries. Some of the most dramatic work tying climate to the fate of human beings has been done by demographers. Studies per- formed in Sweden and in London, in particular—and in England as a whole—determined that a decrease in winter temperature is sig- nificantly correlated with an increase in mortality, independent of the harvest. The same studies in England and London found that cooler summers tend to reduce mortality. Furthermore, the studies showed that colder-than-average winters in Sweden reduced human fertility, and in England cooler winters and warmer summers also reduced fertility. These results are further corrobo- rated by studies in Sweden and Croatia showing decreases in mor- tality associated with abundant harvests. Other studies have been carried out in Sweden, France, and Croatia that demonstrate similar relationships between weather and the increase or decrease in human populations (Galloway 1986:11). The demographer Patrick Galloway therefore can now speak of “the striking synchrony in the long-term movements of temperature, agricultural yield, and population series across space and time. The results of this analysis suggest that an important driving force behind the long-term fluctuations in population may be long-term variations in climate and their effects on carrying capacity and vital rates” (Galloway 1986:20 –21). Enough evidence has now been developed that Ronald Lee can conclude that, in historical Europe, “Typically, a 18C [1.88F] warming would depress prices by about 10 percent through an unknown increase in output and thereby indirectly raise population growth rates by about 0.1 percent per year. So analysis of short-run variations suggests that climate did indeed affect human populations in the past, in roughly equal measure indirectly through agricultural 283 E-mail correspondence to: rbgill@satx.rr.com Ancient Mesoamerica, 18 (2007), 283–302 Copyright # 2007 Cambridge University Press. Printed in the U.S.A. DOI: 10.1017/S0956536107000193 https://doi.org/10.1017/S0956536107000193 Published online by Cambridge University Press