Rapid Climate Change
and the
Collapse of the Maya Civilization

Elizabeth K. Fitch


This webpage created in partial fulfillment of requirements for
ES 767 Quaternary Geology, Fall 2006
http://academic.emporia.edu/aberjame/ice/


Table of Contents
Abstract
The Mystery of the Maya
The Rise of the Maya
The Fall of the Maya
Unlocking the Past
The Maya and Climate
Related Links
References


Abstract

The Maya Civilization existed in some form from 2000 B.C. to A.D. 1500 on and near the Yucatán Peninsula of southern Mexico and northern Central America. The population and culture reached a maximum from A.D. 250 to 830. During the century of A.D. 830 to 930, the population crashed and cities were abandoned across the area. Almost overnight, from a historical standpoint, the Maya Civilization collapsed. The suddenness of this collapse has been shrouded in mystery until recent explorations of sediment records have shed some light on the subject. Cores from lakes in the Yucatán and from the Cariaco Basin off the northern coast of Venezuela reveal overall favorable climatic conditions during the development and height of the Maya. The cores also show that the time period coinciding with the collapse of the Maya was an extended period of drought punctuated by shorter intense droughts in A.D. 810, 860, and 910. These periods of drought, considered rapid climate changes, may have triggered the collapse of the Maya at a time when their population was stretching the limits of the environment.

The Mystery of the Maya: Where Did They Go?

Deep in the jungles of southern Mexico, Guatemala, Belize, El Salvador, and northern Honduras reside the ruins of a civilization long departed. The abandoned cities of the Maya Civilization stand surrounded by the rainforest, testaments to the abilities of a Mesoamerican culture that experienced the height of its existence from around A.D. 600 to 830. By A.D. 930, only a century later, the southern and central portions of the Maya culture had experienced a sudden collapse, with a drastic drop in population and large scale abandonment of cities (Culbert 1988). What happened to create such devestation to a flourishing civilization? Investigations of sediment cores have shed some light on this mystery and point towards a potential cause, rapid climate change.

The ruins of Tikal, one of the abandoned cities of the Maya, are located in present day Guatemala. Photo by Robert S. Webb. Taken from the National Oceanic and Atmospheric Administration (NOAA) Paleoclimatology Program Paleo Slide Set: Climate and the Classic Maya Civilization. Visit the NOAA Paleoclimate Program at www.ngdc.noaa.gov/paleo/paleo.html.

The Rise of the Maya: Setting the Stage for Collapse

The Yucatán Peninsula is a seasonal desert that relies heavily upon seasonal rainfalls, especially in the southern lowlands. The entire area is underline by thick limestone bedrock which exhibits karst topography and as such, sinkholes, disappearing streams, and caves are common throughout the region. The sinkholes, or cenotes, are more common in the northern part of the peninsula and often provide easy access to groundwater. Surface streams are rare, and and unlike the northern areas, the southern and western portions of the peninsula, rely almost entirely on rainfall for water (Haug et al. 2003).

The first Mayans appeared in the Yucatán around 2000 B.C., during the Preclassic Period of Maya prehistory--See Table 1. Because of the lack of surface water in many areas, cities were constructed to capture rainfall and store it in reservoir systems. Agricultural practices were intensified and well developed for the area by the start of the Classic Period. As the Maya culture continued to develop, the population exploded, reaching a maximum of eight to ten million people. In the southern areas, population densities have been estimated at 200 people per square kilometer. These population densities are one of the highest of any ancient culture (Fagan 2004). The Maya population at the end of the Classic Period was stretching the limits of the local environment.

Table 1. Archeological Divisions of Maya Prehistory.
Adapted from Culbert (1988).
Postclassic A.D. 930-1500
Terminal Classic A.D. 830-930
Classic A.D. 250-830
Preclassic 2000 B.C.-A.D. 250

The Fall of the Maya: Collapse of a Culture

After thousands of years, during which the they devloped a system of math, hieroglyphic writing, a calendar, and built elaborate cities and temples, the Maya disappeared into the rainforest. After the Terminal Classic Period, the population was a fraction of the maximum. The abandonment of cities occured in the southern and central areas first and then the north. Some small pockets of population lingered in the south, but these eventually vanished as well. By the end of the Postclassic, the Maya had abandoned their great cities.

Unlocking the Past: Using Sediments as the Key

What could have caused the collapse of the Maya? Why was there a delay in the abandonment of cities between the south and the north? Recent explorations in the Yucatán and surrounding areas have provided evidence that sudden and long-term droughts may be the answer to these questions.

Lake Sediments

Studies of the ratio of oxygen isotopes 18O to 16O in the sediments of lakes in the Yucatán have provided indications of wet and dry spells during the time of the Maya culture. Most of the lakes studied are closed basins, where the oxygen ratios are controlled by precipitation and evaporation, not river inflow/outflow. The oxygen isotopes are recorded by the calcium carbonate (CaCO3) found in the shells of aquatic organisms within the sediment cores. Higher 18O/16O values are signals of dryer conditions.

Within a closed basin, the major movement of water is through precipitation and evaporation. As a result, the sediment cores recoverd from the bottom of such lakes can be used to reconstruct the climatic conditions of an area with respect to precipitation. Image by Patty Catanzaro. Taken from the NOAA Paleoclimatology Program Paleo Slide Set: Climate and the Classic Maya Civilization.
As water levels in a closed basin lake rise and fall, the ratio of 18O/16O also rises and falls. When lake levels are higher than present day, the oxygen isotope ratio is lower and when lake levels are lower than present day, the ratio is higher. Image by Patty Catanzaro. Taken from the NOAA Paleoclimatology Program Paleo Slide Set: Climate and the Classic Maya Civilization.
Lake Chichancanab in the central Yucatán Peninsula. This narrow lake is formed in a depression created by faulting. Only 2 km wide, the lake is 26 km long, joining several basins within the depression. Photo by David A. Hodell. Taken from the NOAA Paleoclimatology Program Paleo Slide Set: Climate and the Classic Maya Civilization.

Hodell et al. (1995) cored sediments out of Lake Chichancanab in the central part of the Yucatán. What they found was the driest perod in the past 7,000 years occured between A.D. 800 and A.D. 1000, a time period that coincides with collapse of the Maya Civilization. Further investigations by Hodell and others have confirmed these results (Rosenmeier et al. 2002). The lake sediment cores do not have high resolution, however. For the Lake Chichancanab cores, one cm represent about 20 years. Punta Laguna, another lake that has been studied, has a finer resolution of 5 years per 1 cm of sediment (Hodell and Lixey 2004).

Oxygen isotope results from Punta Laguna show spikes corresponding to dry periods that correspond with the population drop of the Maya in A.D. 862 and again in A.D. 986. Photo by David A. Hodell. Taken from the NOAA Paleoclimatology Program Paleo Slide Set: Climate and the Classic Maya Civilization.

To obtain a higher resolution, a sediment of a different source is utilized. This time, from the ocean.

Ocean Sediments

Off the coast of Venezuela lies the Cariaco Basin, a depression that is anoxic, or deprived of dissolved oxygen, because it is enclosed by the higher elevation of the continental shelf. The shelf forms a lip around the baisn that prevents ocean waters from easily mixing with the basin waters. Without dissolved oxygen, marine organisms can not live in the sediment trapped by the basin, and so the sediment is laid down undisturbed. This environment has been in existence for at least 14,500 years and as a result, the time resolution obtained from sediment cores from the Cariaco Basin is roughly bi-monthly (Haug et al. 2003; Peterson and Haug 2005).

Even though the Cariaco Basin is nearly 2,000 km away from the Yucatán Peninsula, they both experience the same climatic conditions. As such, the sediments from the Cariaco Basin can be used as an indicator of the paleoclimate during the Maya Civilization.

The sediments from the Cariaco Basin are analyzed for bulk titanium content since there are no marine organism to provide CaCO3 as a source of oxygen isotopes. Titanium content in the sediments is an indicator of weathering and erosion from the land surface. Higher titanium values would correspond to higher erosion values, which are a result of higher precipitation amounts. With this resolution, Haug et al. confirmed that the time period isolated by Hodell et al. was exceptionally dry, but that it was also punctuated by several multi-year droughts even more intense that the general dry period during which they occurred. These droughts occured in approximately A.D. 810, 860, and 910.

The Maya and Climate: Abrupt Changes and Devastating Results

In their book The Ice Chronicles: The Quest to Understand Global Climate Change (2002), Mayewski and White explore abrupt climate changes as indicated by ice cores from Greenland. During the time of the collapse of the Maya Civilization, the ice cores show ammonium spikes, indicating drier conditions for much of the Northern Hemisphere. With the evidence found here and in the sediments of lakes and the Cariaco Basin, these authors wonder if the Maya were not the victims of a rapid climate change event that intiated a rapid social change event.

We know for sure that the Maya were expert at getting as much as possible out of the agriculturally poor soils of their domain. As their agricultural expertiese grew, so did the population, expanding during a climatically favorable period until their civilization was one of the largest on the Earth at the time. When long-term drought punctuated by more severe short-term droughts occured at the end of the Classic Period, the rainwater dependent central and southern parts of the culture collapsed. As the drought drug on for over a century, the northern portion of the Maya civilization also collapsed as their groundwater sources were depleted.

Today, the descendents of the ancient Maya live scattered among the peoples of Mexico and Central and South America and the legacies of their ancestors stand amid the rainforest, testimonies to the power of climate.

Related Links

The Foundation for the Advancement of Mesoamerican Studies, Inc. www.famsi.org

North American Drought: A Paleo Perspective. www.ncdc.noaa.gov/paleo/drought/drght_home.html

Collapse: Why Do Civilizations Fall? www.learner.org/exhibits/collapse

References