Sunday, February 26, 2012

Collapse of Mayan Civilization Related to Drought

As a youngster growing up in Florida I often read about the Indian civilizations in Central America.  The two most talked about in history classes were the Aztec and Maya.  The Mayan civilization was considered one of the most advanced civilizations of its time.  They made significant contributions to math and astronomy.

Mayan Temple
The Mayan civilization ranged over what is now southern Mexico, Guatemala, and parts of Honduras.  Their cities were large with ceremonial pyramids.  They developed quite a culture with fine sculptures, paintings, and ceramics.

Yet, the civilization collapsed between 800-950 B.C.  There have been a number of theories put forth to explain the collapse.  These include, drought, disease, and sociopolitical conflicts.  None of these can be ruled out, but it appears that whatever the ultimate cause was climate change stands out.

A paper has just been published in Science by British and Mexican scientists.  Here are excerpts from the press release from the University of Southampton in the UK:


A new study reports that the disintegration of the Maya civilization may have been related to relatively modest reductions in rainfall.

The study was led by Professors Martín Medina-Elizalde of the Yucatan Center for Scientific Research in Mexico and Eelco Rohling of the University of Southampton in the UK. Professor Rohling says:

“Our results show rather modest rainfall reductions between times when the Classic Maya civilization flourished and its collapse – between AD 800-950. These reductions amount to only 25 to 40 per cent in annual rainfall. But they were large enough for evaporation to become dominant over rainfall, and open water availability was rapidly reduced. The data suggest that the main cause was a decrease in summer storm activity.”

The study combines records of past climate changes from stalagmites and shallow lakes to model 40 per cent reductions in summer rainfall and reduced tropical storm activity over the region. The work is published in the leading scientific journal Science.

Professor Medina-Elizalde, who led the study while at the National Oceanography Centre in Southampton working with Professor Eelco Rohling, says:

“For more than a century, researchers have related the demise of the Classic Maya civilization to climate change, and especially to drought. No sound estimates had been made about the severity of this drought, but some have suggested extreme scenarios. New data made it possible to finally get detailed estimates. To do this, we developed a model that coherently explains changes in critical datasets of change in the region’s balance between evaporation and rainfall.”

Professor Rohling explains why such modest rainfall reductions would cause the disintegration of a well-established civilization:

“Summer was the main season for cultivation and replenishment of Mayan freshwater storage systems and there are no rivers in the Yucatan lowlands. Societal disruptions and abandonment of cities are likely consequences of critical water shortages, especially because there seems to have been a rapid repetition of multi-year droughts.”

The scientists also note that the reconstructed droughts during the demise of the Classic Maya civilization were of similar severity as those projected by the IPCC for the near future in the same region. Professor Medina-Elizalde adds:

“There are differences too, but the warning is clear. What seems like a minor reduction in water availability may lead to important, long-lasting problems. This problem is not unique to the Yucatan Peninsula, but applies to all regions in similar settings where evaporation is high. Today, we have the benefit of awareness, and we should act accordingly.”


The emphasis is mine.  Drought is one of the biggest problems we face as a result of climate change.  In a previous post (Our Changing Local Climate) I showed that the average annual precipitation for Columbia, SC had fallen from 50.47" in 1987 to 44.33" in 2011.  That is a drop of 6.14" in 24 years or a 12.2% drop.  Note that for the Mayas the drop was 25-40%.  A 20% drop would give the Midlands the same average annual precipitation experienced from 1933-1946.  The 1930s were a time of terrible drought for this area causing many problems on the farm.  Thus an even greater decline would be beyond our experience.

As our climate warms the belt of subtropical high pressure systems around the globe will expand northward.  These system are responsible for some of the greatest deserts on the planet like the Sahara.  The deserts are caused by the subsiding air where evaporation exceeds precipitation.  Thus, drought is expected to expand across the southern U.S. with the Southwest feeling the worst effects.  However, the Southeast will feel its fair share of pain.

As professor Medina-Elizalde says "...we have the benefit of awareness, and we should act accordingly."  Sadly, we are not.

Citation: Medina-Elizalde, M.and E. Rohling, Collapse of Classic Maya Civilization Related to Modest Reduction in Precipitation, Science 335, 6071 (2012).