Weekend Edition: No Rain Brought Ruin

Archeologists and anthropologists studying the Classic Maya have often expressed the hypothesis that the highly developed Maya cities of the classic period, (300 AD to 1000 AD), collapsed due to a combination of factors of which climate change, specifically drought, played a leading role. Up until now no consensus has been reached among experts. That may change after a new study published in "Science" by an international team has concluded severe drought was the factor causing social unrest and upheaval ending in mass depopulation of the cities. The drought was severe enough to overwhelm water storage facilities in a region without rivers. Mayan civilization was able to increase agricultural production to an extent that allowed development of densely populated urban centers connected by a road systems. High rainfall amounts allowed the civilization to reach its height between 440 and 660 AD. A drying trend began that lasted between 660 and 1000. The progressively drier climate lead to depletion of resources resulting in political destabilization and war. According to the researchers, years of hardship during a century long drought beginning in 1020 sealed the fate of the Classic Maya.

Their conclusion is supported by natural climate recordings and better understanding of Maya inscriptions covering their surviving pottery, monuments and stelae. Scientists were able to integrate these two data sources to re-construct what was happening in human society at a period of significant climate change. Chemical analysis of stalagmite layers, similar to the growth rings of trees, near Uxbenka and other major Maya centers show increases in war and unrest were associated with periods of drought. Stalagmites grow by the continuous dripping of calcareous water that creates a precipitation record over time. Stalagmites from Yok Balum cave were examined in the study. Other natural climate records corroborate the latest findings of severe drought. Studies of Yucatan lake bed cores show a severe 200 year drought from AD 800 to 1000. Another recent study using computer modeling to estimate rainfall and evaporation rates between 800 and 950 shows a period of modest rainfall decline. Because the Classic Maya civilization was built in tropical swampland without continuous water supply it was highly dependent on rainfall to replenish extensive water management and intensive agricultural systems. Even a modest decline in rainfall of 25-40% could have been enough to disrupt human society. There are critics of the climate change theory as the explanation for the Mayan collapse. They refer to the northern Yucatan cities of Chichen Itza, Uxmal and Coba which continued to thrive after the lowland cities to the south were depopulated. Regardless of the explanation of the demise, the success of such an advanced culture over two millennia in an unfavorable environment is an amazing achievement containing survival lessons, not doomsday prophecies, to be heeded by modern man.