Argument has raged for decades over what doomed the ancient Maya civilization and spurred its people to abandon their awe-inspiring temples and pyramids in the rain forests of Mexico and Central America. Warfare, disease, social unrest and over-farming have all been cited as potential factors in the decline of a culture that was scientifically and culturally advanced for 750 years.
A new study bolsters the theory that large-scale climate change was responsible for the society's demise — and argues that changes in global weather patterns were also responsible for its rapid rise.
Using data from a 13,500-year-old stalagmite taken from the floor of a recently discovered cave in Belize, scientists said they were able to assemble a precise record of rainfall for the region going back 2,000 years.
The ancient cave spire was created by rainwater as it leaked from the ceiling of Yok Balum cave and deposited dissolved minerals in a growing mass on its floor, drip by drip. By examining the ratio of atomic isotopes along the length of the stalagmite, researchers said they were able to determine when portions of it formed and how much rainwater fell during each six-month period.
What they discovered was a period of abundant rainfall during the early days of the civilization, followed eventually by drought. The results were published in Friday's edition of the journal Science.
"Unusually high amounts of rainfall favored an increase in food production and an explosion in the population" beginning around AD 440, said study leader Douglas J. Kennett, an anthropologist at Penn State University. "This led to the proliferation of cities like Tikal, Copan and Caracol across the Maya lowlands."
By AD 700, that wet weather gave way to a "general drying trend that lasted four centuries and was punctuated by a series of major droughts," he said. "That triggered a decline in agricultural productivity and contributed to societal fragmentation and political collapse. ... Maya kings lost their power and influence."
Researchers said the severe drought the Maya experienced was akin to the one that devastated Mexico in the 16th century and brought crop failure, famine and death. Kennett said such circumstances probably visited the Maya during their classic period, which lasted from AD 250 to 1000.
Though the study adds valuable detail to the ancient climate record, other Maya researchers said it was unlikely to end debate on the issue.
Boston University archaeologist William Saturno said he remained unconvinced that climate change was the primary driver of the civilization's collapse.
The worst period of drought detailed in the report was in Belize 100 to 300 years after the time Maya in that region stopped inscribing major monuments and essentially "went dark" as a culture, Saturno said. He called it a mistake to believe that drought in one area affected all areas of Maya civilization, which also covered portions of what is now southern Mexico, Guatemala, El Salvador and Honduras.
Saturno said he believed the growing popularity of climate change theory in Maya studies was based on worries about modern-day global warming.
"Oftentimes, we're looking at ancient societies as an analogue to our own," he said. "We want to drive home the point — if we destroy the environment, we'll reach a point where we can't recover."
The authors of the study wrote that the prolonged drying trend triggered balkanization and fueled brutal warfare. Saturno said he doubted it led to war but that it could well have undermined the Maya leadership.
"If you have a guy who controls the rain, you might agree to build pyramids in his honor," he said. "But if the rains don't come, you might start to say, 'Wait a minute — this guy doesn't really control the rain.'"