Wet ascent dry demise
© D. Kennett/Penn State
Researchers analyzed a stalagmite from this cave in Belize to reconstruct patterns of rainfall during Classic Maya civilization. Evidence suggests climate shifts accompanied the ancient society’s rise and fall.

Newly documented climate shifts helped shape Classic Maya destiny

Classic Maya civilization rose and fell with the rains.

This once-majestic society, known for massive pyramids and hieroglyphic writing, expanded during an unusually rainy time and declined as the sky's spigots dried up and periodic droughts arrived, a new study suggests.

A 2,000-year climate record, gleaned from a stalagmite inside a Belize cave, highlights a central role for climate shifts in the ancient civilization's fortunes, say anthropologist Douglas Kennett of Penn State University and his colleagues.

A bounty of rain nurtured Maya agriculture and city building from the years 440 to 660, Kennett's team reports in the Nov. 9 Science. A drying trend and occasional droughts after 660 were accompanied by declining crop yields, increasing warfare among Maya city-states and a shift of political centers northward into the Yucatan Peninsula, the researchers say. After the collapse of Maya political systems between 800 and 1000, a severe drought hit southern Belize from 1020 to 1100 and apparently motivated remaining Maya to leave the area.

Wet ascent dry demise 2
© D. Kennett/Penn State
Stretches of wet and dry weather influenced the growth and abandonment of ancient Maya political centers, such as Caracol in Belize, a new study suggests.

"It looks like the Maya got lulled by a uniquely rainy period in the early Classic period into thinking that water would always be there," Kennett says.

His team analyzed a stalagmite that grew in Yok Balum Cave from 40 B.C. to 2006 A.D. Rainfall estimates for each year of rock formation were derived from measurements of oxygen that accumulated in the stalagmite as runoff from rains entered the cave.

Yok Balum lies near a half-dozen major Classic Maya sites. The scientists compared the climate data with historical records, carved on stone monuments at these sites, of Maya warfare and political events.

Researchers have argued for decades about whether the Classic Maya collapse stemmed more from droughts or from warfare and weakened political systems. Kennett says the new evidence is consistent with climate changes interacting with social forces to pull Classic Maya civilization in different directions. Maya city-building before the Classic era (SN: 5/22/04, p. 334) may have enabled rapid social advances when early Classic rains pelted down.

Intermittent droughts after 660 probably increased political pressure on already weakened Maya rulers as well as undermined the power of strong kings, Kennett says. Both situations would have upped the chances of wars breaking out.

Kennett's team has produced a "groundbreaking" rainfall history for southern Belize, says anthropologist Diane Chase of the University of Central Florida in Orlando. With her husband, UCF anthropologist Arlen Chase, she co-directs excavations at Caracol, a Classic Maya site not far from Yok Balum.

Further work needs to establish whether the new climate record applies to Classic Maya sites in Guatemala and the Yucatan, says anthropologist Vernon Scarborough of the University of Cincinnati. Droughts could have affected some parts of Classic Maya territory more than others, he says. Reservoirs and canals may have allowed some Maya cities to weather waterless periods better.

The ancient Maya adapted to many environmental challenges, suggesting that droughts alone didn't cause the society to collapse, says Arlen Chase. Still, Scarborough says, "there can be little doubt that droughts played a significant role in the rise and fall of Maya civilization."