April 26, 2004

Climate Change In Mesopotamia Clue
To Culture's Collapse, Says Speaker

Abrupt climate changes thousands of years ago contributed to the development and collapse of civilizations in ancient Mesopotamia, says Harvey Weiss, a professor of Near Eastern archaeology at Yale.

Harvey Weiss of Yale University speaks about the effects of climate change on civilization during the Sackler Art and Archaeology Symposium. Photo by Melissa Arbo

For more than 1,000 years, people lived in northern Mesopotamia and practiced rain-fed agriculture, he says. But archaeological evidence shows that about 8,000 years ago, there was a mass migration to southern Mesopotamia, widely regarded as the birthplace of Western civilization.

"Why in the world would anybody move to southern Mesopotamia, an extremely bleak and forbidding place, and in addition, a place that requires an infinite amount more labor to generate a crop than northern Mesopotamia?" he asks.

The answer, he says, is abrupt climate change.

Weiss was one of four experts who spoke during the Raymond and Beverly Sackler Art and Archaeology Symposium, "Writing Civilization: Literacy and Social Transformation in Early Mesopotamia." The event, attended by a largely student audience, was held in the Thomas J. Dodd Research Center April 16.

Weiss said obtaining ancient archives of climate conditions helps researchers piece together the puzzle of development and collapse of cultures. Lake bottoms, glaciers, and stalactites and stalagmites in caves are good sources of climate information, even from 10,000 years ago.

One of the most important archives of paleoclimatic data is the glacier at Tanzania's Mount Kilimanjaro, Weiss said: "Records from different places seem to be presenting the signatures of the same climate event."

According to Weiss, from approximately 6400 to 6200 B.C., "climate change occurred, and that is the moment when we see the first occupation of southern Mesopotamia. People came from the north and middle regions, and we know this because they carried with them architectural traditions, ceramic-making traditions."

Weiss said evidence of migration is coincident with what was "probably the greatest climate alteration since the termination of the ice ages. It is estimated that for this abrupt climate event, precipitation in West Asia probably decreased more than 40 percent," he added.

"What happens to human societies when they suffer an abrupt climate change event on this order? What happens when 40 percent of the rainfall suddenly evaporates? What happens when people are confronted with disasters?" Weiss asked.

In the absence of technology that would help, he said, and "in the presence of the human desire to perpetuate the species, most human societies, when faced with adversity, choose to vote with their feet - they move to other places."

Irrigation was not feasible in northern Mesopotamia because the Euphrates and Tigris rivers are deeply incised in their beds, Weiss said: "To see them you have to stare down at them like the Grand Canyon. But in southern Mesopotamia, the rivers flow slowly at sea level."

Weiss is widely recognized for the discovery of a major and abrupt climate change that affected the region from the Aegean to the Indus around 2200 B.C.

Since 1993, his findings have become the focus of attention among scholars interested in paleoclimatic and archaeological research.