Climate change drove population decline in New World before Europeans arrived
What caused the rapid disappearance of a vibrant Native American agrarian culture that lived in urban settlements from the Ohio River Valley to the Mississippi River Valley in the two centuries preceding the European settlement of North America? In a new study, researchers from Indiana University-Purdue University Indianapolis reconstructed and analyzed 2,100 years of temperature and precipitation data -- and point the finger at climate change.
|Mississippian sites have been found from Minnesota to Florida, but the culture’s heart was the settlement |
at Cahokia Mounds in St. Louis [Credit: Cahokia Mounds State Historical Site]
"Abrupt climate change can impose conditions like drought. If these conditions are severe and sustained, as we have determined that they became for the Mississippians, it is virtually impossible for societies, especially those based on agriculture, to survive," said paleoclimatologist Broxton Bird, corresponding author of the new study. "From the lake records, we saw that the abundant rainfall and consistent good weather -- which supported Mississippian society as it grew -- changed, making agriculture unsustainable." Bird is an assistant professor of earth sciences in the School of Science at IUPUI.
This failure of their principal food source likely destabilized the sociopolitical system that supported Mississippian society, according to archaeologist Jeremy Wilson, a study co-author. He is an associate professor of anthropology in the School of Liberal Arts at IUPUI.
|Studying finely layered sediments from Martin Lake in LaGrange county, Indiana, IUPUI scientists have reported on |
dramatic environmental changes that occurred in the New World before the Europeans arrived
[Credit: Broxton Bird]
"It's important for us to understand how past civilizations coped with climate change as we encounter things like changing precipitation patterns and temperatures that appear to be rising around the world today."
As the Mississippians' culture waned, the IUPUI researchers found, there were lower temperatures and significantly less summer rainfall than during its rise. They attribute these changes to more El Nino-like conditions in the Pacific Ocean and cooling during the Little Ice Age, which altered atmospheric circulation such that moisture delivered to the Midwest was derived from the northwestern U.S. (Pacific and Arctic) instead of the Gulf of Mexico, as was the case during the Mississippians' rise. The longer transport distance of Pacific air masses during the Little Ice Age left less moisture available for rainfall in the Midwest, resulting in drought conditions that undermined agricultural production.
|Human head effigy pot from the Mississippian culture, on display at the Hampson Museum State Park in Wilson |
[Credit: Herb Roe/WikiCommons]
"Mississippians did not have irrigation and relied on rainfall to grow their crops. Modern agriculture in the Midwest corn belt likewise relies on rainfall with very little irrigation infrastructure, making us similarly vulnerable to drought," Bird said.
"Midcontinental Native American Population Dynamics and Late Holocene Hydroclimate Extremes" is published in Scientific Reports.
The sediment studied was from Martin Lake in northeast Indiana. Bird and Wilson are continuing their research at additional lakes, especially those adjacent to archaeological sites, throughout the midcontinent.
Author: Cindy Fox Aisen | Source: Indiana University-Purdue University Indianapolis School of Science [January 31, 2017]