Ancient Climate Change in South America Caused Populations to Plummet as People Couldn't Adapt

patagonia National Park Torres del Paine Chile getty stock
Researchers studied Torres del Paine National Park in Patagonia, Chile, for insight into the impact of ancient climate change. Getty Images

Ancient populations in South America declined dramatically around 8,000 years ago as people struggled to cope with sudden changes to the climate, archeologists believe.

Hunter-gatherers rapidly populated South America from around 14,000 years ago, setting up colonies in areas spanning from the high Andes to the Amazonian rainforest and the grasslands of Patagonia, at the continent's tip, according to the authors of the study published in the journal Scientific Reports.

Past research has shown that around 8,200 years ago, around the start of the Middle Holocene, which stretched to approximately 4,200 years ago, population levels in South America plummeted. During the Middle Holocene, South America became more arid overall.

To find out more, the team looked at population and climate data, including radiocarbon dates and marine sediments, which could provide an insight into rainfall in millennia past.

Philip Riris, a study co-author and British Academy postdoctoral fellow at the Institute of Archaeology at the University College of London, explained in a statement: "Unpredictable levels of rainfall, particularly in the tropics, appear to have had a negative impact on pre-Columbian populations until 6,000 years ago."

After this period, populations appeared to grow once more, he said in a statement. "This recovery appears to correlate with cultural practices surrounding tropical plant management and early crop cultivation, possibly acting as buffers when wild resources were less predictable."

The research team are not climatologists so they were unable to confirm what caused the changes to the region's climate. However, the changes to the climate that occurred during the Middle Holocene are known to have been a global phenomenon, Riris told Newsweek.

"Our paper develops the argument that around roughly 8200 years ago, the global climate (and South America specifically) was undergoing such rapid and unpredictable change that it limited the ability of some people to adapt quickly enough," he told Newsweek.

Riris told Newsweek the fact that population sizes were more or less "as you would expect" in the years leading up to the decline suggests indigenous populations were already developing strategies for dealing with abrupt climate change.

"[The] abandonment of certain zones and the need to adapt quickly to new circumstances, may have promoted the exploration of alternative strategies and new forms of subsistence, such as incorporating domestic plants," he said.

"Viewed in the context of at least 14,000 years of human presence in South America, the events of the Middle Holocene are a key part of the story of cultural resilience to abrupt and unexpected change."

This is the first time researchers have shown how climate change affected South America on a continent-wide scale in the run-up to Middle Holocene, whereas previous studies have looked at local and regional effects, Riris told Newsweek.

Next, more research is needed on the areas of lowland South America, particularly remote parts of the rainforests in the Guianas and the Amazon.

"Unfortunately, many of these are being illegally logged or targeted for resource extraction in the present. More corroborating data, for example, skeletal studies or genomics, would also help clarify some issues," Riris told Newsweek.

Patrick Ryan Williams, associate curator and professor of anthropology at the Field Museum of Natural History and University of Illinois at Chicago, who was not involved in the work, told Newsweek: "Understanding the relationship between climate change and human demography can reveal important information about how climate affects human populations through time. The goal of the study is laudable. However, there are some issues with the approach presented here."

He said there are problems with equating radiocarbon dates with the estimated population levels of a region "as radiocarbon dates are not a random sample of population."

"They are biased by researcher interest, and radiocarbon dates will be overrepresented by a history of researcher focus on the earliest inhabitants of South America (thus elevating the radiocarbon representation for early Holocene) and research focus on early urbanism and the development of social complexity (which coincides with the 4200 cal B.P. ["calibrated years before the present"] surge in radiocarbon dates after the mid-Holocene)."