UNIVERSITY PARK, Pa. — Why did the Vikings disappear from Greenland 400 years after settling there? New research led by Harvard University and Penn State using geologic and climate records found that sea-level rise likely contributed to the Viking’s disappearance from the island in the 15th century.

“Sea-level change is an integral, missing element of the Viking story,” said Richard Alley, Evan Pugh University Professor of Geosciences at Penn State and co-author on the study that published today (April 17) in the Proceedings of the National Academy of Sciences (PNAS).

Alley noted that changing sea level has always affected people, and it will continue to do so. 

“Today, far more people are now vulnerable to rising seas in a warming world,” he said. “To help these people, we will need a better understanding of the big drivers of sea-level rise, including melting ice, expanding ocean waters and 'mining' of groundwater by pumping out more than is returned. But these must be combined with knowledge of local conditions, as was done in this study, because some coasts are more vulnerable than others.”

The cause of the Viking abandonment of Greenland is not fully understood, he explained. It was likely due to a combination of factors, but the team found that the period coincides with a time of great climatic shift, from the Medieval Warm Period (~900 to 1250 CE) to the Little Ice Age (~1250 to 1900 CE) in which the Southern Greenland Ice Sheet readvanced, growing larger and taking up more of the island’s landmass.

Using geophysical modeling, the researchers demonstrated that the readvance of the ice sheet would have driven up local sea-levels by roughly three meters — or almost 10 feet. They found that the readvance would have caused sea-level to rise near the ice margin due to increased gravitational attraction toward the ice sheet and the Earth’s crust settling.

“The readvance pushed down the land around it, something like the dent that forms around you if you sit on a waterbed; less intuitively, the mass of ice is so large that it significantly attracts the ocean to it,” Alley said. “The greater ice mass close to the shore raised the ocean.”

Such a dramatic change in sea-level over a relatively short period of time would have made settlements close to the ice margin especially vulnerable to gradual flooding and loss of habitable land, he explained. Analyses of human and animal remains from the region show that beginning in the early 12th century, Vikings may have gradually transitioned their diet from a majority of land-based livestock to marine-based animals like fish and seal.

“There's been a shift in the narrative away from the idea that the Vikings completely failed to adapt to the environment, and toward arguments that they were faced with a myriad of challenges, ranging from social unrest, economic turmoil, political issues and environmental change,” Marisa Borreggine, a doctoral candidate at Harvard and lead author of the paper, said in a Harvard release.

Much like modern impacts from climate change, the sea-level rise experienced by the Vikings was compounded by physical and social stressors, Borreggine added. They would have experienced increased vulnerability to storms, coastal erosion and disrupted drainage compounded by the physical changes to their environment. Socially, they would have experienced a dramatic shift in resources, evolving to rely on marine over terrestrial sustenance over time.

While there are modern parallels, there is one critical difference between the climate changes experienced by the Vikings and society today.  

“The Vikings didn't really have a choice,” Borreggine said. “They couldn't stop the Little Ice Age. We can do work to mitigate climate change. The Vikings were locked into it.”

Other authors on the paper are Konstantin Latychev, Sophie Coulson, Evelyn Powell, Jerry Mitrovica of Harvard University and Glenn Milned of the University of Ottawa. The work was supported by the Heising-Simons Foundation, the Los Alamos National Laboratory Director’s Postdoctoral Fellowship, NASA, Harvard University and the John D. and Catherine T. MacArthur Foundation.