Although the films usually show the Vikings as robust souls, who defied sub-zero temperatures, the new findings published in the scientific journal "Geology" indicate that they might be enjoying the 10ºC summer weather when they settled in Greenland.
After analyzing the climate record of southern Greenland for the past 3,000 years, a team at Northwestern University discovered that the climate was relatively warm when the Norse lived there between 985 and 1450 AD, compared to the previous and subsequent centuries.
"People have speculated that the Norse settled in Greenland during an unusually fortuitous period, but there were no detailed local reconstructions of the temperature that would confirm it completely. And some recent work suggests that it was the opposite, "says Yarrow Axford, the lead author of the study. "So this has been a little climate mystery" finally solved.
To reconstruct the past climate, the researchers studied the sediment cores of the lake collected near the Nordic settlements outside of Narsaq in southern Greenland. Because the sediments of the lake are formed by an accumulation of annual layers of mud, these nuclei harbor "secrets" of the past. By looking through the layers, the researchers identified climatic clues.
For this study, Lasher analyzed the chemistry of a mixture of lake fly species, called chironomids (a family of diptera), trapped within the sediment layers. By observing the oxygen isotopes within the preserved exoskeletons of the flies, the team of researchers constructed an image of the past. This method allowed the team to reconstruct climate change for thousands of years, which makes it the first study to quantify past temperature changes.
"The oxygen isotopes that we measure in chironomids record the isotopes of lake water in which the insects grew, and the lake water comes (in one part) from the precipitation that falls on it," explains Lasher, first author of the Article. "The oxygen isotopes in precipitation are partially controlled by temperature, so we examined the change in oxygen isotopes over time to infer how the temperature might have changed."
Because recent studies concluded that some glaciers were advancing around Greenland during the time that the Vikings lived in southern Greenland, Axford and Lasher expected their data to indicate a much more icy climate. Instead, they found that a brief warm period interrupted a steady trend of cooling weather driven by changes in the Earth's orbit. Near the end of the warm period, the climate was exceptionally erratic and unstable, with record highs and lows that preceded Greenland's Viking abandonment. In general, the climate was about 1.5ºC warmer than during cooling. During this warmer period, temperatures in southern Greenland were similar to today's temperatures, about 10ºC in summer.
In addition, Axford and Lasher found that the North Atlantic Oscillation (NAO) -a large-scale fluctuation in the atmospheric mass between the subtropical high pressure zone and the polar low in the North Atlantic basin, often responsible for Climatic anomalies from Central America to Europe, reaching even North Asia-probably were not in a predominantly positive phase during multiple Medieval centuries, as had been thought.
"We discovered that the NAO could not explain the medieval climate changes in our area," Lasher said. "That could question its use to explain long-term climate change in the last 3,000 years elsewhere."
So what caused the fortuitously "warm" climate of the Vikings?
Lasher and Axford are not sure, but They speculate that it could have been caused by warmer ocean currents in the region. The new data will be useful for weather modelers and climate researchers, as they will try to understand and predict what could be reserved for the Greenland ice sheet when the Earth warms up rapidly in the future.
"Unlike heating in the last century, which is global, the medieval heat was localized," said Axford. The Nordic settlements in Greenland collapsed as the local climate apparently became exceptionally erratic, and then eventually became cold. But Axford and Lasher will let archaeologists determine if climate played a role in their departure.
"We entered with the hypothesis that we would not see heat in this period of time, in which case we might have had to explain how the Norse were sturdy people when they settled in Greenland during a cold spell," Lasher said. Instead, the situation was the opposite. "Later, when their settlements became extinct, there was apparently climatic instability. Maybe they were not as resistant to climate change as the indigenous peoples of Greenland, but climate is just one of the many things that could have played a role, "he concluded.