We know Vikings as infamous raiders—was that merely a response to climate change?

Enlarge / Clouds hover above the surrounding geothermal waters at the Blue Lagoon near Reykjavik, Iceland in 2008.
Matt Cardy/Getty Images
This mud is from Glastonbury Festival 2016, so much different cultural studies happen there.
Enlarge / This mud is from Glastonbury Festival 2016, so much different cultural studies happen there.
Ian Gavan/Getty Images

Answers in the mud

When you step into a lake and feel mud oozing between your toes, you’re actually stepping in soil that washed in from the surrounding landscape, carrying with it traces of what that landscape is like. Chemicals called sterols, from human and animal feces, record how densely populated the area is. Plant pollen records whether the surrounding area is forest, farmland, or meadow. Traces of charcoal and ash record cooking fires or slash-and-burn land clearing.

Over time, that soil stacks up in layers to form a long, detailed record. To read that record, scientists drill down several meters and bring up a long cylinder of layered earth encased in a Plexiglass tube: 3,000 years of history, in this case. Back in the lab, they’ll analyze this research season’s 14 core samples for all sorts of data about what the lakes and their surroundings were like in the past and how they changed.

“All of our mud is still in tubes, but the main objective is to ask how population size has changed throughout the Viking Age and how has local climate changed throughout the Viking Age,” said D’Andrea. He and his colleagues will compare that information with evidence from archaeological sites around Lofoten—like the boathouses and the longhouse, along with hundreds of other sites—to see if changes in climate or sea level seem linked to changes in the local economy or population.

Part of those answers may be waiting in sediment cores from five lakes in a wide valley of farmland running the length of the main island. That’s where D’Andrea and his colleagues hope to learn more about when the Lofoten islanders first took up agriculture and how their farming habits changed over the years. In an earlier study, human and livestock populations seemed to fluctuate along with summer temperatures, and the team hopes the new cores will hold further clues about how climate impacted the economy of the islands.

In cores taken from two lakes closer to the coast, the team will look for indications of ancient sea-level changes that probably explain the abandonment of the boathouses.

At the beginning of the Iron Age, the sea level in the Lofoten Islands was higher than it is today. That’s because geological forces have lifted the islands upward for at least the last 6,000 years. Sea level had already begun to fall by the end of the Viking Age, and receding shorelines would eventually have cut off the boathouses’ access to the harbor, making launching fishing boats from Borg exceedingly difficult. The change in elevation could also have let more freshwater from the islands drain into the harbor to create a brackish estuary that would actually have started to freeze over in the winter, effectively stranding the ships.

D’Andrea and his team hope the sediment cores will tell them exactly how much the Borg shoreline here has moved since the days of the Vikings. Remains of aquatic life, long buried in the mud at the bottom the estuary that once formed one of Borg’s harbors, will help researchers understand when the estuary shifted from a saltwater harbor to a freshwater lake.

Together, Lofoten’s lakes could preserve indications of how the people of the Lofoten Islands responded to shifting climate and changing sea levels during the course of the Iron Age. They may tell the researchers, for instance, if shifts in sea level led people to shift to greater dependence on agriculture or if colder summers led people to shift their reliance from farming to fishing.

Modern reconstruction of a Viking longboat.
Enlarge / Modern reconstruction of a Viking longboat.

More complicated than climate

This is not to say that climate change made the Viking Age happen. Many things could have pushed the Vikings to take up pillaging and settling distant lands.

“There are a number of different pressures and circumstances that cause a civilization to make decisions, and it’s really difficult to pinpoint one,” said D’Andrea. “I’m a little skeptical, to be honest, that climate change had a huge impact on their explorations.”

Political power was getting more centralized during this time, and rival Scandinavian nobles may have used raids as a way to keep troops occupied and well-paid. A slump in agriculture—perhaps due to local climate changes—and a growing population could also have driven the Scandinavians to seek out loot and new lands. The wealthy urban cities of Western Europe would have made tempting targets, especially for people already accustomed to sailing on long fishing or trading expeditions. Combine those things with a culture that prized bravery and a willingness to fight, and you get Vikings.

The exact recipe probably varied from place to place. That’s because the Scandinavian Diaspora itself wasn’t one big, organized migration. The Vikings came from all over Scandinavia, and their reasons for leaving varied from one settlement to the next. A lot of research has focused on how climate impacted their arrival in places like Greenland and Iceland, but it’s also important to look at the impact climate changes had in the places they left—places like Lofoten.

“When you talk about the Vikings, you need to look at their jumping-off points in Scandinavia as well as what climate and environmental conditions were like in the places that they settled,” said Balascio. And if climate played a significant role anywhere in Scandinavia, it would have been in a place like Lofoten. “Minor climate changes, whether they’re just on the order of a few decades, can really impact civilizations living on the edge like that,” he said.

Even so, the researchers caution against expecting simple explanations from their results. “I don’t want to be deterministic and say ‘if it gets warmer, when they leave, that means they left because it got warmer,’ or ‘life became easier for them, so they decided to set sail.’ But we can sort of look at the backdrop,” said D’Andrea.

D’Andrea and his team hope to get a better picture of that backdrop at a local level. Most of what we know about climate change in the North Atlantic comes from broad, long-term data, but if you want to link shifts in climate to actual shifts in human activity, it helps to zoom in and look at shorter-term change in a specific area.

“Rather than massive changes during the Pleistocene and the glacial period, to look at smaller periods of time in the Holocene is also very instructive, because it’s something that’s more readily applicable to the situation at any given time,” said Wickler. “We’re looking at periods of centuries or even decades in the past. Focusing on specific periods when we know there was a lot of change taking place—transition both cultural, climatic, and otherwise that had dramatic impacts on surviving and subsistence—can teach us a great deal.”

Back in the lab

Sadly, we won’t have any real answers for a while, because analyzing the cores could take about a year.

“Most of the work happens back in the lab,” said Balascio. Once the cores arrive back at the College of William and Mary, they’ll be split in half so grad students can sketch and describe the layers of sediment, looking for changes in color and grain size. They’ll be sampled for radiocarbon dating and to look for sterols, pollen, and other microscopic traces of past landscapes.

D’Andrea says the team is already encouraged, however, because they caught glimpses of marine shells through the polycarbonate tubing on a few of the cores, which means they have the data they need to start reconstructing changes in sea level.

Those results, combined with the archaeological data that’s also being processed behind the scenes, will help the team pick new sites and ask new questions for next year’s research, so each year in the field builds on the last. This summer’s work built on a previous core study from just one lake from Lofoten, for example.

Whatever the team unearths could hold some insights into how climate change impacts societies, and discovering how people have dealt with those changes could be useful today. “The historical perspective is important,” said Balascio, “especially with the impact that climate change is having on people, particularly those in marginal locations that are more susceptible to these changes, that might not be as resilient as other locations.”

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