For several centuries, Viking settlers eked out a living on Greenland, tending pastureland, hunting walruses, and constructing stone buildings that still stand today. Sometime in the 15th century, however, their civilization collapsed, and all the Vikings either died or fled. Though researchers have pieced together numerous clues about their disappearance—including sea-level rise, drought, a cooling climate, disease, environmental degradation, conflicts with the Inuit, and economic disruption—no one yet knows exactly what happened.

A continuous Viking presence on Greenland first dates to around A.D. 985, when, according to the medieval Icelandic sagas, Erik the Red landed there at the head of a large fleet (after being temporarily banished from Iceland for killing two men in a neighborly feud). Covered by a vast ice sheet, most of Greenland—named by Erik in a possibly disingenuous attempt to lure over more settlers—was uninhabitable.

Yet, where lush meadows existed, largely inside sheltered fjords, the Vikings (also known as the Norse) established two outposts: an Eastern Settlement on the southern tip of the island and a smaller Western Settlement about 240 miles away. In addition to raising goats, sheep and some cows, the Norse hunted seals, caribou, walruses and other prey and built houses and churches out of sod and stone.

Eventually, the Eastern Settlement grew to include some 500 farm sites clustered around 12 major churches, explains Marisa Borreggine, a graduate student of earth and planetary sciences at Harvard University, and the lead author of an April 2023 paper on the Viking collapse. “It was a pretty thriving settlement for a little while,” Borreggine says.

Even so, the settlements were never very populous. Researchers once thought that, at their peak, roughly 5,000 Norse resided on Greenland, but more recent estimates have cut that figure nearly in half.

At any rate, the civilization was in decline by the late 1300s, when the Western Settlement apparently winked out. The Eastern Settlement held on a bit longer, as indicated by a wedding recorded by scribes that took place there in 1408. But by around 1450, archaeological evidence suggests everyone had either died or sailed off.

Their fate remained unknown outside of Greenland until 1721, when arriving missionaries found no Vikings, only their ruins. Ever since, scholars have pondered their mysterious demise, which, akin to the collapse of the Maya or Anasazi, has prompted myriad theories.

The climate, for one thing, likely played a role. At first, the Norse occupied Greenland during the so-called Medieval Warm Period, when pastureland would have been in relative abundance. “Conditions were really favorable,” Borreggine says.

Around 1250, however, the onset of the Little Ice Age purportedly depressed hay production, to the detriment of the Vikings’ livestock. Colder temperatures would have also clogged the surrounding seas with ice and exacerbated storms, making it harder to ship walrus ivory, their main export, or to receive imports of iron tools and weapons, not to mention food.

At about the same time, the European market for walrus ivory crashed, replaced in part by higher-quality elephant ivory from Africa. Suddenly, the Norse had little of value to trade with mainland Europe, a particular blow since the search for more walruses, following the extirpation of Iceland’s walrus population, may have been what led them to Greenland in the first place.

“In the old days, we used to think this was about some Arctic farmers dabbling in walrus hunting,” says Thomas H. McGovern, a professor of anthropology at Hunter College in New York City, who has been studying Greenland’s Norse for nearly half a century. “But that’s just about backwards. These were commercial walrus hunters supporting themselves with some agriculture.”

McGovern points out that they risked weeks-long sailing trips across hundreds of miles of treacherous seas to reach the walrus hunting grounds, even during the height of their farms’ growing season.

Already struggling to maintain ties with mainland Europe, the Black Death of the mid-1300s sealed their isolation. It’s unknown whether the plague reached Greenland, but it certainly devastated the Norse’s benefactors in Norway, which, as McGovern notes, “basically collapsed as a country.”

“Norway is their main connection,” McGovern says, “and the port of Bergen is where the Greenland ships would come and go from.”

Cut off economically and with the climate worsening, the Norse may have furthermore suffered from the self-inflected wound of environmental degradation. Some researchers have posited that overgrazing led to soil erosion and that deforestation of Greenland’s scant trees hindered their ability to repair or build ships or burn firewood.

Meanwhile, the arrival of the Inuit from Canada around A.D. 1200 presented yet another challenge. Ancient Nordic texts mention a couple of skirmishes between the Inuit and Vikings, and Norse artifacts have been found at Inuit sites. Nonetheless, it remains entirely uncertain as to what extent the Inuit contributed to the Vikings’ demise.

“I imagine there probably would have been a range of interactions, but the ones we actually have records of were all hostile,” McGovern says.

Whether in battle or not, the Inuit ended up displacing both the Norse and the Dorset, a separate indigenous group believed to have first arrived on Greenland way back around 800 B.C.

Recent research has added two more potential pieces to the Norse puzzle: persistent drought, which would have decimated hay production, and sea-level rise of up to 10 feet, which, as Borreggine’s paper explains, would have inundated dozens of square miles, including much of the productive farmland near the fjords.

“It’s larger than the entire area covered by Bryce Canyon National Park,” Borreggine says of the flooding. “It’s a lot of land.” In fact, Borreggine’s team determined that medieval Greenland’s sea-level rise significantly exceeded the 20th-century global average.

All in all, the many pressures facing the Norse “eventually reached a tipping point,” Borreggine says, even as “it’s hard to know the relative importance of each of the factors.”

Previously, many researchers believed the Norse stubbornly failed to adapt to their deteriorating circumstances. As new evidence has emerged, however, that more simplistic theory is no longer in vogue. In 2012, for example, a study found that Norse eating habits did change over time, and that, by the 14th century, seafood constituted up to 80 percent of their diets, mostly in the form of seal meat.

“We haven’t got it all figured out … but we’ve come a long way,” McGovern says of the Norse disappearance. He adds that our own society might want to heed some of the lessons the Norse learned the hard way, particularly with regards to, say, climate change and sea-level rise. As McGovern points out, “You can do a lot of things right and still die.”