Can something that happened 1,000 years ago still affect people today? Of course it can. Just ask Iceland.

When Vikings came to Iceland over a millennium ago, they slashed and burned trees to make room for farming. Within a few centuries, they’d wiped out most of the region’s trees so effectively that Iceland is still struggling to regrow those trees today, reports The New York Times.

That’s a problem since trees, as the Lorax said, are what everyone needs. Trees hold the soil together, making it more stable for building on. They also help protect the land from erosion and flooding.

Essentially, the Vikings settled in a forest and turned it into a desert. After clearing most of the trees, ash from the country’s many volcanoes settled on top of the ground, creating large expanses of poor, unstable soil. NPR reports that for about 1,000 years, Iceland’s population didn’t grow at all. These environmental problems along with radical temperature changes may have been part of the problem.

Planting vegetation on volcanic soil Iceland. (Credit: Christian Handl/imageBROKER/REX/Shutterstock)

Already considered a punishing climate for agriculture when the Vikings arrived, “Iceland did reasonably well” in that it survived, says Thomas H. McGovern, an anthropology professor at the City University of New York—Hunter College. But what happened in Greenland is another story: There, the Vikings seem to have disappeared. And we don’t really know why.

Author Jared Diamond believes Viking settlers in Greenland came up against similar issues of deforestation and soil erosion, and has written that their “response was to become hyper-conservative, and to refuse to learn from a neighboring society whose successful solutions to those environmental dilemmas were demonstrated in front of their eyes.”

In recent years, the academic consensus has changed. According to McGovern, Vikings did adapt to conditions in Greenland. But when those conditions changed, they weren’t able to adapt again.

McGovern says that in 1257, a volcanic eruption in Indonesia triggered a little Ice Age that made temperatures colder in Iceland and Greenland. Even though the changes in Greenland were much harsher than those in Iceland, the Vikings in Greenland were able to adapt to the colder temperatures by taking up practices like seal hunting—until, that is, further changes made their environment much stormier.

View of a red little house on a lava field near Vik, south of Iceland. (Credit: Joel Saget/AFP/Getty Images)

In some ways, the new understanding that Greenland’s Vikings were initially able to adapt is “scarier,” he says, because it shows “you can do a lot of things right and become extinct anyway.” For example, McGovern theorizes the increasing storms around Greenland may have made seafaring much more dangerous. That would be a problem considering seafaring was not only a major part of Viking culture, it may have helped them survive the first wave of changing temperatures they experienced.

This, of course, has unsettling implications for the modern world as we try to get a handle on human-caused climate change. How do we prepare for one type of change while still being nimble enough to adapt to coming ones?

“There are unintended consequences of a successful response to one kind of climate threat,” McGovern says, “which may increase your vulnerability to another kind of climate threat.”