Glacier remnants indicate that Greenland was substantially colder when the Vikings settled it a thousand years ago than it is today. The finding undercuts the perception that Greenland was colonized because the climate was relatively inviting at the time – a belief that has been given great weight by those disputing evidence for global warming.

In Science Advances, Columbia University's Professor Nicolas Young reports on the beryllium samples he collected from boulders left behind by glaciers in both southwest Greenland and Canada's Baffin Island. These reveal how long the boulders have been exposed to radiation from space. Young chose to take samples from these two locations because a colony was established near the former location in 985 C.E., which lasted for 450 to 500 years, and there is recent evidence that an offshoot may have existed on Baffin for a while.

Northern Europe was experiencing a balmy climate at the time, known as the Medieval Warm Period (MWP), and the colony's collapse occurred around the start of the Little Ice Age. According to the popular theory, the colony was able to exist because temperatures in Greenland were quite hospitable, but centuries later cooling wiped the residents out. The connection appeared so obvious, it has seldom been questioned.

A dumbed-down version of this idea holds that the colony's founder, Erik the Red, named the location Greenland because it was rich in vegetation. It has long been known that the name had more to do with Erik's marketing genius than any accuracy of color.

Now, as it turns out, Erik was apparently even more dishonest than previously suspected. When Young reconstructed the motions of glaciers using chemical analysis, he found that from 975 C.E. to 1275 C.E., the area's glaciers were far more extensive than they are today, even approaching their subsequent peaks during the Little Ice Age. While glaciers depend on precipitation as well as temperature, Young told IFLScience the “balance is weighted towards temperature... a 50 percent increase in precipitation is needed to offset 1 degree of warming.”

Although Young says the Norse Greenlanders may have had an interlude when it got a little warmer for a while, his work casts doubt on the idea that they were broken by declining temperatures. “If the Vikings traveled to Greenland when it was cool, it’s a stretch to say deteriorating climate drove them out,” Young said in a statement. This raises the question of what might actually have been responsible for the colony's destruction.

The implications are even greater for climate history. The timing of the Greenland settlement has been used as exhibit A in the claim that the MWP was a global event, rather than one restricted to a small part of Europe. Yet, evidence is emerging that many parts of the world were quite cold during the MWP. Greenland is close enough to locations that were unusually warm at the time – Iceland included – for it to have been credible that higher temperatures extended that far. However, Young's work suggests even that did not occur.

The finding has political implications, since an exaggerated version of the MWP has been touted by opponents of climate change to support the discredited claim that modern temperatures are not unusual.

^{During the Little Ice Age, these Greenland glaciers extended to the rock piles just above the water. It is now known that at the time Vikings colonized the area, they were almost at the same spot, indicating a much colder climate than today. Credit: Jason Briner.}