Contrary to popular perception, the so-called Medieval Warm Period, when Europe enjoyed exceptionally mild weather, did not necessarily extend to other parts of the world, says a study.
"It is becoming clearer that the Medieval Warm Period was patchy, not global," said lead study author Nicolas Young, glacial geologist at Columbia University in the US.
"The concept is Eurocentric" - that is where the best-known observations were made. Elsewhere, the climate might not have been the same," Young noted.
Climate scientists have cited the Medieval Warm Period to explain anomalies in rainfall and temperature in far-flung regions, from the US Southwest to China.
For the study, the researchers focused on Greenland weather when the Vikings first colonised it.
Norse, or Vikings, led by Erik the Red, first sailed from recently settled Iceland to southwestern Greenland around 985 AD, according to Icelandic records.
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Some 3,000 to 5,000 settlers eventually lived in Greenland, harvesting walrus ivory and raising livestock. But the colonies disappeared between about 1360 and 1460, leaving only ruins, and a longstanding mystery as to what happened.
The native Inuit remained, but Europeans did not re-inhabit Greenland until the 1700s.
The Greenlandic Vikings' apogee coincided with the Medieval Warm Period, generally dated from about 950-1250; their disappearance followed the onset of the Little Ice Age, which ran from about 1300-1850.
Both periods are firmly documented in European and Icelandic historical records. Thus, popular authors and some scientists have fixed on the idea that nice weather drew the settlers to Greenland, and bad weather froze and starved them.
But there are no early historical climate records from Greenland. Recently, historians have proposed more complex factors in addition to, or instead of, climate -- hostilities with the Inuit, a decline in ivory trade, soil erosion caused by the Vikings' imported cattle, or a migration back to Europe to farms depopulated by the Black Plague.
In the new study, the scientists sampled boulders left by advancing glaciers over the last 1,000-some years in southwest Greenland, and on neighbouring Baffin Island, which the Norse may also have occupied, according to newly uncovered evidence.
The researchers found that Greenland was at least as cold when the Vikings arrived as when they left.
"If the Vikings travelled to Greenland when it was cool, it is a stretch to say deteriorating climate drove them out," Young pointed out.
The study appeared in the journal Science Advances.