Evidence for cause of “Little Ice Age” found in Canada’s North
Scientists ponder the big freeze of the Middle Ages
Melting icefields on Baffin Island, one of the clearest signs of climate change on Earth today, have yielded the strongest evidence yet for the timing and cause of another major climate event from the planet’s past: the so-called Little Ice Age, a sudden and mysterious cooling of the globe that began about 700 years ago.
Recently exposed remains of plants that had been buried under Baffin Island ice for centuries provided the crucial clue that has led an international team of researchers to conclude the Little Ice Age was triggered by volcanic eruptions between AD 1275 and 1300 and was sustained by changes in Arctic sea-ice cover that lasted several centuries.
Writing in the latest issue of the journal Geophysical Research Letters, the team of 13 scientists from the U.S., Iceland and Britain notes that, “there is no clear consensus on the timing, duration, or controlling mechanisms” of the Little Ice Age, which has been attributed by some experts to the onset of a period of reduced heat from the sun.
Without fully discounting the influence of the solar radiation cycle on the medieval cooling trend, the researchers found, however, clear indications on Baffin Island that mosses and other plants that had thrived in the centuries prior to AD 1300 were suddenly killed during a time marked by cataclysmic discharges from volcanoes erupting in the Southern Hemisphere.
A similar series of tropical volcanic eruptions around the year AD 1450 — which initially blocked sunlight but also extended Arctic ice cover and increased iceberg production in the North Atlantic — coincided with another pulse of icefield growth and the flash-freeze killing of plants at different locations on the Nunavut island.
Significantly, the authors note, the “entombed vegetation” found at sites along a 1,000-kilometre stretch of Baffin Island has only become apparent in recent years as “rapidly melting ice caps” in Arctic Canada began to reveal plant material unseen since the Middle Ages.
“From both the Canadian evidence (many sites became ice-covered in the late 13th century and remained so until the past decade) and Icelandic evidence… we can conclude that multi-decadal average summer temperatures never returned to those of Medieval times until the 20th century,” the scientists state in the journal article.
“This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age,” Gifford Miller, a geology professor at the University of Colorado, said in a summary of the study.
“We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time,” he added, pointing to evidence that greater discharges of Arctic icebergs into the North Atlantic led to cooler surface waters and ocean circulation patterns that promoted further sea-ice expansion.
“The dominant way scientists have defined the little Ice Age is by the expansion of big valley glaciers in the Alps and in Norway. But the time in which European glaciers advanced far enough to demolish villages would have been long after the onset of the cold period,” Miller stated.
However, he noted, the team’s Baffin Island study shows that “if the climate system is hit again and again by cold conditions over a relatively short period — in this case, from volcanic eruptions — there appears to be a cumulative cooling effect.”