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The Little Ice Age, a period of global cooling that lasted from the early 14th century to the mid 19th century, was triggered by an exceptionally large outflow of sea ice from the Arctic Ocean to the North Atlantic in the 1300s, according to a new article published in the magazine Scientific advances.
Bathymetric map of the entrance to the Fram Strait and the downstream region; red circles indicate the location of marine sediment cores. Inset: Danish historical ice chart from the early 20th century showing the extent of Arctic Ocean sea ice seen across southwestern Greenland. Image Credit: Miles et al, doi: 10.1126 / sciadv.aba4320.
“We decided to put together different strands of evidence to try to spatially and temporally reconstruct what sea ice was for the last fifteen hundred years, and then see what we found,” said Dr. Martin Miles, a researcher at the Arctic Research Institute and Alpina of the University of Colorado, Boulder and the Norwegian Research Center NORCE and the Bjerknes Center for Climate Research.
Dr. Miles and his colleagues assembled records of marine sediment cores drilled from the ocean floor from the Arctic Ocean to the North Atlantic to get a detailed look at sea ice across the region over the past 1,400 years.
The nuclei included compounds produced by algae that live in sea ice, the shells of single-celled organisms that live in different water temperatures, and debris that sea ice collects and carries over long distances.
The cores were detailed enough to detect abrupt changes in sea ice and ocean conditions over time.
Records indicate an abrupt increase in Arctic sea ice exported to the North Atlantic beginning in the 1300s, peaking in the mid-century and ending abruptly in the late 1300s.
“I have always been fascinated by not only seeing sea ice as a passive indicator of climate change, but how it interacts with the climate system or how it could cause it on long time scales. And the perfect example of that could be the Little Ice Age, ”said Dr. Miles.
For one thing, the new reconstruction provides strong evidence for a massive sea ice anomaly that could have been triggered by an increase in explosive volcanism.
On the other hand, the same evidence supports an intriguing alternative explanation.
Climate models called ‘control models’ are run to understand how the climate system works over time without being influenced by external forces such as volcanic activity or greenhouse gas emissions.
A set of recent control model experiments included results that portrayed sudden cold events that lasted for several decades.
The model results seemed too extreme to be realistic, the so-called ugly duckling simulations, and the researchers were concerned that they would show problems with the models.
The study of the new study found that there may be nothing wrong with those models.
“In fact, we found that number one, we have physical and geological evidence that these multi-decade cold sea ice excursions in the same region can, in fact, occur,” said Dr. Miles.
“In the case of the Little Ice Age, what we reconstructed in space and time was strikingly similar to the development in a simulation of the Ugly Duckling model, in which a spontaneous cold event lasted for about a century. It involved unusual winds, sea ice export, and much more ice east of Greenland, as we find it here. “
The provocative results show that external forcing from volcanoes or other causes may not be necessary for major climate changes to occur.
“These results strongly suggest … that these things can happen out of nowhere due to internal variability in the climate system,” said Dr. Miles.
The marine cores also show a long and distant pulse of sea ice near the Norse colonies in Greenland, coinciding with their disappearance in the 15th century.
A debate has sparked over the reason for the disappearance of the colonies, usually only with the agreement that a cold climate put heavy pressure on their resilience.
The study authors would like to take into account nearby ocean changes – large amounts of sea ice and cold polar waters, year after year for nearly a century.
“This huge belt of ice coming out of the Arctic, in the past and even today, runs all the way around Cape Farewell to where these colonies were,” said Dr. Miles.
“We would like to take a closer look at ocean conditions together with researchers studying the social sciences in relation to climate.”
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Martin W. Miles et al. 2020. Evidence of the extreme export of Arctic sea ice leading to the abrupt onset of the Little Ice Age. Scientific advances 6 (38): eaba4320; doi: 10.1126 / sciadv.aba4320
