Sea ice triggered the Little Ice Age

A new study finds a trigger for the Little Ice Age that cooled Europe from the 1300s through mid-1800s, and supports surprising model results suggesting that under the right conditions sudden climate changes can occur spontaneously, without external forcing.

Sist oppdatert: Oct 15, 2020
Published Oct 15, 2020

The study, published in Science Advances, reports a reconstruction of sea ice exported from the Arctic Ocean through the Fram Strait and transported toward the North Atlantic Ocean. over the last toward the North Atlantic Ocean over the last 1400 years. The reconstruction suggests that the onset of the Little Ice Age was led by an exceptionally large outflow of sea ice from the Arctic Ocean into the North Atlantic in the 1300s.

While previous experiments using numerical climate models showed that increased sea ice was necessary to explain long-lasting climate anomalies like the Little Ice Age, empirical evidence was missing. This study digs into the geological record for confirmation of model results.Researchers pulled together records from marine sediment cores drilled from the ocean floor from the Arctic Ocean to the North Atlantic to get a detailed look at sea ice throughout the region over the last 1400 years.

“We decided to put together different strands of evidence to try to reconstruct spatially and temporally what the sea ice was during the past one and a half thousand years, and then just see what we found,” said Martin Miles, lead author from NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, and the Institute of Arctic and Alpine Research (INSTAAR), University of Colorado. Camilla S. Andresen, of the Geological Survey of Denmark and Greenland, and Christian V. Dylmer, of MMT Sweden AB, were coauthors of the study.

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The map shows Greenland and adjacent ocean currents. Colored circles show where some of the sediment cores used in the study were obtained from the seafloor. The small historical map from the beginning of the 20th century shows the distribution of Storis, or sea ice from the Arctic Ocean, which flows down the east coast of Greenland. The figure are modified from Miles et al., 2020.

The cores 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 picks up and transports over long distances. The cores were detailed enough to detect abrupt (decadal scale) changes in sea ice and ocean conditions over time. The records indicate an abrupt increase in Arctic sea ice exported to the North Atlantic starting around 1300, peaking in midcentury, and ending abruptly in the late 1300s.

“I've always been fascinated by not just looking at sea ice as a passive indicator of climate change, but how it interacts with or could actually lead to changes in the climate system on long timescales,” said Miles. “And the perfect example of that could be the Little Ice Age.”

“This specific investigation was inspired by an INSTAAR colleague, Giff Miller. Miller authored the first paper to suggest that sea ice played an essential role in sustaining the Little Ice Age.

Scientists have argued about the causes of the Little Ice Age for decades, with many suggesting that explosive volcanic eruptions must be essential for initiating the cooling period and allowing it to persist over centuries. One the hand, the new reconstruction provides robust evidence of a massive sea-ice anomaly that could ihave been triggered by increased explosive volcanism. On the other hand, the same evidence supports an intriguing alternate explanation.

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The graphs show the reconstructed time series of changes in the occurrence of sea ice and polar waters in the past. The colors of the curves correspond to the locations on the map. The blue shading represents the period of increased sea ice in the 1300s. The figure are modified from Miles et al., 2020.

Climate models called “control” are run to understand how the climate system works through time without being influenced by outside forces like volcanic activity or greenhouse gas emissions. A set of recent control model experiments included results that portrayed sudden cold events that lasted several decades. The model results seemed too extreme to be realistic— so-called “Ugly Duckling” simulations, as termed in a paper by Camille Li and Andreas Born. This new study found empirical evidence that abrupt cold sea ice excursions lasting several decades in the region around Greenland can actually occur. In the case of the Little Ice Age, the sea-ice reconstruction was strikingly similar to the development in an Ugly Duckling model simulation. It involved unusual winds, sea ice export, and a lot more ice east of Greenland, just as we found in here.” The provocative results show that external forcing from volcanoes or other causes may not be necessary for large swings in climate to occur. These results strongly suggest that these things can occur “out of the blue” due to internal variability in the climate system.

Article in Science Advances

Miles, M. W., C. S. Andresen, and C. V. Dylmer (2020). Evidence for extreme export of Arctic sea ice leading the abrupt onset of the Little Ice Age. Science Advances 6, eaba4320