Guest “I doubt it” by David Middleton
September 16th, 2020
Sea ice triggered the Little Ice Age, finds a new study
>Sea ice can act as an agent of climate change on a variety of timescales and spatial scales—it’s not just a passive responder to change.
>The Little Ice Age may have arisen “out of the blue,” from internal variability within the climate system, rather than in response to an external push from volcanic eruptions or other factors.
>A far-flung pulse of sea ice may have contributed to the demise of the Norse colonies in Greenland in the 14th and 15th centuries.
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.
The study, published in Science Advances, reports a comprehensive reconstruction of sea ice transported from the Arctic Ocean through the Fram Strait, by Greenland, and into the North Atlantic Ocean over the last 1400 years. The reconstruction suggests that the Little Ice Age—which was not a true ice age but a regional cooling centered on Europe—was triggered 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, physical 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.
The full text of the paper is available… And it’s very well done.
There’s no doubt that the Maximum Holocene Arctic sea ice extent was coincident with the coldest part of the Holocene – The Little Ice Age.
Stein et al. 2017, constructed a cross-section of PIP25 curves across the Arctic from the Fram Strait to the Chukchi Sea.
All four core locations currently reflect seasonal ice cover/ice edge situations (PIP25 index 0.5-0.7), with the Fram Strait being an ice edge situation and the other three reflecting seasonal ice cover.
Two key takeaways:
- Maximum Holocene sea ice extent occurred within the past 500-1,000 years at every location.
- The current sea ice extent is higher at all of the locations than over 50% to 85% of the Holocene.
It’s very clear that the maximum Holocene Arctic sea ice extent occurred during the Little Ice Age. And this would have been accompanied by an increase in export of Arctic sea ice… However, it seems unlikely that the expansion of Arctic sea ice caused the Little Ice Age. It seems more likely that whatever caused the Little Ice Age also caused the sea ice expansion and “extreme export of Arctic sea ice.”
The paper basically concludes that sudden, extreme climate change can result from natural internal variability, without external forcing.
Martin W. Miles, Camilla S. Andresen, Christian V. Dylmer. Evidence for extreme export of Arctic sea ice leading the abrupt onset of the Little Ice Age. Science Advances, 2020; 6 (38): eaba4320 DOI: 10.1126/sciadv.aba4320
via Watts Up With That?
September 19, 2020 at 08:45AM