Scientists Fault Warming For Little Ice Age 600 Years Ago

New research from the University of Massachusetts Amherst provides a novel answer to one of the persistent questions in historical climatology, environmental history, and the earth sciences: what caused the Little Ice Age? The answer, we now know, is a paradox—warming --- ScienceDaily reported.

Photo Insert: In the late 1300s, Atlantic Meridional Overturning Circulation (AMOC) strengthened significantly, which meant that far more warm water than usual was moving north, which in turn caused rapid Arctic ice loss.

The Little Ice Age was one of the coldest periods of the past 10,000 years, a period of cooling that was particularly pronounced in the North Atlantic region. This cold spell, whose precise timeline scholars debate, but which seems to have set in around 600 years ago, was responsible for crop failures, famines, and pandemics throughout Europe, resulting in misery and death for millions.

To date, the mechanisms that led to this harsh climate state have remained inconclusive. However, a new paper published recently in Science Advances gives an up-to-date picture of the events that brought about the Little Ice Age. Surprisingly, the cooling appears to have been triggered by an unusually warm episode.

When lead author Francois Lapointe, postdoctoral researcher and lecturer in geosciences at Amherst and Raymond Bradley, distinguished professor in geosciences at Amherst began carefully examining their 3,000-year reconstruction of North Atlantic sea surface temperatures, results of which were published in the Proceedings of the National Academy of Sciences (PNAS) in 2020, they noticed something surprising: A sudden change from very warm conditions in the late 1300s to unprecedented cold conditions in the early 1400s, only 20 years later.

Using many detailed marine records, Lapointe and Bradley discovered that there was an abnormally strong northward transfer of warm water in the late 1300s which peaked around 1380. As a result, the waters south of Greenland and the Nordic Seas became much warmer than usual.

"No one has recognized this before," notes Lapointe. Normally, there is always a transfer of warm water from the tropics to the Arctic. It's a well-known process called the Atlantic Meridional Overturning Circulation (AMOC), which is like a planetary conveyor belt.

Typically, warm water from the tropics flows north along the coast of Northern Europe, and when it reaches higher latitudes and meets colder Arctic waters, it loses heat and becomes denser, causing the water to sink at the bottom of the ocean. This deep-water formation then flows south along the coast of North America and continues on to circulate around the world.

But in the late 1300s, AMOC strengthened significantly, which meant that far more warm water than usual was moving north, which in turn caused rapid Arctic ice loss. Over the course of a few decades in the late 1300s and 1400s, vast amounts of ice were flushed out into the North Atlantic, which not only cooled the North Atlantic waters but also diluted their saltiness, ultimately causing AMOC to collapse. It is this collapse that then triggered a substantial cooling.

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