Uncovering the strangest reason for the occurrence of the mini ice age

Between the 15th and 19th centuries, the Northern Hemisphere witnessed a cold period called the “Little Ice Age”, and the Little Ice Age is the coldest period in the Holocene (the modern period that extends from 11,700 years ago to the present day) in the northern hemisphere.

It started suddenly in the fifteenth century due to low temperatures, but the mechanisms that led to it have not been precisely known until now. The reasons for its occurrence are still subject to disagreement among scholars to this day.


And in a new research – recently published in the journalScience Advances(Science Advances)- Researchers from the University of Massachusetts Amherst have provided a new answer to the unanswered question: What caused the Little Ice Age? The answer came surprisingly and unexpectedly: it’s warming.

According to press release Published on the university’s website, it began last year when lead author of the new study, Francois Lapointe, along with co-author Raymond Bradley of the University of Massachusetts Amherst, published a scientific paper in which they reconstructed the path of changing sea surface temperatures in the Atlantic Ocean over the past 3,000 years.

The researchers observed something unexpected: a sudden shift in temperatures from very warm conditions in the late thirteenth century to unprecedentedly cold conditions in the early fifteenth century, in just 20 years.

In parallel, the researchers discovered – using many detailed marine records in different regions of the Atlantic Ocean – a strong and abnormal northward transition of warm water in the late 13th century AD, culminating in the 1380 AD. As a result, the waters south of Greenland and the North Sea have become much warmer, which was not previously observed by the researchers.

How does warming cause an ice age?

Normally, warm water moves from the tropics towards the North Pole in a belt of ocean currents around the planet called the Atlantic Meridional Overturning Circulation. Heat gradually, until it meets cold arctic waters.

There, the water becomes denser, sinking into the depths of the ocean, and then the current flows south along the North American coast before it travels throughout the other oceans. This current plays a prominent role in making the climate mild, especially in the European continent.

Changing sea surface temperatures in the Atlantic Ocean reveal the relationship of warming to the Mini Ice Age (Science Advances)

The authors of the new study note that the Atlantic longitudinal reversal circulation was greatly enhanced in the late 13th century AD, with more warm water flowing into it than usual, causing a rapid loss of Arctic ice. Over the course of a few decades, this cooled the waters of the North Atlantic, softened their salinity, and eventually caused the ocean current to collapse and cause significant cooling.

To confirm these conclusions, the researchers compared their results with the record of solar activity revealed by radioactive carbon isotopes preserved in tree rings. They discovered that high solar activity was recorded in the late thirteenth century, which resulted in a rise in atmospheric pressure over Greenland.

With the absence of clouds and the low number of volcanic eruptions spewing ash into the air, the atmosphere became very clean; Which means it was more responsive to changes in solar energy output. Therefore, “the effect of solar activity on atmospheric circulation in the North Atlantic was particularly strong,” says Lapointe.

Tree rings recorded high solar activity during the thirteenth century (Getty Images)

Are we waiting for a similar ice age?

As for whether such sudden cooling might occur again in our time, the researchers note that there is much less sea ice now in the Arctic due to global warming; Which reduces the possibility of a similar ice age.

In contrast, the accumulation of freshwater in the Beaufort Sea (northern Alaska), which has increased by 40% in the past two decades, may have a strong impact on the ocean current if it seeps into the North Atlantic.

And persistent periods of high pressure over Greenland in summer have also become more frequent over the past decade, and are linked to record-breaking snowmelt.

According to the researchers, more research is needed to ascertain whether such conditions will lead to the collapse of the ocean current or not in the future.

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