Researchers claim to have discovered the surprising cause of the Little Ice Age – Frustrated by that?
The Cold Era, which lasted from the early 15th century to the mid-19th century, was triggered by unusually warm conditionsPeer-reviewed publications
UNIVERSITY OF MASSACHUSETTS AMHERST
AMHERST, Mass. – New research from the University of Massachusetts Amherst provides a new answer to one of the nagging questions in the history of climatology, environmental history and earth science: what caused the Little Ice Age ? The answer, we now know, is a paradox: warming.
The Little Ice Age was one of the coldest of the past 10,000 years, a period of extreme cold in the North Atlantic. This cold snap, which scholars argue about the exact timeline but seems to have occurred around 600 years ago, was responsible for crop failures, famines, and pandemics across Europe, leading to suffering and death for millions of people. To date, the mechanisms leading to this extreme climate have remained inconclusive. However, a recently published paper in Scientific advance provides up-to-date images of the events that led up to the Little Ice Age. What is surprising is that the cooling seems to be triggered by an unusually warm period.
When the main author Francois Lapointe, postdoctoral researcher and lecturer in geosciences at UMass Amherst and Raymond Bradley, distinguished professor of geosciences at UMass Amherst began to carefully examine 3,000 years of North Atlantic sea surface temperature reproduction, the results of which were published in Proceedings of the National Academy of Sciences 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, just 20 years later.
Using detailed sea records, Lapointe and Bradley discovered that there was an unusually strong northward warm-water shift in the late 1300s, peaking around 1380. The result was waters south of Greenland. and the Nordic Sea getting much warmer than usual. “No one has realized this before,” Lapointe noted.
Normally, there is always a shift of warm water from the tropics to the arctic. It’s a well-known process known as the Atlantic Cycle Overturning (AMOC), which resembles a planetary carousel. Normally, warm water from the tropics flows north along the Nordic coast, and when it reaches higher latitudes and meets the colder waters of the Arctic, it loses heat and becomes denser, causing the water to sink. the bottom of the ocean. This deep water formation then flows south along the coast of North America and continues to circulate around the world.
But by the late 1300s, the AMOC was significantly strengthening, meaning that more warm water than usual was moving northward, thereby rapidly losing ice in the Arctic. Over a few decades in the late 1300s and 1400s, large amounts of ice spilled into the North Atlantic, not only cooling the North Atlantic waters but also diluting their salinity, eventually causing the AMOC to collapse. . It was this collapse that subsequently triggered a significant cooling down.
Fast-forward to our times: between the 1960s and 1980s, we also saw a rapid intensification of AMOC, which is associated with persistently high pressures in the atmosphere over Greenland. Lapointe and Bradley suggest that a similar atmospheric condition occurred just before the Little Ice Age – but what could have caused that persistent high-pressure event in the 1380s?
The answer, Lapointe discovered, was to be found in trees. When the researchers compared their findings with a new record of solar activity revealed by radiocarbon isotopes preserved in tree rings, they found that solar activity was unusually high. have generally been recorded in the late 1300s. Such solar activity tends to lead to high atmospheric pressure over Greenland.
At the same time, fewer volcanic eruptions occur on earth, which means there is less ash in the air. A “cleaner” atmosphere means the planet is more responsive to changes in solar energy output. “Therefore, the impact of high solar activity on atmospheric circulation in the North Atlantic is particularly strong,” said Lapointe.
Lapointe and Bradley wondered if such a sudden cooling event could happen again in our age of global climate change. They note that there is much less sea ice in the Arctic today due to global warming, so such an event in the early 1400s, involving sea ice transport, is unlikely. “However, we must keep an eye on the amount of freshwater accumulating in the Beaufort Sea (northern Alaska) that has increased by 40% over the past two decades. Its export to the North Atlantic can have a dramatic impact on ocean circulation,” Lapointe said. “Additionally, periods of persistent high pressure over Greenland in the summer have been much more frequent over the past decade and are associated with record ice melt. Climate models do not reliably capture these events and so we may be underestimating future ice loss, with more freshwater flooding the North Atlantic, potentially potential for the weakening or demise of the AMOC. The authors conclude that there is an urgent need to address these uncertainties.
This research was supported by a grant from the National Science Foundation.
JOURNEYS
Scientific advance
DOI
ARTICLE TITLE
The sudden Little Ice Age was triggered by the intrusion of Atlantic waters into the Nordic Sea
ARTICLE PUBLICATION DATE
December 15, 2021
Related
