Crossing a tipping point would have precipitated the Little Ice Age

A study recently published in the journal NatureCommunications shows that the circulation of the North Atlantic Ocean likely passed a tipping point before the start of the Little Ice Age. This discovery has strong implications for decades to come, as the accelerated melting of Arctic ice may again destabilize this circulation.

Between the 14th and 19th centuries there was a colder climatic period known as the little ice age. Not in keeping with glacial periods, this climatic anomaly manifested itself primarily on a regional scale, particularly in Europe and North America. Severe winters and inclement summers were then recurrent, which allowed the glaciers to expand several times.

Since the cooling was not globally synchronous, Earth’s average temperature was only a few tenths of a degree lower compared to the one that prevailed during the period 1850-1900. While the sun and volcanic eruptions are often invoked, the causes and mechanisms of this anomaly are still difficult to unravel today, in part because it is a relatively modest fluctuation in global climate.

little ice age
Simplified representation of the North Atlantic ocean circulation. Relatively warm and salty waters are shown in red and cold and less salty ones in blue. Credits: Beatriz Arellano-Nava & col. 2022.

North Atlantic circulation, tipping point and little ice age: a complex but crucial relationship

However, a group of researchers from the University of Exeter (England) showed that the North Atlantic ocean current system had crossed a turning point just before the installation of the Little Ice Age. Indeed, isotopic analysis of multisecular bivalve fossils shows strong susceptibility to ocean circulation during the 13th century. This is then less able to recover after external disturbances such as volcanic eruptions, which has no doubt allowed the system to permanently switch to a colder state.

Basically, this mechanic involves feedback betweenOceansea ​​ice and atmosphere. For example, when sea ice spreads over areas of deep-sea formations located in the Norwegian and Labrador seas, the circulation of the North Atlantic Ocean slows down, bringing less heat to the northern basin and adjacent areas, further amplifying plus the advance of sea ice and subsequent cooling. The process continues until the change to another more stable configuration.

These results are not only important for understanding past climate, but are also relevant to understanding the evolution of the North Atlantic Circulation in a rapidly warming world. ” Our latest analysis suggests that this system of ocean currents could once again reach a tipping point due to global warming, once again causing abrupt climate change in Europe. », emphasizes Paul Halloran, co-author of the study.

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