From about 1400 to arguably 1850, the Earth partially underwent the Little Ice Age – the coldest period in the past 10,000 years. What caused this massive shift in the blue planet’s climate is a heated topic in climate science research. Now, scientists at the University of Massachusetts Amherst have uncovered a surprising phenomenon that caused the Little Ice Age – warming. Francois Lapointe, a postdoctoral researcher and lecturer at the UMass’ Department of Geosciences, and Raymond Bradley, University Distinguished Professor of the department, closely studied the reconstruction of sea surface temperatures of the Atlantic Ocean over the past 2,900 years.
Scientists found that just before the coldest period of the Little Ice Age – from about 1400 to 1620 – started, sea surface temperatures had peaked to a double warm around 1320 to 1380.
Upon further analysis, scientists found that the very warm overall conditions suddenly changed – just over a period of 20 years – to the coldest period of the Little Ice Age, which was unusual and unprecedented.
Usually, warm water from the tropics flows towards the north along the North European coasts and when reaches higher altitudes in the arctic, it meets colder waters. This results in the warm water losing heat and becoming denser. And because of its density, it sinks deep into the sea, now flowing at the bottom of the ocean. Then, this water flows back to the south along the North American coasts. This works like a massive conveyer belt and regulates our planet’s climate.
However, in the late 1300s, the solar activity was unusually high and volcanic eruptions were very few. “Hence the effect of high solar activity on the atmospheric circulation in the North-Atlantic was particularly strong,” said Lapointe, the lead author of the study in a statement. This means that the very warm conditions made the northward flow of warm water much stronger and an unusually more amount of water was moving towards the arctic, which was causing rapid ice loss.
Over the course of the few decades, this resulted in ice being flushed out of the arctic into the north Atlantic ocean, which did not just cool the Atlantic waters down but also reduced their saltiness. Ultimately, this chain of events broke the conveyor belt-like transfer of seawater (AMOC), which further triggered the major cooling.
The study was published on December 15 in the journal Science Advances.
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