September 21, 2023

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When the Gulf Stream really stopped

When the Gulf Stream really stopped

It was a box office hero: The Day After, a sci-fi movie describing the catastrophe caused by the sudden blockage of the Gulf Stream, in fact it’s not just … sci-fi! In fact, the idea comes from events that actually happened in the distant past, even if in reality some of the phenomena described in the film clearly contradict atmospheric physics. So what is the scientific basis for this hit movie?

The last great ice, which began about 80,000 years ago, reached its greatest extent 18,000 years ago: Alaska, almost all of Canada and the northern regions of the United States today are buried under a single layer of ice about a kilometer thick, while In Europe, ice has reached as far as Hamburg and Berlin today.

About 12,000 years ago, temperatures rose rapidly again and glaciers melted, bringing an end to the last great glaciation. However, glaciation had one last strong reaction in store. In fact, about 1,000 years of warming prevailed, and then all of a sudden, About 11,000 years ago, the Earth underwent a new intense cooling And in just 100 years, northern Europe and North America plunged into a typical glacial climate.

Plenty of fresh water, hot stream shorts

This tail frost and ice, commonly known as Upper Dryaswhich lasted more or less a thousand years, and was caused by a blockage Atlantic Conveyor BeltIt is a complex system of surface and underwater currents Very cold, salty (and therefore heavy) waters sinking into the depths of the North Atlantic Ocean to be replaced by warm waters from the Gulf Stream.

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In North America actually at the end of the glaciation Melt water from glaciers has been concentrated for centuries in Lake AgassizIt is a vast catchment area larger than all of North America’s Great Lakes combined. However, at a certain point, the retreating ice opened up an outlet channel to the east, roughly where the San Lorenzo River flows today, and so on. Huge amounts of fresh (and therefore light) water suddenly poured into the North Atlantic OceanSoftening of the salty (and therefore heavy) waters of the North Atlantic to the point of blocking the conveyor belt.

The area was freed from the cold only when, without the influence of fresh melt water, the conveyor belt started working again And through the Gulf Stream to transport heat from the tropics to Europe and North America. In the following centuries, the Great Ice Age definitively greeted: Between 9,000 and 5,000 years ago, temperatures rose by several degrees and what is consideredoptimum climateAnd That is, the period when the climate in Europe was 2-3 degrees Celsius warmer than today, while the monsoons in Asia and Africa also brought heavy summer rains to the Sahara Desert.

Image source: deposit