Jun 9, 2021 06:28 PM
https://news.cnrs.fr/articles/why-the-gu...a-misnomer
EXCERPTS: At school, we learned that the Gulf Stream was the warm current that flows across the Atlantic. Yet according to oceanographer Julie Deshayes, things aren't quite so simple. The scientist prefers to speak of the “Atlantic Overturning Circulation” to describe the many ocean eddies that converge on Europe. But the question is - are these currents really weakening and if so, could they impact the climate?
In your opinion, we shouldn't refer to the warm current that washes the coasts of Europe as the Gulf Stream. Why is this term, which is still very widespread, a misnomer?
JD: The Gulf Stream is a warm ocean current that has been well known since the sixteenth century, as it was used by seafarers returning from the Americas. Until the arrival of the first satellites, it was described as a single continuous stream flowing from Florida (US), where it originates, to Europe and the polar latitudes. We now know that this is not the case: although the Gulf Stream is indeed a continuous, extremely strong current that flows northwards along the coastline of the United States under the effect of the Earth's rotation (it is part of a larger system called the North Atlantic Gyre), scientists have discovered that after breaking away from the coast at Cape Hatteraas, North Carolina (US), it totally changes its appearance, breaking up into a series of ocean eddies that are clearly visible to satellites. Some of this water – around 20%, which is roughly twenty times the discharge of the Amazon – crosses the Atlantic basin from west to east and continues northward, while the rest returns southward.
In addition, a well-identified south-north current is observed off Newfoundland (Canada), which again breaks into small vortices as it heads out to sea. So it is not the Gulf Stream that washes the European coastline, but rather a series of currents and eddies. These have been combined mathematically and dubbed the Atlantic Meridional Overturning Circulation, or AMOC.
[...] Is the Atlantic Meridional Overturning Circulation slowing down due to climate change, as was again recently reported in the media?
JD: ... It is difficult to draw any conclusions at this stage. We need to continue taking measurements and refine them by deploying new instruments at other points in the Atlantic.
[...] If the AMOC were to slow down or even stop, what impact would this have on the climate in Europe?
JD: First of all, it is important to realise that the AMOC is not directly responsible for our relatively mild winters, as compared to those in Canada at the same latitude. The AMOC, and even further upstream, the Gulf Stream, simply warm the North Atlantic Ocean; it is the prevailing westerly winds that blow over it and warm up on contact with it that bring us air that is not as cold as might be expected. As for the impact of a weaker AMOC on Europe's climate, here again it is difficult to say, because there are a huge number of variables involved. One thing is certain: it won't make Europe cooler, since human-induced global warming is far too powerful to be overridden merely by the slowing down of a marine current in our latitudes. On the other hand, a slower AMOC could cause more episodes of severe weather in winter, combined with very intense droughts and heat waves in summer. Finally, it should be remembered that, although some of today’s climate models predict that the AMOC may come to a stop, this will never be the case of the Gulf Stream, which flows along the US coastline and is exclusively related to the Earth's rotation. This is not true of the AMOC, which to a large extent, is linked to the Earth's energy balance and to the circulation of warm and cold water between the equator and the poles... (MORE - missing details)
EXCERPTS: At school, we learned that the Gulf Stream was the warm current that flows across the Atlantic. Yet according to oceanographer Julie Deshayes, things aren't quite so simple. The scientist prefers to speak of the “Atlantic Overturning Circulation” to describe the many ocean eddies that converge on Europe. But the question is - are these currents really weakening and if so, could they impact the climate?
In your opinion, we shouldn't refer to the warm current that washes the coasts of Europe as the Gulf Stream. Why is this term, which is still very widespread, a misnomer?
JD: The Gulf Stream is a warm ocean current that has been well known since the sixteenth century, as it was used by seafarers returning from the Americas. Until the arrival of the first satellites, it was described as a single continuous stream flowing from Florida (US), where it originates, to Europe and the polar latitudes. We now know that this is not the case: although the Gulf Stream is indeed a continuous, extremely strong current that flows northwards along the coastline of the United States under the effect of the Earth's rotation (it is part of a larger system called the North Atlantic Gyre), scientists have discovered that after breaking away from the coast at Cape Hatteraas, North Carolina (US), it totally changes its appearance, breaking up into a series of ocean eddies that are clearly visible to satellites. Some of this water – around 20%, which is roughly twenty times the discharge of the Amazon – crosses the Atlantic basin from west to east and continues northward, while the rest returns southward.
In addition, a well-identified south-north current is observed off Newfoundland (Canada), which again breaks into small vortices as it heads out to sea. So it is not the Gulf Stream that washes the European coastline, but rather a series of currents and eddies. These have been combined mathematically and dubbed the Atlantic Meridional Overturning Circulation, or AMOC.
[...] Is the Atlantic Meridional Overturning Circulation slowing down due to climate change, as was again recently reported in the media?
JD: ... It is difficult to draw any conclusions at this stage. We need to continue taking measurements and refine them by deploying new instruments at other points in the Atlantic.
[...] If the AMOC were to slow down or even stop, what impact would this have on the climate in Europe?
JD: First of all, it is important to realise that the AMOC is not directly responsible for our relatively mild winters, as compared to those in Canada at the same latitude. The AMOC, and even further upstream, the Gulf Stream, simply warm the North Atlantic Ocean; it is the prevailing westerly winds that blow over it and warm up on contact with it that bring us air that is not as cold as might be expected. As for the impact of a weaker AMOC on Europe's climate, here again it is difficult to say, because there are a huge number of variables involved. One thing is certain: it won't make Europe cooler, since human-induced global warming is far too powerful to be overridden merely by the slowing down of a marine current in our latitudes. On the other hand, a slower AMOC could cause more episodes of severe weather in winter, combined with very intense droughts and heat waves in summer. Finally, it should be remembered that, although some of today’s climate models predict that the AMOC may come to a stop, this will never be the case of the Gulf Stream, which flows along the US coastline and is exclusively related to the Earth's rotation. This is not true of the AMOC, which to a large extent, is linked to the Earth's energy balance and to the circulation of warm and cold water between the equator and the poles... (MORE - missing details)