Tuesday, January 25

The Gulf Stream is stopping, and it could stop altogether


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The Gulf Stream, one of the main climate regulators of the land, it is moving more slowly now than it has in the last 1,600 years. That is the main conclusion of a study carried out by researchers from Ireland, Great Britain and Germany and published in ‘ Nature Geoscience‘. The culprit, according to scientists, is climate change caused by human activities. This slowdown will also affect weather patterns and sea levels on both sides of the Atlantic.

For the past 1,600 years, the study says, the Gulf Stream, also called South Atlantic Reversal Circulation (AMOC), has never been as weak as in recent decades. To reach that conclusion, the researchers relied on data collected primarily from ‘natural files‘such as tree rings, ocean sediments, ice cores or corals, going back many hundreds of years in the past to reconstruct the history of the current. The slowdown seen during the 20th century, the study authors say, unprecedented in the last millennium.

The Gulf Stream begins near the Florida peninsula, carrying warm surface water into Newfoundland in the north, before snaking east through the Atlantic. When it reaches the North Atlantic, the warm surface water becomes colder, saltier and denser, sinking into the depths of the sea before being driven south again, where the cycle repeats itself. As explained Stefan Rahmstorf, from the Potsdam Institute for Climate Impact Research PIK and lead author of the study, the current ‘moves about 20 million cubic liters of water per second, almost 100 times more than the flow of the Amazon».

“For the first time,” continues the researcher, “we have combined a series of previous studies and discovered that they provide a coherent picture of the evolution of the Gulf Stream over the last 1,600 years. The results suggest that the AMOC has been relatively stable until the end of the 19th century. With the end of the Little Ice Age around 1850, ocean currents began to decline, with a second, more drastic decline since the mid-20th century. ‘

The 2019 special report on the oceans of the Intergovernmental Panel on Climate Change (IPCC), already concluded with a medium degree of confidence “that the South Atlantic Reversal Circulation (AMOC) has weakened in relation to the period 1850- 1900 ‘. “The new study,” adds Rahmstorf, “provides more independent evidence for this conclusion and places it in a longer-term paleoclimatic context.”

The situation tends to get worse

The chances that the situation will improve in the future, as explained Levke Caesar, a climatologist at the University of Maynooth, in Ireland, and the first signatory of the study, not only are they rare, but everything seems to indicate that things will tend to get worse in the coming decades. In fact, if global warming continues at its current rate, the Gulf Stream will exceed by 2100 a ‘inflection point‘critical that will bring her to a complete stop, regardless of what the weather is like at the time.

“If the Gulf Stream crosses that tipping point,” concludes Caesar, “it will continue to weaken even if we have managed to stop global warming. After that it will slow down a lot, even to the point of coming to a complete stop.

Why is the current slowing down?

Climate models have long predicted a slowdown in the Gulf Stream in response to global warming caused by greenhouse gases. Warming, in effect, disrupts the mechanism that moves warm, salty water north, where it cools and thickens, sinking back to the depths and returning south. The increase in rainfall, in effect, and the melting of the Greenland ice sheet, add fresh water to the surface of the ocean. Which reduces its salinity and therefore the density of the water, inhibiting its sinking and thus weakening the flow of the current.

This slowdown has also been linked to a substantial cooling of the North Atlantic over the last hundred years, a kind of ‘cold drop‘predicted long ago by climate models as a result of a weakened AMOC that carries less heat to this region.

Worrying consequences

The consequences of the slowdown in the Gulf Stream could affect people on both sides of the Atlantic in many ways. As Caesar explains, “the northward surface flow of the AMOC leads to a deviation of the water masses to the right, away from the east coast of the USA. moving objects, such as currents, to the right in the northern hemisphere and to the left in the southern hemisphere. As the current slows down, this effect weakens and more water can accumulate on the east coast of the US, which will cause the sea level to rise ”.

On the other side of the Atlantic, in Europe, things will not be much better. The slowdown of the Gulf Stream, in effect, could lead to more extreme weather events, such as a change in the trajectory of winter storms coming from the Atlantic, which will become increasingly intense. Other studies also found other kinds of consequences, such as extreme heat waves or a decrease in summer rains.

“If we continue to drive global warming,” Rahmstorf concludes, “the Gulf Stream system will weaken further, by 34% to 45% by 2100, according to the latest generation of climate models. And that could get us dangerously close to the tipping point where the flow becomes unstable. “

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