North Atlantic Meridional Circulation on the Verge of Collapse and With Serious Implications for the Climate

The North Atlantic Meridional Circulation (AMOC), also known as the Gulf Stream, is weakening, possibly due to global warming. This evidence is supported by a study published in the journal Oceanography.

The North Atlantic Meridional Circulation (AMOC), also known as the Gulf Stream, is a crucial system for global climate.

This ocean current transports warm water from the surface to the north and cold deep water to the south, responsible for shaping the climate in several regions. However, the AMOC is weakening, possibly due to global warming caused by anthropogenic actions, and this weakening could have serious consequences.

One of the main fears of Stefan Rahmstorf, from University of Postdam, in Alemanha, and that result in the study published in the journal Oceanography, is that the AMOC may reach a point of no return, running the risk of entering an abrupt and irreversible collapse. This collapse, if it happens, could have consequences for climate conditions globally, but particularly in Europe and North America.

Climate models and early warning signs

One of the challenges in studying AMOC is the difficulty in accurately and rigorously modelling behaviour in climate models. Many models exhibit an excessively stable AMOC, unable to demonstrate the possibility of collapse even in extreme global warming scenarios.

On the other hand, models with an AMOC that is too unstable, which collapses under current climate conditions, are considered unrealistic. Furthermore, most climate models do not account for melting ice in Greenland, which could introduce an additional destabilising factor. This melt contributes to the desalination of the Atlantic Ocean, which could bring the AMOC closer to its tipping point.

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Despite the limitations of climate models, scientists have turned to methods from nonlinear physics to look for early warning signs of a tipping point in observational data. These signals are based on the fact that as a system approaches a tipping point, the ability to return to equilibrium becomes progressively weaker. Several studies carried out based on this methodology point to a much greater and closer risk of collapse of the AMOC than previously predicted.

Possible impacts of an AMOC collapse

Even if the AMOC does not completely collapse, a significant weakening would have serious consequences. One of the most immediate impacts would be the worsening of the current cooling pattern in the North Atlantic. This negative anomaly is already influencing the climate in Europe, namely the climatic-meteorological conditions associated with more frequent and intense heat wave phenomena.

Furthermore, a weakening of the AMOC could cause a more pronounced rise in sea levels on the American East Coast. The Coriolis force deflects water in a movement to the right, moving it away from the American coast in the case of the Gulf Stream. When this current weakens, less water is transported north, which leads to a rise in sea levels near the coast. The models project an additional rise of 15 to 20 cm by 2100 due to this effect alone, without taking into account other factors that contribute to sea level rise.

Annual change in near-surface air temperature resulting from a doubling of CO2 and disruption of the AMOC. Source: Rahmstorf (2014).
Annual change in near-surface air temperature resulting from a doubling of CO2 and disruption of the AMOC. Source: Rahmstorf (2014).

An even more worrying scenario is the collapse of convection in the subpolar region. This occurrence, observed in some state-of-the-art climate models, would have a significant impact on the weakening of the AMOC and the abrupt cooling of entire regions. Changes in the temperature distribution between the coldest oceans and adjacent land masses would cause drastic changes in atmospheric dynamics, with unpredictable consequences for meteorological patterns.

The Intergovernmental Panel on Climate Change (IPCC) summarises the potential impacts of the collapse of the AMOC: “If such a collapse were to occur, it would likely cause abrupt changes in regional climate patterns and the water cycle, such as a southward shift of the tropical rain belt, which could result in a weakening of the African and Asian monsoons, the intensification of the southern hemisphere monsoons and the drought in Europe”

The total collapse of AMOC would have devastating consequences at a planetary level. Climate models point to extreme cooling in the North Atlantic region, with much harsher winters. Europe would be particularly affected, with a significant increase in the temperature range between the north and south of the continent, which would likely result in unprecedented storms.

In addition, there would be a southward shift of tropical precipitation zones, worsening the drought in regions such as northern America and Asia.

Reference of the news:

Rahmstorf, S. (2024). Is the Atlantic overturning circulation approaching a tipping point? Oceanography,