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Is the Atlantic Gulf Stream about to collapse due to global warming?

What we call “The Gulf Stream” is a portion of a larger current known as the AMOC (Atlantic Meridional Overturning Circulation) that flows along the east coast of the US, then crosses the Atlantic. The current transfers tropical heat to the northern latitudes, creating more temperate conditions in northern Europe, particularly in the Nordic countries.  

Scientists are warning that due to rising global temperatures, we may be reaching an irreversible tipping point, whereby the AMOC current slows to a stop, creating a cascade of negative environmental effects. A major slowing or collapse of the current would have catastrophic results in Northern Europe and worldwide, including extreme weather events and agricultural failures.

What is the tipping point? The critical point at which a small additional change in the system induces a large result is known as the tipping point. This change in status can be abrupt or irreversible. Irreversibly implies that regardless of the countermeasures taken, once a tipping point is passed, returning to a past condition is no longer an option.  

In October 2024, Stefan Rahmstorf, Professor of Physics of the Oceans, Potsdam University, presented an Open Paper signed by 44 leading climatologists from around the world at the Arctic Circle Assembly Conference in Reykjavik, Iceland. Rahmstorf’s presentation focused on whether the AMOC was near a ‘tipping point’ in the next few decades, which would result in a rapid decrease in the speed of the AMOC and possible collapse. Rahmstorf presented the results of several Earth climate computer models and showed that a tipping point is reached in the AMOC when certain conditions are met.

Historical data show that the AMOC stopped in the past, most recently during the last Glacial Period around 12,000 years ago. Rahmstorf argued that current computer models are based on information that does not accurately reflect the increasing changes in the environment, including discharge from the Greenland Ice sheet and the subsequent desalination of the AMOC stream. Therefore, the models show a more stable AMOC than in reality, and the tipping point for possible collapse of the stream is closer in time than the models predict. 

In its Synthesis report (2023 3.1.3), the International Panel on Climate Change (IPCC) stated that the likelihood of abrupt or irreversible changes in the climate system will increase with the level of global warming”. The IPCC further states that “risks associated with large-scale singular events or tipping points will transition to high risk between 1.5°C – 2.5°C of global warming”. This range is beyond the agreed upon 1.5-degree Celsius limit set in the 2015 Paris Agreement signed by over 190 nations.

Governments at international conferences have submitted national climate action plans, and some countries are trying to achieve their goals by 2050 instead of 2100. The bad news is that the mitigating actions suggested by top greenhouse gas producers will not come close to meeting the Paris Agreement limits.  Some countries, such as the United States, may withdraw from the agreement.

However, we may have already breached the 1.5C  limit.

Some studies have shown that warming trends began sooner than groups such as the IPCC have calculated, and are rising more rapidly.  “Our revised record of industrial-era warming now clearly shows that terrestrial environments have been subject to a much faster rate of warming since the 1990s” says McCulloch, et. al. in a paper published in Nature Climate Change (05 February 2024). They used skeletons of long-lived sponges in the Caribbean to determine the rates of global warming over time.  They go on to state “The opportunity to limit global warming to no more than 1.5 °C by emission reductions alone has now passed and at current emission rates, the 2 °C threshold for global mean surface temperatures (GMST) will be reached by the late 2020s”, decades sooner than expected. The bad news is that “It appears that humanity has missed its chance to limit global warming to 1.5°C and has a very challenging task ahead to keep warming below 2°C” says McCulloch.   

Will global warming cause the AMOC tipping point to occur in the near future?   “We predict with high confidence (95%) that the tipping point could happen as soon as mid-century (2025–2095)” say Peter and Suzanne Ditlevsen in a paper published in Nature Communications (Nat Commun 14, 4254 (2023). They concluded that the issue is complex and the degree of uncertainty is large. But they urge that “due to the importance of the AMOC for the climate system, we ought not to ignore such clear indicators of an imminent collapse.”  

This conclusion has sparked considerable discussion among climate scientists. Other scientists have expressed doubts regarding these results. In an article on BBC News (July 26, 2023), Georgina Rannard explains “The reason for many scientists’ reservations is that they say that the study’s authors made a series of assumptions about how to understand AMOC. The climate system is extremely complex, and experts do not have all the evidence to fully understand AMOC”.  The predictions that it could collapse as early as 2025 or by 2095 should be taken with a large grain of salt, according to Jon Robson at the National Centre for Atmospheric Science, University of Reading.

How accurate are Earth climate computer models? Most climate models have not incorporated the increasing contribution of Greenland’s Ice Sheet meltwater, the lower albedo (reflectiveness) of the ice sheet, and the reduced salinity of seawater, which directly affects water density and contributes to AMOC flow.  

Note that both groups of scientists use the “incomplete data argument” to support opposing positions. Scientists critical of the conclusions justify their objection owing to a lack of better data and an incomplete understanding of AMOC mechanics. 

Rahmstorf argued that computer models are too stable because of a lack of current data. The Open Paper presented in Reykjavik highlights the fact that “Recent research since the last IPCC report, does suggest that the IPCC has underestimated this risk and that the passing of this tipping point is a serious possibility already in the next few decades.” Signatories to the Paper state that their goal is to spur world leaders and policymakers to take measures to prevent the worst catastrophes from occurring. “Even with a medium likelihood of occurrence, given that the outcome would be catastrophic and impacting the entire world for centuries to come, we believe more needs to be done to minimize this risk” say the scientists.

Additional research is required, and better computer models that incorporate recent data are required. However, as suggested by Rahmstorf, a more accurate input to computer models can certainly move the tipping point up in time, not back.

The Intergovernmental Organization for Economic Co-operation and Development (OECD) has also concluded that “the current scientific evidence unequivocally supports unprecedented, urgent and ambitious climate action to tackle the risks of climate system tipping points.”   Governments and policymakers should take serious actions to avoid the worst of the consequences. regardless of when the tipping point occurs.  

Of course, the question remains: If further research simply confirms our trajectory into the unknown, how many tipping points will we cross before the world recognizes the dangers and begins addressing the crisis?

JB Varner  11-9-2024

Jim studied Microbiology and Physics at the Ohio State University. His early career included work in cancer research (University of Colorado School of Medicine) and molecular biology at Syngene Inc., a pioneering biotech company. He has produced many technical communications including the series, “Determining Aquifer Properties” for the US Geological Survey. As a science writer, he enjoys keeping abreast of science and technology topics while explaining the complexities of technical topics to a general audience.

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