In the film “The Day After Tomorrow”, the main current system of the Atlantic Ocean is disturbed and causes a chain of catastrophic events from storms to glaciers throughout the northern hemisphere. While Hollywood has the appetite for exaggeration, scientists are sincerely concerned about their seriousness and timing when this ocean scheme could collapse – discussing if it has already begun to weaken.

Some studies have shown a recent slowdown, but a new study adds further evidence to the discussion. A team of researchers represent this crucial ocean circulation system – called Atlantic Meridional Overturning Circulation, or Amoc – on computer models. They have found no evidence of long -term weakening over the last 60 years, which contradicts a recent study.

However, the results do not mean that it will not be destabilized in the future, with climate models predicting some kind of weakening this century.

“We are still fully expecting AMOC to retreat in the future,” said Nicholas Foukal, co-author of the study. If AMOC is more stable than previously believed, he said that “it is good news because it gives us time to act.”

Struggle to ‘re -create’ the past

AMOC is like a “transport strap” that diffuses water, nutrients and heat throughout the Atlantic Ocean. If this metaphorical belt becomes actively weaker, the results could be significant – though not exactly as attributed by Hollywood.

Areas such as Southeast Asia and parts of Africa may face “unreliable” rain (inconsistent and unpredictable). Agriculture and fishing could be disturbed. Disease could migrate to non -protected populations. Average temperatures in Western Europe could be reduced, but they could be somewhat treated by global warming.

“Without this transfer of heat from the atmosphere and the ocean, the strip of hospitable geographical wids in society would be much narrower,” said Foukal, a natural oceanographer at Georgia University. “I think about people’s migratory patterns, climate refugees, agriculture and diseases.”

These terrible consequences motivate many scientists to study the system and appreciate when it can weaken a lot. But it’s not an easy task.

First, anchors and buoys in the Atlantic Ocean collect immediate observations of the traffic system only since 2004. As a result, scientists have to consider other features that could be a footprint for AMOC. But the second problem is that “alternate” measurements are not perfect indicators of what is happening with ocean currents.

The most important set of data used for the indirect AMOC measurement is the temperatures of the sea surface. Previous studies, especially one in 2018, have been representing AMOC for decades using sea surface temperature data and top climate models of that time, and found a slowdown in circulation. They managed to connect an observed “cold spot” in the North Atlantic with the fall of AMOC.

Initially, Foukal and his colleagues tried to recreate this previous research using sea surface temperature data with newer climate models that have higher resolution and include more processes for better representation of the atmosphere, ocean and ecosystems.

It didn’t work very well. They could see a relationship between the temperature of the sea surface and the previous AMOC behavior, but the relationship was too weak to give a steady conclusion. The “cold blotch” may not be caused by a decrease in AMOC.

“The real mechanism that connects the temperature of the sea surface with the AMOC is not as immediate as one would expect,” Foukal said. “When the AMOC changes, you would expect to see a change in sea surface temperature, not necessarily a direct cold spot.”

Returning back to the beginning, the team examined what other parts of the northern Atlantic heat budget could be significantly affected if the AMOC is changed. They saw ligaments between AMOC and heat exchanges between the air and the ocean called air-seed flows.

If AMOC is reinforced, more heat is transported north and released into the atmosphere, said co-writer Jens Terhaar, who was a postdoctoral student at the Woods Hole oceanographic institution when conducting the research. If weaken, less heat moves to the north and less heat is absorbed into the atmosphere.

Using air-seal flow data and calculations in the North Atlantic, the team rebuilt the AMOC from 1963 to 2017 and did not find a weakening when it was calculated on average on a decades of scale. They actually found volatility at shorter periods, but led them to natural changes in the atmosphere.

Compared to previous studies, Terhaar said “it is not that we have corrected a wrong case”. He said the case was good based on the available data and models at that time – stressing that scientific understanding is always evolving.

An ongoing discussion: is it slowing?

Stefan Rahmstorf, who was the author of the 2018 study showing that AMOC was weakening, said that he is not so sure that this new result is more reliable than the previous ones – including his study or indirect Paleoklima data.

First, he said that newer climate models are struggling to “reproduce well the evolution of previous temperature” compared to observed data and believes that the older model may be better suitable for re -creation of AMOC.

Secondly, he said that the air-seal heat-to-air heat flow data used in the model are not as strong as the temperatures of the sea surface, so the authors of the study used certain calculations to fill the gaps temporarily. Both Terhaar and Foukal understand the limitations of the data, but believe it is a more sensitive “footprint” of AMOC.

Overall, Rahmstorf did not change his assessment that AMOC is weakened. The only way to know certainly if it is destabilizing is through immediate observations, “but because we do not have a continuous stream measurements that go back enough in time, there is some uncertainty about it,” said Rahmstorf, a professor at the University of Potsdam.

Other scientists who did not participate in either of the two studies said that the new research is a step forward to help understand previous behavior and where it can be directed.

“We see many studies that seek to determine if AMOC slows down … There is no clear unanimity,” said Fiamma Straneo, a researcher at Harvard University. Praised the study not only for the proper assessment of previous approaches to address this query, but also to provide a more powerful indicator of AMOC behavior.

The Peter Ditlevsen climate scientist said the study was a “valuable contribution” to understanding whether AMOC is in a downward trend or not.

For him, it was “no surprise” that air-seal heat exchanges better functioned as a “imprint” of Amoc’s behavior in relation to the temperatures of the sea. It is a more direct physical connection: the whole AMOC engine is the heat transferred to the atmosphere, which cools the water and has other results deeper in the ocean.

However, Terhaar warns people not to have a false sense of security simply because AMOC does not seem to have a downward trend.

Multiple studies predict a weakening of AMOC at some point in this century. In October, 44 Oceans experts wrote an open letter calling for a more direct mitigation of the climate to minimize the risks of a fading or collapsing system. The time of a complete collapse is still discussed, but even some weakening could have problematic results.

“Hope [οι άνθρωποι να μην πιστεύουν] That climate change is just not going on or not as bad as we think it is, because it’s not that, “Terhaar said. “It doesn’t mean it will remain stable in the future.”

Kasha Patel writes the weekly Hidden Planet column, which covers Earth -related scientific issues, from our inner core to space storms targeting our planet. It also covers weather, climate and environment news.