“The Day After” is not for tomorrow. While a 2018 study claimed to demonstrate that the meridional overturning circulation of the Atlantic had slowed down over the last 70 years, raising fears of a collapse scenario close to that of Roland Emmerich's film (United States, 2004), new work seems to prove the opposite.
Thus, according to a study published on January 15 in the journal Nature Communications (J. Terhaar et al.2025), this marine current with a major influence on the climate of the northern hemisphere has not actually weakened over the last six decades. The difference between these two teams? They are not based on the same parameter.
A more distant tipping point?
While their predecessors looked at the average water surface temperature, the authors of this new study chose to look at heat exchanges between the ocean and the atmosphere in the North Atlantic – a good best indicator, according to them, of the strength of the AMOC.
Indeed, when the overturning circulation is stronger, a greater quantity of heat is released from the ocean to the atmosphere above this region, and vice versa, they explain in a press release from the Woods Oceanographic Institute Hole.
The team relied on new data from the Coupled Model Comparison Project (CMIP), Earth climate models. The authors included ocean-atmosphere heat exchanges in these digital representations, then launched the simulations using observational data dating back to the late 1950s in order to reconstruct the past of the ocean current.
“Based on these results, AMOC is more stable than we thought”declared Linus Vogt, who left Woods Hole to join the LOCEAN laboratory (Sorbonne University). “This could mean that the AMOC is not as close to a tipping point than what was previously suggested.he added (press release).
-“There is still time to act”
Based on the air-sea heat flow anomalies, the study thus concludes: “the ten-year average of the AMOC did not weaken between 1963 and 2017”. At this time scale, the correlation between this indicator and current strength is indeed high, as opposed to annual averages, with many processes leading to high year-to-year variability.
“At present, it is almost unanimously agreed that reversal circulation will slow down in the future (because of the cold water brought by the melting of polar ice, Editor's note)but whether it will collapse or not is still debated.”distinguished Nicholas P. Foukal, co-author of the study.
“This work indicates that there is still time to act before we reach this potential tipping point”he judges.
The last two years have exceeded on average the limit of 1.5°C of warming set by the Paris agreement, a sign of a continued rise in temperatures unprecedented in modern history, the European Copernicus Observatory recently announced. (GEO with AFP). However, every tenth of a degree less warming would limit the damage.
