The Longer the Delay in Carbon Neutrality, the Greater the Risk... Atlantic Ocean Circulation 'Tipping Point' Warning [Reading Science]

"Collapse Possible Even With Mitigation Policies...
A Delay of Just 5 to 10 Years Could Cross the Tipping Point"

Even if carbon neutrality is achieved, a delay in its implementation could push the Atlantic Meridional Overturning Circulation (AMOC)-a key component of the Earth's climate system-into an irreversible state of collapse, according to new research. The study scientifically demonstrates that not only the 'success' of climate mitigation policies, but also 'how early they are implemented,' is a critical factor determining the future stability of the climate.

This research was conducted by the team led by Professor Kook Jongseong of Seoul National University and Dr. Oh Jihoon of the Scripps Institution of Oceanography. The findings were published online in the international journal Nature Communications on December 13 of last year.

Changes in the Strength of the Atlantic Meridional Overturning Circulation (AMOC) According to the Period of Carbon Concentration Stabilization. (a) Changes in atmospheric carbon dioxide concentration, (b) Ensemble average changes in AMOC strength, (c) Changes in AMOC strength in scenarios where carbon concentration stabilization is achieved in 2070, 2080, 2090, and 2100, respectively, (d) Changes in AMOC strength in scenarios where carbon concentration stabilization is achieved in 2105, 2110, and 2115, respectively. Provided by the research team

The Atlantic Meridional Overturning Circulation (AMOC) is a massive circulation system that acts as the 'engine' of the climate system by circulating heat and salinity around the globe. According to paleoclimate records, most cases of abrupt climate change that occurred repeatedly during the last Ice Age were closely linked to sudden changes in this circulation.

Recent studies have warned that the strength of this ocean circulation is gradually weakening due to ongoing global warming, bringing it closer to a critical tipping point where collapse could occur.

By analyzing large-scale climate model ensemble simulations, the research team confirmed that even under identical or similar carbon mitigation scenarios, the future of the Atlantic Meridional Overturning Circulation could diverge into either a recovery path or a collapse path. This suggests that as the ocean circulation approaches a 'tipping point,' even very small additional changes can rapidly and irreversibly shift the system.

In particular, near the tipping point, unpredictable random fluctuations that naturally occur within the climate system-so-called 'stochastic noise'-were found to be a key factor determining the fate of the ocean circulation.

Global Climate Change Patterns Due to the Collapse of the Atlantic Meridional Overturning Circulation (AMOC). (a) Temperature Change, (b) Precipitation Change, (c) Sea Level Change. Provided by the Research Team

The researchers revealed that once the ocean circulation enters an unstable state, internal atmospheric variations, such as the persistent high-pressure anomaly that forms over the waters south of Greenland, can act as triggers to accelerate the collapse of the circulation. This demonstrates that even if external changes in carbon concentration are not significant, small internal variabilities within the system can push the ocean circulation onto a collapse trajectory.

This study also quantitatively highlighted the importance of the timing of achieving carbon neutrality. The analysis showed that if climate mitigation measures are delayed by just 5 to 10 years, the probability of the ocean circulation surpassing the tipping point and collapsing increases nonlinearly and dramatically. It was also confirmed that once the tipping point is crossed, even if carbon emissions are halted afterward, it is difficult to reverse the collapse of the ocean circulation.

Professor Kook Jongseong stated, "This study demonstrates how nonlinearly the Atlantic Meridional Overturning Circulation responds within the climate system," adding, "We have scientifically identified for the first time that even if carbon concentration is stabilized, a delayed response near the tipping point can lead to irreversible climate collapse."

Dr. Oh Jihoon emphasized, "Current climate models are likely overestimating the stability of ocean circulation," and warned, "Since the actual tipping point may be much closer than expected, it is urgent to establish stronger and more immediate international carbon neutrality policies." The research team explained that these results suggest that even in climate predictions after achieving carbon neutrality, the nonlinear behavior and internal variability of critical elements such as ocean circulation must be considered as key variables.