Ocean alarm spelled out
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The Atlantic’s key ocean current may collapse soon.
Forty-four climate scientists have issued a stark warning about the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC).
In an open letter published this week (PDF), researchers raise concerns that the risks associated with this critical ocean current have been underestimated, with global repercussions if the AMOC falters.
The AMOC, often described as the ocean's “conveyor belt”, is vital to Earth's climate.
It transports warm water from the tropics northward, helping to maintain mild temperatures in the Northern Hemisphere, particularly in Northwestern Europe.
This current is central to regulating global heat distribution, supporting ecosystems, and even influencing rainfall patterns.
However, recent scientific findings suggest that the AMOC is weakening and could be nearing a tipping point.
The scientists caution that a collapse of this system would have “devastating and irreversible impacts”, particularly for Nordic countries - Denmark, Iceland, Norway, Finland, and Sweden.
They point to evidence of a “cold blob” already forming over the North Atlantic, a result of reduced heat transport.
If the AMOC were to shut down, the cold blob could expand significantly, causing abrupt cooling, increased storm activity, and changes in weather patterns that could disrupt agriculture and infrastructure across Northern Europe.
The ripple effects would not be limited to the Nordics; shifts in tropical monsoon systems could severely affect agriculture in regions as far away as South America, Africa, and Asia.
Scientists are particularly concerned about AMOC's ‘bistability’, meaning it has two stable states - a strong circulation mode, which currently exists, and a weak mode, which has occurred during past ice ages.
Research indicates that AMOC is not simply slowing down but might be losing stability, approaching a threshold beyond which it could suddenly switch to this weaker state.
This critical transition would not just impact local climates but could also contribute to rapid sea-level rise along the American Atlantic coast, reduced carbon dioxide absorption by oceans, and upheaval in marine ecosystems.
Niklas Boers of the Potsdam Institute for Climate Impact Research, who led a 2021 study on AMOC's stability, says that the system could be “nearing a critical threshold”.
His recent findings (PDF), suggest that observed declines in sea-surface temperature and salinity align with early warning signals of AMOC destabilisation.
“The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse,” Boers says.
Despite such warnings, the Intergovernmental Panel on Climate Change (IPCC) currently maintains “medium confidence” that AMOC will not collapse before 2100.
The authors of the letter argue that this level of certainty is insufficient given the potential consequences.
“Only 'medium confidence' in the AMOC not collapsing is not reassuring,” the letter states.
They call for more robust measures to mitigate this risk, noting that the AMOC could collapse within this century, with consequences lasting for centuries.
The scientists urge countries to use their diplomatic influence to advance global efforts to limit temperature rise to the 1.5°C target of the 2015 Paris Agreement.
This would help reduce the likelihood of triggering climate tipping points, such as the AMOC, which become more probable as temperatures rise between 1.5°C and 2.5°C above pre-industrial levels.
Their message aligns with recent findings from the Organisation for Economic Co-operation and Development (OECD), which emphasised the need for “unprecedented, urgent, and ambitious climate action” to address tipping point risks.
The OECD's report further supports the call for accelerated emission reductions, noting that existing evidence clearly shows the need to stabilise climate systems like the AMOC to prevent cascading impacts on global weather, agriculture, and ecosystems.
While it remains uncertain when exactly a collapse might occur, scientists agree that the potential impacts could be catastrophic, reinforcing the need for a precautionary approach.