The ocean current known as the Atlantic meridional overturning circulation (Amoc), which gives Ireland a benign climate, may be able to withstand future global warming and avoid collapse this century, scientists have found.
Although it is likely the circulation will weaken, a study published in Nature on Wednesday indicates other ocean processes could prevent its collapse. It has a critical role in regulating temperatures around the planet.
Further research is needed to understand interactions between these processes, say the researchers, led by ocean scientist Dr Jonathan Barker of the UK Met Office.
A study published in February 2024 found the Amoc is already on a path towards an abrupt shift that has not happened for more than 10,000 years and which would have dire implications for large parts of the world.
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Amoc is a marine conveyor belt that carries heat, carbon and nutrients from the tropics towards the Arctic Circle, where it cools and sinks into the deep ocean. This churning helps to distribute energy around the Earth and modulates the impact of human-caused global heating.
This process gives Ireland a warmer climate despite its latitude. Collapse of the Amoc would throw northwest Europe into much colder conditions despite global warming elsewhere.
Previous projections suggested Amoc could weaken due to an increase in greenhouse gases (GHGs), a freshwater influx from melting of the Greenland Ice Sheet, and precipitation changes linked to climate change. These projections, however, have varied and the future evolution of the Amoc is unclear.
This latest study used 34 models to assess Amoc’s response to extreme changes in GHGs and North Atlantic freshwater levels. Under these conditions, the authors found it is resilient to climate changes and did not collapse.
They suggest the Amoc continued in a “weakened state that levelled off” across all the models they considered. The models suggest that upwelling of North Atlantic deep water, driven by winds in the Southern Ocean, sustains the circulation and prevents its collapse.
The authors note this “upwelling”, which involves deep, cold water rising to the surface, must be balanced by “downwelling” in the Atlantic or Pacific oceans. They say the Amoc “can only collapse if a Pacific overturning circulation develops”.
“During the last two years, several studies have reignited the debate about whether the Amoc is likely to shut down, suggesting it is more likely to shut down than we previously expected,” said Dr Joel Hirschi of the UK National Oceanography Centre.
“This study provides a counterbalance and provides evidence for stabilising Amoc mechanisms linked to winds in the Southern Ocean,” he added. “In our warming world, both global CO2 concentrations and freshwater discharge into the North Atlantic are increasing in parallel. It is not obvious how both effects put together would combine.”
While the study found no evidence for a switch-off or collapse of the Amoc, it found a weakening in all cases and this, alone, should be cause for concern, said Prof Jonathan Bamber, director of the Bristol Glaciology Centre.
