A RECENT STUDY has found that a system of ocean currents that regulate sea levels and temperatures in parts of Europe is likely to collapse by the middle of the century.
The collapse of this ocean current, known in the scientific community as the Atlantic Meridional Overturning Circulation (AMOC), would mark a “tipping element” that would bring irreversible changes with major effects for the planet.
The study was published this week in the journal Nature and has been widely reported on in the media.
The Danish researchers who carried out the study have a “95% confidence range” that the collapse of the AMOC will occur between 2025 and 2095.
However, some media outlets have erroneously reported that it is the Gulf Stream that is at threat of collapse.
Gerard McCarthy, an oceanographer working in ICARUS (Irish Climate Research and Analysis Unit) in the Department of Geography at Maynooth University, noted that the research is clear on the fact that it doesn’t relate to the Gulf Stream.
“The Gulf Stream on its own is a wind driven western boundary front, so as long as the sun shines and the Earth turns, you’re going to have western boundary fronts,” McCarthy explained.
“It’s a very strong current but it just moves hot water northwards and moves hot water back south again, so it doesn’t move much heat in the net-sense and the Gulf Stream itself will not collapse.”
The research is related to the Atlantic Meridional Overturning Circulation (AMOC), which McCarthy said is “sometimes called the Gulf Stream system”.
“So the Gulf Stream is part of that, but it’s not the same thing,” adds McCarthy.
“The AMOC is really what drives the amount of heat going north in the North Atlantic Ocean.
“What AMOC does is it takes the warm water northwards and returns deeper, cold water and that leads to a lot of heat transport.”
McCarthy said this “gives Ireland a relatively mild climate in comparison to some maritime climates at similar latitudes”.
He added that the “AMOC is a body of climate that’s been strongly predicted to decline with climate change”.
“If the AMOC wasn’t there, it would transform the climate of Ireland into the climate of Iceland,” McCarthy said.
“It’s about that kind of difference in terms of the mean temperature, so it would be significantly cooler here.”
The Maynooth oceanographer added: “In terms of future climate projections, we’d expect it to be stormier and to be drier during the summer, these are the kind of things we’d expect with a strong slowdown in the overturning circulation.”
He added that Ireland is “probably one of the most vulnerable countries in the world to collapse, given our location”.
Globally, McCarthy said a southwards shift in the tropical rain belts would also be expected.
“This will have very strong implications in terms of monsoon regions and vulnerable regions like Sahel in Africa, on the edge of the Sahara,” said McCarthy.
“So it’s certainly something that we need to take very seriously and put a lot of effort into understanding.”
The report noted that AMOC has only been monitored continuously since 2004 and that over the period between 2004 and 2012, a decline in the AMOC has been observed.
However, the report said longer records are necessary to assess the significance of this.
“For that, careful fingerprinting techniques have been applied to longer records of sea surface temperature, backed by a survey of a large ensemble of climate model simulations,” the report added.
Nevertheless, researchers have concluded that there is a “95% confidence range” that the AMOC will collapse between 2025 and 2095.
“This means there’s around a 5% chance of this happening by 2025,” said McCarthy, “but a 95% chance of it happening by 2095 within their model.”
A 2019 report by the UN’s Intergovernmental Panel on Climate Change detected a “weaking in circulation” of the AMOC but predicted that a full collapse was “unlikely in the 21st century”.
McCarthy said the recent research is a “really valuable study and is the only way we can figure out where a tipping point might exist”.
“It’s early days in terms of the study, so linking them to real world changes and to what’s happening in the real world, that takes one more step and a bit more time before we can build a consensus around it.”
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