Ireland must prepare for the potential collapse in the future of an ocean current system known as the Atlantic meridional overturning circulation (Amoc), according to Fianna Fáil Senator Malcolm Byrne.
His call follows publication of a study showing circulation of the Atlantic Ocean is heading towards a tipping point that is “bad news for the climate system and humanity”. The gulf stream, which is part of the current system, ensures Ireland has a relatively benign climate.
Speaking in the Seanad, Senator Byrne added: “The collapse of Amoc – while it may not be something that happens in our lifetime – would have serious consequences for future Irish generations. It could result in Ireland’s climate changing to become similar to Iceland’s, which is something that will have profound implications ... As a State, nothing should be off the table in terms of preparation.”
He said he was encouraged by the Government’s ongoing work on climate adaptation, preparing for inevitable impacts from climate disruption. There was engagement with all sectors on sectoral adaptation plans. “[But] we cannot be complacent. This is a really crucial issue for long-term planning for the State ... Ireland is hugely exposed should it occur.”
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The scientists behind the research said they were shocked at the forecasted speed of collapse once the point is reached, though it was not yet possible to predict how soon that would happen. Using computer models and past data, they developed an early warning indicator for breakdown of the Amoc, which is critical to global climate regulation.
They found Amoc is already on track towards an abrupt shift, which has not happened for more than 10,000 years and would have dire implications for large parts of the world.
Amoc is a marine conveyor belt carrying 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.
But the system is being eroded by the faster-than-expected melt-off of Greenland’s glaciers and Arctic ice sheets, which pour freshwater into the sea and obstruct the sinking of saltier, warmer water from the south. It has declined 15 per cent since 1950 and is in its weakest state in more than a millennium, according to previous research.
Until now there has been no consensus about how severe this will be. One study last year, based on changes in sea surface temperatures, suggested the tipping point could happen between 2025 and 2095. However, the UK Met Office said large, rapid changes in Amoc were “very unlikely” this century.
The recent paper, published in Science Advances, has broken new ground by looking for warning signs in the salinity levels at the southern extent of the Atlantic Ocean between Cape Town and Buenos Aires.
Simulating changes over 2,000 years on computer models of the global climate, it found a slow decline can lead to a sudden collapse over fewer than 100 years.
The results provide a “clear answer” about whether such an abrupt shift was possible: “This is bad news for the climate system and humanity as up till now one could think that Amoc tipping was only a theoretical concept and tipping would disappear as soon as the full climate system, with all its additional feedbacks, was considered.”
They also mapped consequences of a collapse. Sea levels in the Atlantic would rise by a metre in some regions, inundating many coastal cities. Wet and dry seasons in the Amazon would flip, potentially pushing the already weakened rainforest past its own tipping point.
Temperatures around the world would fluctuate far more erratically. The southern hemisphere would become warmer. Europe would cool dramatically and have less rainfall. While this might sound appealing compared with the current heating trend, the changes would hit 10 times faster than now, making adaptation almost impossible.
“What surprised us was the rate at which tipping occurs,” said Dr René van Westen of Utrecht University. “It will be devastating.”
There was not yet enough data to say whether this would occur in the next year or in the coming century, but when it happens, the changes are irreversible on human timescales. “We are moving towards [collapse]. That is kind of scary,” Dr van Westen said. “We need to take climate change much more seriously.”
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