For many years scientists have harboured growing concerns about the Gulf Stream, the vital system of Atlantic Ocean currents that govern weather patterns across the northern hemisphere. It ensures Ireland benefits from milder conditions relative to its latitude.
The Atlantic meridional overturning circulation (Amoc) — as it is known in the scientific world — is a large system of ocean currents that acts like a conveyor belt, carrying warm, salty surface currents from the tropics into the North Atlantic.
It moves towards the Arctic where it cools and sinks, driving the Atlantic’s currents. But an influx of freshwater particularly from the accelerating melting of Greenland’s ice cap, including an abrupt melting of its carbon-rich permafrost, is increasingly smothering the currents.
Why is the Gulf Stream in the news, and what is the significance?
A growing consensus has emerged that the Amoc could collapse this century, though leading climate scientists under the UN Intergovernmental Panel on Climate Change concluded this was unlikely.
It was known to be at its weakest in 1,600 years, however, due to global heating while researchers spotted warning signs of a tipping point in 2021 — a scenario dramatised in the film The Day After Tomorrow.
Evidence from past collapses indicates changes of temperature of 10 degrees within a few decades, although these occurred during ice ages.
Research published on Tuesday by scientists based at the University of Copenhagen, however, flags a much more immediate risk. It suggests the collapse could happen potentially as early as 2025 as the ocean climate system is close to an irreversible tipping point.
Is the prediction accurate?
The strength of the Amoc has only been consistently monitored since 2004, leaving researchers without enough long-term data to make clear estimates of when such a collapse might occur.
In their study, siblings Peter and Susanne Ditlevsen used sea surface temperature data from the subpolar North Atlantic —which dates back to 1870 — as a basis for determining the stability of the Amoc.
They conclude it is becoming increasingly unstable and will soon hit a critical tipping point — with likely catastrophic impacts on a global scale. Assuming greenhouse gas emissions continue on their current trajectory, they suggest a collapse is most likely to occur around the middle of this century, though they warn it could happen at any time between 2025 and 2095.
“The IPCC has said … it is ‘very unlikely’ that Amoc collapses this century. Our results are actually much more negative,” noted modeller Prof Susanne Ditlevsen. “What we would say is that if we continue emissions as now … it will probably happen between 2050 and 2080.”
“I think we should be very worried,” said Prof Peter Ditlevsen. “This would be a very, very large change. The Amoc has not been shut off for 12,000 years.”
The Gulf Stream collapsed and restarted repeatedly in the cycle of ice ages of the past. It is one of the climate-tipping points scientists are most concerned about as global temperatures continue to rise.
What would the consequences be for Ireland and other countries bordering the Atlantic?
The collapse of the Amoc could lead to rapid sea level rise in North America; a sudden and severe drop in temperatures across northern Europe and serious disruption to monsoons across Asia. Ireland would be especially vulnerable because of its exposed location in the Atlantic. It would also further endanger the Amazon rainforest and Antarctic ice sheets.
Such are the complexities of our global climate, researchers at Icarus research centre in Maynooth University have suggested weakening of the Amoc could trigger a sudden change to Ireland’s climate that could last for two decades, leading to a period of rapid temperature rises rather than cooling.
Undoubtedly, it would have disastrous consequences around the planet by severely disrupting rains that billions of people depend on for food in India, South America and west Africa.
Is this now the established view?
The Danish scientists acknowledge further statistical analysis on their findings provides a measure of the uncertainty in their estimate of the collapse. Other scientists say the assumptions about how a tipping point would play out and uncertainties in the underlying data are too large for a reliable estimate of the timing of the tipping point.
Dr Gerard McCarthy of Icarus acknowledges the importance of trying to determine when the Amoc tipping point might be, but underlines it is unclear whether sea surface temperatures can serve as a direct proxy for the resilience of the Amoc. Sea surface temperature is affected by many other things such as aerosols. It is a good indicator but other factors may be at play. Research in this area is different from classical climate modelling and is at an early stage.
His criticism is not of the method deployed, but of the underlining data: “I don’t think the Amoc is going to collapse by 2025 but probing when the tipping point might be is important.”
Peter Ditlevsen acknowledged that the calculations are based on the premise that sea surface temperatures are a “true fingerprint” of the Amoc. “We’re confident in our calculations, in our predictions. But of course, there’s a premise for that,” he said.
He acknowledged that the findings are controversial, but insists they are too important not to be made public.
“If we are right — and we think we are — then this is not something for the next generations to worry about, this is something to worry about now.”
What all the scientists agree on is a collapse of the Amoc should be avoided at all costs.
The Danish analysis is based on greenhouse gas emissions continuing to rise. If emissions are forced down, the world would have more time to try to keep global temperature below the Amoc tipping point.